Garlic (Allium sativum) peel extracts and their potential as antioxidant and antimicrobial agents for food applications: influence of pretreatment and extraction solvent

Garlic peel extracts (GPE) are known to have excellent physiological activity, but research on the pre-processing of garlic peel (GP) to enhance their bioactivity is limited. The aim of this study was to evaluate the effect of two pretreatments applied to GP, such as fermentation with Lactobacillus plantarum and heat processing (10 min roasting) and two extraction solvents (70% v/v ethanol and methanol), on the total phenolic content (TPC), total flavonoid content (TFC), antioxidant capacity (AC), and antimicrobial activity (AA) of GPE. Results showed that GPE contained appreciable quantities of TPC (50.41 & PLUSMN; 0.19 mg(GAE)/g) and TFC (47.58 & PLUSMN; 1.69 mg(GAE)/g), but were further improved by both biological and thermal pretreatments along with their AC and AA against food-spoilage strains (Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, and Listeria innocua). Ethanolic extract of 48 h-fermented GP achieved the highest TPC (140.65 & PLUSMN; 0.47 mg(GAE)/g), TFC (68.8 & PLUSMN; 1.80 mg(QE)/g), TEAC-DPPH (288.88 & PLUSMN; 6.98 & mu;mol(TE)/g), TEAC-ABTS (638.39 & PLUSMN; 5.35 & mu;mol(TE)/g), and the lowest MIC (1.25 & PLUSMN; 0.0 mg/mL), showing that the increase in TPC was strong-positive correlated to AC (Pearson's r > 0.97) and to AA (Pearson's r > 0.90). These findings revealed an innovative approach for the valorisation of garlic residues through a bioconversion process, which enhances their potential as a source of antioxidant and antimicrobial agents for possible food applications.