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Influence of Osmoconcentration, Continuous High-Frequency Ultrasound and Dehydration on Properties and Microstructure of Rabbiteye Blueberries
Drying Technology
Abstract
Rabbiteye blueberries were osmoconcentrated for 12 h, and for 3 h with and without continuous high-frequency ultrasound (CHFU) and then air dehydrated (70°C, 10 h). Osmoconcentration increased solids gain, moisture loss, soluble solids, and bulk density. Long osmoconcentration for 12 h can be reduced with CHFU with similar results. Scanning electron microscopy (SEM) micrographs indicated that berries without pretreatment suffered the highest degree of tissue collapse. They also had the highest rehydration ratio and may be ideal for use in breakfast cereals. Osmoconcentrated berries may be used as snack food or in cereal bars due to high bulk density and low rehydration ratio.
... Moreover, they observed that the application of ultrasound increased the water diffusivity in apples by 117%. A similar study by Stojanovic and Silva (2006) ...
... Deng and Zhao (2008) reported that osmotic-treated apples presented an increase in L value from 77 to 80 compared to the other apples treated with pulsed vacuum and agitation. Similar results were observed by Stojanovic and Silva (2006) for rabbit-eye blueberries. ...
... Amami et al. (2017) observed the total phenolic content (TPC) in ultrasound-assisted osmotically dehydrated-air-dried strawberries and found that an increase in airdrying temperature decreased the TPC compared to that of fresh strawberries. The ultrasound-assisted osmotically dehydration followed by air-dried strawberries at 40 C presented a lower reduction in TPC (38%) than that of fresh strawberries, while the same treat- Similarly, Stojanovic and Silva (2006) observed a reduction in phenolics and anthocyanins content of rabbit-eye blueberries when high-frequency ultrasound was applied. Gamboa-Santos et al. (2013) studied the effect of blanching with ultrasound treatment (0.26 W/cm 3 , 20 kHz) on carrots for 10 and 15 min at a temperature of 60 C and 70 C. ...
Ultrasound technology is a green and environment‐friendly technology that rarely causes thermal damage to food products. In this review, we present an overview of the application of ultrasound technology for the dehydration of food products, including pre‐treatments such as ultrasound, osmotic dehydration, and ultrasound‐assisted osmotic dehydration. Dehydration promotes the preservation of food products and increases the shelf life of the food products by reducing water activity. In addition, the ultrasound‐assisted drying of food products is highlighted. The influence of ultrasound and ultrasound‐assisted osmotic dehydration parameters on drying kinetics and food quality is also discussed. The application of pre‐treatments enhances the mass transfer rate, increases the drying rate and drying efficiency, reduces drying time, and helps to retain food properties such as texture and nutrition value. Generally, ultrasound and osmotic dehydration application decreases water activity, increases rehydration ability, improves product color, and reduces nutrient losses. To conclude, we have discussed the use of ultrasound applications for improving the quality and safety of produce before and after the drying process.
... There was no data detected after 60 min for ultrasonic treatment (UT), because the tissue structure of cherry tomato samples was damaged by ultrasound. This observation was also proved by scanning electron microscopy in previous reports (Stojanovic & Silva, 2006;Deng & Zhao, 2008) that the cells for the ultrasound treated fruit could not be identified and suffered a highest degree of collapse. For control group the osmotic time was expanded to 6 h in order to verify the precision of Peleg model when it was used for predicting the equilibrium moisture content (see in the later text). ...
... Agitation could accelerate the movement of solute near the material and prevent the form of solute layer. The use of ultrasound could not only accelerate the movement of solution by its mechanical action but also damage the cell membrane by its cavitation effect (Stojanovic & Silva, 2006;Deng & Zhao, 2008). That is, the effect of ultrasound is greater than agitation as the mass-transfer rate is concerned. ...
... However, according to the above discussion and the reports in the literature (Stojanovic & Silva, 2006;Deng & Zhao, 2008), too high ultrasonic power level and too long ultrasonic duration are not of advantages in its implementation. The ratio of WL to SG (dehydration efficiency index) was used to evaluate the best osmotic condition. ...
In order to elaborate dehydration and osmotic equilibrium characteristics of cherry tomatoes and to analyse the applicability of Peleg model in prediction of equilibrium moisture content and the methodology of Crank’s solution to Fick’s diffusion law in calculation of effective diffusivity, cherry tomatoes were osmotically treated in ternary solution (water, sucrose and NaCl) with or without ultrasound at 30 °C. Results indicated that, a time cumulative effect of ultrasound occurred about 30 min for water loss (WL), while for sugar gain it happened after 45 min, which made the dehydration efficiency index best at the ultrasonic power of 150 W for 40 min. As a function of salt content, the equilibrium WL followed well the first order exponential decay model, and the equilibrium salt content followed well the second order polynomial. A great relative error (29.13%) between the practical determination and the predicted value indicated that Peleg model was not suitable for prediction of equilibrium moisture content. A great truncation error (865%) occurred when moisture effective diffusivity (6.66 × 10−9 m2 s−1) was calculated with Crank’s solution to Fick’s diffusion law by letting n = 1 as compared to that (0.77 × 10−9 m2 s−1) by letting n = 100.
... This has meant that in recent years dehydrated berries have become part of the research focus of the food industry within the development of healthier products to improve the well-being of consumers (Zura-Bravo et al., 2019). This demand creates an opportunity to dehydrated berries, which can be used to elaborate foods such as biscuits, cereals, cheese, cookies, fermented milk, ice creams, marmalades, snacks, syrups, and yogurts, among others (Bórquez, Canales, & Redon, 2010;Stojanovic & Silva, 2006). ...
... In this regard, dehydrated berries have been proposed as a resource to formulate cereals, confections, ice creams, snacks, or simply to reduce the transporting and storing costs of these fruits. However, success in achieving these goals depends largely on the drying technique and pretreatment used (Stojanovic & Silva, 2006). In addition, considering that drying is a preservation technique, its development can contribute to reducing the high percentages of fruits losses that occur every year worldwide. ...
Berries are among the fruits with the highest nutritional and commercial value. This paper reviews the conventional and emerging dehydration methods most commonly used as postharvest treatment and discusses their efficacy in maintaining and/or improving the nutritional and functional qualities of dried berries. The characteristics of the conventional methods (e.g., convective drying, freeze-drying, spray-drying, osmotic dehydration), their pre-treatments, their combination, and intermittent drying, as well as their potential disadvantages are discussed. The use of emerging dehydration techniques (e.g., electromagnetic radiation drying, explosion puffing drying, heat pump drying, low-pressure superheated steam drying, microwave drying) allows to improve the quality of the dried berries compared to conventional techniques, in addition to reducing drying times, increasing drying speed and energy efficiency. Finally, the use of pre-treatments and the combination of technologies can enhance the quality of the final product as a result of the improvement in the effectiveness of the dehydration process.
... This decrease in total phenolic content could be due to these oxidation reactions. Stojanovic and Silva (2006) showed that ultrasonic waves caused the rupture of the cell membranes in black cherry fruit as a result of cavitation (Stojanovic & Silva, 2006). Microstructural changes induced by acoustic wave energy decrease the total phenolic content and their permeation into the solvent. ...
... This decrease in total phenolic content could be due to these oxidation reactions. Stojanovic and Silva (2006) showed that ultrasonic waves caused the rupture of the cell membranes in black cherry fruit as a result of cavitation (Stojanovic & Silva, 2006). Microstructural changes induced by acoustic wave energy decrease the total phenolic content and their permeation into the solvent. ...
Cornus mas (C. mas) is one of the native horticultural products to Iran that have high pharmaceutical and nutritional values. This study aimed to comparatively investigate different drying methods with ultrasound‐osmotic pretreatment on energy consumption, timing, and qualitative properties of Cornus mas. In this study, C. mas was first dried by the oven (at 40, 50, and 60°C), microwave drying (at 200, 500, and 800W), and infrared (at 40, 50, and 60 °C). Samples were then treated at three concentrations 9, 18, and 27% of salt, three ultrasound power 100, 250, and 400 W, and three intervals 5, 10, and 15 min by the osmotic‐ultrasound method. The optimal osmotic‐ultrasound pretreatment was achieved at a concentration of 27%, ultrasound power of 100 W, and 11.28 min. In terms of qualitative properties, osmotic pretreatment with the supplementary oven method is the best method for drying C. mas fruits.
... This was also shown by Jambrak, Mason, Paniwnyk, and Lelas (2007) for drying of mushrooms. Similar results were collected by Stojanovic and Silva (2006) for rabbiteye blueberries treated with US. From the findings, it is obvious that the water gain is more noticeable in US treated freeze-dried quinces (ranging from 6.38 ± 0.07% to 6.57 ± 0.10%) than for FD samples without US (4.43 ± 0.10%). ...
... This might be clarified by the fact that US leads to physical destruction and membrane deformation of the cells, which provides to easier elimination of pigments from apple tissues. Stojanovic and Silva (2006) reported similar results for rabbiteye blueberries. US is found as more favorable for removing water and preserving color of apples which contributes to high quality and long shelf life of dried products (Deng & Zhao, 2008). ...
The study was conducted to examine the effect of ultrasound (US) pretreatment on physical and chemical/nutritional attributes of freeze‐dried quince slices. The quince fruits were washed, hand‐peeled and cut with a dimension of 1 cm (L) × 0.2 (W) cm × 1 cm (H). The quince samples were treated in an ultrasonic bath in three different times which were 10, 20, and 30 min. Untreated and ultrasonically pretreated quince samples were dried in a freeze dryer. Freeze‐dried samples were analyzed in terms of physical properties such as shrinkage, rehydration, color, water activity, and hardness and bioactive compounds including total phenols, ascorbic acid, and antioxidant capacity. A significant difference was observed among untreated and ultrasonically pretreated quince samples. The freeze‐dried quince slices treated with a US (especially 20 min—treatment) showed a higher preservation of bioactive compounds in addition to improved physical properties compared to the untreated quince samples. In overall, US pretreatment is a promising process as demonstrated in current research by its capability to better retain freeze‐dried quince quality in terms of physical and chemical properties.
