Noriyuki Igura

Effects of Minerals on Resistance of Bacillus subtilis Spores to Heat and Hydrostatic Pressure

ABSTRACT Among Bacillus subtilis IFO13722 spores sporulated at 30, 37, and 44°C, those sporulated at 30°C had the highest resistance to treatments with high hydrostatic pressure (100 to 300 MPa, 55°C, 30 min). Pressure resistance increased after demineralization of the spores and decreased after remineralization of the spores with Ca2+ or Mg2+, whereas the resistance did not change when spores were remineralized with Mn2+ or K+, suggesting that former two divalent ions were involved in the activation of cortex-lytic enzymes during germination.

Inactivation of Escherichia coli by microwave induced low temperature argon plasma treatments

Abstract In this study, the design and plasma generation principle of a microwave induced plasma sterilization technique is described. Generation of low temperature argon plasma was investigated for different microwave power densities. Inactivation effects of the plasma were studied on bio-indicators carrying Escherichia coli as a function of microwave power density and particularly for different locations of the bio-indicator holder. The results showed that argon plasma having a temperature below 60 ° C are generated having less than 4.21 w / cm 3 of microwave power density at an ambient temperature of 34 ° C . Survival of E.coli was significantly reduced when the microwave power density of the plasma treatments increased. While, high inactivation was observed at the center, it was less effective at the two opposite edges of the bio-indicator holder.

Effect of feed gas composition of gas discharge plasmas on Bacillus pumilus spore mortality

Aims: To investigate the effect of gas composition on the sensitivity of Bacillus pumilus spores to gas plasmas.

Kinetics of inactivation of Bacillus spores using low temperature argon plasma at different microwave power densities

The objective of this study was to determine the remarkable role of the microwave power density of argon plasma in the inactivation of Bacillus subtilis, Bacillus stearothermophilus and Bacillus pumilus spores deposited on polypropylene bio-indicator carriers. In particular, spore survival by argon plasma was determined as a function of the initial spore density of the bio-indicators. The microwave induced argon plasmas were generated at 1.47, 2.63 and 4.21 w/cm 3 microwave power densities under a low gas pressure of 50 Pa at an ambient temperature of 15 °C to reach low temperature distribution of 31, 35 and 43 °C, respectively. Our results indicate that the different Bacillus spores showed distinct degrees of argon plasma sensitivity, and spore survival was significantly reduced when the microwave power density of the plasma treatments was increased. Among the three Bacillus strains, Bacillus subtilis was the most argon plasma resistant, whereas Bacillus stearothermophilus was the most sensitive. However, spore survival was not affected by the initial spore density of the bio-indicators. Only a certain degree of the spore inactivation log (No/N) from 1.67 to 1.95 was observed despite the 4-order differences in the initial spore density of the Bacillus pumilus bio-indicators.

Research Note: Inactivation Efficiency of Ozonated Water for Fusarium oxysporum Conidia Under Hydroponic Greenhouse Conditions

ABSTRACT Ozonated water was used for inactivation of Fusarium oxysporum conidia in sterilized water and inorganic soil-less nutrient medium at different treatment temperatures. F. oxysporum conidia were effectively inactivated in both water and nutrient media and the inactivation curves were almost same at 15°C, 25°C and 30°C. Approximate 4-log orders of F. oxysporum conidia were killed when the ozonated water with initial ozone concentration of 1.0 ppm had been used. The surviving curves, however, were characterized by a tailing-off effect, and the effect was related to the residual ozone concentration in the ozone treated suspensions.

The effects of high hydrostatic pressure treatment on the flavor and color of grated ginger.

