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Optimization Study of Sulfur Dioxide Application in Processing of Sultana Raisins
International Journal of Food Properties
Abstract
The current use of sulfur dioxide (SO2) fumigation to bleach Sultana raisins has a number of limitations including poor absorption into the product and air pollution problems. A study was conducted to improve the sulfitation process by use of SO2 solutions as an alternative. A factorial design was used to evaluate the effect of concentration, temperature and raisin/solution ratio on the absorption of SO2 by raisins. It was found that the most important variables were concentration and temperature of the used solutions. The amount of SO2 absorbed by the raisins was time dependent, but the absorption rate declined after the first 15 min of contact. The use of SO2 solutions was found to be more efficient than fumigation with raisins retaining from 9-21% of applied SO2 in solution compared to 3-5% of SO2 applied as a gas. Higher final SO2 tissue concentrations could be achieved in the liquid application method compared to the gas method. There were no negative consequences of the proposed solution-based system with respect to post-treatment drying time and the storability of the raisins.
... The sulphur dioxide content of the golden-raisins ranged from 156 mg/ kg to 206.66 mg/kg. Therefore, the results proved that the amount of sulphur residual in raisins samples depends on the treatment time as well as the sulphur concentration used [44]. ...
... In a study conducted by Zamboni et al. on the measurement of sulphur in dried fruits using the Neutron Activation Analysis method in Brazil, the amount of sulphur in raisin samples purchased from markets in Sao-Paulo was 0.30 ± 0.08 g/kg, which was less than the codex limit [46]. Lydakis et al. [44] investigated the effect of temperature, concentration, time and raisin/solution ratio on the absorption of SO 2 by raisins. They reported that the most important variables were temperature and concentration of the used solutions. ...
... The quantity of SO 2 absorbed by the raisins was time dependent. They also showed that the use of SO 2 solutions can be more effective than fumigation method [44]. Sulphur dioxide contents in treated Sultana raisins in Lydakis et al. study range from 500 to 3000 mg/kg, which was higher than the standard allowable level. ...
In this study, the trace elements lead (Pb), arsenic (As), cadmium (Cd), nickel (Ni), copper (Cu), zinc (Zn) and iron (Fe) quantity have been investigated using graphite furnace atomic absorption spectrometry (GFAAS) and sulphur dioxide (SO2) residual by iodometric titration method in raisin samples in different regions of Iran. The results showed that the concentration of Cu, Zn and Fe were in the range of 0.053–0.212 mg/kg, 0.048–0.170 mg/kg and 0.541–0.843 mg/kg, respectively, whereas Cd, Ni, As and Pb concentrations in the samples were less than detection limit (LOD). The SO2 residual in raisin samples was between 30 and 843.33 mg/kg. The LOD of Cu, Fe, Zn, Cd, Pb, Ni, and As were 0.022 mg/kg, 0.5 mg/kg, 0.047 mg/kg, 0.04 mg/kg, 0.019 mg/kg, 0.024 mg/kg and 0.05 mg/kg, respectively. The Monte Carlo simulation results showed that the indexes of target hazard quotient (THQ) due to ingestion of SO2 residues estimated lower than the safe level (THQ < 1) in all samples, except in the Raisin-B and Raisin-D samples. Accordingly, to ensure consumer health and improve international trade, continuous control and adaptive regulation of sulphur dioxide residues and trace elements in dried fruit are recommended.
... Producers practically do not export apricots where they contain very high SO 2 based on their analysis results. It is also known that the amount of SO 2 absorbed by the fruit tissue depends on time (Lydakis et al. 2003). ...
... In the study of Lydakis et al. (2003), it has been stated that a very rapid initial absorption rate of SO 2 followed by a subsequent absorption which was directly proportional to the square root of the time was observed in raisins (Lydakis et al. 2003). Similarly, Ozturk et al. (2011) stated that 45-50% SO 2 loss occurs in sulphurised apricot during normal storage. ...
... In the study of Lydakis et al. (2003), it has been stated that a very rapid initial absorption rate of SO 2 followed by a subsequent absorption which was directly proportional to the square root of the time was observed in raisins (Lydakis et al. 2003). Similarly, Ozturk et al. (2011) stated that 45-50% SO 2 loss occurs in sulphurised apricot during normal storage. ...
