Abstract
The effects of heat-induced soy protein isolate (SPI) aggregation on enzymatic deamidation by protein-glutaminase (PG) and the emulsifying properties of deamidated products were investigated. The particle size distribution indicated that different aggregates were obtained by preheating SPI at three different temperatures (70 °C, 100 °C, 121 °C) for 10 min. The time-dependent degree of deamidation showed that aggregates formed by preheating treatment had a different influence on the PG deamidation reaction. Preheating treatment at 70 °C could accelerate the PG deamidation reaction and preheating treatment at 121 °C restrained this reaction. The molecular weight distribution revealed that PG deamidation caused the formation of larger aggregates. Electrophoresis analysis and the structural properties indicated that the aggregation caused by PG deamidation was probably a result of hydrophobic interaction and the formation of disulfide bonds. PG deamidation of native or preheated SPI can improve the emulsifying activity, especially in the sample preheated at 70 °C. For SPI samples preheated at 70 °C and 100 °C, the emulsifying stability increased by PG deamidation. In conclusion, preheating can influence the PG deamidation reaction and the emulsifying properties of deamidated products.
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