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Moisture loss, gain and migration in foods and its impact on food quality
Abstract
Moisture loss, gain and transfer, whether originating from exchanges with the atmosphere or with another component of the food, always cause deterioration in the overall quality of the food through softening, toughening, breakdown, and swelling or shrinkage caused by phase transitions or dissolution (Petersen et al., 1999). In most cases, water migrations lead to a deterioration of the overall quality (organoleptic or hygienic) of the food.With a view to better understanding physical deterioration of food and to provide a tool to better control food quality (and give a longer shelf life) this chapter reviews the water relationships in foods with a particular focus on glass-transition-related phenomena, and illustrates these relationship with examples of foods affected by moisture exchanges with the atmosphere or within the product itself. The mechanisms controlling these migrations are presented together with some experimental approaches (measurements of moisture content, water activity and migration and modelling).
... But shorter shelf life has significant impact on the economy of the bakery businesses and on the environment (WRAP 2011;WRAP 2013;SIK 2014). It has been demonstrated that the main reason for moisture migration observed in baked products is water activity (a w ) gradients within the product and its environment (Roudaut and Debeaufort 2010;Katz and Labuza 1981). ...
... This phenomenon is well documented in case of bread where softening of crust and hardening of the crumb are related to moisture redistribution occurring during storage (Cauvain and Young 2007b), (Cauvain and Young 2010). In composite or multi-component foods, such as breakfast cereals, biscuits and ice cream wafers the a w gradient and rate of migration is minimize by lowering final moisture content or by use of humectants (Labuza and Hyman 1998;Roudaut and Debeaufort 2010;Bourlieu et al. 2008). Moisture exchange between a product and its surrounding atmosphere can be controlled by adequate packaging material (Coles et al. 2003;Paine and Paine 1992). ...
... Also, by knowing the critical water activity limits of a product it is possible to calculate shelf life based on the relevant barrier properties of the packaging material or dictate the barrier specification of the package to obtain a desired shelf life. Water activity of a product is measured using either a resistive hygrometer or a dew point hygrometer (Roudaut and Debeaufort 2010). Table 2 provides information on MC and a w values of croissants and other baked products. ...
Very short shelf life of ‘freshly’ baked croissants is a growing concern for food retailers. It is affecting the economics of business, causing 10 to 40% in-store food wastage, and puts natural resources under severe stress. The factors affecting the shelf life are loss of crispness of the crust, and increased firmness of the crumb. This is largely due to migration of water from crumb to crust during storage period. Using appropriate packaging material the rate of moisture migration can be slowed down. Currently paper/polyethylene laminate, polyethylene terephthalate and polypropylene materials are used to pack croissants. However, the product shelf life is not more than 12 hrs. The study concluded that using monolayer oriented-polypropylene film with perforations (WVTR of 10-14 g m-2 day-1) and multilayer oriented- polyethylene terephthalate film with or without ethylene vinyl alcohol polymer (WVTR of 9.2-9.5 g m-2 day-1) the moisture migration phenomenon in croissants is slowed down. Further, the crispness of packed croissants was lost at 6 h storage, however softness of crumb is preserved up to 24 h.
... Chemical/biochemical reactions in foods affecting their quality [135]. Food spoilage is influenced by oxygen availability, temperature, relative humidity, water content, and pH [137]. For this reason, besides the characteristics of the edible films and coatings themselves, it is of great interest to maintain the characteristics of the food, including: (i) preservation of microbiological parameters in accordance with established laws; (ii) preservation of nutritional content; and (iii) preservation of physical and sensory characteristics (e.g., smell, taste, and texture); which together extend the shelf-life of the product [136]. ...
... Table 6 reports different development works aiming at extending the shelf-life of plenty fruits, vegetables, animal, and dairy products; where the edible film/coating influenced positively the chemical, biochemical and physical parameters, minimizing the food spoilage, and thus increased the shelf-life of the food product. Food spoilage is influenced by oxygen availability, temperature, relative humidity, water content, and pH [137]. For this reason, besides the characteristics of the edible films and coatings themselves, it is of great interest to maintain the characteristics of the food, including: (i) preservation of microbiological parameters in accordance with established laws; (ii) preservation of nutritional content; and (iii) preservation of physical and sensory characteristics (e.g., smell, taste, and texture); which together extend the shelf-life of the product [136]. ...
Food preservation technologies are currently facing important challenges at extending the shelf-life of perishable food products (e.g., meat, fish, milk, eggs, and many raw fruits and vegetables) that help to meet the daily nutrient requirement demand. In addition, food preservation has gone beyond only preservation; the current techniques are focused on the fulfillment of two additional objectives, the suitability of the used processes and generation of environmentally friendly products with non-presence of any side effect on health. Moreover, they are also looking for additional nutritional properties. One of these preservation protocols deals with the use of edible films and coatings. Therefore, this review shows an overview of synthetic materials (e.g., glass, aluminum, plastic, and paperboard), as well as the regulations that limit their application in food packaging. Further, this review releases the current-state-of-the-art of the use of films and edible coatings as an alternative to conventional packaging, providing the main features that these biodegradable packaging should meet towards specific uses for the conservation and improvement of various food products. Herein, particular attention has been paid to the main used components (e.g., biopolymers, additives, bioactive, and probiotic components), manufacturing methods (for edible films or coatings) and their application to specific products. In addition, an outlook of the application of edible films and coatings as quality indicators of perishable products is shown.
... Researchers also use the similar theories in food engineering (Roudaut and Debeaufort 2010). As shown in Table 1, the moisture content was divided into four groups, and one of three theories-Fickian or Knudsen diffusion, Hagen-Poiseuille law, or Darcy's law-was assigned to each group. ...
... Moisture content and corresponding theory(Roudaut and Debeaufort 2010). ...
Macroscopic and microscopic theories on moisture migration in bulk materials are reviewed in this work. Macroscopic theories were mostly based on diffusion or infiltration theories driven by temperature gradient or water potential. Some simulation models have also been developed through coupling computational fluid dynamics (CFD) and discrete element method (DEM). Microscopic theories were based on the liquid bridge and its vibration. The liquid bridges between different shapes of particles were introduced, as well as the liquid bridge between rough surfaces. Some limits and outlook of future studies were also discussed in the end.
... The moisture content of PSP pehtze was significantly influenced by temperature and Rh during incubation ( Figure 1A). (Roudaut and Debeaufort, 2010). Abbasi et al. (2009) explained that an increase in temperature could accelerate the diffusion of moisture from the surface of materials to the environment. ...
Background. Fermented tofu, a traditional product of Asian countries, is produced using Actinomucor elegans. The product is popularly consumed because of its unique nutrients, taste, and flavor. The fortification of tofu with purple sweet potato (PSP) can provide many health benefits, especially antioxidative properties. However, incubation conditions including temperature and relative humidity affect the growth of Actinomu-cor elegans, leading to changes in product quality.
