Determination of kelp (Laminaria digitata) technological characteristics depending on the drying method

Abstract

The paper considers four methods of drying kelp (Laminaria digitata): convective dehydration at an air temperature of minus 5 oС, relative air humidity of 55 and 90 %; vacuum drying at a metal carrier temperature of 20°C and a vacuum depth of 250 Pa; convective dehydration at an air temperature of 20°C and a relative air humidity of 35 %. In dried algae, the final moisture content, water activity, and strength characteristics were evaluated. To determine the swelling coefficient, dry algae were pre-crushed. It was established that at a temperature of minus 5°C and a relative air humidity of 90 %, dehydration had an unsatisfactory result in terms of the final moisture content of the finished product 27.4 %. This type of drying at a relative air humidity of 55 % provides a final moisture content of the product (12.3 ± 0.48) % and a relatively high swelling coefficient of 6.9. Algae, dehydrated at minus 5°C, had elastic properties, in contrast to other considered methods. Vacuum drying made it possible to obtain the minimum final moisture content of dry algae and the highest swelling coefficient of 7.7. However, drying to constant weight lasted 25.5 hours. Of the considered drying options, the convective method (t = 20°C) showed the highest rate. The duration of drying to constant weight was 8 hours. The final moisture content of the product was acceptable (9.8±1.52) %. However, the water activity after algae swelling had the highest value of 0.97±0.004, and the swelling coefficient had a relatively low value of 6.5. In further studies, it is planned to study the effect of various methods of algae dehydration on the preservation of its biologically active substances.