Abstract
The paper describes changes in thermal properties in the process of freezing of marine raw materials. The study objects were the skin of giant octopus (Octopus dofleini L.), pallium of Pacific squid (Todarodes pacificus L.), milt of Pacific herring (Clupea pallasii L .), a nd muscle t issue of Japanese c ucumaria (Cucumaria japonica L.). The mathematical relations of the studied thermal parameters allowing the calculation of specific heat capacity, thermal conductivity coefficient and tissue density of the studied objects in the process of freezing were obtained. It was found that the change in the total specific heat capacity during the freezing of all the objects under study was of the same type: first, this figure increases due to the intensive ice formation in the tissues of hydrobionts, and then decreases due to a significant decrease in the content of the liquid aqueous phase. The values of the total specific heat capacity before the freezing of seafood were determined (kJ/kg·K): 4.26 for squid, 3.58 for milt of Pacific herring, 3.66 for octopus skin, and 3.95 for the shell of cucumaria. It was revealed that an increase in the amount of frozen out water decreased the density of samples of frozen raw materials. This was due to the high (77.4–88.9%) content of water, turning into ice, which has a lower density index. The values of hydrobionts’ tissue density before freezing were obtained ( 0 ρ , kg/m3): 1226.74 for squid, 1209.6 for milt of Pacific herring, 1128.55 for octopus skin, and 031.26 for shell of cucumaria. It was established that the thermal conductivity of the hydrobiont tissue samples in the process of freezing increased with the growth of the proportion of frozen out water contained, approaching the thermal conductivity of ice. The calculated values of thermal conductivity coefficient of seafood tissue prior to freezing equal (W/m·K): 0.52 for squid, 0.47 for milt of Pacific herring, 0.63 for octopus skin, and 0.53 for cucumaria. The obtained thermal characteristics values of the objects studied are recommended for use in technical and technological calculations of aquatic biological resources cooling treatment processes.
Highlights
Containing a number of nutrients in their composition, some parts of commercial hydrobionts are not widely used in food production, being wasted while processing
It was found that the change in the total specific heat capacity during the freezing of all the objects under study was of the same type: first, this figure increases due to the intensive ice formation in the tissues of hydrobionts, and decreases due to a significant decrease in the content of the liquid aqueous phase
It was established that the thermal conductivity of the hydrobiont tissue samples in the process of freezing increased with the growth of the proportion of frozen out water contained, approaching the thermal conductivity of ice
Summary
Containing a number of nutrients in their composition, some parts of commercial hydrobionts are not widely used in food production, being wasted while processing These include octopus skin, which makes up to 37% by weight of raw material and is rich in caratinoids, collagen, taurine, selenium, high-limit fatty acids [1,2,3,4]. Among other insufficiently used raw materials, sources are the Pacific squid and Japanese cucumaria [6, 7] These commercial objects provide sources of such biologically active substances as complete protein, hexosamines, chondroitin sulfate, triterpene glycosides, and polyunsaturated fatty acids [3, 8,9,10]. Getting with food in the human body, they slow down the aging process and have a corrective effect on metabolic processes, improving the quality of life and promoting longevity
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