Performance of a Heating Block System Designed for Studying the Heat Resistance of Bacteria in Foods.

Knowledge of bacteria's heat resistance is essential for developing effective thermal treatments. Choosing an appropriate test method is important to accurately determine bacteria's heat resistances. Although being a major factor to influence the thermo-tolerance of bacteria, the heating rate in samples cannot be controlled in water or oil bath methods due to main dependence on sample's thermal properties. A heating block system (HBS) was designed to regulate the heating rates in liquid, semi-solid and solid foods using a temperature controller. Distilled water, apple juice, mashed potato, almond powder and beef were selected to evaluate the HBS's performance by experiment and computer simulation. The results showed that the heating rates of 1, 5 and 10 °C/min with final set-point temperatures and holding times could be easily and precisely achieved in five selected food materials. A good agreement in sample central temperature profiles was obtained under various heating rates between experiment and simulation. The experimental and simulated results showed that the HBS could provide a sufficiently uniform heating environment in food samples. The effect of heating rate on bacterial thermal resistance was evaluated with the HBS. The system may hold potential applications for rapid and accurate assessments of bacteria's thermo-tolerances.

[Study on Rotavirus detection by nucleic acid sequence based amplification].

Rotavirus is one of the major cause of the viral gastroenteritis throughout the world. A nucleic acid sequence-based amplification(NASBA) technique for the detection of rotavirus in faecal specimens was developed and compared to the RT-PCR technique. Primers were designed according to the high conserved region of VP7 gene. Amplicons were detected by denaturating agarose gel, and then demonstrated by Northern hybridization with digoxigenin-labeled oligonucleotide probe. The anticipative specific amplification product is 392bp,and no nonspecific products appear even the concentration of nontarget nucleic acid as high as 1 microg/microL. A detection limit of 50 pg target RNA/mL is obtained when the optimal amplification time of 3h used.The NASBA assay will be a favourable alternative to RT-PCR for the investigation of rotavirus outbreaks as a routine diagnostic test in the near future because it is shown to be highly sensitive, specific and do not require specialized equipment.