Moisture Sorption Characteristics of Freeze Dried Blueberries

Moisture sorption isotherms of freeze dried lowbush blueberries at 4, 16, 25, 35, and 45°C were determined using indirect gravimetric method. Moisture sorption kinetics at these temperatures and 75% RH were also investigated. The isotherms followed a type III shape with a temperature inversion effect at 0.9 water activity. They were best described by the GAB equation. Net isosteric heat of moisture sorption in freeze dried blueberries, determined using the Clausius Clapeyron equation, varied from 5.5 to 0.25 kJ/mol as moisture content changed from 8 to 36% (dry basis). Moisture adsorption kinetics in freeze dried blueberries were well described by the first order kinetics equation. The rate constant followed the Arrhenius relationship with an activation energy of 38.6 kJ/mol.     

Effect of storage parameters on freeze‐dried kefir grains

The purpose of this study was to use freeze‐drying to preserve microbial activity while extending the shelf life of kefir grains and to determine the best storage temperature. Freeze‐dried kefir grains were lyophilised and were later stored in a multilayer plastic film with a moisture barrier for 90 days at varying temperatures. Microbial activity continued until the 60^th day of storage at 4 °C. PCR analysis was performed to determine Lactobacillus kefiranofaciens as an indicator kefir micro‐organism. It was concluded that the conservation of kefir grains by freeze‐drying protects the natural embedded microbiota; therefore, both the shelf life of kefir grains and the consumption of natural kefir increase.     

Moisture sorption isotherms of potato slices

Water vapour sorption isotherms of Norchip, Russet Burbank and Norland potatoes were determined by the salt solution technique at 10, 25 and 40°C. The adsorption isotherms of potatoes were of sigmoid shape and were affected by drying method, temperature and sugars addition. The freeze dried products adsorbed more water vapour than the vacuum dried materials. Addition of glucose, sucrose or lactose to the potatoes caused the equilibrium moisture content to decrease in the low and intermediate water activity ranges. The sorption was temperature independent in the a _w range 0.11–0.35 and showed a hysteresis loop at intermediate moisture levels.     

Role of precursors on greening in crushed garlic (Allium sativum) bulbs, and its control with freeze-dried onion powder

BACKGROUND: Lachrymatory factor (LF) synthase in onion bulbs reacts with S‐1‐propenyl‐L ‐cysteine sulfoxide (1‐PeCSO), a key compound in garlic greening. In this study, freeze‐dried onion powder containing LF synthase was used in treatments to control garlic greening. Prior to the use of freeze‐dried onion powder to treat greening garlic bulbs, model reactions were conducted to confirm the reactivity of 1‐PeCSO in onion bulbs to garlic greening. RESULTS: While pink pigments were generated from 1‐PeCSO, green pigments were produced from the combination of 1‐PeCSO and S‐2‐propenyl‐L ‐cysteine sulfoxide (2‐PeCSO). However, pigments were formed in the systems containing 1‐PeCSO, amino acid and alliinase. Even non‐greening garlic bulbs stored at 20 °C turned green with the reaction of 200 g L^?1 1‐PeCSO; therefore 1‐PeCSO isolated from onion bulbs had the same role as 1‐PeCSO in garlic bulbs in terms of greening. Onion bulbs turned green after the addition of 600 g L^?1 2‐PeCSO. The addition of freeze‐dried onion powder inhibited garlic greening, and treatment with 15 g kg^?1 onion powder gave the best storage stability of crushed garlic bulbs. CONCLUSION: The addition of freeze‐dried onion powder inhibited the greening in crushed garlic bulbs, and treatment with 15 g kg^?1 onion powder gave the best storage stability of crushed garlic bulbs. Copyright © 2011 Society of Chemical Industry     

Foam‐Mat Freeze‐Drying of Bifidobacterium longum RO175: Viability and Refrigerated Storage Stability

Foaming as a pretreatment was used prior to freeze‐drying of Bifidobacterium longum RO175 to investigate the potential acceleration of the drying rate and increase in microorganism viability after the process. A study on storage of foamed and nonfoamed freeze‐dried products at 4 °C completed this study. B. longum RO175 in foamed medium could be freeze‐dried in 1/7 to 1/4 of the time required for nonfoamed suspensions. In addition, foamed suspensions presented higher viability immediately after freeze‐drying (13.6% compared to 12.81 % or 11.46%, depending on the cryoprotective media). Refrigerated storage led to a reduction in B. longum RO175 viability for all tested protective agents (foamed and nonfoamed). No correlation between glass transition temperature and stability of probiotic powders was observed during storage. In addition, lower viability after 56 d of storage was observed for foamed materials, probably due to foam porous structure and higher hygroscopicity, and oxygen presence and moisture pickup during storage.     

