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Shelf-life of Dahi (yogurt) with or Without Potato Mash

M. R. Amin
Department of Dairy Science, Faculty of Animal Husbandry, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

M. N. Islam
Department of Dairy Science, Faculty of Animal Husbandry, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

M. A. Habib
Department of Animal Breeding and Genetics, Faculty of Animal Husbandry, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

F. Islam
Department of Dairy Science, Faculty of Animal Husbandry, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Abstract/ Executive Summary:

Four different types of Dahi (Yogurt) were prepared and kept at room and refrigeration temperatures with different concentrations of potato mash (0, 5, 10 and 15%). These Dahi samples were analyzed for smell and taste, body and consistency, colour, texture and acidity and pH at pre and post storage period. The quality of Dahi deteriorated quickly at room temperature than at refrigeration temperature. With (5%) or without potato mash keeping quality was preserved for up to three days but at refrigeration temperature they were suitable up to 12 days. Addition of 10% and 15% potato mashes were suitable for keeping Dahi up to two days at room temperature while in refrigeration temperature it was acceptable up to ten and eight days, respectively. Preparation of Dahi in incorporating potato mash may be economically feasible without compromising it qualities.

Keywords: Dahi (Yogurt), Potato mash, Shelf-life

Location: BAU, Mymensingh

Start Date:

End Date:

Program Area: Quality and Nutrition

Commodity: Yogurt

Objectives:

This study was undertaken to assess the shelf-life of Dahi using potato mash at different concentrations.

Methodology:

Chemical analysis of whole milk: Before preparing Dahi, initial quality of collected milk from the university dairy farm was estimated for specific gravity, total solids (TS; %), solids-not-fat (SNF; %), fat (%), acidity (%), protein (%), ash (%), moisture (%) and pH value. Protein content was measured by micro-Kjeldahl method (AOAC, 1990). Fat was determined by the Gerber method (Bradly et al., 1992). Ash content was determined by dry ashing of the samples for 24 hours at 550°C. Total solids content was determined by gravimetric method by drying the samples in an oven at 105°C for 24 hours (AOAC, 1990). Total titratable acidity was determined by AOAC (1990) method. The pH was measured using an electric digital pH meter (HANNA-pH 210, Germany) according to AOAC (1990). Preparation of potato mash: The purchased potato was weighed with the help of balance and boiled, and the skin was separated with the help of clean hand. Black spotted diseased potatoes were removed. Then the potato was mashed by clean hand, kept in different plastic cups and stored at refrigeration temperature (5°C) until used. Preparation of plain Dahi: Required amount of milk boiled for about 10 minutes to reduce some volume of milk and also to destroy the viable organisms. At the boiling time, sugar was added at the rate of 8%. During heating, milk was stirred thoroughly with the help of a stirrer. After desired heating milk pan was taken out from the heater and allowed to cool down near 42°C and inoculated with 2% starter cultures collected from local market. After inoculation warm milk of 42°C was then poured into several pre washed plastic cups and kept undisturbed at an incubation temperature of 37°C until complete coagulation. After complete coagulation (5 - 8h), the Dahi samples were taken out from the incubator and were stored in a refrigerator at about 5°C for further analysis. This type of Dahi was designated as type "A" Dahi for the study purpose. Preparation of Dahi mixed with potato mash: The preparation of Dahi with potato mash is similar with the preparation of plain Dahi. Potato mash @ 5, 10 and 15% was added during boiling and was blended for proper mixing. After proper heating, the milk pan was taken out from the heating source and was kept to cool down to 42°C. At that time starter culture @ 2% was added and was kept in an incubator at 37°C until the complete coagulation (5 - 8h). Then the Dahi samples were stored at about 5°C in the refrigerator until used. Four different types of Dahi were prepared and designated as: i) Type A Dahi (plain Dahi without adding potato mash), ii) Type B Dahi (added 5% potato mash in milk), iii) Type C Dahi (added 10% potato mash in milk) and iv) Type D Dahi (added 15% potato mash in milk). Shelf-life assessment: In this case, the prepared Dahi samples were preserved at room temperature (32°C) and refrigeration temperature (5°C) to assess the shelf-life. The qualities of Dahi were assessed as: (a) Physical tests: i) Smell and taste (50 marks), ii) Body and consistency (30 marks) and iii) Colour and texture (20 marks) and (b) Chemical tests: i) Acidity test and ii) pH value. At room temperature, the said parameters of four samples were measured every day for every sample but at refrigerator temperature the same tests were done every alternate day until spoilage was evident. Statistical design and data analysis: All study materials were completely homogenous and statistical analysis done as per Steel and Torrie (1960) using Completely Randomized Design. Data collected were analyzed by using (MSTAT) statistical program.

Source of Information: Bangl. vet. 2012. Vol. 29, No. 1, 22 – 30

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Considering the shelf-life assessment of Dahi samples, it is suggested that potato mash (5%) may be added for improving the quality of Dahi that can be consumed up to three days at room temperature and 12 days at refrigeration temperature.

Knowledge Management: Journal