Practical Applications
The freeze drying of quince fruit with the aid of US pretreatment was investigated. A significant development in the quality preservation of freeze‐dried of quince slices with an US‐pretreatment was accomplished. This research will contribute a useful technique to produce freeze‐dried quinces with a significantly enhanced product quality. Drying of quince samples with a freeze drying in addition to US‐pretreatment might be applied to get a high‐quality fruit with an improved bioactive compounds and physical property.
... The highest reduction in phenolic contents was 75.73% for apple slices treated with 50% sucrose solution, while the lowest reduction was 65.52% for apple slices treated with 40% sucrose solution. These results are in a good agreement with those of Stajanovic & Silva (2007) and Nuez-Mancilla et al. (2013), who reported that osmotic concentration caused a loss in phytonutrients like total phenolics for berries. ...
... Antioxidant activity of apple slices is lower than that of the apple cubes. Stajanovic & Silva (2007) reported that antioxidant activity was low in osmotic air dried blueberries. Combination of high temperature, high sugar concentration caused largest negative influence on the antioxidant activity. ...
Deep-fat frying process produces desirable and undesirable compounds that can cause impairments to the quality
of frying of different oils and the fried foods produced. The quality and stability of frying oils are therefore of concern
to food technologists, nutritionists, and consumers. The present study was performed to investigate performance of
canola oil (CO) and its blends with either sunflower oil (CO+SF) or palm olein (CO+PO) blended at 1:1( w: w) by
using different frying cycles of potato chips up to consecutive 10 frying cycle/ 3 day for each oil /days. Significant
chemical changes in the frying oil quality have been occurred during frying process. Different chemical deterioration
parameters: Iodine value (IV), Free fatty acid (FFA), Peroxide value (PV), Ansidine value (An.v), Totox value, conjugated dienes , total polar compounds (TPC), fatty acids composition (FAs) and Fourier transform infrared (FTIR) of
these frying canola oil and blends were investigated .
The conjugated dienes at 232nm throughout the frying periods were the lowest (3.12) in CO+PO with the highest (43.04) value in CO+SF after 30 frying cycles. At the end of frying period, CO+SF had the lowest ratio of TPC
2.15 than found in CO+SF F30 and CO F30 (23.88 and 18.2), respectively. Generally, all blends did not exceed the
25% cut-off point for rejecting used frying oil. The blend of CO+PO was the superior in regard to frying stability and
lowering TPC after deep-fat frying process.
The results of 30 potatoes deep-frying cycles in CO and its blends due to higher saturation, which can be seen
from the chemical parameters and (FTIR) data. FTIR provides very useful information about the chemical composition and impaired in oil quality during thermal oxidation, which is equivalent to that used in the ordinary food preparation. Furthermore FTIR method predicting a modification in the oil’s nutritional value. The results showed that FAs
of blends, that contain PO had oxidative stability for the most of fatty acids with lower values than those occurred in
frying of CO or CO+SF oils after 30 frying cycles. Furthermore, these results showed evidence that, the oxidation
rate for PO in monounsaturated fatty acids (ƩMUSFAs) is much slower than that of the polyunsaturated fatty acids
(ƩPUFAs). The ƩMUSFAs, were oxidized, and lower adverse contributed to the improvement of CO stability. Oil
blends and frying process caused modifications in the FAs compositions and ω-3/ω-6 ratio.
These results indicated that frying may be hazardous due to the formation of lipid oxidation products as a result
of thermal degradation of lipids during deep- fat frying process. Therefore in the CO+PO oil blend provided a frying
oil alternative for the production deep–fried food, delivering low proportions of trans and saturated fatty acids.
Key Words: Oil Blends, canola oil, palm olein, sunflower oil, fatty acid composition, frying, oil deterioration,
ɷ-3/ɷ-6 ratio, oil stability, totox value, total polar content.
... The highest reduction in phenolic contents was 75.73% for apple slices treated with 50% sucrose solution, while the lowest reduction was 65.52% for apple slices treated with 40% sucrose solution. These results are in a good agreement with those of Stajanovic & Silva (2007) and Nuez-Mancilla et al. (2013), who reported that osmotic concentration caused a loss in phytonutrients like total phenolics for berries. ...
... Antioxidant activity of apple slices is lower than that of the apple cubes. Stajanovic & Silva (2007) reported that antioxidant activity was low in osmotic air dried blueberries. Combination of high temperature, high sugar concentration caused largest negative influence on the antioxidant activity. ...
Doum (Hyphaene thebaica) fruit, and doum-fruit flour (DFF) were studied in terms of physicohemical properties
as well as technological processing to prepare biscuits, crackers and pudding containing DFF. Chemical composition
showed that DFF possessed low contents of crude protein and crude ether extract being, 2.87 and 0.76%, respectively.
Non reducing sugars represented about (91.94 %) of the total sugars (43.70%). The DFF could be considered as a good
source of minerals (K, Ca, Na, and Mg). The results also indicated that DFF had very good values in terms of dietary
fiber, total phenolic content, flavonoid content and antioxidant activity in addition to some vitamins such as B3, B6 and
B1. The edible portion of doum fruits (DFF) was used to formulate some functional foods. The organoleptic properties
of biscuits and crackers containing DFF up to 20% and budding up to 50% showed that generally all the treatments
were well accepted by the panelists
... Structural changes were examined in various studies to confirm greater cell and tissue destruction and formation of microscopic channels after ultrasound application. [5,48,52,55,57] Nowacka et al. [5] observed increasing destructive influence of ultrasound on the tissue collapse with time of US pretreatment. In their research, larger intercellular spaces were linked with 9-14% higher porosity and 9-11% higher shrinkage of convective dried apples pretreated by ultrasound. ...
... In their research, larger intercellular spaces were linked with 9-14% higher porosity and 9-11% higher shrinkage of convective dried apples pretreated by ultrasound. However, no distinct shrinkage was observed in the case of ultrasound-enhanced atmospheric freeze-dried peas, [51] in bulk density of ultrasound freeze-dried bell pepper, [54] and convective dried blueberries formerly subjected to ultrasound enhanced osmotic 1390 WITROWA-RAJCHERT ET AL. dehydration [57] compared with the control samples. Garcia-Perez et al. [6] suggested that materials of higher porosity are more susceptible to compression and expansion cycles and, therefore, the impact of ultrasound on structural damage and drying rate can be more significant. ...
According to the U.S. Energy Information Association (EIA), world energy consumption will increase by 56% in 2040. Therefore, a lot of effort is being dedicated to maintaining economic development with minor impact on the environment. This can be done altering existing technologies or introducing completely new technologies. Due to the fact that drying can be considered one of the most energy-consuming processes, researchers have focused on ways to save energy while minimally changing the physicochemical properties of food, which shape its quality. Additionally, the increasing growth of consumer expectations and their nutritional knowledge have further stimulated efforts to seek new solutions. Non-thermal technologies such as pulsed electric field (PEF), ultrasound (US), and high hydrostatic pressure (HHP) seem to meet the expectations of both producers and consumers. This article reviews the impact of PEF, US, and HHP on drying kinetics and the quality attributes of dried food.
... [51] Similarly, high-frequency ultrasound had a negative influence on the anthocyanins and phenolics contents of rabbiteye blueberries. [75] On the same note, ultrasound treatment showed the lowest titratable acids values due to damage produced by the ultrasonic treatments, which eventually increased the permeability of plant tissues and made it easy for organic acid and its derivatives to leach from the tissue. [76] Ultrasound pretreatment was reported to result in higher retention of carotenoids than blanching at 80 C for 3 min in hot air-dried carrots. ...
... [83] Ultrasound resulted in the highest degree of cell deformation and the most severe tissue collapse of the surface layer, which explains the lower rehydration rate. Similar results were obtained by Stojanovic and Silva [75] for rabbiteye blueberries treated with ultrasound. ...
Evolving advanced pretreatment techniques such as application of ultrasound prior to fruit drying have attracted significant research and development efforts due to the rising demand for high-quality dried fruits at reduced operating costs. Drying processes can be destructive to the quality of fruits due to long drying times and high temperatures in some cases. The effects of ultrasound pretreatment on quality aspects of dried fruits and on drying kinetics are reviewed. Ultrasound is known for its varying effects on different fruits; however, it has been proved to greatly increase drying rates and hence reduce the overall processing time. Ultrasound pretreatment in distilled water as the media is an interesting concept when low-calorie dried fruits are required.
... Ultrasonic treatments increased by 117% the water diffusivity in apples, which was slightly higher than the findings of this work. Stojanovic and Silva [26] have concluded that long osmoconcentration (12 h) of blueberries can be reduced to 3 h with the application of high frequency ultrasound with similar results. The findings of Stojanovic and Silva [26] also supports the findings of this work that showed that the application of ultrasound helps reducing the processing time of the osmotic dehydration and air-drying processes. ...
... Stojanovic and Silva [26] have concluded that long osmoconcentration (12 h) of blueberries can be reduced to 3 h with the application of high frequency ultrasound with similar results. The findings of Stojanovic and Silva [26] also supports the findings of this work that showed that the application of ultrasound helps reducing the processing time of the osmotic dehydration and air-drying processes. ...
This work examines the influence of ultrasonic and ultrasonic assisted osmotic dehydration pretreatments on the dehydration of eight fruits (banana, genipap, jambo, melon, papaya, pineapple, pinha, and sapota). An overview of the effects of ultrasound application on water loss, sugar gain, and effective diffusivity of water during the dehydration process is presented. The results showed significant differences for water loss and sugar gain among the fruits that were studied, which were analyzed based on the changes observed on the tissue structure of the fruit. The results also showed that the effective diffusivity of water in the fruit increased after application of ultrasound reducing air-drying time.
