Formulation of focaccia with acorn flour from Tunisian Quercus canariensis Willd.: A strategy for lowering the glycemic index while enhancing nutritional value

Acorns have recently attracted interest as sustainable and nutritionally rich ingredient. However, the use of Quercus canariensis Willd. acorn flour has not been previously investigated in food applications. Therefore, this study aimed to valorize this ingredient in focaccia flat bread, partially replacing wheat flour, hypothesizing that its incorporation would enhance its nutritional and functional properties. Two replacement levels were considered: 15% (F15) and 30% (F30), compared with a control of 100% wheat flour (CTR). The effects of acorn flour on the nutritional, physicochemical, and technological properties of focaccia were evaluated. F30 showed significantly higher (p < 0.05) total phenolic compounds (+800%) and carotenoids (+24%) compared to CTR. The nutritional profile and mineral content were also improved, allowing the nutritional claim “source of fiber” to be applied to F30, according to EC Regulation 1924/2006. Both F15 and F30 showed a reduced predicted glycemic index (pGI), classifying them as “low glycemic index” according to the International Organization for Standardization (ISO) (pGI<55), based on an in vitro estimation of glycemic response. Acorn flour led to a more compact crumb structure, characterized by smaller pores, reduced specific volume, and greater hardness compared to the CTR. The acorn flour affected the physical properties of focaccia due to gluten dilution and fiber. Another difference was the brown color imparted by the acorn flour, which evoked a rustic, whole-grain product. The use of acorn flour is therefore a promising strategy for improving the nutritional properties and sustainability of food production.