The association between dietary fiber and phenolic compounds allows the latter to reach the colon, where most polysaccharides undergo fermentation. This bioprocessing weakens the matrix and promotes the release of the phenolic compounds, which then exert beneficial effects on intestinal function. Although this notion is widely accepted, supporting evidence remains scarce. In this study, we subjected grape pomace skin to in vitro digestion to obtain an indigestible fraction suitable for SHIME bioreactors. Throughout these stages, we observed a sequential increase in the release of phenolic compounds, with colonic fermentation playing an important role. Although we did not observe an increase in short-chain fatty acid (SCFA) production by the gut microbiota, we performed a repeated-challenge design on differentiated Caco-2 monolayers. With this approach, we found that the phenolic-rich ferment prevented the transepithelial electrical resistance (TEER) drop on the second challenge and modulated the transcriptomic profile assessed by RNA-seq. Our findings indicate that the Caco-2 cellular responses mentioned above were SCFA-independent and likely due to the differential impact of phenolic compound load after colonic fermentation of grape pomace skin.

The growing demand for healthier and more sustainable foods has driven interest in plant-based formulations with improved nutritional and sensory quality. In this context, this study evaluated the effect of extra-virgin olive oil (EVOO) addition and different cooking methods (baking, air-frying, and deep-frying) on the nutritional composition, fatty acid profile, total polyphenol content (TPC), antioxidant capacity (ORAC, FRAP, and DPPH), and sensory acceptability of vegetable patties. Patties were prepared with or without EVOO and cooked using the three methods. Deep-frying markedly increased fat content (45–75%), whereas baking and air-frying effectively limited oil absorption (0–10%). EVOO addition increased monounsaturated fatty acids, particularly oleic acid (37.2 g/100 g DW), and enhanced the transfer of phenolic compounds to the patties. Deep-fried, EVOO-enriched samples showed the highest TPC (3.93–5.22 mg GAE/100 g DW), while raw patties exhibited the highest ORAC values (5.17–6.02 µmol TE/100 g DW). Sensory evaluation indicated that EVOO-enriched patties achieved the highest overall preference when air-fried or baked (77–89%). Overall, enriching EVOO with less oil-intensive cooking methods improved the lipid profile, antioxidant capacity, and sensory quality of vegetable patties. These findings should be interpreted within the context of a single frying cycle representative of domestic cooking practices and a sensory evaluation conducted with an untrained panel mainly composed of young adults.

Dietary fiber usually comes associated with phenolic compounds either trapped in a network formed by indigestible polysaccharides or, in some cases, bound to this matrix by covalent bonds. This natural association protects some phenolic compounds during their journey through the gastrointestinal tract, reaching the colon, where most polysaccharides undergo fermentation, weakening the matrix and promoting the release of these compounds to exert benefits by modulating intestinal function. Unfortunately, there are still difficulties in investigating the impact of the human microbiota on the release of phenolic compounds from the indigestible fraction and on their effects on the intestinal epithelium. In this study, grape pomace skin was subjected to in vitro digestion to obtain an indigestible fraction, which was further incorporated into SHIME bioreactors with human colonic microbiota. Throughout these stages, we monitored the release of phenolic compounds using HPLC-DAD. We determined the impact of a phenolic-rich indigestible fraction on the fermentative capacity of human microbiota by measuring the short-chain fatty acids (SCFA) levels and the effect of the resulting colonic ferments on the barrier properties of differentiated monolayers of Caco-2 cells by monitoring the transepithelial electrical resistance and the transcriptomic profile by RNA sequencing. Our results indicated that digestive processing sequentially increases the release of phenolic compounds and that colonic fermentation releases even more phenolic compounds trapped in the polysaccharide network. Unexpectedly, neither the phenolic-rich nor the depleted fractions increased SCFA levels in the colonic microbiota. Despite the lack of effect on the microbial community, the phenolic-rich ferments had a positive impact in the manner that monolayers of Caco-2 cells adapted better to repeated exposures with the ferments compared with phenolic-depleted ferments. In addition to his subtle difference, Caco-2 cells exposed to phenolic-rich ferments showed a remarkable increase in proteins associated with tight junctions, like claudin-3, -4, -15 and − 19, other proteins that connect the cytoskeleton with tight junctions, such as VASP (Ena/vasodilator-stimulated phosphoprotein) and CGNL1 (cingulin), supporting the idea that phenolic-rich ferments strengthened intercellular communication. In addition to this finding, we observed significant decreases in the transcription of genes encoding apical ion channels, such as CFTR, and the basolateral Na ⁺ /K ⁺ /Cl ⁻ cotransporter, both of which are relevant to intestinal chloride secretion and therefore may reduce fluid loss by the gut. In conclusion, our data support the positive impact of a subset of phenolic compounds that reach the colon, independent of SCFA levels. To achieve this finding in a biologically relevant context, we had to process grape pomace through physiological processes of digestion and fermentation. The latter stage was performed in a realistic colonic environment with human microbiota. The transcriptomic profile induced by the phenolic-rich ferments was observed following repeated exposures, a characteristic that warrants exploration of experimental designs to simulate dietary habits.

Murtilla pomace (the by-product generated during juice production) shows a high phenolic content. Recovering phenolics from murtilla pomace is a sustainable approach towards zero waste. In this study, murtilla pomace was subjected to enzyme-assisted extraction using Viscozyme. The extracts were analyzed for TPC and phenolic profile. Antioxidant activity was evaluated by chemical-based assays and the antioxidant property was demonstrated for the first time in an ozone-induced oxidation process applied to a raw fish model system. Enzymatic pretreatment with Viscozyme increased the total phenolic content by up to 57%. The antioxidant activity also increased upon enzymatic treatment. The concentration of quercetin was positively affected, while the content of rutin decreased upon enzymatic pretreatment, likely reflecting the enzymatic hydrolysis biotransforming rutin glycoside into quercetin aglycone. Phenolics from murtilla pomace obtained upon enzyme-assisted extraction were shown to be effective as natural antioxidants against ozone-induced oxidation in salmon. Therefore, enzyme-assisted extraction may be an environmentally friendly strategy in the recovery of these natural antioxidants.