Turkey plays an important role in the international trade of apricots as it has the largest
production rate in the world. Since the sulphurisation process is allowed to be used for different
products, the effect of residual sulphur and its compounds (which can be found in products as
pesticide residues or additive residues) on the positive detection of carbon disulphide (CS2) still
creates a big challenge in international trade. Therefore, the main objective of the present study
was to investigate the effects of residues of sulphur or sulphur compounds on dithiocarbamate
analysis methods based on CS2 measurement. In this study, apricots were chosen since they
contain sulphur residues as a result of the sulphurisation process. Sulphur dioxide and dithiocarbamate
analyses were conducted on dried apricots prepared with the sulphurisation process
(SA) and without the sulphurisation process (NSA); analysis was by two different accredited
laboratories. No of pesticide was applied to either SA or NSA samples. Although some of the
NSA samples had <LOQ values, approximately 70 ± 32 mg/kg SO2 and 0.061 ± 0.021 mg/kg
dithiocarbamate were detected for NSA samples. On the other hand, for the SA sample group,
927–2915 mg/kg of SO2 and 0.265–0.825 mg/kg of dithiocarbamate were detected. Furthermore,
a strong correlation between residual sulphur and dithiocarbamate values was observed. This
study showed that the analysis method based on CS2 measurement may lead to false positive
results for dithiocarbamates when residues of sulphur or sulphur compounds are found in
products as pesticide or additive residues. Therefore, residual sulphur compounds as a result of
the sulphurisation process (which is not considered during the evaluation of products) must be
taken into account during the evaluation of products for dithiocarbamates.
... ethyl oleate and olive oil) at different concentrations and times. [15,42] It is worth noting that in the grape industry, the sulfiting technique (i.e. gas SO 2 fumigation or immersion in SO 2 solutions) was by far the commonly-used method for bleaching grapes during storage and drying since sulfur dioxide treatment was known to ameliorate food color development and conserve their quality. ...
... gas SO 2 fumigation or immersion in SO 2 solutions) was by far the commonly-used method for bleaching grapes during storage and drying since sulfur dioxide treatment was known to ameliorate food color development and conserve their quality. [42] However, excessive SO 2 usage may alter the quality of the processed raisins and could cause potential environmental problems such as air pollution [42,43] or certain health concerns about reactions associated with some types of asthma. [44] In order to alleviate these incidents, many authors have assessed other alternative chemical pretreatments. ...
... gas SO 2 fumigation or immersion in SO 2 solutions) was by far the commonly-used method for bleaching grapes during storage and drying since sulfur dioxide treatment was known to ameliorate food color development and conserve their quality. [42] However, excessive SO 2 usage may alter the quality of the processed raisins and could cause potential environmental problems such as air pollution [42,43] or certain health concerns about reactions associated with some types of asthma. [44] In order to alleviate these incidents, many authors have assessed other alternative chemical pretreatments. ...
Processing and conservation of grapes by suitable techniques has been a major challenging issue for a long time. Optimization of drying and pretreatment operations of this fruit have been extensively studied. However, in order to achieve the production of high-quality raisins and reach consumers’ acceptance, special attention for quality attributes should be taken into account. Quality characteristics of grapes such as color, texture, vitamins, phytochemicals, aroma profile and microbial stability are of paramount importance since they could vary throughout the dehydration procedure and would directly determine quality perception and consumer choice. This paper presents a comprehensive review of the physicochemical, nutritional and microbiological characteristics of dried grapes as affected by the drying process. In addition, it investigates the changes of different grapes quality attributes (mainly nutritional and aromatic proprieties) during processing, which enables professionals and scientists to better choose and optimize grape processing to deliver the highest raisin quality to consumers.
KEYWORDS: Drying process, grapes, quality, raisins
... Similar to our results, numerous studies documented in the literature that hue values in the range of 49.2-63.90 varied depending on the variety and the pretreatments applied for grapes(Lydakis et al. 2003;Teker et al. 2023). ...
