تاثیر گرمایش اهمیک بر سرعت انجمادزدایی و خصوصیات ماهی تن منجمد

از نکات مهم در فرایند مواد غذایی منجمد، انجمادزدایی با حداقل آسیب به ویژگی‎های کیفی آن است. با توجه به این‌که روش‌های معمول مورداستفاده برای رفع انجماد موادغذایی سرعت کمی داشته و باعث کاهش کیفیت محصول می‌شوند، استفاده از روش‌های انجمادزدایی کارآمد ضروری به‌نظر می‌رسد. انجمادزدایی اهمیک یک روش حرارتی-الکتریکی با توانایی تولید گرمای یکنواخت‌تر نسبت به دیگر روش‌های انجمادزدایی می‌باشد. در این روش با تعیین میزان جریان الکتریکی گذرا از محصول می‌توان سرعت انجمادزدایی را تغییر داد. در این پژوهش تاثیر انجمادزدایی مکعب‌های منجمد ماهی تن با روش اهمیک به‌صورت غوطه‌وری در ولتاژ 50، فرکانس ثابت 50 هرتز و در سه غلظت مختلف آب‌نمک (0.3، 0.4، 0.5 درصد) موردبررسی قرار گرفت و خواص شیمیایی و فیزیکی نمونه‌ها طی سه روز نگهداری در دمای 4 درجه سانتی‌گراد بعد از انجمادزدایی اندازه‌گیری شد. مطابق با نتایج آزمون تجزیه واریانس طرح کاملاً تصادفی، گذشت زمان باعث افزایش حلالیت پروتئین، ph، کل نیتروژن فرار باندشده، کاهش افت سانتریفوژ و افشره دارای اسانس گردید. اثر غلظت بر سرعت رفع انجماد معنی‌دار نبود ولی بر افت انجمادزدایی، افت تبخیر، افت سانتریفوژ، تلفات عصاره و کل نیتروژن فرار باندشده در سطح احتمال 5% اثر معنی‌داری نشان داد.

Effect of Immersion Ohmic Heating on Thawing Rate and Properties of Frozen Tuna Fish

Introductıon: The Scombridae family of fish consists of tuna, bonito and mackerel species that are found in warm waters. Tuna species is important because of economic value and prevalence in global trade. Although, they are usually not consumed fresh because of the limited fishing season, lack of accessible markets at certain locations and cost of transport to other areas. Therefore, long-term preservation methods must be used. For many years, freezing has been the method of preserving food for a longer period without a significant quality decrease. Thawing with minimal damage to the products quality is very important. Since common thawing methods are usually slow and reduce food quality, a substituted technique seems necessary. Ohmic thawing is a thermal-electrical method with a more uniform heat compared to other thermal-electrical methods. The speed and relative uniformity of ohmic heating is possible by passing direct electrical current through the product. In this process, the electrical resistance of frozen food is utilized. Electrical energy passes through food by means of electrical current and is dissipated in the form of heat (Joule effect). Based on Ohm’s law, the amount of dissipated heat is directly related to the used voltage and the electrical conductivity of the product or its parts. Materials and Methods: Muscles of the frozen tuna fish were cut into 3x3x3 cm cubes and kept in zip lock bags and stored at -30  for 24 h. Then the samples maintained at -18  until the experiments time. The ohmic cell was filled with saline solution (0.3%, 0.4% and 0.5% respectively) and the thermocouple was connected to the geometric centre of the frozen fish at -18. Then a voltage of 50 volts with 50Hz frequency was applied until the sample centre reached -7. The samples were then removed from the cells and protein solubility, pH, TVBN, centrifuge loss, thawing loss, drip loss, evaporation loss, and press juice were measured at 0, 24 and 48 h after thawing. Completely randomize design in factorial form with three replications was carried out for the experiments. Data were analyzed by SAS software. Results and Discussion: In this research, ohmic thawing was evaluated as a new method for thawing fish. According to the results of ANOVA, with passing of time the protein solubility, pH, TVBN, centrifuge loss and press juice was increased. With further study of ANOVA of thawing loss and drip loss, it was concluded that salt concentration had a significant effect on dependent parameters (P<0.05). While keeping a high thawing speed, no burning marks appeared on the edges and around the samples in the ohmic method.