| The high performance liquid chromatography system was applied, with98pear cultivars from different species as experimental material, to determine the contents of soluble sugars,organic acid and to comprehensively evaluate the distribution characteristics of components and contents of soluble sugars and organic acid. At the same time, the conformation rule of soluble sugars and organic acid in pear fruits from different species were studied,during fruit development. The accumulations of soluble sugar and organic acid of pear fruits of different species were primarily known.The research results were as follows:1. The contents of soluble sugar and organic acid were determined by the high performance liquid chromatography.The results showed that the limits of detection of each component were from1to50μg/ml, the correlation coefficients were more than0.9992, the variation coefficients were between0.48%and11.83%, and the recoveries were from96.28%to103.97%, moreover, the detection speed was fast. Therefore, high performance liquid chromatography method for determining the components of soluble sugar and organic acid had lower detection limits, better linear correlation, repeatability and higher accuracy and recovery, it can be applied to measure the soluble sugar and organic acid in pear fruits.2. The major components of soluble sugars in mature pear fruits were fructose, glucose, sucrose and sorbitol, and the pear fruit had the highest value in fructose content, with a mean of51.17mg/g FW. The contents of fructose and glucose were relatively stable among different cultivars, while the contents of sucrose and sorbitol significantly varied among different cultivars, the value ranged from1.14to47.75mg/g FW and from4.46to47.29mg/g FW, respectively. The level of fructose was the highest in four certain kinds of sugars, accounted for42.22%-57.02%. While the other three compoents of soluble sugars showed some varieties in different cultivars. Glucose content was similar to sorbitol in both P. bretschnrideri Rehd. and P. sinkiangensis Yu., and sucrose content was the lowest in total sugars; the contents of fructose and sucrose were equal in both P. communis Linn, and P. ussuriensis Msxim.. However, sorbitol content was higher in P. communis Linn., and was lower in P. ussuriensis Msxim. Sucrose content was equal to sorbitol in P. pyrifolia Burm Nakai.,and glucose was the lowest. We draw a conclusion that the distribution characteristics of soluble sugars in different species by using principal component analysis: P. bretschnrideri Rehd. mainly distributed in the high glucose and sorbitol area; P. pyrifolia Burm Nakai. mainly distributed in the high sucrose and sorbitol area; P.communis Linn, mainly distributed in high fructose and sorbitol area; P. ussuriensis Msxim. mainly distributed in the high glucose and sucrose area; P. sinkiangensis Yii. mainly distributed in the high fructose and glucose area.3. The organic acid contents were in the range of1.29～23.50mg/g FW among the98pear cultivars. P.communis Linn. had the highest total acid contents, followed by P.ussuriensis Msxim., P.bretschnrideri Rehd. and P.pyrifolia Burm Nakai.. P.sinkiangensis Yii had the lowest organic acid contents. Malic and citrate acid were the predominant organic acids in pear fruits, which ranged from0.73to23.16mg/g FW and from0.02to15.19mg/g FW, respectively. The proportions of the two organic acids in total acids were55.91%and37.08%, respectively. According to the ratio of citric/malic acid,98cultivars were classified as malic-dominant and citric-dominant types. In P.communis Linn., the ratio was more than1(1.38in an average), and was exhibited citric-dominant type; in other species, including(P.ussuriensis Msxim., P.bretschnrideri Rehd. and P.pyrifolia Burm Nakai.. P.sinkiangensis Yii), the ratios of citric/malic acid were less than1, exhibited as malic-dominant type. Through principal component analysis, the data showed that P. bretschnrideri Rehd. and P. sinkiangensis Yu had relatively higher shikimic and quinic acid contents; P. pyrifolia Nakai had relatively higher quinic acid contents; P. communis L. had higher citric acid contents; and P. ussuriensis Maxim. mainly distributed in the area of malic-dominant types.4. The accumulation of soluble sugar were observed in the later period during fruit development, especially sucrose accumulation.The levels of total sugar, fructose, glucose and sucrose frocose increased with fruit growth. The levels of sorbitol firstly rose and then declined at later period of fruit development. The components of sugar varied among cultivars during fruit development stage. In the previous period of fruit development, the proportion of sorbitol to total sugar was the biggest, others sugars levels were low; with fruit development, the contents of sorbitol reduced, fructose, glucose and sucrose increased successively; at maturity stage, the proportion of fructose to total sugars reached the highest, but proportion of glucose, sorbitol and sucrose decreased successively. The levels of soluble sugar components significantly varied in different periods of fruit development. The contents of fructose, glucose and sucrose accumulate showed different at55,70,85days after flowering, respectively. The difference of the metabolic pattern was probably due to the difference of sugar content. Sugar accumulation characteristics in pear fruit from different species were different, total sugar contents of P. ussuriensis Msxim. were the highest during fruit development and the range was23.69～137.68mg/g FW; total sugar content of P. pyrifolia Burm Nakai. was the lowest during fruit development and the range was18.02～108.39mg/g FW; total sugar content of P.bretschnrideri Rehd. was higher, and the range was21.44～124.83mg/g FW; total sugar contents of P. communis Linn.was the higher, and the range was45.37～124.31mg/g FW, the accumulation of soluble sugar contents in the early period, and the accumution speed was fast, then the speed was low in the later period.5. The levels of organic acids accumulated in the previous period of fruit development were higher, but rapidly drop in the later period of fruit development. There were some difference in the proportion of different acids to total acids during fruit developmental periods. In the early period of fruit development, the proportion of quinic to total acid was the highest, other organic acid ratios were lower; with fruit development, the contents of quinic acid drop rapidly; in the maturity stage, malic and citric acid were dominating acids, the proportion of quinic to total acid were low.The characterics of accumulation of organic acids were difference during fruits development, the contents of malic,citric and shikimic acid dropped rapidly at55,55～70,40～55day after flowering, respectively. The variations in acid level were due to the difference content of malic and citric acid during fruit development. The contents of organic acid among experimented species were different, the total acid contents of P. bretschnrideri Rehd., Ppyrifolia Burm Nakai. and P.ussuriensis Msxim. were higher in the early period of fruit development, there were a sharp decline in the middle period, and slowly down in the late period; total acid contents of P. communis Linn, increased slightly in the early period of fruit development, and then reduced fastly in the late period. During fruit development, total acid and malic acid contents had a downward trend. The pear cultivars of citric-dominant type showed that citric and quinic acid content early drop and later rose, then declined in the end; the content of shikimic acid falled in the way; the pear cultivars of malic-dominant type showed that citric and quinic acid contents fell sharply and in the middle period, the contents fluctuated in narrow range at later stage. |
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