Analysis on the Changes in Fruit Quality of ‘Beishan’ Apricots during Storage at Room Temperature

Guoquan FAN Yatong WANG Zhanghu TANG Shaopeng WANG Tasiheng•Jieensi Shikui ZHANG

Abstract ［Objectives］This study was conducted to understand the changes in fruit quality during storage of local high-quality apricot variety ‘Beishan’ in Xinjiang at room temperature, and to clarify the suitable storage time of the variety.

［Methods］ Under normal temperature storage conditions, the changes of fruit weight, firmness, soluble solids, titratable acid, soluble sugar, vitamin C and rot rate were observed every day.

［Results］ With the increase of storage days at room temperature, the fruit weight and firmness of ‘Beishan’ apricots gradually decreased; the contents of titratable acid and vitamin C decreased gradually; and the contents of soluble solids and soluble sugar increased slightly on the 2nd day of storage, and then gradually decreased. The fruit quality began to decline sharply after the 6th day of storage. The fruit began to rot on the 3rd day of storage, and the rot rate was higher than 60% and increased significantly after the 6th day.  After the ‘Beishan’ apricots were stored at room temperature until the 6th day, the fruit quality began to decline sharply, and the rot rate exceeded 60%. The suitable storage time at room temperature was about 6 d.

［Conclusions］ This study provides data support for the research and promotion of the ‘Beishan’ variety.

Key words Apricot; Fruit; Storage at room temperature; Quality

Received: May 23, 2022  Accepted: July 26, 2022

Supported by Special Fund for the Construction of Innovation Environment (Talents, Bases) in the Autonomous Region (Resource Sharing Platform Construction); Tabei Apricot Experiment Station of Autonomous Region Apricot Industry Technology System.

Guoquan FAN (1980-), male, P. R. China, associate researcher, master, devoted to research about fruit tree germplasm resources and breeding.

*Corresponding author.

Apricot trees have a relatively long history of cultivation in China. Xinjiang is known as the hometown of apricots in China. The planting area and yield of apricots in Xinjiang rank first in China. The apricot industry occupies an important position in the forest and fruit industry in Xinjiang, and is an important focus for industrial and rural revitalization in southern Xinjiang［1-2］. However, in the development of Xinjiang apricot industry, there are still problems such as less variety types, unreasonable variety matching, and lack of special varieties［3］. Xinjiang is the origin center of apricots in the world, and has abundant apricot germplasm resources, especially some characteristic local varieties, which have extremely high development and utilization value.  Through the development and utilization of these resources, the above problems can be better solved［4］. The quality of fruit will gradually decline during storage, and some of the fruit will rot. During the whole storage period of fruit, the change of fruit quality presents a certain change law［5］. The storage characteristics and suitable storage time of fruit can be clarified by studying the changing law of fruit quality during storage. In this study, with high-quality local apricot variety ‘Beishan’ in Xinjiang as the research object, its fruit weight, firmness, soluble solid content, soluble sugar content, titratable acid content, vitamin C content and fruit rot rate of the fresh fruit of this variety under normal temperature storage conditions were tracked and tested, aiming to clarifying the suitable storage time of ‘Beishan’ apricots at room temperature, and to provide data reference for the research on horticultural characteristics and variety certification of ‘Beishan’ apricots.

Materials and Methods

General situation of the experimental fields

The experimental site was located in the Fruits Germplasm Resources Garden of Xinjiang Academy of Agricultural Sciences in Luntai. Luntai County is located at the southern foot of the Tianshan Mountains, the northern edge of the Tarim Basin, and the western part of the Bayingol Mongolian Autonomous Prefecture. Luntai County has a warm temperate continental arid climate, with an annual average temperature of 10.6 ℃ in the central plain area. The average annual precipitation in the plain area is 52 mm; the annual average evaporation is 2 072 mm; the annual sunshine is 2 777 h; and the frost-free period is about 188 d［6］.

Experimental materials

In this study, the 30-year-old apricot variety ‘Beishan’ in the Fruits Germplasm Resources Garden of Xinjiang Academy of Agricultural Sciences in Luntai was used as the test material. The apricot trees of ‘Beishan’ were healthy and moderate in vigor, and the planting row spacing was 3 m × 5 m.

