Studies on the quality of Misti Dahi collected from Kolkata and its suburbs

The storage studies on the misti dahi samples have shown that there is a sharp increase in the titratable acidity during storage at 302 0C while the rate of increase of titratable acidity of misti dahi samples during storage at 52 0C was rather slow. During storage at 302 0C the maximum increase in acidity was noticed after 24 hrs of storage while increase in acidity during storage at 52 0C was always steady. Yeast and mould in the products increased progressively during storage. A sharp increase in the yeast and mould population is noticeable during storage at 302 0C while increase is relatively gradual during storage at 52 0C. The rates of destruction of coliform organisms were higher at room temperature (302 0C) than at refrigeration temperature (52 0C). The overall relatively poor results obtained for all the samples in relation to their microbiological quality indicate that step should be taken to improve their quality.

Introduction

Next to milk dahi is the most important dairy product prepared and utilized in various forms at most households in this country. Misti dahi is quite popular in the eastern parts of India, mainly West Bengal and partly in Assam, Bihar and Orissa. Cane sugar in varied proportions 6 to 25 per cent-Ray and Srinivasan (1972) [6] ; 15.8 to 22 per cent-Mukhopadhyay and Singh (1973) [4] ; 12.8 to 18.7 per cent-Ghosh and Rajorhia (1987) [4,1] is added to milk either before or at the time of inoculation for preparation of misti dahi in unorganized sector. Prolonged heating of sweetened milk at simmering temperature leads to partial concentration and browning. A characteristic cooked flavour and firm body develop after setting of the curd. Use of colour or sugar caramel or gur is also in vogue. Dahi, a rich source of nutrients, is subject to microbial contamination at various stages of manufacture and during addition of ingredients. The handling by the operators who happen to be carries of certain diseases may also contaminate the product with potential pathogenic organisms. Hence, to ensure the safety of the product, microbiological quality of misti dahi should be as high as possible and it must be free from any of the pathogens as the people largely consume the product. In order to safeguard the consumer health, which is of primary concern, there is a need to impose firm control on the quality of misti dahi. In the present investigation, the microbiological examinations will help in determining the quality of the product, the sanitary and hygienic conditions maintained and the effect of public health for the marketed product available in Kolkata and its suburbs.

Materials and Methods

Materials and Methods

Collection of samples

The samples (30 Samples) of misti dahi were collected from Kolkata and its suburbs.

Analytical Methods

Methods relating to estimation of various microbial population in the samples, the following microbiological examination along with testing of titratable acidity were carried out:

Storage studies

Storage studies were done at 3020C and 520C till the quality remain good in term of titratable acidity, Yeast and mould count and Coliform count. population is noticeable during storage at 3020C while increase is relatively gradual during storage at 520C. It is observed that the rate of growth of yeast and mould count is higher when sufficient acidity is produce to bring the pH down to around 5.0. It may be concluded that the chance of spoilage of misti dahi is higher during storage at room temperature (3020C) due to higher rate of growth of yeast and mould at room temperature.

Results and Discussions Effect of storage period on Titratable acidity of Misti dahi: From

Results and Discussions Effect of storage period on Titratable acidity of Misti dahi: From

Effect of storage period on Coliform count of Mist dahi

From Table-1 and Table-2 it is clear that during storage the rates of destruction of coliform organisms were higher at room temperature (3020C) than at refrigeration temperature (520C). In regard to the effect of storage temperature it was observed that these organisms survived for longer period of time at refrigeration temperature (5  20C) than that at room temperature (3020C). In this connection, it has been reported that viable counts of coliform decreased very rapidly with the fall of ph below 4.0 (Tiwari and Singh, 1966; Goel et al., 1971) [6,7] . The slow rate of destruction of the coliform is ascribed to gradual increase in acidity, which perhaps permits development of acid tolerant strains (Prasad IN VI., 1984) [5] . In the light of the above report, it may be concluded that misti dahi stored at a lower temperature is of no value in preventing the destruction of coliform if the product is already contaminated. It is possible that misti dahi kept at room temperature during summer months is less likely to be a source of coliform than that samples of misti dahi stored at the temperature during winter months.

Figures and tables from the paper

No. of samples	Storage periods (hrs.)	Acidity (% L. A.)	Yeast and mould count (c.f.u./ml)	Coliform count (c.f.u./ml)
D S1	0	0.74	6  102	Nil
D S2		0.58	31  102	43  102
D S3		0.44	4  102	21  103
D S4		0.96	25  103	71
D S5		0.65	17  103	5  102
Average	24	0.662	92  102	5174.2
D S1		1.050	18  102	Nil
D S2		0.94	61  102	20  102
D S3		0.85	17  102	11  103
D S4		1.11	81  103	31
D S5		0.96	68  103	38
Average	48	0.982	317  102	2682.2
D S1		1.26	74  102	Nil
D S2		1.20	24  103	5  102
D S3		1.12	81  102	37  102
D S4		1.38	24  104	nil
D S5		1.24	20  104	84
Average	72	1.24	959  102	856.8
D S1		1.44	15  103	Nil
D S2		1.39	64  103	180
D S3		1.32	11  103	170
D S4		1.53	73  104	nil
D S5		1.44	80  104	21
Average	96	1.424	324  103	74.2
D S1		1.59	61  103	Nil
D S2		1.51	18  104	93
D S3		1.46	84  103	130
D S4		1.66	11  105	nil
D S5		1.60	13  105	nil
Average		1.564	545  103	44.6
D S1	120	1.70	15  104	Nil
D S2		1.64	63  104	22
D S3		1.62	25  104	35
D S4		1.77	64  105	nil
D S5		1.73	71  105	nil
Average		1.692	29  105	11.4

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Effect of storage at 302 0C on the Titratable acidity, Yeast and mould count and Coliform count of Misti dahi samples collected

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No. of samples	Storage periods (hrs.)	Acidity (% L. A.)	Yeast and mould count (c.f.u./ml)	Coliform count (c.f.u./ml)
DS1	0	0.74	6  102	Nil
DS2		0.58	31  102	43  102
DS3		0.44	4  102	21  103
DS4		0.90	25  103	71
DS5		0.65	17  103	5  102
Average		0.662	92  102	5174.2
DS1	24	0.78	9  102	Nil
DS2		0.66	33  102	49  102
DS3		0.54	6  102	28  103
DS4		0.93	30  103	13  10
DS5		0.71	20  103	7  102
Average		0.724	109.6  102	6746
DS1	48	0.81	14  102	Nil
DS2		0.74	37  102	54  102
DS3		0.60	9  102	35  103
DS4		0.95	36  103	20  10
DS5		0.76	24  103	34  10
Average		0.772	132  102	8188
DS1	72	0.87	21  102	Nil
DS2		0.81	45  102	56  102
DS3		0.67	13  102	40  103
DS4		1.00	42  103	14  10
DS5		0.80	28  103	20  10
Average		0.83	155.8  102	9188
DS1	96	0.90	26  102	Nil
DS2		0.85	53  102	53  102
DS3		0.73	18  102	38  103
DS4		1.06	50  103	91
DS5		0.86	33  103	14  10
Average		0.88	185.4  102	8706.2
DS1	120	0.95	32  102	Nil
DS2		0.89	65  102	30  102
DS3		0.79	23  102	17  103
DS4		1.09	56  103	65
DS5		0.91	39  103	93
Average		0.926	214  102	4031.6

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Effect of storage at 5 2 0C on the Titratable acidity, Yeast and mould count and Coliform count of Misti dahi samples collected

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