Effect of Lactic Acid Bacteria Fermentation on the Polar Compounds Content with Antioxidant and Antidiabetic Activity of Avocado Seed Extracts

Avocado seeds, a common waste in the avocado processing industry, have been found to have several bioactivities, such as anticancer, antimicrobial, hypocholesterolemic, antioxidant, and antidiabetic activities, among others. Nowadays, this wastage is causing an environmental problem, so the use of new technologies to take advantage of it is a novel field of research. In this study, the submerged fermentation by lactic acid bacteria was used as a novel tool for improving the bioactive compound extraction from avocado seeds. Avocado seeds were fermented by different strains, their polar compounds were identified and quantified by HPLC-ESI-TOF-MS, the antioxidant activity was measured by DPPH and FRAP assays, and the antidiabetic activity was analyzed by the alpha-amylase assay. A total of 32 polar compounds were identified, with 13 of them being described in avocado seeds for the first time. Avocado seeds fermented by Pentosaceus acidilactici showed the highest sum of polar compounds (6279.63 +/- 67.74 mu g/g d.w.), and by extension, of hydroxytyrosol glucoside (2989.76 +/- 3.64 mu g/g d.w.). Lactiplantibacillus plantarum CECT 9567 showed the highest antioxidant activity measured by both DPPH and FRAP assays (6294.67 +/- 19.44 and 6846.91 +/- 2.13 mu g TE/g d.w., respectively). Furthermore, Lactiplantibacillus plantarum CECT 748T had the highest antidiabetic activity (52.15% +/- 0.67% inhibition of alpha-amylase activity), attributable to the polyphenols. According to the results, submerged fermentation by lactic acid bacteria led to an interesting increase of the polar compounds' extractability of avocado seeds, consequently improving the bioactivities of the extracts, which could then be used for food nutraceutical or cosmetic purposes.