... The inner tissue showed a loose and porous structure in the later drying stage, which would allow water to be transferred more easily from the inside to the surface of blueberries. Stojanovic and Silva (2006) reported that the tissue structure of sugar-infused blueberries changed less than in blueberries without sugarinfusion pretreatment under convective air-drying. The internal tissue of sugar-infused blueberries suffered small changes with reduced intercellular space and swollen dendritic formations, even at significantly reduced moisture level. ...
... The internal tissue of sugar-infused blueberries suffered small changes with reduced intercellular space and swollen dendritic formations, even at significantly reduced moisture level. The cells in sugar-infused blueberries were filled with sugar (Stojanovic & Silva, 2006). Therefore, more opened structure and greater decrease of diameter might contribute to the higher increase of D e for fresh blueberries than sugar-infused blueberries. ...
We evaluated the finished product quality and infrared (IR) drying characteristics of fresh and sugar-infused blueberries dried with a catalytic infrared (CIR) dryer. IR drying tests were conducted at four product temperatures (60, 70, 80, and 90 °C) to evaluate the drying rate and the color and texture of the finished product. Fresh blueberries dried with convective hot air drying at 60 °C were used as control for comparison. The experimental data of moisture changes during IR drying were modeled with eight different models, including Page, modified Page, Thompson, Newton, Wang and Singh, and Henderson and Pabis, and two models developed in this study. The Thompson model showed the best fit to all experimental data. The CIR drying produced firmer-texture products with much reduced drying time compared with hot air drying. For fresh blueberries, CIR drying conserved drying time by 44% at 60 °C. The effective moisture diffusivity ranged from 2.24 × 10−10 to 16.4 × 10−10 m2/s and from 0.61 × 10−10 to 3.84 × 10−10 m2/s for fresh and sugar-infused blueberries, respectively.
... Prolonged sonication causes further damage to the tissue, resulting in the formation of empty areas [26]. Other researchers have observed a similar effect during the sonication of pineapple [71], melon [72], and berries [73]. In our study, the lack of an effect on the beetroot tissue could also be related to the further drying process, which leads to shrinkage, affecting the final characteristics of the cells in the dried tissue. ...
Beetroots are sources of bioactive compounds and valued pigments such as betalains. The purpose of this study was to determine the influence of ultrasound pretreatment on the beetroot infrared–hot air drying process and the functional properties of the obtained product. In this study, there were two used frequencies—21 and 35 kHz—and three different periods of time—10, 20, and 30 min. Since beetroots are usually subjected to thermal treatment, another aim was to examine the influence of blanching and soaking on the beetroot tissue properties in order to compare traditional and ultrasound-treated methods. As a result of this study, it was found that ultrasound pretreatment changed the dry matter content, water activity, thickness of the tissue, total color difference, and contents of betanin pigments in the beetroot. It was revealed that the drying process is shorter after ultrasound pretreatment using a 21 kHz frequency. Drying tissue exposed to ultrasounds showed a significant increase in the L* parameter; however, the decrease in the a* parameter was caused by a reduced content of betalain pigments. Taking into consideration parameters important from a technological point of view, it was found that the best condition for beetroot pretreatment is 20 min treatment, regardless of the frequency used.
... Similar observations were made by Stojanovic and Silva when treating blue berries with ultrasound (Stojanovic and Silva 2006), they showed that the diffusion rates of moisture throughout osmotic dehydration of rabbit eye blueberries are notably enhanced with application of ultrasound though, this is attributed to the loss of anthocyanins and phenolics. Sánchez et al. (1999) also confirmed the increase of the rate of expulsion of water and sodium chloride in the case of cheese brining, when ultrasound are used. ...
Abrupt change in local pressure within a liquid medium is susceptible to break the liquid molecules cohesion, particularly when a gas is dissolved in the liquid. The created “cavity”, filled of gaseous/vaporous content is known as Cavitation. When the pressure perturbation is induced by an acoustic source, namely ultrasound, the phenomenon is then called Acoustic Cavitation. Although occurring at microscopic scale, the repletion of acoustic cavitation events presents a broad range of applications owing to the physical effects directly related to the oscillation of the bubbles, but also to their indirect chemical consequences. Nowadays, the acoustic cavitation is not only an attractive topic for fundamental research in physics and chemistry, but is recognized as a promising up-scalable solution in several fields, including agri-food. The present chapter sheds light on the applications of ultrasound and acoustic cavitation in the agri-food domain, by linking the fundamental aspects of this non-thermal process, ranging from physical to chemical effects, to the intended applications in terms of extraction, pasteurization, crystallization, synthesis and oxidation. The chapter discusses the mechanisms of action of ultrasound leading to the aforementioned applications, and emphasizes on the green and sustainable features characterizing their pathways. At the end of the present chapter, several case studies are reported from the literature in order to highlight the most promising agri-food applications harnessing the principle of acoustic cavitation, and exhibit their advantages relatively to conventional techniques, but also the challenges still facing their large-scale adoption, especially from a technological point of view.
... Moreover, the impregnation of apple slabs in sucrose solutions increased the density from ≈0.82.10 3 kg/m 3 to over 0.90 ×10 3 kg/m 3 [36]. Likewise, osmoconcentration of blueberries increased their densities from 0.493 ×10 3 kg/m 3 to 0.709 ×10 3 kg/m 3 [37]. ...
Autumn olive fruits were osmo-dehydrated in sucrose solution at 70 ◦C under vacuum and
atmospheric pressure. The mass transfer kinetics data were applied to the models of Azuara, Crank,
Page, and Peleg. The Peleg model was the best-fitted model to predict the water loss and solid gain
of both treatments. The vacuum application decreased the effective diffusivities from 2.19 × 10−10
to 1.55 × 10−10 m2
·s
−1
for water loss and from 0.72 × 10−10 to 0.62 × 10−10 m2
·s
−1
for sugar gain.
During the osmotic dehydration processes, the water activity decreased and stabilized after 5 h,
while the bulk densities increased from 1.04 × 103
to 1.26 × 103 kg/m3
. Titratable acidity gradually
reduced from 1.14 to 0.31% in the atmospheric pressure system and from 1.14 to 0.51% in the vacuum
system. pH increased significantly in both systems. Good retention of lycopene was observed even
after 10 h of treatments. For the color parameters, the lightness decreased and stabilized after 30 min.
In comparison, the redness and yellowness increased in the first 30 min and gradually decreased
towards the initial levels in the fresh fruit.
... Many osmotic media are applied as concentrated solutions (e.g., sucrose, sugar, corn syrup, salt). Several process parameters have been found to be critical for the mass transfer, such as the osmotic solution concentration, treatment temperature, solute properties, sample to solution ratio, agitation, time, pressure (vacuum, high pressure), and food characteristics (e.g., shape, size, structure, tissue compactness) [17]. ...
Autumn olive fruits are a rich source of nutrients and functional compounds, making them functional foods against many diseases and cancers. To increase the consumption, its processing, and its transformation into new products would help spread them to the consumer’s table. In this study, after giving an overview of the physicochemical characteristics and the antioxidant activity, the objective was to optimize the osmotic dehydration (OD) of the berries. Response surface methodology was used to investigate the effect of dehydration factors: syrup concentration (30–70%), temperature (20–70 °C), and fruit-to-syrup ratio (1:10–2:10) on the water loss (WL), sugar gain (SG), weight reduction (WR), density (ρ), water activity (aw), and total color change (ΔE) of fruits after 10 h of OD. Results obtained by employing Box–Behnken design (three variables, three levels), and significant terms of regression equations indicated that the syrup concentration and temperature variation are the most affecting factors on the previously mentioned independent variables (WL SG, WR, ρ, aw, and ΔE). Fruits to syrup ratio appeared to have a significant effect only on WL. Under the optimum conditions found (70%, 70 °C, 1.8:10), the predicted values were 59.21%. 19.21%, 32.34%, 1.22 g/cm3, 0.850, and 3.65 for WL, SG, WR, ρ, aw, and ΔE, respectively.
... The resulting supernatant was lyophilized and redissolved in 400 µL of hydrochloric acid: methanol solution. The extraction solution was finally stored at −80 • C. The total anthocyanin content was determined by using the pHdifferential method (Stojanovic and Silva, 2006). The extraction was diluted with KCl buffer (pH 1.0) and CH 3 CO 2 Na·3H 2 O buffer (pH 4.5). ...
Proanthocyanidins (PAs) and anthocyanins are two vital groups of flavonoid compounds for grape berries and red wines. Several transcription factors (TFs) have been identified to be involved in regulating PA and anthocyanin biosynthesis in grape berries. However, research on TFs with different regulatory mechanisms for these two biosynthesis branches in grapes remains limited. In this study, we identified an R2R3-MYB TF, VviMYB86, whose spatiotemporal gene expression pattern in grape berries coincided well with PA accumulation but contrasted with anthocyanin synthesis. Both in vivo and in vitro experiments verified that VviMYB86 positively regulated PA biosynthesis, primarily by upregulating the expression of the two leucoanthocyanidin reductase (LAR) genes in the Arabidopsis protoplast system, as well as in VviMYB86-overexpressing grape callus cultured under 24 h of darkness. Moreover, VviMYB86 was observed to repress the anthocyanin biosynthesis branch in grapes by downregulating the transcript levels of VviANS and VviUFGT. Overall, VviMYB86 is indicated to have a broad effect on flavonoid synthesis in grape berries. The results of this study will help elucidate the regulatory mechanism governing the expression of the two LAR genes in grape berries and provide new insights into the regulation of PA and anthocyanin biosynthesis in grape berries.
... reported that the simultaneous application of heat (60 °C) and power ultrasound on grapefruit skin facilitated the extraction of pectin and induced more destruction and depolymerization of pectin molecules.Liu et al. (25) also reported that application of power ultrasound on citrus pectin decreased the molecular weight of the pectin immediately after pre-treatment with ultrasound waves.Microstructural analysisSEM images of dried apricots are shown inFig. 5. SEM image of dried apricot with no pretreatment (control) showed destruction in cell walls and structure collapse in apricot tissue. This observation is similar to the reported microstructure of dried Rabbiteye blueberries, which dried without any retreatment(26). SEM images of OD samples showed swollen inner tissue compared to that of control. ...
