Study of the antioxidant activity of plant extracts and their effect on the growth of lactic acid bacteria isolated from koumiss

Abstract

This article describes the effect of plant extracts on the growth and reproduction of lactic acid bacteria (LAB) Lactobacillus acidophilus strain 0015k-1 and Lactobacillus delbrueckii subsp. bulgaricus strain 018k-3, isolated from the traditional fermented milk drink-kumis. In this study, analyses were carried out on plant extracts obtained from Rubus caesius L. (gray blackberry), Rubus idaeus L. (common raspberry) and Punica granatum L. (common pomegranate) with water as principal extragent. The focus was on the antioxidant activity and the total content of polyphenols. Antioxidant activity was measured using amperometry with quercetin taken as the calibration standard. It was determined that the extract from Rubus caesius L. had the highest content of antioxidants (3.30 mg/dm 3) followed by pomegranates (2.40 mg/dm 3) and then raspberries (2.37 mg/dm 3). The total polyphenol content was highest in gray blackberries (8.20%) followed by raspberries (2.99%) and pomegranates (2.78%). To test the prebiotic activity of aqueous plant extracts, LAB were cultured in milk with and without plant components (10%, 15% and control samples) until a clot was formed. The colony-forming unit (CFU) titer was determined for each sample. The results of the in vitro test showed a significant growth of bacterial colonies in samples containing plant extracts (10%) compared to control samples. However, a slight inhibition of LAB growth was observed when the content of plant extracts was increased from 10% to 15%.