Effect of lipoxygenase activity in defatted soybean flour on the gelling properties of soybean protein isolate

Soybean lipoxygenase was inactivated to different degrees by dry heating of defatted soybean flour for 0, 5, 10, 15, 20 and 25 min and soy protein isolates were prepared thereof by isoelectric precipitation of the water extract of the defatted soybean flour. The fluorescence emission intensity at 420 nm of the chloroform–methanol extract of soy protein isolates, which was indicator of the existence of peroxidized lipid, varied in parallel with the lipoxygenase residual activity in defatted soybean flours. The dispersion of soy protein isolate showed an increasing turbidity with the increase of lipoxygenase residual activity in the starting defatted soybean flour, suggesting an elevated tendency to form insoluble aggregates during the preparation of soy protein isolate. Small deformation rheological test revealed that the gelling times were shorter for those soy protein isolates derived from low lipoxygenase activity defatted soybean flours than that of high lipoxygenase activity. Frequency sweep showed that G′ of soy protein isolate derived from low lipoxygenase defatted soybean flour was independent of oscillation frequency in contrast to that of derived from non dry-heated defatted soybean flour, the latter showed a marked frequency dependence. Large deformation test revealed that the gel hardness increased about 10 times after dry heating of defatted soybean flour for 20 min. As the increase of the lipoxygenase residual activity, the gel permeability increased markedly, suggesting that soy protein isolate from high lipoxygenase defatted soybean flour produced coarser textured gel, which corresponded well with the results of scanning electron microscopy.     

Effect of Extraction pH and Temperature on Isoflavone and Saponin Partitioning and Profile During Soy Protein Isolate Production

ABSTRACT: Soy protein isolates (SPIs) are produced industrially using methods using various protein extraction temperatures and pH values. The effects of process temperature (25°C or 60°C) and pH (8.5, 9.5, or 10.5) on isoflavone and group B saponin extraction, partitioning, and profile during bench-scale SPI production were evaluated. Protein, isoflavone, and saponin extraction increased with increasing temperature and pH. Substantial quantities of isoflavones and saponins remained in the insoluble fraction waste stream. Isoflavones were also lost to the whey waste stream, whereas saponins were not detected in the whey. Neutralization of SPI samples at the time of analytical extraction increased measured isoflavone concentrations for the pH 8.5 process extraction treatments, whereas neutralization substantially increased measured saponin concentrations in SPIs for all process extraction treatments. Malonylglucoside isoflavones were primarily converted to β-glucoside forms as temperature and pH were increased, and these conditions caused conversion of αg, βg, and βa saponins to saponin V, I, and II forms, respectively. Analytical extraction pH should receive careful consideration when analyzing soy matrices for isoflavones and saponins.     

Production of Soy Isolates by Ultrafiltration: Factors Affecting Yield and Composition

Water extracts of defatted soy flour were prepared by multiple extraction and centrifugation. Ultrafiltration of extracts in hollowfiber units showed significant deviation from ideal behavior for removal of nonprotein components, probably due to solute-solute and solute-membrane interactions. These interactions affected the retentate composition as well as the yield of protein. Membrane adsorption losses increased with feed concentration and were higher for the XM than for the PM series of membranes. A retentate washing step, such as the continuous diafiltration mode of operation, was necessary to produce a true protein isolate. Overall yield of protein was 86% of that in the defatted soy flour.     

Abundant proteins associated with lecithin in soy protein isolate

A new method for fractionating acid-precipitated soy proteins, so called soy protein isolate, involving three step acidification of a water extract of defatted soy flour was developed. Soy protein isolate was shown to be mostly composed of not only β-conglycinin and glycinin, but also a group of lipophilic proteins associated with lecithin (phospholipids). The proportions of three major proteins were 23%, 46%, and 31%, respectively. The proportions changed as the nitrogen solubility index (NSI) of defatted soy flour changed. The yield of lipophilic proteins depended on the NSI of defatted soy flour, different from those of β-conglycinin and glycinin. The variation in the proportions of the three major proteins may be due to the yield of lipophilic proteins.     

