The comparison of antioxidant properties between frozen and freeze-dried strawberries (Fragaria x ananassa)

Strawberries (Fragaria x ananassa) are a delectable fruit renowned for their numerous health benefits, due to their high concentrations of active compounds, including antioxidants, vitamin C, phenolic acids, and flavonoids. However, the phytochemical composition of strawberries is vulnerable to degradation during post-harvest storage and food preparation. Both freezing and freeze-drying are commonly used techniques in strawberry processing, but their effects on nutritional quality and antioxidant activity have not been thoroughly studied. This study aims to investigate the nutritional compounds of fresh strawberries and compare the physical quality and antioxidant activity of frozen and freeze-dried strawberries. An observational analytical design was used. Chemical profiling using LC-MS was conducted to identify major antioxidant compounds, while also comparing changes in colour, texture, and weight between frozen and freeze-dried strawberries. Additionally, antioxidant activity was measured using the DPPH free radical scavenging assay, and the levels of total tannins, flavonoids, and polyphenols were quantified in both frozen and freeze-dried strawberries. The results showed that 88 phytochemical compounds were found in fresh strawberries, with kaempferol and quercetin being the dominant antioxidants. Freeze-dried strawberries had better physical qualities, including a brighter colour and crunchier texture, but they lost more weight compared to frozen strawberries. The freeze-drying technique also improved antioxidant capacity, as shown by lower IC50 values and higher levels of tannins, flavonoids, and polyphenols compared to frozen technique. This study implies that the freeze-drying technique is a promising method for preserving the nutritional and health-promoting properties of strawberries in post-harvest periods.