COMPARATIVE STUDY OF QUALITY CHARACTERISTICS, SHELF LIFE AND SENSORY EVALUATION OF STIRRED AND SET YOGHURT INCORPORATED WITH CHOCOLATE

Abstract

Yoghurt is a very popular flavourful and healthful dairy product in all over the world. The classifications are as follows: set type, stirred type, drinking type and frozen type. Flavoured yoghurt contains fruit and berries, vanilla, honey, coffee essences, colourings, sucrose or aspartame and sugar free dietary sweeteners.

This study was carried out to formulate chocolate layered set yoghurt and chocolate incorporated stirred yoghurt and to compare the quality characteristics, shelf life and sensory evaluation of both stirred and set yoghurt initially, the best formula was developed for the chocolate that were taken to incorporate into both set and stirred yoghurt. The effect of different percentage of liquid chocolate on the quality of set and stirred yoghurt production was investigated. Liquid chocolate was added to cultured milk and stirred gel to give chocolate levels of 5, 10, 15 and 20%. The experimental yoghurts were compared with control yoghurt produced without incorporation of chocolate.

Fat, total soluble solids, viscosity, whey separation were determined in the experimental yoghurts on 1st day. Total solids, protein, ash were measured on 2nd day after manufacture.pH, Yeast and Mould count, Coliform count was determined after 1, 7, 14, 21 and 28 days.Sensory properties of the yoghurts were evaluated during storage.

Fat, total soluble solids, total solids, viscosity, whey separation were increased in both set and stirred yoghurt with the increase of chocolate percentage. pH was increased in both set and stirred yoghurt with the increase of chocolate percentage. But with the time being pH was decreased in both yoghurt types. Viscosity level was high in set yoghurt than stirred yoghurt. On the other hand, amount of whey separation was high in stirred yoghurt than set yoghurt.According to the sensory analysis data, the best sample for the set yoghurt was 10% chocolate added product and the best sample for the stirred yoghurt was 15% chocolate added product. Both yoghurt types were microbiologically safe. Coliform, Yeast and mould content were under SLSJ standard level. But Coliform count was somewhat high in stirred yoghurt than set yoghurt.