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Food Quality Control
Food Quality Control
Chapter 1
Introduction
Analysis of Contamination Points of Milk
through the Whole Value Chain Process
and the Quality of Milk Products in the
Dairy Industry
Peter Chege1* and Zipporah Ndungu2
1
Kenyatta University, Kenya
Jomo Kenyatta University, Kenya
2
Corresponding Author: Peter Chege, Kenyatta University, P. O. Box 43844 00100, Nairobi, Kenya, Tel: +254722 642356; Email: [email protected]
*
First Published June 04, 2016
Copyright: © 2016 Peter Chege and Zipporah Ndungu.
This article is distributed under the terms of the Creative
Commons Attribution 4.0 International License
(http://creativecommons.org/licenses/by/4.0/), which
permits unrestricted use, distribution, and reproduction
in any medium, provided you give appropriate credit to
the original author(s) and the source.
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Product value chain is the full range of activities including production, processing, marketing and distribution a product takes until it gets to the consumer. In the
dairy world, milk is a very vital food commodity for the
growth and development of individuals; it’s a good source
of calcium, vitamin B2, vitamin C and D and amino acids.
Milk however, goes through a number of very important
steps before it can be presented in the markets and stored
to be purchased by the consumers. At every stage, there is
milk contamination, starting from the health of the animal, the hygiene of the personnel, the safety levels of the
animal’s feed, to more advanced levels of contamination
such as during transportation, preservation, processing
and at the shelves [1,2]. To ensure quality milk, it is necessary to understand the various causes and sources of milk
contamination. It is also important to understand the effects of these contaminants to the consumers of milk and
milk products.
Milk and milk products are rich in nutrients, contain
high moisture and have an early neutral pH. Based on the
above characteristics, milk thus easily favour the growth
and multiplication of many bacteria. This is observed even
in cases where the milk has been pasteurized or refrigerated. Milk contamination can originate from different
sources such as air, milking equipment, feeds, soil, faeces
and housing [3]. Contaminated milk may cause diseases
such as tuberculosis, brucellosis, lysteriosis, different
kinds of gastrointestinal disorders, poisoning among othwww.avidscience.com
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ers [15]. This chapter focuses on all the major hot spot
areas regarded as important in milk contamination.
Health of the Animal
Milk is normally sterile when it is synthesized from a
healthy cow’s udder. Interestingly, cow’s milk, has numerous beneficial bacteria. However, some bacteria are harmful to human beings. Sometimes the mammary glands of
a cow may be inflamed due to mastitis. Mastisis produces
pus that can easily get into the milk.
Moreover, cows can also release toxins through their
milk, as milk is a natural exit-portal for substances that
the body cannot use. Hormones introduced to relieve
these animals from stress such as pituitary, steroid, hypothalamic and thyroid hormones may deteriorate the cows’
health. The rate of microbial contamination of milk is influenced by the health status [1].
Feeding of Animals
Low nutritive value forage can produce low quality
milk. The number and types of micro-organisms in milk
are also affected by the feeds [3]. Research that the quality
of the animal feeds affects the quality of milk produced
[4].
Milking Process
Most farmers lack knowledge on hygiene during the
milking process. Poor hygiene during milking and the
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subsequent handling of the milk increases the risk of contamination with bacteria [5]. This reduces the milk shelf
life and can cause diseases to the consumers. Quality milk
requires adequate measures to be taken to improve udder health, milking process and the management routines.
Proper farm hygiene measures can ensure availability of
milk free from contaminations [6].
Milking involves manipulation of the teats which are
the main point of entry of microorganisms. This occurs
due to the opening of teat canal. Prevalence of mastitis
is higher in cows with poor hygiene during the milking
process than in cows where good hygiene is observed in
the milking process [7].
Cleaning the udder before milking is very important
because it would have come into contact with the ground,
urine, dung and feed refusals while resting. Not washing
the udder before milking can impact possible contaminants into the milk.
Studies show that some farmers do not wash the cow’s
under before milking [8], but rather let the calves to suckle before milking. Such practices cannot however replace
washing. Some don’t use a towel while washing the under
at all, while others use the same towel to clean the udder of
two or more cows which is not recommended.
Dirt bacteria and pathogens may also emanate from
the milkers hand. Hand hygiene is particularly important
in hand milking. Therefore, the cleanliness of the cow
in general as well as the immediate environment durwww.avidscience.com
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ing milking may also have a great contribution to under
health and eventually the milk hygiene.
If milking takes place inside a shade, there is a high
risk of contamination of the milk from the air and by insects [8]. The optimal shade should protect against rain,
wind, and excessive heat but at the same time have sufficient light and ventilation. The floor should be made of
concrete so that it can be cleaned easily.
The cow itself is a significant source of dirt or contamination and mastitis bacteria [8]. The skin provides a large
surface area for possible contamination as well as urine,
manure, uterine discharge, dirt, hairs and dust that drop
from the skin and the udder.
Equipment used for milking, processing and storage
similarly determines the hygiene level of milk and milk
products. The milk contact surface must be effectively
cleaned and where appropriate, disinfected immediately
after each milking. All equipment must therefore be kept
clean and in good condition. All rubber parts must be
changed regularly. Notably, failure to change the teat cup
liners may also be a source of contamination [9].
