Rapid Estimation of Quality of Raw Milk for its Suitability for Further Processing in the Dairy Industries of Bangladesh
Md. Manirul Islam,
Md. Nasim Ali Mandal
Gazi Md. Noor Uddin
Milk is prone to rapid microbial spoilage because of having high nutrients.
Improper or delayed chilling or long term storage may lead to increased growth
of bacteria in raw milk, causing spoilage of milk products. Due to high perishable
nature, rapid reception and processing of raw milk is mandatory in the processing
factory. Instead of expertise dependent, lengthy, laborious, expensive direct
microbiological methods (e.g. standard plate counts, coliform bacterial counts
and direct microscopic counts); rapid, simple and inexpensive quality determination
methods including physical, chemical tests and Methylene Blue Reduction Time
(MBRT) test could be opted. Little interlinked data on physical, chemical and
MBRT in relation to raw milk quality are available. This study accordingly estimated
the quality of raw milk for its suitability for further industrial processing.
Physical examinations including color, flavor, taste and specific gravity (1.030±0.001),
chemical and indirect microbiological tests including fat, solids-not-fat, total
solids, water, acidity, pH contents and MBRT, respectively revealed their acceptable
standard limit. While the yearly average fat, solids-not-fat, total solids and
water content were 3.98, 7.4, 11.38 and 88.62%, respectively along with the
highest fat percentage 4.06 in the autumn and the lowest 3.83 in the summer
season which were not varied significantly (p<0.05). On the other hand, the
yearly average acidity, pH and methylene blue reduction time were 0.137%, 6.84
and 56.75 min, respectively along with similar dye reduction times in different
seasons. The results obtained in this study satisfied close to the minimum standard
of raw milk for further industrial processing.
to cite this article:
Tahmina Bilkis, Md. Manirul Islam, M.C. Sumy, Md. Nasim Ali Mandal and Gazi Md. Noor Uddin, 2013. Rapid Estimation of Quality of Raw Milk for its Suitability for Further Processing in the Dairy Industries of Bangladesh. International Journal of Dairy Science, 8: 1-11.
Received: November 05, 2012;
Accepted: March 14, 2013;
Published: April 11, 2013
Milk is the natures single most nearly complete food in the world. Bangladesh
is a small milk producing country in the world whose domestic milk production
is not sufficient to meet up the national demand. The major volume of milk comes
from the milk pocket zones of Bangladesh which is developed by Bangladesh Milk
Producers Co-operative Union Limited (BMPCUL)-popularly known as Milk
Vita. In addition to Milk Vita, raw milk collection, processing and marketing
throughout the country have been carried by a number of companies likely PRAN
(Programme for Rural Advancement Nationally) Dairy Ltd., BRAC (Bangladesh Rural
Advancement Committee) Dairy and Food Project, Aftab Milk and Milk Products
Ltd., Bikrampur Dairy Ltd., Akij Food and Beverage Limited. Therefore, hundreds
of raw milk collection and chilling centers have been established and operated
in the milk pocket zones of Bangladesh by these Dairy companies.
Milk is produced in rural or peri-urban areas of the country and transported
from point of production to the neighboring chilling centers of different dairy
companies of Bangladesh. Dairy cows suffering from subclinical mastitis used
to excrete pathogens in raw milk but milk of healthy animals udder is
free from pathogenic bacteria (FAO, 1989). Consequently,
pooled milk gets contaminated after mixing with such kind of milk containing
Over and above, microbial contaminants in raw fresh milk mainly come from dirty
or poorly disinfected milking utensils, environment, animal skin, dirty teat
surface, milkers hand, flies, untreated water supplies or adulteration
with untreated water etc. (FAO, 1989). Even though sterile
milk is let down from the udder of healthy animals, but in practice contamination
of the raw milk with ranged from 102-103 microorganisms/mL
is unavoidable. This might be due to the microbial residents in the interior
of the udder or in the teat canal (Heeschen, 1996).
