MOISTURE TRANSFER PROPERTIES of WILD RICE

Working isotherms for processed wild rice and desorption isotherms for unprocessed wild rice were determined at temperatures ranging from 10 to 43.5°C. the constants for the Guggenheim-Anderson-DeBoer (GAB), Day and Nelson, Chen and Clayton and modified Halsey equations were determined by using a nonlinear optimization technique. the GAB equation showed extremely good fit to the experimental data (less than 5% error). the diffusion coefficients for moisture transport in both broken and whole processed wild rice and for unprocessed wild rice samples were determined at room temperature. the processed broken wild rice kernels had an effective diffusion coefficient of 2.66 × 10^?9 m²/h, whereas the effective diffusion coefficient was 7.08 × 10^?10m²/h for the processed whole wild rice kernels. Unprocessed wild rice had moderate effective diffusivity (1.4 × 10^?9 m²/h). These results predicted quite well the equilibrium water activities and time to equilibrium of wild rice-white rice mixtures using both analytical methods and the finite element method. the transfer of moisture to or from packaged wild rice was also illustrated for different distribution systems.     

An Improvement of the Cell Diffusion Method for the Rapid Determination of Diffusion Constants in Gels or Foods

A diffusion cell was designed to study the apparent diffusion coefficient of solutes through foodstuffs. The mathematical model corresponding to the experimental setup did not assume quasi-steady state diffusion within the slice of food. It was used to obtain the effective diffusion coefficient of NaCl through 3% Agar gels. The results were compared to those obtained by using two agar gel cylinders at different concentrations. The diffusion coefficient of Cl^? in gel at 25°C was obtained with at least the same precision (D = 1.30 × 10^?9 m²/sec, S_D= 0.03 × 10^?9 m²/sec) within less than 110 min compared to a few hours with the two cylinder technique. With the mathematical model used to determine diffusion coefficients, the equilibrium ratio between solute concentration in solution and at the interface of foodstuff can be determined.     

Effect of Freezing on Diffusion of Ascorbic Acid during Water Heating of Potato Tissue

The effect of freezing on ascorbic acid losses during water heating of potato cylinders at 50°, 65° and 85°C was studied at different periods of time. Loss of ascorbic acid in frozen potato was mainly by diffusion and greater than for fresh potato. The estimated apparent diffusivities of ascorbic acid in frozen potato during water blanching were 13.64 × 10^-10 m²/sec at 50°C, 17.78 × 10^-10 m²/sec at 65°C and 20.30 × 10^-10 m²/sec at 80°C. The activation energy of the diffusion process was 3,007 cal/mol. Ascorbic acid aparent diffusion coefficients in potato tissue with pre-freezing treatment were between 80 and 90% of ascorbic acid diffusion coefficients in water in the 50–80°C range.     

Dual mode diffusion of NaCl in Japanese radish under cooking conditions

ABSTRACT:  Sorption and diffusion of NaCl in Japanese radish have been studied. The sorption isotherm was obtained at 98 °C by the conventional method. The concentration profile by the 1-dimensional diffusion of NaCl in Japanese radish from the 3.0% solution was measured at 98 °C with the FRITRUC method involving a foodstuff rod in a thin rubber casing. Fick's diffusion coefficient, D , calculated therefrom showed a threefold variation with a maximum. This variation was quantitatively interpreted by applying a dual-mode sorption and diffusion theory under an assumption that the rate determining step of the diffusion is that in the cell wall. Two thermodynamic diffusion coefficients, D_T ( p ) and D_T ( L ), where p and L are the species of NaCl sorbed by partition and Langmuir modes, respectively, a parameter, α, derived from the local equilibrium relations between the p and L species, and S , the concentration of the Langmuir adsorption site in the cell wall of the radish, were estimated. D_T ( p ) was found to be smaller than D_T ( L ). As an explanation of the larger D_T ( L ), we invoked the higher hydration state of the adsorption site of the L species, being ascribed to residual anionic pectin in the radish than the local environment of the p species. The sorption isotherm showed a convex upward deviation from the linear relation. By using the parameters for the local equilibrium and some assumed parameters, the isotherm was found to be explainable. We suggest possible applications of the present method and interpretation to the diffusion study on the cooking systems comprising varieties of seasoning components and foodstuffs.     

