Effect of Calcium Treatment During Production on Quality of Stored Huangguan Pear Fruit

Tiezheng LIU Xueying LI yong LI Guosheng LIU Jingtao WANG Yongbo WANG Yali FU Yanxiao HAN

Abstract The effect of calcium treatment during production on the quality （soluble solids， fruit firmness， soluble sugar content， titratable acid content， etc.） of Huangguan pear was studied. The results showed that the calcium treatment during production improved the comprehensive quality of Huangguan pear fruit， delayed and reduced the occurrence of browning of fruit core， and enhanced its storage effect in the cold storage. Therefore， the calcium treatment improved the quality of stored pear fruit.

Key words Calcium treatment; Huangguan pear; Storage

Pear belongs to the Pomoideae of Rosaceae， and it is widely cultivated in China because of its adaptability， drought resistance and waterlogging resistance[1]. Huangguan pear is a midearly variety with good maturity， excellent quality and high scab resistance. It is one of the varieties regarded as the foremost in pear tree structure adjustment in China. However， for a long time， much attention has been paid to preharvest management and yield of the fruit， while less has been paid to quality and postharvest storage of the fruit， which has caused serious losses in the circulation of fruits after harvest. In particular， the browning of fruit during storage causes the fruit to lose its commercial traits， causing serious losses to pear farmers.

Calcium plays a very important regulatory role in fruit development and maturity and aging[2-5]. During fruit storage， with the aging of the fruit， endogenous ethylene is generated， accompanied with the destruction of cell structure， disintegration of cell wall， hydrolysis of original pectin into soluble pectin and leakage of contents， and the oxidases such as PPO and SOD and their substrates （phenolic substances） react with oxygen， which causes the enzymatic browning of pear fruit[6-8]. Previous studies have investigated the browning of fruits such as Yali and Korla pears[9-11]. In this study， the effect of calcium treatment on the quality of Huangguan pear fruit was studied through calcium spraying during production， with an attempt to provide a theoretical basis for improving the storage and preservation of Huangguan pear.

Materials and Methods

Calcium spraying during production

This experiment was carried out in the Huangguan pear garden of Shijiazhuang Fruit Institute. Twelveyearold Huangguan pear trees with regular management， moderate growth and uniform growth were selected as experimental materials. Both the treatment and control （CK） had three plants per plot， with three replicates. Calcium spraying during production： At the young fruit stage， 0.3% calcium nitrate （analytical pure） was sprayed （20 d after full bloom）， once every 7 d， 3 times in total， before bagging. The CK was sprayed with water.

Contents of investigation and determination

Fruit calcium content determination; fruit firmness determination; fruit soluble solid content and titratable acid content determination; fruit MDA， PPO， SOD and other enzyme activity determination （determination period： 0， 80， 120， 150， 180， 210 and 230 d after storage）.

Results and Analysis

Effects of calcium spraying on total calcium content in postharvest and stored pear fruit

It could be seen from Fig. 1 that the total calcium contents in different fruit parts ranked as the seed>fruit core>fruit flesh， and the calcium contents in different fruit parts of the calcium treatment were greater than those of the CK， overall. The total calcium content in the fruit flesh increased at first and then decreased with the prolongation of storage time， and reached the maximum value at 180 d after storage. The calcium content in the fruit core gradually decreased with the prolongation of storage time. The total calcium content in the seed increased rapidly at first， and then tended to be stable with the prolongation of storage time.

Effects of calcium spray during production on fruit firmness of postharvest and stored pear fruit

As can be seen from Table 1， the calcium treatment improved fruit firmness and soluble solid content of the stored pear fruit and reduced the titratable acid content. The fruit firmness decreased gradually with the prolongation of storage time. The soluble solid content did not vary significantly with the prolongation of storage time， and the titratable acid showed a decreasing trend.

in postharvest and stored pear fruit

Variation of MDA in pear fruit during storage

It could be seen from Table 2 that the calcium treatment during production effectively inhibited the accumulation of MDA content in pear fruit （fruit core and flesh）， indicating that the degree of membrane lipid peroxidation was reduced， and the damage of membrane structure was reduced. The MDA content in the calcium treatment was significantly lower than that in the CK; with the prolongation of storage time， the contents in the two treatments both increased gradually; and the MDA content in the fruit core was significantly lower than that in the fruit flesh. It reached its maximum value at 230 d after storage， and was 1.608 mmol/g in the fruit flesh of the calcium treatment and 1.836 mmol/g in that of the CK; and the MDA content was 1.138 and 1.254 mmol/g in the fruit core of the two treatments， respectively. In summary， calcium treatment can reduce the degree of membrane lipid peroxidation and reduce the damage of membrane structure， thereby reducing the browning of stored pear fruit.

Variation of SOD in pear fruit during storage

It could be seen from Table 3 that the PPO activity of the same treatment was higher in the flesh core than the fruit flesh; and the CK had a higher fruit PPO activity than the calcium treatment. The PPO activity was lower after harvest and before storage， and with the prolongation of storage time， it showed a trend of increasing at first and decreasing then. Moreover， the PPO activity reached its maximum value at 180 d after storage， and was 7.858 and 8.012 （0.01┐A/（g·min）） in the fruit flesh of the calcium treatment and the CK， respectively; and the activity was 9.358 and 10.035 （0.01┐A/（g·min）） in the fruit core of the two treatments， respectively. It could be seen that the calcium spraying treatment during production can slow the increase of PPO activity in pear fruit during storage.

Variation of SOD in pear fruit during storage

As shown in Table 4， the SOD activity of the fruit core was higher than that of the fruit flesh; the enzyme activity of the fruit was the highest after harvest before storage， and then decreased with the prolongation of storage time. The SOD activity reached its minimum value at 230 d after storage， and was 6.572 and 5.428 U/g in the fruit flesh of the calcium treatment and the CK， respectively; and it was 12.188 and 10.952 U/g in the fruit core of the two treatments， respectively.

Conclusions and Discussion

The results of this study showed that the calcium treatment increased the total calcium content in the fruit of Huangguan pear; the calcium treatment slowed the decline of fruit firmness and fruit soluble solids[12]; and the calcium treatment inhibited the accumulation of MDA in fruit （fruit core and fruit flesh）[13]， the increase of PPO activity， and the decrease of SOD activity. Therefore， the calcium treatment better maintained cell stability and higher free radical scavenging ability， alleviated membrane lipid peroxidation， and reduced the conversion of phenolic substances into quinones. The calcium treatment improved the quality of stored Huangguan pear fruit.

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