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 includeLactobacillus delbrueckii subsp. Bulgaricus and Streptococcus thermophilus. The average size ofLactobacillus 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 soya beans (Glycine max) and is quiet similar in appearance to cow milk (Agure-Dam, 1997). It is commonly characterized as having a beany, grassy or soy flavor, which reportedly can be improved by lactic acid fermentation, as in yoghurt-like products Microorganisms possess endogenous β-glucosidases which can be utilized to hydrolyze predominant isoflavone glucosides in soymilk to improve biological activity.
It has been reported that probiotic organisms including Bifidobacteria and some other lactic acid bacteria hydrolyze isoflavone glycosides into corresponding aglycones (Cheng., 1998).
Recent reports indicate that some probiotic bacteria could better compete with yoghurt cultures in a soy-based substrate. Soy has been examined as a substrate for the Lactobacillus species such as L. Casei, L. helveticus, L. fermenti, L. fermentum and L. reuteri (Garro et al., 1999; Murti et al., 1993b;( Chumchuere and Robinson, 1999; Garro et al., 2004; Tzortzis et al., 2004).
The problems of which is beany flavor can be improved by lactic fermentation, so production of fermented soymilks such as soy yoghurt is important (Nsofor et al., 1992; AbdEl Khair, , 2009).
Due to continuous increase in the population and inadequate supply of animal milk protein leading to malnutrition in Nigeria many research works have been geared finding alternative protein source from legume.
Soymilk can serve as a very good alternative to the expensive cow milk as it contains all the essential amino acid even though some are in a low concentration
It is well known from experiment that diets containing containing casein or other animal protein could induce elevation of plasma total LDL cholesterol concentration but this can be prevented by vegetable protein such as soy protein (caroll and kurowska 1998)
1.2 HISTORY OF THE YOGURT MAKING
Milk fermentation is one of the oldest methods practiced by the human beings to preserve milk with an extended shelf life. The exact origination of milk fermentation is not clear; however, it seems that it is dated back to the dawn of the civilization.
It has been reported that the early civilizations such as the Samarians, Babylonians, Pharoes and Indians were well advanced in agricultural and animal husbandry practice. This can be supported by the findings of Copley et al., 2003 in which the dairy fat residues were found in pottery fragments from Neolithic Bronze-age and Iron-age settlements, which suggests that the practice of dairying had existed in Britain approximately 6500 years ago.
However, it is questionable that the milk fermentation was practiced during this period. Therefore, the origin of the fermented milk products including yogurt remains unsolved. It has been reported that the Anatolian goatherds conserve their milk by thickening as they used to dry it in the sun and transport in animal stomachs. It is generally accepted among the historians that the fermentation of milk is discovered accidentally by the Neolithic people of Central Asia when they stored milk in primitive methods such as in sheep-skin bags in warm climates.
With reference to yogurt, it can be suggested that it has been evolved in Turkey as the term “yoghurt” has been derived from a Turkish verb, “jugurt” that means “to be curdled or coagulated”.(Belleville, 2002)
The earliest writings about yogurt can be found from those of Pliny who lived in the first century A. D. and wrote about ancient barbarous nations that knew how to thicken the milk into a substance with an agreeable acidity. According to the literature,(Douglass et al.,2006) the founder of the Mongol empire, Genghis Khan and his armies lived on yogurt and spreading of this news among the people had made the yogurt consumption to spread throughout the East.
Moreover, according to the Persian tradition, Abraham owed his fecundity and longevity to the regular ingestion of yogurt, and the emperor Francis I of France was said to be cured of severe diarrhea by consuming yogurt made of goat milk leading to introduce the health benefits of yogurt into the western world in 1542(Howell and Caldwell, 1978)
The first industrialized production of yogurt took place in 1919, in Barcelona, Spain at a company named Danone. Yogurt was firstly introduced to the USA in the early 20th century in the form of tablets especially designed for those with digestive intolerance. However, it became popular in the North America when Danone, a small-scale yogurt factory started manufacture of yogurt in New York in 1940(Fennel, 1966)
Even though, yogurt has been evolved for centuries, it was subjected to a significant and dynamic evolution process in the 20th Century to originate a vast array of products. For instance, fruit yogurts, yogurts with fruit on bottom and blended yogurts were introduced in 1937, 1947 and 1963 respectively. It seems that the evolution process of yogurt has taken place in different regions of the world once it had been originated in the Central Asia. This might be the reason of having different types of yogurts and yogurt-like products in different names.
1.3 STATEMENT OF THE PROBLEM
Animal protein (milk) are more expensive in Nigeria and not easily affordable by all for yogurt production necessitates the need to seek for ways of producing yogurts from plant protein (soy beans).Combination animal protein provides more complete amino acid , hence better nutrition .
Improving product nutrient value by fruit addition and increased new product variety. Reduce postharvest losses of soybean due to underutilization in Nigeria.
Therefore , many researches have been carried out on yogurt but none have being established on using pineapple as sweetener, aimed at achieving the aforementioned solution.
To produce yogurt from plant protein (soymilk)
To evaluate the sensory attributes of yogurt made from soymilk and cow milk using pineapple as sweetener.
To determine the proximate composition attributes of the yogurt made from soymilk and cow milk using pineapple as sweetener.
To check if there is a significant difference in the texture, appearance, colour, taste and general acceptability of the yogurt produce using ANOVA
To check the proximate contents of the samples produced