Non-nutritional Factors Affecting Milk Yield, Milk Quality and Prevalence of Food Borne Pathogens in Milk and Milk products in Central Highlands of Oromia, Ethiopia
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Date
2020
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Abstract
Nutritional and non nutritional factors are the major contributors for variation in milk yield and
physicochemical parameters. On the other aspects as milk is nearly perfect food it is also a good
growth media for spoilage and pathogenic microorganisms. This study was aimed at analyzing
the effects of non-nutritional factors on milk yield and composition, physicochemical and
microbial quality. The prevalence of some food borne pathogens in milk and its products was
also evaluated in study areas. The study was conducted from, February 2017 to June 2019 in
Holeta Agricultural Research Center (HARC) dairy Lab., milk and its product samples were
collected from producers and collectors in Bishoftu and Sebeta town’s while pasteurized milk
was sampled from shops in Addis Ababa. The study was conducted in three categories where
dairy farm recorded data analyis, physicochemical, microbial and food borne pathogenic
investigations of milk and milk products samples collected from study sites. Twelve years
recorded data of Holstein Friesian crossbred dairy cows were categorized and summarized into
parameters of study to see the effects of season, exotic blood level, parity and lactation stages
on monthly milk yield and composition from records of HARC dairy farm. Analysis of physicoche
mical parameters of one hundred raw milk and twelve pasteurized milk samples collected from st
udy areas were conducted using lacto scan in dairy laboratory of HARC. In addition to the
retained one half amount of samples used in physicochemical analysis, samples of 40 locally
fermented yoghurt and 40 cottage cheese(ayib) summed up to 192 samples were used for
investigating microbial quality and food borne pathogens of milk and milk products from Sebeta
and Bishoftu areas. The microbial quality and food borne pathogens analysis were done
following standard procedures of laboratory in dairy laboratory of HARC. General linear model
of SAS was used for statistical analysis of variances. Season significantly affected milk yield, fat
and protein content of milk. Higher yield and fat percent composition was recorded in dry
season while higher protein percent was recorded during wet season. Genotype significantly
affected milk yield where 62.5% and >75% crossbred cows produced significantly higher milk
yield than that of 50% crossbred cows. Differences in parity affected milk yield and protein
content of milk where higher milk yield and protein content was recorded in parity five. Milk
yield and protein content had shown increasing trend as dam parity advances.
Mean monthly milk yield, percent of protein and total solid was varied significantly between diffe rent lactation stages where protein and total solid percentage was significantly higher in late ges of lactation. Differences in sample types were affected physical parameters of milk pH, specif
ic gravity and freezing point.The overall result showed that percent composition of raw milk sam
ple from Sebeta and Bishoftu area include: lactose (4.91±0.12)%, protein(3.28±0.08)%, fat(3.68
±0.25)%, solid-not fat(8.93±0.22)%,total solids(12.61±0.41)%, ash(0.74±0.02)%; and lactose(4.
36±0.06)%, Protien(2.90±0.04)%, fat(3.59±0.13)%, solid-not-fat (7.93±0.11)%, total solids(11.5
2±0.20)%, ash (0.66±0.01)% respectively. Significant difference was observed in lactose, protein
, and solid not fat, total solid and ash values between the study sites. Raw milk samples
from Sebeta area had higher percentage of composition where as physicochemical components
of pasteurized milk was significantly lower than that of raw milk and also below the minimum
requirement of Ethiopian standard for protein, fat, total solid and specific gravity. Results of raw
milk fulfill minimum requirements of standards to be accepted. There was significant variation
due to difference in study site for TCC, E. coli, YMC, S.aureus and L.monocytogenes of raw milk
samples but no variation in TABC due to differences in study sites on raw milk and milk products
. There was also significant difference in S. aureus in cheese, TCC and E. coli in yoghurt due to
difference in study site of sampling. Except E.coli, TCC, YMC, S.aureus and L. monocytogenes of
raw milk samples were significantly higher in Bishoftu than sebeta milk samples.On the other ha
nd, lower count of TABC, TCC, S. aurus and E.coli were found in pasteurized milk. There was
high microbial count in milk and milk products of the two sampling site and sources where
counts of the respective sites of TABC, TCC, yeast and mould (YMC), E.coli and
L. monocytogenes were above Ethiopian quality standards. Given their high count, milk spoilage
and health risk is inevitable if these products are consumed untreated. Pasteurized milk had
showed less microbial loads, therefore it is one option recommended as solution for reducing the
high microbial counts. The high L. monocytogenes in pasteurized milk suggested that the
existence of either post process contamination or inefficient pasteurization. Hence, minimizing
contamination through proper barn and equipment cleaning, animal health care, facilitating
milk cooling systems, strict hygienic practices at farm, collection sites and in dairy processing
plants are necessary.
Description
PhD Thesis
Keywords
Season, parity, genotype, lactation stage, milk composition, Foodborne pathogens