High hydrostatic pressure (HHP) was applied to grated ginger in order to inactivate quality-degrading enzymes in a non-thermal manner. The effects of HHP treatment on the flavor and the color of the grated ginger were investigated just after treatment and during storage. After HHP treatment (400 MPa, 5 min), geraniol dehydrogenase (GeDH) was inactivated to less than 5%, but the activity of polyphenol oxidase (PPO) was reduced only to 37%. Heat treatment (100 °C, 10 min) inactivated GeDH to 43% and PPO to about 10%. In storage, the reduction of geranial, neral, and citronellal to the corresponding alcohols was observed in the untreated and the heat-treated ginger, while it was not in the HHP-treated grated ginger. In the HHP-treated sample, terpene aldehydes almost disappeared without the formation of the corresponding alcohols. Browning was not observed immediately after HHP treatment, while it was complete in the heat-treated sample. The color change during storage appeared to reflect the residual activity of PPO.

The Effect of Low-Pressure Carbonation on the Heat Inactivation of Escherichia coli

The heat inactivating effect of low-pressure carbonation (LPC) at 1 MPa against Escherichia coli was enhanced to 3.5log orders. This study aimed to investigate the mechanisms of this increase in heat inactivation efficiency. The increased inactivation ratio was found to be the result of LPC-induced heat sensitization. This sensitization was not due to any physical damage to the cells as a result of the treatment. Following the depletion of intracellular ATP, the failure of the cells to discard protons caused an abnormal decrease in the intracellular pH. However, in the presence of glucose, the inactivation ratio decreased. In addition, a further increase in inactivation of more than 2log orders occurred in the presence of the protein synthesis inhibitor chloramphenicol. Hence, the decreased heat resistance of E. coli under LPC was most likely due to a depletion of intracellular ATP and a decreased capacity for protein synthesis.

Degradation Profiles of Potato Starch Melts Through a Capillary Tube Viscometer

The effects of time-temperature and strain history on potato starch melts at 150 °C were investigated by use of a capillary tube viscometer. Reciprocating and single extrusions were performed in this study. Shear stress at single extrusion decreased gently as initial heating time increased, while shear stress at reciprocating extrusion decreased rapidly as the number of extrusion strokes increased. A high degree of cold water solubility was obtained by reciprocal extrusion at lower moisture content. From the results of gel filtration it could be concluded that starch molecules were depolymerized by high and reciprocal shear stress. According to these results time-temperature history was more effective on the depolymerization of starch molecules and degradation of starch granules at higher moisture content, while strain history was more effective at lower moisture content.

Effect of moisture content and applied pressure on flow-starting temperature of starch melts

Abstract The flow-starting temperature (Ts) of low-moisture starches (potato, sweet potato, corn and wheat starch) was measured using a capillary tube viscometer under varying moisture content and applied pressure. Ts increased with decreasing moisture content and applied pressure. There was no significant difference between starch varieties. Ts converged to a temperature Tc (270.9 °C) at a pressure Pc (0.32 MPa). Because Ts was in inverse proportion to the moisture content and logarithm of the applied pressure, it was expressed as T s = T c − (a + bW) log ( P P c ) . The lines calculated from the equation were in a good agreement with experimental data.

Combined effects of carbonation with heating and fatty acid esters on inactivation and growth inhibition of various Bacillus spores

The effects of carbonation treatment (1 to 5 MPa, 30 min) plus heat treatment (30 to 80°C, 30 min) in the presence of various fatty acid esters (FAEs; 0.05 and 0.1%, wt/vol) on counts of viable Bacillus subtilis spores were investigated. FAEs or carbonation alone had no inactivation or growth inhibition effects on B. subtilis spores. However, carbonation plus heat (CH; 80°C, 5 MPa, 30 min) in the presence of mono- and diglycerol fatty acid esters markedly decreased counts of viable spores, and the spore counts did not change during storage for 30 days. The greatest decrease in viable spore counts occurred in the presence of monoglycerol fatty acid esters. Under CH conditions, inactivation and/or growth inhibition occurred at only 80°C and increased with increasing pressure. The greatest decrease in spore counts (more than 4 log units) occurred with CH (80°C, 5 MPa, 30 min) in the presence of monoglycerol fatty acid esters. However, this treatment was less effective against Bacillus coagulans and Geobacillus stearothermophilus spores.