In vitro and in vivo glycemic responses and antioxidant potency of acorn and chickpea fortified gluten-free breads

Abstract

Gluten-free (GF) breads, based on rice flour and corn starch (50:50), were fortified with a mixture of acorn flour (ACF) - chickpea flour (CPF) at 30% substitution level of corn starch (i.e., rice flour:corn starch:ACF-CPF 50:20:30) using different flour blends of ACF:CPF at weight ratios of 5:25, 7.5:22.5, 12.5:17.5, and 20:10 in order to improve the nutritional quality and antioxidant potential as well as the glycemic responses of the GF breads; a control GF bread with rice flour:corn starch 50:50 ratio was also prepared. ACF was richer in total phenolic content than CPF, whereas CPF was characterized by higher amounts of total tocopherols and lutein compared to ACF. For both ACF and CPF as well as the fortified breads, the most abundant phenolic compounds were gallic (GA) and ellagic (ELLA) acids as found by HPLC-DAD analysis, while a hydrolysable tannin, valoneic acid dilactone, was also identified and quantified by HPLC-DAD-ESI-MS in high amount in the ACF-GF bread having the highest level of ACF (ACF:CPF 20:10), even though it seemed to decompose during breadmaking, possibly into GA and ELLA. Therefore, the inclusion of these two raw materials as ingredients in GF bread formulations resulted in baked products with enhanced concentrations of such bioactive compounds and higher antioxidant activities, as indicated by three different assays (DPPH, ABTS and FRAP). The extent of glucose release, as evaluated by an in vitro enzymic assay, was negatively correlated (r = -0.96; p = 0.005) with the level of added ACF, and was significantly reduced for all ACF-CPF fortified products when compared with their non-fortified GF counterpart. Furthermore, the GF bread containing a flour mixture of ACP:CPF at a weight ratio of 7.5:22.5, was subjected to an in vivo intervention protocol to assess the glycemic response when consumed by 12 healthy volunteers; in this case, white wheat bread was used as reference food. The glycemic index (GI) of the fortified bread was significantly lower compared to the control GF bread (97.4 versus 159.2, respectively), which along with its lower amount of available carbohydrates and the higher level of dietary fibers, resulted in a significantly reduced glycemic load (7.8 versus 18.8 g per serving of 30 g). The present findings underlined the effectiveness of acorn and chickpea flours in improving the nutritional quality and glycemic responses of fortified GF breads with these flours.

Keywords: Antioxidants; Ellagic acid; Gallic acid; Glycemic load; Hydrolysable tannin; In vitro digestion; In vivo glycemic index; Phenolic compounds.