适宜含水率保持油茶籽贮藏品质

为了确定油茶籽贮藏适宜的含水率,研究了在4℃,不同含水率(7%、10%、13%、16%、20%)油茶籽贮藏期间的品质变化。结果表明,较低的含水率能较好保持油茶籽的贮藏特性及营养品质。其中,含水率为7%的油茶籽贮藏效果较好,但与10%处理效果差异不明显(P>0.05)。在整个贮藏期,含水率为7%时油茶籽可溶性蛋白下降了13.05 mg/g,油酸含量下降了2.38%,酸值、过氧化值等品质指标上升速率较慢,同时能较好保持β-谷甾醇和角鲨烯等生物活性成分;其次是10%的含水率处理。而含水率为20%的油茶籽贮藏期间可溶性蛋白下降较快,贮藏结束时为25.47 mg/g,油茶籽劣变严重,所提取的油样品质变差,营养物质含量较少,因此含水率20%的油茶籽不适宜长期贮藏。综合考虑油茶籽品质因素和处理成本,认为控制含水率在10%以下能较好保持油茶籽的贮藏品质。该研究可为科学合理地贮藏油茶籽提供参考。

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

Abstract: 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°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<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°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°C and pH value of 2.0, and this will facilitate the application of soy protein fibrillar aggregates in food industry.