Selenium nanoparticles (SeNPs) are gaining importance in the food and medical fields due to their antibacterial properties. The microbial inhibition of these kinds of particles has been tested in a wide range of Gram (+) and Gram (−) pathogenic bacteria. When SeNPs are synthesized by biological methods, they are called biogenic SeNPs, which have a negative charge caused by their interaction between surface and capping layer (bioorganic material), producing their high stability. This review is focused on SeNPs synthesis by bacteria and summarizes the main factors that influence their main characteristics: shape, size and surface charge, considering the bacteria growth conditions for their synthesis. The different mechanisms of antimicrobial activity are revised, and this review describes several biosynthesis hypotheses that have been proposed due to the fact that the biological mechanism of SeNP synthesis is not fully known.

Three experimental variables [methanol concentration, extraction time, and materialto-solvent ratio (w/v)] were optimized in the ultrasonic-assisted, Box-Behnken extraction of biocompounds (total phenols and flavonoids) from xoconostle (Opuntia oligacantha) to determine the antibacterial activity against Salmonella typhimurium and Staphylococcus aureus. The total phenols and inhibitory effect on Staphylococcus aureus were optimal with 10 min of ultrasound and 40% methanol, and a ratio of 1:20 (w/v); the total flavonoids was optimal with 20 min of ultrasound, 40% methanol, and a 1:30 ratio (w/v); and the biocompound effect on Salmonella typhimurium was optimal with 10 min of ultrasound, 60% methanol and a ratio of 1:10 (w/v). The polynomial equations showed satisfactory accuracy in predicting the extraction yield. The total phenol content and Salmonella typhimurium and Staphylococcus aureus parameters were fit to a quadratic model, while for flavonoids, the fit was linear. The results showed that biocompounds extracted from xoconostle have a high inhibitory effect on Salmonella typhimurium and a moderate effect on Staphylococcus aureus. These xoconostle extracts can be used as a natural antibacterial additive in the food industry. PRACTICAL APPLICATIONThe use of natural antibacterial compounds in the food industry has been increasing. Xoconostle is the acidic fruit of the Nopal, or the cactus pear, which is endemic in the Americas. In this study, three variables of the ultrasound-assisted extraction of biocompounds from xoconostle were optimized for antibacterial activity using the surface-response Box-Behnken design, namely, the methanol concentration, extraction time, and material-to-solvent ratio (w/v). The results showed that the best conditions for the extraction of phenols and biocompounds with inhibitory activity against Staphylococcus aureus were the same, while the optimal conditions for the extraction of flavonoids and biocompounds with inhibitory activity against Salmonella typhimurium were different. The ultrasound-assisted xoconostle extractions of flavonoids, phenols, and biocompounds with antibacterial activity against pathogenic bacteria have potential applications as food additives.

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Gut microbiota is a group of microorganisms that are deposited throughout the entire gastrointestinal tract. Currently, thanks to genomic tools, studies of gut microbiota have pointed towards the understanding of the metabolism of important bacteria that are not cultivable and their relationship with human homeostasis. Alterations in the composition of gut microbiota could explain, at least in part, some epidemics, such as diabetes and obesity. Likewise, dysbiosis has been associated with gastrointestinal disorders, neurodegenerative diseases, and even cancer. That is why several studies have recently been focused on the direct relationship that these types of conditions have with the specific composition of gut microbiota, as in the case of the microbiota–intestine–brain axis. In the same way, the control of microbiota is related to the diet. Therefore, this review highlights the importance of gut microbiota, from its composition to its relationship with the human health–disease condition, as well as emphasizes the effect of probiotic and prebiotic consumption on the balance of its composition.

Blackberry processing generates up to 20% of residues composed mainly of peel, seeds and pulp that are abundant in flavonoids. The objective of this study was to optimize the ultrasound conditions, in a closed system, for antioxidants extraction, using the response surface methodology. Blackberry (Rubus fructicosus) residues were analyzed for total phenolics, total anthocyanins, and antioxidant activity by ABTS and DPPH. The selected independent variables were ultrasound amplitude (X 1 : 80%-90%) and extraction time (X 2 : 10-15 min), and results were compared with conventional extraction methods. The optimal conditions for antioxidants extraction were 91% amplitude for 15 min. The results for total phenolic content and anthocyanins and antioxidant activity by ABTS and DPPH were of 1201.23 mg gallic acid equivalent (GAE)/100 g dry weight basis (dw); 379.12 mg/100 g¨dw; 6318.98 µmol Trolox equivalent (TE)/100 g¨dw and 9617.22 µmol TE/100 g¨dw, respectively. Compared to solvent extraction methods (water and ethanol), ultrasound achieved higher extraction of all compounds except for anthocyanins. The results obtained demonstrated that ultrasound is an alternative to improve extraction yield of antioxidants from fruit residues such as blackberry.