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Chemical and Microbiological Quality Assessment of Raw and Processed Liquid Market Milks of Bangladesh

Tanim Jabid Hossain
Department of Biochemistry and Molecular Biology, University of Chittagong, 4331 Chittagong, Bangladesh.

Khorshed Alam
Microbiological and Industrial Irradiation Division, Institute of Food and Radiation Biology, Atomic Energy Research Establishment, Savar, 1349 Dhaka, Bangladesh.

Dwipayan Sikdar
Department of Biochemistry and Molecular Biology, University of Chittagong, 4331 Chittagong, Bangladesh.

Abstract/ Executive Summary:

Twelve different liquid market milks of Bangladesh were examined to evaluate their chemical and sanitary quality. Six of these were open raw milk bought from local daily markets and the other six were processed packet milk (both pasteurized and UHT (Ultra High Temperature)-processed) available in shops. The twelve samples were examined for the determination of percentage of water, total soluble solids, fat, solids non-fat, lactose, protein and ash, measurement of titratable acidity, detection of adulterants, enumeration of total bacterial count, staphylococcal count, coliform count, fecal coliform count, Salmonella and Shigella count, Aeromonas hydrophila count and psychrophilic count. Results revealed that most of the raw and pasteurized milks were substandard in both chemical and sanitary quality whereas the quality of UHT-treated milks was excellent. All the pasteurized and raw milks were found to be contaminated having bacterial load exceeding the acceptable limit. Pathogenic bacterial genera (Aeromonas, Salmonella and Staphylococcus) were identified in some of these samples. But none of the UHT-processed milk contained any bacteria. Water had been added in six samples whereas, sucrose was found in five of the six temperature-processed samples.

Keywords: Liquid Market Milks, Bacterial distribution, Quality evaluation, Chemical composition, Adulteration

Location: Local market Bangladesh

Start Date:

End Date:

Program Area: Food Safety and Security

Commodity: Milk

Objectives:

To determine; the bacterial load, food value and degree of cleanliness surrounding the production and handling of the milk as well as to find out the differences among the raw, pasteurized and UHT-processed milks in terms of chemical composition and bacterial distribution.

Methodology:

In Bangladesh, milk is generally sold in two ways. In most cases, the farmers bring milk in open pots and sell it directly in the market without any processing and packaging. In other cases, milk companies collect milk from the farmers or dairy farms, process it via pasteurization or UHT treatment and package the processed milk which is then sold in shops under specific brand name. In this study, raw milks were purchased from a local daily market while brand milks were bought from different shops. A total of twelve samples were examined. Six (designated as R-1 to R-6) were raw milk bought from different vendors. Of the remaining six, three (P-7 to P-9) were pasteurized milks each from different brand and the other three (U-10 to U-12) were UHT-processed also from different brands. All the samples were aseptically collected and immediately transported to the laboratory for examination. Percentage of water was determined by subtracting the value of Total Soluble Solids (TSS) from 100. TSS was determined by using refractometer (Portable refractometer, model: FG 103, Brix 0-32%). Milk fat was measured by Rose-Gottlieb’s method. Amount of Solids Non-fat (SNF) was determined by subtracting the amount of fat from TSS. Lactose was determined by volumetric method. About 20 mL of milk was diluted with water to a volume of 400 mL and 8-16 drops of a 10% solution of acetic acid added. The precipitate was filtered off and washed with cold water. The filtrate was boiled in a flask and the albumin precipitated. This was filtered off also and the precipitate was washed with cold water. The filtrates and wash water were mixed and measured accurately. A portion of the filtrate was placed in a burette and this was run into a boiling mixture of 20 mL Fehling’s solution and 80 mL water. After the copper had been completely precipitated, the number of mL used was read. About 20 mL Fehling’s solution corresponds to 0.135 g milk-sugar. Ash content was determined by the method described. Acidity was measured by titration with 0.1 normal sodium hydroxide solution and using 1% alcohol solution of phenolphthalein as indicator. Presence of the adulterants was tested by specific qualitative tests. Standard Plate Count (SPC) method recommended for dairy products was followed for quantitative analysis of bacteria. For obtaining single colony isolate, the method described. Morphologically, dissimilar well-spaced colonies were picked up with the help of a sterile loop from the plates which had from 30-300 colonies. Each colony was streaked on to freshly prepared plates of the same media and incubated at 37°C for ≥24 h. After incubation, typical pure colonies were taken as isolates. The selected isolates were then purified through repeated streak plating. When plating produced only one type of colony in a particular plate, it was considered to be pure. The purified isolates were then transferred to nutrient agar slant in one drum screw capped culture vial and preserved as stock culture. Identification was done up to genus by following the Bergey’s manual of determinative bacteriology. For identification, different morphological characteristics including shape, size, form, texture, opacity, edge, elevation of the isolated colonies were studied carefully and after gram staining, microscopic examination was carried out. The biochemical tests performed were Catalase test, Oxidase test, Methyl-red test (MR test), Voges-proskauer test (VP test), production of hydrogen sulphide (KIA test), hydrolysis of starch and fermentation tests.

Source of Information: Research Journal of Dairy Sciences, Year: 2010 | Volume: 4 | Issue: 4 | Page No.: 28-34

Article Link (Online Journal): DOI: 10.3923/rjdsci.2010.28.34

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Results revealed that most of the raw and pasteurized milks were substandard in both chemical and sanitary quality whereas the quality of UHT-treated milks was excellent. All the pasteurized and raw milks were found to be contaminated having bacterial load exceeding the acceptable limit. But none of the UHT-processed milk contained any bacteria. In essence, the UHT-treated (Ultra High Temperature) milks were of excellent quality.

Knowledge Management: Journal