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Bile acid retention of structurally modified common bean matrices during in vitro digestion

T Lin1, S O’Keefe1 and C Fernández-Fraguas1,2

1Department of Food Science and Technology, Virginia Tech, Blacksburg 24060, VA, US

2Macromolecules Innovation Institute, Virginia Tech, Blacksburg 24060, VA, United States

The cholesterol-lowering properties of common beans (Phaseolus vulgaris L.) are primarily attributed to their high content in dietary fibre (DF). The most documented mechanisms underlying the lowering of blood cholesterol involve binding of bile acids (BA) and are related to the physicochemical properties of soluble DF1. The functionality of DF might also depend on the nature and distribution of DF fractions - soluble and insoluble, including resistant starch (RS) – and it is controlled by the complexity and structure of the food matrix2.

While the ability of legume seeds to sequester BA has been previously studied, whether microstructural and compositional modifications of the bean matrix influence this capacity is not yet understood. Additionally, whether different BA can influence the in vitro binding ability of beans also remains unknown.

In this study, we have examined the in vitro BA-binding ability and BA-binding preferences of bean matrices varying in (micro)structure, and content and distribution of DF fractions. Thermal and high-hydrostatic pressure processing were applied to generate different bean microstructures. The BA-binding ability of these matrices was determined under physiological conditions by simulating oral, gastric, and duodenal in vitro digestion using a mixture of primary BA (TC, GC, TCDC, GCDC). We used a dialysis approach and compared it with a centrifugation method using both structurally modified bean matrices and isolated DF fractions. Individual unbound BS were quantified separately by reversed-phase HPLC without prior deconjugation and derivatization

Both thermal and pressure treatments were able to generate different bean microstructures, modify DF fractions and RS content, and further impact the ability of beans to retain BA during in vitro digestion. A high non-linear correlation between BA-binding ability and both, IDF content and viscosity of bean matrices, was observed. Preliminary results showed that bean matrices preferentially retained glycine-conjugated and more hydrophobic di-hydroxy-BA, suggesting a hydrophobic interaction between bean components and BA. Our findings support the hypothesis that a single mechanism is unlikely to explain the ability of beans to bind BA, and instead a combination of combination of viscosity, microstructural and compositional factors are triggering the BA-binding capacity of beans.

References:

1 Gunness, P., & Gidley, M. J. (2010). Mechanisms underlying the cholesterol-lowering properties of soluble dietary fibre polysaccharides. Food & Function, 1(2), 149

2 Grundy, M. et al., (2017). The impact of oat structure and b-glucan on in vitro lipid digestion. Journal of Functional Foods, 38, 378–388

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