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.     

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。     

EFFECTS OF SOY PROTEIN AND FREEZING TREATMENTS ON COOKING LOSS AND COMPOSITION OF BEEF PATTIES

All-beef and soy-extended patties were frozen to −18°C in either 24, 48, 72 or 96h and stored at −23, −18 or −7°C for 6, 9, 12, 18 or 24 months. The addition of soy resulted in a substantial reduction in cooking loss for patties cooked from the frozen state with a greater retention of moisture in cooked patties. Freezing reduced cooking loss for soy-extended patties, but increased cooking loss for all-beef patties. Faster freezing (-18°C in 24 h vs. −18°C in 96 h) reduced cooking loss and produced higher moisture values in all-beef patties. Patties stored at –7°C lost more moisture during cooking. Increased frozen storage time had a minimal effect on cooking losses, moisture and fat levels. Where it is essential for frozen patties to sustain minimal cooking losses with maximal moisture in cooked patties, the inclusion of soy protein concentrate, faster freezing, and storage at –18°C or colder are suggested.     

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.     

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.     

混合条件对大豆蛋白塑料特性的影响

研究了高速混合机混合，捏合，研磨和粉碎机混合4种不同混合方式，及不同混合时间对大豆蛋白生物降解塑料机械特性和吸水率的影响。结果表明采用研磨混合方式大豆蛋白塑料具有最大拉伸强度、伸长率及最小吸水率，其值分别为4．50MPa、309％、145％和170％；研磨时间为25min时，大豆蛋白塑料拉伸强度最大，伸长率及吸水率最小，分别为5．30MPa、220％、143％和206％。     

HEAT INDUCED GELS FROM PARTIALLY HYDROLYZED SOY PROTEIN ISOLATE1

Heat induced gels can be obtained from partially hydrolyzed soy protein isolate (HSPI). The gel forming ability of each of the HSPI fractions (peptides of varying molecular weight and solubility) were studied, after being separated by preparative Sephadex gel filtration chromatography. The insoluble peptide fraction had no gel forming ability. Peptides larger than 5,000 Daltons, those lower than 5,000 Daltons and a fraction of the very hydrophobic peptides formed weak gels when heated alone. Interactions between several peptide fractions were necessary in order to yield a gel with the strength of the one formed by whole HSPI. A mechanism explaining (1) the action of the proteolytic enzyme in breaking down the protein and (2) the peptide interaction needed for the gel formation, is proposed.     

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。     

ELECTROSTATIC EFFECTS ON PHYSICAL PROPERTIES OF PARTICULATE WHEY PROTEIN ISOLATE GELS

Physical properties of particulate whey protein isolate gels formed under varying electrostatic conditions were investigated using large strain rheological and microstructural techniques. The two treatment ranges evaluated were adjusting pH (5.2‐5.8) with no added NaCl and adjusting the NaCl (0.2‐0.6 M) at pH 7. Gels (10% protein w/v) were formed by heating at 80C for 30 min. The large strain properties of fracture strain (γ_f), fracture stress (σ_f), and a measure of strain hardening (R_0.3) were determined using a torsion method. Gel microstructure was evaluated using scanning electron microscopy (SEM) and gel permeability (B_gel). Overlaying σ_f and γ_f curves for pH and NaCl treatments demonstrated an overlap where gels of equal σ_f and γ_f could be formed by adjusting pH or NaCl concentration. The high fracture stress (σ_f～ 23 kPa and γ_f～ 1.86) pair conditions were pH 5.47 and 0.25 M NaCl, pH 7.0. The low fracture stress (σ_f～ 13 kPa and γ_f～ 1.90) pair conditions were pH 5.68 and 0.6 M NaCl, pH 7.0. The 0.25 M NaCl, pH 7 treatment demonstrated higher R_0.3 values than the pH 5.47 treatment. When the sulfhydryl blocker n‐ethylmaleimide was added at 2 mM to the 0.25 M NaCl, pH 7 gel treatment, its rheological behavior was NSD (p>0.05) to the pH 5.47 gel treatment, indicating disulfide bond formation regulated strain hardening. Altering surface charge or counterions, and disulfide bonding, was required to produce gels with similar large strain rheological properties. An increase in gel permeability coincided with an increase in pore size as observed by SEM, independent of rheological properties. This demonstrated that at the length scales investigated, microstructure was not linked to changes in large strain rheological properties.     

EFFECTS OF SOY PROTEIN ISOLATES ON QUALITY OF CHOCOLATES DURING STORAGE

The effect of soy protein isolate (SPI) on oxidation rate, changes in color and hardness, and microbiological aspect of chocolates during storage were studied. The Peroxide Value (PV) of the control and 5% showed SPI were highest in week 3 and decreased at the following week, while 10% SPI showed the lowest PV in week 10 as compared to the others. The Anisidine Value (AV) of all chocolates showed an increasing pattern during 10 weeks of storage. The Total Oxidation Value (TV) of all chocolates was found to be highest at week 3 and lowest at week 10 when 10% SPI was used. During storage, all chocolates slightly increased in hardness and turned darker in color. The Total Plate Count (TPC) of the control and SPI chocolates was less than 1,000 colonies/g.     

EFFECTS OF PROCESSING ON ADSORPTION OF OFF-FLAVORS ONTO SOY PROTEIN1

Heats of adsorption and adsorption coefficients for the reversible adsorption of several aliphatic alcohols, aldehydes, and ketones on soy protein were measured using gas chromatography. The physical state of protein samples was changed by heating at 100°C and 121°C at moisture contents of 29%and 40%. A comparison was made with values for untreated soy isolate and sheared soy isolate, and the effects of moisture, temperature, and their interaction were examined by analysis of variance. Heats of adsorption were unchanged, but changes in adsorption coefficients of the treated samples demonstrated a significant decrease in binding that can be attributed to protein denaturation. The response depended on the interaction of moisture and temperature effects.     

大豆不同脱腥方法对豆乳中蛋白质含量及脱腥效果影响的研究

大豆在加工过程中所产生的豆腥味是研究开发新的蛋白食品的主要障碍。在众多的脱腥专利技术中,结合热处理钝化大豆中的脂肪氧化酶是广为采用而较为有效的方法。由于热处理虽则使豆乳风味及口感有明显改善,但也程度不同地降低了大豆蛋白的可溶性,影响了大豆蛋白的得率。本文就几种行之有效的脱腥方法进行了比较,并对豆乳中蛋白质的影响规律作了某些探讨。     

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.