Materials and methods. In this study, the effects of various temperatures (25, 30, and 35°C) and relative humidities (75, 85, and 95%) on the fermentation of tofu supplemented with PSP were carried out. The nutrient composition, including moisture, protein, lipid, ammonia, glucose, and free amino acid contents, bioactive compounds (total phenolic-TPC, total flavonoid-TFC, and anthocyanin contents), antioxidant activity in terms of DPPH and ABTS radical scavenging activities, and inhibitory activity (IC 50) were monitored.
Results. The results indicate that tofu supplemented with PSP can be successfully catalyzed by Actinomucor elegans at a suitable temperature and relative humidity of 30°C and 95%, respectively. The pehtze contained 63.8% moisture, 15.36% protein, 9.43% lipid, 12.49% free amino acid, 0.05% ammonia, and 125.41 mg/g glucose. The TPC, TFC, and anthocyanin contents were 62.91 mg GAE/g d.w., 17.32 mg QE/g d.w., and 309.54 µg/g d.w., respectively. The DPPH and ABTS radical scavenging activities, and the IC 50 value were 85.50 µmol TE/g d.w., 120.79 µmol TEAC/mg, and 6.61 mg/mL, respectively.
Conclusions. Fermentation at 30°C and a relative humidity of 95% produced fermented PSP tofu with high nutrition, bioactive compounds, and antioxidant activity.
... Loss of water as well as other nutrients from the foods during cooking is the most common and concerning phenomenon [47]. Weight loss during cooking is shown in Table 2. CON and CE2 samples from day 0 had no noticeable difference in weight loss (p > 0.05). ...
The effect of chitooligosaccharide-EGCG conjugate (CEC) at different concentrations (0, 1, and 2%; w/v) and depuration times (DT; 3, and 6 h) on the total viable count and Vibrio spp. count of Asian green mussels (AGMs) was studied. Depurated samples showed a reduction in both microbial counts as compared to fresh AGMs (without depuration) and AGMs depurated using water (CON). A similar TVC was noticed at both DTs; however, a lower VC was attained at a DT of 3, irrespective of CEC concentrations (p < 0.05). AGMs were depurated for 3 h using 1 and 2% CEC (CE1 and CE2, respectively) solutions and stored for 6 days at 4 • C. The CE2 sample showed the lowest microbial counts as compared to fresh AGMs, CON, and CE1 throughout the storage (p < 0.05). CE2 extended the shelf-life of AGMs by 4 days, which was also supported by the lower peroxide value (0.48 mg cumene hydroperoxide/kg sample) and TBARS (0.94 mmol MDA eqv/kg sample) when compared with other samples. Moreover, CE2 had a lower total volatile nitrogen base (TVB; 4.72 mg N/100 g) and trimethylamine (TMA; 3.59 mg N/100 g) on day 4. Furthermore, 2% CEC was able to maintain the DHA content; however, a slightly lower EPA was noticed as compared to the CON. Next-generation sequencing suggested that the CON had a larger microbial community, especially Vibrio sp., than the CE2. All the treated samples showed similar likeness scores to the cooked CE2 and CON on day 0. However, slightly lower likeness was attained when CE2 was stored for 4 days, but the likeness score was higher than the acceptable limit (5). No difference in cooking loss was noticed between CON and CE2 samples on day 0. Nevertheless, cooking loss was increased on day 4. Thus, depuration using CEC solution enhanced the shelf-life of AGMs by 4 days without having negative impact on consumer acceptability and textural properties.
... There was a decrease in the moisture content as the proportion of OFSP flour increased in the puffed snack formulation. Moisture content is a crucial factor influencing the shelf life and safety of food products [28,42]. The moisture content reduced from 5.67% in the S 100 (100% sorghum) samples to 3.94% in the S 20 O 80 (samples composed of 20% sorghum and 80% OFSP flour blends) puffed snacks. ...
This study is aimed at producing extrudates using sorghum and orange-fleshed sweet potato (OFSP) flour in varying ratios (90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, and 20:80), with extrudates made from 100% sorghum serving as the control. The puffed snacks’ physicochemical, nutritional, textural, and sensory qualities were assessed, and the obtained data were analyzed through ANOVA. Our findings revealed notable variations in the physicochemical properties of the puffed snacks, showing a decrease in moisture, fat, protein, and crude fibre content as the percentage of OFSP flour increased. Furthermore, increased substitution of sorghum flour with OFSP in the extrudates led to a corresponding rise in vitamin A, B1, and C levels from 0.24, 0.15 and 0.21 mg/100 g in the control to 1.30, 0.19, and 1.82 mg/100 g in the extrudates made from 20% sorghum. More so, samples with increased OFSP content were preferred regarding springiness, chewiness, gumminess, and cohesiveness, whereas those with elevated percentages of sorghum received higher likeness for adhesiveness and stringiness. Extruded samples containing 80% and 90% sorghum levels received the highest overall acceptance ratings of 7.15 and 7.18, respectively. The research results are essential for the food industry to produce nutritious extrudates with appealing sensory characteristics and textures.
... Important properties characterizing the quality of products during storage are MC and the ratio of free and bound moisture in the product. It has been established that the rate of moisture loss depends on the food's chemical composition and the amount of pectinous substances, proteins, and sugars as well as and the presence of reducing substances (glucose, maltose, fructose, etc.) [54]. ...
This paper analyzes the possibility of using pomace powder of musky squash (PPMS, 10–30% of the formulation) for the manufacture of foamy confectionery products based on Jerusalem artichoke syrup, which is a natural substitute for sugar syrup used in the food industry. The content of biologically active compounds (polyphenols, carotenoids) as well as the antimicrobial and antioxidant properties of pumpkin powder were evaluated. Sensory analysis was applied to measure the degree of product acceptance and the analysis revealed that the optimal amount of PPMS accepted by the tasters was 15%. The addition of PPMS increased pH and free water retention, color, and lightness intensification. During the storage period (40 days), the hardness and gumminess showed an essential increase and the cohesion of the samples gradually decreased. The addition of PPMS led to the improvement of textural parameters, thus contributing to the extension of the shelf life of products by 10 days, compared to the control sample. Mutual information analysis was applied to determine the influence of PPMS concentration and storage time of foamy confectionery products on mean total score, mean sensory profile score, moisture content, water activity, antioxidant activity, hardness, cohesiveness, and gumminess. The results of this research indicate that the use of pumpkin pulp in the manufacture of foamy confectionery products can significantly increase their biological value and sensory characteristics and ensure an extension of the products’ shelf life.
