TITLE:
Antioxidant Activities of Exopolysaccharides Produced by Lactic Acid Bacteria Isolated from Commercial Yoghurt Samples
AUTHORS:
Aminat O. Adelekan, Taiwo O. Olurin, Abiola O. Ezeani
KEYWORDS:
Antioxidant Activities, Exopolysaccharides, Lactic Acid Bacteria, Commercial Yoghurt
JOURNAL NAME:
Advances in Microbiology,
Vol.10 No.8,
August
14,
2020
ABSTRACT: An antioxidant is a substance that inhibits
the oxidation of other molecules caused by free radicals. The inbuilt antioxidant
systems possessed by living organisms are generally not enough to prevent them from
oxidative damages and the uses of synthetic antioxidants also have some harmful effects.
This study was aimed at evaluating the antioxidant activities of exopolysaccharides
produced by lactic acid bacteria isolated from
yoghurt. Lactic acid bacteria (LAB) were isolated from six different brands
of commercially available yoghurt using deMan Rogosa Sharpe (MRS) agar. The LAB
isolates were identified based on morphological and biochemical analyses and were
screened for exopolysaccharide (EPS) production. The LAB isolates screened positive
were used for EPS production in a liquid medium and the EPS produced were purified
and quantified using standard methods. Antioxidant activities of the EPS were evaluated by determining the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity, ferric
ion reducing power, and total phenolic contents. Data obtained were analysed using
Analysis of Variance. Total lactic acid bacterial count obtained from the yoghurt
samples ranged from 0 - 3.9 × 104 CFU/mL with sample A (Fan Yoghurt)
having the highest LAB count (3.9 × 104 CFU/mL). The isolated LAB and
their incidence rate were Lactobacillus plantarum (25.49%), L. delbrueckii (19.61%), L. fermentum (15.69%), L. acidophilus (13.73%), Leuconostoc mesenteroides (11.76%), Lactococcus lactis (7.84%), and Lactobacillus casei (5.88%). Fifty-one out
of the 64 LAB isolates were screened positive for EPS production and only six were
able to produce substantial quantity of EPS ranging from 127.4 - 208.5 mg/L. The
exopolysaccharides produced by L. fermentum had the highest DPPH radical scavenging activity (62.90%) while that of L. plantarum had the lowest (23.10%) at a
concentration of 1000 μg/mL. Also, the EPS produced by L. fermentum recorded
the highest ferric ion reducing power (12.89 mg AAE/mL) at 1000 μg/mL while that
of L. plantarum had the lowest (5.62 mg
AAE/mL). At 1000 μg/mL, the total phenolic contents of the EPS samples ranged from
1.41 - 1.58 mg GAE/mL, and the EPS produced by L. fermentum had the highest (1.58 mg GAE/mL) while those produced by L. paracasei had the lowest (1.41 mg GAE/mL).
This study revealed that the exopolysaccharides produced by the LAB isolates showed
high antioxidant activities with respect to their DPPH free radical scavenging activity,
ferric ion reducing power and total phenolic contents.