The magnitude of microbial loads in raw milk is mainly influenced by contamination
during milking, storage temperature and on the time elapsed between milk production
and collection. Unhygienic milking, inefficient storage practice will allow
higher microbial growth in raw milk as it is highly rich growth medium of microbes
(Ensminger, 1993; Nooruddin et
al., 2006). Transportation of raw milk from point of production to the
collection centers at ambient temperature might leads to high microbial growth,
causing quality deterioration of raw milk (Schmidt and Van
Vleck, 1974). In principle, higher microbial loads in raw milk are mainly
responsible for quality defects in Pasteurized milk (Blankenagel,
1982), UHT milk (Bjorck, 1973; Law
et al., 1977; Richardson and Newstead, 1979),
dried skimmed milk (Muir et al., 1986), butter
(Antila, 1982) and cheese (White
and Marshall, 1973; Mohamed and Bassette, 1979).
Moreover, both living bacterial population and enzymes including heat resistant
proteinases (Fairbairn and Law, 1986) and lipases (Downey,
1980) may also be responsible for the spoilage of dairy products. For these
reasons, the standard limit of microbial counts in raw milk has been set by
the European Community (EC) at 1x105 CFU mL-1 or 4x105
CFU mL-1, according to the dairy product to be manufactured from
Estimation of microbial load in raw milk is highly recommended in relation
to its keeping quality. Several laboratory methods to determine bacterial load
in raw milk including Direct Microscopic Count (DMC), Most Probable Number (MPN)
and Standard Plate Count (SPC) can be opted which are expensive, lengthy and
expertise dependent. Consequently, the attention in rapid methods for microbial
examination of milk has been growing gradually in the last few decades (Fung,
1995, 1991). Currently a number of instrument aided
methods are frequently employed for rapid estimation of bacterial load following
metabolic activity, light scattering, electrical impedance, chemiluminescence
and fluorescence (Pettipher, 1993; Spencer
et al., 1994; Vanderzant and Splittstoesser, 1992)
e.g. direct epifluorescent filter technique (Champange
et al., 1997) for determination of viable bacterial population in
raw milk and detection of metabolic changes in microorganisms in raw milk during
incubation (Shelef and Eden, 1996).
However, the need for rapid, simple and economical methods for assessing the
quality of raw milk still subsists. The simplest and economic dye reduction
tests e.g. Methylene Blue Reduction Time test (MBRT) are still convenient means
of detecting the metabolic activity of microorganisms in a relatively short
time for grading of raw milk in the commercial dairies of the developing countries
(Edmondson et al., 1985; Harding,
1995). Nevertheless, the dye reduction methods are favored over more other
precise methods because they are easy to perform and economical indeed and also
suitable in rapid grouping of raw milk samples into classes or grades (Dabbah
et al., 1967). For example, raw milk can be graded into good and
excellent grades based on methylene blue reduction time of 2 to 5 and more than
5 h, respectively and reduction time of around 1 h is considered to be suitable
for further processing in the developing tropical and sub-tropical countries
(Kotaratititam, 1995). In contrary to other countries
milk produced in Bangladesh could be categorized under close to poor grade.
Climatic condition, unhygienic milking, flies, disease, improper handling, improper
sanitation and cleaning of utensils, together milk itself enriched media, facilitate
growth and yield of higher number of bacteria, even the highest number of bacterial
load/ml of raw milk in the world (Chanda et al.,
2008). Little information is available on the rapid determination of raw
milk in the rural dairies for further industrial processing particularly about
the convenient methods. Therefore, the study was aimed to rapid determination
of physical, chemical and microbiological quality of raw milk for further processing
based on some simple, faster and economic methods.
MATERIALS AND METHODS
Study area: Baghabari, Bera, Selonda, Demra of Pabna district and Vatara
area of Jamalpur district were selected for this study which are recognized
as milk pocket zones of Bangladesh. The Dairy cattle population of these areas
is principally composed of local/native cows called Pabna cattle and cross breed
of Holstein Friesian and native cows. Farmers were selected and brought under
an agreement that they will supply milk to keep smooth flow of milk to the factory
which is refereed as contract farmers. These areas are covered with Jamuna River,
its branches and submerged under water up to 4 months in a year. During winter,
vast areas of these regions are used as pasture land in this period where the
dairy cattle are reared under free range system. The farmers those who have
more than 100 liters of raw milk production per day and can ensure constant
flow of raw milk to the company were selected and contracted (Fig.