... It prevents the oxidation of lipids, deterioration of color, autolysis of fish, nutritional concentration, and moisture loss. However, at the same time, it puts down the crispness of food and dehydrates the uncovered food goods (Roudaut and Debeaufort, 2010). ...
... The food industry is now required to provide consumers with food that is tasty, fresh, of high quality, and has positive health effects [8]. As a result of the natural deterioration brought on by chemical, biological, and physical changes, no food can be kept in ideal circumstances or preserve its attributes permanently, making it difficult to meet customer needs [103]. (Figures 4) [104]. ...
The food sector addresses perhaps of the main business with regards to degree,
speculation, and variety. In a forever evolving society, dietary requirements and inclinations
are broadly factor. Alongside offering an extraordinary mechanical help
for inventive and valued items, the ongoing food industry ought to likewise cover
the essential necessities of a consistently expanding populace. In this unique circumstance,
designing, examination, and innovation have been joined to offer supportable
arrangements in the food business for a solid and fulfilled populace. While wellbeing
and prosperity are key drivers of the food business, market influences take a stab at
development all through the total pecking order, including unrefined substance/fixing
obtaining, food handling, quality control of completed items, and bundling. Food
safeguarding strategies have been experimentally utilized starting from the beginning
of mankind. Thus, our ancestors used to handle raw materials such as milk, meat
or fish in a way that extended their shelf-lives by using practical methods based on
what we now know as drying, curing or fermentation. Hundreds of years after the fact
and during the modern transformation toward the start of the nineteenth 100 years,
Appert fostered the cycle for business cleansing of canned food items, which thusly
opened the way to the advancement of safe food items with delayed timeframes of
realistic usability. Active food packaging strategies have experienced a tremendous
push forward in the last two decades. During this time, the improvement of fresher
materials and the consolidation of bioactive mixtures in the bundling films have addressed
an upheaval in the food business and have run in equal (and in some cases
prodded by) with the improvement of cutting-edge procedures for the recognition of
arising and safe food-borne microbes. When the microbial dangers for each sort of
food item are known and the microbial targets definitively distinguished, it is an ideal
opportunity to conclude what bioactive compound will be more reasonable for every
particular application.
... Kadar air merupakan parameter penting daam kualitas bahan makanan. Jumlah air yang terkandung dalam bahan makanan berpengaruh pada kualitas, stabilitas dan keamanan produk pangan, juga mempengaruhi masa simpannya (Roudaut, 2010). Pengujian kadar air yang dilakukan dalam penelitian ini disajikan pada Gambar 1. ...
Pewarna adalah salah satu bahan tambahan pangan yang berfungsi untuk meningkatkan kualitas penampilan makanan. Keanekaragaman bahan pewarna pangan merupakan inovasi yang terus berkembang untuk meningkatkan mutu dan daya jual pangan di pasaran. Namun hingga saat ini pewarna makanan di pasaran masih banyak yang menggunakan pewarna tekstil, padahal sudah jelas bahwa pewarna tekstil sangat berbahaya bagi tubuh. Oleh karena itu, dilakukan penelitian ini agar bisa dijadikan alternatif pewarna alami untuk makanan yang berasal dari buah bit sebagai pengganti pewarna buatan. Pada penelitian ini bahan yang digunakan hanya buah bit dan asam sitrat yang selanjutnya dilakukan dua pengujian yaitu uji kadar air dan uji intesitas warna. Pada pengujian intesitas warna dilakukan dengan metode kolorimeter. Hasil pengujian kadar air menunjukkan bahwa konsentrasi asam sitrat dengan hasil humiditas berpengaruh pada serbuk buah bit, maka hasil yang memiliki kadar paling rendah yaitu dengan konsentrasi asam sitrat 0,5% terdapat pada sampel (4). Sedangkan hasil dari pengujian intesitas warna asam sitrat juga berpengaruh pada nilai warna. Penggunaan asam sitrat dengan kadar yang lebih tinggi dan juga waktu yang lebih lama dapat memperbaiki intensitas warna serbuk bit dan meningkatkan kecerahan warna. Hasil warna yang didapat adalah warna merah stabil (a*) yang diperoleh dari bantuan asam sitrat, namun adapula hasil warna kuning tetapi dengan notasi (b*) yang lebih kecil.
... Such targets have been successfully achieved by edible films and coatings based on CS, for instance, Table 4 summarizes outstanding studies in which several food products (e.g., fruits, vegetables, animal products, and dairy) have been preserved with CS-based edible films and coatings, highlighting the meaningful impact of using such materials in the productsʹ quality. Inhibition of mesophilic, psychrotrophic, yeast, mold, and bacteria growth [175] By keeping in mind that food spoilage is influenced by oxygen, water content, temperature, relative humidity, and pH [176], the physicochemical and mechanical properties of the films should efficiently control such storage conditions, and as a consequence, maintain the physical and sensory characteristics together with the protection against microbiological pathogens and increase foods' shelf-life [177]. This becomes more important in perishable natural foods (e.g., fruits and vegetables), which continue to metabolize and breathe after harvest, which means they consume oxygen to produce carbon dioxide, ethylene, and water (in different proportions), which causes the product ripening and later its decomposition [178], whereas the decomposition in perishable foods of animal origin (e.g., meat and seafood) begins immediately after death because they are highly susceptible to microbial attack by Staphylococcus aureus, Listeria monocytogenes, and Salmonella [179]. ...
Some of the current challenges faced by the food industry deal with the natural ripening process and the short shelf-life of fresh and minimally processed products. The loss of vitamins and minerals, lipid oxidation, enzymatic browning, and growth of microorganisms have been the main issues for many years within the innovation and improvement of food packaging, which seeks to preserve and protect the product until its consumption. Most of the conventional packaging are petroleum-derived plastics, which after product consumption becomes a major concern due to environmental damage provoked by their difficult degradation. In this sense, many researchers have shown interest in edible films and coatings, which represent an environmentally friendly alternative for food packaging. To date, chitosan (CS) is among the most common materials in the formulation of these biodegradable packaging together with polysaccharides, proteins, and lipids. The good film-forming and biological properties (i.e., antimicrobial, antifungal, and antiviral) of CS have fostered its usage in food packaging. Therefore, the goal of this paper is to collect and discuss the latest development works (over the last five years) aimed at using CS in the manufacture of edible films and coatings for food preservation. Particular attention has been devoted to relevant findings in the field, together with the novel preparation protocols of such biodegradable packaging. Finally, recent trends in new concepts of composite films and coatings are also addressed.
... When a water-based material is added, it is essential to a drying process that proceeds without delay so that moisture penetration is minimal (Manley, 2011). Increased water diffusion from the filling to the shells can diminish the organoleptic and microbiological quality of this product with a reduction of its shelf life (Labuza and Hyman, 1998;Roudaut and Debeaufort, 2011;Gulati et al., 2015;Ozturk and Takhar, 2018). The drying process is highly used to halt or slow down the growth of spoilage microorganisms as well as the occurrence of chemical reactions that could reduce the nutritional value. ...