In the last 2 decades, Turkey and the United States have produced half of the world's dried grape production. Sultani seedless grape, used as a material in the study, is the most important grape variety since being economically growing in Turkiye for dried grape production and its exportation. The aim of the present study was to investigate the drying of seedless grapes by carbonic maceration (CM) pretreatment and following hot air drying. By the way statistical analysis was carried to determine how the process parameters affected the drying behavior of grape samples. Finally, the studied parameters of both process steps, pretreatment and following drying, were simultaneously optimized according to the investigated responses. The results showed that drying temperature and CM process parameters significantly affected the drying efficiency. Notably, when compared to the control, the CM treatment accelerated the drying process by more than 24%. Furthermore, antioxidant potential, surface color, and texture were found to be better preserved in the dried grapes treated with CM. While pH, hue, TPC, and TEAC values of optimum dried grapes were significantly higher, TA and HMF values were remarkably lower than control samples (without CM pretreatment) (p ≤ 0.05). Throughout CM pretreatment and following the drying process, the dependent variables, being elasticity, antioxidant capacity, drying time, and hue value, were optimized by the response surface methodology (RSM). The optimal drying temperature (DryT), CM pressure (CMP), CM temperature (CMT), and CM time (CMt) parameters were as 77°C, 0.30 MPa, 4°C, and 8 h, respectively. For drying operations, CM's significant advantages should be considered in terms of enhancing the process and the product. As a result, this study offers significant findings in this context. The CM has been found to be an effective technique utilized before drying grapes based on the results that were achieved.
... K 2 CO 3 , NAOH, ethyl oleate, sulfur compounds, and their combinations (oil emulsions) used in chemical pretreatment are methods that farmers prefer because the methods increase drying rate, improve color quality, and are available in the market at low cost. In physical methods, they can be listed as abrasive pretreatment of grape peel, hot air-water blanching, ohmic heating, microwave heating, pulsed electric field, and ultrasound, which are the subject of recent research [6,7]. Traditionally, farmers dry the grapes in the sun by laying them in a thin layer on a concrete floor or polypropylene canvas that will be exposed to direct sunlight and wind in Turkey. ...
... Sulfur dioxide (SO 2 ) also has antioxidant and antimicrobial properties; it can prevent the growth of microorganisms as well as preserve the color and flavor of various foods, especially dried fruits (Mischek and Krapfenbauer-Cermak, 2012;Papadopoulou-Mourkidou, 1991). Sulfur dioxide treatment has been used since early times to preserve the color of golden raisins (Lydakis et al., 2003). Fumigation with SO 2 results in the deposition of sulfur residues on the dried fruit (Clary et al., 2005), mostly in the form of sulfites (Paull et al., 1998). ...
A sulfur dioxide treatment is often used to preserve the color and flavor of raisins. We used a life table approach to examine the effects of residual sulfites on Plodia interpunctella (Hubner) when larvae fed on raisins under controlled laboratory conditions. Raisins were fumigated with 66 g/m³ or 133 g/m³ SO2 for either three or six hours, or received no SO2 exposure (control). A two sex life table was constructed for insects in each treatment (n = 70 per treatment). Total immature mortality exceeded 90% in 66 g/m³ SO2 treatments, and 80% in 133 g/m³ SO2 treatments, compared to 28.6% in controls. Sulfur dioxide treatments significantly extended developmental time relative to controls, again more so in the 66 g/m³ SO2 treatments than in the 133 g/m³ treatments, but did not affect the adult longevity of survivors. All SO2 treatments reduced the fecundity of surviving female moths to a small fraction of controls, without significant differences among them. These effects combined to result in significantly diminished life table parameters in all treatments relative to controls, although generation times were increased more in the 66 g/m³ SO2 treatments than in the 133 g/m³ treatments. These inverse dosage-dependent effects may reflect increased feeding avoidance of sulfite residues in the higher dose treatments that resulted in reduced consumption. We conclude that residual sulfur and sulfites deposited on fruit surfaces during SO2 treatment provides substantial control of P. interpunctella, and should effectively suppress the proliferation of moths within bulk stores of dried raisins.
... In the case of Zante currants, pre-treatment methods are not applied as it is a traditional and naturally produced food, although some pre-treatment steps with sulfitation may be employed for the Sultanina in Crete to prevent microbiological spoilage after drying [24,30]. ...
