The effect of several variables on the texture of freeze-dried formulated strawberry slices

Freeze-dried slices of natural strawberries are rather fragile and susceptible to disintegration during packaging and handling while in the dry state. In addition they rapidly lose their integrity and become very flaccid during the process of rehydration. Little work has been done on these two aspects of the freeze-drying of the straw-berry . Wegener et al. (213)* used low methoxyl pectin, a kelp extrac-tive, and an Irish moss extractive with frozen strawberries. Murphy et al. (137) studied the effect of low methoxyl pectin on the texture of frozen strawberries. Hanson et al. (67) investigated the effect of additives such as pectin, gelatin gums and Irish moss extractives on texture stability during the frozen storage of foods. Lloyd (107) received a patent for improving frozen food texture by the use of starch conversion syrup solids. Swenson and Miers (131,188) worked with the effect of low methoxyl pectin, calcium chloride, and sucrose on fruit texture. Collins and Wiley (31) used calcium salts to increase apple slice firmness by interaction with inherent pectic substances. In most cases the texture of the fruit being studied was improved by the use of such additives. Several workers have investigated the relationship of sweeteners to the texture of frozen products. Some of these workers are Dawson et al. (41), Talburt et al. (198), Sistrunk et al. (176), Joslyn (85), Bartlett and Hard (15) and Bockian and Aref (20). In general it could be said that monosaccharides and disaccharides usually harmed texture and higher molecular weight carbohydrate polymers improved texture. This study was undertaken to determine the feasibility of im-proving the dry texture (resistance to shattering) and the rehydrated texture (resistance to loss of integrity when placed in water) of freeze-dried strawberry slices. The process led to a sliced, freeze-dried, formulated strawberry product incorporating a sweetener and a colloidal stabilizer. The variables which were tested are as follows: 1. Effect of amount and type of sugar 2. Effect of method of blending 3. Effect of method of freezing 4. Effect of amount of water 5. Effect of kind and level of colloidal stabilizer. 6. Effect of deaeration immediately following the blending process 7. Effect of temperature of the water used in blending