Maximizing cholesterol-lowering benefits of soy protein isolate by glycation with soy soluble polysaccharide

Abstract

The cholesterol-lowering benefits of two by-products of soybean processing, soy protein isolate (SPI) and soy soluble polysaccharide (SSPS), have been well known in the field, but it remains to be determined whether the combined use of both ingredients can produce synergic benefiting effects. In the work, we reported that the glycation with SSPS with increasing degrees of glycation (DG) progressively improved the potential cholesterol-lowering benefits of SPI. The cholesterol-lowering benefits were evaluated with an in vitro pepsin-trypsin digestion model, by determining the cholesterol-lowering activities (including cholesterol and bile acids binding capacities, and inhibition of micellar cholesterol solubilization) of the gastrointestinal digests. As compared with the conventional heating method (at 60 °C for 7 days under controlled relative humidity conditions), the microwave treatment was much more efficient and effective to form covalent SPI-SSPS conjugates with excellent cholesterol-lowering benefits. An extensive glycation (e.g., with DG values > 40%) significantly inhibited the hydrolysis of the proteins by the proteases, and greatly facilitated the formation of insoluble aggregates during the post digestion. The remarkably improved cholesterol-lowering benefits of the extensively glycated SPIs with SSPS could be largely attributed to the enhanced tendency to form the insoluble aggregates in the digests. In contrast, the improved benefits of the moderately glycated SPIs might be mainly associated with the formation of micelle-like SPI-SSPS conjugate assemblies in the digests. This is the first report to indicate that proteins and polysaccharides may produce synergic cholesterol-lowering benefits. Considering that both SPI and SSPS are important food ingredients, the results may have great implications for the development of plant protein-based functional foods with outstanding cholesterol-lowering benefits.