Study On Inhibiting Effects Of Chlorine Dioxide On Enzymatic Browning In Fruits And Vegetables

Chlorine dioxide (ClO₂), which is experimented for a long time by American Food and Drug Administration (FDA) and American environmental protection Administration (FPA), is confirmed as an ideal sterilization and deodorization medicament used in medical treatment, food processing, food fresh-keeping (aquatic products, fruits and vegetables), environment, drinking water and industry circulating water. Chlorine dioxide is acknowledged as a safe, high efficient bactericide by the World Health Organization (WHO), which is also recommended internationally as the most ideal product replaceing the present chlorine family disinfectant. In 2004, U. S. FDA approved chlorine dioxide as an antimicrobial used in fruits and vegetables. In 1996, GB-2760 in China ranked stable chlorine dioxide as antiseptics and food processing agent in food additive, and confined it used in fruits and vegetables'fresh keeping and fish processing.In this research, apple juice and fresh-cut lotus root were treated with chlorine dioxide that worked as anti-browning agent and bactericide. The main research contents included the anti-browning effect and fresh-keeping effect of chlorine dioxide treatments on fruits and vegetables and their function mechanisms. The purpose of this research was to provide the theory basis and study foundation for further application of chlorine dioxide. The main results were as follows:1 The determination of ClO₂ in liquid sterilization under two wavelengths (360nm and 430nm) was studied. The results showed that under 360nm wavelength, the linearity equation was A=0.0123[ClO₂]-0.0196, the linear correlation coefficient was 0.99549, and standard curve was linear in the concentration range 10.6～63.6mg/L. Under 430nm wavelength, the linearity equation was A=0.0018[ClO₂]+0.01, the linear correlation coefficient was 0.99935, and standard curve was linear in the concentration range 116.60～424.00mg/L. Comparing to the results under 430nm, lower coefficient of variation and higher average recovery rate were obtained when determining under 360nm.2 Experiments were performed to optimize the extraction conditions of PPO in'Golden Delicious'apple fruit. Some enzymatic characteristics of PPO were also studied. The results indicated that the most efficient extraction was obtained by using the 1.6mL/g (sodium phosphate buffer/apple fruit) sodium phosphate buffer (0.05M, pH7.4) plus 2% PVPP and 0.25% TritonX100. The absorptive wavelength of enzymatic reactive product was 412nm. When catechol as the substrate, the kinetic equation of PPO was V=3333.33*[S]/0.027+[S] and its Km was 2.6667×10-2mol/L. The optimal pH value of PPO was 5.0 and the optimal reaction temperature of PPO was 40℃. With pH value range from 5.0 to 6.8, the PPO exhibited a higher stability.3 Effects of ClO₂ treatment on the activity and characteristics of PPO in Golden Delicious apples were studied. The results indicated that treatment with 50mg/L ClO₂ for 1 hour did not affect some characteristics of the PPO, including its optimum pH value (5.0) and temperature (40℃) as well as the maximum absorption wavelength (412nm) of the final products. With increasing ClO₂ concentrations from 0 to 100 mg/L, the V'max value reduced and K'm value changed irregularly. When the concentration of ClO₂ increased from 0 to 60mg/L, residual PPO activities significantly decreased, showing a negative linear-correlation with ClO₂ concentration. For 10mg/L and 50mg/L ClO₂ treatments, partial inhibition of PPO was achieved within 0.5 hour and the PPO activities did not significantly decrease after 0.5 hour. The inhibition and inactivation of PPO by ClO₂ treatment were observed at processing temperatures (30℃and 70℃) and storing temperatures (20℃, 0～4℃, and -18℃).4 The effects of ClO₂ and Vc on browning and clarifying of Fuji apple juice were studied. The results indicated that adding ClO₂ and Vc did not affect the absorption curves of the apple juice in range of 380 to 600nm wavelength. When 4～12mg/L ClO₂ were used to treat the apple juice, the 4, 6, and 8 dosage were found to have anti-browning effect on the samples; However, the 10 and 12mg/L dosage had less effect on the juice browning. No significant anti-browning effect was found when the apple juice was treated with Vc, especially when the sample was exposed under the air once in a while. The anti-browning effect of ClO₂ and Vc on apple juice was affected by the adding sequence. The results also show that adding ClO₂ benefited clarification and maintaining clarity of apple juice.5 After treated with ClO₂, the fresh-cut lotus root was stored at 4℃. Then the browning parameters, PPO activity and sense quality of fresh-cut lotus root were investigated at one-day interval. Higher ClO₂ concentration and longer time treatment benefited to maintaining the color and lightness, inhibiting PPO activity, delaying browning, and holding good sense quality of the fresh-cut lotus root. In this study, the PPO of fresh-cut lotus root was inhibited efficiently by treated with 100mg/L ClO₂ for 10min, and the sense quality was maintained up to 10 days.