Alkali-modified soy proteins: Effect of salts and disulfide bond cleavage on adhesion and viscosity

Soy protein isolates were treated with NaCl, Na₂SO₄, or Na₂SO₃ (disulfide bond-cleaving agent) at a pH of 10.0 and 50°C, and the effects of these salts on viscosity, adhesive strength on woods, and water resistance of the treated isolates were investigated. Viscosity and adhesive strength decreased with increasing concentrations of these salts. At a concentration of 0.1 M, these three salts reduced the viscosity of soy proteins with no significant adverse effects on adhesive strength and water resistance. Addition of 0.1 M NaCl, Na₂SO₄, or Na₂SO₃ reduced adhesive strength insignificantly from 1230 N to 1120, 1060, or 1013 N, respectively. The viscosity of protein isolate modified at pH 10.0 and 50°C in the absence of salts was >30,000 cP. Treatment with NaCl or Na₂SO₄ resulted in viscosity reductions to 6000 or 1050 cP, respectively. The Na₂SO₃ treatment yielded an isolate with the lowest viscosity of 110 cP and which retained adhesive and water-resistive properties. The water resistance of modified soy proteins with and without 0.1 M Na₂SO₃ treatment was not significantly different with 3.3 and 6.6% cumulative delaminations occurring after four water soaking cycles. Treatment with 0.1 M Na₂SO₃ resulted in an isolate with a 28% decrease in disulfide linkages.     

Effect of three drying methods on the drying characteristics and quality of okra

The objective of this study was to compare the drying characteristics and quality of dried okra obtained by vacuum freeze drying (VFD), microwave vacuum drying (MVD), and pulse-spouted microwave vacuum drying (PSMVD). The quality parameters include color (L*, a*, and b*), texture (hardness and fracturability), shrinkage ratio (SR), nutrient retention (chlorophyll, flavonoids, and vitamin C), and sensory score was investigated. Vacuum freeze drying maximally preserved the original properties of samples. And the samples dried by PSMVD showed higher quality and more uniformity compared to MVD. Considering of all aspects comprehensively, such as cost-effectiveness, practicability, and scale-up, PSMVD was a promising technique which would match results obtained by vacuum freeze drying.     

Effects of maturation and storage on solubility,emulsion stability and gelation properties of isolated soy proteins

Solubility, emulsion stability and gelation of isolated soy proteins and their 7S and 11S fractions from three stages of seed maturity were studied. The pH-solubility profile was similar irrespective of maturation and six-month storage. The 11S protein was more soluble in the acidic pH range than the 7S protein. Oil-in-water emulsion stability of isolated soy protein from mature soybeans was higher than that from the immature ones. This is due to the fact that there was more 7S fraction in the mature soybeans, and 7S protein was found to form a more stable emulsion than that formed from 11S protein. The result suggests that isolated soy protein from mature soybeans would serve as a better emulsifying agent. Heat-induced soy protein gels became weaker as the soybeans became more mature. This can be attributed to the higher content in the immature soybeans of 11S fraction which gives a stronger gel than 7S fraction in the protein from immature soybeans.     

Comparative study on the flavonoids extraction rate and antioxidant activity of onions treated by three different drying methods

Onions, rich in flavonoids, with antioxidant, antibacterial, and other biological activities, are often used as extraction of raw materials to obtain health products with high flavonoids content. However, the amount of raw material consumption is large due to low yield of extracts from fresh onions. As a result, dried onions often are used as extraction materials. The effects of air drying (AD), freeze-drying (FD), and microwave freeze-drying (MFD) on the flavonoids extraction yield of onions were investigated. The most effective and economical method was hot AD. On the other hand, the flavonoids extraction rate of onions dried by MFD was the fastest. FD could also obtain high extraction rate, but it cost the highest energy consumption. In order to obtain relatively rapid, economic, and effective extraction of onion flavonoids, onions can be dried by MFD or AD method.     

