Study On The Effect Of Microwave Treatment On Lipid Quality Of Atlantic Salmon

Microwave sterilization can overcome the traditional heating method of relying on slow heat transfer medium in heat treatment.Microwave heating is a high-speed alternating electric field where polar molecules in food rotate and vibrate,causing friction between molecules to generate heat,converting electromagnetic energy into thermal energy,and heating the entire food with short time consumption and high energy efficiency.In addition,the special heating principle of microwave can also lead to some phenomena that cannot be explained by traditional heating,namely "non-thermal effects".Compared with traditional water bath sterilization,microwave sterilization can inactivate more Sporogenic Clostridium at the same or lower heat treatment level（F value）,which may be due to the strengthening of non-thermal response to the destruction of microbial cell membranes,proteins,and DNA components.Traditional sterilization methods through heating medium,such as water and then transfer heat to food,through the physical process of heat convection and heat conduction,so that food from outside to inside gradually increase the temperature.The traditional way of heating food has low energy efficiency and slow heating rate,which leads to a relatively long time for target microorganisms to meet the requirements of thermal lethality.In order to achieve sterility,traditional canned products are usually over-sterilized or over-sterilized.The prolonged heating time aggravates the loss of nutrients of salmon products,especially polyunsaturated fatty acids.However,there is limited research on the impact of non-thermal effects on fish meat components,especially salmon lipid quality,during the microwave sterilization process.In the process of microwave sterilization,both thermal and non-thermal effects exist simultaneously.Therefore,in order to study the non-thermal effects of microwave,it is necessary to eliminate thermal interference,usually using low-temperature microwave radiation method and synchronous heating method.Due to the need to control the reaction system in a low-temperature environment,the low-temperature microwave radiation method is not suitable for studying the impact of nonthermal effects on food quality during food thermal sterilization processes;The synchronous temperature rise method is designed that the water bath heating and microwave heating have the same time temperature curve,the microwave heating is uneven,the food has cold and hot spots,and the sample needs homogenization for physical and chemical analysis,so the time temperature distribution at the two positions of the cold and hot spots cannot replace the temperature change of the entire sample during the heating process.In the process of microwave sterilization,surface overheating will occur,especially for polyunsaturated fatty acids,which may be affected by heat decomposition,so we need to further study the effect of microwave sterilization on food.In the same time,previous studies have found that nonthermal effect exists in the process of microwave sterilization,which improves the sterilization efficiency.Compared with traditional sterilization methods,microwave can significantly kill more microorganisms at the same target sterilization degree.However,many researchers wonder whether the high heating rate of microwave is caused by the thermal effect,especially accompanied by the thermal effect in the process of sterilization,so that the non-thermal effect can be not independent in the heating process,and it is impossible to judge the effect of the existence of non-thermal effect on the quality of food.In order to study non-thermal effect,it is necessary to eliminate the interference of thermal effect,which generally includes low power microwave radiation method and synchronous temperature rise method.Since low power microwave radiation method requires rapid cooling while microwave heating,it is not suitable for the study of non-thermal effect in the process of food heating and sterilization.Secondly,due to the large sample area and uneven microwave heating,it is not accurate to judge the non-thermal effect only by matching the time and temperature curve of hot and cold spots in the process of microwave heating sterilization,that is,synchronous warming method is not suitable for the study of food quality.Using traditional water bath method for heat treatment,the time temperature curve of the cold point water bath treatment group is designed to be lower than and approach the time temperature curve of the microwave cold point,while the time temperature curve of the hot point water bath treatment group is higher than and approach the time temperature curve of the microwave hot point.The Double Sides Approximate Method to study the effect of microwave on the lipid quality of salmon.Due to the two water bath treatment groups approaching the time temperature curve of the microwave treatment group from the upper and lower boundaries,the heat treatment degree of the cold point water bath treatment group is lower than that of the microwave treatment group,and the heat treatment degree of the hot point water bath treatment group is higher than that of the microwave treatment group.Therefore,the heat treatment degree of the microwave treatment group is between the two water bath treatment groups.If the lipid quality of the microwave treatment group changes between