Modification of Proteins from Soymilk Residue (Okara) by Trypsin

Okara protein isolates were hydrolyzed by trypsin to about 5% to 14%. Solubility was increased more than twofold by the modification, and water hydration capacity and emulsification activity index were also improved. The okara protein products had good essential amino acid profiles and the trypsin-hydrolysates also had increased in vitro digestibility and available lysine content. The low solubility of okara protein makes it difficult to incorporate it into many food systems. Okara protein hydrolysates, with improved solubility and other functional properties, could be used as a low-cost protein ingredient in processed foods.     

Effects of electron beam irradiation pretreatment on the structural and functional properties of okara protein

The structural and functional properties of okara protein pretreated with electron beam irradiation (EBI) at different doses (0–10 kGy) were investigated. The results of Fourier transform infrared spectroscopy spectra and fluorescence spectra indicated that EBI treatment decreased the α-helix and β-sheet proportion, contributing to a less compact tertiary conformation, thereby increased the fluorescence intensity with a red shift of λ_max. Scanning electron microscopy images indicated that okara protein was fragmented into smaller pieces and the surface was uneven with pores after EBI treatment. The solubility, thermal stability and emulsification characteristics of okara protein were regulated by modifying its structure by EBI treatment. When the EBI treatment dose was 6 kGy, the protein had the highest solubility, as well as emulsification characteristics. Taken collectively, these results demonstrate that EBI can improve the functional properties of okara protein, which may widen the application of the protein.     

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.     

小麦淀粉改性技术及应用研究进展

小麦淀粉是小麦中含量最高的成分，约占籽粒干重的75%，但天然小麦淀粉耐热、耐剪切、耐酸能力差，且易老化回生，在很大程度上影响小麦淀粉功能性能及小麦产品的产品品质，因此小麦淀粉改性技术受到了广泛关注。淀粉颗粒形态及结构的改变会影响其糊化特性、老化特性、水溶性、消化率等功能特性，功能特性的改变可进一步扩大淀粉的应用范围。本文主要论述了小麦淀粉主要改性方法（物理改性、化学改性、酶法改性及复合改性）的改性机制及改性后淀粉性质的变化，并总结了改性小麦淀粉的相关制品以及改性小麦淀粉在不同领域中的应用, 以期为改性小麦淀粉在食品及工业的应用提供参考。     

豆渣固态发酵过程中主要营养成分及抗氧化特性变化

目的：研究豆渣固态发酵过程中主要营养成分及抗氧化特性的动态变化,为利用豆渣开发功能性食品或配料提供理论参考。方法：分别以米根霉、少孢根霉为发酵菌种对豆渣进行固态发酵,测定发酵过程中还原糖含量、可溶性蛋白含量、纤维素酶活力、糖化酶活力、蛋白酶活力及还原力、2,2’-联氮-二3-乙基-苯并噻唑-6-磺酸二铵盐（2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid),ABTS）自由基清除能力、Fe2＋螯合能力为评价指标的抗氧化活性的变化。结果：与未发酵豆渣相比,还原糖含量、可溶性蛋白含量、纤维素酶活力、糖化酶活力、蛋白酶活力均随着发酵时间的延长而增加。豆渣经米根霉发酵24 h,其还原力、ABTS＋·清除活性、Fe2＋螯合能力分别提高了1.63、1.48、2.82 倍;经少孢根霉发酵24 h,分别提高了1.88、1.63、3.18 倍。结论：用米根霉和少孢根霉发酵豆渣可以提高豆渣的营养成分及抗氧化活性。     

Enzymatic modification as a tool to improve the functional properties of heat‐processed soy flour

