Digestibility of sustainable muffins enriched with Tannat grape pomace

Abstract

Background: Vitis vinifera cv. Tannat, Uruguayan emblematic grape variety, is rich in bioactive phenolics, many of which remain in its abundant byproduct, grape pomace. This makes Tannat grape pomace (TGP) a promising functional ingredient. 

Objective: To analyze the residual phenolic compounds and bioactive properties of TGP after digestion and incorporate it into a muffin formulation as a functional ingredient. 

Methods: In vitro digestion simulation of TGP and muffin was assessed following the INFOGEST protocol. UHPLC-MS/MS performed phenolic compound identification. Total phenolic compounds (Folin-Ciocalteu method), antioxidant capacity (ABTS and ORAC-FL methods), and antidiabetic capacity (α-glucosidase activity inhibition) were assessed, as well as antioxidant and anti-inflammatory effects on cells. TGP was added to a muffin formulation.  

Results: After in vitro digestion, bioaccessible (BF) and colonic fractions (CF) were obtained. UHPLC-MS/MS results of TGP BF showed the presence of phenolic acids, flavan-3-ols, flavonols, and anthocyanins. TGP BF showed TPC, ABTS, ORAC-FL, and α-glucosidase lower values than TGP CF, indicating most of the TGP phenolic compounds may be retained by the grape matrix. TGP BF and CF showed intracellular antioxidant effect on CCD-841CoN colon cells and anti-inflammatory effect on RAW264.7 macrophages. The addition of TGP to the muffin formulation demonstrated increased bioactive properties (p < 0.05). However, the BF of the TGP muffin showed similar bioactive properties (p>0.05) with the control muffin (without TGP), while the CF of the TGP muffin presented higher than the control muffin (p<0.05). 

Novelty of the Study: This is the first study on TGP phenolic compound identification and bioactive properties after in vitro simulation of digestion, as well as its incorporation in muffins and confirmation of its bioactive properties after digestion. The most novel findings of the present study underline the colonic fraction of TGP and muffin with potential antioxidant and anti-inflammatory effects that may promote colon health. These findings contribute to the development of foods with confirmed functionality. 

Conclusion: The persistence of phenolic compounds and bioactive properties from TGP after digestion was confirmed, showing potential as a functional ingredient. However, these compounds appear to be non-bioaccessible when incorporated into a muffin formulation. Future studies on the microbiota effect of the TGP muffin CF are needed to state the potential as a functional food.

Keywords: digestibility, functional foods, phenolic compounds, sustainable muffins, Tannat grape pomace