Effect of denaturation during extraction on the conformational and functional properties of peanut protein isolate

Peanut protein isolate (PPI) was extracted by alkali dissolution and acid precipitation from defatted peanut flour. The effects of extraction conditions on the denaturation and functional properties of PPI were investigated. In comparison with native peanut protein (NPP) which was extracted by ammonium sulfate, the PPI extracted by alkali dissolution and acid precipitation had a higher extent of denaturation. Arachin was affected more easily by the extraction process than conarachin and led to a noticeable decrease of thermal stability of PPI. PPI contained much lower sulfhydryl and disulfide bond contents than NPP. The analyses of intrinsic fluorescence spectra indicated a more compacted tertiary conformation of NPP than PPI. Extraction process influenced the functional properties of PPI, such as protein solubility, emulsifying activity index and foaming capacity. The relatively poor functional properties of PPI might be associated with protein denaturation/unfolding and subsequent protein aggregation.

Industrial relevance

Peanut is an important oilseed crop and a well-accepted food. After oil production through thermal treatment, the defatted peanut flour is the main byproduct, which possesses a large amount of proteins. However, due to the low extraction yield and poor functional properties of these proteins, they are not well utilised in industry till now. In this work, peanut proteins were extracted by two techniques. The results indicated that extraction technique could significantly modify the functional properties of peanut proteins. Therefore, this work is helpful for industrial utilisation of peanut proteins.     

Improvement of functional properties of peanut protein isolate by conjugation with dextran through Maillard reaction

Reaction mixtures containing peanut protein isolate (PPI) and dextran (1:1 weight ratio) were dry-heated at 60 °C and 79% relative humidity for 7 days. SDS-PAGE analysis indicated that PPI had become complexed with dextran to form conjugates of higher molecular weight. Arachin, accounting for 50% of peanut proteins, was hard to glycosylate with dextran, which might limit the extent of glycosylation of PPI. The thermal stability of PPI was remarkably improved by mixture/conjugation with dextran. Proteins in mixtures/conjugates might have a more compacted tertiary conformation than PPI. The protein solubility of conjugates at pH 4.5-6.0 was remarkably increased compared with the PPI/mixture. Mixture with dextran could significantly improve the emulsifying and foaming properties of PPI (p < 0.05). Conjugation with dextran could further enhance emulsifying and foaming properties of PPI.     

Effect of peanut protein isolate on functional properties of chicken salt-soluble proteins from breast and thigh muscles during heat-induced gelation

In this study, we investigated the impact of peanut protein isolate (PPI) on the functional properties of chicken salt-soluble protein (SSP) prepared from breast and thigh muscles during heat-induced gelation. The addition of PPI increased the water-holding capacity, gel strength and elasticity of heat-induced chicken SSP mixed gel. Breast and thigh SSP had the best gel properties at the addition of 2.5% and 3.5% PPI, respectively. Rheology indicated that thigh SSP showed higher storage modulus (G') than breast SSP. Differential scanning calorimetry showed that the addition of PPI changed transition temperatures (Tmax) and enthalpy of denaturation (ΔH) of chicken SSP. Scanning electron microscopy indicated that the PPI-treated SSP gels had more compact ultrastructures than controls. The results suggested that PPI may be a potential protein additive for improve the characteristics of SSP gelations.     

Effects of limited enzymatic hydrolysis with trypsin on the functional properties of hemp (Cannabis sativa L.) protein isolate

Effects of limited enzymatic hydrolysis induced by trypsin on the physicochemical and functional properties of hemp (Cannabis sativa L.) protein isolate (HPI) were investigated. The enzymatic hydrolysis was confirmed by sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and size exclusion chromatography (SEC). SEC and differential scanning calorimetry (DSC) analyses confirmed the presence of aggregates in the corresponding hydrolysates (with the degree of hydrolysis of 2.3–6.7%). Functional properties, including protein solubility (PS), thermal properties, emulsifying and foaming properties, and water holding and fat adsorption capacities (WHC and FAC) were evaluated. The PS was remarkably improved by the limited enzymatic hydrolysis at all tested pH values. However, the enzymatic hydrolysis led to the marked decreases in emulsifying activity index, foaming capacity and foam stability, WHC and FAC. These decreases were to a great extent related to the presence of aggregates in the hydrolysates.     

