Studies On Juice Processing Characteristics Of Pear Varieties And Browning Control Technology Of Pear Juice

Pear is the third largest output fruits in China,13670 tons was harvested in 2008, which is almost 2/3 of all the world harvested, ranking the first. While, the amount of pear being processed is less than 10% of the total.In the harvest period, there are so many pears in the market that many can't be sold and rot at last. Studying the pears' processing characters deeply, solving the problems occurred during processing and storage are effective ways to improve benefits and promote development of the industry. 23 pear varieties such as Yali,TsuLi,Whangkeumbae, Huagai, Nanguo were referred in the experiments, which offered academic guidance for pear industry by studying the pears' juice-processing characters, screening juicing suitable varieties and summarizing methods to select juicing variety. Effects of ripening degree on juicing performance were also studied, and then mechanism of nonenzymatic browning and the control of enzymatic browning were discussed in order to provide technical support. The experiments investigation indicates:1. Physical and chemical indicators (total sugar, reducing sugar, titratable acid, soluble solid content, juice yield),degree of browning (total phenolics, PPO activity, OD420nm, L) and sensory evaluation (appearance, taste, smell) should be considered before identify a juicing variety, which should be good in taste, high in juice yield, low in browning degree. Jinxiang, Whangkeumbae, Anli were the best varieties of all the 23. Total phnolics are richest in fruit skin, and then in fruit core, poorest in fruit flesh, and total phenolics of pear skin correlated significantly with colour value. Most varieties' PPO activity in fruit skin is high, while, in flesh is relatively low.2. Juice of Yali and taste less flavor, mix them with palate fullness juice, orthogonal experimental design to get two best recipes:Ⅰ:TsuLi-juice 50ml, Anli-juice 25ml, jinxiang-juice 30ml;Ⅱ:Yali-juice 50ml, Huagai-juice 15ml, jianbaer-juice20ml.3. For Pyrus ussuriensis Maxim, ripen firstly before juice until the firmness is suitable, the juice yield is high, the tannic is less, and the browning is light. When the firmness is 2.5～4.0kg/0.5cm2 can meet the demands above.4. In the nonenzymatic of Whangkeumbae juice and Qiubai juice during storage, the concentration of total amimo acid,sugar and total phenolics decreased, and they are correlated negatively with OD420,positively with L value. Maillaid reaction and phonelics oxidation were the main factor of nonenzymatic browning. Storage in low temperature can inhibit nonenzymatic browning effectively.5. OD420 of Whangkeumbae juice and Qiubai juice increased with both time and temperature. Storaged in 20℃, Whangkeumbae juice fits two stages combined reaction kinetic, and Qiubai juice fits parabola kinetic. While storaged in 0℃, both fit zero order. Browning activation energies of Whangkeumbae juice and Qiubai juice are 12.13kcal/mol and 10.73 respectively, Whangkeumbae juice browns easier than Qiubai juice.6. Antibrowning agents can inhibit enzymatic effectively during pear juice is being processed. With the same concentration, the inhibition ability of studied antibrowning agents was: Na2SO3>Vc>L-Cysteine>Citric acid>CaCl2。The PPO inhibition ability was:L-cysteine> Na2SO3> Citric acid>Vc> CaCl2。Inhibition ability strengthen significantly when mixed, according response surface methodology, the optimum combination was determined as Vc 0.046%,L-Cysteine 0.037%, Citric acid 0.0401%.