Effects of thermal and electron beam (e-beam) processing on microbial inactivation and physichochemical properties of surimi and surimi seafood were investigated. Thermal-death-time (TDT) concept was used to model Staphylococcus aureus inactivation by heat and e-beam. Gurney-Lurie charts were used to estimate temperature during thermal processing of surimi seafood. Dose mapping technique was used to estimate dose absorbed by surmi seafood during e-beam processing. The dose absorbed increased up to 2 cm and then it gradually decreased, reaching a minimum at 5 cm depth of surimi seafood. It was determined that one and two-sided e-beam can efficiently penetrate 3.3 and 8.2 cm of surimi seafood, respectively. The D-value for thermally inactivated S. aureus was 0.65, 1.53, 6.52, 49.83, and 971.54 s, at 95, 85, 75, 65, and 55°C, respectively. The D-value for S. aureus inactivated with e-beam was 0.34 kGy. The z-value for thermally inactivated S. aureus between 55-95°C was not linear. Thermal processing degraded texture and color of surimi seafood. E-beam enhanced firmness and decreased the b* value of surimi seafood. Myosin heavy chain (MHC) degraded proportionally to the e-beam dose. Actin was not affected by e-beam except treatment at 25 kGy. Hydrophobic interactions and disulfide bonds were formed in raw Alaska pollock surimi when treated with e-beam. / Graduation date: 2002

The major portion of Pacific whiting (PW) is commercialized in the form of frozen surimi. Alternative products for PW were investigated focusing on fresh surimi and texturized meat from PW mince. Fresh surimi is made without additives and kept refrigerated instead of frozen. Texturized meat is a meat-like product made from PW mince through freeze-texturization. Fresh surimi was stored at 5°C and analyzed for its total aerobic plate count (APC), shear stress, shear strain, and color during 7 days storage. Frozen surimi from PW was prepared with 0, 3, 6, and 9% cryoprotectants and was compared with fresh surimi for its gel forming ability. Fresh surimi had a shelf life of 5 days and the gel forming ability remained unchanged throughout storage time. Shear strain of fresh surimi was not different from frozen surimi with 9% cryoprotectants but shear stress was almost 3 times higher than the frozen one. Texturized meat from PW mince was prepared from unwashed or 1-washed mince kept frozen for 6-8 mo with or without the addition of 6% cryoprotectants. The minces were comminuted into a protein slurry, formed into patties, and frozen at -7, -18, and -50°C. The evaluations of ice formation (by microscopic study), hardness, cook loss, color, and water holding capacity were carried out during 20 days storage. The results showed that texturized meat with parallel layers was made from 1-washed PW mince. Unwashed PW mince created a sponge-like texture and had rapid quality deterioration, thus it is not recommended for this product. Cryoprotectants did not significantly affect the texture formation of the product and are not required to store mince as raw material for the texturized meat. The optimum freeze-texturized temperature for this product was -18°C or lower because it minimized quality changes during storage depending on the desirable texture. The lower the temperature (higher freezing rate), the finer the layers created. / Graduation date: 1996

The rheological, color, micro-structural, and electrical properties of surimi seafood gels were investigated. Various starches and protein additives at different ratios were evaluated with Alaska pollock surimi under ohmic heating at different heating rates to determine their functional properties and further to compare these properties with those of conventionally cooked gels. Native starches at low concentration were able to enhance rheological properties due to their gelatinization during heating. Pregelatinized starch decreased texture properties; however, it could suppress the undesirable appearance of the final product because its granules could absorb the surrounding water during chopping and perform a higher degree of retrogradation when cooling. A mixture of native and pregelatinized starches showed a positive trend at high concentration. The more starch added, the lower the L* and b* values of the gels. Protein additives improved textural properties, but negatively affected gel colors. Lower moisture content of the final products showed higher strength in texture, but lower lightness values. Gels cooked under ohmic heating with a slow heating rate mostly exhibited better texture properties than conventionally cooked gels. Electrical conductivities increased when temperature increased, resulting in a linear relationship. Electrical conductivity also significantly increased with moisture content, and slightly increased with applied frequency and voltage. There were some changes in the magnitude of electrical conductivity of surimi-starch paste when temperature increased, most obviously seen at a high concentration of native starch with slow ohmic heating. This indicated that starch gelatinization affected the electrical conductivity of surimi-starch paste while heating. / Graduation date: 2003