Modification of soy proteins and their adhesive properties on woods

Adhesive properties of trypsin-modified soy proteins (TMSP) on woods were investigated. A simple method developed in our laboratory, consisting of measuring the force required to shear the bond between glued wood pieces in the Instron universal testing machine, was used to examine adhesive strength of modified soy proteins on wood. Adhesive strength of TMSP was measured for cold-pressed (ambient temperature for 2 h) and hot-pressed (60, 80, 100, and 120°C for times varying from 0.5 to 2.5 h) woods. Of the woods examined, soft maple gave the highest strength [743 Newtons (N) at a protein glue concentration of 2 mg/cm²]. For soft maple and cold-pressing, TMSP at 2 mg/cm² gave twice the adhesive strength of unmodified protein controls, 743 vs. 340 N. Also, the adhesive strength of TMSP increased from 284 to 743 N as glue concentration was increased from 1 to 2 mg/cm². However, hot-pressing of wood pieces beyond 1 h at 120°C and 30% relative humidity resulted in decreased adhesive strengths of TMSP compared to controls. Further, adhesive strengths of hot-pressed glued wood samples decreased when the relative humidity at which they were kept for curing increased from 30 to 60%. This negative effect of increased humidity on adhesive strengths of glued wood pieces was not observed with cold-pressed TMSP.     

Effect of infrared pretreatment on low-humidity air drying of apple slices

The dried apple is used in the preparation of weaning foods and bakery products. The current drying processes, especially hot air (HA) drying, still face the problem of longer processing time and product quality degradation. The low-humidity air (LHA) drying can be an option to retain product quality in heat-sensitive food such as apple. The present work focuses on the effect of pretreatment of apple slices with potassium metabisulfite and infrared (IR) waves on drying characteristics when subjected to LHA drying and comparing the product quality with conventional hot air and freeze drying (FD). Pretreatment with IR waves reduced the drying time by nearly 23 and 17% in LHA and HA drying, respectively. The results indicated that IR-treated and LHA-dried slices retained nearly 82–90 and 72–74% of ascorbic acid and total phenolic content, respectively and was comparable to FD slices. The drying time for LHA was nearly 37% lesser than that for HA drying. LHA-dried apple slices had better color and rehydration ratio compared to FD- and HA-dried slices.     

Thermal denaturation of soy proteins as related to their dye-binding characteristics and functionality

The binding of Cresol Red and of Acid Orange 10 (in the absence and presence of urea) to unheated and progressively heated, defatted soy meal was compared with their NSI values, urease activities,in vitro digestibilities, unreactive lysine contents, and foaming and emulsifying capacities. These results suggested that increased amounts of Cresol Red and of Acid Orange 10 (in the presence of urea) bound to the heated samples were due to the progressive exposure of hydrophobic residues caused thermal denaturation. High statistical correlations were obtained between dye-binding, the duration of heating, and functional properties. Our results indicate that dye-binding has potential for predicting certain functional properties as well as for monitoring thermal denaturation of soy proteins.     

Impacts of desugarization and drying methods on physicochemical and functional properties of duck albumen powder

Desugarization of duck albumen using glucose oxidase/catalase was optimized before drying. Optimum condition for desugarization using response surface methodology was as follows: glucose oxidase 31.24 units and catalase 781 units/mL albumen and incubation time of 6.55?h at 30?°C. Foaming capacity (FC) and foam stability (FS) were enhanced, while the solubility decreased after desugarization. This coincided with the increase in surface hydrophobicity (p?<?0.05). Higher trypsin inhibitory activity was found in freeze-dried albumen powder than spray-dried counterpart. Trypsin inhibitory activity was continuously decreased as the inlet temperature for spray-drying increased (p?<?0.05). Desugarization could increase FC and FS, but slightly decreased solubility of powders. No marked differences in protein patterns were observed in all the powders, regardless of desugarization and drying methods. L* of albumen powder decreased but ΔE, a*-, b*-values and browning index increased as spray-drying temperatures increased (p?<?0.05). Therefore, prior desugarization could lower browning and increased foaming property of duck albumen, particularly when spray-dried with inlet temperature of 160?°C.     

The drying strategy of atmospheric freeze drying apple cubes based on glass transition

Freeze drying (FD) yields the best quality of dried apple cubes but at the cost of long drying time and also the overall cost. To achieve economical freeze drying along with a high quality product an atmospheric freeze drying (AFD) technique was developed to dry apple cubes. The effect of different air temperature loading scheme on product quality and drying process was studied during AFD. According to the glass transition temperature of apple, a step-up temperature loading strategy for AFD process was developed to reduce the drying time by almost half and provided a similar good product quality.     