Sorption isotherms and thermodynamic properties of freeze‐dried colostral whey powders with different additives

Moisture adsorption isotherms of colostral whey (CW) powders with different additives (maltodextrin and sucrose) were determined using gravimetric static method at 15–35 °C in the water activity range of 0.067–0.76. The moisture adsorption isotherms obtained were typical sigmoid curves, and the modified‐Halsey and Guggenheim–Anderson–de Boer (GAB) equations gave the best fit to experimental data among five well‐known equations. Addition with maltodextrin into CW powders could effectively decrease equilibrium moisture content (EMC), whereas addition with sucrose increased EMC in the water activity of 0.43–0.76 at 15 and 25 °C and in the water activity of 0.21–0.76 at 35 °C, respectively. Thermodynamic properties including net isosteric heat of sorption and differential entropy were determined from adsorption data using Clausius–Clapeyron equation. The results showed that net isosteric heat of sorption of all the samples decreased exponentially with increasing EMC. Enthalpy–entropy compensation theory was applicable for adsorption process of all the samples, and the adsorption processes were enthalpy‐driven.     

Physicochemical properties and storage stability of spray‐dried soya bean sprout extract

Amylase is a very important enzyme due to its wide food applications. To preserve amylase activity in soya bean sprout extract (SSE), SSEs were spray‐dried with 10% maltodextrin and 0–3% alginic acids, and their physicochemical properties and storage stability were compared with freeze‐dried one. SSE exhibited maximum amylase activity at pH 7.0 and 60 °C, with the most active substrate specificity towards soluble starch. Spray‐dried SSEs exhibited higher water solubility index (WSI) and in vitro relative amylase activity but lower water vapour sorption (WVS) and smaller particle size than freeze‐dried SSE. For spray‐dried SSEs, particle size, WSI and in vitro relative amylase activity increased while WVS decreased with increasing % alginic acid. This study demonstrated that spray drying of SSE, especially with 10% maltodextrin and 2% alginic acid, was effective in keeping amylase active and stable during 7‐week storage at room temperature (25 °C).     

Effect of adding fresh and freeze‐dried buckwheat sourdough on gluten‐free bread quality

This study demonstrates new possibilities in using freeze‐dried buckwheat sourdoughs in the processing of gluten‐free bread (GFB). Fresh and freeze‐dried (at temperatures of 20, 40 and 60 °C) sourdoughs were added in the amounts of 10, 20, 30 and 40% of the total flour content. Significant and beneficial changes in the quality of bread under the influence of different quantities of fresh and freeze‐dried sourdoughs additive were observed. Freeze‐dried buckwheat sourdoughs at the level of 20 and 30% gave the best baking results for GFB. pH of bread significantly changed, which had a positive effect on increasing its suitability for the storage. Buckwheat sourdough dried at 40 °C is the most highly recommended for GFB processing. Higher temperatures (60 °C) caused the least change in bread volume; however, a bitter aftertaste from burning was slightly detectable. Freeze‐dried buckwheat sourdoughs can be used directly in processing, thus eliminating the long fermentation of sourdough.     

Water Adsorption of Peanut Kernels in a Closed System with Respect to Moisture Transfer

Adsorption isotherms of peanut kernels, Tainan # 9 and #11, were determined at 30°C and used as reference to determine the a_w at equilibrium. The changes of the apparent a_w and moisture of three weighed dried kernels in closed systems stored with distilled water were determined in an electric hygrometer and a series of vessels at 30°C. A nonequilibrium state of moisture and apparent a_w gradients of the kernels was observed in the early stages of 144 hr storage. In a 90 min experiment with the hygrometer at 30°C, the vapor adsorption rate and final apparent a_w decreased in order with the increase of the number of kernels, from 1 to 7, stored with saturated K₂Cr₂O₇ salt (a_w= 0.98 at 30°C). Vapor adsorption rate and final apparent a_w of Tainan # 9 were slightly higher than those of # 11.     

