The impact of sour cherry juice (Prunus cerasus) on reducing glucose release during in vitro starch digestion

Sour cherry (Prunus cerasus) juice of the Hungarian cultivar Érdi bőtermő was tested during in vitro co-digestion with white bread to obtain information on its impact on starch digestion. Co-digestion experiments of a standard white bread were carried out with either i) sour cherry juice (SCJ), ii) SCJ enriched with dissolved sour cherry polyphenols (DISP), iii) SCJ enriched with insoluble constituents associated polyphenols (INSP), or iv) SCJ control solution (polyphenol and insoluble constituents-free cherry juice simulant), v) buffered control, vi) control solution with added chlorogenic acid (5-CQA). Digestion simulation was based on the Infogest method but applying semi-dynamic gastric phase. Samples taken at different time points were analysed to quantify the released glucose. Based on the measured glucose content, a method for calculating the in vitro glycaemic index (GI)-like value in agreement with the ISO standard is described. Results show that sour cherry juice can hinder starch digestion of white bread and reduce glucose release. Although the effect is limited to the gastric phase of digestion it is reflected in the reduction of GI. The cause of the observed effect was associated to two key factors: i) the acidity of the juice, and ii) the presence of inherent polyphenols.