Nutritional, Microbiological, and Sensory Qualities of a Peanut Beverage Prepared Using Various Processes

Nutritional, microbiological and sensory qualities of peanut beverages processed at 85°C, 100°C and 121°C for 15 min and 121°C for 3 sec were determined. Heating improved the digestibility of peanut beverages, particularly those processed at 121°C for 3 sec and 85°C for 15 min. Methionine was particularly sensitive to the treatment at 121°C. The limiting amino acids were threonine, cystine, valine, lysine and tyrosine. No microbial growth was observed in products processed at 100°C and 121°C followed by storage at 4°C and 30°C for 20 days. Beverage processed at 85°C and stored at 30°C for 3 days contained an aerobic microbial population of 2.4 × 10⁴ CFU/mL. The beany flavor was least pronounced in beverages processed at 100°C for 15 min and strongest at 121°C for 3 sec.     

The mathematical modelling of the osmotic dehydration of shark fillets at different brine temperatures

The effect of brine temperature (20, 30, 40 and 50 °C) on the osmotic drying behaviour of shark slabs (10 × 5 × 1 cm) in saturated (100°) brine was investigated. The parameters investigated were weight reduction, water loss, salt gain and water activity. Salt uptake and moisture data were analysed using various mathematical solutions based on Fick's Law of Diffusion and the effective diffusion coefficients were predicted after considering the process variables. The expressions presented by Azuara et al. (1992) , based on the model presented by Crank (1975) , were successfully used to predict the equilibrium point and to calculate diffusion coefficients at not only the initial stages of dehydration, but also at different times during the osmotic process.     

Diffusion of Sucrose in Osmo-Dehydrofrozen Apple

Apple parallelepipeds were dewatered by osmosis in sucrose solution at 30°C for 3 h, and at 70°C for 1 h. Dewatered material was air-frozen at ?12, ?20, and ?35°C and stored for 1, 3, and 6 months. After a prescribed time of storage, cryoscopic temperature, amount of non-frozen water, and effective diffusion coefficients were calculated based on sucrose concentration profiles in the frozen material. In frozen, osmotically dewatered apple, mass transfer was very slow. After 6 months of storage, large concentration gradients still occurred in the frozen material. Effective diffusion coefficients, based on sucrose concentration expressed as percent of the total mass of the sample, were statistically not dependent on storage temperature. They were dependent on sucrose concentration and varied from 2·10^?14 m²/s, at high sucrose concentration, to 5·10^?11 m²/s, at low sucrose concentration. On the other hand, effective diffusion coefficients, based on the sucrose concentration in non-frozen water, were dependent on storage temperature and sucrose concentration as well. They were from 1·10^?15 m²/s to 2·10^?12 m²/s.     

Moisture Transfer Properties of Dry and Semimoist Foods

Equilibrium moisture content, mass diffusion coefficients, and densities were collected for wheat flour, shredded wheat, raisins, nonfat dry milk, and freeze-dried apple, turnip, and ground beef at 25 ± 1°C. Flour adsorbing to 0.75 a_w had the largest mass diffusion co-efficient, 1.15 × 10^?7 m²/hr and raisins had the smallest value of 0.015 × 10-⁷ m²/hr. Two of the food uroducts. flour desorbing to 0.11 a_w, and the freeze-dried turnip, exhibited diffusion coeffcients which were dependent on the moisture content. Most of the foods reached equilibrium within 1 wk based on an objective criterion of no more than a 0.5% dry basis moisture difference over three successive readings at 1 wk interval.     

Time–temperature study of the kinetics of migration of DPBD from plastics into chocolate,chocolate spread and margarine

Migration of low molecular weight substances into foodstuffs is a subject of increasing interest and an important aspect of food packaging because of the possible hazardous effects on human health.The migration of a model substance (diphenylbutadiene) from low-density polyethylene (LDPE) was studied in foodstuffs with high fat contents: chocolate, chocolate spread and margarines (containing 61% and 80% fat).A simplifying mathematical model based on Fick’s diffusion equation for mass transport processes from plastics was used to derive effective diffusion coefficients which take also kinetic effects in the foods into account and to determine partition coefficients between plastic and food. With this model migration levels obtainable under other storage conditions can be predicted. The effective diffusion coefficients for both margarines stored at 5 °C (3.0–4.2 × 10⁻¹⁰ cm² s⁻¹) and at 25 °C (3.7–5.1 × 10⁻⁹ cm²  s⁻¹) were similar to each other, lower than for chocolate spread stored at 5 °C (9.1 × 10⁻¹⁰ cm² s⁻¹) and higher than the diffusion coefficient for chocolate stored at 25 °C (2.9 × 10⁻¹⁰ cm² s⁻¹). Good agreement was found between the experimental and the estimated data, allowing validation of this model for predicting diffusion processes in foodstuffs with high fat contents.     

