Linear Heating Rate Affects Gelation of Alaska Pollock and Pacific Whiting Surimi

Shear stress of Alaska pollock surimi gels with and without beef plasma protein (BPP) increased as heating rate decreased, but shear strain was unaffected. An increase in shear stress was accompanied by an increase of cross-linked myosin heavy chain. Slow heating rates increased proteolysis in Pacific whiting surimi as shown by degradation of myosin heavy chain and low shear stress and shear strain. Proteolysis of whiting surimi was lessened by BPP to a greater extent at rapid heating rates (20 and 30°C/min) than at slow heating rates (1 and 5°C/min).     

Rheological Behavior and Potential Cross-Linking of Pacific Whiting (Merluccius productus) Surimi Gel

Gelation behavior and potential cross-linking of Pacific whiting (Merluccius productus) surimi were affected by setting temperatures and an enzyme inhibitor. Gels of Pacific whiting surimi with salt and beef plasma protein were compared with those containing guanidine hydrochloride, sodium dodecyl sulfate, and β-mercaptoethanol. The strongest gels were formed at 25°C setting followed by 90°C heating. Hydrogen and hydrophobic bonds appeared to strongly influence gel formation, while the influence of disulfide bonds was moderate. Viscosity scanning during setting at different temperatures was also useful to estimate effects of enzymes and inhibitors.     

CHARACTERISTICS OF SARCOPLASMIC PROTEINS AND THEIR INTERACTION WITH MYOFIBRILLAR PROTEINS

The protein solubility and molecular‐weight distribution of freeze‐dried sarcoplasmic proteins (SPs) from rockfish treated under low and high pH as well as various NaCl concentrations were elucidated. The solubility of SPs was significantly suppressed at an acidic pH (2.0–4.0) and in the presence of high salt concentration (0.5 M NaCl). The least amount of protein was lost when SPs were treated at pH 2.0 or 3.0 followed by precipitation at pH 5.5. The interaction of SPs with Alaska pollock surimi (myofibrillar proteins) was also investigated. The addition of SPs appeared to delay the thermal denaturation of myosin and actin. The SPs positively contributed to the gelation of myofibrillar proteins as judged by breaking force.     

Degradation Kinetics of Myosin Heavy Chain of Pacific Whiting Surimi

Pacific whiting surimi paste was ohmically heated to investigate degradation of myosin heavy chain (MHC) caused by endogenous proteinase over a range of 40–85°C and 0.5–35 min. Degradation was best described with an apparent reaction order of 1.4. Changes of degradation rate increased with temperature and reached a maximum at 57°C. Then, rate of MHC degradation decreased with higher temperature and reached a minimum at 75°C. E_a values of activation and inactivation zone were 142.3 and 83.1 kJ/mol, respectively. Generally, failure shear stress and shear strain increased linearly with MHC content. Proteolytic degradation of actin exhibited the same trend as that of MHC but at a slower rate. The synergistic effect of actin in the gelation of whiting surimi was predominant at ≥75°C.     

Ohmic Heating Maximizes Gel Functionality of Pacific Whiting Surimi

Surimi without enzyme inhibitors containing 78% moisture and 2% NaCl was heated conventionally and ohmically to 90°C after holding at 55°C for 0, 1, 3 and 5 min. Gels heated slowly in a water bath exhibited poor gel quality, while the ohmically heated gels without holding at 55°C showed more than a twofold increase in shear stress and shear strain over conventionally heated gels. Degradation of myosin and actin was minimized by ohmic heating, resulting in a continuous network structure. Ohmic heating with a rapid heating rate was an effective method for maximizing gel functionality of Pacific whiting surimi without enzyme inhibitors.     

CROSS-LINKING OF ACTOMYOSIN BY CRUDE TILAPIA (OREOCHROMIS NILOTICUS) TRANSGLUTAMINASE

Tilapia muscle (Oreochromis niloticus) contained the highest transglutaminase (TGase) activity of 60.8 units/g, while striped snake‐head fish (Channa striatus) contained the lowest TGase activity of 2.7 units/g. Optimal temperature and pH of crude tilapia TGase were 50C and 7–7.5, respectively. Crude tilapia TGase had high thermal stability at 6 and 25C for 2 h. TGase activity towards actomyosin was highest at 0.4 M NaCl, but its activity towards monodansylcadaverine (MDC) decreased as NaCl increased. Dithiothreitol (DTT) had no effect on TGase activity regardless of substrate. Solubility and ε‐amino group content of actomyosin were highest at 0.4 and 0.3–0.4 M NaCl, respectively. At optimum conditions, crude tilapia TGase displayed high activity for myosin cross‐linking.     

TEXTURE DEGRADATION KINETICS OF GELS MADE FROM PACIFIC WHITING SURIMI

Degradation kinetics of whiting surimi gel texture were examined over a temperature/time range (40–85C, 0.5–35 min). Changes in textural properties of whiting surimi gel were mainly affected by proteolytic activity of endogenous proteinase. A decrease of failure shear stress and shear strain followed first order kinetics. The kinetic parameters developed using either isothermal or nonisothermal principles were similar. Degradation rate of gel texture increased with temperature, reaching a maximum at 55C. It then decreased to a minimum at 70C. E_a values for the activation and inactivation temperature range were 138.6–162.6 and 13.5–35.0 kJ/mol, respectively.     

AN ALTERNATIVE APPROACH FOR MODELING OF INTERFERENCE IN DISCRETE-EVENT SYSTEMS

Simulation modeling represents a framework within which discrete-event systems such as construction processes can be analysed, designed and improved. Modeling of some characteristics inherent in general construction processes, however, is difficult. One such characteristic is interference. This paper proposes a construction process-based methodology developed from a Petri Net approach for the modeling of the behavior. This new methodology provides an intuitive approach by the addition of three new modeling elements to basic Petri Net constructs. The functionality of the new elements is described and the implementation of the proposed methodology is provided. The approach provides a means of reflecting reality and practicality in construction-process modeling. It properly addresses the consequences of interference in terms of what happens to the interfered activities and to the involved resources.