| Saury is rich in a variety of unsaturated fat acids,including EPA and DHA,with large catch and low price.It is a marine fish with high nutritional value and is popular with consumers.The main products on the market for autumn saury are canned autumn saury and ready-to-eat autumn saury pieces,with a relatively single product form.In order to extend the shelf life of products,high-temperature sterilization combined with additives is usually used.However,traditional high-temperature sterilization,limited by slow heat transfer rates,has become a recognized fact that it severely damages the thermal sensitive components and texture.The use of additives,especially excessive sodium salt addition,is detrimental to human health.Therefore,seeking new methods to produce high-quality,low additive,room temperature ready to eat autumn saury products not only enriches the variety of autumn saury products,but also lays a theoretical foundation for the production of high-quality room temperature ready to eat food.Drying can reduce the water activity in food,thereby inhibiting the growth of microorganisms.Therefore,dry products typically have a longer shelf life at room temperature.However,during the drying process,especially during the slow drying stage,the water inside the food is tightly combined with the tissue,resulting in poor fluidity.It takes a long time and a large amount of energy to remove this part of water,reducing drying efficiency and causing serious deterioration of food quality.Semi dry food has a moderate moisture content and can stop drying halfway through,effectively avoiding problems such as low efficiency,high energy consumption,and poor quality during the slow drying stage.The existing semi dry foods are often combined with additives to extend their storage time,but they still cannot be eaten at room temperature.Thermal sterilization is considered the most common and effective method for producing ready to eat food.The application of fence technology has revealed that using pasteurization with low heat treatment intensity can achieve instant food consumption at room temperature.However,traditional pasteurization still has a significant impact on food quality due to its slow heat transfer rate.Microwave pasteurization has the advantages of rapid heating,short-term sterilization,and non thermal effects,which not only kill more microorganisms but also have a small impact on food quality.Therefore,combining traditional drying technology with new microwave pasteurization technology,using microwave pasteurization to treat semi dried autumn saury,a combination of two milder processing methods is used to produce high-quality,healthy,and ready to eat autumn saury products at room temperature under low additive conditions.This article first reduces the water activity of saury through vacuum drying combined with seasoning pickling,and finally obtains a low sodium semi dry saury with a water content of 30% and a water activity of 0.795～0.810;The effects of microwave pasteurization and steam pasteurization on the quality of semi dried saury were studied;Using a dynamic model combined with the Arrhenius equation,predict the shelf life of microwave pasteurized semi dried saury products,and conduct shelf life validation experiments.The main research content and results are as follows:(1): A intermediate moisture saury with moderate moisture content and low water activity was developed.Firstly,some water was removed from the saury by vacuum drying to reduce the water activity by reducing the moisture content.Next,the fish is seasoned with seasoning,which contains sodium salts and polyphosphates as water activity reducers to further reduce the water activity while seasoning.Finally,through secondary drying,the moisture content was restored to 30% and the water activity was further reduced to obtain a intermediate moisture saury with moderate moisture content and low water activity.The moisture content of the fish was 60 % and the water activity was 0.920.The vacuum degree of vacuum drying was 0.1 MPa and the drying temperature was 60 ℃.The moisture content of the saury was reduced to 30 % when the drying was stopped,at this time the saury had good texture and color,and the corresponding water activity was0.868,which was close to 0.85.During the seasoning marination process,the ratio of material to liquid was 3:1,and the marination time was 1.5 h,and the corresponding water activity at the end of marination was 0.825.then the second vacuum drying was carried out,and the drying temperature was 60 °C and the drying time was 1 h.drying The surface seasoning of the saury at the same time,so that the moisture content of the saury back to 30 %,while further reducing the water activity,in order to achieve low sodium added at the same time as possible to reduce the water activity.The final moisture content of the saury is about 30 % and the water activity is 0.795 ～ 0.810,which meets the requirements of intermediate moisture foods.(2): To investigate the effect of microwave pasteurization and steam pasteurization on the quality of intermediate moisture saury at the same thermal processing level,using C value,texture,peroxide value,thiobarbituric acid,sodium content,and total plate colony as indicators.The final F value of microwave pasteurization was 10.56 min.The parameters of steam pasteurization were: microwave net power of 7 KW,chain rotation speed of 2.2 cm/s,microwave heating for 2 min,water temperature in the holding area of 93°C,and holding time of 4 min.The final F value of microwave pasteurization was 10.56 min.The final F-value was 10.51 min.c-value,microwave pasteurization was significantly lower than steam pasteurization(P < 0.05).In terms of texture,microwave pasteurization had better overall texture.For thiobarbituric acid values,microwave pasteurization was significantly lower than steam pasteurization(P <0.05).There was no significant difference in sodium content between the two treatment groups.In terms of colony count,the total number of bacteria at the end of sterilization and storage at 37 °C for 7 days was significantly lower than that of steam sterilization by microwave pasteurization(P < 0.05).Microwave pasteurized intermediate moisture saury products had better quality and longer shelf life.(3): A chemical reaction kinetic model combined with the Arrhenius equation was used to predict the shelf life of microwave pasteurized intermediate moisture ready-toeat saury,and the actual shelf life of the product was measured and validated.The values of each indicator were measured at 4,25 and 37 ℃ for 0,5,10,15 and 20 days,mainly using thiobarbituric acid,volatile salt-based nitrogen and total plate colony as indicators,respectively.By establishing the kinetic equations between thiobarbituric acid,volatile salt-based nitrogen,total plate colony and storage time(t)and the rate of change constants(k)of thiobarbituric acid,volatile salt-based nitrogen and total plate colony with storage.The Arrhenius equation was used to predict the shelf life of microwave-pasteurized intermediate moisture ready-to-eat saury products at room temperature.The results showed that thiobarbituric acid predicted a lower shelf-life value of 115 days.The actual shelf life of the product was determined and it was found that it was the TBARS that ultimately determined the shelf life time,which was 4～5months for room temperature storage.Microwave pasteurized saury could be stored at room temperature for 4～5 months. |
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