Hazard, B. A. | Search bioRxiv

bioRxiv2022

Development of a high-throughput starch digestibility assay reveals wide variation among the A. E. Watkins wheat landrace collection

Breeding for less digestible starch in wheat can improve the health impact of bread and other wheat foods. Based on an established in vitro starch digestibility assay by Edwards et al. (2019) we developed a high-throughput assay to measure starch digestibility in hydrothermally processed samples for use in forward genetic approaches. Digestibility of purified starch from maize and wheat was measured using both methods and produced comparable results. Using the high-throughput assay, we estimated starch digestibility of 118 wheat landraces from the core Watkins collection and found wide variation across lines and elite UK varieties, (20% to 40% and 31% to 44% starch digested after 90 minutes respectively). Sieved flour fractions and purified starch for selected lines showed altered starch digestibility profiles compared with wholemeal flour, suggesting that matrix properties of flour rather than intrinsic properties of starch granules conferred the low starch digestibility observed.

biochemistry↗

bioRxiv2022

Impact of storage on starch digestibility and texture of a high-amylose wheat bread

Staling is a complex process that determines the shelf-life of baked products like bread. Breads made using high-amylose flour may elicit a lower glycaemic response, with benefits for health, however the impact of storage on novel high-amylose wheat foods structure are not known. We investigated the staling behaviour of high-amylose bread made from a starch branching enzyme II (sbeII) wheat mutant compared to a wild-type (WT) control, by measuring starch digestibility (susceptibility to amylolysis) and bread texture over time in different storage conditions. Breads prepared from sbeII and WT control wheat flours were subjected to fresh, refrigerated and frozen storage, and starch digestibility and crumb texture were measured up to three days. Starch from sbeII flour was characterised by a larger proportion of long chains resulting in increased amylose content, typical of sbeII mutant wheat. Starch in sbeII bread was less susceptible to amylolysis when freshly baked (~17% difference of starch digested at 90 min, C90) and after storage (26%-28% C90 difference, depending on the storage condition), compared to the WT control. Texture of freshly baked sbeII bread was similar to the WT control; storage conditions affected the progression of crumb firming and resilience to touch for both breads, but changes in crumb texture were less pronounced in sbeII bread. Overall, sbeII bread was less prone to staling than conventional WT bread during the first three days of storage, particularly when stored in the fridge or at room temperature.

biochemistry↗