Sufficient supply of water is required for hand washing, udder washing, teat washing, rinsing and cleaning
equipment. Storage areas for the water must be completely
protected to prevent contamination by rodents, birds, insects and dust. Keeping the milk for long before collection
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exposes the milk to mesophilic microflora. Due to this,
cooling is needed. However, low temperatures may also
allow the growth of psychrotrophic microflora in milk
[10].
Regula et al. [11] have stated that the bacterial count in
milk is lower in loose housing compared to the system of
stanchion housing. Gonzalo et al. [12] also reported lower
microbial contamination of milk in loose cubicle littered
housing with milking in a milking parlour in comparison
with stanchion littered housing and an in-stall milking
pipeline system. In addition, it is known that loose housing provides cows with more comfort [13].
Milk Delivery to Collection Centers
Milk in the formal markets is normally transported
to chilling and bulking centers and finally to a processing
facility. Once milk is processed, it is normally delivered by
agents or distributers to a point of sale or directly to the
consumers through brokers and hawkers. This is through
milk bars, milk traders, shops and kiosks. The means of
circulation is through motorbike, bicycles, or through the
public transport. The composition of several nutrients and
other features of the milk, such as high water activity make
the milk an outstanding medium for bacterial growth.
When the milk is not well cooled, there is also high
risk of diseases such as zoonoses, tuberculosis and bru-
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cellosis. A large problem in this section is the absence of
proper ways to maintain a cold chain. The cold chain from
farmer to processor is under developed and together with
unhygienic milking and handling practices all results in
poor milk quality.
Milk Distribution from Collection
Centers to Industry
The dairy industry in Kenya is heavily dependent on
the transportation of milk from the highly productive areas to factories and milk processing plants. Milk transportation methods employed currently include; use of trucks
by farmers where milk is transported in plastic buckets or
drums or milk cans. The conditions of the milk cans used
in the process of transportation largely affect the quality
of milk.
Milk Processing
If milk is untreated, spoilage occurs within a few days.
This spoilage is due to the action of the bacteria’s. Bacteria
can change the flavor, texture or color of dairy products.
This spoilage renders the milk unacceptable for sale. There
are four main methods used to process and preserve milk.
These include; heating to destroy both contaminating
micro-organisms and naturally occurring enzymes that
change the flavor, making the milk acidic to slow down
the growth of spoilage bacteria or food poisoning bacteria
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and reducing the amount of water in milk products to slow
down or prevent the growth of bacteria. Notably, milk can
be processed and preserved using different forms for use
at a later time. Milk can be processed into dry milk powder, sterilized milk (Ultra-High-Temperature of Long-life
milk) and bottled sterilized milk, canned (evaporated or
condensed) milk, or milk by-products such as casein.
Milk Packaging
Milk is a complex mixture of protein, water, lipids,
carbohydrates, enzymes, vitamins and minerals. Due to
its specific composition and its pH being close to neutral,
it is a highly perishable product with high spoilage potential that can result in rapid deterioration of its quality and
safety.
Light and oxygen causes light induced oxidation
and anti-oxidation of the milk fat. Physico-chemical or
microbial changes in the product may cause off-flavors.
Psychotropic bacterial activity/enzymic activity results in
considerable flavor changes in product. Pick-up odorous
compounds at any stage of production and processing or
interaction with the packaging material moreover result
in product flavor deterioration [14].
Some packaging materials like styrene is the precursor
to polystyrene and several co-polymers. It is a weakly toxic
chemical. Bisphenol A (BPA) is used to make polycarbonated plastic and epoxy resins coating of the can. It could
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migrate from the can into the milk powder, concentrated
liquid formula, ready-to-eat liquid formula and whole
evaporated milk. Fluorochemical-treated paper, grease/oil
resistant, is generally used for food in the fast-food industry. The major incorporated contaminants form rappers
are di-isoprpylnaphthalates (DiPNS) and phthalates. To
avoid these, proper packaging, forms an integral part of
milk processing operations which can offer effective protection to the product from such hazards.
Milk at Supermarket Shelves
The milk in supermarket shelves and stores has been
approved by regulatory bodies. Most high-end supermarkets demand packaged products to have bar codes for ease
of sales and stock control. The extension of shelf life from
hours to months has been a prime objective of the dairy
industry for many years to meet the demands for increasing distribution times and distances (Goff and Griffiths,
2006). Milk products in poorly labeled containers and
wrappings in the case of butter and cheese ultimately affect the quality of the milk.
Conclusion
Milk quality is assessed by checking on the numbers
of bacteria that exceed the maximum acceptable limits
specified by regulatory bodies. Additionally, the quality
of milk is as a result of the level of control of all activities
performed throughout the production process. Quality of
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milk ensures consumers’ confidence and ensures generation of high income. Milk quality control is thus key in
the dairy industry. The hazards can either be biological
hazards, chemical and physical hazards. Milk quality can
be affected through contamination at the various points
within the value chain. It is essential to identify the Critical Control Points (CCP), and develop standard operating
procedures to minimize contamination arising from these
points. Moreover, Hazard Analysis and Critical Control
Point (HACCP) system is necessary during milk production to ensure high quality milk. All milk handlers as
well as institutions dealing with milk need public health
license with constant monitoring and evaluation of the
process. In addition, continued training on quality milk
production should be enhanced. When these controls are
ensured throughout the whole milk value chain, quality
milk free from any contaminants will be produced for increased income and better health of the population.
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