A nonconventional method for drying of Pseudomonas aeruginosa and its comparison with conventional methods

In this study, preparation of dried cultures of Pseudomonas aeruginosa using nonconventional drying method, namely, low-temperature low-humidity (LTLH) drying was investigated. The effect of carrier materials (whey protein, corn starch, and trehalose) was examined one at a time and also in combinations (to explore the synergistic effect). The results were compared with those obtained using spray drying and freeze drying in terms of cell survival and dry cell powder yield. The powder samples were analyzed also for morphology, flowability, particle size, and moisture content. In LTLH drying, good cell survival was observed along with high powder yield when compared with that in spray drying. Corn starch showed the highest cell survival (91%) and powder yield (94%, w/w) among the carrier materials employed besides resulting in good cell survival (65%) even after a storage period of 6 months.     

固态食品常压吸附流化冷冻干燥的研究

至今为止,冷冻干燥技术得到应用的只有真空冷冻干燥一种,本文提出了常压吸附剂流化冷冻干燥,并具体阐述了数学模型和实验装置。通过与真空冷冻干燥进行比较,认为常压吸附流化冷冻干燥值得进一步深入研究,具有发展和应用前景。     

Emulsifying properties and surface behavior of native and denatured whey soy proteins in comparison with other proteins. Creaming stability of oil-in-water emulsions

In this work a comparative study of emulsifying and surface behaviors of native whey soy proteins (NWSP) and denatured whey soy proteins (DWSP) with those of native soy isolates, denatured soy isolates (DSI), and sodium caseinate was done. These samples showed different molecular mass distributions in gel filtration profiles. Dissociation and soluble high-M.W. species in DWSP and DSI were observed. Lower interfacial and surface pressure values were obtained with native samples. Thermal treatment and salt addition enhanced tensioactivity in all fractions. Backscattering measurements of all oil-in-water emulsions, which exhibited a trimodal size distribution of droplets, showed the existence of a negative correlation with the median diameter of droplets. Greater droplet sizes were observed with NaCl addition. The NWSP emulsion had the lowest stability against creaming. Denaturation of this sample increased stability and favored air incorporation in emulsions. Destabilization depends not only on median droplet size but also on floc formation and structure. NaCl addition negatively affected the creaming stability only in emulsions formulated with soy isolates. The use of denaturation to enhance the surface and emulsifying properties of whey soy proteins would allow their use in food emulsions.     

Effect of different drying methods on morphological,thermal, and biofunctional properties of lulo (Solanum quitoense Lam.) fruit powders

Four different powders of dried lulo (Solanum quitoense Lam.) were obtained by hot air drying (HD), ultrasound-assisted hot air-drying (HDUS), freeze-drying (FD), and spray-drying (SD). The morphological (SEM) and thermal (TGA–DSC) characterization were made, and some biofunctional properties such as dietary fiber (DF) content and antioxidant capacity (ABTS and DPPH assays) were evaluated. The homogeneous morphology of SD particles was evident from SEM analysis, in contrast to the irregular morphology of the other dried powders. All of the dried lulo powders were thermally stable until 220°C. Although, the initial composition of the mixtures (fruit pulp/maltodextrin DE-20, 2:1, w/w) was the same, some differences on DF content and antioxidant activity were found, indicating that the drying method influenced significantly the chemical composition of powdered products. A higher insoluble dietary fiber (IDF) percentage was found in FD sample; in contrast, a higher in vitro antioxidant capacity values against ABTS and DPPH free radicals were found for HD and SD powders.     

Effect of value-enhanced texturized soy protein on the sensory and cooking properties of beef patties

Texturized soy protein (TSP) originating from varieties of value-enhanced soybeans and commodity soybeans, which were processed by extrusion-expelling, were incorporated into ground-beef patties. The soybean varieties included high-cysteine, low-linolenic, lipoxygenase-null, high-sucrose, low-saturated-fat, and high-oleic. The lower the bulk density was, the better the water-holding capacity of TSP. Neither property was affected by the protein dispersibility index or residual oil of the low-fat soy flours from which the TSP was prepared. All extruded-expelled processed flours from value-enhanced soybeans made acceptable TSP. The high-sucrose soybeans produced TSP with higher expansion and improved water-holding capacity. There were no differences in cooking properties or proximate compositions of patties for all treatments. Inside and outside colors were darker for the TSP-extended patties than for the all-beef control, and there was little difference among soybean varieties. The patties containing TSP had significantly more soy flavor and were harder than the all-beef control patties. Some TSP treatments produced more tender and less cohesive cooked patties than did the all-beef control.     

