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.     

鱼种和亲水胶体对鱼糜制品凝胶性质的影响

考察了添加复合亲水胶体对鲢鱼、带鱼、金线鱼等鱼糜制品凝胶特性的影响。结果发现,添加亲水胶体后,带鱼鱼糜制品凝胶强度从58.38 g·cm提高至107.27 g·cm,金线鱼鱼糜制品从328.68 g·cm下降至137.55 g·cm,但鲢鱼鱼糜制品没有明显变化。另一方面,添加亲水胶体后鱼糜制品的硬度、粘结性、咀嚼性等发生下降,但水分含量、持水性、蒸煮吸水率均有显著提高。而且,添加亲水胶体后带鱼鱼糜制品中肌球蛋白重链的降解受到一定的抑制。SEM结果发现亲水胶体可以填充到带鱼和鲢鱼鱼糜制品中,但在金线鱼鱼糜凝胶结构中容易形成胶体块状,导致凝胶强度下降。      

Changes of microwave structure/dielectric properties during microwave freeze‐drying process banana chips

This experimental study investigated the trend of structure and dielectric properties during microwave freeze‐drying process banana chips. The mass of banana samples was 160 g, the microwave power set as 2 W g^?1 and the highest drying temperature set as 55 °C. The whole drying process can be finished within 6 h. A network analyser and light microscope were used to determine the dielectric properties and structure. The dielectric properties, ε′ (from 20.80 to 1.20) and ε′′ (from 7.74 to 0.15), and the size of cell get smaller as the drying process continues, especially during the 3–4 h drying, which is the end of primary drying stage and the beginning of secondary drying stage. The trend of dielectric properties and microstructure of samples during drying can be an exact indication of drying stage of MFD.     

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.     

Development of a freeze‐dried mixture of Nile tilapia (Oreochromis niloticus) croquette using a GA‐based multiobjective optimisation

BACKGROUND: The mechanically separated meat (MSM) of Nile tilapia is an example of a by‐product that can be used in the development of new foods. The aim of this study was to optimise the mixture of different flours in the development of a freeze‐dried mixture of fish croquette using Nile tilapia MSM. Flavour, texture and overall acceptance of seven formulations were evaluated by an acceptance test. A genetic algorithm (GA) with desirability functions was combined with a multiobjective optimisation of the response surface models. RESULTS: The combination of flours was chosen to minimise cost and maximise overall acceptance and fibre content. Overall acceptance showed a statistically significant correlation (P?0.05) with flavour (r = 0.67) and texture (r = 0.61). The GA‐based approach indicated that the highest overall acceptance was obtained when using wheat and rye flours in equal parts. This formulation had an overall acceptance of 7.52, a fibre content of 11.50 g kg^?1 and a cost of US$ 2.21/kg. After 24 h of freeze‐drying, the water activity of the mixture was 0.11. CONCLUSION: The GA‐based approach was able to optimise the croquette formulation. The freeze‐drying process contributed to the development of a value‐added product with high quality and long shelf‐life. © 2012 Society of Chemical Industry     

Radical scavenging and anti‐proliferative capacity of three freeze‐dried tropical fruits

Tropical fruits are rich in antioxidant and anticancer phytochemicals, but their nutraceutical potential could be enhanced by drying technologies. Mango cv. Ataulfo, papaya cv. Maradol and pineapple cv. Esmeralda ripe pulps were freeze‐dried (?42 °C, 0.12 torr, 48 h) and their physicochemical and phytochemical profile, radical scavenging and antiproliferative capacity evaluated. The content of soluble solids, phenolic compounds and ascorbic acid was higher in mango (16.1^oBrix, 9.9 mg GAE per g and 9.6 mg g^?1) than in papaya/pineapple, but the later had more flavonoids (0.45 ± 0.05 mg QE per g). A fruit‐specific phenolic profile was detected by HPLC‐ESI‐QTOF‐MS, being shikimic (mango), chlorogenic (papaya), and protocatechuic (pineapple) acids the most abundant. Mango was the strongest radical scavenger and showed antiproliferative capacity (IC₅₀, μg mL^?1) in RAW 264.7 (100.7), HeLa (193.1) and L929 (138.5) cell lines. Papaya and pineapple extracts showed no antiproliferative activity. Freeze‐dried mango is a ready‐to‐eat functional food with better cancer preventing properties than papaya or pineapple.     

Rehydration characteristics of freeze‐dried strawberry pieces as affected by whey protein edible coatings

This paper is about the use of whey protein isolate (WPI) edible coatings to improve the rehydration behaviour of freeze‐dried (FD) strawberry pieces. First, the optimal ratio sample mass/volume of coating solution was optimised by determining the rehydration ratio, bulk density and nutritional quality of the samples. Coating time is also determined in coated samples by light microscopy. Second, the effect of changing the pH and the variation in temperature–time to denaturate WPI on rehydration characteristics was also evaluated. The rehydration ratio of strawberry pieces decreased with increasing the denaturation temperature and denaturation time, while it increased with increasing pH of the coating solution. Third, according to the rehydration curves, coating was not a single layer but small pieces attached to strawberry pieces. The soluble protein contents in water after rehydration confirm this conclusion.     

