Suitability Of Different Cultivars For Juice Processing And Pysiological Base Of Browning In Pear

The study used 113 culitivars, which belong to different species, as experimental material to evaluat the character and suitability of juice-processing and select the excellent germplasm. The experiment revealed the primary physical basis of enzymatic browning and the change of nutrient material in non-enzymatic browning by way of studing physiological characteristics of different species and cultivars. The effects of different treatment on browning inhibition of pear juice were also be explored, and the optimum method were selected. The primary results were as follows:1. According to the study of characteristics for juice-processing of 113 cultivars belong to different species, results showed that juice yields of different cultivars varied greatly, ranged from 16.6% to 68.1%, with average value 45.6%. The value of soluble solid contents ranged from 8.5% to 16.3%, average value was 11.9. The value of soluble sugar contents ranged from 6.3% to 15.3%, average value was 9.1%. The value of titratable acid ranged from 0.05% to 1.14%, average value was 0.29%. The value of sugar/acid ratio ranged from 7.13 to 126.40, average value was 48.59. The total phenol contents ranged from 0.096mg/g to 0.546mg/g, average value was 0.190mg/g. The browning degree ranged from 0.030 to 0.625, average value was 0.160. Comparing different species, a majority of cultivars of Pyrus pyrifolia (Burm.) Nakai and Pyrus hybrid were suitable for fresh juice processing because of their less browning character, moderate sugar/acid ratio, good sense quality, higher yields and good storage ability. A part of cultivars from Pyrus bretschneideri Rehd. and Pyrus sinkiangensis Yu also had good quality of sensory and nutrition. few cultivars of Pyrus communis L. were suitable for juice-processing because most cultivars had soft flesh and their juice were cloudy and serious browning. The cultivars of Pyrus ussuriensis Maxim. had highest sugar and acid contents among different species, but their juice brown easily and had worse quality of sensory for brown colour. The 'Wakahikari'(belonging to Pyruspyrifolia (Burm.) Nakai),'Xingchengxiehuatian' (belonging to Pyrus bretschneideri Rehd.),'Seerkepu'(belonging to Pyrus sinkiangensis Yu),'Nanguo'(belonging to Pyrus ussuriensis Maxim.),'Sanjili'(belonging to Pyrus communis L.),'Qiuxiang li'(belonging to Pyrus hybrid), which showed less browning, were good cultivars for juice processing with higher soluble sugar and titratable acid contents, good flavor and storability, and its sugar/acid ratio was moderate.2.10 different phenolic compounds were identified in fresh fruit with high performance liquid chromatography(HPLC) analysis. There was a great difference on content of different phenolic compounds among different species and cultivars. The content of gallic acid ranged from 0.14mg/kg to 3.41mg/kg, the content of catechin ranged from 0.19mg/kg to 7.60mg/kg, the content of epicatechin ranged from 0.029mg/kg to 6.70mg/kg, the content of caffeic acid ranged from 0.052mg/kg to 0.72mg/kg, the content of vanillin ranged from 0.43mg/kg to 13.82mg/kg, the content of chlorogenic acid ranged from 0.53mg/kg to 21.05mg/kg, the content of ferulic acid ranged from 0.14mg/kg to 1.40mg/kg, the content of violaquereitrin ranged from 0.22mg/kg to 3.95mg/kg, the content of phloridzin ranged from 0.063mg/kg to.09mg/kg, the content of quercetin ranged from 0.15mg/kg to 2.32mg/kg. The content of chlorogenic acid was the highest, vanillin, violaquereitrin, epicatechin, catechin were also primary phenolic compounds for their higher content, and the caffeic acid were lowest. The gray correlation of total phenols, chlorogenic acid, epicatechin,catechin and antioxidative activity with browning revealed that the content of total phenols had the largest effect on browning degree, the content of chlorogenic acid had the largest effects on browning degree among three phenolic compounds, while ntioxidative activity had smallest effects on browning degree. Chlorogenic acid should be the primary browning substance because of highest content in fruit and capacity in combination with polyphenol oxidases(PPO).'Housui' could used as breeding parent for selecting processing cultivars because of its low content of chlorogenic acid.3. The characteristic of non enzymatic browning of 10 cultivars juice-processed belong to different species during the storage were studied, results showed that the browning degree of juice of different cultivars increased immediately and changed smoothly until 28d. After storage of 35d,'Housui' had the most serious browning in contrast with 'Dahebai'.The browning degree and 5-HMF content of different cultivars increased remarkably during storage; the value of pH and the animo nitrogen content of different cultivars decreased; the TSS content of juice of different cultivars changed irregularly; sugar content of different cultivars increased at the early stage of storage and decreased finally. The 5-HMF and reducing sugar content were positive correlation with browning degree; while the value of pH,TSS and animo nitrogen content showed passive correlation with browning degree. The juice of'Xibaqingshui'and'Xinxiang'were storable and suitable for storage and processing for their little change of quality of sensory and nutrition during storage. The browning degree of Pyrus bretschneideri Rehd. had less changing, this infered that the juice of Pyrus bretschneideri Rehd. was more suitable for prolonging storage time.4. The effects of different methods on browning inhibition of pear juice were conducted, results showed that the best method of browning inhibition of'Zaosu'of single element was treatment of 1.5% ascorbic acid, the ratio of browning inhibition was 94.21%; the best method of browning inhibition of'Huasu'of single element was treatment of 0.75% ascorbic acid, the ratio of browning inhibition was 85.62%; the best method of browning inhibition of'Nanguo'of single element was treatment of 0.25% L-cysteine, the ratio of browning inhibition was 92.02%. The optimum inhibition combinations for different cultivars were also selected, the optimum combination treatment for'Zaosu'was 0.1%citric acid+0.2%honey+0.2%ascorbic acid+70℃; for'Huasu'was 0.3%citric acid+0.3%honey+0.1%ascorbic acid+70℃; for'Nanguo'was 0.3%citric acid+0.2%honey+0.3%ascorbic acid+90℃.