Isolation and characterization of proteins from soymilk residue (okara)

Protein was extracted from okara at pH 9.0 and 80 °C for 30 min, giving a recovery of 53% protein. The extracted protein was isolated by isoelectric precipitation at pH 4.5, and the dried, defatted protein isolates (prepared at 25 and 80 °C) had over 80% protein.

The okara protein isolates have essential amino acid profiles similar to the FAO scoring pattern, and high in vitro protein digestibility, with methionine and cysteine as the limiting amino acids. Polyacrylamide gel electrophoresis in sodium dodecyl sulfate showed that okara protein isolates had a large quantity of high molecular weight components suggesting protein aggregation. Differential scanning calorimetry and hydrophobicity data suggested extensive protein unfolding in the okara products.

Okara protein isolates had lower solubility than a commercial soy protein isolate at both acidic and alkaline pH, probably due to protein aggregation. Other functional properties, including emulsifying, water and fat binding, and foaming properties, were found to be comparable to the commercial soy isolate.     

Thanh法提取7S、11S球蛋白功能特性的研究

以中豆36为原料,分别提取大豆分离蛋白(SPI)、7S、11S球蛋白,系统地比较了它们的功能性质的差异。结果表明:SPI、7S及11S的功能特性之间存在较大差异,11S球蛋白具有较强的凝胶性、吸油性和溶解度;7S球蛋白具有较高的持水性和乳化性。     

添加豆渣膳食纤维对不同小麦粉糊化特性、热力学性质及面团质构的影响

通过RVA、DSC和TPA分析了添加豆渣膳食纤维后不同小麦粉的性质,RVA结果分析表明,添加少量豆渣膳食纤维可使高筋粉和中筋粉糊化参数略有增加,而添加量增加到一定程度时,由于体系中淀粉分子数量减少,使小麦粉的黏度参数降低。DSC结果分析表明,豆渣膳食纤维的添加可以增大高筋粉和低筋粉的糊化温度,降低中筋粉的糊化温度,并且由于淀粉含量的减少,使三种小麦粉的糊化焓值均降低。TPA结果分析表明,添加膳食纤维对高筋粉来说,面团弹性、黏性和回复性略有降低,对低筋粉来说,面团弹性、黏性和回复性略有升高,而对中筋粉来说,面团弹性和回复性均升高,而黏性略有降低。     

Modification of insoluble dietary fibres in soya bean okara and their physicochemical properties

The changes in physicochemical and physiological properties of modified soluble dietary fibre (mSDF) in the okara using enzymatic [cellulase/substrates ratio of 2.0–6.0% (w/w) at 50 °C for 90–150 min], chemical [water bath of 1–3 h, water bath temperature of 50–90 °C, Na₂HPO₄ concentration of 0.1–0.9% and sample/reagent radio (S/R) of 1:40–1:60 (w/v)] and physical (homogenised once or twice under the optimal cellulase treatment condition) treatments were evaluated. The mSDF yield with chemical treatment (57.16%) was significantly (P < 0.05) higher than that of physical treatment [homogenisation once (16.54%) or twice (42.02%)] in combination with cellulase treatment. All treatments improved swelling capacity of mSDF and promoted bile acid‐ and cholesterol‐absorption capacity, but enzymatic and chemical treatments decreased the total reducing power of mSDF, except homogenisation‐cellulase treatment (141.74 μm  TE g^?1). Therefore, homogenisation‐cellulase treatment may be the appropriate method to improve the SDF proportion and ameliorate the functionality of okara.     

The localization of phytate in tofu curd formation and effects of phytate on tofu texture

ABSTRACT:  The localization of phytate on tofu making and its effects on tofu texture were investigated. Thirty-eight percent and 3% of phytate in soymilk were bound to soluble protein and particulate protein, respectively, and the others were in free form. In the early stage of curd formation, phytate bound to particulate proteins and then a large part of phytate was taken into the tofu curd. Increase of phytate contents in soymilk resulted in the increase of coagulant requirement to make firm tofu. Optimal coagulant concentration (OCC) for making tofu was influenced by phytate contents. The increase of phytate in tofu caused decrease of hardness at OCC and resulted in the increase of brittleness and viscosity of tofu. We concluded that the phytate content is one important factor that contributes to tofu texture.     