Influence of degree of hydrolysis on functional properties,antioxidant activity and ACE inhibitory activity of peanut protein hydrolysate

Functional properties, antioxidant and Angiotensin-converting enzyme (ACE) inhibitory activities of peanut protein isolate (PPI) and peanut protein hydrolysate (PPH) prepared using Alcalase, at different (10%, 20%, 30% and 40%) degrees of hydrolysis, (DH) were investigated. Hydrolysis (at DH > 10%) significantly (p < 0.05) improved the solubility (>80%) of PPI, especially in the pH range of 4–6. However, PPI showed better emulsifying and foaming properties than PPH (p < 0.05). As DH increased, ferrous ion chelating activity, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity and ACE inhibitory activity of PPH increased, while reducing power decreased (p < 0.05). Bleaching of beta-carotene by linoleic acid was suppressed better by PPI and PPH at 10% DH than of PPH at higher DH. Thus, the results reveal that DH affects functional properties, antioxidant and ACE inhibitory activities of peanut protein.     

响应面设计法优化花生分离蛋白酶解条件的研究

以花生粕为原料,利用响应面设计对其花生分离蛋白的酶解条件进行了优化。通过对花生分离蛋白水解的最佳用酶进行了筛选,确定以碱性蛋白酶Alcalase水解效果最好。在单因素实验基础上,以水解度为指标,设计了响应面分析方案,通过数学推导及实验分析,得出Alcalase可控酶解花生分离蛋白的动力学模型及相关参数:Alcalase水解花生分离蛋白的最优工艺参数为反应温度53.11℃、酶浓度为135.94μL/g、pH为8.05、预测蛋白水解度为24.15%,实际结果与拟合方程预测结果(24.57%)基本吻合。      

双低菜籽分离蛋白的酶解条件及活性肽抗氧化特性研究

以双低菜籽分离蛋白为原料,采用风味蛋白酶Flavourzyme酶解制备菜籽蛋白活性肽产品。结果表明,实验的最佳条件为：加酶量92000U／g,酶解时间6h,酶解温度50℃,酶解初始pH6．0,底物质量分数1％。在最佳条件下双低菜籽分离蛋白水解度达32．09％,氮收率达16．12％。产品双低菜籽蛋白肽具有较强的抗氧化性和羟自由基清除能力,且随着水解度的增加而增大。     

Enzymatic preparation and functional properties of wheat gluten hydrolysates

The water-insolublity of wheat gluten is one of the major limitations for its more extensive use in food processing. Wheat gluten was enzymatically hydrolyzed by several commercially available proteases (Pancreatin Trypsin 6.0S, Porcine pepsin, Pancreatin and Alcalase 2.4L) with protein recovery varying from 42.5 ± 0.7% to 81.3 ± 0.1%. The hydrolytic efficiency of these proteases on wheat gluten was also compared. Alcalase served best for the preparation of wheat gluten hydrolysates (WGHs). Thus, Alcalase-assisted hydrolysates of wheat gluten (AWGHs) with different degrees of hydrolysis (DH 5.0, 10.0 and 15.0%) were further assessed for their functionalities. All the AWGHs had excellent solubility (>60%) over a pH range of 2–12. The emulsifying and foaming properties of AWGH with relatively low DH (5.0%) were remarkably higher compared to the original gluten. However, extensive hydrolysis of gluten resulted in remarkable reduction in emulsifying and foaming properties.     

花生肽的酶法生产工艺研究

采用酶法水解制备营养性花生低肽,对其酶制剂的筛选,酶水解工艺参数,酸溶性花生肽得率与水妥度的相关性分析及酶解液的溶解性变化等进行了系统研究。     

不同干燥方法对花生蛋白功能特性的影响

以花生蛋白为原料,分别采用热风干燥、真空干燥、微波干燥和微波结合真空干燥对花生蛋白进行干燥处理,比较不同的干燥方式对花生蛋白功能特性(吸油性、持水性、乳化性、乳化稳定性、起泡性能和起泡稳定性)的影响。实验表明,微波结合真空干燥的花生蛋白不仅干燥时间短,而且具有较好的功能特性,微波结合真空干燥是一种干燥花生蛋白的适宜方法。     

