Abstract: The experiment was carried out with an aim to assess the quality of Dahi prepared from cow, goat and buffalo milk. With that understanding, milk samples were collected from Bangladesh Agricultural University Dairy farm; Senbari, Mymensingh; Gobiddocher, Mymensingh and Dahi samples were analyzed in the Dairy Technology and Animal Nutrition Laboratory of the Bangladesh Agricultural University, Mymensingh. The parameters used to monitor the quality of Dahi samples were physical (smell and taste, body and consistency, color and texture), chemical (protein, fat, total solids, ash, acidity and pH) and microbiological (gram positive rods and cocci, total viable count, coliform and mould count). From the result of all parameters it can be concluded that Dahi prepared from cows milk in the Dairy Technology Laboratory, Department of Dairy Science was superior to Dahi samples in same place from buffalo and goat milk. Most of the nutritional parameters it can be found that Dahi sample prepared from buffalo milk scored the highest. From the nutritional point of view it can be showed that Dahi prepared from buffalo and goat milk was not so bad. So, the people of our country are suggested to prepare Dahi from cow, buffalo and goat milk and also follow to strict hygienic conditions in order to get good quality Dahi.
INTRODUCTION
Milk is very nutritious and perhaps an indispensable food for human being. But in this area of industrialization, food habit of common people is changing. They are preferring moor healthy, delicious foods to fresh raw foods. Hence, milk is converted to various products. Yoghurt is one of them locally called Dahi. About 4% of the total milk produced in Bangladesh is used for the preparation of Dahi (Mustafa, 1997). Dahi is prepared by using mixed culture of Streptococcus lactis, Lactobacillus bulgaricus, Streptococcus thermophilus, Streptococcus citrophilus, Lactobacillus plantarum etc. Like milk, Dahi is also very nutritious. It has been demonstrated that acid milk is somewhat digestible than normal milk. For some individuals, Dahi has a definite therapeutic value, especially who usually suffer from stomach and intestinal disorders. The use based on the assumption that the acid fermenting bacteria and lactose of milk are able to create conditions in the intestinal tract which are unfavourable for the growth of putrefactive bacteria and thereby prevents the formation of gas and a condition known as 'autointoxication'. Yoghurt is also effective in lowering the blood cholesterol level. Following this discovery, considerable amount of L. acidophilus were distributed in the form of a milk culture of the organism. If acidophilus therapy is to be of any value, large number of viable cells of a readily implantable strain of the organism must be consumed daily, along with a suitable carbohydrate such as lactose or dextrin. Presumably these carbohydrates are effective because they are absorbed from the tract fairly slowly, thus remaining available longer as food for the lactobacilli (Foster et al., 1958).
The nutritive value of milk and milk products depends upon their cleanliness, purity and wholesomeness. Milk products having those characteristics are great consumer's demand. But they lack uniformity from place to place. To solve this problem, we have a unique fermented milk product Dahi. For this, a desirable standard for the manufacture of Dahi should be established according to the average consumer's of Bangladesh.
Some research works have been done in different countries on the quality of Dahi prepared from cow and buffalo milk. But very limited works have been done on the quality of Dahi made from goat milk. Hence, an attempt was made to judge the quality of Dahi prepared from cow, buffalo and goat milk. This experiment is carrying significance in this country condition because the people of our country have no idea about the new food product. This new food product can bring significant change in our national health. Moreover, the availability of data on cow, buffalo and goat milk and its Dahi is scanty, so this experiment is very important for practical point of view.
MATERIALS AND METHODS
This research was conducted at the Dairy Technology and Animal Nutrition Laboratory, Bangladesh Agricultural University, Mymensingh during the period of July 04 to August 19, 2005. Cow milk was collected from Bangladesh Agricultural University (BAU) Dairy Farm. Buffalo milk was collected from Senbari; Mymensingh and goat milk was collected from Gobiddochar Mymensingh. Every three liters of fresh whole cow milk and buffalo milk and two liters of fresh whole Goat milk was collected.