Experimental design and methods

Experimental design

The fruit was harvested when it was almost fully ripe. Specifically, 300 pieces of fruit without damage and diseases were randomly selected, put on a foaming net one by one, randomly divided into three groups, and placed in three plastic baskets of 35 cm×25 cm×15 cm (the bottom of each plastic basket was placed with a 0.5 cm foam board, and two layers of coarse paper were laid at the bottom and around). The fruit was stored at room temperature (between 25-30 ℃). The fruit rot rate was counted every day, and then, 5 pieces of fruit were randomly selected from each basket, totaling 15 pieces of fruit, for the detection and analysis of the single fruit weight, soluble solids, soluble sugar, titratable acid, vitamin C and fruit firmness.

Experimental methods

The single fruit weight was determined according to the method in Descriptors for apricot germplasm resources and data standards［7］. An electronic balance (Mettler Toledo Technology (China) Co., Ltd. PL602E/02) was used for the determination.

For the determination of fruit firmness, the method in Descriptors for apricot germplasm resources and data standards was adopted［7］. The fruit firmness was measured with a fruit firmness meter (Beijing Jingcheng Huatai Instrument Co., Ltd. GY-1) on the positive side of the fruit, and the average value was calculated.

The determination of soluble solids adopted the method in Descriptors for apricot germplasm resources and data standards［7］. Specifically, the peel was removed, and the juice was collected from the edible part of the flesh, and the soluble solid content was measured with a handheld digital sugar measuring instrument (Japan Atago PAL-1).

The determination of soluble sugar content adopted the method in Experiment Guidance of Postharvest Physiology and Biochemistry of Fruits and Vegetables［8］. The soluble sugar content of fruit was determined by anthrone colorimetry.

The determination of titratable acid content was carried out according to the method in Experiment Guidance of Postharvest Physiology and Biochemistry of Fruits and Vegetables［8］. The acid-base neutralization titration method was used to determine the titratable acid content of fruit.

The determination of vitamin C content adopted the method in Experiment Guidance of Postharvest Physiology and Biochemistry of Fruits and Vegetables［8］. The 2,6-dichloroindophenol titration method was used to determine the vitamin C content of fruit.

The rot rate was calculated according to the method in the Experiment Guidance of Postharvest Physiology and Biochemistry of Fruits and Vegetables［8］. The number of rotten fruits is counted with fruit softening and festering as the standard. After each count, the rotten fruit was removed, and the number of rotten fruit was the cumulative value.

Data processing

The experimental data were subjected to basic data processing, standard error calculation and chart plotting in Excel 2019.

Results and Analysis

Changes of single fruit weight during storage at room temperature

As shown in Fig. 1, under normal temperature storage conditions, with the increase of storage days, the single fruit weight of the fruit gradually decreased. Before storage, the single fruit weight was 33.54 g; on the 6th day of storage, the single fruit weight was 31.54 g; and on the 10th day of storage, the single fruit weight was 26.73 g. From day 0 to day 6 during storage, the reduction rate of the single fruit weight was 0.33 g/d FW, and the reduction rate of the single fruit weight from the 6th day to the 10th day was 1.20 g/d FW. It could be seen that the single fruit weight began to decline rapidly from the 6th day of storage at room temperature.

Changes in fruit firmness during storage at room temperature

As shown in Fig. 2, under normal temperature storage conditions, with the increase of storage days, the fruit firmness gradually decreased. On day 0 of storage, the fruit firmness was 1.61 kg/cm2; on the 6th day of storage, the fruit firmness was 0.96 kg/cm2; and on the 10th day of storage, the fruit firmness was 0.19 kg/cm2. The reduction rate of fruit firmness was 0.11 kg/cm2 from the day 0 to day 6 during storage, and 0.19 kg/cm2 from day 6 to day 10 during storage. It could be seen that the fruit firmness began to decline rapidly from the 6th day of storage at room temperature.

Changes of soluble solid content in the fruit during storage at room temperature

As shown in Fig. 3, under normal temperature storage conditions, the soluble solid content of fruit increased slightly from the 0 day to the 2nd day of storage, and gradually decreased from the 2nd day to the 10th day. On the 0 day of storage, the fruit soluble solid content was 20.53%; on the 6th day of storage, the fruit soluble solid content was 20.37%; and on the 10th day of storage, the fruit soluble solid content was 17.32% FW. The fruit soluble solid content decreased at a rate of 0.03% from the 0 day to the 6th day of storage, and at a rate of 0.76% from the 6th day to the 10th day of storage. It could be seen that the content of soluble solids in the fruit began to decline rapidly from the 6th day of storage at room temperature.