Research background. The worldwide demand for healthy and sulphur-free dried vegetables and fruits has grown. Combined ultrasound-assisted osmotic dehydration (UOD) and application of active coatings incorporating natural preservatives represents an attractive alternative to sulphuring to preserve the sensorial and nutritional quality of dried fruits. The aim of this study is to investigate the effect of osmotic dehydration (OD) and UOD, and the use of pectin coatings (alone or with citric acid or ascorbic acid) on physical, textural and microstructural properties of hot air-dried apricots.
Experimental approach. Fresh apricot cubes (1 cm3) were pretreated with either OD at 55 °C for 30 and 45 min or UOD at two ultrasonic frequencies of 25 and 35 kHz for 30 and 45 min followed by application of active coatings with pectin alone, pectin with citric acid or pectin with ascorbic acid for 10 min. All pretreated coated samples were then hot air-dried at 60 °C until a final moisture content of 20 % (wet basis) was reached. Physical (shrinkage, apparent and bulk densities), chemical (browning value and water activity) and textural properties (firmness and shrinkage), microstructure and microbial load of dried apricots were studied.
Results and conclusions. Application of OD and UOD improved physical and textural properties of the dried apricots. Moreover, apparent and bulk densities, rehydration capacity of OD and UOD pretreated samples increased, while shrinkage, water activity and microbial load decreased. Firmness of UOD pretreated samples was significantly (p
... Residual activity of PPO may be a problem affecting the stability and color of drying products that make its inactivation as industrial signifi- them, but at IR temperature of 70 C, the samples showed very small pores and cavities with regular and firm structure. There were clear differences observed among treated and untreated samples since ultrasound frequencies during drying process has been reported to cause structural changes in many fruits and vegetables (Fernandes & Rodrigues, 2008;Stojanovic & Silva, 2006). ...
Different ultrasound frequencies as pretreatments with different infrared drying temperatures were tested for drying of sweet potatoes to study the drying kinetics, mathematical modeling, energy activation, and thermodynamic properties of dried sweet potatoes. The treated samples showed a significant reduction in drying time by 110 to 60 min as compared to the control ones. Hii model, Page model, and Silva models found satisfactorily described the drying kinetics among 13 different tested mathematical models. The effective diffusion varied from 1.01 × 10⁻⁰⁶ to 9.21 × 10⁻⁰⁶, while the lowest activation energy recorded as 24.69 kJ/mol in samples pretreated with 40 kHz. The enthalpy and Gibbs free energy decreased with the increase in drying temperature while entropy decreased and obtained as negative during drying. In addition, the moderate ultrasound frequency of 40 kHz positively and significantly (p < 0.05) influenced the surface color, enzyme inactivation, enzymatic browning, and microstructure of dried sweet potatoes.
Practical applications
This study investigated the impact of sequential ultrasound (US) frequencies and infrared (IR) temperatures. The study provides significant evidence that the US in combination with IR not only reduces drying time but also improve the quality of the dry product on moderate US frequency. Higher US frequency (60 kHz) at higher temperature did not significantly improve the drying time but also showed big pores in SEM analysis.
... Excessive ultrasound power could cause cell rupture in the product,thus affecting the distribution of the water evaporation effect during the drying process, which is unfavourable with respect to the formation of evaporation channels.Therefore, the rehydration rate of heat-pump dried tilapia filletswas lowered. Similarly, Stojanovic et al. [32] investigated the impact of ultrasound-assisted osmotic dehydration on rabbit-eye blueberries and found that although ultrasound enabled the material to generate a porous structure, the rehydration rate remained low. ...
The dehydration of a tilapia fillet is conducive to its preservation. However, dehydration results in high energy consumption and quality variation. Ultrasound-assisted osmotic dehydration as a pre-treatment combines the advantages of strong permeability by preservatives and the cavitation effect and can improve the quality of tilapia fillets dried by heat-pump drying while decreasing the drying time and maintaining the quality of the dried products. The whiteness, texture, rehydration rate, Ca²⁺ adenosine triphosphate synthase (Ca²⁺-ATPase) activity and the comprehensive score were used as criteria in single-factor experiment son ultrasound power, ultrasonication and permeate concentration. Based on the results of the single-factor experiment, the Box-Behnken central composite design was adopted to achieve response-surface optimisation. The results indicated Ultrasound-assisted osmotic dehydration as a pre-treatment with suitable ultrasound parameters can significantly improve the quality of heat-pump dried tilapia fillets and provides references for optimising the drying process.
... These results showed that blueberries pretreated with OD were slightly less firm and stiff than those pretreated with HAD. This behavior may be explained by the fact that the sugar uptake during OD minimized shrinkage, thus reducing the compactness of the dried samples [51]. ...
In this work, we examined and compared two combined alternatives for the drying of blueberries (O’Neal). Pretreatments of osmotic dehydration (60°Brix sucrose solution at 40°C for 6 h) and hot air drying (HAD) (60°C, 2.5 m/s for 90 min) were performed to reach the same water content. Pretreated blueberries were then dried by microwave at different microwave output power values: 562.5, 622.5, and 750 W. The combined drying processes were also compared with HAD alone (control). The effects of the processes over blueberries were studied in terms of decrease in water content, drying rate (DR), mechanical properties (firmness and stiffness), optical properties (L*, a*, and hue angle (h)), antioxidant capacity, and rehydration capacity. The hot air–microwave drying decreased the process time and presented a high drying rate compared with the osmotic dehydration–microwave processes and the control drying. In terms of quality, the antioxidant and rehydration capacities were the most affected. The results showed that the best drying method to obtain the desired final product was the hot air–microwave drying (750 W).
... Water activity was reduced further below 0.82 only after drying in infrared drier. Drying by infrared radiation found to restore texture [29] this texture retention could be due to sugar infusion into the intercellular spaces [30].Infrared radiation also controlled enzymatic browning .Samples stored in aluminum foil cups with clin wrap packing showed more natural texture and color. However, 50% moisture loss was observed in aluminum foil cups with clin wrap in the first month of storage. ...
Development of safe, shelf stable foods are necessary to reduce dependence on refrigeration during their storage and distribution. Studies were conducted to develop Shelf stable intermediate moisture (IM) Pineapple (Ananas comosus) based on 'hurdle technology', (HT) using gamma irradiation. Processing conditions were established to observe the effect of radiation on development of shelf stable IM pineapple. The most important hurdles used were reduction of water activity (aw) by osmosis, infrared drying (IR), 400 gauge polyethylene bags along with mild dose of irradiation(R) (1kGY). IM pineapple subjected to Infrared drying and radiation (IRR) and non radiated (IR) were evaluated for shelf life at ambient (34 ± 2 ºC and 65% RH) temperature. The shelf life of the IRR was found to be 4 months where as IR spoiled within 3 months at ambient temperature. On storage, IRR showed no significant (p>0.05) changes in a w, moisture and reducing sugars. Total sugars, total soluble solids and acidity increased in both the treatments significantly (p>0.05). pH, ascorbic acid decreased significantly as storage period increased. Vitamin 'C' retention was up to 65.3% in IRR treatment. The combination of hurdles including osmotic dehydration, infrared drying and gamma radiation dose of 1 kGy, successfully reduced the microbial load and showed high product quality. This treatment can be considered the most adequate for obtaining high quality IM pineapple with optimum sensory, microbial nutritional quality and storability. These IM pineapples are energy efficient, satisfactory and give great prospects to commercial application opening new possibilities for processed food markets.
... Since it can be carried out at room temperature, OD obtains a series of desired attributes, such as low energy consumption, less nutriment loss and well preservation of color, flavor and structure. Hence, the traditional process has gained a renewed and increased interest, especially as a pretreatment in hybrid drying technologies (Torreggiani, 1993;Stojanovic and Silva, 2006). ...
... These results showed that blueberries pretreated with OD were slightly less firm and stiff than those pretreated with HAD. This behavior may be explained by the fact that the sugar uptake during OD minimized shrinkage, thus reducing the compactness of the dried samples [51]. ...
In this work, we examined and compared two combined alternatives for the drying of blueberries (O´Neal). Pretreatments of osmotic dehydration (60°Brix sucrose solution, at 40°C for 6h) and hot air drying (60°C, 2.5 m/s for 90 min) were performed to reach the same water content. Pretreated blueberries were then dried by microwave at different microwave output power values: 562.5W, 622.5W and 750W. The combined drying processes were also compared with hot air drying alone (control). The effects of the processes over blueberries were studied in terms of decrease in water content, drying rate, mechanical properties (firmness and stiffness), optical properties (L*, a* and hue angle (h)), antioxidant capacity and rehydration capacity. The hot air-microwave drying decreased the process time and presented a high drying rate compared with the osmotic dehydration-microwave processes and the control drying. In terms of quality, the antioxidant and rehydration capacities were the most affected. The results showed that the best drying method to obtain the desired final product was the hot air-microwave drying (750W).
... [3,4] Osmotic dehydration can be carried out to obtain several types of products, such as high-moisture or intermediatemoisture fruits, or it can be used as a pretreatment before drying or freezing. [5][6][7][8][9] As high temperatures are not normally used in OD processes, and no water phase changes occur, changes in sensory attributes, such as color, aroma, flavor, and texture, are minimized. [10,11] Sugar uptake during osmotic dehydration of fruit modifies the composition (sugar to acid ratio) and the taste of the final dehydrated food. ...
Raspberries are very labile fruits that have a short postharvest life; therefore, there is a need to develop alternative storage and processing methods for extending their shelf-life. The effect of wet (WI) and dry (DI) sucrose infusions (aw = 0.85) on color and bioactive compounds of raspberries has been studied. Additives were included: citric acid, sodium bisulfite, or both. Moisture content decreased from 85% (w/w) for control fruit to approximately 51% (w/w) for infused samples. The shrinkage of fruits was approximately 27% and 46% after WI and DI, respectively. No major color changes occurred, except for WI-bisulfite treatment. Although the total polyphenols and anthocyanin content were significantly reduced in fruits during osmotic dehydration, mainly due to the dilution effect to the medium, 100 g serving of processed raspberries would supply, in some cases, over 50% of polyphenols provided by a glass of wine. The proposed infusion dehydration methods may be considered an alternative to produce shelf-stable products based on raspberries, with an improved quality in terms of appearance.
