Addition of red dragon fruit (Hylocereus polyrhizus) on yogurt: Effect on lactic acid content, pH, and the inhibition of Escherichia coli growth

Abstract

Red dragon fruit contains carbohydrates, flavonoids and other nutrients that can be used as energy sources by lactic acid bacteria (LAB). The addition of red dragon fruit in making yogurt can improve the characteristics and functional properties of the final yogurt product. The purpose of this study was to determine the effect of various concentration of red dragon fruit (Hylocereus polyrhizus) in yogurt to lactic acid content, pH value, and inhibition of E.coli growth. The parameters measured in this study were lactic acid content, pH, and inhibition zone of E. coli. The design used was a completely randomized design (CRD) with three treatments and five replications. The process of making yogurt was as follow: distilled water mixed with skim milk 10% (w/v), red dragon fruit 3%, 5% and 7% (w/v) and sugar 3% (v/v). The mixture was heated at 105°C for 5 minutes, cooled, then inoculated with lactic acid bacteria starter as much as 3% (v/v) and incubated at 42°C for 12 hours. This study showed that the concentration of 7% red fruit dragon produced higher lactic acid content, a lower pH value, and higher inhibition to E. coli growth compared to the concentration of 3% and 5%. The result indicated that the use of 7% red dragon fruit would produce good quality yogurt.