Abstract: Bacteriostatic effects of plant derived polyphenols are generally proposed for food protection against microbial spoiling. This study aimed at characterizing distinct growth modification and cell-lytic properties of an apple pomace extract (APE) containing short-chain and long-chain PP on food spoiling and fermenting starter bacteria.
APE contained 6.76 wt % PP, 0.46 wt % glucose, 1.69 wt % fructose, 1.26 wt % starch, 3.8 wt % sorbitol, and 0.64 wt % nitrogen with a pH-value of 4.1. APE caused growth modification of prominent bacterial food spoilers, yeasts, moulds and food fermenting starter bacteria was analyzed turbidometry (180° light absorption measurement at 600 nm wavelength). Cell-lytic activity of APE was measured by a SYTOX® Green fluorescence cell viability assay.
APE 1.5 w/w % reduced the growth of gram-positive and gram-negative food spoiling bacteria in dose-dependent manner up to 35.00%. Bacillus subtilis growth was reduced up to 10.53% comparable to 1.01 µg/ mL ampicillin or 0.144 mg/ mL sulfamethoxazol. In contrast, the growth of several fermenting starter bacteria increased at 1.5 w/w % APE up to 167.65% whereas expansion of yeasts and moulds were unaffected.
Neither specific cell-lytic activities of APE could be examined on gram-positive and gram-negative food spoiler nor food fermenting starter bacteria.
This study indicates that APE is a bacteriostatic but not a cell-lytic agent against food spoiling bacteria. Instead, the growth of specific lactic acid bacteria was supported by APE. Therefore, APE might stabilize explicit food fermentation processes.