Bitterness of saponins and their content in dry peas

The bitterness of a saponin mixture (containing saponin B and DDMP (2,3‐dihydro‐2,5‐dihydroxy‐6‐methyl‐4H‐pyran‐4‐one) saponin in a ratio of 1:4) and saponin B obtained from dry peas were established by a trained panel using line scaling. Both saponins were found to be bitter. However, the saponin mixture, and hence DDMP saponin, was found to be significantly more bitter than saponin B. The bitterness perceived correlated with the saponin concentration. In addition to saponin bitterness, the saponin content and composition of 16 dry pea varieties were also investigated. In two varieties, DDMP saponin was the only saponin present whereas, in the rest of the varieties, DDMP saponin was more abundant than saponin B. The pea varieties investigated differed significantly in saponin content. The amounts of DDMP saponin ranged from 0.7 to 1.5 g kg^?1 (dry matter), whereas those of saponin B ranged from 0 to 0.4 g kg^?1. As saponins are bitter, pea varieties with lower saponin contents would be preferred for use in food production. Copyright © 2006 Society of Chemical Industry     

INFLUENCE OF GERMINATION ON SAPONINS IN SOYBEAN AND RECOVERY OF SOY SAPOGENOL I

Soysaponins are considered major bioactive components. Ethanol extractives prepared from mature soybean and germinated seeds (0–4 days) were examined for saponin content (found to be 2.8 and 6.1–8.9%, respectively). The saponin content increased 3.2 times after germination. The predominant hydrolytic product of saponin – soysapogenol I – content increased from 1.8 to 7.3% during the course of germination. Defatted soy flour, soy protein isolate and toasted flour contain saponins at 2.3–3.5%, suggesting that the germinated soybean seeds are the richest source of saponins among soybean products.     

Effects of fermentation on the phytochemical composition and antioxidant properties of soy germ

Soy germ is a remarkable source of bioactive phytochemicals offering an interesting alternative as starting ingredient for fermented food. This work aimed to determine whether lactic acid bacteria fermentation of soy germ induces changes on its phytochemical composition. The antioxidant properties of fermented soy germ samples periodically taken during the fermentation process were evaluated and correlated with the concentration and structural modifications of isoflavones, saponins, phytosterols and tocopherols. Fermented soy germ extracts exhibited a higher inhibition effect against the superoxide anion radical, and lesser but significant ferric-reducing and DPPH radical scavenging effects compared with raw soy germ. By comparison to the traditional whole seed-based products, soy germ exhibits higher levels of isoflavones, saponins, phytosterols and tocopherols. All these phytochemicals contributed to the antioxidant capacity of soy germ and were conserved under lactic acid bacteria fermentation.     

大豆糖蜜的综合利用

大豆糖蜜是醇法生产大豆浓缩蛋白的副产物,主要成分有糖类、蛋白质、异黄酮和皂苷等.介绍了大豆糖蜜的综合利用:即从大豆糖蜜中提取异黄酮、皂苷和大豆低聚糖等的研究进展;利用大豆糖蜜作发酵底物的应用和研究进展,以及大豆糖蜜的其他应用.     

High-power ultrasonication-assisted extraction of soybean isoflavones and effect of toasting

The effect of high-power ultrasonication (HPU) on extraction of soybean isoflavones and components, including total phenolic and DPPH radical scavenging activities (RSA) were evaluated. Isoflavones from defatted soybean flakes were extracted using a bench scale HPU system at 20 kHz and varying amplitudes (18–54 μm) for 1 and 3 min. Aqueous acetonitrile, and aqueous ethanol based solvents were evaluated for extraction at samples-to-solvent ratios of 0.1:1 and 0.2:1. The non-sonication control extraction was with mixing with magnetic stirrer for 2 h. Preliminary data indicated 1.2–1.5 times more genistein recovery at 1, and 3 min sonication compared to control, however, total phenolic decreased. The genistein recovery was lower at higher sonication levels. RSA also decreased to 40% for HPU-assisted extractions. Total isoflavones recovery in HPU-assisted extractions increased from 600 to 5813 μg/g. The concentration of major isoflavone components, genistein, daidzein, and glycitein also increased by 10-fold. HPU for 3 min reduced the average particle size of treated soy flakes from 530 μm to 60 μm. Toasting at 150 °C of defatted soy flake for longer period of time led to higher aglycone concentration in extract; however, 2 h toasting was sufficient prior to HPU-assisted extraction.     

