| Lotus root is an important aquatic vegetable in China. It win warm praise from customers with great nutritional and medicinal value. And it is the broad-spectrum food with great market potential. As Lotus root easily brown, senescent and decay, it shortens the period of selling and processing, and restricts the development of Lotus production. The development of annona fruit production is restricted due to the difficulty in fresh-keeping of the fruits during storage and transportation.This thesis studied the quality, physiology and enzymactic browning changes of Lotus roots to offer the bases of the storage and process technique. The results were as follows:1,During the storage, the browning degree and PPO activity were in a general trend of increasing. Solute protein content rises firstly and then decreases. Reducing sugar content showed significant differences between room temperature and lower temperature. When stored at a lower temperature, the browning degree and PPO activity were lower, but solute protein content and reducing sugar content were high.The time of respiratory peak appeared at the 4th day and the 15th day respectively. The PPO activity was positively correlated with the degree of browning,and reducing sugar content was positively correlated with the respiratory rate.2,Lotus roots cleaned in cold water after decortication and cutting off the nelumbonucifera,and homogenated with PBS (pH6.5) and centrifuged at 4℃, the general physical and chemical characters of Lotus PPO were studied. PPO was extracted by using high centrifugation, acetone precipitation,ammonium sulfate precipitation to separation PPO, then obtained 5.6 fold purification PPO. Different bands were obtained by the analysis of SDS-PAGE, and the molecular weight were 25.1 kDa of the maggi and 15.9 kDa of pure ensyme. The optimum pH and temperature for the oxidation reaction by purification PPO were pH5.4 and 30℃, and the stability of PPO was better at pH6.0～7.0 or/and 40℃or lower. Kinetic studies showed the Km value and Vmax for catechol is 15.08 mmol/L and 49.02×103 U/min, respectively.3,The fresh-cut lotus roots were treated with four natural antioxidants,then stored at 4℃.Based on single factor experiment, different composite antioxidants are investigted by orthogonal experiment.The result shows that: In the single factor experiment, PA and SDA have the better effect ,and their suitable content are 0.2% PA,0.3% CA,0.1%AA and 0.3%SDA. The best ingredients of compound reagent for inhibiting fresh-cut lotus roots browning are 0.1%PA+0.2%CA +0.1%AA+0.2% SDA.4,Four browning inhibitors were studied. Comparing the effect of 4 inhibitors, the best concentration and order was 0.25%EDTA > 0.5%CA > 0.2%Vc > 0.5% sodium hexametaphate. The best inhibitor combination was 0.5%CA + 0.1%Vc+ 0.2%EDTA from orthogonal test. The quality of boiled lotus root was better worked in 0.1%CaCl2 for keeping-brittle during processed.5,Principle of Hurdle Technology will be used in the Lotus technology. Through the associative action of a few Hurdle Factors, including salinity, pH, redox potential and fencing and heat sterilization, meanwhile by reducing heat sterilization strength, it can avoid organizations soft rotten and excessive acidification decline in the quality owning to the high-temperature sterilization, and prolong the shelf life of products. After treatment of 3.5 per cent of the salt, pH4.3 soup used with citric acid, sterilization for 90℃/10 min, the Lotus samples can be stored for 28 days at (37±2)℃without bulging bags phenomena, under (15±2)℃constant temperature conditions can be stored more than 180 days. |
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