CHAPTER ONE

1.0       INTRODUCTION

Yogurt is a fermented milk product that contains the characteristics of bacterial cultures lactobacillus bulgaricus and streptococcus thermophiles. All yogurts must contain at least 8.25% solids not fat. Full fat yogurt must contain not less than 3.25% milk fat, low fat yogurt not more than 2% milk fat and non-fat yogurt less than 0.5% milk. The full legal definitions for  yogurt and non-fat yogurt are specified in the standards of identity listed in the U.S code of federal regulations (CFR) in section 21 CFR 1319200, 21CFR 131.203 and 21CFR 131.206 respectively. Some state organizations and private companies such as National Diary, Tosco Ltd and many other small scale industries in Nigeria have started the production of yoghurt. Yoghurt simply means fermented milk thickened to a custard consistency by certain acid forming bacteria such as Lactobacillus Bulgaricus and Streptococcus thermophilus. The coagulation and fermentation of milk sugar into lactic acid is caused by these bacteria. The action curdles the protein in yoghurt and acts as a preservative. Before the addition of bacteria, the milk is pasteurised and cooled. Pasteurisation is the heating of milk to destroy bacteria that are harmful. It normally takes two forms or stages. Firstly, heating to at least 63oC and holding it at that temperature for thirty minutes, secondly, heating to at least 72oC and holding it for fifteen minutes which is known as short time method. (John W. and Sons 1972).

Homogenisation is a mechanical process whereby whole milk is forced through a series of jet at 2 – 3 kilos of pressure which breaks fat globules. The heated treated milk is incubated with a minced culture containing Lactobacillus Bulgaricus and Streptococcus thermophillusand held at 42oC – 45oC for three hours (Incubation).Citizens of Nigeria started consuming yoghurt as food since its existence as fermented milk. The rate of consumption is on the increase for its nutritional value, as people of all stages are involved.

1.1       AIMS AND OBJECTIVES

The aim of this research project is the production and study of shelf life of yogurt without preservative.

The objective is:

-        To produce quality and hygienic yogurt.

-        To characterize (conduct quality control analysis) on yogurt.

-        To determine the shelf life of yogurt produced from powdered milk without preservative.

1.2       RESEARCH PROBLEM

Many yogurt products available in the market are produced using various kinds of preservatives in most cases; these preservatives have adverse effect on the health of consumers of such products. There have been cases where the consumption of the products led to poisoning and subsequently death. This research project was strategically carried out to solve or tackle such outcomes.

1.3       RESEARCH SCOPE AND LIMITATION

The research work is limited to the characterisation of the yogurt produce and determination of the yogurt shelf life without adding artificial preservative. However detail biological and chemical mechanism of fermentation is beyond the scope of this research work.

1.4       RESEARCH JUSTIFICATION

Production of yoghurt is on the increase in the society but there is still need to produce quality yoghurt. As a process engineer, quality control must be considered as the most important factor in any production process. The available products are of poor standard. Yoghurt should be sweet, fresh, creamy and moderate in viscosity. Therefore, the production of quality and hygienic yoghurt naturally preserved without the use of any chemical preservative is the most priority of this research to meet the required standard.

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