This review elaborates on the significance of Mediterranean raisins, focusing particularly on indigenous Greek varieties (e.g., Zante currants) as a previously overlooked traditional food, currently brought on the spotlight, resulting from the increased consumers’ awareness to improve wellness through diet modification. Recent studies on the effect of processing steps on final quality, along with findings on the potential health benefits raisins and currants elicit, are also presented. The development of novel functional food products to further exploit the nutritional value and the bioactive compounds of raisins is evidenced in view of indicating potential food industry applications. Moreover, valorization options of waste and by-product streams obtained from processing facilities are also proposed. Conclusively, raisins and currants should be further enhanced and incorporated in a balanced diet regime through the inclusion in novel foods formulation. Evidently, both the processing of the onset material and side-streams management, are essential to ensure sustainability. Hence, the article also highlights integrated biorefinery approaches, targeting the production of high-value added products that could be re-introduced in the food supply chain and conform with the pillars of bio-economy.
... Naturally, dried grapes are subjected to sulphation after washing. Then the dried grapes are dried in special dryers and then packed according to their size [17,[19][20][21]. Although drying reduces the microbial load in the product, some microbial contamination from environmental factors may occur. ...
... It is common industry practice in Australia to trellis-dry grape bunches in situ ($80% of the Australian production) by spraying them with an alkaline drying solution to enhance the speed of drying (Clingeleffer 2002). However, uneven spray coverage may result in darkening of some berries on a bunch due to the activity of polyphenoloxidase (PPO) and some non-enzymatic reactions (Aguilera et al. 1987, Lydakis et al. 2003, and, consequently, uneven colouring (Grncarevic andLewis 1973, May et al. 1983) and darkening of the fruit during drying. This inconsistency in coloration of berries within a batch requires grading upon receival at packinghouses; the grade assigned to a batch determines the price paid to the grower. ...
Background and Aims
Evaluation of dried grape berry quality in Australia is currently based on visual assessment by trained humans, a process that is subjective and prone to error. The goal of this work was to develop an objective methodology to evaluate the quality of dried grapes from Vitis vinifera L. cv. Thompson Seedless, referred to as ‘sultanas’.
Methods and Results
A non‐destructive method for berry quality assessment based on digital image analysis using the MATLAB programing language enabled the development of a novel quality index and computer application for classification of berry quality based on surface colour. The method separated individual berries into several colour classes and assigned the batch an overall crown grade that was consistent with industry assessment.
Conclusion
Digital image analysis of berry surface colour using the new method was an accurate and reliable method for objectively evaluating dried sultana quality.
Significance of the Study
This method will facilitate the rapid and objective evaluation of sultana quality at packinghouses to ensure that a fair price is paid to growers and to reduce potential conflicts arising from subjective fruit grading by humans.
Bu çalışmada, kayısı işletmelerinin tedarikçi değerlendirme sürecinde dikkate alması gereken kriterleri ve bunların önceliklerini belirlemeye yönelik bir araştırma gerçekleştirilmiştir. Bu amaçla sektör raporları incelenmiş, uzmanlarla ve kayısı işletmelerdeki tedarik sorumluları ile görüşülmüştür. Elde edilen veriler ışığında olası ana kriterler, kalite-kontrol, fiyat, hijyen, mekanizasyon ve üretim performansı başlıkları altında gruplandırılmıştır. Fiyatta 6, kalitede 10, hijyende 4, mekanizasyonda 6 ve üretim performansında 8 alt kriter olmak üzere toplamda 34 kriter belirlenmiştir. Belirlenen temel ve alt kriterler bulanık mantık çerçevesinde ağırlandırılmış ve sıralanmıştır.
Raisins are highly produced value‐added products that are extracted from grape processing. The most important unit operations in raisin production are pretreatment, followed by drying. Due to the presence of waxy layer, the drying cannot be used alone; however, the layer can be removed by pretreating the grapes with chemicals or physical abrasion. The food safety and environmental issue with the chemicals have forced to find alternative methods. The physical method, such as surface abrasion, is explored but showed negative effect of color. The nonthermal methods such as microwave (MW) heating, pulsed electric field, ultrasound, and ohmic heating are observed, and their outcomes are discussed in this review. Carbonic maceration, high‐humidity hot air impingement blanching, and MW hydrodiffusion and gravity are the novel methods that showed promising results. In the latter part, the traditional drying process of grapes is discussed, where shade drying is found to be used remarkably in raisin production. However, the time of drying was long, and the process required large land area. Alternatively, novel methods such as hot air, MW, vacuum, and infrared drying provide higher drying rate and good‐quality raisins. However, the combined drying methods such as MW‐assisted air drying, pulsed vacuum drying, and MW vacuum drying have shown better results than single drying. Pretreatment and drying cause changes in physical and chemical properties of grapes, such as changes in color, size, nutrient content, and polyphenol content. Overall, the review covered the crux output with the advancement in raisin development, which could be useful for novel research on grape processing.