Mass transfer evaluation of ultrasonic osmotic dehydration of cherry tomatoes in sucrose and salt solutions

In order to elaborate dehydration and osmotic equilibrium characteristics of cherry tomatoes and to analyse the applicability of Peleg model in prediction of equilibrium moisture content and the methodology of Crank’s solution to Fick’s diffusion law in calculation of effective diffusivity, cherry tomatoes were osmotically treated in ternary solution (water, sucrose and NaCl) with or without ultrasound at 30 °C. Results indicated that, a time cumulative effect of ultrasound occurred about 30 min for water loss (WL), while for sugar gain it happened after 45 min, which made the dehydration efficiency index best at the ultrasonic power of 150 W for 40 min. As a function of salt content, the equilibrium WL followed well the first order exponential decay model, and the equilibrium salt content followed well the second order polynomial. A great relative error (29.13%) between the practical determination and the predicted value indicated that Peleg model was not suitable for prediction of equilibrium moisture content. A great truncation error (865%) occurred when moisture effective diffusivity (6.66 × 10^?9 m² s^?1) was calculated with Crank’s solution to Fick’s diffusion law by letting n = 1 as compared to that (0.77 × 10^?9 m² s^?1) by letting n = 100.     

A study of the apparent diffusion coefficients for ascorbic acid losses from peas during blanching in water

Blanching is an important pretreatment in the processing of many vegetables. The previous studies concluded that the major losses of ascorbic acid from peas during blanching in water are due to leaching process. Therefore this study is concerned with the loss of ascorbic acid from peas during water blanching at 50,60,70,80 and 90°C for 0, 2, 4, 6, 8, and 10 min, in an attempt to elucidate the mechanisms involved in such losses. When the agitation of the blanch water is sufficient, the surface resistance is made negligibly small, and the total resistance to the loss of ascorbic acid from peas to the blanch water is controlled by diffusion mechanism only. So the apparent diffusion coefficients (D) for ascorbic acid loss from peas were calculated after blanching under various conditions. When the temperature ranged from 50°C to 90°C, values of D were found to be in the range of 0.94 × 10^?8 to 1.94 × 10^?8 m² s^?1, having an activation energy of 18.71 kJ/mol. Also the results indicated that, if there was a sufficient agitation, the leaching of ascorbic acid from peas during blanching in water was controlled by “diffusion”.     

Diffusivity of potassium sorbate in κ-carrageenan based antimicrobial film

The diffusion of potassium sorbate incorporated into κ-carrageenan based antimicrobial film was measured at 5 s intervals using a diffusion cell. The kinetics of potassium sorbate release followed Fick's law of diffusion, as shown by diffusional exponent characteristic n-value and high correlation coefficients between experimental and theoretical data. The effects of solution pH at the film surface (3.8, 5.2 and 7.0) and temperature (5, 25 and 40 °C) on diffusion were investigated. Diffusion was found to be unaffected by adjacent solution pH in the range of values tested, but a decrease in temperature from 40 to 5 °C resulted in a reduction of diffusion coefficients from 4.24×10⁻¹³ to 1.29×10⁻¹³ m²/s at pH 5.2.     

Dual mode diffusion and sorption of sodium chloride in pre-cooked egg white

The concentration profiles of NaCl by the one-dimensional diffusion in pre-cooked EW (egg white) were obtained at 5-80 °C. D's (Fick's diffusion coefficients) estimated at respective concentrations of NaCl in EW showed peaks at a certain NaCl concentration in the substrate. The peak became prominently high with the increase in temperature. These variations were interpreted in terms of the dual mode sorption and diffusion theory, which was successfully applied to the diffusion behavior of NaCl in Japanese radish. In EW, the water swollen protein phase coexists with the dispersed liquid water phase. It is in the former phase where the diffusion rate in EW is determined via the dual mode mechanism. By applying the theory, thermodynamic diffusion coefficients, D_T(p), of the partitioned species at respective temperatures were found to be smaller than those, D_T(L), of the Langmuir sorption species. The variations of D with peaks were interpreted with these two D_T's and equilibrium parameters of the two species. The sorption isotherms of NaCl by EW were found to be slightly convex upward at low NaCl concentrations, which were successfully interpreted by considering the two phases mentioned above and the equilibrium parameters for the partitioned and Langmuir species.     

