Abstract:
Yogurt is a popular dairy product made from concentrated milk fermentation. There are
several types of yogurts, such as set, stirred, drinking, frozen, concentrated and flavoured
yogurt. Among them the set type yogurt is very popular and common. Quality of a yogurt
basically determine according to the flavour, aroma, viscosity, consistency, appearance,
freedom from whey separation and long shelf life.
The research was carried out to analyze the quality variation of the set yogurt over the
period of one month to diagnose the quality defects of the existing “Kotmale” yogurt and
to improve the quality and shelf life of the yogurt. Quality variation was measured by
using chemical, microbiological and organoleptic tests. Under chemical tests, pH was
measured by using pH meter and acidity was measured by titration method. Coliform,
Yeast and Mould counts were counted by using pour plate count technique and
organoleptic properties of color, smell and taste were tested everyday over the period of
one month.
According to the results obtained from the above microbiological, chemical and
organoleptic tests; high acidity, high sour taste and presence of yeast and mould were the
predominant quality defects that were significant in the existing set yogurt. Therefore to
eliminate the above quality defects, a new yogurt culture was selected with low post
acidification and developed a improved yogurt with existing formulae. In third day after
manufacturing, nine point hedonic scale sensory analysis was carried out to check the
consumer preference. There were more consumer preference in texture and taste for
improved yogurt but high overall acceptability for existing “kotmale” set yogurt. Chemical
and microbiological tests were carried out to the improved set yogurt in 3rd, 14th, 22nd and
28 days after manufacturing. pH of the improved yogurt varied from 4.85 to 4.35 and
acidity was varied from 0.79 to 0.99 over the period of 28 days. Coliform and Yeast and
Mould counts of the improved yogurt were also conformed to the microbiological limits
specified by the Sri Lanka Standard Institute. In 28* day after manufacturing another nine
point hedonic scale sensory analysis was conducted to check the keeping quality of the
r improved yogurt. According to the analyzed sensory data there were more consumer
preference on texture, sourness and overall acceptability to the improved yogurt over the
other meritet sample o f set yogurt and existing “Kotmale” set yogurt.
