Вестник МГТУ. 2019, Т. 22, № 3.

Results and discussion In accordance with the current regulatory documentation2, the recommended shelf life of frozen seaweed from the date of production is 12 months at a storage temperature not higher than -18 °C. At the same time, only organoleptic properties are indicators of the quality of this type of food products, and only the amount of mineral impurities normalizes the physicochemical properties. Pharmacopoeias of various countries, including Russia, standardize the content of polysaccharides and iodine in the dried thalli of brown algae, setting a shelf life of 3 years3. However, there is no document where the content of pigments normalized for both dry and frozen algal thalli. Considering the prospect of freezing as the best way to preserve native algal BAS, as well as the timing of possible collecting of brown algae in the conditions of the Murmansk coast of the Barents Sea, a study was conducted on the stability of pigments (fucoxanthin and chlorophyll a), which have the greatest practical value, during 6 months of storage in the freezer chamber at a temperature of -25 °C (Fig. 1). It has been revealed that after 6 months of storage the total content of investigated pigments in thalli for F. vesiculosus and F. distichus has increased. The total content of fucoxanthin in A. nodosum remains unchanged - 0.30 mg/g DW, and the content of chlorophyll a decreases from 0.57 to 0.40 mg/g DW. The received data show that the extraction efficiency of fucoxanthin and chlorophyll a from the thalli of F. vesiculosus and F. distichus after long-term storage in the freezer is 1.5-2 times higher than from fresh ones (Fig. 1). It can be assumed that during the storage of algae in a frozen state, various physicochemical processes take place, as a result of which the pigments pass into a more accessible form for extraction. It is likely that cellular structures can be destroyed, which leads to a change in the release of BAS (Roshanak et al., 2016; Chang et al., 2006; Arslan et al., 2008). The structure of the thallus of A. nodosum and its biochemical composition are significantly different from studied algae of the genus Fucus , which could affect the results of the experiment on long-term storage (Obluchinskaya, 2014; Stengel et al., 1998). It is known that pigments easily decompose under the influence of environmental factors such as temperature, light radiation and oxidizing agents. Fucoxanthin and chlorophyll a are very sensitive to decomposition under the influence of heat, low pH, long shelf life and exposure to light (Mercadante, 2008; Acedo, 2010; Spinardi et al., 2012). When stored in a freezer with unchanged conditions (lack of light and constant temperature), fucoxanthin and chlorophyll a remain better than under conditions with increasing temperature, for example, when stored after drying. According to the literature, the content of carotenoids and chlorophyll a in some species of medicinal plants immediately after freezing remains almost unchanged (Prokofev et al., 2014). The air-dry method of algae dehydration changes the content of BAS, including pigments. In the work of Tkhan Tajk and co-authors (Tajk et al., 2016) it was shown that the content of fucoxanthin in dried Cylinrotheca microalgae decreased by almost 2 times during storage for 1.5 months at room temperature. During storing dried algae Laminariajaponica under these conditions the content of chlorophylls decreased by 20 %. The issues of maintaining high values of the quantitative characteristics of BAS of algae are little studied. According to studies (Lin et al., 2005; Hii et al., 2010), the addition of an antioxidant compound, such as ascorbic acid, showed the greatest preservation of fucoxanthin content both in dark and light conditions. The algae of the Barents Sea studied by us contains 100-400 mg/g of vitamin C. Therefore, it can be assumed that this compound could contribute to the preservation of pigments. According to the Kawee-ai (2013) study, fucoxanthin should be stored at a temperature below 4 °C in an alkaline environment. 2 GOST 31583-2012. Sea frozen kale. Specifications. M., 2013. 3 State Pharmacopoeia. XI ed., Vol. 2, Art. 83. M., Medicine, 1987 ; European Pharmacopoeia. 9th Ed. Suppl. 9.2. Rockville: United States Pharmacopoeial Convention. Inc., 2016. P. 1405-1406.