Microbial and enzymatic changes in natural soursop puree during storage

Microbial and enzymatic comparisons were made on natural soursop puree stored at 15, 4 and −20°C without pasteurisation and with pasteurisation at 79°C for 69 s. Results showed that pasteurisation caused significant decrease in microbial count in soursop puree from 6.4×10³ to 8.5×10¹ cfu per g. Generally, storage at −20°C exhibited greater stability of samples as compared to those kept at 4 and 15°C. In contrast to microbial reduction, pasteurisation caused significant increase in cloud from 0.318 to 0.529 and completely inactivated the pectinesterase enzyme. The puree packed into foils kept at 4°C exhibited decreased cloud loss as compared to others packed in cans and bottles kept at 15 and −20°C. No pectinesterase enzyme regeneration was observed for pasteurised puree in this study during 12 weeks of storage time.     

NONDESTRUCTIVE MEASUREMENT of TRANSIENT MOISTURE PROFILES and the MOISTURE DIFFUSION COEFFICIENT IN A POTATO DURING DRYING and ABSORPTION BY NMR IMAGING

A nondestructive method to measure the internal moisture distribution and to determine the effective moisture diffusion coefficient for a potato during drying and absorption was developed using NMR imaging and numerical modeling techniques. the coefficients obtained were 1.04 to 7.28 × 10^?10 m²/s, for moisture contents between 40% and 55% (wb), during drying with a sample temperature of 40°C; and were 9.78 × 10^?12 to 2.33 × 10^?11 m²/s, for moisture contents between 56% and 60%, during absorption at 23°C.     

Behavior and incidence of Vibro parahaemolyticus in Sydney rock oysters (Crassostrea commercialis)

Vibrio parahaemolyticus grew poorly or not at all during storage of unopened Sydney rock oysters (Crassostrea commercialis) at 15 and 30°C for 2 and 7 days. Although V. parahaemolyticus counts often increased at 30°C, counts above 10⁴/g were not observed. Escherichia coli counts did not usually change substantially under these conditions. V. parahaemolyticus grew more readily during storage of unopened oysters under more severe conditions, with counts approaching or exceeding 10⁶/g after continuous or intermittent storage at 37°C. Opened oysters provided a much more favourable environment than unopened oysters for growth of V. parahaemolyticus. Growth occurred at 15, 30 and 37°C, with counts > 10⁶/g after overnight storage at 30 or 37°C. A survey of 30 market samples of oysters was conducted. Sixteen samples of unopened oysters were collected at the wholesale level and 14 samples of refrigerated opened oysters were purchased from retailers. V. parahaemolyticus was present in all samples of unopened oysters (range 0.4/g?2.3 × 10⁴/g) and in 13 samples of opened oysters (range 4.3/g? > 1.1 × 10³/g).     

Preserving Melons by Osmotic Dehydration in a Ternary System Followed by Air-Drying

In this study, the effect of different osmotic solution concentrations (20–60% w/w of sucrose with 10% w/w NaCl salt), fruit to solution ratios (1:9–1:3), immersion times (0.5–4 h), and temperatures (15–55°C) on the mass transfer kinetics during osmotic dehydration of melons (Curcumis melo L.) in ternary solution namely sucrose–salt–water followed by air-drying were investigated. The effective diffusion coefficients for sucrose and water during osmotic dehydration were determined, assuming osmotic dehydration to be governed by Fickian diffusion. The estimated parameters allowed optimizing the system to reduce total processing time. The optimum treatments were with 50% sucrose and 10% NaCl salt concentration, fruit to solution ratio of 1:4 for 1 h at 45°C. Samples non-treated and pre-treated in optimized conditions were dried in a hot-air dryer at 60°C until equilibrium was achieved after 2.5 h. Pre-treatment reduced the air-drying period in up to 6.8 h.     

