This set of Fruits Processing Multiple Choice Questions & Answers (MCQs) focuses on “Fruit Drying Principles”.
1. What is the process of drying fruit called?
a) Dehydration
b) Hydration
c) Rehydration
d) Moisture hydration
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Explanation: The process for making dried fruit is also known as dehydration. It is a general term to describe removing water from the fruit. The most common dehydration methods are sun (solar) drying, oven drying and hot air drying.
2. What is the best temperature to dehydrate fruit?
a) 105°F and 120°F
b) 125°F and 140°F
c) 145°F and 150°F
d) 165°F and 170°F
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Explanation: The best temperature to dehydrate fruit is between 125°F and 140°F. Dehydrating at 125°F will result in a more evenly dehydrated end product. While setting the temperature of the fruit at 140°F will burn the product.
3. What are the disadvantages of drying food?
a) Taste
b) Shelf life
c) Quality
d) Cost
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Explanation: Dried foods do not taste like fresh food. Moisture in the dried food can cause mold on food. The fruits, vegetables which are over dried can be hard and cannot be easily softened. Therefore the drying should be done until all the moisture in food is removed.
4. What is the disadvantage of sun drying?
a) Taste
b) Shelf life
c) Time
d) Cost
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Explanation: Sun drying is a very slow dehydrating process. The molding in the food can occur due to this slow drying process. This process is seasonal as it cannot be carried out in dust or rainy season. The benefit of the sun drying is that these processes do not require any mechanical energy.
5. What is the advantage of sun drying?
a) Taste
b) Quality
c) Time
d) Cost
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Explanation: The advantage of the sun drying is that it does not need any mechanical energy. It is labor saving. The quality of the product is better in terms of nutrients, hygiene and color compared to other mechanical drying.
6. Why drying is supposed to be a good method of food preservation?
a) Removes water from the product
b) Freezes the water in the product
c) Makes the water acidic
d) Makes the water basic
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Explanation: Drying basically dehydrates or removes the moisture from the food. This simple action inhibits the growth of bacteria, mold and yeast. These factors ensure that food does not spoil easily and hence, makes drying an effective food preservation technique.
7. Which of the following factor does not affect drying?
a) Initial moisture content
b) Composition of raw material
c) Size of raw material
d) Pressure in the drier
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Explanation: Some of the factors that affect drying are the initial moisture content of the raw material and composition of raw material. Size, shape and arrangement of stacking of the raw material play a key role in drying. The temperature, relative humidity and velocity of air used for drying also important.
8. Drying rates are controlled by the rate at which heat is applied to the product.
a) True
b) False
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Explanation: Drying rates are measured by the rate at which heat is given to the product. The important factor is the rate at which the internal moisture of the products is released from the product surface. It also depends on the rate at which moist air is eliminated from the surrounding area. It helps in constructing the dryers.
9. Higher relative humidity promotes faster drying.
a) True
b) False
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Explanation: As the temperature of air is increased, it can absorb more liquid and, therefore, the relative humidity is decreased. Lower relative humidity promotes faster drying. As temperature is increased, the amount of water required to saturate a specific volume of air increases.
10. What is constant rate period in drying?
a) Period where rate of diffusion of free water to the surface exceeds the rate of evaporation
b) Period where droplet surface is not saturated anymore
c) Period where the rate of evaporation exceeds rate of diffusion of free water to the surface
d) Period where droplet surface is saturated heavily
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Explanation: Constant rate period of drying is the period where the rate of diffusion of free water to the surface exceeds the rate of evaporation. It depends on rate of diffusion of water vapor by the air film. This is equal to evaporation at the liquid surface.
11. What is falling rate period in drying?
a) Period where rate of diffusion of free water to the surface exceeds the rate of evaporation
b) Period where droplet surface is not saturated anymore
c) Period where the rate of evaporation exceeds rate of diffusion of free water to the surface
d) Period where droplet surface is saturated heavily
View Answer
Explanation: Falling rate period is when the droplet surface is not saturated anymore. The drying is controlled by internal mass transfer of the volatile solvent to the surface. The reduction on the evaporation rate increases the droplet temperature until the heat and mass transfer rates are stable again.
12. Why is equilibrium moisture content important?
a) To know the stability of food at particular moisture content
b) To know the instability of food at particular moisture content
c) To know the biological properties at particular moisture content
d) To know the chemical properties of food at particular moisture content
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Explanation: The model of equilibrium moisture content (EMC) is very significant in the study of drying and storage of foods. The EMC helps to decide the stability of food at particular moisture content in the given environment. It helps in designing the drier.
13. What does water activity mean?
a) Amount of unbound water present in the product
b) Amount of bound water present in the product
c) Amount of unbound hydrogen bonds present in the product
d) Amount of bound hydrogen bonds present in the product
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Explanation: Water activity is the amount of unbound water present in the product. … In relation to fruits, a water activity measurement of 0.5 or lower would mean the likelihood of microbial growth is very low. If the water activity is measured at 0.78aw, it appears too many water molecules are unbound facilitating mold growth.
14. What is the critical moisture content?
a) Period where rate of diffusion of free water to the surface exceeds the rate of evaporation
b) Period where droplet surface is not saturated anymore
c) Moisture content at which the drying rate begins to decline
d) Moisture content at which the drying rate begins to increase
View Answer
Explanation: The critical moisture content (CMC) is known as the average moisture content of the product where the drying rate starts to decline. It marks the instant when the liquid water on the surface is insufficient to maintain a continuous film covering the entire drying area. This can be obtained from drying curve.
15. Which of the following factors that does not influence total dehydration time?
a) Surface area
b) Humidity
c) Size of raw material
d) Pressure in the drier
View Answer
Explanation: The factors that influence total dehydration time are surface area, temperature, air velocity and humidity of the drying air. Surface area is desirable to maximize the surface-to-volume ratio of the food to be dehydrated to minimize the resistance to heat and mass transfer. It also depends on the atmospheric pressure.
Sanfoundry Global Education & Learning Series – Fruits Processing.
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