Preparation of Dahi in the Laboratory
After collecting each whole milk, an attempt was made to prepare Dahi in
the laboratory. At first, milk was boiled to prepare Dahi. At the time of boiling
sugar at the rate of 8% was added to the whole milk. Milk was heated to boiling
temperature until reduced up to 20-25% of the volume of milk. Boiled milk was
then cool down to near 42°C and inoculated with 2 to 3% starter culture
collected from Dairy Science Laboratory. After inoculation, warm milk of 42°C
was then poured into plastic cups and kept at an incubation temperature of 37°C
until complete coagulation. After complete coagulation (8-10 h) titrable acidity
percentage of the curd was measured. The samples were then stored in a refrigerator
at about 4°C for further analysis.
Judging of Dahi
Organoleptic test (smell and taste; Body and consistency; Color and texture)
were done immediately after preparation of each batches of Dahi. Organoleptic
test was performed by a panel of expert judges (Nelson, 1948).
Chemical Analysis
Before preparation of Dahi, initial quality of collected milk samples was
measured by conducting several tests in the laboratory. The tests were as follows;
Acidity (%), Specific Gravity, Fat (%), Total Solids (TS%) and Protein (%).
Milk and Dahi
Before preparation of Dahi, initial quality of collected milk samples was
measured by conducting several tests in the laboratory. The tests were acidity
(%), specific gravity, fat (%), total solids (TS%) and protein (%). Total solids
content of the milk samples were determined by oven dry method according to
AOAC (1990). Specific gravity was performed by using Quevenne lactometer, according
to the method described by Aggarwala and Sharma (1961). Fat per cent was determined
by Babcock method and acidity was determined by titrating with N/10 sodium hydroxide
(NaOH) solution using the procedure described by Aggarwala and Sharma (1961).
Protein was determined by Kjeldahl procedure (AOAC, 1990). PH was measured with
the help of a pH meter-215 (Ciba Corning Diagnostics Ltd. Sudhury, Suffolk,
England Co 106xD). Ash per cent of Dahi samples were determined by oven dry
method according to (AOAC, 1990).
| Microbiological Test |
| • | Determination of gram positive rod and cocci: According to gram staining method (APHA, 1967) gram positive and cocci per cent were determined. |
| • | Determination of Total Viable Count: For Total Viable Count of Dahi samples, Standard Plate Count (SPC) was done according to the method described in Standard Methods for the Examination of Dairy Products (American Public Health Association, 1967). |
| • | Determination of Coliform Count: Coliform count of Dahi was done according to the method as described in the Standard Methods for Examination of Dairy Products (APHA, 1967). |
| • | Determination of Yeast and Mould Count: According to the method of Standard Methods for Examination of Dairy Products (APHA, 1982), Yeast and Mould count of Dahi was done. |
Statistical Analyses
Statistical analyses of the collected information were carried out by using
Completely Randomized Design (CRD) with one factor in MSTAT program. The differences
among sample means were compared by calculating LSD value with the help of Least
Significant Difference (Gomez, 1984).
RESULTS AND DISCUSSION
Initial Quality of Milk
The milk samples were collected from Dairy farm of Bangladesh Agricultural
University (Cow); Senbari, Mymensingh (Buffalo); Gobiddochar, Mymensingh (Goat)
and analyses were carried out according to procedure suggested by Aggarwala
and Ahmed (1940) in order to determine the quality of milk (Table
1).
This result indicates that the milk used in the current experiment is good quality and the findings are almost similar to that of Biswas (1997) and Ghatak et al. (1998).
Quality of different types of Dahi
In this experiment, three different types of Dahi (Cow, Buffalo and Goat)
were prepared and their physical (Organoleptic), chemical and microbiological
qualities were measured by various tests.
Physical (Organoleptic) Parameters
Smell and Taste
Smell and taste score of different types of Dahi prepared from Cow, Buffalo
and Goat milk were 45.50±1.29, 40.50±2.52 and 38.75±2.22,
respectively (Table 2). Statistical analysis showed that there
was significant difference (p<0.01) with in the smell and taste scores of
different types of Dahi.
| Table 1: | The initial quality of Cow, Buffalo and Goat milk |
| Table 2: | Comparison of average score of various Organoleptic characteristics of Dahi prepared from Cow, Buffalo and Goat milk |
Dahi prepared from cow milk obtained the highest score followed by Dahi prepared from Buffalo and Goat milk. So, sensory properties of samples of goat milk Dahi were rated as being inferior to those of samples prepared from cow and buffalo milk. Duitschaever (1978) reported that in his study a 32% consumers gave preference for goat milk Dahi and 68% preferred cow milk Dahi.