Content composition and antioxidant activity of isoflavones in commercial and homemade soymilk and tofu

BACKGROUND: Isoflavones, found in soymilk and tofu, are one of the phytochemicals in soy‐based products that may promote good health. Homemade tofu and various homemade soymilk samples were made using different soaking, grinding, and cooking methods. The homemade samples were compared to commercial tofu and soymilk for total isoflavone content and composition as well as their antioxidant capacity. All samples were freeze‐dried and extracted with a 58% acetonitrile solution which was subsequently used to determine the isoflavone content by reverse‐phase high‐performance liquid chromatography. The antioxidant activity of extracts was determined using a modified 2,2‐azino‐bis‐(3‐ethylbenzthiazoline‐6‐sulfonic acid) method and total antioxidant capacity was reported as ascorbic acid equivalents. RESULTS: The total isoflavone, aglycone, and antioxidant levels were significantly higher in homemade soymilk and tofu (1571 µg) than in commercial samples. Homemade soymilk made by the extended boiling method yielded the highest total isoflavone (2567 µg) and glucoside (1525 µg) content. A strong positive correlation was observed between the total isoflavone, aglycone conjugates, and genistein series concentration and antioxidant capacity of soymilk. CONCLUSION: Increased moist heating time yielded the highest concentration of total isoflavones as well as aglycone conjugates and the genistein series. Increasing the duration of boiling can increase the isoflavone content of both homemade and commercial soymilk and tofu. Copyright © 2007 Society of Chemical Industry     

干法制浆工艺对豆浆品质的影响

采用高速粉碎机对大豆进行干法粉碎制取豆粉,以豆粉为原料分别制作熟浆豆浆和全豆豆浆,省去传统豆浆制作过程中的大豆浸泡工序。以豆浆平均粒径和稳定性为质量指标,通过单因素试验和正交试验,优化了豆浆制作工艺参数。结果表明:熟浆豆浆的最佳工艺参数为大豆粉碎时间120s、料水比1:11(g/mL)、保温时间30min;全豆豆浆的最佳工艺参数为大豆粉碎时间120 s、料水比1:12(g/mL)、保温时间15min。与传统全豆豆浆相比,干法全豆豆浆的平均粒径降低了66.43%,可溶性固形物以及可溶性蛋白质含量分别提高14.41%和16.57%;与传统熟浆豆浆相比,干法熟浆豆浆的平均粒径提高78.03%,可溶性固形物含量以及可溶性蛋白质含量分别提高42.36%和42.76%。干法工艺所制得的豆浆与传统豆浆相比在感官评价上无显著差异(P0.05)。     

Effects of calcium chloride and sodium hexametaphosphate on certain chemical and physical properties of soymilk

ABSTRACT:  Soymilks with sodium hexametaphosphate (SHMP) (0% to 1.2%) and calcium chloride (12.50, 18.75, and 25.00 mM Ca) were analyzed for total Ca, Ca ion concentration, pH, kinematic viscosity, particle diameter, and sediment after pasteurization. Higher added Ca led to significant ( P ≤ 0.05) increases in Ca ion concentration and significant ( P ≤ 0.05) decreases in pH. At certain levels of SHMP, higher concentrations of added Ca significantly increased ( P ≤ 0.05) kinematic viscosity, particle diameter, and sediment. Increasing SHMP concentration reduced Ca ion concentration, particle diameter, and dry sediment content, but reduced kinematic viscosity of samples ( P ≤ 0.05). Adding SHMP up to 0.7% influenced pH of soymilk in different ways, depending on the level of Ca addition. When the pH of Ca-fortified soymilk was adjusted to a higher level, ionic Ca decreased as pH increased. There was a negative linear relationship between the logarithm of ionic Ca concentration and the adjusted pH of the soymilk. Ionic Ca appeared to be a good indicator of thermally induced sediment formation, with little sediment being produced if ionic Ca was maintained below 0.4 mM.     

Structural and Functional Analysis of Various Globulin Proteins from Soy Seed

Storage proteins of soybean mostly consist of globulins, which are classified according to their sedimentation coefficient. Among 4 major types: 2S, 7S, 11S, and 15S of globulins, 7S and 11S constitute major fraction. The 11S fraction consists only of glycinin and 7S fraction majorly consists of β-conglycinin, small amounts of γ-conglycinin and basic 7S globulin (Bg7S). Glycinin exist as a hexamer while β-conglycinin as a trimer and Bg7S as a tetramer. Glycinin subunits are coded by 5 genes of a family, whereas about 15 genes are present for β-conglycinin subunits. Bg7S gene is present in four copies in soybean genome. Synthesis of all proteins takes place as a single polypeptide chain, which is cleaved after folding to yield different chains or subunits. Glycinin and β-Conglycinin are made for storage purpose. However, Bg7S has potential xylanase inhibition activity and protein kinase activity. Primary structure of Bg7S reveals 12 conserved cysteine residues involved in forming 6 disulfide bonds, which provides appreciable stability to protein. Secondary structure is predominately rich in β-sheets with few alpha helices. Bg7S shares structural similarity with various aspartic-proteases. In this review, our aim is to discuss sequence, structure, and function of various globulins present in Glycine max.     