The hot air drying process for cheese cracker fillings was assessed. Fillings with sheep-milk cheese and corn starch were prepared. Sodium alginate, carrageenan, locust bean, and xanthan gum were employed in order to obtain fillings with different structures and properties to study their behavior during the drying process. Drying curves were modeled by applying a diffusional model to determine the hot-air drying kinetic parameters. The structures of the fillings before and after cooking, and after drying were analyzed by confocal laser microscopy, and their texture was measured at these same times. The selected model proved to be suitable to represent the thin-layer drying characteristics of cheese cracker fillings. The cheese fillings with carrageenan showed the highest drying rate, great hardness, and a low adhesiveness at the end of drying. The sodium alginate cheese fillings exhibited the lowest drying rate, high hardness and gumminess, preserving a certain degree of adhesiveness at the end of drying. The cheese fillings with locust bean and xanthan gum presented an intermediate drying rate and a moderate increase in hardness and gumminess. Results showed the relationships among kinetics, microstructure, and texture parameters in the hot air drying process of cheese cracker fillings.
... The migration of moisture is controlled mainly by the water activity (in other words, partial pressure), not by the water content, while the hydration of the components tends to achieve a balance in their water activity, not in their water content [73][74][75]. It is a well-known fact that most of the water in fresh or wet food exerts a vapor pressure that is very close to that of pure water [76]. ...
Water loss, gain or transfer results in a decline in the overall quality of food. The aim of this study was to form a uniform layer of sodium alginate-based edible coating (1.25% sodium alginate, 2% glycerol, 0.2% sunflower oil, 1% span 80, 0.2% tween 80, (w/w)) and investigate the effects on the water barrier characteristics of fresh-cut cantaloupe and strawberries. To this end, a uniform and continuous edible film formation was achieved (0.187 ± 0.076 mm and 0.235 ± 0.077 mm for cantaloupe and strawberries, respectively) with an additional immersion step into a calcium solution at the very beginning of the coating process. The coating application was effective in significantly reducing the water loss (%) of the cantaloupe pieces. However, no significant effect was observed in water vapor resistance results and weight change measurements in a climate chamber (80%→60% relative humidity (RH) at 10 °C). External packaging conditions (i.e., closed, perforated, and open) were not significantly effective on water activity (aw) values of cantaloupe, but were effective for strawberry values. In general, the coating application promoted the water loss of strawberry samples. Additionally, the water vapor transmission rate of stand-alone films was determined (2131 g·100 µm/(m2·d·bar) under constant environmental conditions (23 °C, 100%→50% RH) due to the ability to also evaluate the efficacy in ideal conditions.
Dut yaprakları, gıda endüstrisinde yenilebilir film ve kaplamalar için yeni bir potansiyel kaynak olarak öne çıkmaktadır. Dut yaprakları, içerdiği biyoaktif bileşenler sayesinde antioksidan, anti-inflamatuar, antimikrobiyal ve antikanser gibi çeşitli sağlık faydaları sağlayabilmektedir. Dut yaprağı tabanlı yenilebilir kaplama ve filmler, gıda ürünlerinin kalitesini ve raf ömrünü artırdığı gibi aynı zamanda gıdaların fiziksel ve duyusal özelliklerini koruma potansiyeline sahiptirler. Bu bağlamda, yenilebilir doğal film ve kaplamalar gıda bozulmalarını minimize ederek, gıda endüstrisinde taze, sağlıklı ve kaliteli ürünlerin elde edilmesine olanak sağlayabilir. Bu nedenle yapılan çalışmada dut yapraklarının besinsel bileşimleri, fitokimyasal, biyolojik ve farmakolojik özellikleri, genel kullanım alanları ve gıda endüstrisinde yenilebilir kaplama ve film olarak kullanımları özetlenmiştir.
Aim
Evaluate the stability of microparticles loaded with fish oil produced by spray drying, spray chilling and by the combination of these techniques (double-shell) and use the microparticles for food application.
Methods
Samples were stored for 180 days at 6 °C and 24 °C (75% RH). Performed investigations included encapsulation efficiency, moisture content, aw, size (laser scattering), colour (L*, a*, b*), polyunsaturated fatty acids (PUFAs) (GC), thermal behaviour (DSC) and crystalline structure (XRD).
Results
Double-shell microparticles containing 26 wt% core material, 22.74 ± 0.02 µm (D0.5) and 2.05 ± 0.03 span index, 1.262 ± 0.026 wt% moisture content and 0.240 ± 0.001 of aw had PUFAs retention higher than 90 wt% during storage at 6 °C without changes in crystalline structure (β’-type crystals) and melting temperature (54 °C). The sensory evaluation suggested low fish oil release in oral phase digestion.
Conclusions
Double-shell microparticles were effective to protect and deliver PUFAs.
The potential of neat poly(lactic acid) (PLA) and PLA/cellulose nanocrystal (CNC) blown films in extending the shelf-life of crackers, a moisture-sensitive food product, was assessed. Product’s shelf-life, i.e., the time required by the crackers to reach its critical moisture content (CMC) of 8%, was determined experimentally from moisture content versus storage time plots at a constant temperature (25 °C) and various conditions of relative humidity (RH). Neither crackers within PLA nor PLA/CNC packages reached the CMC when stored below 50% RH at 25 °C, indicating that crackers packaged in both films were shelf stable at these conditions. Above this RH, the crackers inside both packages reached the CMC at different times, however crackers in CNC-based packages had approximately 40% longer shelf-life than those in neat PLA package. The shelf-life of crackers packaged in films predicted from various simulation mathematical models supported the experimental data that the crackers packaged in the PLA/CNC films had higher shelf-life compared to those packaged in neat PLA films; clearly demonstrating the potential of CNC-based films to extend the shelf-life of dry-foods.
High-protein nutrition bars (HPNBs) contain 20–50% protein and can effectively and quickly provide the energy needed by the body for performance. They are widely used as sustenance in sports, fitness, and the military as a means of replenishing vital nutrients after physical endurance. However, the hardening of HPNBs occurs quickly during storage due to the interaction of ingredients in the bar's matrix and effects of the external environment. This will lead to deleterious changes in the qualities of the HPNBs, such as taste, and it can seriously affect their market value. This review expounds the factors affecting the hardening of HPNBs during storage, such as sugar crystallization, water migration, protein self-aggregation, phase separation, and Maillard reactions. Research advances in the current anti-hardening methods are summarized, and the characteristics, advantages, and mechanisms of various methods employed in anti-hardening strategies are also expounded. The hardening of HPNBs is a complicated process involving physical changes during the early stage and chemical reactions during the middle and late stages of the storage period. Measures such as the selection of raw materials, substitution of protein with hydrolyzed protein, protein modification, addition of polyphenols, storage conditions, and other methods have achieved promising preliminary anti-hardening results. However, the development of anti-hardening HPNB methods that enable prolonged shelf lives and maintain or enhance taste and nutritional benefits represents a crucial focus for improving the processing and storage of HPNBs.
