Effects of Freeze-Drying on Sensory Characteristics and Nutrient Composition in Black Currant and Sea Buckthorn Berries  
[PERSON]  
1 Department of Food Technology and Processing Products, Technical Faculty, Saken Seifullin Kazakh Agrotechnical Research University, Zhenis Avenue, 62, Astana 10011, Kazakhstan; [EMAIL_ADDRESS] (I.T. ); [EMAIL_ADDRESS] (A.A.); [EMAIL_ADDRESS] (Y.Y. ); [EMAIL_ADDRESS] (D.T. ); [EMAIL_ADDRESS] (L.M. ); dj.dj.dj.dj.dj.dj.dj.dj.dj.dj.dj. (_Hippocampharnmoides_ L.) is a shrub plant native to temperate regions of Asia and Europe, utilized worldwide both in traditional medicine for treating various ailments and in the food industry for producing jams, juices, non-alcoholic beverages, liqueurs, wines, or as an addition to beer, kefir, and cheees. Oil extracted from its seeds and pulp is used as a cosmetic and food additive, and less commonly as a culinary ingredient. Production waste can serve as a functional ingredient in meat or animal feed [7; 8]. Black currant [9] and sea buckthorn [10] have high antioxidant, immunomodulatory, cardioprotective, anticarcinogenic, anti-inflammatory, and other beneficial properties [8; 11; 12; 13]. There are studies on [14] producing lyophilized berry candies based on black currant, yogurt, and various sweeteners as a healthy alternative to traditional llollipops. Black currant and sea buckthorn berries are rich in vitamins, unlike strawberries and raspberries, since they have an increased content of provitamin A (carotenoids), B vitamins (thiamine, niacin), vitamin C (ascorbic acid), and vitamin E (tocopherol) [10; 15]. The vitamin C content in black currant berries ranges from 120 to 280 mg/100 g [16; 17], in sea buckthorn berries it can range from 250 to 300 mg/100 g [18; 19]. Organic acids and sugars are also important components affecting the qualitative indicators of berries [20]. Their quantitative content varies depending on the time of harvest [21], varietal characteristics, and soil-climatic conditions of growing [22]. The ratio of sugars and organic acids is responsible for the taste, color, and aroma of berries [23; 24]. For example, sweet-tasting berries usually contain relatively high levels of sugars and low levels of organic acids [25]. In the studies by [PERSON] et al. [26], it was found that in ripe black currant berries, the amounts of sugars vary in the range of 7 to 10 g/100 g and mainly consist of fructose, glucose, and sucrose. Among the organic acids, citric acid predominates, with its content ranging from 2473.43 mg/100 g to 3336.95 mg/100 g [27; 28]. The main carbohydrates in ripe sea buckthorn berries are glucose and fructose [29], whose total content is between 2.7 to 5.8 g/100 g. According to studies by [PERSON] et al. [30], malic acid prevails in sea buckthorn berries, the content of which ranges from 1940 to 4660 mg/100 g, and there is also a relatively high content of quinic acid 810 to 2820 mg/100 g and citric acid 90 to 160 mg/100 g.  
Berries are seasonal and perishable products, so different processing methods are used to preserve their quality for a long time. One of the effective methods is berry drying, which allows for increasing the duration of storage while reducing their volume and weight [31]. Many drying methods such as convective, osmotic [32; 33], vacuum [34], and solar [35] are used worldwide. However, their use leads to darkening, degradation of biologically active compounds, and deterioration of the texture and taste of dried berries [36; 37]. Despite its high energy cost, freeze-drying is recognized as one of the gentlest drying methods, preserving biologically active compounds, vitamins [38; 39; 40; 41; 42; 43; 44; 45], phenolic substances [46], and carotenoids [47]. In addition to a high rehydration rate, this method is able to preserve the original color and distinctive flavor of fresh berries.