Study On The Sterilization Technology Of Pulsed Light And Its Applications In Food

The sterilization technology of pulsed light was one kind of no-thermal sterilization technology with physical method, which using momentary and intense light energy to inactive microorganism on the surface of solid food and package material or in the transparent liquid food material and keeping food quality and extending food store period effectively. These fields, common food microorganism lethal effect and sterilization mechanism, sterilization effect and influence factors in water treatment, synergetic effect of pulsed light and O₃ on killing microorganism, microorganism resistance with pulsed light sterilization, activity effect of enzyme with pulsed light, sterilization effect and quality influence of food with pulsed light, were studied in the paper. The parts of content in the paper could fill in the blanks of research data in the world and enriched the research data of food sterilization in the domestic. The results of the paper could offer theoretical basis during sterilization on the surface of objects or in the water treatment, and the results of the paper could establish application basis in the food sterilization with pulsed light pulsed light. The results were as follows:(1) The effect of pulsed light killing microorganism on the surface of culture medium were studied. The results showed that the amount of Escherichia coli, Salmonella enteritidis, Staphylococcus aureus, Bacillus subtilis, Saccharomyces cerevisiae, Torulopsis bacillaris, Penicillum citrinum, Apsergillus Niger were reduced up to 7 log10 orders respectively when these culture medium were treated with 12 seconds flash with flash distance 20cm, microbe dosage 1.2×10⁷～1. 5×10⁷ cfu. ml^-1. The factors, which influenced the effect of pulsed light sterilization, were in the order of flash time, microbe dosage, and flash distance. The plastic material of polypropylene(PP), polyethylene(PE), polyamide(PA) were suit for package material during pulsed light sterilization.(2) The effect of pulsed light killing microorganism with different spectrum were studied. The results showed that ultraviolet ray were main spectrum on pulsed light sterilization, UV-C was the most important spectrum on sterilization, and white light and infrared ray had synergetic effect on pulsed light sterilization. The culture medium temperature of 1mm depth increased about 15°C with 100s pulsed light treatment, but the culture medium temperature of 15mm depth increased no more than 1.5°C. The mechanism of pulsed light sterilization was that complicated synergetic effect of different spectrum could cause microorganism death rapidly with intense heat effect, mechanical pound effect and ultraviolet ray chemical effect.(3) The effect of pulsed light killing microorganism in the distilled water were studied. The results showed that the amount of Escherichia coli, Salmonella enteritidis, Staphylococcus aureus, Bacillus subtilis, Saccharomyces cerevisiae, Torulopsis bacillaris, Penicillum citrinum, Apsergillus Niger were reduced up to 7 log10 orders respectively when these distilled water were treated with 16 seconds flash with flash distance 20cm, microbe dosage 1.2×10⁷～1.6×10⁷ cfu. ml^-1, water depth 3cm. The factors, which influenced the effect of pulsed light sterilization, were in the order of flash time, microbe dosage, water depth. The water temperature increased was no more than 3°C with 60 seconds flash pulsed light sterilization , and the change range of electric conductivity was no more than 100μs/cm, the change range of pH was, no more than 1. 0.(4) The effect of pulsed light on killing contaminated Escherichia coli in the distilled water at different turbidity, color degree and water temperature were studied. The results showed that turbidity of >6 degree has more obvious influence on Escherichia coli inactivation compared with turbidity of <6 degree, and particulate distribution of>10μm fraction has more obvious influence on Escherichia coli inactivation compared with particulate distribution of <10μm fraction. The sterilization effect of pulsed light reduced gradually with color degree increased, and color degree of Fecl₃ solution has more obvious influence on Escherichia coli inactivation compared with color degree of putty carbon extract solution. The sterilization effect of pulsed light was optimum at water temperature 45°C, and the sterilization effect of pulsed light was lowest at water temperature 35°C. (5) The synergetic effect of pulsed light and O₃ on killing contaminated Escherichia coli on the surface of culture medium were studied. The results showed that synergetic effect of sterilization was more efficient than pulsed light sterilization or O₃ sterilization. The synergetic effect of pulsed light treating after O₃ treating was superior to the synergetic effect of O₃ treating after pulsed light treating. The synergetic effect of sterilization increased respectively 29. 17%, 23. 61% compared with pulsed light treating with flash distance 22cm, flash time 2s, O₃ treating time 2 min. The regression equation of inactivation Escherichia coli was founded using uniform experiment designs. The factors, which influenced the sterilization effect, were in the order of flash time) O₃ treatment time > flash distance.