... However, vacuum drying methods are not suitable for timber with high initial moisture contents (Welling 1994), and surface checking and internal checking can be significant problems with wood vacuum drying when the drying temperature is high (Li et al. 2009); This is because of insufficient moisture movement from the center of the wood samples to the surface during the vacuum drying process which can cause steep moisture gradients from the core to wood surface layers; such gradients can lead to checking (Avramidis et al. 1994). In order to reduce the drying defects and to reduce the drying time, various methods of pretreatment of wood before drying have been reported to modify the material tissue structure (Madamba and Lopez 2002, Stojanovic and Silva 2006, Yong et al. 2006. ...
The influence of ultrasonic pretreatment prior to vacuum drying of Chinese fir specimens was examined in this work. In the pretreatments, wood samples were immerged in a distilled water bath and were treated using two wave frequencies for four different elapsed times to investigate effects of ultrasonic frequency and treatment duration. Then the wood samples were vacuum-dried at 80°C and absolute pressure of 0,05 MPa. After the pretreatment, microscopic analysis was carried out on the wood samples to check micro-cracks, the loss of extractives from the cell walls and other micro-structural changes on the wood. Results show that the ultrasonic treatment prior to vacuum drying significantly shortened the wood drying time. The drying time decreased with increase in the wave frequency and the treatment time. Furthermore, ultrasound pretreatment tended to reduce the content of extractives in the wood cell walls and cause cell-wall micro-cracking.
... Therefore, ultrasonic waves could promote cavitation and induce the formation of microchannels within the tissue of wood samples, which could be found in many existing researches. [27,28] However, wood was hard to pretreat, compared with food. Wood was hard and consisted of cellulose, hemicellulose, and lignin. ...
Ultrasound pretreatment of wood prior to drying was examined as a method to increase the effective water diffusivity, reduce drying time, and improve product quality of Chinese Catalpa wood. Pretreatment tests were carried out at three pretreatment durations, three absolute pressure levels, and three ultrasonic intensities. All specimens were then dried at 60°C and the absolute pressure level of 0.02 MPa to determine the effects of pretreatment parameters on vacuum drying characteristics. A microscopic analysis was carried out to visualize the formation of microchannels and view any other changes to wood tissue structure that occurred. Results showed that ultrasound pretreatment prior to vacuum drying enhances the effective water diffusivity; the higher the ultrasound power level, the longer the pretreatment time, and the lower the absolute pressure, the shorter is the drying time. Ultrasound creates micro channels within the tissue of wood during pretreatment. However, the pretreatment time should not be too long when the ultrasound is high.
... High power ultrasound in food industry processing is considered to be an emergent technology which is becoming increasingly appreciated. Power ultrasound may be applied during drying to improve the rate of the process [9] or as a pretreatment to accelerate the subsequent drying rate [10]. The use of ultrasonic energy is very promising because it can act without affecting the main characteristics and quality of the products. ...
Drying kinetics of carrot cubes were carried out at 1 m/s air velocity at different air drying temperatures (30, 40, 50, 60 and 70±0.1 °C) (AIR experiments), and also at the same experimental conditions but applying high power ultrasound (US experiments). Two kind of diffusion models were used to simulate the drying kinetics, according to external resistance to mass transfer being considered (ER model) or neglected (NER model) for solving the diffusion equation. Diffusion ER model was solved using a finite difference method. Drying rate increased as air temperature was higher. Ultrasound also increased drying rate at the different temperatures, but the improvement on drying rate decreased at high temperatures, and almost disappeared at 70 °C. Effective moisture diffusivities only showed an Arrhenius type relationship with temperature for AIR experiments. The NER diffusion model was not accurate to simulate the drying kinetics at any experimental conditions tested. However, diffusion ER model provided a high closeness between experimental and calculated drying data (VAR>99.80). Through the parameters identified of the ER diffusion model, effective moisture diffusivity and mass transfer coefficient, the influence of the power ultrasound application on internal and external resistance to mass transfer was shown to be significant (p<0.05).
... Drying by infrared radiation has also been reported earlier, to stabilize the texture of sugar-infused IM blueberries during storage (Shi et al, 2008). This texture retention could be due to sugar infusion into the intercellular spaces (Stojanovic & Silva, 2006). The combination of potassium metabisulfite dip, osmotic dehydration and infrared drying treatments, were fairly successful in maintaining texture values up to 6 days of storage. ...
A process has been developed to prepare shelf stable ready-to-eat (RTE) intermediate moisture pineapple (Ananas comosus) slices using hurdle technology. The combination of hurdles including osmotic dehydration, infrared drying, and gamma radiation dose of 1kGy successfully reduced the microbial load to below detectable limit. The shelf life of the intermediate moisture pineapple slices was found to be 40 days at ambient temperature (26±2°C). The untreated control samples spoiled within 6 days. The RTE intermediate moisture pineapple slices were found to have good texture, colour and sensory acceptability during this 40 days storage.
... [1] Usually, some form of pre-treatment is used to reduce the initial water content or to modify the fruit tissue structure to reduce the total drying processing time. [2][3][4][5][6][7][8][9][10] Ultrasonic waves can cause a very rapid series of alternative compressions and expansions, in a similar way to a sponge when it is squeezed and released repeatedly (the so-called sponge effect). The forces involved in this mechanical mechanism can be much greater than those due to surface tension, which holds the moisture inside the capillaries of the fruit creating microscopic channels which may ease moisture removal. ...
This work examined the influence of the ultrasonic pretreatment prior to air drying on dehydration of melon (Curcumis melo L.). Ultrasonic pretreatment for air drying of fruits was studied and compared with osmotic dehydration. This study allowed estimate of the effective diffusivity water in the air-drying process for melons submitted to ultrasonic pretreatment. Results show that the water effective diffusivity increases after application of ultrasound causing a reduction of about 25% in the drying. During ultrasonic treatment the melons lost sugar, so such a pretreatment stage can be a practical process to produce dried fruits with lower sugar content. Compared to osmotic dehydration, the use of ultrasonic pretreatment performed better when large amounts of water need to be removed from the fruit, since the combined processing time (pretreatment and air drying) is shorter.
... Usually, some form of pre-treatment is used to reduce the initial water content or to modify the fruit tissue structure to reduce the total drying processing time. [1][2][3][4][5][6][7] In this work the use of ultrasound as a pre-treatment to air-drying was investigated. ...
This work examines the influence of ultrasonic pretreatment prior to air drying on dehydration of sapota (Achras sapota L.). This study allowed estimate of the effective water diffusivity in the air-drying process for sapotas submitted to ultrasonic pretreatment. Results show that the water effective diffusivity increases after application of ultrasound, causing a reduction of about 23% in the drying time. During ultrasonic treatment in distilled water, the sapota fruit displayed reduction in sugar content, so such a pretreatment stage can be a practical process to produce dried fruits with lower sugar content if it is made cost-effective.
... New pretreatments of materials to be dried, usually based on chemical manipulation , have successfully reduced drying times.1234 Traditional processes such as osmotic dehydration have recently gained a renewed and increased interest, mainly as a pretreatment in combined techniques.5678 Osmotic dehydration consists of immersing the material to be dried in a hypertonic solution. ...
Pretreatment of fruits prior to drying has shown success in reducing drying time and costs. In this work, ultrasound-assisted osmotic dehydration has been implemented as a method to increase water diffusivity and reduce drying time in strawberries. Strawberry halves were immersed in distilled water and in two different concentrations of sucrose solutions while pretreatment time and ultrasonic frequency levels were varied to determine their effect on drying time, water loss, and soluble solids gain. A microscopic analysis was carried out to evaluate the formation of microchannels and other changes to the fruit tissue structure. Greater sucrose concentration used in ultrasound-assisted osmotic dehydration resulted in greater water loss with greatest loss observed for the strawberry halves pretreated for 45 min in a 50% w/w sucrose solution. The pretreatment carried out for 30 min employing an osmotic solution of 50% w/w of sucrose resulted in the highest drying rate among the pretreatments. Osmotic dehydration used alone during pretreatment increased total processing time, whereas osmotic dehydration combined with ultrasonic energy during pretreatment reduced total processing time and increased effective water diffusivity. Cell distortion and breakdown were observed not only in pretreatments employing ultrasound-assisted osmotic dehydration but in conventional osmotic dehydration. Formation of microchannels through ultrasonic application and effects of osmotic pressure differential were considered to be largely responsible for reducing drying time for strawberry halves.
... Conversely, Deng and Zhao [24] observed that when dehydrated apple pieces were rehydrated, the rehydration rates were slower for apples pretreated with ultrasound probably due to severe tissue damage at the surface and cell deformation (Fig. 2). Similar observations were made when blue berries were treated with ultrasound [72]. Deng and Zhao [24] reported an increased hardness and crispness of apples pre-treated with osmo-dehydration assisted by ultrasound upon air drying or freeze drying. ...
Ultrasonic processing in simple terms is the application of sound waves in the frequency range of 20kHz–1MHz which is above
the range of human hearing. This review focuses on the applications of ultrasound to accelerate processes such as dehydration,
drying, freezing and thawing, tenderization of meat, crystallization of lactose and fat and to improve processes such as cutting,
extraction, emulsification, ageing of wines and esterification. The effect of ultrasound on physical properties such as viscosity,
opacity, particle size and gel strength is also considered. We find that it is the physical effects of ultrasound that predominate
in most applications considered to date. Ultrasound increases heat and mass transfer, disrupts aggregates and can break macromolecular
chains.
... Conventional air-drying is a simultaneous heat and mass transfer process, accompanied by phase change being a high cost process. Usually, some form of pre-treatment is used to reduce the initial water content or to modify the fruit tissue structure to reduce the total drying processing time (Madamba & Lopez, 2002;Beaudry et al., 2004;Stojanovic & Silva, 2006). Ultrasonic waves can cause a very rapid series of alternative compressions and expansions, in a similar way to a sponge when it is squeezed and released repeatedly (the so-called sponge effect). ...
