In this study, composition, structure and the functional properties of protein concentrate (WPC) and protein isolate (WPI) produced from defatted walnut flour (DFWF) were investigated. The results ...showed that the composition and structure of walnut protein concentrate (WPC) and walnut protein isolate (WPI) were significantly different. The molecular weight distribution of WPI was uniform and the protein composition of DFWF and WPC was complex with the protein aggregation. H(0) of WPC was significantly higher (p < 0.05) than those of DFWF and WPI, whilst WPI had a higher H(0) compared to DFWF. The secondary structure of WPI was similar to WPC. WPI showed big flaky plate like structures; whereas WPC appeared as a small flaky and more compact structure. The most functional properties of WPI were better than WPC. In comparing most functional properties of WPI and WPC with soybean protein concentrate and isolate, WPI and WPC showed higher fat absorption capacity (FAC). Emulsifying properties and foam properties of WPC and WPI in alkaline pH were comparable with that of soybean protein concentrate and isolate. Walnut protein concentrates and isolates can be considered as potential functional food ingredients.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
•Soy protein was reduced to obtain increasing sulphydryl groups content.•Larger aggregates and more viscous dispersion were obtained when heated.•Disulphide bond content and production of disulphide ...lined polymer were decreased.•Sulphydryl/disulphide reaction was not the driving force for aggregation.
In this study, soy proteins were reduced with 0.1–10mM dithiothreitol (DTT) to obtain an increasing number of sulphydryl groups (SH) with a similar particle size. Aggregation was promoted by increasing the degree of reduction when heated (100°C, 30min), resulting in larger sized aggregates (from 40 to 70nm) and a higher viscosity of the aggregate dispersion. The disulphide bond (SS) content decreased and the less SS linked polymer, which was composed of acidic (A) polypeptide of glycinin, basic (B) polypeptides of glycinin, and a small amount of α′ and α subunits of β-conglycinin, was formed with increasing reduction degree, suggesting that SH/SS polymerisation was not the driving force for aggregation. The larger aggregates with increasing degrees of reduction were composed of more B of glycinin and β of β-conglycinin, suggesting that the A and the small amount of α′ and α in the SS linked polymer have an inhibiting effect on protein aggregates formation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
Soybean oil bodies (OBs), naturally pre-emulsified soybean oil, have great potentials to be used in foods and cosmetics. In this study, OBs were recovered from soybean aqueous extract at pH 6.8, 8.0, ...9.5, and 11.0, and recovered OBs contained decreased extrinsic protein amount and composition with increasing recovery pH. In unheated condition, particle size and viscosity decreased, whereas isoelectric point (pI) and oxidative stability increased in the order of pH 6.8-, 8.0-, 9.5-, and 11.0-OB. By heating, it was observed that 1) coalescence of OBs occurred in pH 6.8-OB emulsion, but not occurred in pH 11.0-OB emulsion; 2) pIs of all OB emulsions increased; 3) pH 9.5-OB emulsion showed the highest viscosity, followed by pH 8.0- and 6.8-OB, and pH 11.0-OB still showed the lowest viscosity; 4) gels were formed from OB emulsions with solid content of 40% except pH 11.0-OB; 5) oxidative stability was greatly improved for all OB emulsions. This study is meaningful for supplying fundamental information for selecting proper conditions for aqueous extraction of soybean OBs.