Viscosity and starch particle size effects on rehydration of freeze‐dried carrots

A Correction has been published for this article in Journal of the Science of Food and Agriculture 85(4): 707 (2005). Rehydration is a critical step in the utilization of dry food particulates. The effects of viscosity and average particle size of four starches, namely corn, rice, potato and pre‐gelatinized Ultra Sperse 2000 were assessed and compared with water as the control. Average starch particle size diameters determined with image analysis showed that only the native starches swelled after 5 min treatment in 85 °C water. Rehydration curves were modelled utilizing a normalized Weibull distribution. The derived Weibull β‐shape parameter indicated that water uptake followed both imbibition and Fickian diffusion. Both viscosity and starch particles size distribution influenced the rehydration kinetics and their effect could not be explained by a simple mechanism. Medium uptake during rehydration could be improved and customized by choosing the most appropriate thickening agent. Copyright © 2004 Society of Chemical Industry     

Effects of hydrocolloids on chemical properties and cooking quality of gluten‐free spaghetti

The effects of different hydrocolloids on chemical composition and cooking quality of spaghetti based on maize and oat flours were investigated. Rheological and texture properties of the gluten‐free dough were also assessed. Amount of 2% of gellan gum, carboxymethylcellulose, pectin, agar, egg protein powder, tapioca starch, guar seed flour and chitosan were separately added to the formulation. The samples enriched with hydrocolloids generally showed a different rheological behaviour compared with the control samples. As regards chemical composition, spaghetti with chitosan showed a value of insoluble dietary fibres (8.0%) higher than the control ones (3.9%). Moreover, results highlighted that most hydrocolloids improved cooking quality and texture properties of spaghetti (adhesiveness, cooking loss, hardness), thus supporting their application in gluten‐free pasta.     

The use of selected hydrocolloids to enhance cooking quality and hardness of zero‐salt noodles

The effects of table salt (TS) and hydrocolloids on water‐holding capacity, optimum cooking time, cooking qualities, pH and textural properties of noodles were investigated. TS, xanthan gum (XG), carrageenan (CRG), Arabic gum (AG) and locust bean gum (LBG) were added at 0.5%, 1.0%, 1.5% and 2.0% of flour weight. XG, CRG and LBG contributed to significantly (P < 0.05) higher water‐holding capacity of dough and firmer texture, but significantly (P < 0.05) lower cooking loss than zero‐salt noodles (ZSNs) and white‐salted noodles (WSNs). Hydrocolloids contributed in shorter optimum cooking time than ZSNs. Springiness of noodles was not significantly (P > 0.05) affected by increment of TS and hydrocolloids. TS1.5, ZSN‐XG1.5, ZSN‐XG2.0 and ZSN‐CRG1.5 had significantly (P < 0.05) higher cooking yield than ZSNs. The increment of TS and hydrocolloids had significantly (P < 0.05) increased the pH values of noodles. ZSN‐XG2.0, ZSN‐CRG1.5 and ZSN‐LBG1.5 may be useful to enhance ZSNs due to the better noodles qualities than ZSNs.     

Determination of biochemical properties of foam‐mat dried mango powder

Investigations were carried out to see the impact of drying air temperature (65, 75 and 85 °C) and milk as foaming agent in different concentration levels (0%, 10%, 15%, 20% and 25%) on the chemical properties of foam‐mat dried mango juice powder. Chemical properties such as total sugars, ascorbic acid, total carotenes, minerals, total acid, pH, total soluble solids (TSS) and microbial load (fungal and bacterial) of foam‐mat dried mango powder were determined. Data were analysed as per two‐way anova , Duncan’s multiple range test and l.s.d. of Ag Res Software statistical package. Almost all chemical properties show decreasing trend with increase in drying air temperature. Microbial load was not detected in foam‐mat dried mango powder. It was found that addition of 10% milk as foaming agent and drying at 65 °C temperature gave better results.     

Acid adaptation for improvement of viability of Saccharomyces cerevisiae during freeze‐drying

This work was aimed to investigate its adaptation to moderate acid stress and the resulting improvement in its viability during freeze‐drying. When Saccharomyces cerevisiae UP3OY5 strain was adapted to acid condition (pH 3.5), the viability of acid‐adapted cells (79.9%) was significantly higher than that of control cells (40.5%) after freeze‐drying with trehalose as a carrier. Membrane fatty acid profile of acid‐adapted cells changed significantly in comparison with that of control cells. An increase in fatty acid saturation degree that led to 1.76‐fold increase in the ratio of saturated to unsaturated fatty acids was shown. Intracellular glycogen content was found to be higher than that of control cells. On the contrary, the trehalose content of acid‐adapted cells was found to be much smaller than that of control cells. The key role of acid adaptation in acquiring cross‐protection mechanism was suggested to permit yeast to better survive to freeze‐drying.