Moisture sorption isotherms and thermodynamic properties of safflower seed using empirical and neural network models

Experimental work was conducted to obtain the adsorption isotherms of safflower seed using a semi static gravimetric method at 25, 40, and 60 °C over a water activity range from 0.11 to 0.94. Fourteen isotherm equations and multilayer artificial neural network approach were employed to analyze the experimental data. In order to evaluate the goodness of fit of each model determination coefficient, Chi Square and root mean square error were used. The Peleg (at 25 and 40 °C) and Osvin (at 60 °C) models were selected to best describe the sorption isotherms of safflower seed. Accordingly, the results showed that the predicted values of ANN model were more accurate than those predicted by nonlinear regression method. The adsorption monolayer moisture content was also determined using Brunauer, Emmett and Teller equation. The monolayer moisture content values were 0.028, 0.024, and 0.022 gH₂O/g solid at 25, 40, and 60 °C, and the corresponding constant values of the Brunauer, Emmett and Teller equation were found to be ?13.029, ?10.873, and ?17.255, respectively. The safflower seeds heat of sorption values was also found. The heat of sorption values was large at low moisture content and decreased with an increase in the moisture content, whereas the magnitudes increase with increases in temperature and could be well adjusted by an exponential relationship. The experimental data revealed that enthalpy-entropy compensation theory was satisfactorily applicable to the moisture sorption behavior of the safflower seed.     

Moisture sorption isotherms of green chilli

The adsorption and desorption equilibrium moisture contents of green chilli were determined experimentally in relative humidity range of 11‐97% and at the temperatures of 20, 30, 40 and 50°C. The experimental procedure used was a dynamic method with periodically recording of sample mass. The effect of temperature on adsorption and desorption isotherms was found significant. Hystereses were observed for entire range of relative humidity and hysteresis loops decreased with the increase of temperature. Nine sorption isotherm models were fitted the experimental data at the temperatures of 20, 30, 40 and 50 °C. The modified Smith equation was the best fitted equation to the experimental data for relative humidity range of 11‐97% for the adsorption and desorption isotherms of green chilli.     

Preparation and evaluation of pizza cheese made from blend of vetch–bovine milk

The objective of the study was to develop vetch–bovine milk (VBM) pizza cheese low in animal fat and its acceptability was determined through physico‐chemical, functional and sensory evaluations. Vetch (Lathyrus sativus) was detoxified by steeping in double its quantity of water for 8 h at 70 °C, changing the water seven times, draining and sun drying. Dried vetch was then treated with water at pH 4.0 at 90 °C for 60 min to deplete the beany flavour, then dried and milled into fine flour with Quadrumate Senior mill. The seed coat was separated as one of the mill fractions. Four types of VBM blends were prepared from vetch flour and bovine skimmed milk powder and were used to prepare cheese using 2.5% lactic acid bacterial culture of Streptococcus thermophillus and Streptococcus bulgaricus and rennet (0.15 mL L^?1, 1:40 ratio with water). The cheese was stored at 4 °C for 14 days and used as topping over the pizza shell. Physico‐chemical analyses, such as moisture, total solids, lactose, ash, fat, titratable acidity and pH, and sensory evaluations of both cheese and pizza were carried out at 0‐, 7‐ and 14‐day intervals. The stretchability and meltability of cheese increased significantly (P < 0.05) during storage. Commercial Mozzarella cheese was taken as a control. The results of this study suggested that VBM blend at the ratio of 12.5:87.5 (vetch flour:bovine milk powder) could be utilised to prepare a cheese of desirable characteristics for pizza topping.     

Development of vacuum‐dried probiotic milk powder with Bacillus coagulans

The present study explored the possibilities of using Bacillus coagulans as a probiotic culture in vacuum‐dried milk powder. The operational drying temperature at 63 ± 2 °C under 0.7 kg/cm² pressure emerged as the best temperature at which to prepare dried milk powder within 4.5 h with a mean (±SEM) Bacillus coagulans B37 spore count of 8.78 ± 0.03 log cfu/g and moisture content of 4.82 ± 0.12%. The total spore counts in vacuum‐dried milk powder did not change (P > 0.10) at storage temperatures of 7 °C, 37 °C or 45 °C over a three‐month period.     