BACKGROUND: There are a number of antinutritional factors present in soybeans that exert a negative impact on the nutritional quality of the protein. Among those factors that are destroyed by heat treatment are protease inhibitors and lectins. Protease inhibitors show antinutritional effect and moreover the digestibility of the protein is limited by the presence of these antinutrients. The aims of the present study are (1) to study the effect of autoclaving on the trypsin inhibitor inactivation, nitrogen solubility and protein digestibility of defatted soy flour and (2) to study the effect of enzymatic modification on the functional properties of autoclaved soy flour. RESULTS: The solubility of the soy flour decreased with increase in autoclaving time. Partial hydrolysis of the autoclaved soy flour increased its acid solubility (pH 4.5) from 17% to 56% over a control value of 24% without affecting its functional properties. Inactivation of trypsin inhibitors improved the protein digestibility of soy flour from 25% to 95%. Particle size analysis of the autoclaved flour indicated the formation of soy protein aggregates, which resulted in poor solubility. The enzymatic modification of autoclaved soy flour resulted in its property as a good emulsifying agent with an emulsion capacity of 118 ± 4 mL. CONCLUSION: Enzymatic modification of the heat‐processed soy flour increased its solubility and other functional attributes. The increased acid solubility would be advantageous in the utilization of soy proteins in acidic foods. Thus the autoclaved and partially modified soy flour is a potential source for specific functional foods. Copyright © 2007 Society of Chemical Industry     

Drying kinetics and quality of okara dried in a jet spouted bed of sorbent particles

Okara or soy residue is a byproduct of soymilk and tofu production process. Okara has high protein content and can be used as an ingredient in many food products or can be used as animal feed. However, okara deteriorates rapidly; hence raw okara must be dried as early as possible under appropriate conditions. Drying could also help eliminating undesirable antinutritional factors in okara. The present study investigated the feasibility of drying okara using a combined convection-sorption drying, i.e., the use of a jet spouted bed of sorbent particles. The effects of various parameters such as drying air temperature and velocity, mass ratio of sorbent particles to okara, and initial bed height of okara on the drying kinetics were investigated. Also, various quality attributes of okara viz. color, oxidation level, rehydration ability, urease activity and protein solubility as well as the specific energy consumption during drying were investigated in both low- and high-temperature ranges.     

Pea pod, broad bean pod and okara, potential sources of functional compounds

Disposal of by-products generated by plant food processing represent an important problem in the industry, but these by-products are also promising sources of compounds which may be used for their technological or nutritional properties, and today they are considered as a possible source of functional compounds. This work has contributed to the knowledge of three legume by-products, pea pod (Pisum sativum L.), broad bean pod (Vicia faba L.) and okara from soybean (Glycine max L.). These three by-products have in common that their major fraction is dietary fibre (pea pod: 58.6 g/100 g; okara: 54.3 g/100 g; broad bean pod: 40.1 g/100 g). Sucrose, glucose and fructose are the most important soluble sugars in both pods; however α-galactosides (stachyose and raffinose) are in greater concentration in okara. Protein is also a considerable component, although in higher amount in okara than in pods. Okara presents a large quantity of fat however both pods show similar low contents. Linoleic acid is the most important fatty acid; oleic acid is remarkable in okara and pea pod and linolenic acid in broad bean pod. Mineral amount is major in by-product pods than in okara, and the most important minerals are potassium, calcium and iron.     

改性豆渣膳食纤维的理化性质、结构及其益生活性研究

以豆渣膳食纤维为对象,分别采用高速剪切、复合酶解、高速剪切协同酶解改性豆渣膳食纤维,分析其理化性质、结构以及益生活性的变化。结果表明,3种改性方法均能显著改善豆渣膳食纤维的持水性、膨胀力和持油力(P<0.05)。改性后的豆渣膳食纤维可溶性组分增多,粒径减小,微观结构变得疏松多孔;傅里叶变换红外光谱分析结果表明,改性后的豆渣膳食纤维特征吸收峰的分布未发生明显变化,部分峰强度减弱;X射线衍射结果表明,改性处理并未改变豆渣膳食纤维晶体构型。体外发酵实验表明,改性豆渣膳食纤维对嗜酸乳杆菌和乳双歧杆菌均有一定的促进增殖作用,其中对嗜酸乳杆菌的增殖作用更显著;3种改性方式中,高速剪切协同酶解改性制备的豆渣膳食纤维的益生活性最高,主要体现在提高益生菌活菌数和降低培养基pH。因此,高速剪切协同酶解可作为一种改性豆渣膳食纤维的优良方法,提升膳食纤维的理化性质和益生活性,为其在功能食品中应用提供参考。     

