Solution Of Critical Issues For Microwave-assist Sterilization And Application To Aquatic Products

Microwave sterilization process is a promising alternative to conventional retorting methods for producing high quality shelf stable foods. In order for this technology to produce high quality shelf stable aquatic products there is a need for a rapid and reliable method to determine the location of cold spots in food. My dissertation overcomes the limitations of no model food for low dielectric loss factor seafood with a special focus on the development of a new model food to determine heating patterns using chemical maker M-2based computer vision method for microwave sterilization. A case study of rehydrated sea cucumber was as follows:The dielectric constant (ε’) and loss factor (ε") of rehydrated sea cucumber (Apostichopus japonicas) were investigated over the frequency range of300KHz-3000MHz at temperatures ranging from20to125℃. Influences of frequency and temperature on rehydrated sea cucumber dielectric properties as well as that of penetration depth were analyzed at915MHz in the temperature range20to121.1℃. Logarithmic (exponential) and quadratic relationship were observed, respectively.Study the effect of whey protein concentrate (WPC) and whey protein isolation (WPI) on dielectric properties of model food with five different formulation for development a model food for rehydrated sea cucumber; based on comparison of the measured dielectric properties of the rehydrated sea cucumbers and model food samples with different formulations and the calculated microwave power penetration depths among the sea cucumbers and model foods in the temperature range20to121.1℃at915MHz, appropriate formulation (WPC5%, WPI3%, gellan gum1%, D-ribose0.5%and distilled water90.5%) was chosen as the model food for rehydrated sea cucumbers for the purpose of predicting heating pattern in microwave processing development.Through interactive programming an IMAQ Vision Builder script was designed to get the3-D heating pattern in model food to predict the heating patterns in rehydrated sea cucumber during thermal processing; relationship among thermal lethality (Fo) and color RGB value with model food was studied, quadratic curve was observed; Sensitivities to the heating patterns were tested for model food with different thickness. Results indicated that microwave heating patterns were similar, the average cold spot was located at the point23.33mm from the right edge and3.44mm from the front edge in the middle layer; heating patterns were tested for model food and rehydrated sea cucumber and cold spots were analyzed which is close to model food,(-21.68,-2.38) mm; F0value in cold spot was calculated through color RGB value during microwave sterilization.The method here was further improved to facilitate the comparison of the heating patterns for model food with ellab sensor and frame or without sensor and frame; model food in different belt position during the same processing, the results showed that the heating patterns were similar, and the errors (within2mm) were acceptable; the temperature of the cold spot predicted by the model food was validated using ellab sensors, F0value was calculated; data sets were collected from four heat penetration test runs, relationship of Fo value and microwave heating time (T) was analyzed: Fo=105.6*T-245.14(R2=0.9744), microwave-assist processing parameters were determined for package rehydrated sea cucumbers; Septuple heating time was needed for the same F0value in hot water sterilization processing using the same system with the same processing parameters; the method here was further improved to facilitate the comparison of heating patterns between computer simulation and microwave processing. The result showed the similar heating pattern:Validation tests confirmed that the method based on chemical marker M-2and computer vision can accurately determine the cold spot location in pre-package model food and rehydrated sea cucumber processed by microwave, Fo value in cold spot was calculated through microwave heating time for developing microwave-assist sterilization processing parameters.The dielectric constant (ε’and ε " of mussel (Mytilus edudis linne), octopus (Octopus ocellatus) and scallop (Patinopecten yessoensis) were investigated. Influences of frequency were analyzed in the temperature range20.to121.1℃, Logarithmic(exponential) relationships were observed, and those data could be used for developing model food, simulating with computer and designing new equipment for microwave sterilization processing.