Cryogenic freezing of some berry species using an experimental model of multi-functional quick-freezing equipment

For the preservation of horticultural products, the best results in keeping the attributes and quality at a level as close as possible to that of the fresh product are obtained when artificial cold (refrigeration, freezing) is used, unlike other methods. Among the existing freezing methods, freezing with cryogenic agents allows obtaining average linear freezing rates superior to the other methods. The fastest procedure for cooling food products involves the use of liquid nitrogen, which comes into direct contact with the surface of the food product that needs to be frozen. The paper analyzes the quick freezing process of three species of berries, namely blueberries, strawberries and raspberries, using an experimental model of multifunctional quick-freezing equipment -ICR, developed by INMA Bucharest as part of a national research programme. Total times and average linear freezing rates, as well as liquid nitrogen consumptions for each of the three species subjected to freezing, were tracked. Following the analysis of the experimental data, there were found the following: the minimum total freezing time, 498 s, was recorded for blueberries and the maximum total freezing time, 773 s, was recorded for strawberries; for blueberries and strawberries the average linear freezing rates recorded values of 6.32 cm/h and 6.29 cm/h corresponding to a very fast freezing process and for raspberries the average linear freezing rate recorded a value of 1.62 cm/h corresponding to a fast freezing process; liquid nitrogen consumption recorded a minimum value of 6.90 kg for blueberries and a maximum value of 7.20 kg for raspberries. In the case of blueberries, at the end of the freezing process, cracks and fissures of the epidermis and pulp were observed as a result of the thermal shock induced during the very rapid freezing process.