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Shelf Life Study of Yogurt by Using Different Concentration of Lactobacillus Acidophilus

Anis Alam Siddiqui
Associate Professor
Department of Food Engineering & Technology, State University of Bangladesh.

Md. Nurul Abadin Chowdhury
Lecturer
Department of Food Engineering & Technology, State University of Bangladesh.

Abstract/ Executive Summary:

There are several types of yogurt like stir curd, set curd and drinkable yogurt and they all need to be refrigerated. Moreover there are very few dairy products that can be stored at room temperature and not many dairy foods are finger foods. A novel yogurt product like a yogurt with L. acidophilus could be a dairy product that is a finger food, which can be stored at room temperature and have health benefits. The objectives of the research were to study the effects of 0, 1, 10 and 100g of Lactobacillus acidophilus /gal of yogurt product on L. acidophilus, yogurt bacteria, coliform, yeast and mold counts over 0, 1, 2 and 3 months of storage of the novel yogurt product at room temperature. Yogurt bacterial counts were significantly higher in all treatments at month 3 compared to control. With the use of 10g and 100g/gal addition of L. acidophilus there was a significant decrease in L. acidophilus counts at month 2 and month 3 when compared to month 0. Novel yogurt product such as a yogurt capable of being stored at room temperature.

Keywords: Yogurt, Dairy, Microbial count

Location: Dept. of Food Engineering & Technology, State University of Bangladesh, Dhanmondi, Dhaka, Bangladesh and Microbiology & Industrial Irradiation Division of Institute of Food and Radiation Biology, Atomic Energy Research Establishment, Savar, Dhaka, Bangladesh.

Start Date:

End Date:

Program Area: Postharvest and Agro-processing

Commodity: Yogurt

Objectives:

To shelve study of various levels of Lactobacillus acidophilus namely 0, 1, 10 and 100g/gal of yogurt product over 0, 1, 2 and 3 months of storage at room temperature.

Methodology:

Novel yogurt product was manufactured with 0g/gal, 1g/gal, 10g/gal and 100g/gal of Lactobacillus acidophilus culture and the samples were analyzed at 0,1,2 and 3 months for Lactobacillus acidophilus count, lactobacilli count, coliform count, yeast and mold count. Randomized complete block design was used as the experimental design. Three replications were made for each treatment and the data was analyzed as repeated measures in time. Replications were blocks. This experiment was conducted at the Dept. of Food Engineering & Technology, State University of Bangladesh, Dhanmondi, Dhaka, Bangladesh and Microbiology & Industrial Irradiation Division (MIID) of Institute of Food and Radiation Biology (IFRB), Atomic Energy Research Establishment (AERE), Savar, Dhaka, Bangladesh.The yogurt product base was poured in a clean tray wipe d and sterilized with 70 % ethyl alcohol which was air dried and spread with clean aluminum foil again sterilized with 70 % ethyl alcohol and spread in the shape of long strips (like jerkey) that were approximately 0.5cm thick and 20cm long and 4cm wide. The tray was air dried in a clean ethanol sterilized incubator set at 22°C for 24 hrs; the strips were turned over after 12 hrs. with sterilized forceps. After drying samples are div ided separately for each month and vacuum packed in ultra violet sterilized Rival. Seal - a - Meal vacuum storage bags model# VSB4 - A, Multivac model A300/52, vacuum packing machine was used. Care was taken to prevent contamination. The vacuum packed samples were stored at room temperature (22 - 25°C) till further analysis. Eleven grams of the appropriate samples were weighed aseptically in to 99 mL of sterilized Butterfield buffer in pre - filled dilution bottles and they were kept in the refrigerator for 24 hours for softening. After softening the entire content of the dilution bottle was transferred aseptically in to an ultra violet light sterilized stomacher bag (Seward medical stomacher 400) and homogenized for 10 minutes using a Stomacher 400 Lab blender. The resultant dispersion was the first dilution of that sample.Yogurt bacteria counts for yogurt samples serially diluted to the appropriate dilution with 99 mL of sterilized Butterfield buffer in pre - filled dilution bottles were performed by the pour plate method using Difco Lactobacilli MRS agar. Petri dishes were placed in BBL Gas Paks and incubated anaerobically at 40 ºC for 48 hrs. A Quebec Dark field Colony Counter was used to assist in enumerating the colonies. The Lactobacillus counts were enumerated at 0, 1, 2, and, 3 months of product storage at room temperature. Coliform counts (cfu/ml) were determined. Coliform count Petrifilms (3M, St. Paul, MN) were used to enumerate coliforms at 0, 1, 2, and, 3 months of storage. Yeast and Mold counts (cfu/ml) were determined. Yeast and Mold Petrifilms (3M, St. Paul, MN) were used to enumerate Yeast and Mold counts at 0, 1, 2, and, 3 months of storage.

Source of Information: Journal of SUB 4(2): 43-54, 2013

Article Link (Online Journal): http://www.sub.edu.bd/sites/default/files/journals_files/5_Anis_Abedin_FET.pdf

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The results indicate that incorporation of Lactobacillus acidophilus at levels as high as 100g/gal in to the novel yogurt product can be achieved with out affecting its textural characteristics. L. acidophilus counts significantly decreased over months. The initial counts were not as high as regular yogurt. The stage of culture addition appears to play a significant role in the growth. There seems to be inhibitory effect on acidophilus as well as yogurt bacteria due to increased total solids content and added sugar content possibly of production of inhibitory substances by L. acidophilus and/or yogurt bacteria. Yogurt bacterial counts also significantly reduced over time. The drying of the product over time had a significant effect on viable counts of organisms. The low coliform and yeast and mold counts indicate that there was no post processing contamination and this novel product could be manufactured with out having contamination problems and can be stored at room temperature for extended period of time.

Knowledge Management: Journal