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Effect of pH on emulsification performance of a new functional protein from jackfruit seeds

Zhang, Yanjun, Zhou, Xin, Zhong, Junzhen, Tan, Lehe, Liu, Chengmei
Food hydrocolloids 2019 v.93 pp. 325-334
creaming, disulfide bonds, electrostatic interactions, emulsifying, emulsifying properties, emulsions, food industry, hydrocolloids, jackfruits, molecular weight, pH, particle size, polypeptides, protein conformation, protein isolates, seeds, solubility, thermodynamics
An important goal in the food industry is to search for new sources of functional protein, the particular interest of which in food systems are emulsification that is influenced by processing conditions. In this study, the effects of pH on emulsification performance of a protein extracted from a new source, namely, jackfruit seeds, were investigated. The molecular weights of most of jackfruit seed protein isolates (JSPI) polypeptides were approximately 10–26 kDa, and the presence of intermolecular disulfide bonds was observed. The solubility of JSPI first decreased with increasing pH, and a minimum solubility of JSPI reached at pH 4.0; then, the solubility increased as the pH increased further. Emulsions stabilized by JSPI under different pH values (3, 5, 7 and 9) were prepared. JSPI under neutral conditions displayed a higher emulsifying activity index value and the highest emulsifying stability index value, which are in line with the greater stability against creaming, lower particle size, higher moduli values under small strain, and higher flow properties. A schematic for the formation and destabilizing mechanism of the JSPI emulsion prepared at different pH values was hypothesized: 1) the JSPI emulsion was mainly stabilized by electrostatic repulsion; and 2) the destabilization of JSPI emulsion over time was related to three factors: the thermodynamic instability, the presence of competing proteins, and changes in protein conformation, which was affected by pH.