Characterizations of a pectin extracted from Premna microphylla turcz and its cold gelation with whey protein concentrate at different pHs.

In this study, the physicochemical properties of an ammonium oxalate extraction pectin (AOP) from Premna microphylla turcz was investigated. Moreover, its cold gelation with undenatured whey protein concentrate (WPC) was studied at room temperature and different pHs. Characterizations of AOP demonstrated that AOP was a linear low-methoxyl pectin rich in homogalacturonan with low branching degree of RG-I, leading to its good gelling properties. Gelation between AOP and WPC was mainly investigated by turbidity measurement, FTIR, CLSM and ITC. The results showed that an optimal complex ratio for gelation was observed at 1:5 at pH 6.0. Moreover, AOP was the backbone of the composite gel and WPC might act as crosslinking agents through electrostatic or hydrophobic interaction at different pHs. When pH was around the pH of the complex, composite gel was mainly constructed by electrostatic interaction. With the increase of pH, the electrostatic interaction between AOP and WPC gradually weakened, while the hydrophobic interaction constantly increased. When pH was higher than the pH of the complex, composite gel was mainly formed by hydrophobic interaction. The results of this study are conducive to further utilization of Premna microphylla turcz pectin to develop related food products.