Biopolymers Used as Cryoprotectants in Food Freezing

Abstract

Living cells, biological materials (plant and animal tissues) and food derived from them contain a large proportion of water. Water is a very important component in foods affecting quality attributes and shelf-life stability. Freezing involves lowering the temperature of a system below its initial freezing point, converting water to ice by elimination of the latent heat associated to thechange of phase. During freezing water is removed from the food matrix by forming ice crystals. Consequently, the concentration of the dissolved substances in the unfrozen regions increases, lowering the water activity (aw) of the product. Freezing is considered a very efficient method for long-term food preservation not only because the effect of low temperatures on chemical reactions and microbial growth, but also due to the decrease of water activity (Fennema et al. 1973; Zaritzky 2000, 2006). Freezing inhibits the growth of deteriorative and pathogenic microorganisms, and retards biochemical and enzymatic reactions that would otherwise occur in unfrozen food. Although the physico-chemical reactions slow down at low temperatures, they continue during frozen storage conditions. In this chapter, the basic principles of freezing and the effect of hydrocolloids as cryoprotectants in frozen food systems are discussed.