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Water Activity in Fruits and Vegetables


What is Water Activity in Fruits and Vegetables?

A microorganism such as fungi may harm fruits and vegetables when there is a sufficient amount of moisture is present.

The activity of an enzyme also depends on the amount of moisture present in fruits and vegetables.

Dehydration is a process which decreases the moisture content present in fruits and vegetables.

There is a direct relationship between microorganisms and moisture content. Content of moisture is responsible for the activities of microorganisms and enzymes.

Also read: Alarm water

Contents
(1). What is water activity?
(2). Important points
(3). Usefulness
(4). Water activities of some micro organisms
(5). Frequently Asked Questions

(1). What is water activity in fruits and vegetables?

The amount of water or moisture content which is necessary for the proper activity of microorganisms is Water Activity in fruits and vegetables. It is denoted as a↓w.

Definition of Water Activity?

Water Activity is the ratio of the vapor pressure of the solution of food materials and the vapor pressure of pure water.

Formula of W. A. is as follows:

a↓w = d/d↓1

Where,

a↓w = Water Activity

d = Vapor pressure of solution

d↓1 = Vapor pressure of pure water

(2). Important points

Bacteria require more moisture content than yeast for proper activity.

Fungi require less moisture content than yeast for proper activity.

W. A. for most of the bacteria is 0.90.

Bacteria find it hard to harm the dry-foods.

a↓w of 0.80 to 0.85 is sufficient for fungi. In this situation, food materials strat decaying within two moths.

Conclusion: Bacteria require more water contents than fungi to harm the food materials.

(3). Usefulness

  • Determination of harmful microorganism which is of post harvest importance.
  • To stable the chemical stability of food materials.
  • Reducing non enzymatic browning.
  • To maintain the activities of enzymes.

(4). Water activities of some micro organisms

S. N.Micro
Organism
Water ActivityHarmful
to
1.Pseudomonas1 – 0.95Milk, fish, fresh food etc.
2.salmonella0.95 – 0.91Cheese.
3.Various yeast0.91 – 0.87Spoge cake, dry cheese etc.
4.Most of the fungi0.87 – 0.80Concentrated juice, sweet milk, syrup etc.
5.Halophilic bacteria0.80 – 0.75Jam.
6.Zerophilic mould0.75 – 0.65Jelly, raw sugar, dry fruits etc.
7.Osmophilic yeast0.65 – 60Dry fruits, toffee, honey.
8.No major attack<0.60……
Source: View Chart 1983

(5). Frequently Asked Questions

Also read: Pomology multiple choice questions

Question 01. What is the relation of W. A. with relative humidity?

Answer: The relation of W. A. with relative humidity is as follows-

Relative humidity = W. A. × 100 or,

W. A. = Relative humidity / 100.

Question 02. Which is an osmophilic yeast?

Answer: Saccharomyces rouxii is an osmophilic yeast.

Question 03. What is a↓w for S. rouxii?

Answer: a↓w for S. rouxii is below 0.65.

Question 04. What is the theory of Water Activity?

Answer: W. A. is based on the two theories –

Theory of thermodynamics.
And, the theory of physical chemistry.

Question 05. How to control water activity in food materials

Answer: Methods are as follows –

Cooking.
Baking.
Dehydration.

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