CHAPTER
ONE
1.0 INTRODUCTION
Yoghurt is a fermented dairy product
obtained from the lactic acid fermentation of milk. It is one of the most
popular fermented milk products in the world and produced commercially at home.
(Willey et al., 2008). In its commercial production, non fat or low fat
milk is pasteurized cooled to 43°c and are inoculated with known cultures of
microorganisms referred to as starter cultures. The starter cultures may be a
pure culture of a particular species of Lactobacillus or a mixed culture
of Streptococcus thermophilus and Lactobacillus bulgaricus in a
1: 1 ratio. The coccus which is the Streptococcus thermophilus grows
faster than the Rod which is the Lactobacillus bulgaricus and is
primarily responsible for acid production while the rod adds flavor and aroma.
The growth of these Microorganisms causes the transformation of milk's sugar,
lactose into lactic acid. This process gives yoghurt it's texture. The
associative growth of the two organisms results in acid production at a rate
greater than that produced by them individually.
Yoghurt is generally made from a
standardized mixture containing whole milk, partially defatted milk, condensed
skim milk cream and non fat dry milk. Alternatively milk may be partly
concentrated by removal of 15- 20% water in a vacuum pan or by heating. While
the microorganisms fermenting milk confers on it certain health benefits
inadequate pasteurized milk may contain microorganism of special importance to
man. (Boor and Murphy, 2002). In which its presence or absence in milk may
reflect success or failure of good manufacturing practice (GMP) or cause
infection when consumed together with food. This is of economic significance in
Africa where the HIV/AIDS and cancer scourge has left the public who consume
milk products immune suppressed and prone to bacterial and fungi infection.
(Boor,2001).
Health complications associated with consumption
of inadequately pasteurized milk products include serious infections that are
hard, to treat with antibiotics. This becomes clinically significant if
organisms isolated from an assessed sample is resistant to conventional
antibiotics. Thus, can confer antibiotic resistance to the infected host while
providing no alternative drug (Gould, 1994). Heat treated yoghurt do not
contain lactic acid bacteria as these are killed during post fermentation.
Yoghurt manufacturing companies mainly market "heat treat" yoghurt to
prolong it's shelf life (Hove et al, 1999). It is important however to
evaluate the microbial gravity of some milk products sold in Nigeria. This
project work aims at assessing the antimicrobial susceptibility pattern of
microorganisms present in yoghurt sold in Enugu.