EFFECT OF SOY PROTEIN ISOLATE AND SOY FIBER ON COLOR, PHYSICAL AND SENSORY CHARACTERISTICS OF BAKED PRODUCTS

Quick breads were formulated to contain 0%, 40%, 50% or 60% Soy Protein Isolate and Fiber (SPI/Fiber), and yeast breads were formulated to contain 0%, 14%, 21% or 28% SPI/Fiber replacement for wheat flour. Physical and sensory data were collected. As SPI/fiber level increased, muffin batter specific gravity, baked product air cell number, Instron peak force to compress by 75%, a value, beany flavor, grain-like flavor, aftertaste, moistness and denseness increased while muffin peak height at the crown, baked volume, L and b values, hue angle, sweetness and crumbliness decreased. There were significant negative correlations between increased level of SPI/fiber in muffins and acceptability of flavor and texture, as well as willingness to purchase or purchase the product at a higher price. As SPI/fiber level increased, bread dough pH after fermentation, air cell number, Instron peak force to compress by 75%, a and b values, beany flavor, grain-like flavor, and aftertaste increased while loaf volume, peak height at the crown, L value, hue angle, cohesiveness and crumbliness decreased. There were significant negative correlation coefficients between level of SPI/fiber and acceptability of flavor and texture, as well as willingness to purchase the product or to purchase it at a higher price.     

磷酸化大豆分离蛋白质功能特性的研究

本文采用三氯氧磷（POCl3）对大豆分离蛋白（SPI）进行磷酸化改性，并研究了磷酸化前后SPI功能特性的变化。结果表明：磷酸化SPI的溶解性、乳化性以及粘度等功能特性都有不同程度的改变。     

DYNAMIC VISCOELASTIC PROPERTIES OF SOY ISOLATE DOUGHS

The linear viscoelastic properties of soy isolate doughs have been determined as a function of flour concentration and temperature using a Rheometrics Mechanical Spectrometer. The material of lowest concentration (15%) which is classified as a dispersion rather than a dough exhibited values of storage (G') and loss moduli (G") which increased with increasing temperature above 50°C. On the other hand, values of G' and G" for 20% and 25% doughs showed only a slight increase with increasing temperature. The shape of the G' and G" versus frequency (ω) curves is suggestive of solid-like behavior for the doughs. The shape of these curves does not change with temperature which indicates there is very little change in the ability of the protein molecules to undergo configurational rearrangements as the result of heating. The phenomenon of gelation does not arise in the doughs but only in the dispersion of lower concentration. The data indicate that the bonds between protein molecules are noncovalent in nature and that the process of cooking soy dough does not involve the formation of crosslinks.     

PHYSICAL AND RHEOLOGICAL CHARACTERISATION OF A CONFECTIONERY PRODUCT

The mechanical and rheological properties of caramel have been measured in the context of a continuous extrusion forming operation, including a repetition of the processing route. The sensitivity of mechanical testing of samples to processing is borne out by the changes in microstructure, as observed using the scanning electron microscope, which also affect the velocity of transmitted ultrasound. The effect of repeated processing is also greater at a lower processing temperature.     

TEXTURAL AND MICROSTRUCTURAL PROPERTIES OF RENNET-INDUCED MILK COAGULUM AS AFFECTED BY THE ADDITION OF SOY PROTEIN ISOLATE

The effect of the addition of soy protein on the textural properties and microstructure of reconstituted nonfat dry milk coagulum with time after rennet addition was studied using an Instron Universal testing machine with a newly developed test cell, and by scanning electron microscopy. Soy protein added to reconstituted nonfat dry milk at 5% of the total solids resulted in a reduction in firmness, a decrease in syneresis and a looser microstructure of the coagulum at any given time up to two hours after rennet addition as compared to the control without added soy protein. An increase in the level of soy protein to 10 and 20% of the total solids resulted in a further reduction in coagulum firmness and in syneresis. Syneresis was also followed during changes in coagulum firmness. Analysis of the textural as well as microstructural data suggests that changes in coagulum firmness and syneresis of rennet-induced milk coagulums (with or without added soy protein) with time after rennet addition were associated with the extent to which casein micelles coalesced during coagulum formation. The Instron test and the syneresis test developed in this study were simple and practical.     

