Introduction the effects of freezing and thawing on berry texture

Freezing and subsequent frozen storage causes excessive softening of berries, and frozen strawberries are characteristically very soft and moist. The great susceptibility of strawberries to textural damage is due to their low solids content, large cells and thin cell walls. During freezing the ice crystals formed rupture the parenchyma cell walls and induce loss of turgor. These structural characteristics account for the loss of instrumental firmness. The right choice of cultivar is important in producing a high-quality frozen product (Oswin, 1979) and so grading involving possible defects, size and texture is necessary before freezing.

The rate of freezing is a critical issue with regard to tissue damage. The fast freezing method allows better retention of texture, and higher texture values can be obtained with freezing in liquid nitrogen and plate freezing. However, berries immersed in liquid nitrogen may crack due to ultra-rapid freezing. Slow freezing results in formation of large ice crystals and significant damage to cell walls. Disruption of the intercellular structure will also release enzymes and substrates which will cause further problems with the flavor and color.

High pressure offers new opportunities to treat samples at temperatures below zero. By using high pressure, the freezing point of water can be lowered to -22 °C allowing storage of foods in liquid state without freezing. The cost-effectiveness can be greatly increased by using pressure-shift freezing and pressure-induced thawing. In the latter case the high-pressure treatment is used only for freezing and thawing.

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Berry Boosters

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