Identification of the phenolic profile, antioxidant and antimicrobial activity of black garlic obtained at different fermentation times

Black garlic is a product obtained by aging fresh garlic (Allium sativum) under controlled temperature and humidity. Recent studies highlight that this product has bioactive substances such as phenolic acids, flavonoids and organo-product compounds that give them antioxidant, antimicrobial, anti-inflammatory, hepatoprotective and anticancer properties, associated with the prevention of various types of diseases. Thus, this study aims to identify the phenolic profile and total phenolic content (TPC), in addition to the antioxidant and antimicrobial activity of hydroalcoholic extracts of black garlic produced during 15 (AN15) and 30 (AN30) days of fermentation. The black garlic samples studied were obtained from fermentation in an air circulation oven at 72 ± 2ºC and 40% saturated sodium chloride solution, and subsequent natural drying at room temperature for 7 days. The TPC was identified by spectrophotometry by the Folin-Ciocalteau method, at 760 nm, while the phenolic profile was determined by Liquid Chromatography. Antioxidant activity was obtained by the DPPH method (1,1-diphenyl-2-picrylhydrazyl) and antimicrobial activity by microdilution in microplates, against three bacterial cultures: Escherichia coli (ATCC 35218), Staphylococcus aureus (ATCC 23235) and Salmonella typhimurium (ATCC 14028). The results showed that the content of phenolic compounds did not differ between the black garlic samples (17.13 ± 1.36 mg Ac Gal/g for AN15 and 18.15 ± 1.49 mg Ac Gal/g for AN30), however were superior when compared to the TFT of garlic in natura (4.48 ± 0.17 mg Ac Gal/g). No reduction of DPPH free radical was identified in in natura garlic, while black garlic showed no difference between the different fermentation times used (88.57 ± 4.08 μmol Tx/g for AN15 and 90.73 ± 0.23 μmol Tx/g for AN30). As for the phenolic profile of black garlic fermented for 15 and 30 days, compounds such as 2,5-dihydroxybenzoic, p-coumaric, gallic, caffeic and vanillic acids were identified, in addition to myrecetin, hespertin and chrysin, being the highlight for both samples in the concentration of protocatechuic acid (70.4 mg compound/g extract for AN15 and 73.00 mg compound/g extract for AN30). This major compound has strong antioxidant and anti-inflammatory activity and may promote health benefits such as preventing liver disease and brain damage by providing cellular protection against oxidative stress. Regarding the analysis of antimicrobial activity, the black garlic extracts did not show efficiency regarding the inhibition of S. aureus, E. coli, and S. typhimurium strains. Thus, it appears that it was possible to obtain black garlic with different fermentation times and that there were no significant differences between the samples with 15 and 30 days of fermentation for the CPT and antioxidant activity levels, but with an emphasis when compared to in natura garlic. Still, the presence of several phenolic compounds can be verified, especially protocatechuic acid. The black garlic extracts did not show antimicrobial activity, however, it can be concluded that a product with an interesting bioactive composition was obtained after 15 days of fermentation.