Roasting and frying modulate the phenolic profile of dark purple eggplant and differently change the colon microbiota and phenolic metabolites after in vitro digestion and fermentation in a gut model

The way of cooking vegetables could differently affect the phenolic profiles of foods and their impact on human colon microbiota. In this work, we investigated the stability and bioaccessibility as well as the impact and fate of dark purple eggplant (DPE) phenolic compounds in the gut microbiota after grilling or frying in comparison to the raw one. After cooking, DPE underwent a gastro-intestinal digestion along with a proximal colon fermentation using the short-term batch model MICODE (multi-unit in vitro colon gut model). During the process, the phenolic compounds profiles (through high-resolution mass spectrometry) and microbiomics (qPCR of 14 core taxa) analyses were performed. Results showed that thermal treatments increased the amount of extractable phenolic compounds as well as their bioaccessibility. The highest gastro-intestinal release was observed in fried DPE (2468.46 ± 13.64 μmol/100 g), followed by grilled DPE (1007. 96 ± 12.84 μmol/100 g) and raw DPE (900.93 ± 10.56 μmol/100 g). Mass spectrometry analysis confirmed that colonic bacteria were able to metabolize DPE phenolic compounds mainly to 3-(3'-hydroxyphenyl)propanoic acid. Furthermore, results indicated that frying was better than grilling in terms of fostering more the growth of beneficial bacterial taxa and limiting that of opportunistic taxa. For example, fried DPE determined an increase in abundance of Bifidobacteriaceae Lactobacillales of 2.66 and 3.80 times. This work is one of the first exploring how cooking methods can affect the phenolic composition of DPE and differently impact on the colon microbiota tuning and modifying the food functionalities.