Changes of quality and free radical scavenging activity of strawberry and raspberry frozen under different conditions

Abstract

The effects of different freezing methods and long-term frozen storage on quality of strawberry and raspberry were investigated, that is, the retention of initial property and free radical scavenging (AO) activity after individual quick freezing (IQF) and conventional (discontinuous) freezing. The physicochemical properties, vitamin C, and AO activity were more affected by long-term frozen storage than by freezing itself; however, their better retention was obtained after IQF. Moreover, AO activity was found to be higher in frozen samples compared to fresh fruits, but significant decrease was detected after 8 months of frozen storage. Despite the significantly higher initial content of vitamin C in strawberry, it demonstrated a lower AO activity than raspberry. Sensory attributes were significantly affected by freezing; the most considerable changes were recorded on their texture/firmness, especially after conventional (slow) freezing. Therefore, IQF can generally be suggested as a more suitable method of preserving these delicate fruits than slow freezing. Practical applications: Nowadays, consumers are increasingly interested in foods that possess not only good nutritional value but also health-promoting property. Berries are known as rich sources of micronutrients and antioxidant compounds, but consumption of fresh strawberry and raspberry fruits may be limited because of seasonal and market availability; therefore, they must be preserved commonly by freezing. Frozen food industry is of crucial importance for developing countries, in which the fast freezing industry is rapidly developed. Investigation of the effect of industrial freezing and frozen storage on retention of the quality-related property and antioxidant activity is important for providing the best quality for consumers and health benefits, as well as international fruit trade. In addition, the results obtained in this study could provide best practice and guidance for the frozen fruit industry.