This work evaluated the production of dehydrated papayas (Carica papaya L.) with low sugar content. The product was obtained applying ultrasonic waves to enhance the loss of sugar from the fruit.
To achieve this goal, this paper examined the influence of the ultrasonic pre-treatment before air-drying on dehydration of
papaya. Ultrasonic pre-treatment for air-drying of fruits was studied and compared with osmotic dehydration. This study allowed
estimate of the effective diffusivity water in the air-drying process for papayas submitted to ultrasonic pretreatment. Results
show that the water effective diffusivity increases after application of ultrasound causing a reduction of about 16% in the
drying time. During ultrasonic treatment the papayas lost sugar (13.8% in 30min), so such a pre-treatment stage can be a
practical process to produce dried fruits with lower sugar content.
The study aimed to optimize the ultrasound assisted osmotic dehydration process of white mulberry using response surface methodology. Effects of three variables including ultrasonic treatment time (10, 20, and 30 min), osmotic solution concentration (25, 42.5, and 60 % w/w), and frequency intensity (10‐90 %) were investigated. Three responses were studied; water loss (WL), sugar gain (SG), and color parameters (a*, b*, L*, and ΔE). Results represented that, in comparison to the osmotic dehydration alone, the application of ultrasonic treatment reduced the total processing time and increased effective water diffusivity. Results revealed that frequency intensity had significant effects on all response variables except for L* and b *. Increasing the frequency intensity led to increased WL (10 times) and ΔE in the samples and a decrease in SG (2.8 times). It was also observed that time‐ concentration interaction term of response models is statistically significant for all responses except for ΔE, a*and b*, while time‐amplitude interaction term was statistically significant for ΔE, alone. Finally, multi objective optimization according to the response surface models showed that the best conditions are osmotic solution concentration: 60%, frequency intensity: 75% and ultrasound time: 10 min. At this optimum conditions, WL, WR, SG, a*, b*, L* and ΔE were found to be 0.127%, 0.097%, 0.03 %, ‐3.700, 32.071, 81.969 and 3.955 respectively.
Hot-air drying is an important unit operation in agriculture products processing, whereas the energy efficiency utilization rate is low currently. Recently, there is growing development trend in hot-air drying towards high standards like energy conservation, high efficiency and further improvement of the product quality. As an effective medium of energy, power ultrasound can be used to enhance mass and heat transfer with outstanding advantages, due to its good propagation directivity and high acceleration of medium particle vibration. In this review, we presented the principle of high power ultrasound for gas media design, illustrated the system types and composition of enhanced ultrasound hot-air dryers. Summarized the study and progress of the enhanced high power ultrasound for gas media applied for drying wet materials, and discussed some existing problems during the research and the future development trends.
High hydrostatic pressure, pulsed electric fields, ultrasound, and cold plasma are emerging technologies that have already found application in the food industry. This summary aims to describe the basic principles of these nonthermal technologies as well as the state of the art concerning their impact on biological cells, enzymes, and food constituents. Current and potential applications will be discussed focusing on process-structure-function relationships as well as recent advances in process development.
The aim of the study was to investigate the influence of ultrasound treatment on the carrot tissue microstructure, colour and carotenoids content. To avoid adverse effects of rinsing out substances contained in the raw material, carrot slices were vacuum-packed and treated with ultrasounds in an ultrasonic bath using 21 and 35 kHz frequency for 10, 20 and 30 min. Images of the carrot tissue made by scanning electron microscope were analysed by calculating the cross-section area for each cell. The colour was measured using CIE L∗a∗b∗ method. To determine total carotenoid content spectrophotometric method was used. Obtained results indicate that the structural properties of carrots treated with ultrasound were significantly different from the samples without any treatment and it was clearly noticed during analysing images of scanning electron microscope. There was observed the influence of ultrasound treatment on colour L∗, a∗ and b∗ parameters, especially for carrot treated with ultrasound for 30 min, independent of the applied frequency of the ultrasonic waves. Similarly, sonic treatment resulted in substantial increase of carotenoid in comparison to raw carrot, especially in the case of 35 kHz frequency ultrasounds. Probably, such significant increase is caused by the destruction of the original structure and thus higher extraction ability of these compounds.
Fresh foods like vegetables, fruits and aquatic products have high water activity and they are highly heat-sensitive and easily degradable. Dehydration is one of the most common methods used to improve food shelf-life. However, drying methods used for food dehydration must not only be efficient and economic but also yield high quality products based on flavor, nutrients, color, rehydration, uniformity, appearance and texture. This paper reviews some new drying technologies developed for dehydration of vegetables, fruits and aquatic products. These include: infrared drying, microwave drying, radio frequency drying, electrohydrodynamic drying, etc., as well as hybrid drying methods combining two or more different drying techniques. A comprehensive review of recent developments in high-quality drying of vegetables, fruits and aquatic products is presented and recommendations are made for future research.
The aims of this study were to: (i) evaluate the effect of each stage of HACD + MWVD on the drying
kinetics and quality parameters of blueberries, including color, overall appearance, mechanical and physical
attributes, and rehydration potential; (ii) select proper combination order and conversion point of HACD +
MWVD to minimize physicochemical changes and maintain high quality of blueberries. The results were
compared with HACD and MWVD alone. A linear equation produced a good fit to data describing the drying
kinetics of the constant or first falling rate period, whereas the Henderson and Pabis model was a good fit for the dataset describing the second falling rate period. The color changes induced in berries by HACD + MWVD were limited (ΔE* ranged from 3.08 ± 2.25 to 3.65 ± 2.28) in comparison with HACD (ΔE* ranged from 7.90 ± 2.29 to 8.21 ± 1.77). HACD + MWVD contributed to the achievement of significantly lower values of hardness,
chewiness and gumminess in blueberries, compared to HACD. Multi-stage HACD + MWVD with hot air predrying at 80 °C until the achievement of the moisture content of 1.95 ± 0.05 kg · kg-1 db caused the lowest
shrinkage of blueberries. Blueberries dried by multi-stage HACD + MWVD with hot air pre-drying at 80 °C
until the achievement of moisture content of 1.95 ± 0.05 kg · kg-1 db were characterized by the highest
rehydration potential, in terms of moisture content, rehydration ratio and water gain, i.e. 4.15 ± 0.02 kg · kg-1 db, 4.02 ± 0.05 g · g-1 db, 4.07 ± 0.01 g · g-1 db, respectively.
The quality of freeze drying (FD)4.5 h-microwave vacuum drying (MVD) iron yam slices was almost the same with FD samples in terms of bulk density, color, etc., in the previous experiments. This work verified it by comparing the microstructure of the samples. In addition, the microstructure and quality of samples with different conversion point during combined FD and MVD were tested in order to illuminate the change mechanism for cell structure and the relationship between microstructure and corresponding quality. Moisture conversion point and melting significantly affected the microstructure of samples. The cell structure of samples dried by FD3.5 h-MVD with melting samples was maintained very well. However, obvious cell wall breakage and even collapse was observed in FD2 h-MVD samples. Quality indices such as bulk density and color are positively related to microstructure change. FD3.5 h-MVD with melting was better than FD4.5 h-MVD because of almost the same quality and shorter drying time.Practical ApplicationsIn most previous researches, the optimal moisture conversion point was usually the end of sublimation stage during freeze drying (FD)-microwave vacuum drying (MVD). There was no obvious ice crystal in sample at this point, which showed that the materials absorbed the microwave energy uniformly and caused high quality of final products. However, for vegetables and fruits materials that are rich in starch, such as iron yam, moisture conversion point was chosen in advance. Ice crystal in the samples melted slowly in low temperature and well-distributed moisture again after FD. The structure of the materials was maintained very well because of the support from raw starch granules. Therefore, high-quality dried products were also obtained under this technique conditions. In general, energy consumption for FD-MVD drying was decreased further while the quality of the materials was maintained well.
The effect of ultrasound pre-treatment on quality attributes of air-dried pears was investigated, with the aim of shortening the overall processing time, maximizing the production yield and maintaining the optimum contents of saccharides and bioactive compounds. The contents of saccharides, total phenols and flavonoids, as well as the antioxidant capacity were determined spectrophotometrically. Consumer evaluation of sensory properties was conducted using hedonic scale preference analysis. Under the same air-drying conditions, prolonged ultrasound pre-treatment led to a decrease in the contents of total saccharides, phenols and flavonoids, as well as to a decrease in antioxidant capacity and sensory quality (appearance of brown spots, grainy mouth feel, hard texture) of dried pears. The highest contents of fructose, glucose and saccharose amounted to 381.95 mg·kg-1, 279.81 mg·kg-1 and 28.52 mg·kg-1 of dry matter of sample, respectively, while non-treated pears dried for 720 min exhibited the highest total phenol content of 4.33 g·kg-1 of dry matter (expressed as gallic acid equivalent). According to the performed experiments, the combination of a shorter ultrasound pre-treatment (up to 10 min) and 360 min of air drying is the most efficient for obtaining a product with the best nutritive composition, in terms of saccharide and polyphenol contents, as well as the best sensory properties.
The effect of ultrasound pretreatment at various power (360 W, 600 W and 960 W, frequency 20 kHz) on the glass transition temperature of freeze dried pear (Pyrus pyrifolia) has been studied. DMA temperature plots were divided into four sections (A = glassy region, B = transition region, C = Rubbery plateau region and D = terminal region) with the aim to analyze their properties changed with sonication. Under the same freeze drying condition, with the increase in ultrasonic power, dried pear showed higher glass transition in term of storage modulus, loss modulus and loss tangent peak. Also a decrease in aw (0.31 to 0.23) and in moisture content (0.12 to 0.08 g/g d.b.) has been observed. Samples pretreated with ultrasound showed a better texture profile and much porous structure compare to control one. The results from the study indicated that, ultrasound pretreatment prior to freeze drying can improve the stability during storage of freeze dried pear.
