Study On The Cloudy Lily Juice

As a kind of vegetable which has high nutritional and economic value, lily has been widely planted in many provinces in China. To develop cloudy lily juice with good color and cloud stability is not only in accordance with the trends of nutritional, healthy and convenient, but also beneficial to enhance the economic income of farmers. The objective of this dissertation was to develop an enzymatic technology for processing cloudy lily juice and investigate its stability. The main results are as follows:A study of crude polyphenol oxidase (PPO) from lily bulbs was carried out. The enzyme activity showed two pH optima, at pH 4.0 and 7.0 with catechol as substrate. The optimum temperature was 40℃, and the enzyme began to inactivate at 40℃. Heat inactivation of PPO followed first order kinetics. Lily PPO had activity with catechol, catechin, and gallic acid, and activity with L-tyrosine was not observed. The most effective inhibitor was sodium sulphite, however, ascorbic acid, L-cysteine, and thiourea were also effective inhibitors at high concentration. But NaCl, CaCl2, and citric acid were poor inhibitors of the enzyme. The effect of PPO on the browning of lily was much greater than that of peroxidase at the natural pH of lily. Furthermore, enzymatic browning could be inhibited by heating the lily bulbs in boiling water.The cloudy lily juice was produced using enzymatic hydrolysis method. The optimum enzymatic parameters were 0.2%α-amylase at 60℃for 1h, and then 0.08% protamex at 45℃for 45min.The stability of cloudy lily juice during storage was studied. The effect of xanthan gum on the stability was better than that of carboxymethyl cellulose (CMC). It was found that the range of the aggregation of the starch materials, most of which were dextrins, was very wide. The ultra microstructure which was observed by transmission electron microscope showed that the sediments of lily juice were composed of global, elliptic and amorphous particles, some of which had second structures like chains. An increase in temperature and storage time induced the color to brown, and maillard reaction was considered to be the important reason of non-enzymatic browning during storage of lily juice.Pulsed electric field (PEF) had an obvious effect on the sterilization of lily juice. The effect of sterilization was increased as the increase of the electric field strength and the treatment time. The total bacteria of lily juice could reduce 4 logarithms with electric field strength of 30kV/cm and total treatment time of 400μs, and the juice had no significant changes in its color and other indexes.