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Effect of Microwave Sterilization on Quality of Mushroom

Author: XiaoFei
Tutor: LiYunFei
School: Shanghai Jiaotong University
Course: Of Food Science
Keywords: microwave mushroom microorganism quality
CLC: TS219
Type: Master's thesis
Year: 2012
Downloads: 172
Quote: 0
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Abstract


Fresh mushrooms with high content of water and no protective structure are easy to be invaded by microorganisms, and thus there would be a great loss in production and transportation. It is of great significance to maintain its commodity value and shelf life. According to the foreign and domestic literatures, microwave sterilization as a newly emerging sterilization technology has many advantages, such as strong penetrating power, high heating efficiency, and no pollution.There are few literatures about effects of microwave sterilization on mushrooms. Exsiting literatures ignored the microwave effect on various nutritional and sensory indexes and quality changes of mushrooms during storage. In order to provide basis and proof for mushroom storage, this study researched on effects of microwave sterilization on a series indexes of mushrooms, such as microorganisms, color and texture, oxidase activity, total polyphenol content, vitamin C content, and antioxidation activity, and followed up their changes during storage.First, this thesis studied the instant effects of different microwave treatments on mushroom qualities. Low-power, medium power and high power microwave treatments are used to heat the mushrooms for 0-2.5min and then microbiological, physical, chemical and sensory profiles of mushrooms were measured and the appropriate treatment conditions were chosen. Results indicated that microwave treatments can achieve obvious germicidal efficacy and oxidase inactivation in a short process time under a comparatively low temperature. While low-power and medium-power treatments maintained water content better, medium-power and high-power treatment in short time could better preserve color. Texture quality will decrease if treatment time exceeded 1min no matter in which power. Medium-power and high-power treatment in short time can preserve total polyphenol and vitamin C better than low-power treatment in long time. According to the observation about microstructure change, 1000W 2.5min could hardly preserve the orginal and intact structure of Mycelium. Considering those indexes comprehensively, this study concluded that high-power 1000W treatment for 0.5-1min, medium power 700W for 1.5-2min, low-power for 2-2.5min are appropriate conditions, which can achieve obvious sterilization and enzyme inactivation effect while maintaining relatively good nutritional and sensorial quality.Then appropriate microwave treatments (1000W 0.5min and 1000W 1min) and two common storage temperature (15℃and 4℃) are chosen for experiments. Four kinds of main spoilage microorganisms in mushrooms are determined. Data were simulated by Gompertz Model to acquire growth parameters and compare with the control samples. Results showed that: both short time treatment (0.5min) and long time treatment (1min) can decrease the intial cell number. However, the maximum cell number and maximum growth rate of pseudomonads and yeasts in short-time treated samples(1000W 0.5min) exceeded the number in control sample under 15℃storage temperature. Therefore, when 15℃storage temperature is used, the treatment time should not be too short to achieve the expected antimicrobial effects and enzyme inactivation.This thesis also studied the physical, chemical and sensory charateristics of microwave-treated mushrooms during storage and compared with the control sample. Results showed that: long time treatment (1min) did decrease the color and texture properties of mushrooms. On the other hand, although short-time treatment performed better in maintain texture property, this advantage became unconspicuous during the late storage. 1000W 1min treatment had a significant and obvious effect on inactivating polyphenol oxidase and peroxidase and their activity cannot be detected during the whole storage. Microwave treatments can preserve the antioxidation ability, vitamin C content, and total polyphenol content in a good way and 4℃low-temperature storage also help preserve those nutritional and sensory traits.In all, combining adequate microwave treatments with low temperature storage could obviously reduce the total microorganisms and inactivate the polyphenol oxidase activity while maintaining relatively good nutritional and sensorial quality.

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