A crispy snack model, composed of maltodextrin, wheat flour, salt, and water, with a clearly measurable glass transition was designed and produced by extrusion. The material was used to investigate effects of glass transition and water plasticization on mechanical properties and sensory crispness. Water sorption and the glass transition temperature range were determined gravimetrically and using differential scanning calorimetry (DSC) for samples stored at 0 to 85% relative humidity (RH), respectively. Mechanical properties were determined for extradates rehumidified at 0 to 76% RH. Three sensory panels evaluated crispness intensities of extrudates rehumidified at 33 to 76% RH by either breaking samples with fingers (Finger Task), biting using the incisor teeth (Bite Task), or biting and chewing (Bite‐and‐Chew Task). The extrudate was plasticized by water, as observed from a typical decrease of Tg with increasing water content. Changes in mechanical properties and loss of crispness occurred at an intermediate water activity level coinciding with the extent of plasticization depressing the Tg to below ambient temperature. The changes in mechanical properties and sensory crispness intensities with increasing water activity had sigmoid shapes following the Fermi's model. Loss of crispness as a result of water plasticization is likely to apply to a number of low‐moisture food materials, although various mechanical and sensory properties do not necessarily change in unison as the materials undergo a glass transition.
Standard white breads were stored with or without crust at 25 degrees C in hermetic pouches. During two weeks of storage, the crumb moisture content and water activity (a(w)) decreased significantly when stored with crust. When stored without crust, moisture content and a(w) remained relatively unchanged The causes of the initial fuming of both breads over zero to seven days were not conclusive. But when stored beyond seven days, bread stared with crust was significantly firmer in texture and higher in amylopectin recrystallization than bread stored without crust. Moisture redistribution from crumb to crust played a significant role. This was accompanied by a decrease in freezable water in the bread crumb stored with crust. This loss in freezable water coincided with changes in the thermomechanical profile only in the case of sample stored with crust intact (and with a significant total and freezable water loss). Bread crumb stored without crust did not change in total and freezable water and showed less change in thermomechanical transitions. The transition occurring at approximate to 60 degrees C (T-2) correlated with amylopectin recrystallization but it could also have been caused by moisture loss during the analysis. Moisture migration from crumb to crust greatly reduced the total and freezable water in the crumb region resulting in a significant reduction in the magnitude of the mechanical transition at approximate to 0 degrees C (T-1) as well as an increase in the storage modulus.
A determinant factor of the quality of a processed food product is the behavior of the aroma during the processing operations. Even at moderate temperatures, changes in the aromatic composition may occur. These changes may originate in chemical reactions responsible for the deterioration of aroma compounds, or for the formation of off-flavors from non-volatile components. But losses of physical character can also greatly affect the quality of the product.
The transport and equilibrium properties of water in food mixtures are important in various processing operations and in storage stability of food products. The dough/raisin mixture is a typical mixture of different food materials, used in bakery products. The water diffusivity at 15–70 °C in dough of 20–60% moisture and in raisins of 20–40% moisture was determined from moisture distribution measurements in two contacted cylinders of dough/raisin pulp, applying the diffusion equation. The sorption isotherms of the two materials were determined using a water activity apparatus and the standard gravimetric method. A sharp discontinuity in moisture distribution was observed at the dough/raisin interface with higher concentration in the raisin side, evidently due to differences in water activity of the two materials. The water diffusivity in raisins, estimated from moisture distribution was similar to the diffusivity obtained from drying data (1–5 × 10−10 m2/s). The water diffusivity in the dough was in the same range. The diffusion and equilibrium properties of moisture may control the physicochemical and microbial changes occurring in dough/raisin mixtures.
Wheat starch and gluten have been gelatinized/heat-set in excess water and then dried to various extents to give materials with moisture contents in the range 2-15%. Fracture behaviour was examined by three-point bending, and glass transition behaviour was probed by dynamic mechanical thermal analysis.
Wheat starch and gluten were also processed via a cooker extruder to give a model granular food covering the same moisture range noted above. Extruded granules were subjected to an instrumental compression test and the sounds produced (acoustic emission) during crushing were measured. The influence of extrusion conditions (amount of added water and die temperature) were evaluated.
It was found that there were marked differences between starch and gluten in terms of the dependence of acoustic emission on moisture content. The degree of acoustic emission was also dependent on extrusion conditions. These differences are discussed in terms of: (i) the contrasting fracture behaviour observed in the bend test; and (ii) the different glass transition temperatures of starch and gluten.
During storage, some volatile constituents of packaging materials may migrate, through the air, into foodstuff. To predict migrants concentration in a cylindrical food at a given storage time, two-dimensional transient diffusion in a cylinder was solved by finite the difference method. A computer program was developed to model migrant concentration in cylindrical packaged food. The mathematical model was then validated by experimental tests applied to a high humidity food analog stored in wooden packaging. The food analog was made of 2% of agar and 98% of distilled water (w/w). Volatile compounds extracted from poplar trees were used as diffusing gas. The poplar tree is a major source of wood in food packaging in France. The gas concentrations in volatile compounds were detected by chromatography coupled with mass spectrometry. From these components, benzaldehyde was selected as the volatile component for experimental model validation. The benzaldehyde diffusion coefficient in simulated food was equal to 1.1 ± 0.1 × 10−6 cm2 s−1. Partition coefficients of benzaldehyde between packaging material and free space air of packaging and also between air and food analogs were determined.
Experimental methods for studying the transport of gases in polymers may be divided into three categories: integral permeation rate measurement, in which the cumulative amount of a penetrant that has passed through a membrane is determined; differential permeation rate measurement, in which the rate of penetration through a membrane is measured directly; and sorption rate measurement, or determination of the cumulative amount of a penetrant absorbed in a polymer sample. This paper reviews commonly used techniques for estimating diffusion coefficients from transport data of all three types. Several new estimation formulas are presented, and the relative merits of different measurement and estimation methods are discussed. A general relationship between the traditional time lag method for integral rate data analysis and a recently developed moment method for differential rate data analysis is established, extending the applicability of the moment approach to the analysis of non-ideal transport in membranes of arbitrary geometry and composition.