Collection of raw milk: Milk Vita and other private dairies including
PRAN, BRAC Dairy, Bikrampur Dairy and Aftab Milk and Milk Products Ltd., Shilaidah
Dairy and Akij Food and Beverage Ltd. have collected raw milk from the selected
areas. The farmers of these regions are more apt in dairy cattle management
than the farmers of other areas of the country. This is due to the provision
of better animal health care and technical support by the Milk Vita and other
private dairy industries of these areas.
However, they failed to maintain standard milking system due to illiteracy
of the farmers, lack of awareness about the prevention of microbial contamination
of milk and lack of training about the health and hygiene. Milk Vita used to
collect milk from its members as the organization run by cooperative system.
But the private dairies used to have milk from the contract farmers who are
or are not the members of the Milk Vita. Farmers used to perform milking following
the traditional method. Then milk is brought to the neighboring chilling centers
by loading the milk can through travelling around 10 miles away by rickshaw
or van and sometimes by motor vehicles with or without any preservatives.
|| Study areas (Milk Pocket Zones) indicating in the Map of
Thus, they accumulate milk in a large vat from different cows of different
farmers house. Raw milk is received by the quality controller based on
organoleptic tests and sometimes on the basis of physico-chemical parameters.
The price is determined based on fat content of raw milk. Then all the collected
milk is being allowed to chill at 4°C in the chilling center. From the chilling
center, all of the collected milk brought to the factory by insulated road milk
tanker to the factory. The test samples were collected from the road milk tanker
by sterilized beaker and dilution bottle both for physico-chemical and indirect
microbiological tests and brought under different physico-chemical and indirect
microbiological tests immediately.
Samples: A total of 365 mixed samples were collected from the road milk
tanker by sterilized beaker and dilution bottle and brought under different
tests for reception and commence for processing immediately.
Physical study: Organoleptic tests were carried out with different sensory
organs of man which are eyes, tongue and nose. Of which Color, flavor and taste
of raw milk were evaluated with the help of eyes, nose and tongue.
Chemical tests: The chemical tests like Alcohol Precipitation Test (APT),
Clot on Boiling (COB) test, fat test, acidity test, pH test, Corrected Lactometer
Reading (CLR) test and Solids-not-fat (SNF) calculation by using fat% and CLR
were done following the instruction of standard methods for the determination
of dairy products (Wehr and Frank, 2004).
Microbiological study: Milk is the enriched media for the growth and
multiplication of micro-organism. Therefore, for the sake of public health it
is important to observe the magnitude microbial load in the raw milk. As Standard
Plate Count (SPC) and Coliform Count (CC) are time consuming to interpret about
the quality of milk, the rapid method Methylene Blue Reduction Test (MBRT) were
carried out following the instruction of the standard methods for the determination
of dairy products (Wehr and Frank, 2004).
Adulterants determination: Hydrogen per oxide, sodium hydroxide, formalin,
sugar, starch, urea and gelatin were determined in the raw milk following the
method described by Wehr and Frank (2004).
Data analysis: Data were analyzed using the statistical package Statistical
Program for Social Studies (SPSS). confidence interval at 95% was considered
as level of significance (Zar, 1984).
RESULTS AND DISCUSSION
In this study, physical properties of raw milk were found to be satisfactory.
On the other hand, the commercial parameters including fat%, SNF%, TS% and water%
satisfied the recommended standard of raw milk. Indirect microbiological evaluation
based on acidity%, pH values and methylene blue reduction time revealed that
raw milk of rural dairies of Bangladesh can be classified as close to the poor
grade. Moreover, all of the raw milk samples tested in this study were free
from all kinds of adulterants including Hydrogen per oxide, sodium hydroxide,
formalin, sugar, starch and urea.
Physical parameters: The color of all milk samples collected from the
different regions of Bangladesh was normal (Whitish) which is mainly depends
on the breed, the level of fat and solid present and in most cases the nature
of feed consumed by Eckles et al. (1951). The occurrence
of normal flavor of all raw milk samples might be influenced by rapid chilling,
prompt preservation and quick transportation and rapid examination of raw milk
samples without lingering. In addition, the cows might have not been allowed
eating some sorts of odd flavored feed prior to milking them.
The results obtained from this study corroborate findings in other similar
studies (Islam et al., 1984; Chanda
et al., 2007). The taste of all collected milk samples was found
slightly sweet which is similar to the finding of Islam
et al. (1984) and Chanda et al. (2007).