高固形物浓度对大豆分离蛋白酸性蛋白酶酶解产物功能特性的影响

本文系统研究了提高固形物浓度对酸性蛋白酶酶法改性大豆分离蛋白分子量分布、氮溶解指数、分散稳定性、持水力、乳化性、起泡性和泡沫稳定性的影响。结果表明:大豆分离蛋白经过酸性蛋白酶控制酶解制备的改性大豆分离蛋白,其产物氮溶解指数、起泡性均有明显提高,分散稳定性略有提高;但持水力、乳化性、泡沫稳定性有所降低。在相同水解度下,随着酶解体系中固形物浓度的提高,改性大豆分离蛋白的分散稳定性、持水力、乳化活性均呈上升趋势,酶解产物中分子量小于10 kDa的肽段以及氮溶解指数呈下降趋势。当水解度小于8%时,低浓度酶解产物起泡性高于高浓度酶解产物,而水解度超过8%时,高浓度酶解产物起泡性大体高于低浓度酶解产物。     

Rice bran-soy blends as protein supplements in cookies

The effect of incorporating one of three stabilized full-fat rice brans in combination with each of four soy ingredients in a sugar-snap cookie was investigated. The four soy ingredients in a sugar-snap cookie were two soyflours (full-fat and defatted), a soy concentrate and a soy isolate. Rice bran and soy were added in place of wheat flour to increase protein content from 6% to a minimum of 9%, and the cookies were compared with each other and with a 100% wheat flour cookie. Quality characteristics evaluated included protein, spread, physical texture and colour, and sensory preference by ranking for colour, crispness and flavour. In general, the rice bran-soy cookies had less spread (even with added shortening, water and emulsifier), were less crisp and more chewy, and were somewhat darker in colour than the 100% wheat flour cookie. The soy isolate, USDA and Protex 20-S cookies were as acceptable in colour, crispness and flavour as the control.     

脱脂豆粕大豆皂苷提取物的定性分析和抗油脂氧化

以乙醇为溶剂从脱脂豆粕中提取大豆皂苷,AB-8大孔树脂纯化后对其进行薄层层析、红外光谱和高效液相色谱定性分析,同时研究其抗油脂氧化能力。结果表明:脱脂豆粕提取物经纯化后得到的大豆皂苷具有抗豆油氧化能力,且有剂量效应关系,0.5%大豆皂苷纯化品抗油脂氧化能力较强,相当于0.02%BHT,随着时间的延长,作用甚至强于0.02%BHT;大豆皂苷与柠檬酸、抗坏血酸均有较好的协同作用,并且抗坏血酸的增效作用强于柠檬酸,是较好的天然抗氧化剂。     

Utilizing the R-Index Measure for Threshold Testing in Model Soy Isoflavone Solutions

ABSTRACT: Twenty-eight untrained panelists used the signal detection rating method to determine thresholds for daidzein and genistein. Five concentrations of genistein and daidzein were suspended in starch solutions. The starch solution represented the noise, and isoflavone suspensions represented the signal. Blindfolded panelists received 15 replicates of noise and signal. To determine group detection thresholds, the concentration at an R-index of 75% was calculated. The group thresholds for genistein and daidzein were 4.006 × 10⁻³ M and 2.921 × 10⁻³ M, respectively. These results indicate a much higher threshold value than reported in the literature and in soymilks. This strongly suggests that daidzein and genistein individually do not contribute to bitterness or astringency in soy food products.     

Peanut protein concentrate: Production and functional properties as affected by processing

Peanut protein concentrate (PPC) was isolated from fermented and unfermented defatted peanut flour by isoelectric precipitation and physical separation procedures. PPC was dried by spray or vacuum drying. PPC powders from each drying technique were evaluated for proximate composition and functional properties (protein solubility, water/oil binding capacity, emulsifying capacity, foaming capacity and viscosity) along with defatted peanut flour and soy protein isolate as references. PPC contained over 85% protein versus 50% protein in the defatted peanut flour used as raw material for PPC production. PPC had a solubility profile similar to that of peanut flour, with minimum solubility observed at pH 3.5–4.5 and maximum solubility at pH 10 and higher. Roasting of peanut reduced all functional properties of defatted peanut flour while fermentation had the reverse effect. The type of drying significantly affected the functional properties of PPC. Spray dried PPCs exhibited better functional properties, particularly emulsifying capacity and foaming capacity, than vacuum oven dried PPC. Spray dried PPCs also showed comparable oil binding and foaming capacity to commercially available soy protein isolate (SPC). At equivalent concentrations and room temperature, PPC suspension exhibited lower viscosity than soy protein isolate (SPI) suspensions. However, upon heating to 90 °C for 30 min, the viscosity of PPC suspension increased sharply. Results obtained from this study suggest that the PPC could be used in food formulations requiring high emulsifying capacity, but would not be suitable for applications requiring high water retention and foaming capacity. PPC could be a good source of protein fortification for a variety of food products for protein deficient consumers in developing countries as well as a functional ingredient for the peanut industry. The production of PPC could also add value to defatted peanut flour, a low value by-product of peanut oil production.     

