Microbial Growth - Food Microbiology - Engineering Sciences Previous Year Questions

1

2008 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2008

Which of the following is an intrinsic factor influencing microbial growth in food?

A

Temperature

B

Relative humidity

C

Nutrients

D

Gas composition

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2

2008 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2008

The specific growth rate of Bacillus cereus in a food sample is 0.4 h⁻¹. Doubling time of the cell is

A

2.0 h

B

1.73 h

C

1.25 h

D

1.0 h

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3

2008 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2008

Five grams of cheese was mixed with 45 ml of sterile diluent. Two successive dilutions of 1:100 each were made and one-tenth milliliter from the last dilution was plated onto each of two plates containing plate count agar (PCA) medium. Following incubation, 56 colonies were counted on one plate and 54 on the other. The average number of colony forming units (CFUs) per gram of cheese is

A

5.5 × 10⁵

B

5.5 × 10⁶

C

5.5 × 10⁷

D

5.5 × 10⁸

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4

2009 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2009

The z-value (°C) of the microorganism is

A

9.91

B

9.19

C

1.99

D

0.19

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5

2010 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2010

A bacterial strain isolated from meat is inoculated in a growth medium at a cell density of 2 × 10⁶ cells/ml. Then, 0.2 ml of the culture broth is withdrawn immediately and mixed with 0.8 ml of sterile saline. This sample is diluted by mixing 0.1 ml of it with 99.9 ml sterile water. Then 0.1 ml of this diluted solution is spread on appropriate nutrient agar plate. The number of colonies expected on the agar plate is

A

4

B

40

C

400

D

4000

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6

2010 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2010

D₀ value of a bacterium is determined by using two thin walled glass capillary tubes filled with same bacterial suspension in distilled water. The sealed capillaries are dipped in an oil bath maintained at 121°C and kept for 60 s and 135 s, respectively. These capillaries are cooled immediately in ice water. Number of survivors remained in the respective tubes are 2000 and 300.
D₀ value (in minutes) of the bacterium is

A

1.32

B

0.52

C

1.52

D

2.52

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7

2011 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2011

In an actively growing (exponential phase) yeast culture, the cell concentration increased from 10³ cells per ml to 10⁵ cells per ml in 4 h. The doubling time of the yeast is

A

120 minutes

B

30 minutes

C

18 minutes

D

60 minutes

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8

2011 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2011

The D_o value of the organism will be

A

10.8 min

B

0.3 min

C

6.0 min

D

0.2 min

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9

2012 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2012

Thermal destruction of microorganisms follows a kinetics of

A

Zero order

B

First order

C

Second order

D

Fractional order

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10

2014 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2014

Saccharomyces cerevisiae (mean doubling time 3.2 h) is grown in a batch fermenter with an operating volume of 12 m\(^3\). A 2% (v/v) inoculum, which contains 5 kg cells per 100 m\(^3\) is mixed with the substrate. The residence time in the fermenter is 24 h and the density of broth is 1010 kg m\(^{-3}\). The mass of S. cerevisiae obtained from the fermenter, in kg, is ______________

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11

2017 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2017

A pure strain with generation time of 60 min is used in a fermentation process. Following inoculation (0 h), the strain takes 2 h for adaptation, 10 h to achieve maximum growth and 12 h to arrive at the point where the death rate is higher than the growth rate. If the inoculation load is 100 cells, the total population at the end of 10 h will be ______.

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12

2017 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2017

A suspension containing 2 × 10⁴ spores of organism A having a D₁₂₁.₁°C value of 1.5 min and 8 × 10⁵ spores of organism B having a D₁₂₁.₁°C value of 0.8 min is heated at a constant temperature of 121.1 °C. The heating time needed to obtain a probability of spoilage ‘1 in 1000’ is ______ min.

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13

2018 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2018

A microbial sample taken at 10 AM contained 1x10⁵ CFU/mL. The count reached to 1x10¹⁰ CFU/mL at 8 PM of the same day. The growth rate (h⁻¹) of the microorganism would be ______. (up to two decimal points)

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14

2020 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2020

The initial population of a bacterial strain increases from 1×10⁴ cells per mL to 1×10⁶ cells per mL in 120 minutes. The generation time for this strain (round off to 2 decimal places) is ______ minutes.

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15

2020 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2020

Which among the given options correctly explains the nature of the microbial culture represented by curves 1, 2 and 3 in the following figure?

A

1. Germination of spores
2. Homogeneous population
3. Mixed population of spores and vegetative cells

B

1. Homogeneous population
2. Mixed population of heat sensitive and heat resistant microbes
3. Germination of spores

C

1. Mixed population of heat sensitive and heat resistant microbes
2. Homogeneous population
3. Germination of spores

D

1. Germination of spores
2. Mixed population of heat sensitive and heat resistant microbes
3. Homogeneous population

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16

2021 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2021

In a typical bacterial growth curve, the first order kinetics for growth rate is observed in

A

Lag phase

B

Log phase

C

Stationary phase

D

Death phase

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17

2022 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2022

The lowest water activity (a_w) supporting the growth of Staphylococcus aureus in food under aerobic condition is

A

0.98

B

0.91

C

0.89

D

0.86

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18

2023 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2023

The time required for stipulated destruction of a microbial population at a given temperature is

A

value

B

value

C

z-value

D

Q10 value

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19

2024 · Engineering Sciences · Food Microbiology · Microbial Growth

Engineering Sciences (XE) 2024

Thermal resistance constant (z-value) is defined as the change in temperature required to reduce the decimal reduction time of a microorganism by __________ percent (Answer in integer).

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