介電質常壓電漿於塑膠包裝材料之殺菌應用

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Title:	介電質常壓電漿於塑膠包裝材料之殺菌應用
Other Titles:	Sterilization of Plastic Packaging Material Using Dielectric Barrier Discharge at Atmospheric Pressure
Authors:	劉曜寬 Yao-Kuan Liu
Contributors:	徐詮亮 Chuan-Liang Hsu 食品科學系
Keywords:	殺菌;介電質放電;電漿;塑膠包裝材料薄膜 Sterilization;Dielectric barrier discharge;Plasma;Plastic Films in Food Packaging
Date:	2014
Issue Date:	2015-04-16
Abstract:	摘要目前的食品包裝材料上的殺菌法，主要有物理性的紫外光、?射線；化學性的液體殺菌(過氧化氫、酒精等)、氣體?菌(環氧乙烷)。這些方法雖然已用於業界多年，但還是有其缺點存在，易造成食品包材上產生某些問題，如待殺菌物不耐熱、形狀改變甚至會有化學藥品殘留等。由於現存的問題，本研究將應用介電質常壓電漿(Dielectric barrier discharge, DBD)於食品包裝材料上的殺菌並測試其殺菌效果。包裝材料樣品選用常用的塑膠包裝材料(PE、PP及PET)，以常見食品汙染菌如大腸桿菌（Escherichia coli）、金黃色葡萄球菌(Staphylococcus aureus)、沙門氏菌(Salmonella typhimurium)及李斯特菌(Listeria innocua)等為測試菌種，測試條件為頻率60 Hz、功率20、30及40 W、電極間距0.5 cm、工作氣體種類(氧氣、空氣、氮氣)以及測試時間(0 ~ 10、0 ~ 20分鐘)以及另外探討電漿處理對包裝載體之溫度變化，以及利用原子力顯微鏡觀察電漿殺菌處理後的菌體。實驗結果顯示，電漿功率與時間增加能提升殺菌效果，E. coli起始濃度7.21 log CFU/ml，用電漿功率40 W處理10分鐘，可以減少2.71 log CFU/ml，以氧氣為工作氣體處理10分鐘，可減少2.73 log CFU/ml效果為三種氣體中最好的。包裝材料樣品部分PE、PP及PET，在功率40 W處理10分鐘，可減少2.63、2.67及2.25 log CFU/ml，差異不明顯。在菌種的方面，E. coli、S. typhimurium、S. aureus及L. innocua起始濃度分別為7.25、6.97、6.76及6.72 log CFU/ml，處理20分鐘後，減少了3.37、3.28、1.07及1.15 log CFU/ml，S. aureus、L. innocua對電漿殺菌之抗性比E. coli與S. typhimurium好，即革蘭氏陽性菌較陰性菌對電漿有較強的抗性。在溫度變化上，起始溫度為22.1℃，以三種不同功率處理10分鐘後，溫度變化量約2.2℃，並無明顯的溫度變化。電漿處理完後，利用原子力顯微鏡觀察菌體本身，顯示菌體會因為電漿處理而被破壞。本研究之殺菌技術，主要特色為乾式且非熱殺菌，未來可望應用於食品包裝材料之表面殺菌。關鍵字：電漿、介電質放電、殺菌、塑膠包裝材料薄膜 AbstractMany methods have been widely applied in food packaging material for sterilization which include physical sterilization (such as thermal, ultraviolet (UV) light, and irradiation) and chemical sterilization (such as hydrogen peroxide, ethanol, and ethylene oxide). Although those methods have been used in industry for many years, they still exist more or less limitation and may cause some undesirable conditions such as objects are sensitive to heat, the shape changed due to high temperature, and chemical residues. The objective of this study was to evaluate the efficacy for the reduction of four bacterium, Escherichia coli, Staphylococcus aureus, Salmonella typhimurium, and Listeria innocua artificially inoculated on PE, PP and PET using dielectric barrier discharge (DBD). The processing parameters were frequency 60 Hz, input power (20, 30, 40 W), electrode spacing (0.5 cm), and plasma exposure time (0, 10, 20 min) using air, oxygen and nitrogen as working gas (500 sccm). In addition, the influences of plasma treatment on the surface temperature of plastic packaging material and on the surface of microorganisms were examined. The results indicated that microbial log reduction increased with increasing of input power and plasma exposure time. The initial bacterial count of 7.21 Log CFU/ml on PE film was decreased 2.73 Log CFU/ml after 10 min of plasma treatment at 40 watt using oxygen (O2) as the working gas. The reduction of bacterial count on the surface of packaging material of PE, PP and PET, was 2.63, 2.67, and 2.25 log CFU/ml individually after 10 min of plasma treatment at 40 watt indicating no significant difference for sterilization effect among those packaging materials. The bacterial count of E. coli, S. aureus, S. typhimurium, and L. innocua was decreased 3.37, 3.28, 1.07 and 1.15 log CFU/ml indicating that S. aureus and L. innocua (G+) were more resistant for of plasma than E. coli and S. typhimurium (G-). The temperature on the surface of the plastic packaging material was below 25℃ after 10 min plasma treatment at 20, 30, and 40 watt, individually. The alteration of cell morphology observed by atomic force microscopy (AFM) revealed that the etching effect on cell membrane caused by electrons, ions, and radicals emitted by DBD plasma was the primary mechanism for sterilization.Keywords : Plasma , Dielectric barrier discharge , Sterilization , Plastic Films in Food Packaging.
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