the water bath treatment group,it indicates that the non-thermal effect of the microwave field does not exist;If the changes in lipid quality in the microwave treatment group are not between the water bath treatment groups,it indicates the existence of nonthermal effects in the microwave field.This article takes total fat,peroxide value（POV）,thiobarbituric acid reactive substances（TBARs）,acid value（AV）,and fatty acid extraction coefficient as indicators.Firstly,the effect of microwave pasteurization on the lipid quality of salmon is studied through bidirectional approximation method.The lipid quality differences between microwave and two water bath treatment groups are compared to determine the existence of non-thermal effects in the microwave field,providing theoretical reference and data support for the impact of microwave heating on food quality.Secondly,before studying the impact of microwave high-temperature sterilization treatment on the nutritional composition of food,it is necessary to reveal the changes in the nutritional composition of food during different high-temperature and short-term treatments under traditional heating methods.Finally,the effect of non-thermal effects on the lipid quality of salmon during microwave hightemperature sterilization process was studied using the bidirectional approximation method,and the effect of extending the insulation time on the non-thermal effects of microwave was also explored.The main research content and results are as follows:（1）Under microwave pasteurization conditions,the influence of non-thermal effects on the lipid quality of salmon was studied using bidirectional approximation method.The lipid quality differences between microwave and two water bath treatment groups were compared to determine the presence of non-thermal effects in the microwave field.The results showed that the total fatty acid content of the microwave treatment group was not between the results of the two water bath treatments.Among the 28 measured fatty acid components,20 had extraction coefficients higher than those of the two water bath treatments.For trans oleic acid（C18:ln9t）and trans linoleic acid（C18:2n6t）,the extraction coefficient of the microwave treatment group was lower than that of the two water bath treatment groups;POV and AV results after microwave treatment were between the water bath treatment groups,but TBARs of the microwave treatment group was significantly lower than that of the water bath treatment group（P<0.05）.The research results indicate that there is a non-thermal effect during the microwave heating process,which makes it easier to extract lipid components and increases the extraction coefficient of fatty acids;The fish meat in the microwave treatment group had a lower degree of oxidation and better lipid quality.（2）Based on a self-developed high-temperature short-term heating system,the effects of high-temperature short-term processing with different heating rates（12.71-21.53℃/min）,heat treatment degrees（F₀=3.0min,6.0min）,and maximum heating temperatures（123,133℃）on the fatty acid composition and oxidation index of salmon were studied.The results showed that under the same degree of sterilization（F₀=3.0 min）,the total fatty acid content gradually decreased with the increase of heating rate;At the lowest heating rate（12.71℃/min）,as the degree of heat treatment increases,the thermal degradation of fatty acid components is intensified,and the content of MUFA and PUFA significantly decreases;At the highest heating rate（21.53℃/min）,the total fatty acid content measured significantly increased with the increase of heat treatment degree（P<0.05）.At the highest heating rate,when the degree of sterilization is F₀=3.0 minutes,the temperature of the heating medium water is significantly increased,the heating time is shortened,and the total fatty acid content is significantly increased（P<0.05）;However,when the degree of sterilization is F₀=6.0 minutes,a significant increase in the temperature of the heating medium water results in a significant decrease in total fatty acid content,exacerbating the thermal degradation of salmon fatty acid components.Research has shown that high-temperature short-term treatment can retain more fatty acid components in salmon,and it is not recommended to increase the temperature of the heating medium for a long time.（3）By using the bidirectional approximation method,the effect of nonthermal effects on the lipid quality of microwave high-temperature sterilization salmon was studied,and the lipid quality differences between microwave and two water bath treatment groups were compared to determine the existence of non-thermal effects in the microwave field.And the influence of prolonged insulation time on the non-thermal effect of microwave was explored.The results showed that at a lower microwave final temperature（102℃）without insulation,the total fatty acid content measured after microwave treatment was higher than that of the water bath treatment group;As the insulation time prolonged,most of the fatty acid components underwent thermal degradation.The total fatty acid content was observed at a higher microwave final temperature（115℃）,with the same trend as the lower microwave final temperature treatment group.The research results indicate that there is a non-thermal effect during the microwave heating process,which makes it easier to extract lipid components and increases the extraction coefficient of fatty acids.