ACCELERATED STORAGE, SHELF LIFE AND COLOR OF MANGO POWDER

Vacuum‐dried mango powder was produced from mango pulp through the addition of glycerol monostearate and tricalcium phosphate at 0.015 kg each per kg mango solids and maltodextrin at 0.62 kg per kg dry mango solids. The mango powder was packed in aluminum foil‐laminated pouches and stored in an accelerated storage environment maintained at 90% relative humidity (RH) and 38 ± 2C. The sticky‐point moisture content at 38 ± 2C was considered as the maximum moisture content to which the mango powder would remain stable. The shelf life of the powder predicted from this consideration and the Guggenheim‐Anderson‐de Boer (GAB) model for the water activity moisture content relationship was 114.68 days, whereas the actual shelf life was 105 days. The color change of the powder during storage followed first‐order reaction kinetics with a rate constant of 0.038 per day.     

Spray drying of red (Hylocereus polyrhizus) and white (Hylocereus undatus) dragon fruit juices: physicochemical and antioxidant properties of the powder

This study aims to investigate physical stability and antioxidant properties of spray‐dried red (Hylocereus polyrhizus) and white (Hylocereus undatus) dragon fruit powder upon storage at various relative humidity (RH). Inlet air temperatures of 120 °C (red dragon fruit) and 110 °C (white dragon fruit) as well as maltodextrin concentration of 30% (w/v) were selected as the spray drying conditions as powder was obtained at these minimum conditions. The powder was ranging from 3 to 7 μm in particle size with spherical morphology. The powder had lower antioxidant content and antioxidant activities compared with the control before spray drying. Storage of powder at 43%, 54% or 75% RH at 25 °C for 25 days resulted in structural changes correlating to the depression of glass transition temperatures (T_g) to below storage temperature. At 33% RH, no visible structural changes were observed. Antioxidant properties of the powder remained unchanged after 25 days' storage at the studied RHs.     

Application of the GAB model to the moisture sorption isotherms for dried fruits

The moisture adsorption isotherms for dried raisins, figs, prunes, and apricots were determined at 15, 30, 45 and 60°C, using the gravimetric static equilibrium method. The applicability of the GAB (Guggenheim-Anderson-de Boer) model to the experimental results was found to depend on the regression method employed. So, using direct non-linear regression analysis, five constants of the GAB model were estimated which enables the equilibrium moisture content of each dried fruit in the temperature range 15–60°C to be predicted with reasonable accuracy. The indirect (successive) non-linear regression method is not recommended since the basic three constants of the GAB equation are interrelated.     

Stability of anthocyanins in frozen and freeze-dried raspberries during long-term storage: in relation to glass transition

Abstract: Anthocyanins, natural plant pigments in the flavonoid group, are responsible for the red color and some of the nutraceutical benefits of raspberries. This study explores anthocyanin degradation in frozen and freeze‐dried raspberries during storage in relation to glass transition temperatures. Frozen raspberries were stored at ?80, ?35, and ?20 °C, while freeze‐dried raspberries were stored at selected water activity (a_w) values ranging from 0.05 to 0.75 at room temperature (23 °C) for more than a year. The characteristic glass transition temperatures (T′_g) of raspberries with high water content and glass transition temperature (T_g) of raspberries with small water content were determined using a differential scanning calorimeter. The pH differential method was used to determine the quantity of anthocyanins in frozen and freeze‐dried raspberries at selected time intervals. The total anthocyanins in raspberries fluctuated during 378 d of storage at ?20 and ?35, and ?80 °C. Anthocyanin degradation in freeze‐dried raspberries ranged from 27% to 32% and 78% to 89% at a_w values of 0.05 to 0.07 and 0.11 to 0.43, respectively, after 1 y. Anthocyanins were not detectable in freeze‐dried raspberries stored at a_w values of 0.53 to 0.75 after 270 d. First order and Weibull equations were used to fit the anthocyanin degradation in freeze‐dried raspberries. The 1^st‐order rate constant (k) of anthocyanin degradation ranged from 0.003 to 0.023 days^?1 at the selected water activities. Significant anthocyanin degradation occurred in both the glassy and rubbery states of freeze‐dried raspberries during long‐term storage. However, the rate of anthocyanin degradation in freeze‐dried raspberries stored in the glassy state was significantly smaller than the rate of anthocyanin degradation in the rubbery state.     