Body and Consistency
The mean value of body and consistency scores of Dahi prepared from cow,
buffalo and goat milk were 25.00±3.56, 28.00±2.16 and 23.75±2.63.
Statistical analysis showed that there was no significant difference with in
the body and consistency score of different Dahi samples. Among the samples,
mean value for body and consistency score was highest in case of Dahi prepared
from buffalo milk and lowest for Dahi prepared from goat milk. Venkateshaiah
et al. (1996) reported that higher levels of fat and SNF improved the
body of Dahi. Bozanic et al. (1998) prepared yoghurt from goat milk and
cow milk. They reported that yoghurt samples prepared from goat milk had a softer
consistency and lower viscosity than those prepared from cow milk.
Color and Texture
The color and texture score of Dahi prepared from cow, buffalo and goat
milk were 17.00±1.83, 15.5±1.29 and 14.5±1.29, respectively.
Statistical analysis showed that there was no significant difference with in
the color and texture score of different Dahi samples. The color and texture
score was highest for cow milk Dahi and lowest for goat milk Dahi. That might
be due to the fact that cow milk contains more carotene that might help to develop
golden, yellowish in cow milk Dahi. Goat milk had lower content of fat and total
solids, hence the color and texture score was lowest in goat milk Dahi.
Chemical Parameters
Acidity (%)
The acidity per cent of Dahi samples made from cow, buffalo and goat milk
were 0.82±0.04, 0.74±0.06 and 0.93±0.03, respectively (Table
3). Highly significant difference (p<0.001)were found among those mean
values. Mean percentage of acidity was highest for Dahi made from goat milk,
followed by cow milk where as the value was lowest for Dahi made from buffalo
milk. The result agree with the reports of Cardoso et al. (1991), these
were found that buffalo milk Dahi acidity was 1%.
| Table 3: | Comparison of average chemical composition of Dahi prepared from Cow, Buffalo and Goat milk |
Wide variation in the titrable acidity could be attributed due to different types of buffering action of protein, citrates, lactose, phosphates etc. (Jenness and Patton, 1959).
Fat (%)
The fat percent of different types of Dahi prepared from cow, buffalo and
goat milk were 5.82±0.35, 10.85±0.85 and 5.16±0.65, respectively
(Table 3). Statistical analysis showed that fat content of
different Dahi samples differ highly significantly (p<0.01). Maximum fat
per cent was seen in buffalo milk Dahi, followed by cow milk Dahi and lowest
in goat milk Dahi. Akin et al. (1995) reported that cow milk and buffalo
milk Dahi contained 4.9 and 9.08% fat, respectively. El-Samragy and Samragy
(1988) reported that goat milk Dahi contained 4.08% fat. The findings of these
research accorded to it,
Total Solids TS (%)
The total solids per cent of cow, buffalo and goat milk Dahi were 29.99±1.64,
40.73±2.77 and 27.89±1.27, respectively (Table 3).
Highly significant difference (p<0.001) were found among those mean values.
Average total solids content was highest for buffalo milk Dahi, followed by
cow milk Dahi and that was lowest for goat milk Dahi. Ali (1998) found that
fresh cow milk Dahi contained 29.06% total solids which is similar to our experimental
result. Chakraborty (1998) observed that total solids content of buffalo milk
Dahi was 30-67% which supports our experimental result. El-Samragy and Samragy
(1998) and Park (1994) reported that goat milk Dahi contained 14.16% TS which
is very low than our experimental value. Generally variation in TS content of
Dahi could be attributed due to different types of milk, addition of sugar in
different concentration or extent of concentration of milk during heat treatment
(Ray et al., 1972). In our experiment the variations in TS content was
mainly due to different species of milk used in the study.
Protein (%)
The protein percent of Dahi prepared from cow, buffalo and goat milk were
4.58±0.34, 5.13± 0.17 and 4.00±0.36, respectively (Table
3). Statistical analysis showed that there was significant difference (p<0.01)
with in the protein content of different types of Dahi. Maximum protein percent
was seen in Dahi of buffalo milk, followed by cow milk and lowest protein content
was noted in Dahi of goat milk. The results of this experiment agreed with the
findings of Chakraborty (1998) and Ali (1998) whom found that cow milk and buffalo
milk Dahi contained 4.22-4.44 and 5.1% protein, respectively. In case of goat
milk Dahi the result agreed with the findings of El-Samragy and Samragy (1988)
and Park (1994) whom found that average percentage of protein content of goat
milk Dahi 3.80 and 3.99, respectively. Concentration of milk to about 60-70%
of the original volume due to prolonged heating (Ray and Srinivasan, 1972) has
positive effect on protein content of Dahi.