棉籽7S及12S球蛋白的分离纯化及其物化性质的研究

以棉籽贮存蛋白为原料,采用蛋白纯化系统(配备凝胶层析柱)对棉籽7S和12S球蛋白进行分离纯化,对所得7S和12S球蛋白的蛋白质含量、氨基酸组成、变性温度及荧光强度等物化性质进行了测定分析。结果表明:棉籽7S及12S球蛋白的蛋白质含量分别为(91.59±0.53)%和(93.35±0.62)%,其SDS-PAGE谱图中除显示各自特征条带外无其他杂带,其氨基酸组成与绝大部分油料种子中球蛋白的基本一致,含有丰富的谷氨酸、天冬氨酸和精氨酸,而半胱氨酸和甲硫氨酸含量较低;差示扫描量热仪(DSC)分析棉籽7S及12S球蛋白的变性温度分别为93.3℃和107.7℃;棉籽7S及12S球蛋白的荧光发射光谱最大荧光强度均在325 nm左右。     

Changes of soybean quality during storage as related to soymilk and tofu making

ABSTRACT:  Soybeans are stored and transported under various humidity and temperature conditions. Soymilk and tofu are two of the most important foods made from whole soybeans. The objective of this study was to investigate the influence of storage conditions on soybean quality as related to soymilk and tofu-making properties. Soybeans of 3 different genotypes (Proto, IA2032, and Vinton 81) were stored in varying conditions: temperature ranging from 4 to 50 °C, relative humidity from 55% to 80%, initial moisture content from 6% to14%, and storage time up to 15 mo depending upon storage conditions. The effects of different storage conditions on soybean color, solids and protein extractability, soymilk pH, tofu yield, tofu solids and protein contents, tofu color, and texture were investigated. While no significant changes occurred for the soybeans stored at 4 °C, the soybeans stored at high temperatures (30 to 50 °C) exhibited significant quality loss ( P < 0.05). The degradation of soybean lightness (Hunter L ), color difference (Δ E ), and solid extractability exhibited a linear relationship with time. Soak weight decreased at high temperature and relative humidity, but increased at mild storage conditions. Several combinations of storage conditions at temperatures exceeding 30 °C produced a drastic loss in tofu yield. Storage also affected the tofu making process by reducing optimum mixing time to produce the highest tofu yield. Varietal difference in soybean storability was observed. The results provided useful information for the soybean processing industry to store soybeans using the optimal storage conditions and to estimate soybean quality after storage.     

Effect of calcium carbonate,calcium citrate,tricalcium phosphate,calcium gluconate and calcium lactate on some physicochemical properties of soymilk

Soymilk fortified with 25 mm Ca (Ca carbonate, Ca citrate, triCa phosphate, Ca gluconate or Ca lactate) was compared with the properties of unfortified soymilk (control). Calcium carbonate, Ca citrate and triCa phosphate did not significantly affect [Ca²⁺], absolute viscosity and particle size of soymilk, but Ca gluconate and Ca lactate significantly increased these properties. The pH of soymilk was significantly increased by adding Ca carbonate but significantly reduced by adding Ca gluconate and Ca lactate. Dry sediment of soymilk increased significantly with the addition of all Ca salts excluding triCa phosphate. Freezing point depression increased significantly only for Ca gluconate and Ca lactate, mainly owing to their higher solubility.     