Diffusion of Acetic and Propionic Acids from Chitosan-based Antimicrobial Packaging Films

The diffusion of acetic or propionic acids from thin (44 to 54 μm) chitosan‐based antimicrobial packaging films in which they were incorporated was measured after immersion of the films in water, and the effects of pH (5.7, 6.4, or 7.0) and temperature (4 °C, 10 °C, or 24 °C) on diffusion were investigated. The kinetics of acetic‐ and propionic‐acid release deviated from the Fickian model of diffusion. Diffusion was found to be unaffected by pH in the range of values tested, but a decrease in temperature from 24 °C to 4 °C resulted in a reduction of diffusion coefficients from 2.59 × 10^?12 m².s^?1 to 1.19 × 10^?12 m².s^?1 for acetic acid and from 1.87 × 10^?12 m².s^?1 to 0.91 × 10^?12 m².s^?1 for propionic acid. The effect of temperature on diffusion was well (r² > 0.9785) described by an Arrhenius‐type model with activation energies of 27.19 J.mole^?1 (acetic) and 24.27 J.mole^?1 (propionic). Incorporation of lauric acid or essential oils (cinnamaldehyde or eugenol) into the chitosan film at the time of preparation produced a subsequent reduction in the diffusion of acetic or propionic acid, and maximum effects were obtained with lauric acid and cinnamaldehyde incorporated to final concentrations of 1.0% and 0.5% (w/w), respectively.     

Characteristics of mince from pond-bred silvercarp (Hypophthalmichthys molitrix) and preliminary experiments on its use in sausages

The quality of fresh, chilled and frozen mince made from the flesh of pond-bred silvercarp (Hypophthalmichthys molitrix (Val)) was evaluated. Flavour panel scores for all minces were acceptable and this quality did not deteriorate during storage for one week in a domestic refrigerator (5–6°C) or for one year at ?20°C. The levels of oxidative rancidity (2-thiobarbituric acid analysis) in the minces were consistent with this maintenance of quality. Aerobic plate counts at 25°C of fresh mince rose from 7–9 × 10⁴ to 1.1 × 10⁵ after 6 days' storage at 5–6°C. Coliform and psychrotroph counts rose from 1.0 × 10¹ and 7–8 × 10³ to 5–4 × 10² and 1.3 × 10⁴, respectively. The functional and textural properties of pond-bred silvercarp mince in terms of salt-soluble protein content, water binding capacity and penetrometer values were measured on fresh, refrigerated and frozen samples. All-fish sausages and frankfurters developed from pond-bred silvercarp mince were assessed in laboratory and consumer tests against commercial beef sausages and frankfurters. The fish products competed well and achieved levels of acceptance similar to those of the beef-containing products. Texture measurements revealed slight changes in the fish products during storage for 7 days at 5–6°C. No spoilage was detected in any of the products after a week at 5–6°C. The nutritional advantages of the fish sausages and frankfurters are discussed.     

Water Diffusion and Concentration Profiles During Osmodehydration and Storage of Apple Tissue

The objective of this work was to study the mobility of water and sucrose during osmotic dehydration and storage of apple tissue and to conduct an analysis of the behavior of the effective diffusion coefficients determined from concentration profiles. Osmotic dehydration (OD) of apple was carried out at 40°C for 1 h, and the solution: sample ratio was 20:1 (w/w). Samples of 20-mm diameter were extracted from the dehydrated apple immediately after the OD process and after 4 and 24 h of storage at 25 °C. Moisture of these samples and soluble solids content were analyzed. Our results showed, after 1 h of OD, the outer layer of the apple sample lost 0.37 kg water/kg apple and gained 0.30 kg sucrose/kg apple. These values decreased toward the internal layers of the apple. A fine layer of greatly dehydrated cells was formed on the surface around the sample, which determined the mass transfer rate in the whole tissue. Smaller mass transport rates were observed in the development of concentration profiles during storage. Diffusion coefficients obtained for the outer layer after 1 h of OD were 1.53 × 10⁻¹⁰ and 1.05 × 10⁻¹⁰ m²/s for water and sucrose, respectively. The analysis of compositional profiles developed during osmodehydration was a useful tool to get a better understanding of the changes in the water activity of the outer layer of the apple tissue.