Effect of Addition of Coffee Extract on Microbial Growth and Functional Properties of Yoghurt

Abstract

Yoghurt is a popular probiotic milk product. Coffee flavoured yoghurt was developed to enrich the product with functional properties and help enhance local coffee consumption. The aim of the research was to study potential interaction of polyphenolic compounds present in coffee extract on the viability of lactic acid bacteria, yeast and moulds and, functional properties of coffee flavored yoghurt. Coffee flavoured yoghurt was prepared by adding coffee flavour extract to the yoghurt in varying amounts; 0.0%, 0.1%, 0.2%, and 0.3%. Treatment 0.0% was the control. A complete randomized design (CRD) was used, in which yoghurt was divided into 4 treatments in triplicate and was randomly assigned to 12 experimental units. The sampling for analysis was done at intervals of one week for 28 days from day one. Microbial analysis was done using standard AOAC 2016 method using MRS and PDA media and results were reported as CFU/ml of the coffee flavored yoghurt. Functional properties were determined by evaluation of total polyphenols and antioxidant activity using the Free radical scavenging activity by DPPH method and Folin ciocateau method. Data was analyzed by use of ANOVA, means separated by LSD at p<0.05 level of significance. From the findings, lactic acid bacteria in coffee flavoured yoghurt ranged between 3.7x107-1.09x108CFU/ml. Yeast and moulds ranged between 3.6x101-8.33x100 CFU/ml. TPC between 5.76±0.4-97.89±0.6mgGAE/ml while Antioxidant properties ranged from 15.82±0.9- 68.55±0.9 % DPPH. There were significant differences between coffee flavoured yoghurt and the control on the functional properties. In conclusion, addition of coffee flavour extract into the yoghurt improved the keeping quality of the yoghurt while maintaining its probiotic potential. More studies on addition of natural coffee flavour into other milk products are recommended.