Effects Of Hydrogen Peroxide Treatments On Polyphenol Oxidase And Related Substrates From Konjac

Browning reactions in fruits and vegetables are recognized as a serious problem during handling,processing and storage.Polyphenol oxidases(PPO) activity that has been extensively reported is the main factor involved in browning.In order to whiten the product,protecting color is necessary in the process of konjac powder.Physical method and inhibitor aimed at the PPO in fresh konjac are used to eliminate enzyme activity to protect color.SO₂ can blanch product and eliminate enzyme activity,which is used to protect the color of konjac powder.However,the residue of SO₂ has negative effect on the finished product,and SO₂ is negative to human beings.Therefore,research and development studies for finding effective substitutes are still ongoing.In recent years,the use of hydrogen peroxide(H₂O₂) for bleaching and decoloring in the process of preparing some food additives is common.It has been reported that H₂O₂ treatments is effective in inhibiting fresh-cut fruits and vegetables browning.But there are some questions about the mechanism of anti-browning.The objectives of the research focus on investigation of the effects of H₂O₂ process on PPO and polyphenol compound from konjac,in order that provide a theory foundation for studise of anti-browning mechanism of H₂O₂ treatments.Research for extraction and purification of PPO and polyphenols from Amorphophallus albus at first and obtain purified samples,and then using H₂O₂ treatments on the purified samples respectively that analyse the effects of H₂O₂ process on them.The mian results of the research as follows:(1) Extraction and purification of PPO from konjac:fresh konjac was made into acetone powder,then the PPO was extracted from the powder with pH 6.8,0.2 mol/L phosphate buffer.The crude enzyme was fractionated with solid ammonium sulfate of 40%-80%saturation,and then purified by Sephacryl S200 and DEAE-Cellulose-52 column chromatography.Through these steps,PPO was purified.The sample obtained showed a single protein band with a molecular weight of about 31.0 kDa on SDS-PAGE. The final purification fold of recovering protein was 18.65.(2) The optimized extraction process for the konjac polyphenols was:extracting proportion 1:9(w/v),extracting temperature 80℃,extracting time 3h and ethanol concentration 50%,the concentration was up to 10.64 mg/g(raw material).The effects of four factors on konjac polyphenol extraction was:extracting temperature＞ethanol concentration＞extracting proportion＞extracting time.(3) Static absorption and desorption experiments were carried out to screen the suitable resin from 5 types of macroporous resins for konjac polyphenols.Results indicated that macroporous resin H103 possesses the strongest absorption ability and easier desorption property,which was a better candidate for purificating konjac polyphenols.When feeding rate was 2BV/h,concentration of feed was 4.85mg/mL, H103 can absorb konjac polyphenols all right,while elute volume was 6BV,elute-ethanol concentration was 80%,elution rate was 1-3BV/h,H103 had a better effect for desorbing konjac polyphenols.(4) PPO activity was highest at a pH of 6.0 and a temperature of 30℃.The PPO activity was stable at temperature of 30℃.The effects of H₂O₂ process on PPO and polyphenol compound,the results showed that H₂O₂ can break PPO obviously.The activity of PPO was almost eliminated by the process of H₂O₂ treatment in the presence of 70%concentration of ethanol.With the growing quantity of H₂O₂,the absorption of polyphenol compound was increasing.