Whey protein isolate polydispersity affects enzymatic hydrolysis outcomes

The effects of heat-induced denaturation of whey protein isolate (WPI) on the enzymatic breakdown of α-La, caseinomacropeptide (CMP), β-Lg A and β-Lg B were observed as hydrolysis proceeded to a 5% degree of hydrolysis (DH) in both unheated and heat-treated (80 °C, 10 min) WPI dispersions (100 g L⁻¹). Hydrolysis of denatured WPI favoured the generation of higher levels of free essential amino acids; lysine, phenylalanine and arginine compared to the unheated substrate. LC–MS/MS identified 23 distinct peptides which were identified in the denatured WPI hydrolysate – the majority of which were derived from β-Lg. The mapping of the detected regions in α-La, β-Lg, and CMP enabled specific cleavage points to be associated with certain serine endo-protease activities. The outcomes of the study emphasise how a combined approach of substrate heat pre-treatment and enzymology may be used to influence proteolysis with attendant opportunities for targeting unique peptide production and amino acid release.     

不同干燥方法对花生蛋白功能特性的影响

以花生蛋白为原料，分别采用热风干燥、真空干燥、微波干燥和微波结合真空干燥对花生蛋白进行干燥处理，比较不同的干燥方式对花生蛋白功能特性（吸油性、持水性、乳化性、乳化稳定性、起泡胜能和起泡稳定性）的影响。实验表明，微波结合真空干燥的花生蛋白不仅干燥时间短，而且具有较好的功能特性，微波结合真空干燥是一种干燥花生蛋白的适宜方法。     

不同酶切方式对乳清蛋白疏水性和乳化性的影响

采用不同的蛋白酶对乳清蛋白进行水解,考察了肽键断裂方式对乳清蛋白肽疏水性和乳化性的影响,以及乳清蛋白不同酶解产物的疏水性和乳化性的关系。结果表明:不同蛋白酶作用于乳清蛋白得到的水解产物疏水性不同,6种蛋白酶解液的疏水性均随水解度的增大而降低,其中以胰凝乳蛋白酶酶解液的疏水性下降的最慢。研究还发现,乳化性随着水解度增加而先升高后下降,以双酶复合酶解液最差。不同蛋白酶水解液的乳化性指数随疏水性指数的降低而升高,乳化性指数与疏水性氨基酸质量分数成正相关。     

Enzymatic hydrolysis of hemp (Cannabis sativa L.) protein isolate by various proteases and antioxidant properties of the resulting hydrolysates

Enzymatic hydrolysis of hemp protein isolate (HPI) by six proteases (alcalase, flavourzyme, neutrase, protamex, pepsin and trypsin) and antioxidant activities of the resulting hydrolysates, obtained for 2 and 4 h were investigated. The yield of trichloroacetic acid (TCA)-soluble peptides (Y_sp), protein composition and surface hydrophobicity (H_o) of the hydrolysates were evaluated. The results showed that the hydrolysates exhibited varying DPPH radical scavenging (with lowest IC₅₀, ∼2.3 mg/mL) and Fe²⁺⁺ chelating (with lowest IC₅₀ of 1.6–1.7 mg/mL) abilities and reducing power (with highest absorbance at 700 nm of 0.31–0.35), depending on their Y_sp and H_o values. The DPPH radical scavenging and Fe²⁺⁺ chelating abilities of the hydrolysates were positively correlated with their Y_sp or H_o values. The results suggest that enzymatic hydrolysis can be used as an effective technique to produce high value-added products of hemp proteins.     

马来酸酐酰化改性对大豆分离蛋白功能性质的影响

研究马来酸酐酰化改性对大豆分离蛋白功能性质的影响。结果表明:随着马来酸酐用量的增大,大豆分离蛋白的酰化度增大,等电点降低;随着酰化度的增大,大豆分离蛋白构象松散,色氨酸残基的微环境趋向于暴露于水的状态,亲水性增强;经马来酸酐酰化改性后,大豆分离蛋白的溶解性、发泡性、乳化性及乳化稳定性均显著提升,但泡沫稳定性有所下降。研究表明,马来酸酐酰化改性大豆分离蛋白是一种非常有前景的功能性食品添加剂。     

Functional properties and structural characteristics of phosphorylated pea protein isolate

