Combination of Syzygium cumini (L) Skeels seed extract with acetic acid to control Escherichia coli on mint (Mentha cordifolia opiz.) leaves

Abstract

Four extraction methods were applied to extract phenolic compounds from Syzygium cumini seeds (SCS) with 50% ethanol solution. The microwave-assisted extraction provided the extract with highest yield and highest total phenolic and total flavonoid concentration which followed by ultrasonic-assisted extraction. The high-temperature and ambient extractions with a shaker provided no difference (p ≥ 0.05) in phenolic and flavonoid content. The HPLC analysis of SCS extracts illustrated gallic acid as the main component. The extract demonstrated a bactericidal effect against Escherichia coli at 6.25 mg ml−1. Mint leaves were found to carry high number of total viable count (TVC) and E. coli. The leaves soaked in acetic acid (AA) demonstrated a reduction of microbial number, but dark spot defect was found. Soaking in the mixture of 4.68 mg ml−1 SCS extract and 0.39 mg ml−1 AA caused the number of TVC and E. coli to reduce by 1.8 and 1.3 log10 CFUg−1, respectively, while black spot was not detected. Nine day storage leaves showed satisfactory level of microbial quality and fresh-liked appearance. This demonstrated the potential application of SCS extract with AA as a synthetic substitute for microbial control on fresh leaf vegetables.