The average mean and standard deviation of specific gravity of milk samples
were 1.030±0.001 (Table 1). Statistical analysis showed
that the difference among specific gravity of milk of the test samples was not
significant (p<0.05). Islam et al. (1984)
reported that the mean of specific gravity of milk of Bangladesh Agricultural
University (BAU) dairy farm was 1.031 and milk from local market was 1.026.
Similarly, Yadav and Sarawat (1982) reported a lower
specific gravity in market milk of Varansi town, India. Chanda
et al. (2007) also reported lower specific gravity in market milk
of Chittagong city of Bangladesh. Filliptovic (1953)
obtained the specific gravity of 1.032 for cows milk in Yugoslavia. Commercial
industries used to accept raw milk with minimum specific gravity of 1.025.
Chemical and microbiological parameters
Month wise variation of Fat, SNF, Total solids and water contents: The average
fat% was found 3.98% (3.98±0.20) which is non-significant and much lower
than Jebu and Taurine cattle like Red Sindhi (4.9%), Gir (4.73%), Tharparker
(4.55%), Sahiwal (4.55%) and Jersy (5.37%). It is also lower than Crossbred
cows (4.5%) but higher than the Friesian (3.4%) cows (ICAR,
2002) (Table 2). The highest fat% was found 4.19% (4.19±0.18)
in January and the lowest was found 3.78% (3.78±0.26) in April both of
which displayed similarity with the aforesaid results (Table 2).
The average SNF% was found 7.4% (7.4±0.09) which is non-significant
and much lower than the milk of Jebu and Taurine cattle like Red Sindhi (8.76%),
Gir (8.67%), Tharparker (8.7%), Sahiwal (8.82%), Jersy (9.54%), Friesian (8.86%)
and Crossbred (8.63%) cows (ICAR, 2002) (Table
|| Observed physical qualities of raw milk samples (average)
|aND = No difference, b NS = No significance
|| Monthly status of fat%, SNF%, Total Solids (TS) % and Water%
of raw milk
|Values are Mean±SD
The highest SNF% was found 7.48% (7.48±0.09) in November and the lowest
was found 7.31% (7.32±0.19) in October (Table 2).
The average total solids and water contents were found 11.38% (11.38±0.48)
and 88.62% (88.62±0.52) which is lower and higher than the milk of Jebu
and Taurine cattle like Red Sindhi (13.66%), Gir (13.30%), Tharparker (13.25%),
Sahiwal (13.37%), Jersy (14.91%), Friesian (12.26%) and Crossbred (13.13%) in
respect of Total Solids and Red Sindhi (86.34%), Gir (86.7%), Tharparker (86.75%),
Sahiwal (86.63%), Jersy (85.09%), Friesian (87.74%) and Crossbred (86.87%) in
respect of water% (ICAR, 2002) (Table 2).
Season wise variation of Fat, SNF, Total solids and Water contents:
Seasons have had influence on the milk composition where the highest fat% was
found 4.06% (4.06±0.16) in the autumn and the lowest has been found 3.83%
(3.83±0.23) in the summer. The fat percentage starts to fall gradually
from the autumn till the early period of summer. Then it starts again increasing
steadily, showing a remarkable rise in the September (Tables 2,
The highest SNF% has been found 7.43% (7.43±0.07) in the rainy Season
and the lowest has been found 7.36% (7.36±0.10) in the winter season.
Regular seasonal variations have also been reported in the raw milks content
of lactose, ash and citric acid (SNF), but these variations seemed to be comparatively
little compared to those of fat and protein. The average citric acid and ash
content in milk generally varied over the year at the rate of a couple of hundredths
of a percent.
The highest total solid was 11.48% (11.48±0.52) in the autumn and the
lowest was found 11.23 (11.23±0.47) in the summer (Table
3). The highest Water% was found 88.79% (88.79±0.47) in the summer
and the lowest was found 88.53% (88.53±0.41) in the autumn (Table
3). By and large, these variations generally repeat themselves in the following
years, but the variations of fat and SNF contents might differ from one year
to another depending on weather and feed.