The effect of pulsed vacuum and ultrasound pretreatments on glass transition, texture, rehydration, microstructure and other selected properties of air- and freeze-dried apples (Fuji) were investigated. Apple cylinders (15mm height×15mm diameter) were first osmoconcentrated in a 60g/100g high-fructose corn syrup solution containing 7.5g/100g Gluconal Cal® combined with agitation, pulsed vacuum (PV), or ultrasound for 3h, then hot-air or freeze dried. Changes in glass transition temperature, hardness, crispness, and rehydration rate were measured, microstructure was observed using scanning electronic microscopy (SEM), and calcium ions distributions were analyzed by a laser ablation inductively coupled mass spectrometry (LA-ICP-MS). Under the same drying method, ultrasound led to a higher glass transition temperature, lower water activity, moisture content and rehydration rate, severer structure collapse, less cavities and calcium uptake than PV did. Different osmoconcentration pretreatment had no significant (P
High hydrostatic pressure (HHP), pulsed electric fields (PEFs), ultrasound (US), and cold plasma (CP) are emerging technologies that have already found application in the food industry or related sectors. This review aims to describe the basic principles of these nonthermal technologies as well as the state of the art concerning their impact on biological cells, enzymes, and food constituents. Current and potential applications will be discussed, focusing on process-structure-function relationships, as well as recent advances in the process development.
Several vegetables and fruits, apple, ginger, carrot, and pumpkin were dehydrated under various osmotic conditions using sucrose and salt as the permeating agents. The dehydrated materials were then dried. The influence of solute concentration, process temperature and the type of solute on osmotic dehydration and further thermal drying were investigated. The nutrition loss during the osmotic process was measured using carotene as the nutrition index. The effect of calcium chloride present in osmotic solution on the product quality was also studied. A first order kinetic model was chosen to describe the mass transfer phenomena of the osmotic process. The equilibrium value of water loss, solute gained, kinetic constants KWL and KSG under various conditions are successfully predicted by the model. The relationship between the equilibrium value and four major factors that influence osmotic process of carrot was obtained based on the experimental data. The relations between the loss constant of carotene and the solute concentration in carrot and pumpkin were obtained based on the experimental data. The qualities of dried products are better for the osmotic dehydration pretreated samples than those dried directly.
Frozen blueberries (Vaccinium corymbosum L cv. ‘Elliott’) were dried in a microwave and spouted bed combined dryer (MWSB) at 70C air temperature and 3.7 W/g microwave power (wet material). the effect of pretreatment using a 2.5% Ethyl Oleate & 0.2 NaOH dipping solution followed by sucrose osmotic treatment was investigated. the drying kinetics of MWSB drying was compared with spouted bed (SB) drying with dipping treatment, and with tray drying. the rehydration ratio, the color, and the bulk density of MWSB dried blueberries were compared with those of freeze, tray, and SB drying. the drying time needed to reduce blueberry moisture content from 82.5% to 15% (wet basis) using MWSB drying was 1/19 and 1/24 (with and without pretreatment) of the time for tray drying. the MWSB drying resulted in a low bulk density and more reddish and less blue color compared with other methods. MWSB dried frozen blueberries exhibited a higher rehydration ratio in short soaking times. Analysis of flavor volatiles by GC/MS identified ten heat-generated compounds. Microwave heating generated three unique flavor compounds (2-Butanone, 2-methyl butanal, and 3-methyl butanal). Freeze-dried frozen blueberries lost several flavor compounds including the typical blueberry aroma, the 1, 8-Cineole.
High-intensity ultrasound accelerates diffusion of materials into biological membranes and can be used to improve food processes. Some possible mechanisms are presented, as well as an attempt to explain theoretically how and why sound affects mass transfer. Some important factors to acoustically-mediated diffusion processes are classified. A summary of acoustic drying and research on such processes is presented.
The drying rates, rehydration ratios, color, texture and sensory evaluations of blueberries that were pretreated with ethyl oleate and sodium hydroxide, osmotically dehydrated in sucrose and dried in various regimes were compared. The drying regimes were: convection (35 ºC or 45 ºC at 2 m s-1); microwave-assisted convection (0.1 or 0.2 W g-1 incident power and freeze-drying. Convection and microwave assisted convection trials were performed in a 750 W multimode cavity microwave drier equipped with electrical heaters and blower. The berries were dried to 15% moisture content (wet basis). It was concluded that the procedure involving pre-treatment, osmotic dehydration and microwave-assisted drying led to a dried blueberry that was comparable to the freeze-dried berry in a much shorter time. Convection drying took the longest time.
The kinetics of moisture loss and solids gain during osmotic dehydration of blueberries under different conditions of temperature (37 degrees C - 60 degrees C), Concentration of the sucrose solution (47 degrees Brix - 70 degrees Brix) and contact time between fruit and sucrose solution (0.5 h - 5.5 h) were studied, and modeled based on Fick's law of unsteady state diffusion. The study showed that all factors influenced moisture loss and solids gain (p < 0.001), both generally increasing with temperature (T) and sucrose concentration (C). Based on the diffusion model, the calculated effective moisture diffusivity (D-m) ranged from 1.98 x 10(-10) to 5.10 x 10(-10) m(2)/s and the effective solids diffusivity (D-s) ranged from 2.54 x 10(-11) to 2.22 x 10(-10) m(2)/s. Both D-m and D-s showed increasing trends with temperature and sucrose concentration, and could be modeled as quadratic functions of T and C.
Drying causes many chemical and physical changes in plant tissue. Physical changes are mostly due to stresses developed in the tissue and are pronounced by macro- and microalterations of size, shape and internal structure. The extent and direction of these changes depend on the mode of drying. Convective drying of apple tissue results in numerous breaks of cell walls and formation of many microcavities. In consequence, the dominating cross-sectional area of cells moves toward values smaller than those observed in raw apple. Cavities formed during convective drying can be pictured in 2D plane as pentagons joined together or ellipses with large ratio between axes. Puff-drying forms porous structure with cavities twice as large as in raw apple. The process homogenizes the structure, and spread of cell sizes is even smaller than that observed in raw apple. Broken cell walls are clearly visible in microphotographs of sliced samples. Many large cavities with cross-sectional area exceeding 40,000 µm are characteristic of puff-dried apple while such areas are hardly found in raw apple. The structure of freeze-dried apple is similar to that formed during puff-drying. Large irregular cavities and broken cell walls are clearly seen in microphotographs. However, larger cavities are present in freeze-dried apple than in puff-dried one. Cross-sectional area of cavities in freeze-dried apple can be simulated by pentagons joined together or elongated ellipses.
With reference to typical food preservation processes which consist of changing the water binding to material, the technology and application of osmotic dehydration were discussed as an initial treatment before convection drying of fruit and vegetables. Particular attention was paid to the possibilities to produce more shelf-stable food while keeping the high quality of final product. The course of osmotic dehydration of plant tissue as well as its influence on convection drying and on the properties of preserved fruit and vegetables were presented.
The color, texture and rehydration ratios of two-stage osmo-convective dried blueberries were evaluated. The parameters analyzed for color were the total color difference (ΔE) and the red-blue (a/b) ratio. The textural parameters of hardness and stickiness of the osmo-convective dried blueberries were evaluated. The results were compared with those of conventionally air-dried blueberries (worst case scenario) and freeze-dried blueberries (best case scenario). The results showed that osmotic dehydration for a short contact time minimized color losses during convective air-drying. The osmo-convective dried blueberries were not significantly harder (p > 0.05) than the conventional air-dried blueberries. The rehydration ratios of the osmo-convective dried blueberries were lower than the rehydration ratios of freeze-dried and air-dried blueberries. The best osmotic dehydration condition under which the osmo-convective dried blueberries had better color and texture and, a shorter drying time than the conventional air-dried blueberries was 50°C – 55°Brix for 4.5 h.
This study reports on finish drying of osmotically pretreated (dehydrated and sugar-infused) cranberries. The halved fresh berries pretreated in a standard osmotic solution (67.5 Brix at 50°C for 5 h) were then freeze-dried, vacuum-dried and air-dried in various dryers (cabinet-air-through, fluid bed, pulsed fluid bed, and vibrated fluid bed dryers) in order to identify the best drying technology. Energy consumption and product quality were chosen as the comparison criteria. The best product quality, quantified by the anthocyanins content, rehydration ratio, color and taste, was noted for freeze-dried berries. As all other drying methods gave similar, albeit slightly lower quality products than freeze-drying, the selection of a drying method could be based on the unit heat consumption. The vibrated fluid bed and the pulsed fluid bed should be favored because of the highest energy efficiency. Even though sugar infused into cranberries during osmotic pretreatment reduces drying rates during the second drying period as compared to untreated berries, osmotic dehydration reduces the total energy consumption on top of the preferential sensory characteristics of the final product.*The copyright is held by © Her Majesty the Queen in Right of Canada, represented by the Minister of Natural Resources and Agriculture and Agri-Food Canada, 2002.
In order to design, manufacture, and commission a commercial dryer to dry individually quick frozen (IQF) wild blueberries (Vaccinium angustifolium), The Nova Scotian Fruit Company completed a series of experiments to characterize the effect of air velocity, air temperature, and packed bed depth on drying. Based on previous experience with forced air packed bed drying systems at air temperatures up to 65°C, the experiments focused on measuring the effect of air temperature and velocity during the first few hours of drying. The data collected suggest that drying occurs solely in the falling rate period. These data were used to successfully design, build, and commission a commercial dryer with a tenfold increase in production capacity over previous equipment.