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•Particle size and viscosity of OB emulsions decreased with increasing extraction pH.•pIs and oxidative stability of OB emulsions increased with increasing extraction pH.•Coalescence of OBs occurred in pH 6.8-OB emulsion by heating.•Gels were formed from 40% emulsions of pH 6.8-, 8.0-, and 9.5-OB by heating.•pIs and oxidative stability of OB emulsions increased by heating.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
As a by-product of oil production, walnut proteins are considered as an additional source of plant protein for human food. To make full use of the protein resource, a comprehensive understanding of ...composition and characteristics of walnut proteins are required. Walnut proteins have been fractionated and characterized in this study. Amino acid composition, molecular weight distribution and gel electrophoresis of walnut proteins and protein fractionations were analyzed. The proteins were sequentially separated into four fractions according to their solubility. Glutelin was the main component of the protein extract. The content of glutelin, albumin, globulin and prolamin was about 72.06%, 7.54%, 15.67% and 4.73% respectively. Glutelin, albumin and globulin have a balanced content of essential amino acids, except for methionine, with respect to the FAO pattern recommended for adults. SDS-PAGE patterns of albumin, globulin and glutelin showed several polypeptides with molecular weights 14.4 to 66.2 kDa. The pattern of walnut proteins in two-dimension electrophoresis (2-DE) showed that the isoelectric point was mainly in the range of 4.8-6.8. The results of size exclusion chromatogram indicated molecular weight of the major components of walnut proteins were between 3.54 and 81.76 kDa.
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In recent decades, the process of lipase (LIP) activation hydrolysis and lipoxygenase (LOX) oxidation for energy supply during soybean germination has been well understood, but the formation ...mechanism of volatile flavor substances in soymilk grinding has not been understood in detail. Different model systems were prepared using protein, LOX, LIP, and triacylglycerol (TAG) derived from soybeans to study the reaction process of soymilk flavor. The study revealed that the simultaneous existence of LOX, LIP, and TAG was a necessary condition for flavor formation, and the type and amount of volatile flavor substances were related to the composition of the lipid substrates. Compared with soymilk, the model system with LOX and LIP had a high degree of similarity in the composition of volatile flavors, but there were differences in quantity. This indicates that the flavor formation of soymilk is also positively influenced by other ingredients in soymilk.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Oil bodies (OBs) are lipid-storing organelles of plant seeds; they provide energy for seed germination and seedling growth by oxidative degradation as substrate. Soybean OBs are assumed to be ...involved in the enzymatic oxidation reaction of volatile flavor formation of soymilk. In order to establish a soymilk model system with soybean OBs as the enzymatic oxidation substrate to study the formation mechanism of soymilk flavor, the effects of extraction times and extraction pH on the composition, particle size and volatile flavor of soybean OBs extracted from raw soymilk were studied. The results showed that most of the extrinsic proteins on the surface of the OBs were removed with increasing extraction times. When the extraction pH increased from 7.0 to 11.0, the relative content of neutral lipids in OBs increased by 6.22%, and the relative content of protein and phospholipids in OBs decreased by 3.23% and 2.88%, respectively. The particle sizes of the OBs gradually decreased from 424 nm to 334 nm. The concentrations of volatile flavor components also gradually decreased from 129.29 μg/L to 52.75 μg/L. The integrity and stability of the OBs were compromised when the extraction pH was ≥12.0. The pH 11.0-OBs were the appropriate substrate for the soymilk model system because of their high purity and stability, better emulsion dispersion stability, and weaker flavor. These results are of great significance for exploring the formation mechanism of soymilk flavor in soymilk model systems to further improve the flavor of soymilk.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The water absorption of soybeans during soaking is directly related to the quality characteristics and the flavor properties of soybeans for processing. In this paper, the effects of water absorption ...of soybean seed on the quality of soymilk and the release of flavor compounds were investigated during soaking at 4 °C, 25 °C, and 50 °C at different pH values. The results showed that the water absorption rate increased as the soaking temperature and pH increased, while the equilibrium value was relatively stable. Peleg's equation with good fitting of the absorption kinetics was used to predict the hydration characteristics of undehulled soybean. MALDI-TOF/TOF-MS results showed that the major released proteins are basic 7S globulin, which is released in large amounts at high temperature. The water absorption of soybean seed significantly enhanced the extraction yields of protein, fat and solids of the prepared soymilk, and alkaline soaking pH further promoted the extraction of proteins and solids. A high soaking temperature can significantly decrease the required soaking time; however, it is unfavorable to the extraction yields of fat, proteins and solids, as well as the whiteness values and the particle sizes. The beany odor compounds of soymilk mainly consisted of hexanal,
trans
-2-hexenal, 1-octene-3-ol, hexanol, and 2-pentylfuran, and their contents were positively correlated with soaking temperature. A good balance of soymilk quality and flavor compound release can be achieved with soaking conditions of 25 °C and pH 9.
