Aktivitas protease dan kandungan asam laktat pada yoghurt yang dimodifikasi Bifidobacterium bifidum dan diinokulasi pseudomonas fluorescens

Abstract

Main health benefical related to yoghurt is its ability to improve lactose digestion and to control the pathogenic bacteria in digestion tract. This benefical health is threatened by natural existence of contaminant in milk especially P. fluorescens, that reduces shelf life of milk. The aim of this research is to determine the antagonistic nature of B. bifidum in inhibiting growth P. fluorescens and the effect of B. bifidum on protease activity and lactic acid content of yoghurt inoculated by P. fluorescens. Antagonism test of B. bifidum to P. fluorescens is conducted using turbidimetric method. Total titratable acid was measured to determine the percentage of lactic acid content by using acid base titration principle. Protease activity was measured with modification of Lowry method. The result of antagonism test showed that B. bifidum can inhibit P. fluorescens with minimum inhibitory concentration (MIC) of 2%. Lactic acid content of yoghurt with formula 1:1:0, 1:1:0.5, 1:1:1, and 1:1:1.5 on 0 day was 0.3747%, 0.3654%, 0.3732%, and 0.347% respectively and then increased during 25 day storage to 0.5709%, 0.5202%, 0.6638%, and 0.5945% respectively. Addition of B. bifidum decreased protease activity indicated by less protease activity of yoghurt modified by B. bifidum till 15 day storage compared to yoghurt without B. bifidum.