Ash (%)
The ash per cent of cow, buffalo and goat milk Dahi samples were 0.809±0.04,
0.98±0.06 and 0.784±0.06, respectively (Table 3).
Significant differences (p<0.01) were found among those mean values. Maximum
ash percent was seen in buffalo milk Dahi, followed by cow milk Dahi and lowest
in goat milk Dahi. In case of cow milk Dahi the result agreed with the findings
of Rahman (1998) who reported that cow milk Dahi contained 0.825±0.06
per cent ashes. The result of goat milk Dahi agreed with the work of El-Samrangy
and samrangy (1988) and those found that ash content of goat milk Dahi were
0.78 and 0.818±0.019% , respectively. Buffalo milk contained higher amount
of total solids than cow and goat milk. For this reason buffalo Dahi showed
higher percent of ash.
pH Value
The average pH value of different Dahi prepared from cow, buffalo and goat
milk were 4.88±0.20, 5.01±0.48 and 4.25±0.06, respectively.
Statistical analysis showed that there was significant difference (p<0.05)
with in the pH value of different Dahi samples.
Microbiological Parameters
Total Viable Count
The total viable bacterial count per mL. of different types of Dahi prepared
from cow, buffalo and goat milk were 5.878±0.03, 5.996±0.05 and
5.859±0.05 (Log value), respectively (Table 4). Statistical
analysis showed that significant differences (p<0.05) were existed among
the different Dahi samples. Average highest total viable count was recorded
for Dahi samples of buffalo milk, which that was lowest for goat milk Dahi.
The present investigation partially supported by the result of Adeyl (1998),
who found that the total viable bacteria contained per mL of Laboratory made
sweet Dahi samples were with in the range of 6.2 to 6.3 (Log value).
Coliform Count
The average coliform count per ml. of cow, buffalo and goat milk Dahi were
1.75±1.20, 2.70±0.21 and 1.00±1.15 (Log value), respectively
(Table 4). Result demonstrated that there were wide variation
in average coliform count per mL of different Dahi samples. Average highest
colifom count per mL was found in buffalo milk Dahi, followed by cow milk Dahi
and it was lowest for cow milk Dahi. Statistical significant differences were
found in respect of coliform count per mL. of different Dahi samples. Overall
result of this parameter agreed with that of the result of Islam (1999) who
found that coliform count per mL of Laboratory made Dahi was 2.64±2.05
(Log value). The presence of coliform organisms in Dahi samples indicate that
contamination during its production and handling may cause public health problems.
The possible sources of contamination of product are un cleaned hands of the
manufactures, poor quality water used to cleaned earthen pots and exposure of
the product to open air during setting of curd.
Yeast and Mould Count
Microscopic examination showed that average mould count per mL of cow, buffalo
and goat milk Dahi were 1.44±1.07, 1.889±0.59 and 2.064±0.44
(Log value), respectively (Table 4). Average highest mould
count per mL was found in goat milk and lowest in cow milk Dahi. No significant
differences were found among the different Dahi samples. No yeast count was
observed, may be due to strict sanitary management.
From the result of overall analysis, it could be advocated that Dahi made from
cow milk was the best among the Dahi made from cow, buffalo and goat milk. However,
Dahi made from buffalo and goat milk, respectively adorned the 2nd and 3rd position.
Although buffalo and goat milk Dahi ranked second and third position, respectively
but their nutrient content were also excellent.
| Table 4: | Comparison of average microbiological status of Dahi prepared from Cow, Buffalo and Goat milk |
This sort of innovation may carry benefit for utilization of buffalo and goat milk. In our village condition only a little amount of goat milk and their Dahi is used as medicinal product, like for healing wounds. Attempts should be made to popularize buffalo and goat milk Dahi through the country. So, introduction of buffalo and goat milk for Dahi preparation will not only support better utilization of it but also reduces extra load on cow milk.