A milk fat fraction enriched with high melting triglyceride was extracted by using a continuous, pilot-scale supercritical CO2 system and recombined into butter. Compared with market butter, the high melting butter had higher contents of unsaturated long-chain fatty acids, high melting triglycerides, and β-carotene; higher intensity of yellow color; and lower cholesterol content. At similar temperatures, the high melting butter exhibited higher solid fat contents, complex viscosities, and power law consistency indices for viscoelastic parameters, indicating that its behavior is more like that of solids. The viscoelastic properties of high melting butter at 32°C were comparable with those of market butter at 22°C. The high melting triglyceride butter revealed higher emulsion stability without oiling off at 34°C. Because of its stable behavior at high temperatures, the product also offers good potential for application in bakery, chocolate, and confectionery industries in which stability of fat is a desired characteristic. Water activities were lower for high melting triglyceride butter than for market butter at similar temperatures, which should enhance microbial stability as well. Lower cholesterol and saturated fatty acid contents should also make high melting butter more attractive to consumers.
The glass transition temperature (Tg) and structure collapse (volumetric shrinkage) of a freeze-dried fish protein hydrolyzate (HFP) were studied. An increase in the water activity from 0 to 0.64 reduced the Tg of HFP from 79.1 to −42.8 °C. The Gordon—Taylor equation was a good predictor for the plasticizing effect of water on Tg. At room temperature (19 °C), collapse was initiated at aw = 0.44 corresponding to a T — Tg value of 35.8 °C, and browning was evident above aw = 0.55. Above these critical values several structural changes occurred: shrinkage, collapse, browning, and setting into a sticky, high-viscosity brown liquid. The viscosity of the matrix at the onset of collapse was 105–107 Pa·s, as estimated using the Williams—Landel—Ferry equation.
Extruded puffed corn starch was equilibrated to various water activities over saturated salt solutions. After equilibration the samples were stored in sealed containers for a period of eight weeks. A trained descriptive sensory panel determined the textural characteristics of the samples, after equilibration and after eight weeks of storage. The critical water activity, the water activity at which the textural characteristics of the samples significantly changed was determined to be between water activities 0.36-0.58. Principal component analysis showed that samples equilibrated to water activities above the critical water activity (0.36) were perceived to be low in fracturability and high in cohesiveness.
Published sigmoid relationships between sensory crunchiness/crispness scores of five breakfast cereals and water activity (Sauvageot and Blond 1991) were fitted with the model Y(aw) = Yo/{1 + exp [aw - awc)/b]}, where Y(aw) is the sensory score at a given aw level, Yo the score of the cereal at the dry (glassy) state, awc a critical water activity representing the inflection point of Y(aw) and b a constant representing the steepness of Y(aw) in the aw region where much of the plasticization occurs. In all five cases the fit of the model, which had previously been used with instrumental mechanical parameters of stiffness and crunchiness, was almost perfect (r2 in the range of 0.997–0.999). All the cereals had similar Yo and awc values, Yo between 7.5 and 7.9, on a scale of 10, and awc between 0.62 and 0.68. The range of water activity in which most of the perceived crunchiness/crispness loss took place, however, varied considerably among the five cereals, with the constant b being in the range of 0.046–0.093. Since according to this model about 90% of the perceived crunchiness/crispness loss occurs within awc± 3b these numbers correspond to water activity spans between about 0.28 and 0.55, respectively.
Glass transition temperatures of yellow and white corn cakes were investigated within the moisture range of 2 to 32% (w/w) using dynamic differential scanning calorimetry. All measurements were conducted at 10°C/min heating rate, 30 sec equilibrium period, and 1°C amplitude. Effects of water plasticization on corn cakes were predicted by the Gordon-Taylor's equation. Moisture sorption isotherms were established using BET and GAB equations. Relationships were found among glass transition temperature, moisture content and cake texture. The loss of crispness of corn cakes occurred within the glassy state. The initial loss of crispness occurred around monolayer moisture content, and the complete loss of crispness occurred at about 9% moisture with the highest hardness.
The L number, a dimensionless number that describes the ratio of the moisture permeance of a food substance to that of a coating material, was used to predict the effectiveness of available edible coating materials to prevent moisture migration from or into coated foods. A computer model was developed using the finite difference method to simulate moisture migration through coated food materials. the results indicated that when the L number is smaller than 0.04, the main resistance to moisture transfer for a coated food material is the diffusion of moisture within the food material itself. On the other hand, if the L number is larger than 4, the main resistance to moisture transfer is the permeance of the coating material. the application of this approach to predict the effectiveness of different coating materials for various dried foods is presented.
The loss or gain of moisture through a package depends on the sorption isotherm of the food material, the conditions of temperature and relative humidity at which it is stored, and the water vapour permeability of the packaging material. The water vapour permeability (WVP) characteristics of paperboard, polypropylene, and polyethylene used for pasta were determined at 30 to 45°C and from 11 to 85% r.h. Both temperature and relative humidity affected the water vapour permeability of all the three films. Paperboard showed a greater WVP at 30°C compared to 45°C due to a higher moisture content which swells the matrix. Thus, it did not follow the typical Arrhenius relationship of a higher permeability at higher temperature. Polyethylene and polypropylene, on the other hand, showed a higher WVP as the temperature was increased. A second degree polynomial was fitted to predict the WVP of paperboard as a function of the ambient conditions. It was found that the creases and end openings on a typical paperboard box increase the overall transmission rate by two times over that of paperboard alone, therefore reducing the shelf life to half under adverse conditions.
A dynamic mathematical model to predict mixture transfer for pasta packages under controlled unsteady state conditions of temperature and r.h. was developed and tested; good predictions were obtained.
The validity of the physical model on which the Hailwood and Horrobin (Trans. Far. Soc. 42B: 84; 1946) isotherm equation was developed was investigated. The results indicate that although the equation may fit sorption data for almost any type of food, it satisfies thermodynamic requirements (i.e. prediction of the temperature dependence) only for proteins and starchy foods. The results also show that plotting enthalpic changes against entropic changes for water sorption satisfies the enthalpy/entropy compensation phenomenon.
A number of textural properties of precooked, freeze-dried beef were examined by a cutting-extrusion test (force) and by a compression test (seven different properties). The tests were performed at different points of the moisture sorption isotherm over the complete range of water activity, Aw. In cutting-extrusion experiments (Allo Kramer Shear Press), a maximum in the force vs. Aw curve was observed at about Aw= 0.85. In compression experiments (Instron Universal Testing Apparatus), important changes of the textural properties were found in the range Aw= 0.15–0.30. These changes were paralleled by changes in the thermodynamic functions of water vapor sorption, especially in the standard differential entropy. Thermodynamic theory and mechanical measurements were used to interpret the textural changes in terms of increased crystallinity and subsequent swelling of the food structure.
