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THE EFFECTS OF BLENDING COW MILK WITH SOYMILK ON YOGHURT QUALITY

ABSTRACT

A quantity of 1 litre each of cow milk and blended (cow/soy) milk was pasteurized and each was inoculated with 5g of a mixed starter culture comprising streptococcus thermophillus, Lactobacillus acidophilus and Lactobacillus bulgariuos and incubated at 500C for 5 hours to ferment to yoghurt. Proximate analysis on both yoghurts showed that there was no significant difference (P>0.05) between the moisture content, protein content and fat content of the two yoghurts samples. The ash content and carbohydrate content of the blended (cow, soy) milk yoghurt were significantly (p<0.05) than that of cow milk yoghurt. Also, significant difference (p, 0.05) was observed in terms of colour between the two yoghurt samples. However, no significant difference (p>0.05) was observed in terms of taste, aroma, consistency and general acceptability of the two yoghurts. Physicochemical analysis showed that the specific gravity of blended (cow/soy) milk was significantly higher (p<0.05) than that of cow milk yoghurt but there was no significant difference (p>0.05) observed in pH and T.T.A of both yoghurts. However, the two yoghurt were generally accepted.

CHAPTER ONE

INTRODUCTION

Interest in functional foods has recently increased among consumers due to a greater consciousness of health and nutrition; as well as the need to cure diseases and also the increasing scientific evidence of their effectiveness. Fermented products are a significant part of many indigenous diets.

Yoghurt is a Turkish name for a fermented milk product. It is originated by early normadic herdsman, especially in Asia, Southern and Eastern Europe. Yoghurt is made by adding a culture of acid forming bacteria to milk that is usually homogenized, pasteurized and fermented. Yoghurt is defined as a fermented milk product that evolved empirically some centuries ago by allowing naturally contaminated milk to sour at a warm temperature, in the range of 40-50 °C (Kwon  et al., 2011). The micro-organisms which are used conventionally in this process are referred to as “Starter Culture”. They include Lactobacillus delbrueckii subsp. Bulgaricus and Streptococcus thermophilus. The average size of Lactobacillus bulgaricus ranges from 0.8 to 1.0μm in diameter (Rakis .,1978 , Sanfu. , 2009).

During the fermentation, hydrolysis of the milk proteins occurs, the pH drops, the viscosity increases and bacterial metabolites are produced that contribute to the taste and possibly to the health promoting properties of yoghurt. The sugars are fermented by the bacteria into lactic acid, which causes the formation of the characteristic curd. The acid lowers the pH of the yoghurt and restricts the growth of food poisoning bacteria (putrefactive or pathogenic).

Not only is yoghurt a wonderful quick, easy and nutritious snack, but also research evidence point to the fact that milk and yoghurt may actually add years to life as found in some countries where fermented dairy products are a dietary (Wolf.,1978) Several health benefits have been reported for traditional yoghurt and this healthy image is enhanced by supplementation with probiotic bacteria ( ; Magenis, et al 2006).

Soymilk is an aqueous extract of

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