Changes of soluble sugar content in the fruit during storage at room temperature

As shown in Fig. 4, under normal temperature storage conditions, the soluble sugar content of the fruit increased slightly from the 0 day to the 2nd day of storage, and gradually decreased from the 2nd day to the 10th day. On the 0 day of storage, the fruit soluble sugar content was 148.97 g/kg·FW; on the 6th day of storage, the fruit soluble sugar content was 130.49 g/kg·FW; and on the 10th day of storage, the fruit soluble sugar content was 114.35 g/kg·FW. The soluble sugar content of fruit decreased at a rate of 3.08 g/kg·FW from the 0 day to the 6th day of storage, and at a rate of 4.04 g/kg from the 6th day to the 10th day. It could be seen that the soluble sugar content of fruit began to decline rapidly from the 6th day of storage at room temperature.

Changes of titratable acid content in the fruit during storage at room temperature

As shown in Fig. 5, under normal temperature storage conditions, the titratable acid content of fruit gradually decreased. On the 0 day of storage, the titratable acid content of fruit was 32.46 g/kg·FW; on the 6th day of storage, the titratable acid content of fruit was 26.78 g/kg·FW; and on the 10th day of storage, the fruit titratable acid content was 18.21 g/kg·FW. The titratable acid content of fruit decreased at a rate of 0.95 g/kg·FW from the 0 day to the 6th day of storage, and at a rate of 2.14 g/kg·FW from the 6th day to the 10th day of storage. It could be seen that the titratable acid content of fruit began to decline rapidly from the 6th day of storage at room temperature.

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Changes of vitamin C in the fruit during storage at room temperature

As shown in Fig. 6, under normal temperature storage conditions, the vitamin C content of fruit gradually decreased. On the 0 day of storage, the fruit vitamin C content was 15.44 mg/100 g·FW; on the 6th day of storage, the fruit vitamin C content was 12.48 mg/100 g·FW; and on the 10th day of storage, the fruit vitamin C content was 6.73 mg/100 g·FW. The reduction rate of vitamin C content in the fruit was 0.49 mg/100 g·FW from the 0 day to the 6th day of storage, and 1.44 mg/100 g·FW from the 6th day to the 10th day. It could be seen that the vitamin C content of fruit began to decline rapidly from the 6th day of storage at room temperature.

Changes of fruit rot rate during storage at room temperature

As shown in Fig. 6, under normal temperature storage conditions, the fruit began to rot from the 2nd day of storage, and the rot rate gradually increased from the 3rd day to the 10th day of storage. On the 3rd day of storage, the fruit rot rate was 6.33%; on the 6th day of storage, the fruit rot rate was 33.33%; and on the 10th day of storage, the fruit rot rate was 84.67%. From the 3rd to the 6th day of storage, the fruit rot rate increased at a rate of 5.33%, and at a rate of 15.59% from the 6th to the 10th day of storage. It could be seen that the rot rate of fruit began to increase rapidly from the 6th day of storage at room temperature.

Discussion and Conclusions

The results of this study showed that with the increase of storage days at room temperature, the fruit weight and firmness of ‘Beishan’ apricot fruit gradually decreased; the content of titratable acid and vitamin C decreased gradually; and the soluble solids and soluble sugar increased slightly at the beginning of storage, and then gradually decreased. The fruit quality began to decline sharply after the 6th day of storage. Zhu Xinwei’s experiments on the storage of Luntai white apricots and Saimaiti apricots at room temperature showed that under normal temperature storage conditions, the fruit quality would decrease with the increase of storage days, and there was an inflection point in the changes of quality indexes. The suitable storage days for the two varieties at room temperature was 4 d or so, which is similar to the results of this study［9］. Chen et al.［10］ also found that the storage days of ‘Baishui’ apricots at room temperature did not exceed 5 d when studying the quality of apricots during storage. Gu［11］ compared the changes in quality indexes of four Xinjiang apricot varieties during storage and found that there were certain differences in the shelf life of different apricot varieties at room temperature, and the varieties with higher firmness had a relatively longer shelf life at room temperature. ‘Beishan’ apricot fruit began to rot on the 3rd day of storage, and the rot rate was higher than 60% and increased significantly after the 6th day. The reason for this phenomenon might be related to the climacteric change of fruit during storage, resulting in fruit senescence, cell structure damage, tissue loosening, fruit resistance-related enzymes not fully functioning, and reduced effect of resisting bacterial infection［12-14］.

Under the storage conditions of ‘Beishan’ apricot fruit at room temperature, with the increase of storage days, the fruit weight and firmness gradually decreased; the contents of titratable acid and vitamin C decreased gradually; and soluble solids and soluble sugars increased slightly on the 2nd day of storage and then gradually decreased. After the 6th day of storage, the fruit quality began to decline sharply, and the rot rate exceeded 60%. Therefore, the suitable storage time at room temperature was about 6 d.

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