不同大豆蛋白对小麦面条加工品质和血糖生成指数的影响

为改善小麦面条品质,在小麦粉中添加大豆蛋白(全脂豆粉、脱脂豆粉、大豆分离蛋白、大豆浓缩蛋白、大豆组织蛋白),以拉伸特性、蒸煮特性、微观结构以及血糖生成指数为评价指标,研究大豆蛋白添加量(0%、5%、10%、15%、20%)对面条加工品质及血糖生成指数的影响。结果表明:随蛋白添加量的增加,脱脂豆粉、全脂豆粉的增加使面条的拉断力呈明显上升趋势,拉伸距离呈先上升后下降趋势,大豆分离蛋白、大豆浓缩蛋白添加量的增加使拉断力呈先上升后下降趋势,拉伸距离呈下降趋势,而大豆组织蛋白的增加使面条拉伸性能均逐渐降低;当大豆蛋白添加量为10%时,混合粉面条拉伸特性较优;五种大豆蛋白的添加均使面条的烹煮损失率及断条率上升,全脂豆粉的增加使面条的吸水率、膨胀率逐渐下降,其余四种均使其上升;微观结构表明,脱脂豆粉和全脂豆粉的添加使混合粉面条的面筋网络结构更加连续均匀,而其余三种大豆蛋白添加量的增加造成混合粉面条微观结构的劣变;利用体外复合酶方法测定GI值,血糖生成指数依次为:小麦粉 > 脱脂豆粉 > 全脂豆粉 > 大豆组织蛋白 > 大豆浓缩蛋白 > 大豆分离蛋白。     

Development of protein-Rich Sorghum-Based Expanded Snacks Using Extrusion Technology

Sorghum is an important staple crop in semi-arid regions of Africa and India because of its drought tolerance. But low protein content and quality limit its widespread use. This project focused on developing sorghum-based extruded snacks. Results from preliminary lab-scale extrusion experiments were used to design a 2×5 factorial pilot-scale study. Two blends of sorghum flour and corn flour were prepared (6:1 and 5:2 w/w ratios) as the controls. Three different sources of protein—whey protein isolate, defatted soy flour, and mixed legume flour—were added to the sorghum/corn flour blends at 30%. A 50:50 blend of defatted soy flour and whey protein isolate was also added at 30% to the sorghum/corn flour blends. The resultant ten formulations were extruded on a pilot-scale twin-screw extruder to investigate the effects of sorghum/corn flour ratio and protein addition on product expansion, microstructure, mechanical properties, and sensory attributes. Expansion ratio of extruded product increased at the higher level of corn flour, and decreased with the incorporation of protein sources. Extrudates with defatted soy flour had a lower expansion ratio (5.3–5.4) than those with whey protein isolate (7.7–7.9), legume flour (7.1–9.9), or whey protein isolate-defatted soy flour (6.1–6.9). Extrudate microstructure, obtained by X-ray microtomography, corresponded well with expansion characteristics. Extrudates with defatted soy flour had the lowest cell diameter. Average crushing force (ranging from 40.9 to 154.87 N) was lower for extrudates with a higher level of corn flour. However, contrary to expectations, crushing force and crispness work both decreased with incorporation of protein sources. Consumer acceptability results showed that the addition of protein sources enhanced taste and overall acceptability of the extruded snacks, with the treatment sorghum/corn flour 5:2 and whey protein isolate-defatted soy flour as the protein source having significantly higher ratings than the other treatments.     

