Graduate Thesis Or Dissertation

 

Textural and electrical properties of Pacific whiting surimi under ohmic heating Public Deposited

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  • Feasibility of ohmic heating to overcome gel-weakening in Pacific whiting surimi was investigated. An ohmic heating apparatus was developed using two rhodium-coated stainless steel electrodes inside a polyvinyl chloride (PVC) tube, a variable transformer, and voltage and current transducers. Rapid heating associated with the ohmic process quickly inactivated endogenous proteinase(s), resulting in significantly high shear stress and shear strain of surimi gels (78% moisture content, 2% NaCl). Degradation of myosin heavy chain (MHC) and actin examined by SDS-PAGE were significantly reduced and continuous gel structure were shown by scanning electron microscopy. Whiting surimi heated in a 90°C water bath for 15 min exhibited poor gel quality and disordered microstructure due to proteolysis of MHC. Electrical conductivity, a critical parameter influencing rate of heat generation during ohmic heating, was elucidated. Electrical conductivities of whiting surimi pastes with four moisture contents (75, 78, 81, and 84% wet basis) and added NaCl (1, 2, 3, and 4%) were measured from 10 to 90°C using ohmic heating at voltage gradient of 3.3, 6.7, and 13.3 V/cm. Electrical conductivity significantly increased with temperature and salt content and slightly increased with moisture content. The effect of the voltage gradient was evident at combinations of high moisture (81, 84%) and NaCl content (3, 4%), due to electrochemical reactions at the electrodes. The empirical model of electrical conductivity as a function of temperature and compositional characteristics predicted values with an error range of 0-15.6%. Finally, kinetic models of textural degradation of whiting surimi were developed using two different approaches: isothermal and nonisothermal procedure over a range of temperature (40-85°C) and time (0.5-35 min). The effect of thermal lag was accounted for using the models derived from the Arrhenius equation. Textural degradation obtained from both methods followed first order kinetic. Degradation of MHC derived from nonisothermal procedure was best described by apparent reaction order of 1.4. Degradation rate of gel texture and MHC increased with temperature and reached the highest rate at 55 and 57°C, respectively. Then they decreased to minimum rate at 70 and 75°C, respectively. The kinetic model for the loss of MHC satisfactorily estimated MHC content of the controls with an averaged error of 10.8%. Relationship between degradation of MHC and gel texture are discussed.
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