Rehydration of Freeze‐Dried and Convective Dried Boletus edulis Mushrooms: Effect on Some Quality Parameters

ABSTRACT: Quality of rehydrated products is a key aspect linked to rehydration conditions. To assess the effect of rehydration temperature on some quality parameters, experiments at 20 and 70 °C were performed with convective dried and freeze‐dried Boletus edulis mushrooms. Rehydration characteristics (through Peleg's parameter, k₁, and equilibrium moisture, W_e), texture (Kramer), and microstructure (Cryo‐Scanning Electron Microscopy) were evaluated. Freeze‐dried samples absorbed water more quickly and attained higher W_e values than convective dried ones. Convective dehydrated samples rehydrated at 20 °C showed significantly lower textural values (11.9 ± 3.3 N/g) than those rehydrated at 70 °C (15.7 ± 1.2 N/g). For the freeze‐dried Boletus edulis, the textural values also exhibited significant differences, being 8.2 ± 1.3 and 10.5 ± 2.3 N/g for 20 and 70 °C, respectively. Freeze‐dried samples showed a porous structure that allows rehydration to take place mainly at the extracellular level. This explains the fact that, regardless of temperature, freeze‐dried mushrooms absorbed water more quickly and reached higher W_e values than convective dried ones. Whatever the dehydration technique used, rehydration at 70 °C produced a structural damage that hindered water absorption; consequently lower W_e values and higher textural values were attained than when rehydrating at 20 °C.     

Changes in the quality of dehydrated broccoli stems during storage

Dehydrated broccoli stems were studied during storage at different temperatures, namely 5, 15, 25 and 40 °C. The parameters studied were rehydration capacity, texture of the rehydrated product and chlorophyll content. A diffusional model was used to study the rehydration process, yielding good agreement with the experimental data when the equilibrium moisture and the effective diffusivity were identified. Samples stored at 5 °C showed little change in any of the parameters studied during the storage time considered (427 days). At 15 and 25 °C the equilibrium moisture and the effective diffusivity varied linearly. At 40 °C, sharp changes were observed up to 115 days, the equilibrium moisture decreasing and the effective diffusivity increasing. From this time on, both values showed moderate changes. With reference to texture, samples stored at 5, 15 and 25 °C showed a similar trend without significant changes during the whole period, the textural values increasing with temperature. At 40 °C the texture suffered a sharp increase up to 145 days, then changes were negligible. Chlorophyll content degradation was increased with temperature. As a result of a calorimetric study a second‐order transition was observed at 34 ± 1 °C. This fact can contribute to the interpretation of the different tendencies observed in all the parameters studied at 40 °C. © 2000 Society of Chemical Industry     

Study of the stability of dried tomato halves during shelf‐life to minimise oxidative damage

Optimal operating conditions for storage of dried tomato halves were investigated to obtain decreased oxidative damage, evaluated in terms of colour variation, combined with microbial stability of the product, ie inhibition of growth of eumycetes. Experiments were planned using a saturated factorial design. Variables studied were the moisture content of dried tomato halves in the range 10–60%, temperature in the range 5–30 °C and storage time in the range 1–38 days. Eighteen storage experiments were carried out in the dark under vacuum at the storage conditions indicated by the experimental design. At the end of each experiment, surface colour was measured by a tristimulus colorimeter, and growth of eumycetes was evidenced by olfactory and visual perception, followed by qualitative microbial analysis. Eumycetes were present in all stored products, except that at 10% moisture, and, generally speaking, storage conditions did not allow micro‐organisms to grow. From isoresponse curves the optimal region for storage to minimise oxidative damage was extrapolated, which was represented by residual moisture values between 20 and 40% and ≤18 °C storage temperature, with a minimum point of colour variation at approximately 30% moisture content and 10 °C. © 2000 Society of Chemical Industry