From grape pomace to functional muffins: development, characterization, bioaccessibility of phenolic compounds and apparent glycemic index

Aim: Grape pomace is the main byproduct of the winemaking process and an important source of bioactive compounds, including phenolic compounds and dietary fiber, making it a viable option for developing new functional foods. This study aimed to develop a muffin partially substituted with grape pomace that would be accepted by regular consumers and to determine the bioaccessibility of the incorporated phenolic compounds and the effect of dietary fiber on the apparent glycemic index. Methods: Two substitutions with grape pomace (15% and 20%) were formulated and subjected to a consumer acceptance test. Macronutrient composition and phenolic compound content were characterized using spectrophotometry and mass spectrometry. Bioaccessibility and apparent glycemic index were determined using an in vitro digestion model. Results: The results showed an increase in dietary fiber content with the incorporation of grape pomace. In contrast, the total phenolic content increased, accompanied by a corresponding increase in ferulic acid and naringenin content. Bioaccessibility increased during the small intestine stage in samples partially substituted with grape pomace. However, this trend changed during the large intestinal stage. The apparent glycemic index in the enriched muffin (25%) was lower than that in the control (26%), indicating that the release of reducing sugars was lower in the enriched muffin. Conclusions: The addition of grape pomace increased fiber content; however, fiber reduced the bioaccessibility of phenolic compounds. Further studies are needed to explore the effect of dietary fiber on bioaccessibility and to conduct clinical trials to assess the bioavailability of phenolic compounds.