Study On The Enzymatic Browning And Browning Control For Fresh-cut Chinese Water Chestnut

Fresh-cut Chinese water chestnut(CWC), which possessed some characters, including fresh, nutrition and ready-to-eat, is a rising and popular produce. But the mechanical processing lead to brown and the quality deterioration. This paper, selected fresh CWC as material, tried to illuminate the browning mechanism of fresh-cut CWC by analysis the change of the enzymic(PPO,POD and PAL) activity correlated with browning, the total content of phenolic compounds(TP) and the browning degree(BD), and analysis the change of main phenolic compounds and their content, and analysis the enzymatic chanracters of PPO. Based on those obtained results, L₉(3⁴)orthogonal tests was designed for selecting the potential effective combination of browning inhibitors to sustitute for sulfite The main results were as follows:1. The change in TP was the same as the PPO and PAL activity, which rose during storage and descended till 12 day in storage, while it was different to the change of POD activity, which descended slightly and then rapidly rose during storage. The possible reasons was: lots of phenolics were synthesized by enzymes which was activized by the mechanical processing, and that the phenolics was catalyzed by PPO led to the change of total content of phenolics and resulted in the formation of brown pigments.2. During storage, fresh-cut CWC was easy to browning. The significantly relationship and between increment of BD and TP(R²=0.9862) or PPO activity (R²=0. 8586) was existed, while the POD and PAL activity showed slight one to BD (R²=0. 2393 and 0.4161 respectively). It inferred from the obtained resulting that enzymatic browning was the main reason which lead to fresh-cut CWC browning.3. Four kind of phenolic compounds in fresh-cut CWC were identified by HPLC,including L-tyrosine, gallic acid, chlorogenic acid, and 3,4-dihydroxycinnamic acid. The major polyphenol was L-tyrosine and gallic acid. L-tyrosine was the major polyphenol in no-storage fresh-cut CWC, while the major one was gallic acid after storage 7 days during at 4°C. The change of content of L-tyrosine and gallic acid was possible correlation with the pathway, which tyrosine was catalyzed and synthesized phenolic compounds by tyrosinase.4. To probe into the change of physiology, three disposal modes (CK, glyphosate and 4-HR) was applied to fresh-cut CWC. The resultings uncoverred that 100umol/L glyphosate could prevented to the browning, while 500umol/L 4-hexylresorcinol could not. The content of chlorogenic acid in no-browning samples was 2 higher than that in browning samples. It can be inferred from it that the substrate of enzymatic browning was cholorgenic acid.5.Possible browning mechanism of fresh-cut CWC was inferred from all of the resultings. Lots of phenolics, including cholorgenic acid, were synthesized by enzymes which was activized by the mechanical processing. Under the catalyzation of PPO, the phenolics, including the major substrates of enzymatic browning cholorgenic acid, was oxidized and formed the browning pigment.6. PPO characters were studied. PPO was extracted by sodium phosphate extraction buffer, and was salted out by 30%-80% (NH4)2SO4, and was purified by Sephadex G-100 column chromatography. 8.3 fold purification PPO was obtained. Two bands were obtained by the analysis of SDS-PAGE, the molecular weight were 14.2 kDa and 15.9 kDa, respectively. The optimum pH and temperature for the oxidation catechol by purification PPO was pH6.5 and 40 °C, respectively, and the stability of PPO was better at pH7.0 or/ and 40-50°C. Kinetic studies showed the Km value and Vmax for catechol is 10.32mmol/L and 64.52 xlO3U/min, respectively. As for the substrate specificity of PPO, it exhibited greater affinity for diphenols than monophenols, which no PPO activity for tyrosine was observed. At the same time, the results showed the effects of various inhibitors on the activity of PPO as follows: Na2HSO3 > 4-HR > N-AC > D-AA > CA.7. The fresh CWC after precooled, cleaned, selected and peeled were treated with different concentration combinations of browning inhibitors according to L? (34)orthogonal tests. During storage at 4°C, BD, TP, PPO and PAL activity were determined periodically. The obtained results recovered that the best combination of browning inhibitors selected for fresh-cut CWC was 0.2%D-AA+0.05% N-AC. Compared with the effects which were treated with 0.1%NaHSC?3 and water, it was a good inhibitors combination.