Artificial neural network (ANN) models were used for predicting quality changes during osmo-convective drying of blueberries for process optimization. Osmotic drying usually involves treatment of fruits in an osmotic solution of predetermined concentration, temperature and time, and generally affects several associated quality factors such as color, texture, rehydration ratio as well as the finish drying time in a subsequent drier (usually air drying). Multi-layer neural network models with 3 inputs (concentration, osmotic temperature and contact time) were developed to predict 5 outputs: air drying time, color, texture, and rehydration ratio as well as a defined comprehensive index. The optimal configuration of neural network model was obtained by varying the main parameters of ANN: transfer function, learning rule, number of neurons and layers, and learning runs. The predictability of ANN models was compared with that of multiple regression models, confirming that ANN models had much better performance than conventional mathematical models. The prediction matrices and corresponding response curves for main processing properties under various osmotic dehydration conditions were used for searching the optimal processing conditions. The results indicated that it is feasible to use ANN for prediction and optimization of osmo-convective drying for blueberries.
The second stage convective drying behavior of osmo-dehydrated blueberries was evaluated in a forced-air cabinet dryer (temperature: 50°C, relative humidity: 14%, air velocity: 0.6 m/s) with a cross-flow tray arrangement. Fick's second law of unsteady state diffusion was used to model the air drying kinetics. The results showed that the convective-air drying of the blueberries occurred in two falling rate periods. The effective diffusion coefficients, Deff, during the first falling rate period ranged from 1.19 × 10 m/s to 2.14 × 10 ms and ranged from 4.04 × 10 m/s to 1.32 × 10 m/s during the second falling rate period. Among the pre-treatment conditions, the temperature and sucrose concentration during osmotic dehydration significantly (p < 0.05) influenced the air drying time, while the effect of contact time was not significant (p > 0.05).
The effect of osmotic dehydration (OD) at atmospheric pressure and vacuum impregnation (VI) treatments on some physiochemical parameters of papaya (aw, pH, color, firmness, and microstructure) was analyzed. Osmotic treatments were carried out on papaya with 55°Brix and 65°Brix sucrose solutions at 30 °C. VI with 65°Brix osmotic solution was the most effective in reducing aw due to the highest sucrose gain during osmotic treatment. Color differences were associated to loss of clarity in line with transparency gain. Scanning electron microscopy observations show that osmotic dehydration caused shape changes and size reduction of papaya cells; also differences in microstructural features were observed between OD-treated and VI-treated samples. Moreover, the largest firmness observed in VI samples compared with OD treatments was associated with the thickness of the middle lamella between cells, which was greater in VI than OD treatments. Improvement in texture and palatability of papaya was obtained with VI rather than OD treatment compared with fresh papaya.
Concentration profiles in apple tissue during osmotic dehydration were studied and compared with simultaneous structural changes. Experiments were conducted in apple slices (20 and 30 mm thick) at 20, 30, 40 and 50°C. After treatments, water and solutes were analyzed in serial slices 1.5 mm thick. The occurrence of an “Advancing Disturbance Front,” (ADF) was proposed to describe the mass transfer. The ADF is located at a distance df to the interface, where the reduced driving force (Y) was 0.99. At distances d>df (undisturbed zone) neither compositional nor structural changes were observed. Advancing constant rates for the ADF were determined, showing slight temperature dependence. A generalized equation Y=f(d/df) described and fitted all the experimental data.
ABSTRACTA raisin-type product was prepared from lowbush blueberries using a sequence of osmotic dehydration, freeze drying, and thermal plasticization. Qualities of osmotically dehydrated blueberries, residual syrup, and final products were studied using various ratios of berry and sugar. An accelerated storage test was also conducted. IQF berries were preferred to fresh berries as a starting material, and a berry/sugar ratio of 3:1 or 4:1 was appropriate. Final products had good texture, flavor, overall acceptability, and a predicted shelf life of 16 and 64 months at 25° and 5°C storage, respectively.
Rabbiteye blueberries were dried using an experimental high temperature fluidized bed (HTFB) dehydrator and the properties of the dried product were evaluated. 15 m/sec air velocity was required for fluidization and at 170°C the moisture content (MC in kg water/kg dry matter) of thawed blueberries was reduced from 5.8 to 0.7 after 8 min. After osmotic dehydration in sucrose, MC was 1.3, and 4 min in the HTFB drier at 150°C reduced MC to 0.28. Reduction of water activity to 0.5 after HTFB required cabinet drying at 60°C and 4 m/ set for 2.13 and 2.75 hr for the untreated and osmotically dehydrated berries, respectively. HTFB simultaneously dried and puffed the berries, resulting in reduced bulk density compared to berries produced using conventional drying. Osmotic dehydration prior to HTFB imparted a raisin-like texture to the product.
Moisture sorption isotherms of freeze dried lowbush blueberries at 4, 16, 25, 35, and 45°C were determined using indirect gravimetric method. Moisture sorption kinetics at these temperatures and 75% RH were also investigated. The isotherms followed a type III shape with a temperature inversion effect at 0.9 water activity. They were best described by the GAB equation. Net isosteric heat of moisture sorption in freeze dried blueberries, determined using the Clausius Clapeyron equation, varied from 5.5 to 0.25 kJ/mol as moisture content changed from 8 to 36% (dry basis). Moisture adsorption kinetics in freeze dried blueberries were well described by the first order kinetics equation. The rate constant followed the Arrhenius relationship with an activation energy of 38.6 kJ/mol.
Antimicrobial effects of cinnamon, sodium benzoate, potassium sorbate, and combinations were examined against Escherichia coli O157:H7 in apple juice at 8°C and 25°C. E. coli O157:H7 was reduced by 1.6 log colony-forming units (CFU)/mL at 8°C and 2.0 log CFU/mL at 25°C by 0.3% cinnamon. At 8°C, 5.2 log CFU/mL of E. coli O157:H7 was eliminated in 11 d by 0.3% cinnamon with 0.1% sodium benzoate, and in 14 d by 0.3% cinnamon with 0.1% potassium sorbate. At 25°C, 5.3 log CFU/mL E. coli O157:H7 was eliminated in 3 d by the same combinations. A synergistic effect was observed between cinnamon and preservatives against E. coli O157:H7 at 8°C and 25°C.
Lowbush blueberries have been processed by freeze dry, forced air, vacuum oven, and micro-convection methods to a moisture content of 16-25%. The drying effect on the product quality was evaluated. There were no significant differences in vitamin A and niacin retention except freeze dried berries had higher vitamin C retention. No significant differences occurred in retention of mineral content except higher sodium and lower magnesium were found in the micro-convection and freeze dry methods, respectively. Freeze dried and vacuum dried blueberries had higher soluble solids retention and were darker and redder than forced air or micro-convection dried berries. Freeze dried berries were found to have highest rehydration ratio and lowest bulk density.
ABSTRACTA blueberry dehydration process which includes the unique continuous explosion-puffing system (CEPS) is described. A drying study including alternate drying pretreatments failed to increase the dehydration rate. It was found that care during processing was necessary to prevent rupture of the berries as rupture caused bleeding during drying which reduced the drying rate. Optimum operating conditions for CEPS were established for blueberries. Measurements of dried blueberry properties such as bulk density, color, rehydration, and disintegration were used to determine optimum operating conditions for pressure (103 kPa), temperature (190°C), and feed moisture (18.5%) for CEPS.
Experiments on osmotic dehydration of 1 cm apple cubes in 70 °Brix sucrose solution using ultrasound treatment were carried out at 40, 50, 60 and 70 °C. Acoustic pressure and frequency was measured to characterize the ultrasonic bath. Mass transfer was described by Fick's unsteady state diffusion equation. An important influence of the solution temperature on water transport was obtained. Measured water diffusivity coefficients (Dw) ranged from 2.6 × 1010−10 m2 s−1 at 40 °C to 6.8 × 10−10 m2 s−1 at 70 °C. Similar sucrose gain was measured at different temperatures, with an average effective sucrose diffusivity coefficient (Ds) (7.9 ± 0.2) × 10−11 m2 s−1. Similar experiments were performed under dynamic agitation conditions. A significant decrease in water and solute transport rates was detected when agitation was applied instead of sonication.
Different cultivars of four Vaccinium species [Vaccinium corymbosum L (Highbush), Vaccinium ashei Reade (Rabbiteye), Vaccinium angustifolium (Lowbush), and Vaccinium myrtillus L (Bilberry)] were analyzed for total phenolics, total anthocyanins, and antioxidant capacity (oxygen radical absorbance capacity, ORAC). The total antioxidant capacity of different berries studied ranged from a low of 13.9 to 45.9 micromole Trolox equivalents (TE)/g of fresh berry (63.2-282.3 micromole TE/g of dry matter) in different species and cultivars of Vaccinium. Brightwell and Tifblue cultivars of rabbiteye blueberries were harvested at 2 times, 49 days apart. Increased maturity at harvest increased the ORAC, the anthocyanin, and the total phenolic content. The growing location (Oregon vs Michigan vs New Jersey) did not affect ORAC, anthocyanin or total phenolic content of the cv. Jersey of highbush blueberries. A linear relationship existed between ORAC and anthocyanin (r(xy) = 0.77) or total phenolic (r(xy) = 0.92) content. In general, blueberries are one of the richest sources of antioxidant phytonutrients of the fresh fruits and vegetables we have studied.
Physicochemical and microstructural properties of fresh highbush and rabbiteye blueberries, their physicochemical changes during refrigerated storage, and method for softening frozen rabbiteye berries
- E Marroquin
Marroquin, E. Physicochemical and microstructural properties of fresh highbush and rabbiteye blueberries, their physicochemical changes during refrigerated storage, and method for softening frozen rabbiteye berries, Ph.D. dissertation; Mississippi State University, 1994.
Use of continuous and pulsed high frequency ultra-sound to disinfect ground water, Ph.D. dissertation
- R S Chamul
Chamul, R.S. Use of continuous and pulsed high frequency ultra-sound to disinfect ground water, Ph.D. dissertation; Mississippi State University, 2000.
Chemistry and processing of high-quality dehydrated vegetables products
- R Toledo
Toledo, R. Chemistry and processing of high-quality dehydrated vegetables products. In Quality Factors of Fruit and Vegetables; Jen, J.J., Ed.; ACS: Washington, DC, 1989; 240–249.
Use of continuous and pulsed high frequency ultrasound to disinfect ground water
- R S Chamul