瓶装物料的冻干规律研究

以脱脂牛奶为物料,进行了瓶装物料的冷冻干燥试验,探索了加热温度,辐射温度与冻干室压强对冻干过程的影响规律,分析了所得冻干曲线的特征,并对冻干机理和物料温度的监测井行阐述,得到在加热温度与辐射温度相同时恒温恒压操作的最佳参数,并提出了一些强经冻干过程的措施。本研究对实验冻干生产有一定的指导作用,也为瓶装物料的二维理论模型研究提供了基础。     

纳米粉体干燥方法的研究进展

由于纳米粒子的表面效应，用湿法制备出的纳米粉体的前驱——胶体的干燥已不能采用传统的干燥方法。根据胶体干燥的理论，阐述了纳米粉体干燥过程的团聚机理，并综述了纳米粉体在超临界干燥、共沸蒸馏、真空冷冻干燥、微波干燥等干燥领域的研究进展。     

干燥技术的进展和应用

文章侧重与化学工业关系较密切的方面，以各种干燥机的开发、改进和应用为主要线索，简要评述干燥技术２０多年来的进展与应用、技术发展趋势和存在的问题、以及我国的基本情况。     

Physical and mechanical properties of soy protein-based plastic foams

Flexible plastic foams using soy protein isolate (SPI), soy protein concentrate (SPC), and defatted soy flour (DFS) were produced by interacting proteins with glycerol-propylene oxide polyether triol (polyol), surfactant, triethanolamine (crosslinking agents), tertiary amine (catalyst), and water (blowing agent). The density, compressive stress, resilience, and dimensional stability of foams with SPI, SPC, and DFS increased as the initial concentration of soy protein increased. The foam density increased with increasing weight percentage of SPI, SPC, and DFS. The resilience values of SPI containing foam increased with the increasing addition of SPI up to a maximum 30% SPI addition. An increase in SPI up to 20% caused an increase in the compressive stress (225 kPa) in comparison to control polyurethane foam (187 kPa). The control foam and foam containing 20% DFS had a similar load-deformation relationship. The foam containing 20% SPI and SPC also exhibited a similar shape, but with a higher compressive stress. The compressive stress of all foams was steeply increased after 55% strain, since the foams completely collapsed upon compression.     

Limited hydrolysis of soy proteins with endo- and exoproteases

Changes in the native state and functional properties of soy protein achieved by limited proteolysis of soy flour were investigated. Different enzyme-to-substrate ratios (E/S) were used to obtain low (3–5%) and medium (5–10%) degrees of hydrolysis (DH). Six protease preparations (three with predominately exopeptidase activities and three with predominately endopeptidase activities) were evaluated, and their effects on solubility, emulsification capacity, SDS-PAGE profiles, and denaturation enthalpies were characterized. Endoproteases (Multifect^® Neutral, Protex^? 6L, and Multifect^® P-3000) and exoproteases (Fungal Protease Concentrate, Experimental Fungal Protease #1, and Experimental Fungal Protease #2) yielded similar increases in soy protein solubility. The modifications to the soy peptide profile were similar for the three exoprotease mixtures at a 1% E/S ratio, whereas the extent of hydrolysis with Protex^? 6L was more pronounced than with the two other endoproteases (Multifect^® Neutral and Multifect^® P-3000). The emulsification capacity of protease-modified soy flour declined regardless of DH and enzyme type (exo- or endoprotease). After hydrolysis to >4% DH, denaturation enthalpies of glycinin and β-conglycinin decreased significantly, whereas hydrolysis to lower DH did not affect these values.     

Optimization of microwave freeze drying strategy of mushrooms (Agaricus bisporus) based on porosity change behavior

ABSTRACT

For dehydrated foods, porosity is a crucial parameter which affects mass and heat transfers, and is related to the product quality. It is important to monitor porosity change behavior to optimize the drying process. To achieve faster drying along with high product quality, microwave freeze drying (MFD) was applied to mushrooms dehydration processing. The relationship between porosity (include total, open-, and closed-pore porosity) and dried mushroom qualities was studied, and a suitable microwave loading strategy was obtained. It was found that lots of open pores could transform to closed pores while the moisture content (MC) was below 0.25?±?0.05?g/g (db), and the closed-pore porosity was arrived at a relatively stable level at moisture content below 0.17?±?0.03?g/g (db). Both total porosity and closed-pore porosity had a significant influence (P?<?0.01) on texture of MFD mushroom, and open-pore porosity had a significant effect (P?<?0.01) on rehydration ratio of MFD mushroom. According to the porosity change behavior of mushrooms, a dynamic microwave loading strategy can be used to reduce drying time and keep product quality during MFD process.