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Dietary changes have accompanied the evolution of humanity and is proven to be fundamental in human evolution and well-being. Nutrition is essential for survival and as a matter of health and equilibrium of the human body. About 1/3 of the human diet is composed by fermented foods and beverages, which are widely distributed and consumed in different societies around the world, no matter the culture and lifestyle. Fermented foods are derived from the fermentation process of different substrates by microorganisms, and more importantly to humans, by those with beneficial characteristics, due to the positive impact on health. Food is transformed in the gut, gaining new proprieties, and increasing its value to the organism. The effects of fermented foods and beverages can be assessed by its influence at the gut microbiota level. Recent studies show the major importance of the gut microbiota role in modulating the organism homeostasis and homeorhesis. More crosslinks between health, gut microbiota and diet are being established especially in the gut–brain axis field. Therefore, the benefits of diet, in particularly of fermented foods and beverages, should be studied and pursued in order to promote a good health status.

The use of fecal inoculums for in vitro fermentation models requires a viable gut microbiota, capable of fermenting the unabsorbed nutrients. Fresh samples from human donors are used; however, the availability of fresh fecal inoculum and its inherent variability is often a problem. This study aimed to optimize a method of preserving pooled human fecal samples for in vitro fermentation studies. Different conditions and times of storage at −20 °C were tested. In vitro fermentation experiments were carried out for both fresh and frozen inoculums, and the metabolic profile compared. In comparison with the fresh, the inoculum frozen in a PBS and 30% glycerol solution, had a significantly lower (p < 0.05) bacterial count (<1 log CFU/mL). However, no significant differences (p < 0.05) were found between the metabolic profiles after 48 h. Hence, a PBS and 30% glycerol solution can be used to maintain the gut microbiota viability during storage at −20 °C for at least 3 months, without interfering with the normal course of colonic fermentation.

Human diet has evolved to include not only nutritious foods but also health-promoting ones.Moreover, there is an increasing interest in replacing animal proteins as the main protein source.Insect based foods, e.g. Tenebrio molitor insect flour (TMIF), show potential as alternative protein sources for the human diet. This work aims to provide insights into the effect of TMIF upon the human gut microbiota and their metabolic end products by using an in vitro fecal model. Digested TMIF had a positive impact on gut microbiota, observed as an increase and/or upkeep of health promoting bacterial groups and by the production of SCFA (1.7 and 2.6 times higher acetate and propionate produced respectively than in the negative control at 48 h) and BCFA. A path is opened to acknowledge TMIF as a possible healthy nutritional source for human consumption, although in vivo trials would be necessary to confirm this.

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