Effects of high hydrostatic pressure and microbial transglutaminase treatment on structure and gelation properties of sweet potato protein

The effects of high hydrostatic pressure (HHP) combined with microbial transglutaminase (MTGase) on the structure and gelation properties of sweet potato protein (SPP) were investigated. MTGase induced the formation of high molecular mass aggregates of SPP by the inter-molecular cross-linking. The average particle size of SPP increased by HHP at 250–550 MPa, being increased from 249.5 nm (0.1 MPa) to 270.2 nm (550 MPa). While it was decreased by the subsequent MTGase catalysis that showed the lowest value of 200.3 nm at 550 MPa, indicating the formation of intra-molecular linkages. The amount of sulfhydryl groups and thermal denaturation temperature were increased by HHP and MTGase, with the highest value of 3.5 μmol/g protein and 80.4 °C in MTGase catalyzed SPP with 400 MPa pretreatment. Textural properties of the gels made from HHP treated SPP or those with further MTGase catalysis were both enhanced due to the covalent linkage of disulfide bonds (-S-S-) and e-(γ-glutaminyl) lysine isopeptide bonds. In addition, low-field NMR results showed an increase in corresponding area fractions of A2b and A21, being attributed to more bound or immobilized water fractions were trapped in the SPP gel matrix.