Effect of processing on functional properties of animal blood plasma

A number of functional and physical properties such as solubility, foam capacity, emulsifying stability and interfacial tension were compared for standard plasma, plasma decationed by ion exchange and plasma deionized by ultrafiltration (UF). The changes in functional properties can determine the use of a protein as an additive to a food product or invalidate its use. All samples had good functional properties and hence could be used in the formulation of food products. Results showed that ion exchange and UF improved emulsifying capacity while having little effect on the other functional properties.     

Properties of acetylated potato protein preparations

The purpose of the present study was to determine the influence of protein isolation from potato juice and acetylation on the chemical composition and chosen functional properties of obtained preparations. Potato protein preparations used for the experiment were obtained by thermal coagulation and membrane technology. Preparations containing thermal coagulated (PPI) and native (PPC) protein, respectively, were subjected to the chemical modification by acetylation with the use of different doses of acetic anhydride. Changes in chemical composition (total and coagulable protein content, ash content and amino acid composition), functional properties (water holding capacity, oil holding capacity, protein solubility index, emulsification properties as well as foam capacity and stability) and extent of chemical modification were determined. The chemical composition and functional properties of obtained preparations were significantly different (p < 0.05).     

Effect of conjugation with glucosamine on the functional properties of lysozyme and casein

BACKGROUND: Modification with carbohydrates usually changes the functional properties of proteins. Such modification might make non‐conventional food proteins (such as plant and microbial proteins) more applicable for human consumption. The purpose of this research was to conjugate glucosamine to lysozyme and casein using a water‐soluble carbodiimide and to investigate the effect of conjugation on the functional properties of these proteins. RESULTS: Glycosylation with glucosamine converted casein to high‐molecular‐weight species which appeared as diffuse bands in sodium dodecyl sulfate polyacrylamide gel electrophoresis. Approximately 2 and 0.11 mol of glucosamine was attached to 1 mol of casein and lysozyme respectively. Both conjugated proteins exhibited improved solubility at different pHs (3 and 6) and different temperatures (25, 45 and 60 °C), increased heat stability and better emulsifying activity, emulsion stability and foaming capacity compared with the unmodified proteins (P < 0.05). CONCLUSION: These changes might increase the applicability of lysozyme as a natural antimicrobial and casein as a protein ingredient in different food systems. Copyright © 2008 Society of Chemical Industry     

Protein glycosylation: a promising way to modify the functional properties and extend the application in food system

Abstract

Modification of functional properties by glycosylating with polysaccharides is an effective solution to improve the internal disadvantages of native proteins. Generally, protein glycosylation belongs to the first stage of the Maillard reaction in essence. Dry-heating, wet-heating, and their combination are the major methods for the preparation of protein-polysaccharide conjugates (PPC). Spectrophotometry, spectroscopy, electrophoresis, calorimetry, chromatography, and mass spectrometry are confirmed to be the most effective methods for the identification of PPC. After glycosylation, functionalities of the native protein, including solubility, rheological properties, emulsifying properties, foaming properties, gel property, film-forming properties, thermal stability, antioxidant activity, allergenicity, and antibacterial properties, are improved. The PPC is extensively used as an encapsulation or a delivering material in order to improve the bioaccessibility of bioactive compounds in food system. Some new applications in food processing could be explored using PPC as an ingredient based on the improved functional properties, such as 3-dimensional printing food, gelled food, and colloid food. Furthermore, the model of protein glycosylation and the application of PPC in food processing could be extended to other protein modification to broaden the exploitation of native protein resource for the processing of novel foods.     

