Effect of Low-Temperature Plasma on Microorganism Inactivation and Quality of Freshly Squeezed Orange Juice

Dielectric barrier discharge is used to generate low-temperature plasma (LTP) for the treatment of freshly squeezed orange juice, which was inoculated with and without three kinds of microorganisms, respectively. Four experiments were designed and conducted: 1) When freshly squeezed orange juice samples inoculated with either Staphylococcus aureus, Escherichia coli, or Candida albicans were treated with LTP for 12, 8, and 25 s, respectively, the numbers of each microorganism decreased more than 5 logs; 2) when orange juices without the aforementioned microorganism inoculation were treated with LTP for inactivating original microorganisms inside and then stored at 4 degrees C refrigeration, the total plate count and the proliferation rate of original microorganism were both reduced significantly (counting per each 4-d during storage); 3) when orange juice samples without microorganism inoculation were treated with LTP, the LTP treatment had insignificant effect on the values of vitamin C, total acid, turbidity, degrees Brix, and pH of orange juice; 4) when orange juice samples were inoculated with S. aureus, E. coli, or C. albicans, respectively, and their pH values were slightly decreased by adding HCl (similar to that after LTP treatment), there was no obvious inactivation effects due to the reduction of pH values. It was proposed that microorganism inactivation was mainly due to reactive species and charged particles instead of slight pH reduction, and LTP treatment was able to effectively inactivate microbes and maintain the quality of orange juice.