不同脂类及添加量对大豆蛋白基可食性膜性能的影响

研究了在大豆分离蛋白（SPI）膜中添加不同脂类物质及含量对膜水蒸气透过系数（WVP）、机械性能、水溶性（WS）的影响。通过添加蜂蜡与月桂酸前后膜性能的比较，发现膜的阻水性、机械性能在添加量为0．02，0．1g／gSPI时达到最佳。将蜂蜡与月桂酸对膜性能影响的比较表明，蜂蜡加入后膜的阻水性、机械性均优于月桂酸。本文用扫描电子显微镜观测膜的微观结构，探讨了脂类在大豆分离蛋白膜中的分布及其对膜性能的影响。     

凝胶多糖与大豆分离蛋白可食性复合膜的制备

以凝胶多糖和大豆分离蛋白作为成膜基材，添加甘油作为增塑剂，研制了一种可食性复合膜，并通过红外光谱谱图初步探讨了复合膜的成膜机理。正交优化实验结果表明：在干燥温度50℃、大豆分离蛋白浓度2％、凝胶多糖浓度1.2％、甘油浓度1％条件下，所得膜具有较好的抗拉强度和阻湿性能。     

INFLUENCE OF TRANSGLUTAMINASE-INDUCED CROSS-LINKING ON IN VITRO DIGESTIBILITY OF SOY PROTEIN ISOLATE

The influence of covalent cross‐linking by microbial transglutaminase (MTGase) on the sequential in vitro pepsin and trypsin digestion process and the digestibility of soy protein isolate (SPI), was investigated by sodium dodecylsulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and nitrogen release analyses. Various subunits of β‐conglycinin and acidic subunits of glycinin were cross‐linked by MTGase to form high molecular weight (MW) biopolymers, while basic subunits of glycinin were unaffected. SDS‐PAGE analysis indicated that the cross‐linking mainly affected in vitro pepsin digestion pattern of various subunits of β‐conglycinin, while the trypsin digestion pattern of native SPI was nearly unaffected. Nitrogen release analysis showed that the in vitro pepsin or/and trypsin digestibility of native SPI (at the end of pepsin or trypsin ingestion) was significantly decreased (P ≤ 0.01) by the MTGase treatment (for more than 2 h). The cross‐linking by MTGase also significantly decreased the in vitro digestibility of preheated SPI. These results suggest that the cross‐linking by means of transglutaminase may negatively affect the nutritional properties of food proteins.     

FUNCTIONAL PROPERTIES AND NUTRITIONAL QUALITY OF ALKALI- AND HEAT-TREATED SOY PROTEIN ISOLATE

Alkali and heat are increasingly utilized in food processing. This study was conducted to evaluate specific functional and nutritional properties of alkali- and heat-treated soy protein isolate (AHSPI) and the relationship between these properties. High pH (12.0) and temperature (100C) increased protein solubility of the isolate from 47 to 99.5% and emulsifying activity index from 74 to 184 m²/g. The values for in vitro protein digestibility (IVPD), computed-protein efficiency ratio, and IVPD-corrected amino acid score of AHSPI were not significantly (P>0.05) affected at pH 8.0 or 10.0, but were reduced At pH 12.0. At pH 12.0, lysinoalanine content significantly (p<0.05) increased from 0.39 to 1.22 g/100g protein as temperature was increased from 40 to 100C. Improvements in functional properties of soy proteins can be obtained through combined alkali and heat treatments. However, very high pH and temperature should be avoided to maintain nutritional quality of the proteins.     

PARTICLE SIZE EFFECT ON SOY PROTEIN ISOLATE EXTRACTION

This study was undertaken to determine if the yield and purity of soy protein isolates could be improved by changing the particle size of the starting raw material. Soy protein isolates were extracted from hexane defatted soy flour ground to three different average particle sizes (89.5 ± 1.1, 184.2 ± 1.6 and 223.4 ± 6.4 µm). By decreasing the average particle diameter of the starting raw material (soy flour) from 223.4 to 89.5 µm the total solids recovery increased from 23 to 32% (P = 0.00008), while the protein recovery increased from 40 to 52% (P = 0.00004). Final protein content (i.e., purity) of the soy protein isolates was not significantly impacted by average particle size. The results clearly demonstrated that protein recovery can be increased by >30% by decreasing the average particle size of the starting raw material (i.e., defatted soy flour), without having any detrimental impact on the purity of the final soy protein isolate.     

PHYSICAL PROPERTIES OF COMMERCIAL BREWING YEAST SUSPENSIONS

The cell surface charge and microstructure of four commercial strains of brewing yeast were examined using electrokinetic and scanning electron microscopic (SEM) techniques. Flocculent and non-flocculent ale and larger strains were observed to possess non-normally distributed surface charges while suspended in buffers of various pH values with and without 1.0 mM calcium, 5% ethanol and 0.5 M KCl. Non-normal charge distributions were also observed when the strains were suspended in commercial ale and lager beers. During SEM examination, a number of distinct structures appeared to be involved in cell-to-cell interactions. Observed differences in cell wall microstructure and the finding of non-normally distributed surface charges indicate that these pure brewing strains possessed substantial phenotypical variation.