蛹虫草固态发酵豆渣的功能性成分与抗氧化活性

目的:用蛹虫草固态发酵豆渣,测定豆渣发酵前后功能性成分含量及抗氧化能力的变化。方法:蛹虫草CM-1固态发酵豆渣7 d,测定发酵前后豆渣水提物中虫草素、总酚和多糖的含量,以及DPPH自由基清除力、还原力、ABTS自由基清除能力、铁离子还原力（FRAP）的变化,并用皮尔森相关性分析以及主成分分析研究了虫草素、总酚、多糖含量与抗氧化指标之间的关系。结果:豆渣经蛹虫草CM-1固态发酵,水提物中多糖、虫草素和总酚含量分别是（236.16±39.91）、（1.88±0.04）μg/mg和（11.94±0.33）μg GAE/mg,多糖、总酚含量分别是发酵前的1.42倍和2.15倍。豆渣经过发酵,在提取物浓度为6 mg/m L时,DPPH自由基清除力由24.63%提高到72.4%,还原力由0.11提高到0.38,ABTS自由基清除能力由76.76%提高至88.71%,FRAP由39.08μmol/L提高至269.55μmol/L。主成分分析和相关性分析表明,抗氧化指标与虫草素、总酚、多糖含量具有非常显著的相关性（p<0.01）。结论:用蛹虫草发酵豆渣可以提高豆渣的功能性成分和抗氧化能力,发酵豆渣有望开发成为功能性食品基料及抗氧化食品。      

豆渣及其胃肠道模拟消化产物的物化特性和抗氧化力分析

为比较分析豆渣原料和胃肠道模拟消化产物的物化特性和抗氧化力,为制备新型食品添加剂提供一定的理论数据支持。本实验以热风干燥豆渣为原料,模拟人体胃肠道消化环境得到不可消化部分(Indigestible Fraction,IF),并对其基本营养成分、物化特性、多酚含量及抗氧化力进行分析。结果表明,豆渣含IF 90.64%,而其中IF中膳食纤维含量为56.54%。此外,与热风干燥豆渣相比,IF的持水力、持油力和结合水力等在25℃和37℃下均有所提高,抗氧化力也显著增强。在多酚含量方面,豆渣中缩合单宁的含量较高,而IF中则是水解多酚含量占比较高。这表明IF可作为一种富含大量优质膳食纤维、能开发具有抗氧化功能性食品的潜在来源。      

大豆渣水溶性大豆多糖提取工艺研究

采用有机酸水溶液提取大豆渣中水溶性大豆多糖(SSPS),通过单因素实验,得到最佳工艺条件:温度110℃,提取时间1.5h,用酒石酸调节pH=3.8。该工艺蛋白质溶出率仅为2.18%;产品分子量由三部分组成,其中5.424×105为主要部分,水溶性大豆多糖得率达27.65%。     

Effect of different coagulants on yield and quality of tofu from soymilk

Soymilk tofu coagulated with four indigenous coagulants was compared in terms of chemical, textural, colour, and sensory attributes with calcium sulphate (CS) coagulated tofu. Coagulants used are Epsom salt (ES), lemon juice (LJ), alum and top water of fermented maize (TWFM). Protein and magnesium content significantly (P < 0.05) increased from 44.5 to 51.7 g/100 g and 252 to 324.6 mg/100 g, respectively, in soybean grain to soymilk. Calcium and magnesium contents increased and decreased significantly (P < 0.05) in tofu coagulated with CS and ES, respectively. Lightness (L) values were 86.3, 86.2, 77.8, 72.4 and 84.6, redness (a) values are 0.34, 0.21, 0.87, 1.05 and 0.32, and yellowness (b) values were 24.0, 23.9, 27.3, 20.3 and 23.4 for CS, ES, LJ, alum and TWFM. The hardness, chewiness and brittleness of textural properties of tofu were significantly (P < 0.05) affected by different sources of coagulation. Sensory evaluation data shows that LJ impacts a significantly acceptable sensory attribute to tofu. This study has demonstrated that tofu quality is affected by the type of coagulant used in curding the soymilk.     

Saio法提取大豆7S球蛋白的纯化及鉴定

研究利用Sephadex G-200凝胶柱层析法和纤维素DE-52离子交换柱层析法分离纯化经过Saio法提取的大豆7S球蛋白样品,采用SDS-聚丙烯酰胺凝胶电泳和高效毛细管电泳进一步鉴定Saio法提取的大豆7S球蛋白样品的组分及含量。结果表明,Saio法提取的大豆7S球蛋白纯度约为81%。     

大豆蛋白质及其组分含量对豆腐产量和品质的影响

通过对大豆蛋白质含量对豆腐产量和品质的影响,蛋白质11S和7S组分及7S的α′亚基和11S的酸性亚基含量对豆腐品质的影响的综述,可以看出大豆蛋白质含量与豆腐产量和品质的关系复杂,研究结果出现正相关、负相关和不相关3种情况,但球蛋白的含量与豆腐产量正相关。多数情况下,7S组分含量与豆腐品质负相关,11S组分含量与豆腐品质正相关,11S/7S比值与11S组分含量相似。7S的α′亚基含量与豆腐硬度负相关,11S的酸性亚基含量与豆腐硬度正相关。