The texture of extruded starch products has been measured sensorially and instrumentally. The instrumental data were analyzed using different approaches such as fractal analysis and peak analysis. The data showed useful correlations between sensory crispness and crackliness and a parameter obtained from the application of a newly developed fractal method to analyze the force deformation curve obtained from a penetration test of the cereal samples. This suggests that fractal analysis of the force-deformation plots could be used instead of sensory analysis.Moreover, it was observed that an increase in water content altered the texture of starch based samples from crispy to crackly, whereas the texture of starch-sucrose samples remained unchanged in the same hydration range.© 2000 Society of Chemical Industry
Comparison was made between the amount of browning and protein quality loss during storage of whey powder under steady state conditions (25, 35 and 45°C and aw's of 0.33, 0.44 and 0.65 at each temperature) and a fluctuating temperature condition of 25/45°C with alternating 5 day periods at each temperature. The results showed that the maximum rate of browning and loss of protein quality (e-DNP-lysine and RNV by Tetrahymena assay) occured at aw 0.44 rather than at a higher aw as is found for many dried foods. The Q10's for the reactions were about 5 and 3.7 respectively, for browning and protein quality loss. Of major importance was that storage losses at constant aw, but under the fluctuating temperature condition, were significantly greater than at the mean temperature of 35°C. Using steady state data from the 25, 35 and 45°C conditions, the prediction of browning and protein quality losses for the fluctuating condition compared favorably (+ 10%) to actual losses, based on the simple Arrhenius relationship which indicates that temperature history does not significantly change reaction mechanisms.
Cheese balls and croutons at various water activity levels (0·11–0·75) were compressed between parallel metal plates using a Universal testing machine and their acoustic emissions were recorded at compact disc quality (sampling rate of 44·1 kHz). The sound wave record (up to about 2 MB) had high intensity bursts at irregular intervals. These records were compressed after the background noise had been filtered out to produce files of less than 48 kB. The compressed signatures were characterised by their mean and peak amplitude, two measures of the sound emission intensity, and by the amplitude's standard deviation and the mean magnitude of the power spectrum, two measures of the acoustic signature complexity. All four parameters could be used to monitor the plasticisation effect of water. Although their magnitudes were correlated, they did not always change in unison upon moisture sorption. The standard deviation and mean magnitude of the power spectrum of the compressed acoustic signatures were only broadly correlated with their correspondents in the normalised mechanical signatures primarily because they were not determined from the same particles and because the latter, for technical reasons, were sampled at the low rate of 6 Hz.
The texture properties of crispy breads were studied as a function of water content using compression tests, acoustic measurements and sensory analysis. The addition of water slowly lowers the characteristics associated with crispness up to 9%, after which they steeply decrease. Dynamic Mechanical Thermal Analysis (DMTA) measurements were carried out, at room temperature and at 5 Hz, on the same bread samples. The evolution of the textural properties of crispy bread are accompanied by an increase of the loss factor prior to the one associated to the glass transition. It was therefore proposed that the effect of water on the brittle character, on crispness and on the intensity of the sound emitted at fracture were due to the onset of molecular motions preceding or accompanying the glass transition.
Published equations for the sorption isotherms of hygroscopic materials cannot be used in solving the Package Life equation, but it has been found empirically that Pearson's typo XII Frequency curve can be fitted to the isotherms of many non-crystalline commodities. Approximate solutions of the equation for the shelf-life of water-sensitive packages are derived. Separate equations are derived for absorption and desorption: the agreement of each with results observed in exposure trials is demonstrated.
W ater Activity in Foods: Fundamentals and Applications is a one-of-a-kind reference text that brings together an international group of food scientists, chemists, and engineers to present a broad but thorough coverage of an important factor known to influence the attributes of foods – water activity (a w). A team of experienced editors designed this book for lasting value as a sound introduction to the concept of water activity for neophytes and seasoned professionals in both academe and industry. Topics have been carefully selected to provide a comprehensive understanding of the mechanisms by which water activity influences the quality, shelf life, and safety of food products. Other approaches for studying water relations in foods are also discussed, including the polymer science approach and water mobility by nuclear magnetic resonance. Concepts in the practical uses and applications of water activity for food formulation, processing, and storage are generously illustrated with practical examples from the food industry that will facilitate later application by professionals in their own laboratories and production facilities. Progressing from the scientific to the practical, the book examines the fundamentals and relationships of water activity, ranging from glass transition theory and the measurement of moisture content, water activity, and isotherms, to ways in which water activity affects microorganisms, chemical reaction rates, and physical properties, to moisture gain and loss through packaging, water activity as a hurdle, and applications of a w management in the food industry and non-food systems. Water Activity in Foods belongs on the shelves of all food science professionals for use in product development, quality control, and food safety. Students and newcomers to these areas will appreciate the instructional approach adopted by the experienced teachers and industry specialists who have contributed chapters to this comprehensive overview.
The moisture barrier properties of a semisweet dark chocolate film, including effective diffusion coefficient and effective permeability constants, were determined at variable film thickness, temperature and relative humidity in the intermediate moisture range. In addition, both adsorption and desorption isotherms were determined. It was found that this chocolate film 0.6 mm (24 mil) thick was a better moisture barrier than a 1 mil thick low density polyethylene film. The mathematical packaging model for nonedible packaging materials worked well for a typical outer barrier coated model system while a new mathematical model predicted well the moisture transfer within a bi-component system of different initial aw with the barrier between them.
The jaggedness of the compressive force-displacement relationship of cheese balls®, cocoa puffs® and peanut butter crunch® particles at various moisture contents was determined in terms of their apparent fractal dimension, and the mean magnitude of the power spectrum of their normalized residuals. The plots of these measures versus moisture contents had a characteristic sigmoid shape very similar to that of the corresponding sensory crispness and crunchiness vs moisture content relationships. This close similarity suggests that the jaggedness of the force-displacement relationship is a manifestation of the same failure events that produce the crispness or crunchiness sensation. (In the context of the tested products the two terms, crispness and crunchiness, were found to be synonymous.) In all three products moisture toughening could be clearly detected instrumentally but only in two there was an unambiguous corresponding increase in the sensory hardness scores. This indicates that at least in certain cereal products moisture toughening can be perceived simultaneously with brittleness loss.
Three breakfast cereals (two commercial products and one experimental product made by extrusion cooking) were placed over 10 saturated salt solutions in desiccators for 3 weeks and then studied by sensory and mechanical analysis. A slight decrease of sensory crispness intensity occurs between 0 and 0.50 (aw) or 7% (water content), after which there is a very rapid decrease. The value of critical water activity given by the intersection between the two straight lines which can be adjusted seems not to depend on the product. Moreover this value is confirmed by the mechanical analysis and, partially, by a Differential Scanning Calorimetry analysis. There is a good correlation between sensory crispness and deformation to the first fracture.
