Effects of high-pressure and transglutaminase, individually and simultaneously applied, on pea and soy protein isolates

Microbial transglutaminase (MTG) is an enzyme broadly used to improve the technological properties of proteins; however, many globular proteins are poorly susceptible or unsusceptible to its action. High-pressure processing (HPP) can change the conformation of proteins; thus it may be a useful tool to increase the accessibility of MTG to some proteins. Still, HPP conditions and the concentration of MTG need to be carefully studied to achieve the desired effects. The effects of combined MTG (up to 30 U per g of protein) and HPP (200–600 MPa; 5–15 minutes) on the solubility, the content of accessible sulfhydryl groups and surface hydrophobicity of pea (PPI) and soy (SPI) protein isolates were evaluated employing response surface methodology. The regression models obtained presented high coefficients of determination and high F values. Overall, all three parameters were differently affected by pressure. HPP increased solubility in both PPI and SPI (up to ∼200% at 600 MPa); however, it decreased the concentration of accessible sulfhydryl groups in PPI (∼80% at 600/10 min) and increased it in SPI (up to 28% at 200 MPa/10 min). HPP also affected the surface hydrophobicity of both protein isolates differently, decreasing it in PPI (up to ∼25% at 200 MPa/10 min) and increasing it in the SPI (up to ∼30% at 200 MPa/10 min). Non-HPP protein isolates were not affected by MTG, most likely due to the low accessibility of the enzyme to the proteins. However, when combined, HPP and MTG seem to have both synergistic and antagonistic effects, thus broadening the potential to alter the properties of these proteins. These results suggest that simultaneous HPP and MTG treatments can be used to modify the structure of proteins to tailor their techno-functional properties.