The effects of calcium chloride and sucrose prefreezing treatments on the structure of strawberry tissues

The structural changes in strawberry tissues during prefreezing treatments, freezing and thawing were studied by means of textural and drip loss measu rements as well as by bright-field and confocal laser scanning microscopy ( CLSM), and by Fourier transform infrared (FT-IR) microscopy. Calcium chlori de or sucrose were used as dipping pretreatment agents before freezing. In the calcium chloride test series a full factorial screening design was used . The three-level factors included were the CaCl2 concentration of the dipp ing solution, the dipping time and the temperature of the solution. Two kin ds of sucrose treatments were used. Strawberries were either dipped in wate r-sucrose solutions or were sprinkled with crystallized sucrose. The CaCl2 or sucrose pretreatments did not significantly affect the drip loss of thaw ed strawberries compared to water dips or untreated reference samples. The pretreated strawberries were firmer than the untreated control samples but some of the CaCl2- and sucrose-treated strawberries were less firm than the strawberries dipped in water. According to microscopical studies, both CaC l2 and crystallized sucrose pretreatments affected the microstructure of st rawberry tissues. These pretreatments especially affected pectin, protein, lignin and structural carbohydrates in the vascular tissue and cortex compa red to the untreated reference samples. CaCl2-treatment had an even stronge r effect than sucrose on the above compounds except lignin. The pretreatmen ts did not seem to affect the epidermis, hypodermis or pith. (C) 2000 Acade mic Press.