糖接枝处理改善大豆蛋白纤维聚集体泡沫稳定性

Improvement of foam stabilty of soy protein on fibrillar aggregate by glycosylation

为了探究糖接枝对大豆蛋白纤维聚集行为和泡沫性质的影响,明确蛋白质结构与功能的关系,该研究以大豆蛋白(soy protein isolation,SPI)和乳糖(lactose)为原料,通过干热法制备糖接枝大豆蛋白(SPI-lactose conjugate,SPI-Lac),以及在酸性条件下加热诱导其形成纤维聚集体(p H值2.0),制备了一种糖接枝大豆蛋白纤维聚集体(SPI-lactose conjugate fibillar aggregates),并考察了糖接枝对大豆蛋白的纤维聚集行为及泡沫性质的影响。研究结果表明:大豆蛋白在酸性条件下(p H值2.0)经加热后会发生水解,同时水解产物不断聚集形成大分子的纤维聚集体。糖接枝导致大豆蛋白的水解速度下降,但荧光光强和粒径的结果表明糖接枝能增强纤维聚集能力。SPI-Lac在中性条件下的溶解度(p H值5.0—7.0)显著高于SPI(P<0.05),且不同时间处理的SPI-Lac纤维聚集体均能改善SPI在酸性条件下的溶解度(p H值2.0—5.0)。此外,不同时间处理的SPI-Lac纤维聚集体在酸性条件下的起泡能力均高于SPI纤维聚集体。SPI和SPI-Lac纤维聚集体的形成会导致SPI起泡能力的下降,但是短时间酸热处理形成的纤维聚集体泡沫稳定性得到显著改善。因此,糖接枝结合短时间酸热处理制备的糖接枝大豆蛋白纤维聚集体在中性条件下的泡沫稳定性显著提高(P<0.05),是合理有效的蛋白质改性方法。

To improve the solubility of the fibrillar aggregates under neutral condition and increase their functional properties, soy protein isolation （SPI） - lactose conjugate fibrillar aggregates were prepared by conjugating SPI with lactose under dry-heated Maillard reaction and then heating at pH value of 2.0 and 85＆#176;C. SPI-lactose conjugate fibrillar aggregates were detected using the dynamic light scattering （DLS） combined with Thioflavine-T fluorometry, transmission electron microscopy （TEM）, and sodium dodecyl sulphate-polyacrylamide gel electrophoresis （SDS-PAGE）. The hydrolysis kinetics of SPI-lactose conjugate showed that its fibrillar aggregation was a multi-stage process, which included the processes of peptide chain hydrolysis, self assembly, and formation of fibrillar aggregates. The protein subunit bands of SPI-lactose conjugate disappeared after heating for 6 h, while the SPI disappeared after heating for 2 h. The results suggested that glycosylation may decrease the hydrolysis rate of SPI. However, the fluorescence intensity and particle size of SPI-lactose conjugate were significantly higher than that of SPI （P＆lt;0.05）, which indicated that glycosylation could promote the growth of fibrillar aggregates and enhance the self-assembly ability of the fiber. Therefore, it can be speculated that glycosylation can promote the aggregation of protein fibrillar aggregates though it may decrease the hydrolysis rate of protein. The TEM images clearly showed that lactose was attached to the branch node of SPI-lactose conjugate fibril aggregates, which further confirmed the formation of SPI-lactose conjugate fibrillar aggregates. Moreover, the solubility of both SPI and SPI-lactose conjugate significantly increased near the isoelectric point （5.0 pH value）, while decreased under neutral condition （7.0 pH value）. Compared with SPI fibrillar aggregates, the solubility of SPI-lactose was remarkably higher under acid condition after heating treatment, which indicated that glycosylation may effectively improve the solubility of SPI under neutral conditions （6.0 pH value）. The formation of fiber aggregates improved the solubility of SPI from 6% to 40% under acid condition （pH value of 2.0-5.0）. In order to study the effect of pH value on foaming properties for the fibrillar aggregates, SPI and SPI-lactose conjugate fibrillar aggregates prepared by heating at 85＆#176;C and pH value of 2.0 were readjusted to pH value of 2.0 and 7.0. The results showed that the foaming capacity of the SPI-lactose conjugate fibrillar aggregates with different heating time was higher than SPI fibrillar aggregates, implying that glycosylation may improve the foaming capacity. The formation of fibrillar aggregates decreased the foaming capacity of SPI, but increased the foam stability under both acid condition （2.0 pH value） and neutral condition （7.0 pH value）. These results confirmed that the foam stability of SPI was improved significantly （P〈0.05） after glycosylation process and short time heating treatment under acid condition （2.0 pH value）. The improvement of foam stability for conjugate fibrillar aggregates may contribute to the fact that lactose provided some hydroxyl group and electric charge to prevent the aggregation of fibrils. Thus, it will be an effective method to improve the functional properties of SPI by glycosylation with lactose and self assembly of SPI-lactose conjugate at 85＆#176;C and pH value of 2.0, and this will facilitate the application of soy protein fibrillar aggregates in food industry.