Barley food structure: implications for in vitro digestibility and glycaemic index

The global rise in metabolic disorders has increased interest in dietary strategies for managing postprandial blood sugar (1) . This study investigates how milling and cooking alter barley’s microstructure, influencing starch digestion and dietary fibre fermentability, with implications for the glycaemic index and gut health. Using simulated in vitro digestion models and INFOGEST protocols, we constructed digesto-grams of starch digestion over 180 minutes for four formats of processed barley (raw kibbled, raw flour, cooked kibbled, cooked flour) and a white bread reference (glycaemic index = 70) (2,3) . Using validated estimates of blood glucose disposal, simulated blood glucose response curves were constructed from the digesto-grams, allowing the calculation of in vitro glycaemic index (GI) from the areas under the simulated blood glucose response curves relative to the area for white bread (4) . The main findings from this study were: (1) GI was strongly dependent on processing. The calculated GI values are as follows: Raw kibbled 22 ± 0.8; cooked kibbled 47 ± 1.5; raw flour, 39 ± 1.4; cooked flour, 87 ±1.2. (2) The GI value was directly related to digested starch (DS), and inversely related to the amount of resistant starch (RS) remaining in the barley residues after digesting (g/ 100 g barley): Raw kibbled, DS 20 ± 0.1, RS 9.6 ± 0.2; raw flour, DS 23.41 ± 0.15, RS 4.21 ± 1.32; cooked kibbled, DS 35.22 ± 2.16, RS 1.2 ± 0.48; cooked flour, DS 46.12 ± 1.38, RS 0.20 ± 1.04. Future work will investigate how the microstructure of processed barley affects its GI and RS content. Undigested residues, varying in RS and complex carbohydrates, will be used in faecal fermentation studies to assess microbiome modulation in normal and high BMI groups, followed by investigations into their impact on satiety signalling (GLP-1/PYY).