1Human Nutrition Unit, Department of Food and Drugs, University of Parma, Parma, Italy.
2Department of Animal Science, Food and Nutrition, Università Cattolica del Sacro Cuore, Piacenza, Italy.
3Department for Sustainable Food Process, Università Cattolica del Sacro Cuore, Piacenza, Italy.
4School of Biosciences and Veterinary Medicine, University of Camerino, Camerino (MC), Italy.
5CHemistry Interdisciplinary Project (CHip), School of Pharmacy, University of Camerino, Camerino (MC), Italy.
6Department of Food, Nutrition and Environmental Sciences, Università degli Studi di Milano, Milano, Italy.
Quercus spp. fruits (acorns) have been traditionally used as animal feed, but their nutritional quality linked to their carbohydrate, fiber, fat and phytochemical contents has raised interest in including acorns in the human diet.
This study aimed to investigate the digestibility of starch and the metabolic fate of hydrolysable tannins in newly designed acorn-containing breads, using static in vitro gastrointestinal digestion and colonic fermentation models.
Acorn-based breads were prepared including different percentages of acorn flour (0%, 20%, 30%, 40%, respectively) using a sourdough fermentation process. Breads were subjected to in vitro gastrointestinal digestion, and rapidly (RDS) and slowly digestible starch (SDS) fractions were determined by measuring glucose release after 20 minutes and 120 minutes of intestinal incubation. Digested samples were then centrifuged, and the supernatants analyzed by UHPLC-MS/MS to determine the (poly)phenols’ bioaccessible fraction. The residual pellet, representing the undigested portion of the breads, was subjected to 48-hour static in vitro colonic fermentation. Fermented samples were extracted and analyzed to elucidate the catabolic pathway of (poly)phenols.
The inclusion of acorn flour into bread led to an increase of SDS and a decrease of RDS per 100 g of product, according to the increasing acorn flour content. A similar inverse relationship between SDS and RDS was observed when RDS and SDS were refereed to available starch in bread. The relevant content of SDS (≥ 40% of SDS/Av. starch) quantified in the samples, highlighted the potential impact of bread consumption in reducing post-prandial glycaemic response in vivo. After in vitro digestion, only a limited fraction of native compounds were quantified in the digested sample, suggesting a low bioaccessibility of (poly)phenols in the upper gastro-intestinal tract. On the contrary, during in vitro colonic fermentation, native tannins were degraded by the gut microbiota into ellagic acid, urolithins and low molecular weight catabolites. A total of 8 new formed-microbial catabolites (6 urolithins, 3 benzoic acids and 1 benzene derivative) were detected. The main catabolites resulted 3,8,9,10-tetrahydroxyurolithin (Uro M6), 3,8,9-trihydroxyurolithin (Uro C), derived from ellagitannin metabolism, and 1,2,3-trihydroxybenzene, derived mainly from gallotannin metabolism. Their concentration gradually increased over the incubation period with a peak at 24-hour incubation.
These findings support the inclusion of acorn flour in daily consumed cereal-based foods, as it represents a valuable source of high-quality carbohydrates and bioavailable (poly)phenols. However, these results should be confirmed through in vivo studies.
This study received funding from the European Union - Next-GenerationEU - National Recovery and Resilience Plan (NRRP) – MISSION 4 COMPONENT 2, INVESTMENT N. 1.1, CALL PRIN 2022 PNRR D.D. 1409 del 14-09-22– (AcorN: a forgotten resource to be rediscOVered and valorizEd in the production of good and heaLThY foods. "NOVELTY") CUP N. J53D23018470001.