(6) The resistance of Escherichia coli and Staphylococcus aureus during continuous 100 generations with pulsed light sterilization were studied. The results showed that Staphylococcus aureus and Escherichia coli produced resistance after continuous 60 and 70 generations with pulsed light sterilization. The resistance of Escherichia coli and Staphylococcus aureus began to reduce gradually after 60 days and 90 days preservation, the resistance of Escherichia coli and Staphylococcus aureus all disappeared after 120 days and 150 days preservation. The influence on Escherichia coli resistance was more obvious than the influence on Staphylococcus aureus resistance with pulsed light sterilization.(7) The effect of pulsed light on killing contaminated Escherichia coli on the surface of baked eel were analyzed, and then its effect on the quality of baked eels after sterilization was estimated. The results showed that the sterilization ratio of Escherichia coli was 100% with 20seconds flash on surface of baked eels with flash distance 20cm, microbe dosage 6.3×10⁵cfu. ml^-1. Baked eels did not obviously changed on sensory organ quality (color, odor, texture, taste) after 25 seconds flash of pulsed light treatment, though the change ratio of physical chemistry quality (peroxide value and acid value )were no more than 0. 35%. Sterilization had no influence on sensory organ quality of baked eels after 30 seconds flash of pulsed light during the 240d store period of baked eels, and the change ratio of physical chemistry quality were all no more than 0.80%, the change range of change ratio of physical chemistry quality were all lower than 0. 50%.(8) The effect of pulsed light killing contaminated Escherichia coli on surface of dried slices of tender bamboo shoots were studied, and then its effect on the quality of dried slices of tender bamboo shoots after sterilization was estimated. The results showed that the sterilization ratio of Escherichia coli was 100% with 20seconds flash on surface of dried slices of tender bamboo shoots with flash distance 20cm, microbe dosage 6.3×10⁵cfu.ml^-1. sterilization had little influence on sensory organ quality (color, odor, texture, taste) of dried slices of tender bamboo shoots after 25 seconds flash of pulsed light, and the change ratio of physical chemistry quality (protein content, cellulose content, repeated rate) were all no more than 0. 15%. Sterilization had no influence on sensory organ quality of baked eels after 30 seconds flash of pulsed light during the 240d store period of dried slices of tender bamboo shoots, and the change ratio of physical chemistry quality were all no more than 9. 0%, the change range of change ratio of physical chemistry quality were all lower than 2.0%.(9) The activation of Penicillum citrinum on surface of snow oranges exposed to pulsed light was studied with mathematical model method using quadratic regression rotational combination designs. The factors, which influenced the effect of pulsed light on the inactivation of Penicillum citrinum, were in the order of flash time) flash distance > initial microbe load > fruit diameter size. The flash time and flash distance had a significant effect on pulsed light sterilization. Moreover, the flash distance, fruit diameter size and flash time had the Synergistic effect on the sterilization. The predicted values of the mathematical model coordinated with the experimental data, and their relative error is within (?)9.5%.(10) The inactivity effect of Polyphenol Oxidase(PPO)enzyme extract from yacon with pulsed light treatment was studied. The results showed that the activity of PPO enzyme solution decreased 68.5% with 80 seconds treatment, and the activity of PPO enzyme in fresh-cut yacon slice decreased about 1. 5% with 80 seconds treatment. Browning speed could been postponed in certain degree on fresh-cut yacon slice surface with pulsed light treatment.(11) The sterilization technology of pulsed light during fresh-cut yacon slice processing was studied. The results showed that the sterilization ratio of Escherichia coli was 100% with 15 seconds flash on surface of fresh-cut yacon slice with flash distance 15cm, microbe dosage 5.6×10⁵cfu. ml^-1. Experimental results showed that the optimized processing parameter was as follows: blanching time 32s, keeping color 23min, flash time 29s. The sensory organ quality of fresh-cut yacon slice could attain stably the first quality standard with the optimized processing parameter.(12) The effect of pulsed light on killing contaminated Torulopsis bacillaris in the wild sweet-scented osmanthus honey were studied, and then its effect on the quality of wild sweet-scented osmanthus honey after sterilization was estimated. The results showed that the sterilization ratio of Torulopsis bacillaris was 100% with 50seconds flash in the wild sweet-scented osmanthus honey with flash distance 15cm, microbe dosage 3.8×10⁵cfu.ml^-1, honey depth 3cm. The change range of wild sweet-scented osmanthus honey temperature was no more than 13°C with 60 seconds flash. Sterilization had little influence on sensory organ quality(colour, odour, texture) of wild sweet-scented osmanthus honey after 60 seconds flash of pulsed light, and the change ratio of physical chemistry quality (reducing sugar, amylase value, hydroxy methyl furfural) were all no more than 5.0%. Sterilization had no influence on sensory organ quality of wild sweet-scented osmanthus honey after 60 seconds flash of pulsed light during the 240d store period of wild sweet-scented osmanthus honey, and the change ratio of reducing sugar, hydroxy methyl furfural were all no more than 2. 0%, the change ratio of amylase value was lower than 7. 5%.