The objective of the study was to investigate the stability of polyphenols and ascorbic acid in osmo-dried fruits: apples, sour cherries and blackcurrants, stored for 12 months. After 1 year of storage, the content of total polyphenols and anthocyanins in convectively dried blackcurrants was decreased by 45% and 90%, respectively. Flavonols remained highly stable. Convectively dried sour cherries contained particularly labile substances, including cyanidin derivatives, which content decreased by 98% after 6 months. Polyphenols in freeze-dried materials were more stable. After 1 year of storage, their content remained at 60-80% of the initial level. A high stability was in particular observed for delphinidin-3-rutinoside in blackcurrants, and cyanidin derivatives, chlorogenic acid, neochlorogenic acid and quercetin glucoside in sour cherries. The stability of ascorbic acid was also much higher in freeze-dried blackcurrants than in convectively dried fruit. After 1 year of storage, almost 70% of ascorbic acid was preserved in freeze-dried material. PRACTICAL APPLICATIONSAnalyzed material was obtained in industrial conditions. Final products were used to produce bars; it can also be used in manufacturing of muesli and similar products. The results of performed analyses show a change in the content of polyphenols and ascorbic acid during product storage and could be useful to define the time in which a product is characterized by the highest content of health-promoting substances. Journal of FoodProcessing and Preservation ISSN 1745-4549 POLYPHENOLS AND VITAMIN C IN OSMO-DRIED FRUITS E. PIASECKA ET AL. POLYPHENOLS AND VITAMIN C IN OSMO-DRIED FRUITS E. PIASECKA ET AL.

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Plums (Najbolia and Stanley) and apples (Idared) were subjected to osmotic dehydration in 50% solutions of fructose, sucrose and fructooligosaccharides (FOS) at 22, 40 and 60 °C for 24 hours. The content of fructooligosaccharides, sucrose and monosaccharides in dried material was determined. Plums osmosed in fructose contained from 22.3% w/w to 29.6%w/w of this saccharide depending on the process temperature. The content of sucrose in plums and apples varied from 18.6% w/w to 30.4% w/w after using sucrose as osmotic agent. Material processed at 40 °C was characterised by the highest content of FOS: 22.6-24.7% w/w in plums (nystose as osmotic agent) and 13.7% w/w in apples (FOS preparation as osmotic agent). The partial replacement of sucrose and monosaccharides by fructooligosaccharides reduced the energy value of carbohydrates in dried material by 12-37% depending on the process conditions.

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