The objective of this study was to investigate the influence of electron-beam and gamma-ray irradiation and temperature (85 to 95 degrees C) on Alicyclobacillus acidoterrestris GD3B strain (NCIMB 13137) spores by calculating and comparing the decimal reduction dose or time (D-values). The survival rate of A. acidoterrestris spores decreased exponentially with irradiation doses of an electron beam or gamma ray. D-values determined for electron-beam and gamma-ray irradiated spores on filter paper ranged from 1.02 to 1.10 kGy. On the other hand, the thermal sterilization effect showed a single exponential decrease within 1.5-log decreases in cell numbers (D85 degrees C = 70.5 min, D90 degrees C = 16.1 min, and D95 degrees C = 5.19 min and z-value [change in temperature required to change the D-value] was 8.83 degrees C), and prolonged heating produced an increase of 10 to 13 times that of the thermal resistance. However, within all time ranges studied (5 to 360 min), a linear decrease in the D-value was observed with an increase in the temperature. A combination of two different methods, irradiation before heating, was appropriate for reducing the duration of the heat treatment required to achieve the inactivation of conidia. Moreover, a necessary radiation dosage for complete inactivation of A. acidoterrestris spores that contaminated dextrin was examined. Dextrin is often used in the juice industry as an augmentor, and it is known to be sometimes contaminated by these spores. The D-values of the spores in dextrin for electron-beam and gamma-ray irradiations were 1.72 and 1.79 kGy, respectively. The doses required for elimination of the spores could be lowered by using irradiation in combination with heat sterilization. When dextrin powder contaminated with 10(4) CFU/g of A. acidoterrestris was preirradiated at 1.0 kGy of electron beam, the citrus juice containing dextrin at a concentration of 10% (wt/vol) was completely sterilized by heating for 20 min at 95 degrees C.
῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍Although heat sterilization is commonly used to sterilize polysaccharides to be used as a food additives, it is di$cult to sterilize heat-resistant bacteria even by heat sterilization method and heat sterilization causes changes of physical properties and color tone in appearance of polysaccharides. It is thus required to develop novel non-heat sterilization method that causes no changes in physical properties of polysaccharides. We investigated e#ects of electron beam irradiation on physical properties of polysaccharides. Electron beam irradiation mostly caused decrease of average molecular weight, leading to the decrese in viscosity and gel strength. Magnitude of changes in these physical properties depended on polysaccharides. It was also found that physical properties of gum arabic were hardly changed by electron beam irradiation. We discussed some factors causing di#erence in physical properties of polysaccharides by electron beam irradiation in terms of the properties of polysaccharides.
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