Thermal operations - Food Engineering - Engineering Sciences Previous Year Questions

1

2010 · Engineering Sciences · Food Engineering · Thermal operations

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.
The processing time (in minutes) to kill 99.999% of the bacteria in any food at 121°C will be

A

7.60

B

6.60

C

12.62

D

2.60

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2

2012 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2012

Thermal death time (TDT) of Clostridium botulinum at 121 °C is 2.78 min with a z-value of 10 °C. The TDT of the microorganism at 116 °C (in min) is

A

5.270

B

8.791

C

1.390

D

0.712

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3

2013 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2013

Thermal death of viable spores of Bacillus subtilis in a food sample follows a first order kinetics with a specific death rate constant of 0.23 min^-1 at 100 °C. The time (in minutes) required to kill 99% of spores in the food sample at 100 °C will be

A

10

B

20

C

23

D

60

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4

2015 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2015

Multiple effect evaporation leads to

A

reduction in operating cost and reduction in capital cost

B

increase in operating cost and increase in capital cost

C

increase in operating cost and reduction in capital cost

D

reduction in operating cost and increase in capital cost

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5

2015 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2015

Which one of the following is NOT a component of an evaporator?

A

Heat exchanger

B

Vacuum separator

C

Condenser

D

Cyclone separator

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6

2016 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2016

The D₁₂₁ and Z values for C. botulinum spores in canned food are 0.2 min and 10 °C respectively. Total time required in min, to reduce the spores from 10⁵ to 10³ at 111 °C is _____.

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7

2016 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2016

A fruit juice with a negligible boiling point rise is being evaporated using saturated steam at 121.1 °C in a triple effect evaporator having equal area in each effect. The pressure of the vapor in the last effect is 25.6 kPa absolute and the corresponding saturation temperature is 65.7 °C. The heat transfer coefficients are U₁ = 2760, U₂ = 1875 and U₃ = 1350 W m^-2 K^-1. The boiling point (°C) in the first effect is __.

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8

2018 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2018

Apple juice of 10% total solids (TS) is being concentrated in a single effect evaporator working with a surface condenser to 40% TS under a vacuum of 20 kPa. After some time the vacuum pump stops but the evaporation process continued. Choose the combination of possible implications from the following.
(P) Product quality is affected
(Q) Substantial increase in thermal energy requirement
(R) Decrease in the rate of evaporation

A

P & Q

B

Q & R

C

R & P

D

P, Q & R

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9

2019 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2019

Sticking of powder to wall of the chamber during spray drying of fruit juice is due to ____.

A

Low glass transition temperature of the compounds in juice

B

High glass transition temperature of the compounds in juice

C

Improper processing parameters of spray dryer

D

Presence of gums in feed material

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10

2020 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2020

During extrusion cooking, food materials are generally subjected to a combination of

A

high shear and low pressure

B

high temperature and high shear

C

low shear and high temperature

D

low shear and low pressure

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11

2020 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2020

During spray drying of a milk sample, inlet and outlet temperatures are maintained at 132 °C and 80 °C, respectively. If the ambient temperature is 29 °C, the thermal efficiency (round off to 2 decimal places) of the dryer will be ______%.

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12

2022 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2022

Which among the given options truly depict the lines 1 and 2 in the figure below with respect to the effect of heat processing on food?

A

1-Safety, 2-Quality

B

1-Yield, 2-Safety

C

1-Yield, 2-Quality

D

1-Quality, 2-Safety

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13

2022 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2022

In a dairy plant, spray drying technology is used to produce whey powder. The rate of spray drying depends on

A

Temperature of the incoming air

B

Shape of the cyclone separator

C

Diameter of the whey droplet

D

Heat transfer coefficient of hot air

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14

2022 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2022

Most commonly used refrigerant in direct immersion freezing of food is

A

Monochlorodifluoromethane

B

Dichlorodifluoromethane

C

Liquid nitrogen

D

Freon

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15

2022 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2022

In a canning industry, the total process time (F₀) was calculated as 3 min. If each can contains 20 spores having decimal reduction time of 1.6 min, the probability of spoilage would be __________ in 100 cans (round off to the nearest integer).

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16

2023 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2023

Extrusion cooking is accomplished in four different stages, which are indicated as I, II, III and IV in the figure given below. Choose the correct option representing the name of each stage.

A

I – Feeding, II – Cooking, III – Kneading, IV – Expansion

B

I – Kneading, II – Feeding, III – Cooking, IV – Expansion

C

I – Feeding, II – Kneading, III – Cooking, IV – Expansion

D

I – Cooking, II – Kneading, III – Feeding, IV – Expansion

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17

2023 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2023

If D₁₀ for Salmonella in egg yolk is 0.75 kGy, calculate the radiation dose in kGy (rounded off to 2 decimal places) required for reducing the Salmonella count in egg yolk by 8 log cycles.

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18

2025 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2025

In canning and retorting of foods, which of the following is the correct expression of Ball process time (B)?
Assume: t_p = processor's process time; t_c = come-up time

A

B = t_p + 0.42 t_c

B

B = t_p + 0.30 t_c

C

B = t_p + 0.50 t_c

D

B = t_p + 0.25 t_c

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19

2025 · Engineering Sciences · Food Engineering · Thermal operations

Engineering Sciences (XE) 2025

The F₁₂₁ value of a known microorganism with Z value of 11 °C is 2.4 min for 99.9999% inactivation. For a 12D inactivation of the said microorganism at 143 °C, the F value (in min) is ____. (rounded off to 3 decimal places)

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