Microbial spoilage pattern of food
Microbial growth in food and its products depends on some factors. These
include
1. The characteristics of the product
2. The way the food and its products were processed
3. The way the food and its products were stored
4. Modes of preservation and processing of the food and its products
Microbial spoilage of meat and meat products
Meat and meat products provide excellent growth media for a variety of micro
flora (bacteria, yeasts and moulds) some of which are pathogens.
The intestinal tract and the skin of the animal are the main sources of these
microorganisms.
The composition of microflora in meat depends on various factors:
(a) Pre-slaughter husbandry practices (free range and intensive rearing)
(b) Age of the animal at the time of slaughtering
(c) Handling during slaughtering, evisceration and processing
(d) Temperature controls during slaughtering, processing and distribution
(e) Preservation methods
(f) Type of packaging
(g) Handling and storage by consumer.
There are two main types of microbial spoilage of meat and meat products
1. Spoilage under aerobic conditions
2. Spoilage under anaerobic conditions
The favorable pH for the growth of spoilage bacteria for meat is in the range of
5.5-7.0.
Microbial spoilage of meat and meat products include slime formation,
structural components’ degradation, off odours and appearance change within
this pH range.
i. Surface slime: This may be caused by species of Pseudomonas, Moraxella,
Streptococcus, Bacillus, and Micrococcus.
ii. Changes in colour of meat pigment: The red color of meat, called “bloom”,
may be changed to shades of green, brown, grey as a result of the production of
oxidizing compound e.g. hydrogen peroxides and hydrogen sulphide.
Lactobacillus is basically responsible for this.
Red spot may be caused by Serratia marcescens or other bacteria with red
pigment.
Chromobacterium lividum and other bacteria gives greenish blue or brownish
black spot.
iii. Stickiness: surface becomes sticky
iv. Green patches: These are due to species of Penicillum
v. Changes in fats: Oxidation of unsaturated fats may takes place chemically in
air and may be catalyzed by light and copper e.g. oxidative rancidity.
Pseudomonas or yeasts are responsible for oxidative rancidity.
vi. Souring: Imparts sour taste to meat due to acids such as formic, propionic,
acetic etc.
vii. Putrefication: Anaerobic decomposition of protein with the production of
foul smelling compound such as hydrogen sulfide, indole, ammonia, amines due
to species Clostridium
viii. Taint: Undesirable odours and tastes
The methylamine, dimethylamine and trimethylamine were commonly detected
during bacterial spoilage.
Microbial metabolism produces fatty acids, ketones and alcohols, which exhibit
a variety of fruity and sweety odours. Generation of hydrogen sulphide,
methylsulphide and dimethylsulphide exhibit putrid and sulphury odours. The
diamines, cadaverine and putrescine (the metabolic by-products of meat
spoilage) have been studied as indicators of meat spoilage.