Influence of oral processing behaviour and bolus properties of brown rice and chickpeas on in vitro starch digestion and postprandial glycaemic response

PURPOSE: Oral processing behaviour may contribute to individual differences in glycaemic response to foods, especially in plant tissue where chewing behaviour can modulate release of starch from the cellular matrix. The aim of this study was to assess the impact of chewing time of two starch based foods (brown rice and chickpeas) on bolus properties, in vitro starch digestion and postprandial glycaemic excursion in healthy subjects. METHODS: In a cross-over trial participants (n = 26) consumed two carbohydrates-identical test meals (brown rice: 233 g; chickpeas: 323 g) with either long (brown rice: 41 s/bite; chickpeas: 37 s/bite) or short (brown rice: 23 s/bite; chickpeas: 20 s/bite) chewing time in duplicate while glycaemic responses were monitored using a continuous glucose monitoring device. Expectorated boli were collected, then bolus properties (number, mean area, saliva amylase activity) and in vitro starch digestion were determined. RESULTS: Longer chewing resulted in significantly (p < 0.05) more and smaller bolus particles, higher bolus saliva uptake and higher in vitro degree of intestinal starch hydrolysis (DH_S(chewing time)%) than shorter chewing for both foods (brown rice: DH_S%(23 s) = 84 ± 4% and DH_%S(41s) = 90 ± 6%; chickpeas: DH_S%(20 s) = 27 ± 3% and DH_%S(37s) = 34 ± 5%, p < 0.001). No significant effect of chewing time on glycaemic response (iAUC) (p > 0.05) was found for both meals. Brown rice showed significantly and considerably higher in vitro degree of intestinal starch hydrolysis and glycaemic response (iAUC) than chickpeas regardless of chewing time. No significant correlations were observed between bolus properties and in vitro starch hydrolysis or glycaemic response (p > 0.05). CONCLUSION: Differences in the innate structure of starch based foods (brown rice compared to chickpeas) have a larger effect on postprandial glucose response than differences in mastication behaviour although oral processing behaviour showed consistent effects on bolus properties and in vitro starch digestion. Trial registration ClinicalTrials.gov identifier: NCT04648397 (First posted: December 1, 2020). SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00394-022-02935-7.