Effects Of High-temperature Pressure Cooking Process On The Formation Of Protein Particles In Soymilk And Its Processing Characteristics

Soymilk protein subunits dissociate and reassociate to form aggregates accompanying denaturation process when soymilk is boiled under atmospheric pressure. As a result, nearly 50% of soymilk protein exists as particulate aggregates with diameters of >40 nm. The contents/characteristic of heat-induced protein particles differs among processing technologies, which significantly influenced the sensory quality and processability of soymilk. In traditional soy food production, cooking increases the temperature of soymilk through convective heat transfer under atmospheric pressure. In industrial-scale production, traditional cooking normally results in the non-uniform heating of soymilk. High-temperature pressure cooking (HTPC) enhances heat transfer efficiency by applying pressure cooking and by increasing the cooking temperature above the boiling point of water. However, studies on the effects of HTPC on the quality and processability of soymilk have been rarely performed. This study focused on the aggregation behavior of protein subunits induced by HTPC and analyzed the interactions between protein molecular in soymilk. Besides, after studying the basic composition unit of protein particle, This study also discusse the effect mechanism of soymilk particle composition and structure change on soymilk processing properties.Results showed that, comparing to traditional cooking method, HTPC promoted the formation of protein particles in soymilk and changed the properties of soymilk colloid, improving the zeta potential of protein particles in soymilk colloid, thus improving the storage stability of the soymilk. Meantime, HTPC method could improve the water holding capacity of soymilk, although Newton fluid characteristics were showed after heating, soymilk prepared by HTPC method exhibited higher viscosity. Soymilk cooked at 115 ? for 10 min exhibited a homogeneous, smooth, and creamy texture with a high acceptability in the sensory test.Although HTPC didn't change the interaction between protein and fat in soymilk, the high temperature resulted in larger denature and aggregation compared with traditional cooking method. During HTPC, more basic subunit from 11S and ?-subunit from 7S participated in protein particle formation through hydrophobic interactions, and the original acid peptides and a/a'-subunits in particle fractions of traditional cooking soymilks were dissociated to non-particle fractions. Those changes resulted the content of protein particles of soymilk particles were higher in HTPC than in traditional cooking.The basic composition of non-protein parti cle(d<20nm and d<28nm fractions)in HTPC soymilk was studied by ultra high speed centrifugation. The results showed that they were composed by a/a'-subunits of 7S or acid peptide of 11S through disulfide bonds. In HTPC soymilk, protein particles aggregated through the strong hydrophobic interactions and disulfide bonds between subunits, forming a kind of new protein particle which was different from traditional cooking soymilk. Besides, the 2-DE results analysis showed that there were more whey protein compositions involved in particle fractions, which might be another reason leading to the increasing of soymilk protein particle content in HTPC soymilk.When HTPC was applied, the content of protein particles increased, thereby contributing to the formation of a dense network of tofu gel. Thus, significant improvement of textural properties, including hardness, chewiness, and springiness, was observed. In addition, HTPC could affect the compositions of soymilk protein particles and non-protein particles, resulting the coagulation process of soymilk induced by Ca2+ become slow, which was conducive to the incorporation of water or dry matter into the gel. This process improved the tofu yield, water holding capacity, protein recovery rate and solid recovery rate.Finally, the effects of two-step HTPC method on protein particle formation and processing properties of soymil? were studied. The results showed that two-step heating method further promoted the protein aggregations, and more 11S were involved in protein particle formations, thus improving the content of soymilk protein particles. Comparing to one-section cooking, the soymilk prepared by two-section cooking exhibited higher storage modulus (G'), and the denser tofu formed to increase the hardness, springiness, and chewiness of the gel. The two-step heating method had no significantly effect on soymilk yield.