Abstract: Yam puree was treated with pressure, temperature and browning inhibitors in single or/and complex combination, the polyphenol oxidase activity and color change in Yam puree were assayed. PPO activity at a temperature range of 20 to 50℃ was investigated while the optimum action temperature of PPO was 35℃. Yam puree packed with PE bag was susceptive to a range of pressures (200, 300, 400, 500, 600MPa). At 20℃,400MPa, a peak of PPO activity was observed. Over or under 400MPa, PPO activity was reduced, but at 600MPa, PPO activity was lowest. Research on effect of orthogonal test with pressure, temperature and time (L 9 (34)) on PPO activity was carried out. The result indicated that the PPO activity reduced down to the lowest at 550MPa, 40℃and 10min. Inhibitive effects of orthogonal test with citric acid, ascorbic acid and EDTA (L 9 (34)) on PPO activity were also investigated while temperature (40℃) and pressure (550MPa) were constant. The optimum combi- nation was found: 0.05% citric acid, 0.4% ascorbic acid and 0.02% EDTA. Treating yam puree with pressure combined with browning inhibitors could obtain better organoleptic quality (e.g. color, texture) than the single factor treatment.

Key words: ultra high pressure, Yam puree, polyphenol oxidase, browning inhibitor