Anisimova K.V., Porobova O.B., Spiridonov A.B., Glavatskikh N.G., Kopysova T.S.

Investigation of instant freezing methods

Strawberries are in demand in confectionery and food industries. Berries are glazed, used in decorating of different confectionery or as a separate tender dessert. The growing season is limited to the summer period, and the demand for berries remains all year round. Low-temperature canning is one of the ways to preserve quality characteristics during the storage of berries. A freezing process is used during storage to maintain quality characteristics. Freezing under conditions of convective heat transfer at a temperature of 18 degrees below zero centigrade does not fully ensure the preservation of the organoleptic properties of the product. For this reason it becomes necessary to conduct an analysis of the existing methods of freezing. The following freezing methods were chosen for the exploring: freezing under conditions of convective heat transfer at a temperature of 18 degrees below zero centigrade, flash freezing under conditions of convective heat transfer at a temperature of 35 degrees below zero centigrade and cryogenic freezing in a carbon dioxide environment using ultrasonic radiation. The conducted studies and their analysis made it possible to obtain the following result: cryogenic freezing provides higher organoleptic characteristics of strawberries, both in frozen and thawed state. This is explained by the size of the forming ice crystals. To limit the growth of crystals, it is proposed to institute ultrasonic vibrations into a laboratory cryogenic freezing machine during the phase transition. The ultrasonic generator puts out oscillations with following parameters: ν≈880 kHz; I ≤0.4 W / cm2.Ultrasonic vibrations affect the strawberries until the temperature in the center of the berries reaches minus 50C.The selected modes of cryogenic freezing in a carbon dioxide environment with intensification of the phase transition are rational, since the freezing time is reduced and the number of crystallization centers increases, ensuring uniform freezing of all moisture. The storage of cryogenically frozen strawberries also showed better preservation.

Keywords: CRYOGENIC FREEZING, FLASH FREEZING, CARBON DIOXIDE, GARDEN STRAWBERRY, ORGANOLEPTIC ESTIMATION, PHASE TRANSITION, ULTRASONIC VIBRATION