Impact of cryoprotection on minimization of ascorbic acid losses in freezing of berries
Ukrainian Food Journal
Introduction. Minimization of ascorbic acid losses during freezing and frozen storage of berries can be achieved by various methods of cryoprotection. The objectives of this research are to confirm the impact of different cryoprotectors on minimization of ascorbic acid losses during freezing and frozen storage of berries. Materials and methods. Bilberries, blackberries, and chokeberries in fresh, frozen and defrosted states were researched in this article. The 10-percent solutions of mono and
... tions of mono and disaccharides, the 1percent solutions of organic acids and the 15-percent solution of inorganic salt (magnesium chloride) were chosen as cryoprotectors. The amount of ascorbic acid in defrosted berries, which was defined by the well-known method (with sodium 2.6-dichlorphenolindofenolate), was the criterion to confirm the effectiveness of cryoprotectors. Results and discussion. The traditional methods to freeze the berries had proved the well-known fact of the significant losses of ascorbic acid. The latter made up 16.8 to 26.3 percents in frozen products and 55.6 to 71.0 percents in those defrosted. This was the result of cryogenous damages of berries' cells by ice crystals, and thereinafter the cause of ascorbic acid oxidation by oxidoreductases and its leakage together with cellular juice during berries' defrosting. The berries processed with cryprotective solutions before freezing were believed to keep the holity of their structure during freezing, longterm (for 12 months) frozen storage, and defrosting. Therefore, the effect of ascorbic acid retention in most cases exceeded 80 percents, relatively to its amount in fresh raw materials. Thanks to protective action of cryoprotectors at the stage of berries freezing, the ascorbic acid losses did not overcome 16.8 to 26.3 percents; after frozen storage for 12 months and defrosting, the residual amount of ascorbic acid made up 62.8 to 83.5 percents. Meanwhile, the control samples (berries frozen without protectors) had got ascorbic acid left on the level of 22.4 to 33.6 percents. The authors of this article proposed to classify the cryoprotectors by four categories according to their cryoprotective effect (relatively to ascorbic acid); the cryoprotectors which showed the effect of ascorbic acid retention less than 40 percents were not recommended to further usage. The compound cryoprotectors turned to be more effective than those simplex. Only the berries frozen by the improved method (with cryoprotectors) had received the highest grade (5 out of 5) by all of the indices. Conclusions. Realization of theoretical knowledge in studying the cryoprotectors by cryobiology scientists had shown the positive effect of cryoprotection in berries freezing.