The SO2 solubility in ionic liquids and absorption mechanisms with different functionalities, including ether, halide, carboxylate, dicarboxylate, thiocynate, phenol, amino, azole groups, etc., are presented in this review. Strategies of improving SO2 capture with low binding energy and the separation performance from CO2 are also concluded. Generally, moderate basicity is favourable for enhancing SO2 capacity and the water (below 6 wt%) effect on absorption is indefinite but generally slight. Introducing electron-withdrawing substituents such as nitrile, halogen, aldehyde and carboxylic groups are proposed to decrease the chemical absorption enthalpy between ionic liquid and SO2 in order to reduce regeneration power consumption. Although it is promising, the absorption enthalpy is still much higher than the physisorption performance especially of the ether-functionalized ones. The biocompatible choline-based, betaine-based, and amino acid ionic liquids have clear trends to be applied in SO2 capture due to their biodegradability, nontoxicity and easy accessibility. Generally, comparing to the traditional solvents, ionic liquids have made great improvement in SO2 capacity, however, the high viscosity and desorption energy are two main obstacles for SO2 absorption and separation. Molecular simulations have been applied to reveal the absorption regimes involving the roles of basic functionalities and physical interactions especially the hydrogen bonds, which could be referred for structure designing of the available ionic liquids with readily fluid characteristics and absorption ability.
The availability of powdery mildew-resistant raisin accessions will lower grower production costs and enhance the environment through reduced fungicide use. To achieve this objective, backcrossing has been employed with Vitis romanetii as the source of non-race-specific powdery mildew resistance. Initial crosses of powdery mildew-resistant F1 hybrid B36-45 with seeded raisin cultivars ‘Rangspray’ and ‘Raisin de Palestine’ yielded seedless powdery mildew-resistant first-generation backcross selections C87-41 and C87-106, which were used to develop second-generation backcross populations. Principal component analyses consistently identified ‘wrinkle,’ ‘meatiness,’ ‘product attractiveness’ and ‘skin persistence’ as being the quality characteristics most important in discriminating among powdery mildew-resistant raisin accessions and commercial raisin cultivars. Raisin quality ratings were much improved across most evaluated characters in second-generation backcross families as compared with parental powdery mildew- resistant accessions C87-41 and C87-106. After two generations of backcrossing, powdery mildew-resistant raisin selections were identified with product quality characteristics similar to those of commercial raisin cultivars.
Sulfur dioxide (SO2) is used as a preservative in osmotically dehydrated papaya to improve product quality and extend shelf-life. The potential of near infrared spectroscopy, as a rapid method, was investigated to determine sulfur dioxide in osmotically dehydrated papaya. Commercial and laboratory osmotically dehydrated papaya samples were selected to determine the sulfur dioxide content using the Monier–Williams method. From the total of 350 samples, subsets were selected randomly for the calibration set (n=250) and validation set (n = 100). Near infrared spectra in the region 800–2400 nm were measured on the samples of osmotically dehydrated papaya. Quantitative analyses of sulfur dioxide in the osmotically dehydrated papaya and their qualitative analyses were carried out using multivariate analysis. Before developing models, a second derivative spectral pretreatment was applied to the original spectral data. Subsequently, two wavelength interval selection methods, namely moving window partial least squares regression (MWPLSR) and searching combination moving window partial least squares (SCMWPLS), were applied to determine the suitable input wavelength variables. For quantitative analysis, three linear models (partial least squares regression, MWPLSR and SCMWPLS) and a non-linear artificial neural network model were applied to develop predictive models. The results showed that the artificial neural network model produced the best performance, with correlation coefficient (R) and root mean square error of prediction values of 0.937 and 114.53 mg SO2kg⁻¹, respectively. Qualitative models were developed using partial least squares-discriminant analysis and soft independent modeling of class analogy (SIMCA) for the optimized combination of informative regions of the near infrared spectra to classify osmotically dehydrated papaya into three groups based on sulfur dioxide. The SIMCA in combination with SCMWPLS model had the highest correct classification rate (96%). The study demonstrated that near infrared spectroscopy combined with SCMWPLS is a powerful procedure for both quantitative and qualitative analyses of osmotically dehydrated papaya. Therefore, it was demonstrated that near infrared spectroscopy could be effective tools for food quality and safety evaluation in food industry.
