Microbial Testing of Sauerkraut and Yoghurt: LAB, Coliforms, and Lactic Acid Analysis

Microbial Testing of Sauerkraut and Yoghurt: LAB, Coliforms, and Lactic Acid Analysis

Abstract

This laboratory report deals with the microbial testing of Sauerkraut and Your hurt in order to identify the “number of mesophilic aerobes, coliforms and LAB” in each of the given food samples. This laboratory report also focusses on the determination of “percentage of lactic acid” produced in every given sample by using phenolphthalein as an indicator.

1.0 Introduction

Sauerkraut is the most prevalent and oldest fermented foods in entire Western Europe which are mainly produced by fermentation of fresh cabbage. As fresh cabbage is the habitat of the various microbial community therefore largely contains Mesophilic aerobes and coliforms bacteria. But on fermentation, the number of these two microbial communities decreases and due to change in pH number of lactic acid bacteria (or LAB) increases in the final mixture of sauerkraut. Moreover, yoghurt also contains a large number of LAB as it is produced by the fermentation of milk product (Vasiee et al., 2018). Hence, the purpose of this microbial testing is to determine the “number of LAB, coliforms and mesophilic aerobes” in each of the food products along with the “amount of lactic acid” produced in each of the samples.

2.0 Material and Method

Materials needed:

NA agar, PCA agar, MacConkey agar, pH meter, phenolphthalein, spreader, Petri dish, test tube, beaker, distilled water, Bunsen burner, LAF
Method: The methodology for doing the entire lab report is the same as the procedure which was previously provided in the class. No changed in any of the procedure, dilution and time have been made while doing the microbiological experiments.

3.0    Result

3.1    Determination of LAB by Spread plate method

                   Table 1: Number of colonies formed by LAB by Spread plate method

Figure 1: Colonies formed by Spread plate method in Yoghurt (10-3) dilution plate

Therefore, for the calculation of Colony Forming Unit for LAB in each of the food samples:

CFU= (Number of colonies in each of the plate)/ (Total volume plate X Total dilution used)

               Table 2: CFU calculation for determination of the number of LAB in every sample

3.2    Determination of Mesophilic Aerobe by pour plate method

                   Table 3: Colonies formed by Mesophilic aerobes in PCA pour plate method

Figure 2: Colonies formed by PCA plate method in Sauerkraut Day 7 (10-7) dilution plate

Therefore, for the calculation of colony-forming unit of mesophilic aerobes in every given food sample:

Table 4: CFU calculation for determination of the number of mesophilic aerobes in every food sample

3.3    Determination of Coliforms by MNP

                      Table 5: Result for number of coliforms using MacConkey Broth

Figure 3: Result of MPN broth

3.4    pH and Titration

                       Figure 4: Titration by phenolphthalein

                   Table 6: pH and % of lactic acid (titration value) for every food sample

For the calculation of % of lactic acid in the considered food samples:

% of Lactic acid= (“titre/ml X molarity of NaOH X mol. Mass of lactic acid”)/(“ml of sample X10”)

                                    Table 7: Calculation of lactic acid in the food samples

4.0 Discussion

The intrinsic property of Sauerkraut and Yoghurt do change the microflora in the samples. Yoghurt is a fermented product of milk and thus will contain a greater number of LAB compared to Sauerkraut which contains more aerobic bacteria. Moreover, if the fermentation was continued, the pH of Sauerkraut would have fallen more as the number of LAB would have increased in the mixture. The result of MNP clearly states that there was no coliform in the given samples. But the temperature at which the MPN method was sacred out may give other bacterial growth such as Bacillus. Further, the best approach for coliform detection is the MPN method as the test provides a colour change in the MPN broth upon coliform detection. Hence, MPN provides advantages over the traditional plate method as by MPN coliform bacteria can be easily detected and differentiated from other aerobic bacteria growing at 37°C. The pH and titre value
 
ratio of both the simple was almost similar as both the samples contained LAB as the primary microbial community.

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