Effects Of Microwave Pasteurization On Fatty Acid Quality Of Atlantic Salmon

Salmon has delicate meat quality and abundant nutrients,moreover,it contains a variety of unsaturated fatty acids as well.Raw salmon maintains the maximum nutritional values,but in the meanwhile,it is easily susceptible to contamination of microorganisms.Since the pace of life is accelerated,consumers are paying more attention to ready-to-eat foods of high-quality and long shelf life.Ready-to-eat foods of long shelf life must be sterilized to ensure food safety.At present,hot water heating and steam heating are the main sterilization technologies applied in industrial food production.However,the lower heat transfer rate leads to longer processing time,thus overheats food and impacts on food quality.Among the new sterilization methods,microwave sterilization is the only sterilization technology approved by Food and Drug Administration?FDA?of the USA that can be used for the industrial production of long-shelf foods.Microwave sterilization is based on the thermal and non-thermal effects of microwave.The penetrating characteristic of microwave is used to rapidly heat up the internal materials of food,kill microorganisms in a short time,therefore achieve sterilization effects.Compared with the conventional sterilization methods,the microwave is a rapid heating approach,which can reduce the heating time and improve the product quality.Many studies have been launched to investigate the nutritional composition and quality of food which is processed by microwave,but many studies have not well controlled the same thermal processing level or the same time-temperature profiles by means of microwave treatment and other treatment methods,therefore it is impossible to distinguish the variations of food quality and ingredient that are caused by different processing time,temperature,unique microwave heating method,or non-thermal effects in microwave treatment.Therefore,in this study,fatty acid quality of salmon was compared between the conventional sterilization treatment and microwave treatment at the same thermal processing level.Moreover,the non-thermal effects of salmon fatty acid are investigated by the same time-temperature profiles.The main research contents and results are as follows:?1?The microwave pasteurization process for soft-packaged salmon fillets was developed.The research and development of microwave sterilization process should follow the below workflow:first,model food with the same dielectric properties was used as the carrier of chemical marker method to determine the cold spot position of microwave pasteurization,and the time-temperature profiles of the cold spot position was recorded;and the thermal processing level was calculated through this profile,in order to determine the microwave pasteurization process parameters according to the target processing level;finally,the microbial verification on the pasteurization process was performed.The microwave pasteurization process parameters obtained in the study were:net microwave power of 8 k W,microwave heating time of 3 min,and hooding time of 5min.The thermal processing level was F₉₀=11.5 min.Microbiological verification results show that after the microwave treatment,the magnitude of the inoculated Clostridium sporogenes in salmon was reduced by 7-log.With the same processing level,the magnitude of Clostridium sporogenes inoculated in retort processed salmon was reduced by 6-log.The lethal effect of microwave on Clostridium sporogenes is better than conventional treatment,which maybe result from the non-thermal effects of microwave field.?2?With the same thermal processing level(F₉₀=11.78 min),compared with the retort treatment?24 min?,the microwave treatment significantly reduced the heating time?14 min?,and the total fat content of salmon after microwave treatment?10.238±0.284%?.And Salmon processed by microwave presented more retort group?8.649±0.231%?.The non-thermal effects of microwave field on fatty acid in salmon was studied using the same time-temperature profiles method during microwave treatment.By adjusting the thickness of the salmon sample?microwave 16 mm,water bath 6 mm?and water bath treatment temperature,the time-temperature profiles matched between microwave treatment and water bath treatment.With the same time-temperature profiles,compared with the water bath treatment,the fatty acid composition of salmon treated with microwave was significantly different.After microwave treatment,salmon has higher contents of n-6/n-3,AI,TI,but lower content of P/S.The variations of these values indicate that the fatty acid has a better quality of salmon after microwave treatment.The results showed that the microwave field have non-thermal effects on salmon fatty acids during the processing of microwave heating for 3.5 min and heating ending temperature of 90?.?3?The main evaluation indicators include the total number of colonies,juice loss rate,total lipid content,volatile base nitrogen,thiobarbituric acid value,and acid value.The quality variations of Salmon processed by the microwave treatment and sterilization cabinet treatment were investigated during storage period while the heat treatment degree was kept at the same level.The results showed that during the 6 weeks storage period,microwave treatment could more effectively inhibit the growth of microorganisms in salmon.TBARS results showed that the salmon treated in the retort was more oxidized during storage.The acid value results showed that there was not obvious difference in the degree of hydrolysis of salmon fat after the two treatments.In summary,the Salmon processed by microwave treatment can maintain a better quality,and slighter quality variation during storage.This may be due to the special heating method of microwave,which shortens the heating time while retaining the nutritional values of salmon.