Grapes are one of the world's most widely planted horticultural crops, used to make a variety of fresh, dried and processed products. The science of grapes and grape production are discussed through an examination of wine grapes as well as grapes for fresh consumption and raisin production. Providing historical and current information about the grape industry, chapters cover genetics, breeding and cultivars, grapevine growth, development and nutrition, climate requirements, pests and diseases and post-harvest production. This informative text thoroughly covers the influence of the environment on grapevine health and productivity, and informs the reader on how grapes are grown and factors affecting grape quality.
A trained sensory panel evaluated the 6 fig cultivars currently sold in the California dried fig market. The main flavor and aroma attributes determined by the sensory panel were “caramel,” “honey,” “raisin,” and “fig,” with additional aroma attributes: “common date,” “dried plum,” and “molasses.” Sensory differences were observed between dried fig cultivars. All figs were processed by 2 commercial handlers. Processing included potassium sorbate as a preservative and SO2 application as an antibrowning agent for white cultivars. As a consequence of SO2 use during processing, high sulfite residues affected the sensory profiles of the white dried fig cultivars. Significant differences between dried fig cultivars and sources demonstrate perceived differences between processing and storage methods. The panel-determined sensory lexicon can help with California fig marketing.
A set of dried fig sensory descriptors was established to provide more information for processors, marketers, and consumers in the dried fig market. Additionally, our results demonstrate at which levels sulfite residues can be perceived in dried figs.
Experiments were conducted to evaluate the feasibility of using high-pressure processing as an alternate for hot-water blanching of peach slices. Peach slices were pressure processed at various combinations of pressures (50–700 MPa) at 25°C with and without citric acid for two holding times (5 and 10 min). Pressure treatment (>300 MPa), in combination with citric acid (1–1.2%), was an effective method to inactivatepeach polyphenoloxidase enzymes. Pressure-treated peach slices, with and without citric acid, were subsequently dehydrated in a cabinet dryer at 70°C. Pressure treatment enhanced the drying rate and reduced the drying time. Logarithmic model satisfactorily described the drying behavior of peach slices. Pressure-processed samples had higher moisture diffusivity than control samples. The results reveals that high-pressure processing of peach fruits suspended in citric acid medium can be used as potential alternative for hot water blanching.
Artichoke polyphenol oxidases (PPOs) were obtained by (NH4)2SO4 precipitation using ascorbic acid, polyvinylpyrrolidone, and Triton X-100. The PPO content of artichoke head (AHPPO) was 8820 units (mg protein)−1 as compared with 3370 units (mg protein)−1 in artichoke leaves-and-stem (ALSPPO) by using catechol as a substrate. The substrates of both AHPPO and ALSPPO are o-diphenols, such as catechol, pyrogallol, and L-DOPA. Optimum pH and temperature of both PPOs were determined. AHPPO had higher thermal stability than ALSPPO. Also, Tm (the midpoint of thermal inactivation) and t1/2 (half-life) values were determined. Km and Vmax of both PPOs were observed to be similar. Twelve inhibitors were tested and their I50 values were determined. The most effective inhibitors were found to be potassium cyanide, ascorbic acid, L-cysteine, and thiourea. Sodiumdodecylsulfate, urea, and cupric sulfate caused an increase about 20–30% in the PPO activity.