Month wise variation of Acidity, pH and MBRT of raw milk: The average
acidity and pH was found 0.137% (0.137±0.008) and 6.84 (6.84±0.02)
which were within the acceptable range while the average MBR time 56.75 minutes
(56.75±18.25) (Table 4). However, the highest acidity
and lowest pH were found 0.143% (0.143±0.005) and 6.83 (6.83±0.019)
in May and the lowest acidity and highest pH were found 0.135% (0.135±0.012)
and 6.85 (6.85±0.005) in the month of December.
The development of acidity in milk depends upon the number of available lactic
acid and other acid producing bacteria like Lactobacillus spp., Pseudomonas
spp., E. coli, Streptococcus spp., Staphylococcus spp., Yeasts
and Moulds. Improper chilling of raw milk may lead to development of higher
acidity and lower pH in raw milk due to increased growth and multiplication
of microbes there.
|| Fat %, SNF %, Total Solids (TS) % and Water% on the basis
|Values are Mean±SD
|| Reduction time of methylene blue reduction time (MBRT) test,
acidity and pH of raw milk on the basis of months
|Values are Mean±SD
|| Reduction time of methylene blue reduction time (MBRT) test,
acidity and pH of raw milk on the basis of season
|Values are Mean±SD
While (May) the highest acidity (0.143%) and the lowest pH (6.83) then MBR
time was found 55.47 minutes (55.47±18.20) which was the lower reduction
time among the other months. And while (December) the lowest acidity (0.135%)
and the highest pH (6.85) then the MBR time 62.37 minutes (62.37±19.00)
which was the highest reduction time in the year (Table 4).
Season wise variation of acidity, pH and MBR time of raw milk: The microbial
load, acidity, pH of raw milk has been influenced by the season where the highest
acidity and the lowest pH have been found 0.139% and 6.83 in the summer. Because,
in the summer the MBR time was found 55.77 (55.77±18.13) min (Table
5). Though the similar acidity and pH have been observed in rainy, autumn
and winter season, but the MBR time slightly differs among different seasons.
Adulterants determination: Determination of adulterants revealed in
the absence of adulterants such as Hydrogen per oxide, sodium hydroxide, formalin,
sugar, starch, urea and gelatin in the raw milk because of rejection of adulterated
milk in the collection centers. Adulterants referred that those agents are added
in raw milk with an aim to enhance self-life, increase specific gravity or density
and volume. This has been practiced by the farmers from the commercial point
of view not taking into account of public health issues. Obviously, the adulterants
like Hydrogen per oxide, sodium hydroxide, formalin, urea and gelatin are harmful
for human body which should be strictly monitored.
As milk is the most perishable product, essential food for infants and olds,
it requires rapid reception, processing, packaging and to ensure constant availability
in the market. Therefore, convenient and rapid method for the determination
of milk quality is essential. Our study explored the chemical composition and
the acceptable values of methylene blue reduction test, acidity, pH and other
chemical tests and their relation which is acceptable to determine the raw milk
quality for reception and further processing satisfying the minimum standard
particularly in the rural dairies of the developing countries. Furthermore,
quick adulterants determination will ensure supply of safe milk to the consumers.
This will be a guideline for determining the quality of raw milk in the rural
dairy industries of the developing countries.
In conclusion, it can be clearly outlined that commercial and hygienic quality
of raw milk determination is crucial prior to reception of raw milk for further
processing. Due to high perishable nature, rapid estimation of physical, chemical
and microbiological quality of raw milk using fast, cheap and less expertise
dependent methods e.g. MBRT has gained remarkable acceptance in contrast to
other costly, time-consuming and high skill dependent methods. Therefore, Methylene
Blue Reduction Time (MBRT) test can be opted for rapid determination of raw
milk quality. Microbiological, Physical and Chemical qualities determined by
using MBRT along with other relevant physical and chemical tests have ensured
faster and efficient raw milk quality determination exercise in this study.
The results of this study explored that physico-chemical and bacteriological
qualities of industrial raw milk of Bangladesh close to satisfy the minimum
standards which were determined by MBRT and other relevant physical and chemical
tests. The qualitative value of raw milk obtained in this study is favorable
for further industrial processing.
The study was conducted in the milk processing factory of Aftab Milk and Milk
Products Ltd., Bhagalpur, Bajitpur, Kishoreganj, Bangladesh. We would like to
express our thanks and gratitude to this organization for supporting the research
work. No competing financial interest exists.
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