Biogenic amines formation in Indian mackerel of tropical region was investigated during storage at ambient (25-29°C) and ice temperature (0°C) in relation with changes of amino acids content and amines forming bacteria. All amines increased significantly during storage at two temperatures except for spermidine and spermine. Histamine concentration of 363.5 ppm was detected after 16 h stored at ambient temperature. Aerobic plate count of fish stored at ambient temperature reached 6.98 log CFU g −1 after 16 h, close to the upper limit (7 log CFU g −1 ) suggested by International Commission on the Microbiological Specifications for Foods (ICMSF). However, proper icing procedure retarded the formation of histamine effectively, resulting only 8.31 ppm after 16 days of ice storage. Aerobic plate count of 5.99 and 7.72 log CFU g −1 were recorded for fish stored in ice after 16 days and ambient temperature after 20 h, respectively. Histamine exhibited high correlation with histidine (r 2 0 −0.963, P<0.01) as well as cadaverine with lysine (r 2 0 −0.750, P<0.05). However, tyramine-tyrosine demonstrated a weaker relationship (r 2 0 −0.138, P>0.05). As storage time progressed, the amines forming bacteria grew significantly except for that stored in ice.

No abstract

An efficient microwave milk pasteurization system requires a rigorous temperature dependent dielectric model of the milk, since the performance of milk pasteurization strongly depends on its dielectric properties. This paper describes the dielectric modelling of cow's raw milk during batch (Vat) pasteurization which covers the frequencies from 0.2 GHz to 6GHz. An open-ended coaxial sensor is used for the measurements of dielectric constant, loss factor, and ionic conductivity at temperature range of 25 • C to 75 • C with an interval of 5 • C. Combinations of Cole-Davison and Debye equations are modified to fit the dielectric measurements. It was found that the measured dielectric constant decreased as the frequency increased, while the high temperature processed produce lower in a convergence manner toward 6 GHz. The loss factor exhibited high losses at higher temperature and lower frequencies, as well as converged at 1.9 GHz then diverged up to 6 GHz. Three relaxation processes are dominated at all temperature treatments within the frequency range. The relaxation time, τ , and the activation energy, Q, are modelled based on linear fitting of measured data according to Debye and Arrhenius approaches.

No abstract

Mono-mode microwave reactors are usually used to heat substances, especially food. This is because heating using a microwave reactor can sustain the flavor, color, and nutrition of the food. Furthermore, this heating technique is cost-effective and time-saving compared to a conventional heating method. The mono-mode reactor is able to determine the absorption of microwave power accurately on the heated substance versus a multimode reactor. In this chapter, a simple and precise mono-mode microwave reactor is designed and developed especially for research laboratories. The advantage of this reactor is to provide a more accurate calibration process, in order to improve the optimum energy use in the heating process, as well as the temperature of the specimen. The reactor can generate output power from 30 watts to 1500 watts, operating at 2.45±0.03 GHz and capable of accommodating a specimen volume of 780 cm3. Pure water is used as a heated specimen to demonstrate the performance and efficiency of this reactor.