The effects of pretreatments, i.e. SO2gasvs.sodium-meta-bisulphite, and operability of a solar drier to replace traditional sun-drying on concrete ground for apricot drying were studied. Increasing initial SO2concentrations and solar drying increased drying rates. Sodium-meta-bisulphite treated products at an initial SO2concentration of about 7800 mg/kg dry matter had nearly the same moisture diffusion coefficients as ones treated with SO2gas at a concentration of 12,500 mg/kg dry matter. Storage stability of differently treated dried apricots having SO2concentrations in the range 850 to 3350 mg/kg dry matter was investigated as packagedvs.non-packaged and at 13°Cvs.5°C. Both during drying and storage, initial SO2concentrations were seen to decline considerably. Nonpackaged apricots stored at 5°C absorbed moisture to undesirable levels and developed Microbial counts were above allowable maximum limits. Microbial counts were below allowable maximum limits in all other treatments.
A mathematical model was proposed to simulate simultaneous sulfur dioxide absorption and reaction during corn steeping. The parameters of the model, the diffusion coefficient and the reaction rate constant, were determined. The reaction rate of sulfur dioxide in corn grain followed first-order 10-7 s-110-7 to 9.78kinetics, with rate constants in the range 1.49 for steeping temperatures from 25 to 55°C. The Arrhenius activation energy for sulfur dioxide loss was 60.5 kJ/mol. The fitting of the mathematical model to the absorption curves determined the diffusion coefficient of sulfur dioxide in corn kernels. These varied from 10-11 m2/s for the temperature range 25-55°C.10-11 to 5.181.17 Temperature-dependent diffusion coefficients was shown to obey the Arrhenius equation with an activation energy of 39.8 kJ/mol.
The effects of pretreatment solutions and drier types (solar vs sun) were investigated for grapes (var. sultanas). Pretreatment solutions containing 5% K2CO3 plus 1.5% olive oil and 4% K2CO3 plus 2% ethyl oleate accelerated drying rates nearly to the same extent, as compared to untreated grapes. Drying rates were classified for the tested drying methods: solar drying > sun drying on concrete ground > sun drying on wooden racks, or on polypropylene canvas sheets. Increasing K2CO3 concentration from 4 to 7% in ethyl oleate (2%) solution increased drying rates on concrete ground. Treatment with SO2 gas (645 mg/kg) in addition to ethyl oleate, further increased the drying rates but the color of the product was rated to be too light and unacceptable to the market. The moisture content and color intensities of the sun-dried grapes were found to be non-uniform. Storage stability of treated, dried grapes was investigated in (1) modified atmosphere (1% O2 plus 13% CO2), (2) vacuum packed and (3) ordinary plastic pouch packed storage at 6 °C. Untreated grapes had the lowest Hunter L (lightness), a (redness) and b (yellowness) values compared to treated grapes. Storage caused color parameters to decline, but this reduction was less pronounced for SO2 gas treated products.
The determination of moisture in Soultanina raisins by drying in a steam bath with diatomaceous earth to constant weight (about 70 min) was compared with the official AOAC Method 22.013, which uses asbestos and requires 6 h of drying at 70°C under <100 mm Hg. Five different samples (moisture 11-22%) were analyzed by the 2 methods; the mean values of 9 replications did not differ significantly. The new method is rapid and simple, and it eliminates asbestos, a known carcinogenic substance, from the determination.
In this paper an alternative physical method for enhancing the drying rate of seedless grapes is proposed. It consists of the superficial abrasion of the grape peel using an inert abrasive material. The effectiveness of this novel process was compared to that of the traditional ethyl oleate dipping process by analysing not only their respective drying times, but also the peel surfaces by scanning electron microscopy. Moreover, the drying kinetics of the above two treatments was reconstructed by using a mathematical model in which the grape pretreatment used was assumed to affect the water diffusivity in the grape peel, but not in the grape pulp. Even though the abrasion method was found to be as effective as the traditional method and gave rise to a darker final product, which is less attractive to consumers, it would allow grape pretreatment thus avoiding the use of chemical additives, and permit safer raisins to be produced.
