Gelation properties of salt-extracted pea protein isolate catalyzed by microbial transglutaminase cross-linking

Abstract

Gelation is a fundamental functional characteristic of plant proteins. In this paper, a salt-extracted pea protein isolate (PPI) was mixed with microbial transglutaminase (MTG) to produce gels and the gelation properties were studied. When the MTG level increased, the magnitude of both the G′ and G″ moduli also increased, which means the gel strength increased. A second order polynomial equation was used to describe the relationships between the G′, G″ modulus and TG level. It was found that with increased heating and cooling rate at the same MTG level, G′ and G″ tended to decrease, resulting in a weaker gel. This was attributed to the rearrangement time of pea protein molecules; slower heating and cooling rates enabled protein molecules to have more time to rearrange and therefore form a stronger gel. At the same MTG level, higher pea protein concentration resulted in higher G′ and G″ values and a power law relationship was found between G′ and pea protein concentration or G″ and pea protein concentration. Frequency sweep data of PPI show that the MTG treatment resulted in higher G′ values and lower tan delta values, indicative of a stronger more elastic gel. The minimum gelation concentration was found to be 3% (w/v) with 10 U MTG treatment, lower than 5.5% required when no MTG was present. When compared to PPI and soy protein isolate (SPI) with and without 10 U MTG treatment, the gel strength of PPI with MTG was stronger than that of SPI with MTG treatment, whereas the opposite was true without the MTG treatment. SDS-PAGE showed that at the same pea protein concentration, higher MTG level induced more cross-linking as fainter bands were seen on the gel and there was a shift in the relative intensities of the bands in the molecular weight range of 35–100 kDa.