Sam's Food Micro Lab Report# 6--93

8/3/2019 Sam's Food Micro Lab Report# 6--93

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BI-208-070 (Food Microbiology)

Lab report # 6

Modification of Carbohydrates in Animal Products

By: Samir Vhora -300618480

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Samir Vhora BI-208-070 Lab report#6

INTRODUCTION

In this laboratory exercise, we have determined the numbers of

viable lactic acid bacteria present in commercially prepared

yogurt and isolated the number of streptococci and lactobacillifrom the plates. We have also evaluated the organoleptic

characters of our prepared yogurt and determined the percent of

lactic acid in that.

MATERIAL AND METHODS

Please refer to the BI-208 LAB MANUAL, as prepared by Allan

Richardson, Centennial College, 2008.

DATA

Table 1: Appearance and count of the aerobic bacteria on TJA

medium, 350C 48 hrs

Aerobic pour

plates dilution10-4 10-5 10-6

Colony count TNTC 160 15

Calculation 160 x 105

1.6 x 107 cfu/ml

Appearance of

growth

Shape: Lenticular

Margin: entire

Surface: smooth

Elevation: convex

Color: off-white

Gram stain

observationsGram negative, Bacilli, pink color

TJA- Tomato Juice Agar

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Table 2: Appearance and count of the anaerobic bacteria on TJA

medium, 350C 48 hrs

Anaerobic pour

plate dilutions 10-4

10-5

10-6

Colony countTNTC 119 20

Calculation119 x 105

1.19 x 107cfu/mL

Appearance of

growth

Shape: small, circular

Elevation: convex

Color: off-white

Surface: smooth

Margin: entire

Gram stain

observation

Gram positive, purple in color, bacilli, long

chain

TJA- Tomato Juice Agar

Table 3: Various tests and results of Yogurt sample

Yogurt sample Results

Gram stainobservations

Gram positive, purple in color, chain and

single rod shaped bacilli and round cocci

pH reading 4.09

Titration volume 19.00 ml

% lactic acid

calculation1.71%

Organoleptic

evaluation

Color: off-white,

Odor : milk or yogurt like

Taste : sour

Texture: smooth, thick and creamy

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Calculations:

% acid = 100 x ml of base x N of base x 0.09*

10g Sample

*ml of base x N of base x 0.09 equivalent of lactic acid / ml

% acid = 100 x 19.00 x 0.1 x 0.09 / 10

= 1.71 %

DISCUSSION

There is no discussion for this lab experiment.

QUESTIONS AND ANSWERS

Que: 1 Which method of incubation (Aerobic vs. Anaerobic) was

better for this group of microbes? Why?

Ans: Anaerobic method is good for the yogurt micro organism S.

thermophilus to L. bulgaricus because, these group of organisms

gives considerable number of colonies as these are facultative

anaerobic microbes(grows best in microaerophilic environment)

for which anaerobic method is favourable.

Que: 2 What is the usual ratio of S. thermophilus to L.

bulgaricus in yogurt? Do you think your plates reflected this

ratio?

Ans: The usual ratio for the two bacteria S.thermophilus to L.

bulgaricus in the yogurt is 1:1(Marth & Steele, 2001). No my

plates does not reflect the stated ratio.

Que: 3 What is the normal pH of yogurt?

Ans: The normal pH range of yogurt is 4.2 - 4.4 but it also

depends on the storage condition, process of manufacturing, andstarter culture etc(2).

Que: 4What is a starter culture?

Ans: An active microbial preparation used in product

manufacturing and added purposefully for desirable changes in

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the product is known as Starter culture. This preparation may

contain different types of bacteria include LAB,

propionibacteria, surface-ripening bacteria, yeasts and moulds

etc. They have different roles with respect to different

products. Thermophilic starter cultures consist of a mixture of

Streptococcus thermophilus and Lactobacillus sp. These cultures

are used to produce Italian and Swiss cheese varieties and

yogurt.

REFERENCES

1. Marth, E.H. and Steele, J.L. (2001). Applied Dairy Microbiology, Second edition. Pg 151-157NewYork: Marcel Dekker Inc.

2. University of Guelph (January, 1995). Dairy science and technology Education Series. RetrievedNovember 10, 2010, from http://www.foodscience.uoguelph.ca/dairyedu/yogurt.html#starter

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http://www.foodscience.uoguelph.ca/dairyedu/yogurt.html#starterhttp://www.foodscience.uoguelph.ca/dairyedu/yogurt.html#starterhttp://www.foodscience.uoguelph.ca/dairyedu/yogurt.html#starter

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Sam's Food Micro Lab Report# 6--93