Microstructural and rheological characterization of NaCl-induced gels of soy protein isolate and the effects of incorporating different galactomannans

Abstract This study aimed to evaluate the properties of NaCl-induced gels of soy protein isolate (SPI) in the presence and absence of different galactomannans (locust bean gum - LBG and guar gum – GG) at pH 7. For this purpose, systems with different ionic strengths (100 – 400 mM), protein concentrations (10-14%, w/v), and galactomannan concentrations (0 – 0.5%, w/v) were evaluated regarding their visual aspects, microstructural organization, and rheological properties. Among the self-supported protein gels (produced with at least 14% SPI and 200 mM NaCl), those with 300 mM NaCl presented higher G’, G”, and Eg values and lower compliance values due to their denser microstructural organization. Such formulations were, therefore, selected for mixed (protein + polysaccharide) gel production. The incorporation of 0.4% and 0.5% galactomannans resulted in heat-induced gels, so only samples with 0.1-0.3% galactomannans were characterized. All mixed gels presented incomplete demixing, but the extent of this phenomenon varied with the concentration of galactomannan and its branching degree. LBG demonstrated higher capacity to self-associate, resulting in gels with higher degrees of phase separation; higher G′, G′′, and Eg values; and lower compliance values than GG. Although the galactomannans did not significantly increase the strength of the SPI gels, they increased the stability of the systems at room temperature.