QUALITY AND BACTERIA IDENTIFICATION OF YOGHURT INCUBATED UNDER ROOM TEMPERATURE USING MIXED STARTER

Abstract

The two-stage study was conducted to establish the procedure of making yoghurt
using liquid starter under room temperature, which is expected to have standard
quality with the absence of non-lactate pathogen bacteria. On the first stage, ready-
for-use pure starters of Streptococus termophillus (St) and Lactobacillus delbrueckii
subsp. bulgaricus (Lb) were made and used for making the yoghurt to be fuI‘ther
used as mixed starter at the rate of 5% with the St:Lb ratio of 1:1 (v/v). Incubation
was done at 45°C for 3 hours (coagulation) and then kept refrigerated. Bacteria
growth was observed every hour. Yoghurt production was done at the second stage
using pasteurisecl milk which was divided into two parts, added with the mixed
liquid starter and the pure starter (both from the first stage), respectively. Incubation was done either under room temperature for 20 hours or at 45°C for 3 hours. Observations were made on acidity (lactic acid equivalent), pH, yoghurt sugar,
bacteria count and identification (St, Lb, Pseudamonas sp, Salmonela and
Stapylocaccus). Data were analysed using 2x2 analysis of variance (2 starters and 2
incubation), with 3 replicmtions and fiirther analysed using Duncan’s new multiple
range test. It was formd that yoghurt could be made using either liquid mixed starter
or pure starters. Incubation could be done under room temperature for 20 hours. The quality of yoghurt made using liquid mixed starter and pure starter were as follows: pH were 4.23 and 4.04, acidity were 1.205 and .965%, yoghu.rt sugar were 2.688 and 3.031%, St bacteria were 1.848x108/ml and 1.432x10/ml, Lb bacteria were 0.182x10/ml and O. 168x108/ml, respectively. No Pseudomonas sp., Salmonela and Staphylocucus growths were observed during the room-temperature incubation. It is suggested to take into accounts the followings: step-by-step of the process of making the yoghurt, equipments and environment sanitations.