High hydrostatic pressure improves the functionality of dietary fibre in okara by-product from soybean

The combined effect of high hydrostatic pressure (HHP) and controlled temperature on total (TDF), soluble dietary fibre (SDF) content, and its associated hydration properties were assayed in okara, a rich-in-insoluble dietary fibre residue from the soydrink- and tofu-making process of soybean. TDF in starting unprocessed okara was 45.7% and its SDF to TDF ratio was 4.6. When dry, hydrated and autoclaved okara samples, were subjected to HHP-treatment (200 and 400 MPa) at 30 and 60 °C, the amount of SDF went up by more than 8-fold. At 200 MPa, TDF was not significantly different from control, but at 400 MPa values varied from 38.1 to 64.8%. In vitro physicochemical properties of okara were also modified by HHP-treatment. Therefore, the effect of a combined treatment with hydration, temperature and HHP-technology on the improvement of the soluble fibre fraction (%) and functionality of certain vegetable by-products from the food industry could be very useful for the elaboration of food ingredients with potential health-promoting effects.Industrial relevanceThis article deals with the effect of HHP-treatment on dietary fibre fractions and associated physicochemical properties in okara by-product from soybean. Results suggested that the higher the hydrostatic pressure and temperature applied, the higher the ratio of soluble to total dietary fibre in okara. Likewise, the effect of combined hydration, mild temperature, and HHP-treatment could increase the soluble fraction (%) of other rich-in-insoluble dietary fibre vegetable by-products, which could potentially be used as valuable ingredients of new functional foods.     

Functional properties of acetylated and succinylated sunflower protein isolate

Sunflower protein isolate was acylated with acetic and succinic anhydride. Succinylation changed the electrophoretic mobility, decreased the lysine and chlorogenic acid content and bulk density, increased the aqueous solubility, shifted the isoelectric point and increased the absorption, emulsification and foaming properties. Acetylation improved the functional properties of the protein to a much lesser extent. Implication of these changes is discussed with reference to food applications.     

不同离子液体处理对豆渣膳食纤维成分变化及物化特性的影响

为明析离子液体对豆渣膳食纤维成分及物化特性的影响,从而拓宽豆渣在食品中的应用,以富含水不溶性膳食纤维(IDF)的鲜豆渣为原料,研究不同种类离子液体处理后膳食纤维成分变化和物化特性。结果表明:离子液体处理可以显著提高豆渣中水溶性膳食纤维(SDF)含量,其提高效果随着离子液体阳离子基团的延长而减弱,含乙酸根的离子液体的提高效果优于含氯离子的离子液体。1-乙基-3-甲基咪唑乙酸盐的效果最好,可将豆渣中SDF含量从最初5.97×10-2 g/g提高到0.17 g/g,SDF/IDF比值从0.17提高到0.69。离子液体处理改变了豆渣中SDF和IDF的单糖组成,豆渣的微观结构因溶胀而变形,结晶结构遭到破坏。离子液体处理后,豆渣膳食纤维的持水力增加10%,持油力增加16%。离子液体可作为提高豆渣中SDF含量,改善豆渣膳食纤维水合性质的有效途径。     

Pulse proteins: Processing,characterization, functional properties and applications in food and feed

Pulses (pea, chickpea, lentil, bean) are an important source of food proteins. They contain high amounts of lysine, leucine, aspartic acid, glutamic acid and arginine and provide well balanced essential amino acid profiles when consumed with cereals and other foods rich in sulphur-containing amino acids and tryptophan. The protein content of most pulse legumes fall within the range of 17–30% (d.w.b.). Apart from their nutritional properties, pulse proteins also possess functional properties that play an important role in food formulation and processing. Examples of such functional properties include solubility, water and fat binding capacity and foaming. Various research studies indicate that some functional properties of pulse proteins may be comparable to those of other frequently used proteins such as soy and whey. The functional properties of pulse proteins have been exploited in the preparation and development of products such as bakery products, soups, extruded products and ready to eat snacks. The growing body of research on the health benefits associated with the consumption of pulses has increased interest in developing innovative technologies to expand the use of pulses in food products. At the same time, there are growing global food security challenges and protein malnutrition continues to be a problem in many countries around the world. Pulses, especially when blended with cereal proteins, may offer a promising alternative source for nutritional and functional proteins. This review provides an overview of the characteristics of pulse proteins, current and emerging techniques for their fractionation, their major functional properties and opportunities for their use in various applications.     

