Study On Dielectric Properties And Quality Changes During Thermal Processing Of Squids (Illex Argentinus)

Illex argentinus is one of the most important parts of the world cephalopodresources. From INIDEP, though productions rose from2011to2012, catchesrestricted because of the market saturation. There is an immediate need for betterproduct consumption patterns appear. In recent years, consumers increasingly concernabout vacuum-packed and ready-to-eat squid products. Ensuring food safety,sterilization becomes the final and key step of product process. Its impact to productqualities directly faces consumer groups. At present, traditional heating sterilizationtechnologies which are widely used in China’s seafood are lagging. It leads to agreater loss of product qualities. The emerging microwave sterilization technology hasthe advantage of quickly heating-up. It has a potential value on getting high-qualitiesand nutritional values relatively intact seafood. To Illex argentinus industry, it’s still anew concept for developing high-qualities ready-to-eat products based on themicrowave sterilization technology. This paper studies dielectric properties andquality changes during thermal processing of Illex argentinus. It also develops modelfoods which dielectric properties are fitting with Illex argentinus. These are forclearing behavior characteristics of Illex argentinus in a microwave field, choosing abest microwave sterilization process and looking for the cold spot of temperaturedistribution during microwave sterilization processing. The main contents include:1. The coaxial probe technology is used to measure dielectric properties of Illexargentines (back, belly, fin and arm) as a function of frequent(339.375-2737.8125MHz) and temperature (20-130℃), calculate penetrationdepths-d_p at915MHz and2450MHz, built prediction equations of two frequencies asa function of temperature. The result shows that:(1) dielectric properties (dielectricconstant-ε’ and dielectric loss factor-ε") of4parts decrease with increasing frequency.εdecreases and increases with the rising of temperature. Dielectric properties of4parts are different with same trends and different degree of changes. That’s becauseof different components in4parts.(2) d_p decreases when temperature rises.d_p at 915MHz decreases faster, and it’s not good for uniform heating. at915MHz isabout two times of d_p at2450MHz. Under2450MHz, d_p of back, belly, fin andarm are4.15±0.08mm,3.87±0.16mm,3.70±0.16mm and4.76±0.29mm at121℃.(3)Polynomial equation, y=Ax~2+Bx+C, can be used to predict,ε’and ε" d_p of4partsas a function of temperature. The fitting effect is quite good. In short, according tod_p,the sheet and list structure of Illex argentinus are quite suitable for microwavesterilization without complex segmentation. At2450MHz, back and belly can be fitfor sterilizing together, while fin and arm may need to be alone. This conclusion stillneeds further experiments.2. Heated aluminum box isolated method is used to study weight loss (WL), areashrinkage (AS), water content (WC), color and texture during thermal processing ofIllex argentinus with different temperatures (20-131℃) and times (4.5-180min).Establishing kinetic models of several qualities is needed. The result shows that:(1)WL and AS firstly increases dramatically with time, then gradually increases slowlyuntil coming back into a balance. Balance points are higher, when temperatureincreases. Reaction activation energy-E_ais45.99kJ/mol and32.72kJ/mol.(2) WCslowly decreases into a balance after a sharp decline with time. Temperature ispositively negatively with balance points. Second-kinetic model at sharp decline stageof E_ais47.71kJ/mol.(3) CIE L*a*b*is used for color of Illex argentinus. Thermalprocessing makes Illex argentinus in vitro face sharply whiten and then darken. It alsobrings getting red and yellow. Color is more dark, red and yellow when temperaturerises. But the balance points of yellow are lighter with the rising of temperature.(4)Flexible experiences an increase-decrease-increase change, while viscosityexperiences a decrease-increase-decrease change.(5) The hardness and tensilestrength firstly decline sharply with time, then decline at different degrees after a briefincreasing and come back into a balance finally. After the brief increasing, hardnessand tensile strength decrease with the rising of temperature. The initial hardness of invitro face is much larger than the in vivo face. In vitro face is more heat-resisting.First-kinetic and second-kinetic models have best fitting effects on the rapid declinestage after a brief increasing in hardness (in vitro) and tensile strength respectively. E_ais46.27kJ/mol and57.90kJ/mol. Comprehensive view, at121℃, time of microwave sterilization (including heating stage) is preferably controlled in7.5-20min, which isgood for better qualities of products.3. Using two kinds of protein components, D-ribose, NaCl, gellan gum and DI waterto develop model foods which are similar with dielectric properties of Illex argentinusat2450MHz is needed. The results show that: At2450MHz, ε’and ε" of8modelfoods decrease with the increasing of protein component content. remainsbasically unchanged,ε" increases with the increasing of NaCl content. Model food D(NaCl:1.2g/100g, protein component:16g), H (NaCl:1.3g/100g, protein component:12g), F (NaCl:1.2g/100g, protein component:20g) and G (NaCl:1.1g/100g, proteincomponent:24g) is respectively fit with back, belly, fin and arm of Illex argentinus ondielectric properties well.4model foods color changes are eligible after inspectionand can be used to as raw materials in microwave sterilization.