| As precious seafood, abalone has high nutritional value. Both the freshness ofabalone and the sterilization process have important influence on the quality ofabalone products. Therefore, to improve the quality of abalone products, accurate andfast evaluations for abalone freshness should be established. In addition, traditionalsterilization may cause loss of nutrients and flavor substances in abalone. So it isdesirable to develop rapid commercial microwave sterilization processes to producehigh quality shelf stable foods.The dielectric properties of the food refer to the interaction ability between foodand electromagnetic waves in electromagnetic field. Currently the dielectric propertiesof food are widely used in the food processing. There is certain relevance betweendielectric properties and food ingredients. According to this, the dielectric propertiescan be applied to the non-destructive testing of the food. Meanwhile, the dielectricproperties of food, particularly, at the300MHz-300GHz frequency range (microwave),determine the heating process in the microwave field. So in order to develop anappropriate microwave heating process, the knowledge of food dielectric properties isessential.In this paper the relationship between the dielectric properties and freshness ofabalone was studied. In addition, in order to develop a microwave heating process, westudied the dielectric properties of four kinds of abalone (fresh abalone; frozen freshabalone; boiled abalone and frozen boiled abalone) at different temperatures andfrequencies. The study of the quality change of abalone after being heat-treated athigh temperature could provide information for developing heating processes. Finallymodel food was developed which could reflect the heating uniformity of abalone. Theconclusions were summarized as follows:(1) During the early stages of storage for fresh abalone meat, there was anegative linear correlation between dielectric loss factor and storage time in the frequency range of1GHz-2GHz. The correlation coefficient (R2) was higher than0.94.At1.5GHz, for example, the relationship between the dielectric loss factor withstorage time could be expressed as: y=-0.487x+27.377(R2=0.962). This suggestedthat dielectric loss factor could be used as a physical indicator reflecting the freshnessof abalone. As a chemical indicator of freshness, lactic acid showed a positive linearcorrelation (R2=0.975) with storage time. The correlation coefficient was slightlyhigher than that above. The correlation coefficient indicated that as a physicalindicator, dielectric loss factor could accurately reflect the freshness of abalone, whichcould evaluate the freshness of abalone non-destructively.(2) Dielectric properties of abalone were measured at frequencies between300KHz and3GHz from20to120℃. Polynomial equations were developed fordielectric properties and penetration depth at915MHz and2450MHz by usingregression calculations.(3) Protein gels containing protein, D-ribose and ultrapure water were developedas model food to determine heating uniformity. The kinetics of color change in modelfood system (24%protein gel) were determined for studying cumulativetime–temperature effects in high-temperature-short-time processes. In addition,mathematical models of color change over time at100,121,130℃were establishedby using regression calculations. The dielectric properties of protein gels could beadjusted by adding NaCl. In this study, protein gels containing0.3g/100g NaCl hadsimilar dielectric properties with fresh abalone and frozen fresh abalone; dielectricproperties of protein gels containing0.5g/100g NaCl were closer to boiled abaloneand frozen boiled abalone.(4) The quality changes of abalone during thermal processing were studied.Abalone samples were heated at100,110,120,130℃for different time intervals. Thecook loss increased with the temperature and time increasing. The colordifference(E) also tended to increase with temperature and time. The elasticityoverall showed a trend of increasing to the maximum and then decreasing, whichsuggested that high temperature short time heating was conducive to the sample’selasticity. In the four kinds of abalone, frozen fresh abalone had greater cooking loss and color change. So in practical processing, if the raw abalone could not beprocessed in time and needed to be frozen, it was appropriate to boil the abalone first. |