The water absorption of soybeans during soaking is directly related to the quality characteristics and the flavor properties of soybeans for processing.
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IJS, KILJ, NUK, UL, UM, UPUK
Oil bodies (OBs) are lipid-storing organelles of soybean seeds and the source of substrates for the enzymatic oxidation reaction of soymilk flavour formation. However, the triacylglycerols (TAGs) in ...the OBs are surrounded by a membrane composed of phospholipids embedded with integral oleosins to prevent them from being hydrolyzed by lipase. Therefore, the specific reaction process of the OBs in the soymilk flavour formation process becomes complicated and is not well understood. In this study, the optimal substrate, OBs, were extracted by sucrose and washed with water at pH 11.0. The oxidation products (i.e., lipid hydroperoxides, and volatile flavour compounds) of the reaction systems, with OBs as substrate, showed that phespholipase A2 (PLA2) can directly hydrolyze external phospholipids (PLs) of OBs, and pancreatic lipase can hydrolyze the internal TAGs of OBs only after oleosins or PLs are hydrolyzed. Phospholipase D (PLD) cannot hydrolyze PLs of OBs. These findings are of great significance for understanding the mechanism of flavour formation in soymilk and further improving the fiavour of soymilk.
•Seven oleosin isoforms were identified.•Alkaline extraction could also remove some oleosin isoforms from oil body.•Oleosin isoforms were not glycoproteins and were thiol-containing proteins.
Oil ...body, an organelle in seed cell (naturally pre-emulsified oil), has great potentials to be used in food, cosmetics, pharmaceutical and other applications requiring stable oil-in-water emulsions. Researchers have tried to extract oil body by alkaline buffers, which are beneficial for removing contaminated proteins. But it is not clear whether alkaline buffers could remove oil body integral proteins (mainly oleosins), which could keep oil body integrity and stability. In this study, seven oleosin isoforms were identified for soybean oil body (three isoforms, 24kDa; three isoforms, 18kDa; one isoform, 16kDa). Oleosins were not glycoproteins and 24kDa oleosin isoforms possessed less thiol groups than 18kDa ones. It was found that alkaline pH not only removed contaminated proteins but also oleosins, and more and more oleosins were removed with increasing alkaline pH.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
•A simple and quick method for low TIA soymilk is supplied.•Heat-induced KTI incorporation into protein aggregates causes KTI’s TIA loss.•Heat-induced peptide bond cleavage of BBI causes BBI’s ...TIA/CIA loss.•NaCl accelerates protein aggregate formation and peptide bond cleavage of BBI.
Trypsin inhibitor activity (TIA) is an important antinutritional factor in soymilk. In this study, the effects of NaCl preaddition on TIA and the heat-induced TIA inactivation mechanisms were examined. The results showed that Kunitz trypsin inhibitor (KTI) and Bowman-Birk inhibitor (BBI) contributed 74% and 26% to raw soymilk TIA, respectively. The heat-induced quick KTI incorporation into protein aggregates was the reason for its quick TIA inactivation. The heat-induced slow cleavage of one BBI peptide bond was the reason for its slow TIA inactivation. Heat-induced protein aggregate formation had little effect on BBI inactivation owing to the fact that BBI and its degradation product tended to remain in the supernatant (197,000g, 1h) in all conditions used in this study. NaCl could accelerate the KTI incorporation into protein aggregates and the cleavage of one BBI peptide bond, which supplied a simple and quick method for low TIA soymilk processing.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
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