Differences in endosperm cell wall integrity in wheat (Triticum aestivum L.) milling fractions impact on the way starch responds to gelatinization and pasting treatments and its subsequent enzymatic in vitro digestibility

Abstract

Wheat grain roller milling disrupts starch containing endosperm cell walls and extracts white flour. Many wheat based food processes involve simultaneous use of heat and water which then cause starch to gelatinize and enhance its digestibility. In this study, the impact of starch enclosure in intact endosperm cell walls on starch physicochemical properties and digestibility was investigated. Wheat kernels milled into coarse farina (average particle size: 705 μm) contained a substantial portion of intact cells and exhibited 15–30% lower Rapid Visco Analyzer peak viscosity readings than flour and fine farina (average particle size: 85 and 330 μm, respectively) since its higher level of intact cell walls limited the swelling of the enclosed starch. Xylanase use in situ substantially degraded coarse farina cell walls and increased their swelling and viscosifying potential. Following full gelatinization of the different samples, the starch in coarse farina was digested at a 40% lower rate in an in vitro gastrointestinal digestion assay, but still to a similar extent to that in fully gelatinized flour. This indicates that while wheat endosperm cell walls are permeable to pancreatic amylase, they can sufficiently slow down enzyme diffusion. When xylanase treatment was performed after starch gelatinization and pasting, the rates of starch digestion were similar for all samples evidencing that cell walls act as physical barriers to enzyme diffusion and thus retard its digestion. The present findings offer ways to produce wheat-based foods with sustained energy release benefits.