Production of okara and soy protein concentrates using membrane technology

Microfiltration (MF) membranes with pore sizes of 200 and 450 nm and ultrafiltration (UF) membranes with molecular weight cut off of 50, 100, and 500 kDa were assessed for their ability to eliminate nonprotein substances from okara protein extract in a laboratory cross-flow membrane system. Both MF and UF improved the protein content of okara extract to a similar extent from approximately 68% to approximately 81% owing to the presence of protein in the feed leading to the formation of dynamic layer controlling the performance rather than the actual pore size of membranes. Although normalized flux in MF-450 (117 LMH/MPa) was close to UF-500 (118 LMH/MPa), the latter was selected based on higher average flux (47 LMH) offering the advantage of reduced processing time. Membrane processing of soy extract improved the protein content from 62% to 85% much closer to the target value. However, the final protein content in okara (approximately 80%) did not reach the target value (90%) owing to the greater presence of soluble fibers that were retained by the membrane. Solubility curve of membrane okara protein concentrate (MOPC) showed lower solubility than soy protein concentrate and a commercial isolate in the entire pH range. However, water absorption and fat-binding capacities of MOPC were either superior or comparable while emulsifying properties were in accordance with its solubility. The results of this study showed that okara protein concentrate (80%) could be produced using membrane technology without loss of any true proteins, thus offering value addition to okara, hitherto underutilized. Practical Application: Okara, a byproduct obtained during processing soybean for soymilk, is either underutilized or unutilized in spite of the fact that its protein quality is as good as that of soy milk and tofu. Membrane-processed protein products have been shown to possess superior functional properties compared to conventionally produced protein products. However, the potential of membrane technology has not been exploited for the recovery of okara protein. Our study showed that protein content of okara extract could be improved from approximately 68% to approximately 81% without losing any true proteins in the process.     

Functional Characteristics of Milk Protein Concentrates and Their Modification

A major deterrent to the usage of milk protein concentrate (MPC), a high-protein milk product with increasing demand as a food and sports drink ingredient, has been its poor functional characteristics when compared with other milk protein products such as whey protein concentrate and sodium caseinates. This review discusses the recent research on functional properties of MPC, focusing on factors that may contribute to the poor functional characteristics before, during, and after production. Current research, methods employed, and new understanding on the causes of poor solubility of MPC at mild temperatures (about 20°C) has been presented, including loss of solubility during storage as these areas have received unprecedented attention over the past decade, and also affects other useful functional properties of MPC, such as emulsifying properties, gelation, and foaming. Processing methods, which include heat treatment, high-pressure application, microwave heating, ultrasound application, and enzyme and salts modification, have been used or have potential to modify or improve the functional properties of MPCs. Future research on the effects of these processing methods on the functional properties, including effects of enzyme hydrolysis on bitterness and bioactivity, has also been discussed.     

脱蛋白结合超微粉碎对豆渣膳食纤维成分及功能特性影响

研究脱蛋白方法结合超微粉碎处理豆渣对其化学组成和功能特性的影响,当豆渣样品进行酶或碱处理时,它的总膳食纤维(TDF),不溶性膳食纤维(IDF)的质量分数分别增加了18.6-32.9%,22.6-34.4%,并且它们的功能特性(持水力,膨胀力和持油力)显著(p < 0.05)增加,但可溶性膳食纤维(SDF)质量分数与处理前豆渣没有显着差异。经超微粉随后,随着豆渣膳食纤维粒径减小,豆渣膳食纤维中可溶性膳食纤维质量分数提高了170% 以上,持水力和膨胀力显着下降(p < 0.05),持油力先下降后上升。结果表明,应用碱性蛋白酶和超微粉碎进行前处理,得到的豆渣中TDF和SDF的含量最高,这可能是在食品中加工高质量膳食纤维的潜在方法。