Biomedical subjects

Satoshi Morozumi

Publications and source records attributed to Satoshi Morozumi.

22 records · Page 2Linked to original sources

PubMed2003

A new logistic model for bacterial growth.

A new logistic model for bacterial growth was developed in this study. The model is based on a logistic model, which is often applied for biological and ecological population kinetics. The new model is described by a differential equation and contains an additional term for suppression of the growth rate during the lag phase, compared with the original logistic equation. The new model successfully described sigmoidal growth curves of Escherichia coli and Salmonella under various initial conditions. Data for E. coli were obtained from our experiments and data for Salmonella from the literature. When the new model was compared with a modified Gompertz model, which is widely used by many predictive microbiology researchers, it proved to be superior to the Gompertz model. Further, Salmonella growth at varying temperature could be well simulated by the new model. These results indicate that the new model will be a useful tool to predict bacterial growth under various temperature profiles.

Bacteria↗

PubMed2003

Estimation of bacterial concentrations in commercial foods by measuring ATP changes during incubation.

Recently we have developed new kinetic methods of bacterial cell estimation in food products by measurement of the increase in bacterial adenosine-triphosphate (ATP) content during incubation using a conventional firefly luminometer [Fujikawa and Morozumi: Jpn. J. Food Hyg. (2002)]. The methods were the end point method and the delay method. We, in this study, evaluated these methods for bacterial concentration estimation in commercial foods. The methods were successfully applied to food products inoculated with Escherichia coli or Staphylococcus aureus. The methods were then used to estimate bacterial concentrations in commercial foods. For estimation, the kinetic parameter values were determined first from the data of bacterial strains studied previously. The bacterial concentrations estimated with these parameter values were slightly smaller than the measured concentrations for most of the food samples. The parameter values obtained with the least-squares method gave better estimations in both methods. The delay method predicted the bacterial concentrations in food products better than the end point method. This study showed that with appropriate parameter values, these methods could be useful tools for bacterial concentration estimation of commercial foods.

Adenosine Triphosphate↗

PubMed2002

New estimation methods of bacterial concentration by measuring ATP changes during incubation.

New estimation methods of bacterial cell concentration in samples by measurement of the increase in bacterial adenosine-triphosphate (ATP) content during incubation using a conventional firefly luminometer were established. When an Escherichia coli cell suspension was incubated in nutrient broth, the increase in the ATP content of the suspension during the incubation period followed a sigmoidal curve. The increase ratio of the ATP content of the suspension at a given period of incubation (5 hours in this study) to the initial ATP content was greater at higher initial cell concentrations. With this relationship, the initial cell concentration of a test suspension could be predicted from the measured ratio; this was called the end point method. On the other hand, the lag period in the ATP increase curve was longer at lower initial cell concentrations. A highly linear relationship was observed between the lag period and the logarithm of the initial cell concentrations. Based on this relationship, a delay method was developed for prediction. The two relationships were also observed for bacterial suspensions of Klebsiella sp., Staphylococcus aureus, Bacillus subtilis, and Pseudomonas sp. These results suggested that the two methods have the potential to estimate the bacterial cell concentration of a sample suspension.

Adenosine Triphosphate↗

PubMed2002

Flavor production from edible oils and their constituents by Penicillium corylophilum.

Production of volatile substances from edible oils and their constituents by Penicillium corylophilum was studied to clarify the mechanism of flavor production from a non-stick oil by the organism in a rice cake system. First, edible oils from plant and animal origins were tested for flavor production. Among the oils tested, coconut oil was the only one from which the flavor was produced. Second, triacylglycerols consisting of fatty acids with various lengths of carbon chain (C6 to C13) were studied for flavor production. Among the triacylglycerols tested, flavors were produced from those consisting of fatty acids with carbon chains of C6 to C11. The flavors consisted of methylketones and secondary alcohols, whose carbon chains were one carbon shorter than the precursor fatty acid molecules of the triacylglycerols. Flavors similar to that from the non-stick oil were produced from tricaprylin (C8), trinonanoin (C9), and tridecanoin (C10) among the triacylglycerols tested. Formation of mould spores was more strongly suppressed by triacylglycerols with shorter chain fatty acids. Third, fatty acids with various lengths of carbon chain (C7 to C15) were studied for flavor production. Among the fatty acids tested, flavors were produced from decanoic (C10) and undecanoic (C11) acids only. The flavors also consisted of methylketones and secondary alcohols one carbon shorter than the precursor fatty acids. Fatty acids with short carbon chains (C7 to C9) completely inhibited the mould growth. Our study showed that the range of carbon chain length of fatty acids capable of the flavor production (C10 to C11) was narrower than that of triacylglycerols (C6 to C11). It was also found that the non-stick oil and coconut oil contain tricaprylin and tridecanoin as triacylglycerols and decanoic acid as fatty acid.

Dietary Fats↗