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Dehydrofreezing of food

1. Introduction

Dehydrofreezing is a technique where food, particularly fruits and vegetables, is dried to the appropriate moisture level before freezing. They are more vulnerable to freezing damage and have a less elastic cellular structure, hence this procedure is advantageous. Cutting back on water before freezing can shorten the freezing time and lower the initial freezing point while still forming ice crystals without compromising the integrity of the cell.

One another preservation technique that comes under dehydrofreezing is osmo-dehydrofreezing which combines osmotic dehydration and conventional freezing methods. In this technique, food or plant tissue is first treated with a solution containing solutes, such as sugar or salt, to draw out water from the cells through osmosis. Then, the treated material is exposed to cold air circulation for freezing.

By using osmotic dehydration before freezing, osmo-dehydrofreezing can selectively impregnate solutes with unique properties into the food or tissue, resulting in enhanced stability and quality of the frozen goods. The unique properties of the solutes can help reduce ice crystal formation and shorten the freezing time, which is particularly useful for sensitive food or plant tissue that is prone to damage during conventional freezing.

Therefore, osmo-dehydrofreezing is a promising technique for preserving high-quality frozen goods with improved texture, flavor, and nutritional value. The current usage of the technology is limited to research purposes only. To commercialize it, further investigation and development are needed.

2. Principle

The basic principle of dehydrofreezing is based on:

i) Dehydration/ drying fruits and vegetables to approx. moisture content of 70%,

ii) Freezing, the remaining water present in the food after drying, using a suitable freezer.

Low moisture content present in food allows the nucleation of ice crystals without damaging the cellular structure of food, preserving the organoleptic quality of food, and preventing it from enzymatic and microbiological spoilage.

3. Key equipments

In dehydrofreezing processing, following equipment are used, starting from pre-processing, dehydration, freezing, till packaging and transportation.

A. Pre-processing

i. Mechanical grader/sorter machine

ii. Fruits and vegetable washing and peeling machine: Mechanical peeler

iii. Coring-slicing machine/ fruits-vegetable belt cutting machine

iv. Pre-treatment Vat (For chemical treatment if required)

B. Dehydration: Vegetable spin-drying machine/ Fruits or vegetable drying machine (tray/ cabinet dryer)

C. Freezing: Air-blast tunnel freezers/ belt freezers

D. Post-processing (including packaging and transportation)

i. Pouch packaging machine- Form Fill and Seal based/ stand up-

zipper filling machine/ container filling machine

ii. Crates/ Pallet/ Material handling equipment

Additionally, Several studies have reported the use of additional equipment, to dehydrate and freeze small portions of fruits and vegetables such as osmotic dehydrators, vacuum vegetable freezers, etc.

4. Advantages

a) Preserve Quality: Due to dehydration, 70% moisture content helps to retain the texture and

flavor of the food upon freezing, as the formation of small-size ice crystals prevents cell

damage and maintains cell integrity.

b) Fasten Freezing: The freezing process becomes quicker due to the presence of less amount

of water content, which might increase energy efficiency.

c) Less Cellular Damage while Freezing: The food's quality is preserved since the water is

removed, allowing ice crystals to form without compromising the food's cellular structure.

d) Increase Space Efficiency: Dehydrated Foods are easier to store because they take up less

freezer space.

e) Improved Reconstitution: Dehydrofreezing-preserved foods reconstitute more quickly than

conventionally dried foods, which may make them more convenient for customers.

f) Inhibit Microbial Growth: The food's shelf life is prolonged by the freezer's low

temperature and decreased moisture content, which prevent microbial growth.

Because of these benefits, the dehydrofreezing technique is a useful method for preserving food quality and flavor while increasing its shelf life.

5. Application of Dehydrofreezing

This freezing technique is used for fruits and vegetables, as they are more prone to damage during freezing due to their high moisture content and less elastic cellular structure. At present, the technique used to freeze is the following on a commercial basis:

5.1 Dehydrofreezing of fruits, such as pineapple, apple, etc.,

5.2 Dehydrofreezing of vegetables, such as potatoes, carrots, and onions.

6. Reference

6.1 A Critical Review of Dehydrofreezing of Fruits and Vegetables | Request PDF (researchgate.net)

6.2 Dehydrofreezing – Principles of the Food Processing & Preservation (inflibnet.ac.in)

6.3 Dehydrofreezing - Dehydrofreezing is a method of food preservation that combines the

techniques of drying and freezing. (romwell.com)

6.4 Dehydrofreezing of pineapple - ScienceDirect

6.5 Dehydrofreezing of Apple Fruits: Freezing Profiles, Freezing Characteristics, and Texture

Variation | Food and Bioprocess Technology (springer.com)

PMG Engineering | Build World-Class Food Factories | Article | Dehydrofreezing of food