Validation of a High-performance Liquid Chromatography-Ultraviolet Method to Quantify Soy Sapogenols A and B in Soy Germs from Different Cultivars and in Soy Isoflavone-Enriched Supplements

An increasing number of studies investigating the health effects of soy phytochemicals has led to the commercialization of many soy‐based products. Due to its particularly high concentration in many secondary metabolites, the use of soy germ as raw material is emerging for the processing of soy dietary supplements. However, the soybean seeds and germs do not exhibit the same major phytochemical profiles. This is particularly the case for soy saponins. Due to their structural diversity, the analysis of each individual soy saponin remains difficult. In this study, the total amount of these health‐protective phytochemicals was determined through the quantification of their aglucon precursors, soy sapogenols A and B. A simple and rapid analytical method was developed using high‐performance liquid chromatography coupled with an ultraviolet detection. The within‐day and between‐day variabilities of total soy sapogenol concentration were 7.3% and 10.9% in the whole seed and 3.3% and 4.7% in the germ, respectively. The total soy sapogenol contents investigated among the germs from 43 cultivars ranged from 32.8 μmol/g to 63.1 μmol/g. High amounts of soy saponins were also observed in several soy‐based dietary supplements, from 5.5 μmol/g to 107.8 μmol/g, with an A/B ratio varying from 0.3 to 8.6, showing large differences between the raw materials and concentration process used. These results indicate that these compounds have to be clearly determined when discussing the biological activity of dietary supplements issued from soy.     

Analysis of Lunasin in Commercial and Pilot Plant Produced Soybean Products and an Improved Method of Lunasin Purification

Abstract: Lunasin is a bioactive peptide present in soybean. It is important to quantify lunasin concentration in soy products to assess its potential impact as functional food. The objectives of this study were to analyze lunasin in commercial soymilk products and implement an efficient method to isolate and purify it from defatted soybean flour. Defatted soybean flour was suspended in water, and the extract was loaded in a pre‐equilibrated diethylaminoethyl column and bound proteins eluted using a step gradient of salt. Most lunasin was eluted from the column at 0.2 to 0.4M NaCl as quantified by immunoassays and purified using ultracentrifugation and ultrafiltration techniques. Lunasin purity was ≥90% and a standard curve was used to quantify its concentration in soymilk products. Concentration of lunasin in soy products, including organic soymilk, soy protein shakes, and soy infant formulas, ranged from 1.78 to 9.26 mg lunasin/100 g product. The concentration per serving ranged from 1.59 ± 0.01 to 22.23 ± 0.74 mg lunasin with variability depending on brand and size per serving. Steam‐ground‐cooked soy had the highest concentration of lunasin (22.23 ± 0.74 mg/serving), similar to some commercial products. Ground‐cooked soymilk contained roughly half the concentration of lunasin (14.39 ± 1.4 mg/serving). Soy infant formulas that used soy protein isolate revealed lower concentrations of lunasin (P < 0.05). It was concluded that all soymilk products analyzed contained lunasin, and a more efficient method to isolate lunasin with higher purity was developed. Practical Application: Soy foods have shown to play a role in cardiovascular health prevention. The quantification of lunasin in commercially available soy products can add to the already existing health claim for soy foods and encourage consumers to include soy products in their diets.     

热水蒸煮大豆蛋白产品的功能性研究

研究了热水蒸煮时间对脱脂大豆粉、醇洗大豆浓缩蛋白、大豆分离蛋白的影响。热水蒸煮提高了浓缩蛋白和分离蛋白的起泡性和乳化性，对脱脂大豆粉的乳化性有所提高，但不能提高其起泡性。破坏胰岛素抑制剂和微生物的热水蒸煮对蛋白质的加工具有重要的意义。     

Processing, Functional, and Nutritional Properties of Okra Seed Products

Okra full-fat flour, defatted flour, protein concentrate, and protein isolate were prepared from whole okra seeds (Spineless Green Velvet variety). Results of proximate analysis, amino acid profiles, in vitro protein digestibility, and calculated protein efficiency ratios (C-PER) indicated that okra products have significant potential as a viable new protein source. C-PER of okra products ranged from 2.16–2.22. Protein solubility indicated that these okra products were generally more soluble than commercial soy products. Emulsion capacity and viscosity of okra products were significantly lower than those for soy products. Overall, foam stability of soy products was consistently higher than that for okra products.