蓝圆鲹酸/碱等电点沉淀法分离蛋白凝胶特性与消化特性

采用酸/碱等电点沉淀(isoelectric solubilization/precipitation,ISP)法制备蓝圆鲹肌肉分离蛋白(acid/alkaline aided protein isolate,API/KPI),并对全蛋白(total protein,TP)、肌原纤维蛋白(myofibrillar protein,MP)与分离蛋白的理化特性、凝胶特性以及消化稳定性进行比较研究。结果表明,蓝圆鲹肌肉蛋白在碱性条件下溶解性显著高于酸性条件,经优化后的API与KPI的回收率分别为65.0%与84.6%,显著高于MP(54.0%)。KPI、API与MP的脂肪与灰分含量明显低于TP,其中KPI的粗蛋白含量最高。十二烷基硫酸钠-聚丙烯酰胺凝胶电泳显示KPI与API的蛋白组成与TP相近,但KPI与API的氨基酸组成中甘氨酸与脯氨酸含量显著低于TP。质构与流变学分析结果显示,KPI与API的凝胶强度与储能模量(G’)均明显低于TP与MP,其中TP、MP与KPI的储能模量在50~55 ℃会出现明显的下降趋势,表明发生凝胶劣化现象,而API组无明显变化。扫描电子显微镜结果表明,与90 ℃相比,经55 ℃加热处理的KPI、TP与MP组凝胶结构更加疏松、多孔,这与流变学分析的结果一致。体外模拟胃肠液消化实验表明,MP具有最佳的消化性,API与KPI的消化性相当,且显著高于TP。综上所述,利用ISP制备分离蛋白可显著提高蛋白回收率,且分离蛋白的消化性明显优于TP。由于分离蛋白失去凝胶化能力,故可考虑将其应用于食品蛋白配料领域。

Gelation and Digestive Properties of Blue Round Scads (Decapterus maruadsi) Protein Recovered by Acidic/Alkaline Isoelectric Solubilization/Precipitation

In the present study, protein isolates were recovered from the muscle of blue round scads (Decapterus maruadsi) using acidic- or alkaline-aided isoelectric solubilization/precipitation. The physiochemical, gelation, and digestive properties of acid (API)- and alkali (KPI)-recovered proteins were investigated, as compared to total proteins (TP) and myofibrillar proteins (MP). D. maruadsi muscle proteins were even more soluble in alkali than in acid. The recovery yield (65.0% and 84.6%, respectively) of API and KPI were much higher as compared with MP (54.0%). API, KPI and MP contained far smaller amounts of lipid and ash, whereas KPI contained the highest protein content. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that there were no significant differences in the protein composition of TP, KPI and API. However, compared with TP, API and KPI had lower contents of Gly and Pro. Textural and rheological analysis revealed that API and KPI possessed lower gel strength and storage module G’ than TP and MP. Meanwhile, although no significant changes occurred in API, remarkable decreases in the G’ values of TP, MP and KPI were observed in the temperature range from 50 to 55 ℃, indicating the occurrence of modori phenomenon. This finding was well consistent with the microstructure observed by scanning electron microscopy (SEM), whereas KPI, TP and MP showed looser, porous and disorganized network when incubated at 55 ℃ for 30 min than at 90 ℃. The results of simulated gastrointestinal digestion showed that MP had the best digestibility among four proteins, while KPI and API possessed better digestibility than TP. In conclusion, ISP can greatly improve the recovery yield of protein from blue round scads. Due to their higher digestibility and poorer gelation ability, the use of the protein isolates as protein ingredients in food products is proposed.