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In this study, fresh fruit of two strawberry varieties, Maya and Queen Elisa, grown in conventional and organic cultivation in Croatia, were investigated and used to prepare low sugar jams (under atmospheric pressure in laboratory conditions and under vacuum). Antioxidant activity of fresh fruit and jams were determined as well as total phenolics and anthocyanins. The antioxidant activity was evaluated by 2, 2-diphenyl-1-picrylhydrazil radical (DPPH۰ ) and ferric reducing antioxidant power (FRAP) assay. The content of total phenolics in all samples was determined spectrometrically according to the Folin-Ciocalteu procedure. Anthocyanins were also determined by using spectrophotometric method (Ough and Amerine, 1998). Total phenol content in both organic strawberries were slightly higher than in conventional whereas there were not marked differences between varieties. The greater variation between varieties was observed in amounts of anthocyanins where fresh fruit of Maya had higher anthocyanin content while remarkable differences between cultivation were not found. During processing fruit into jams the amount of total phenols decreased in all jam samples by 10-30 % which is in accordance with literature where Häkkinnen et al reported that processing fresh strawberry into jams decreased some phenolic compounds by 20 % and even more (Häkkinnen et. all, 2000). Therefore, there were not observed remarkable differences between two types of processing neither between varieties while organic cultivation results in slightly lower amounts of phenolics with comparison to conventional samples. The amounts of anthocyanins in all jams were almost two-fold smaller than in fresh fruit though it has been reported that the manufacturing process decreased the anthocyanin content without effect on the qualitative anthocyanin profile of jams made from strawberries (Garcia-Viguera, Zafrilla, Tomás-Barberan, 1997). The anthocyanins were more stable during processing in all jam samples obtained from Maya variety, conventional and organic. Therefore, the processing under vacuum had positive effect on preserving the stability of anthocyanins so jams processed under atmospheric pressure had slightly lower amounts of anthocyanins. The obtained results showed that fresh samples such as their jams had high antioxidant activity. Type of processing did not affect on antioxidant activity while influence of cultivation indicated that almost all organic samples had higher antioxidant activity than conventional. Although fresh fruit of Maya showed higher antioxidant activity than Queen Elisa, all Maya jams had lower antioxidant activity. Fresh strawberry fruit as well as their jams showed an evident antioxidant activity. |