In order to expand the application of pea proteins in the food industry, pea protein isolate (PPI) was chemically phosphorylated to improve its functional properties. Based on the comprehensive membership value (CMV) degree, the optimal condition for PPI phosphorylation modification was as follows: pH 12, modification temperature at 70 °C and an addition of 7.0% (w/v) sodium tripolyphosphate (STP). Under this condition, the solubility, emulsifying property, emulsifying stability, foaming property and oil absorption capacity of the modified PPI were improved substantially. In addition, the structure of modified PPI was characterised by scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. The results showed that the modified PPI had a smooth and uniform lamellar structure, where the content of α-helix and β-sheet structure increased, but the content of β-corner and random coil structure decreased. The thermodynamic properties were analysed by differential scanning calorimetry (DSC) and the results showed that ∆H of the modified PPI increased significantly. Finally, the optimum phosphorylated PPI was mixed with 0.4% (w/v) xanthan gum to form PPI fat mimics (PPI-FM). PPI-FM was added into mango mousse cake to reduce the amount of light cream, and the result showed up to 20% of light cream could be substituted.     

转谷氨酰胺酶交联木瓜蛋白酶水解产物改善大豆分离蛋白乳化特性的研究

为获得适宜添加到冰淇淋等冷冻食品中的大豆分离蛋白（SPI）,利用转谷氨酰胺酶交联木瓜蛋白酶酶解大豆分离蛋白产物来改善大豆蛋白的乳化特性。将样品经高压均质制成O/W型乳状液,研究不同水解程度的水解产物交联后对样品乳状液的粒度分布、表面积平均粒径、离心乳析率等的影响,同时研究了常温放置、低温放置（4℃）以及冷冻-解冻处理对酶改性蛋白乳状液聚集、聚结稳定性的影响。结果表明,SPI和中低度水解（DH2%¹0%）样品经转谷氨酰胺酶交联后乳化活性和乳化稳定性均显著提高,水解度10%样品交联后的乳化活性和乳化稳定性改善最显著。酶改性可以显著改善SPI新鲜乳状液的聚集稳定性,中度水解度（DH6%¹0%）SPI样品交联后聚集程度最低。冷藏不会明显损坏样品的聚集和聚结稳定性。冷冻-解冻处理使乳状液发生聚结现象,SPI乳状液的聚结程度最大,中度水解度（DH6%¹0%）样品交联后的聚结程度最小。因此,可将中度水解SPI交联样品用于对乳化特性要求较高的冰淇淋等冷冻食品中。      

Enzymatic hydrolysis of protein isolate from hull-less pumpkin oil cake: Application of response surface methodology

Enzymatic hydrolysis of protein isolate from hull-less pumpkin (Cucurbita pepo L.) oil cake was studied by response surface methodology, using a central-composite experimental design. The hydrolysis was carried out with an acid protease, at temperature of 30 °C and pH 3.00. Second-order polynomial model was proposed with regard to of effect of time, enzyme and NaCl concentration. The mathematical model showed good fit with the experimental data, since the R² of 0.946 indicated that 94.6% of the variability within the range of values studied could be explained by the model. A hydrolysis time of 32.5 h, enzyme concentration of 0.137% (v/v) and NaCl concentration of 0.84% (w/v) were found to be the optimal conditions to achieve the highest value of degree of hydrolysis (DH).     

Structure,trypsin inhibitor activity and functional properties of germinated soybean protein isolate

The objective of this research was to investigate the effects of germination on functional and conformational properties as well as the in vitro trypsin digestibility of soy protein isolate (SPI). The influences of germination on the molecular properties of SPI were also evaluated. The germination degraded lipoxygenase, α, α' subunits of β‐conglycinin (7S) and acidic chains of glycinin (11S) of soybean. Concomitantly, the loss of tertiary structures of SPI occurred due to the germination. The trypsin inhibitor activity of germinated SPI presented a decreasing trend, followed by an increase in the growth of hypocotyls. The in vitro trypsin digestibility of germinated SPI followed a consistent trend with the trypsin inhibitor activity. The protein solubility (PS) and emulsifying properties of SPI were improved by the germination, in a hypocotyl length‐dependent manner. The data suggest that some selected functional properties and the in vitro digestibility of soy proteins can be improved by means of the germination.