Published sigmoid moisture sorption isotherms (0 < aw < ∼ 0.9) were fitted by the four parameter models m = k1awn1+ k2awn2 where m is the moisture contents (dry basis), aw the water activity and the k and n values are constants (n1 < 1 and n2 > 1). Not surprisingly, the model had the same or better fit than the GAB model. In contrast with both the BET and GAB models, the proposed model is not based on the assumption that there exists a well-defined monolayer of absorbed water. At aw < ∼ 0.4 and n1 > ∼ 0.55, however, the model produces a practically linear aw/[m(1 – aw)] vs aw plot, of the kind used to calculate the monolayer moisture with the BET model.
The proposed model can be a convenient means to catalog both sigmoid and nonsigmoid isotherms, and used to calculate the equilibrium water activity of dry mixtures with equations solving software.
The polymer science approach can be applied to the understanding of physical changes in foods such as loss of texture upon moisture gain. The glass transition temperature (Tg) of a commercial cracker was measured by Dynamic Mechanical Thermal Analysis (DMTA) as a function of water content. The final state diagram showed that the cracker was plasticized by water with a glass transition temperature that decreased as water content increased. When compared with published glass transition data on cereal ingredients, gluten may be the main component responsible for the mechanical changes and loss of crispness of such products when moisture content is increased.
The mechanical properties of extrusion-cooked foams have been measured as a function of density and moisture content. Extrusion conditions were varied to give a wide range of densities for which the flexural strength and modulus increased with density. The increase of density by low levels of water absorption caused very little change in this response. However, the density increase by absorption of greater quantities of water resulted in a decrease in foam mechanical properties. This has been largely attributed to the changes in the foam wall mechanical properties which have been discussed in terms of plasticization of polymers. There is some evidence that compared to the flexural test method, the higher strain rate of impact testing requires a higher level of water addition in order to cause a decrease in strength.
The quality and marketability of many fried food products is a function of the internal distribution of oil and water. French fries, for example, are well received when they are both crisp and moist, but not when they are soggy. A rapid technique for the measurement of local oil and water content is therefore highly desirable to guide the development and processing of fried food materials.Time-domain nuclear magnetic resonance (TD-NMR) has proven to be a quick, reproducible, accurate, and non-invasive technique, which is particularly well suited to measurements of oil and moisture content. Nuclear spin–spin relaxation times (T2) are an excellent probe of molecular mobility, which in turn can be directly correlated to moisture content.In this work, a precursor to spatially resolved measurements, we measure T2 in a model fried food crust sample as a function of moisture level. We observe multi-exponential behavior, which we assign to specific liquid constituents. We find a direct correlation between the component weightings and the known oil and water contents.By systematically varying the moisture level of the sample, we explore the nature of water uptake in these materials. Absorption is modeled with a modified BET sorption isotherm.These results provide a basis upon which magnetic resonance imaging (MRI) techniques can be applied to investigate cooked starch food crusts.
The ingress of water from various solutions into dense starch and sucrose:starch plaques has been observed over a range of temperatures using stray field nuclear magnetic resonance imaging. Profiles of water content as a function of depth from the surface and sorption time have been analysed to obtain mutual diffusion coefficients. This has been done using the Boltzmann transform and by measuring the front position as a function of time which produces an average mutual diffusion coefficient. This average diffusion coefficient can be fit with an Arrenhius expression with an activation energy of 56±4 kJ mol−1. It was found that the average diffusion coefficients for 30:70 and 50:50 sucrose:starch mixtures could be calculated using a weighted mean of the average diffusion coefficients for pure sucrose and pure starch. Although the diffusion coefficients for amorphous and crystalline sucrose are quite different, this has a minor effect on the calculated diffusion coefficients for the range of crystallinities observed in the sucrose:starch mixtures.
Mass transfer in food systems is generally described using Fick's laws with an effective mass transfer coefficient. There is no standardized method for estimating diffusivity. The published values present a huge variability which is due to the diversity of experimental methods, and variability of products (structure, composition). In this paper, different methods for measuring moisture diffusivity in solid products are briefly presented and discussed. The evolution of experimental moisture profiles in different solid matrices (gelatin and mixed starch and gelatin gels), using a diffusion cell at 10 or 20 °C, was analyzed. The obtained time-dependent water concentration profiles were used for estimating the diffusivities of water for each matrix. Moisture diffusivity varied from 7.5×10−11 to 3×10−11 m2/s in the range of 9.1 kg water/kg DM to 4.3 kg water/kg DM in gelatin and starch gelatin gels at 20 °C and from 5×10−11 to 1×10−11 m2/s in the range of 5.2 kg water/kg DM to 2.5 kg water/kg DM in gelatin gels at 10 °C. Significant effect of temperature was observed on moisture diffusivity but, for the studied matrices, the composition was found to have no significant effect on moisture transfer rates.
Water transfer through different films, as a function of the physical state of water in contact with the film, the relative humidity difference, and the water vapor pressure difference, was investigated. The films were two synthetic packagings (hydrophobic polyethylene and hydrophilic cellophane) and an edible film. The physical state of water affects water sensitive films, such as cellophane, inducing a higher liquid water transfer due to interactions with the polymer. For hydrophobic polymers, such as polyethylene, neither the physical state of water nor the relative humidity has an influence on the water permeability. In complex system, such as an edible film composed of hydrophilic particles dispersed in a lipid phase, barrier efficiency is influenced by the continuous hydrophobic phase but could also be affected by the physical state of water due to the presence of hydrophilic compounds.
Translational diffusion of a fluorescein probe has been measured in iota-carrageenan edible films containing different amounts of glycerol (0, 15, 30, and 45%), using fluorescence recovery after photobleaching (FRAP) experiments. The effects of this plasticizer as well as the plasticizing effect of water on the diffusion of fluorescein have been studied in this edible coating mainly composed of natural biopolymer. Diffusion coefficients of about 10(-13) m2 s(-1) have been measured in these films for water activity (aw) lower than 0.7. Above this water content threshold, fluorescein translational diffusion coefficient increases up to 10(-12) m2 s(-1). Another interesting information obtained from FRAP experiments on this system is the ratio of the diffusing molecules which are immobilized in the carrageenan matrix at aw lower than 0.98. Moreover, films containing more than 30% glycerol (w/w carrageenan) present a huge increase of the diffusion coefficient of fluorescein at high water activity (about 2 orders of magnitude), this effect being less pronounced at low water activity. The increase of diffusion seems to be only related to the water content, and glycerol only acts through the enhancement of water adsorption. Therefore, in biopolymer films containing polyol plasticizers, the gain in mobility could be devoted to the effect of the ubiquitous plasticizing molecule, water, whose adsorption is increased by the plasticizer.