The effect of various dipping pretreatments on drying kinetics of grapes under warm air convective drying conditions has been studied. A dryer was built to perform the experiment under controlled condition of drying air at temperature 60°C and velocity 0.5 m/s. The various pretreatments of the grapes include treatment with commercial dipping oil, ethyl oleate, olive oil, and hot sodium hydroxide solution. Kinetic studies of the treated grapes for all the pretreatments were also made. The drying behaviour of the treated grapes was found to be in good agreement with Page’s model, though drying constants of Page’s model for each pretreatment were found to be different. Sensory evaluation was also carried out for all pretreatments. Dipping oil pretreatment experiments were also conducted at temperatures other than 60°C to determine the dependence of Page’s drying constant k on the drying air temperature
The rates of water absorption of three maizes, dent (PIONEER 3379), semident (ICI RF67) and flint (CARGILL T-42), in plain water and 0.25% SO2 aqueous solution were studied. The steeping temperatures were 45, 55 and 65 °C. The absorption kinetics in plain water and SO2 solution follows a ‘Fickian’ behavior (moisture content of the kernels varies with the square root of time) during the first hours of steeping. The rates of absorption in SO2 solution were slightly higher than in plain water at all temperatures, even though at the onset of steeping, the SO2 seemed to retard the rate of absorption. This increase was relatively higher for flint and semident types than for dent maize. The activation energies for water sorption in SO2 solution were lower than for plain water, this effect being more marked for flint and semident types.
The absorption process of sulphur (IV) in the two major apricot varieties of Majorca has been simulated, assuming the existence of two diffusive species. The diffusivity value of the two species SO2 (aq) and HSO-3, has been obtained by a numerical method of non-linear regression analysis. The dependence of the absorption on the solution operating conditions including temperature, pH and Na2S2O5 concentration has been evaluated. The proposed diffusive model is able to explain 95% of the variance. This model can be also applied to sulfiting of other food products.
Effective diffusivity of sulphur dioxide uptake in green banana was measured as a function of temperature (20‐30°C) and concentration (6,000‐10,000 ppm) of dipping solutions. The effective diffusivity varied from 2.40×10 to 19.05×10 m/s. Diffusivity increased with the increase of concentration and temperature of sodium metabisulfite solution. The estimated values can be used to design a sulfiting pretreatment process of green banana before drying.
Heat inactivation of polyphenoloxidase (PPO) in sultana grapes between 83° and 98°C followed zero order kinetics with an activation energy of 13.7–16.7 kcal/mol. A high correlation (r = 0.973) was found between the residual PPO activity and darkness of the raisins (Hun-terlab L value) after drying at 50°C. Reaction rate for enzymatic browning increased with higher water activities while non-enzymatic browning showed the typical bell-shaped curve with a maximum around 0.8. Light-colored raisins were obtained without the use of SO2 by pretreating the grapes with a 2 min dip in 93°C water that inactivated PPO and improved mass transfer through the skin. This latter effect was compared to that of other treatments such as ethyl oleate and caustic soda by drying studies and scanning electron microscopy.
Raisins had a moisture content of ca 14% and were stored over an 11 mo period. The initial SO2 content was ca 640 ppm. Moisture content, water activity, color, browning, texture, SO2 content, soluble sugars, acidity and pH were periodically determined. A substantial decrease in SO2 content was observed, especially in samples stored at room temperature (20–25°C) which had higher browning indexes. No substantial changes were detected in water activity, acidity and pH. No sugaring was observed. Refrigerated samples (stored at 4 and 11°C) were of higher quality in comparison with nonrefrigerated samples. Both were suitable for consumption after storage.
Food additives In Food Chemistry
- R C Lindsay
- O R Fennema
Lindsay, R.C. Food additives. In Food Chemistry, 3rd Ed.; Fennema, O.R., Ed.; Marcel Dekker, Inc.: New York, 1996; 825–840.
Fisarakis, I. Sultanina (in Greek). Aristotelion University of Thessaloniki
- M Vlachos
Vlachos, M.; Fisarakis, I. Sultanina (in Greek). Aristotelion University of Thessaloniki, 1982.
Optimization Study of Harvesting, Drying, Storage and Industrial Processing of Sultana Raisins
- G Epanomeritakis
Epanomeritakis, G. Optimization Study of Harvesting, Drying, Storage and Industrial Processing of Sultana Raisins; Aristotelion University of Thessaloniki, 1984; Thesis.
Diffusion of gaseous sulfur dioxide into corn grain
- S R Eckhoff
- M R Okos
Eckhoff, S.R.; Okos, M.R. Diffusion of gaseous sulfur dioxide into corn grain. Cereal Chem. 1989, 66 (1), 30–33.