Detailed Explanation of Key Techniques for the Storage and Fresh-Keeping of Huangjin Pear

1. Key points of storage technology

1.1 Timely harvesting In North China, the suitable harvesting period for Huangjin pear is from September 20 to 30. At this time the fruit has developed to maturity, nutrients have accumulated sufficiently, and storability is at its best. Pears harvested early (September 10) have a higher rot rate throughout the storage period, and the peel is highly prone to browning. If harvested too late (early October), brown scald disease occurs more seriously during storage (at 18.94%). During harvesting, special care must be taken to avoid bruising.

1.2 Grading The purpose of fruit grading is to achieve commercial standardization. China's pear grading standards fall into 4 types: national standards, industry standards, local standards and enterprise standards. At present, Huangjin pear grading is mainly done by manual selection based on weight, and large fruit-sorting machines and other equipment have not yet been used for grading.

1.3 Packaging Packaging can be divided into outer packaging and inner packaging. In production, outer packaging uses cardboard boxes, 15-20 kg per box; the boxes must be scientific, sturdy, economical, moisture-proof, attractive and lightweight. Inner packaging means wrapping the fruit with packaging materials (such as fresh-keeping paper, fresh-keeping bags, etc.). Tests have shown that using 0.013 mm thick polyethylene film bags for sealed single-fruit packaging results in lower natural weight loss rate and rot rate, giving a good fresh-keeping effect. Although thicker film bags can reduce the natural weight loss rate, they easily trigger physiological diseases such as black heart disease. Therefore it is recommended that after harvest, Huangjin pear fruit be directly sealed individually in commercially available 0.013 mm thick plastic film bags, and then packed into boxes.

1.4 Precooling At harvest time for Huangjin pear, both the air temperature and the storage temperature are relatively high. If a naturally cooled storage facility (cellar) is used, Huangjin pear must not be put in directly; it must be fully precooled to quickly dissipate field heat. Therefore, low temperatures should be used for precooling as much as possible, and care should be taken to prevent sun exposure and rain. Research results show that Huangjin pear fruit can adapt to rapid precooling after harvest. Therefore, the fruit can be placed directly into a low-temperature cold storage for precooling after harvest.

1.5 Storage period management

1.5.1 Disinfection in the storage and rodent control Disinfection plays a positive role in reducing microbial infection and fruit rot during Huangjin pear storage, and is also an important part of management measures. One month before the Huangjin pears are put into storage (and after storage ends), the storage facility should be cleaned and disinfected. Commonly used agents are sulfur, formaldehyde, bleaching powder and sodium hypochlorite, etc. In addition, attention should be paid to rodent control: seal holes well, and after the fruit is placed in storage, methods such as mouse traps and poisoned bait can be used for control.

1.5.2 Stacking After the Huangjin pear fruit arrives at the cold storage, the stacks in the storage should be arranged neatly and firmly, which facilitates ventilation and management and makes full use of space. The bottom of the stack should be raised with sleepers, and appropriate gaps should be left between fruit boxes (generally 2-5 cm). The stacking height depends on the compressive strength of the boxes, but generally a gap of about 60 cm should be left between the top of the stack and the storage ceiling. Gaps should also be left between the stack and the walls, air inlets, etc. (generally about 30 cm), and walkways should be left. Stacking can use forms such as the "pin-shaped" and "well-shaped" patterns.

1.5.3 Temperature To better grasp the temperature conditions in each part of the storage, thermometers should be placed in different representative locations. During storage, the storage temperature should be kept as stable as possible to reduce large temperature fluctuations. The suitable storage temperature for Huangjin pear is 0-2°C.

1.5.4 Humidity During storage of Huangjin pear, the relative humidity should be maintained at 85%-90%. When the humidity in the storage is too high, dry sawdust or quicklime can be placed; when the humidity is too low, appropriate watering, laying wet sawdust or wet straw curtains, etc. can be done.

1.5.5 Gas composition When controlled atmosphere storage is used, attention must be paid to controlling the concentrations of carbon dioxide and oxygen. Using 0.01-0.02 mm thick polyethylene film bags for sealed single-fruit packaging will not cause black skin or carbon dioxide poisoning, and has a very ideal storage effect.

1.5.6 Appropriate ventilation During the storage of Huangjin pear, there must be sufficient ventilation. Ventilation can remove the heat load in the storage, expel harmful gases such as ethylene, ethanol and carbon dioxide produced during the fruit's physiological metabolism, replenish appropriate oxygen, and prevent uneven temperature in the storage. To prevent large fluctuations in storage temperature, ventilation should be carried out when the temperature difference inside and outside the storage is smallest.

2. Main storage diseases and their control

2.1 High carbon dioxide injury and low carbon dioxide injury Huangjin pear fruit has a high water content after harvest, vigorous physiological activity, and is sensitive to carbon dioxide. When pear fruit is stored for a relatively long time in environments with higher carbon dioxide and low carbon dioxide, high carbon dioxide injury and low carbon dioxide injury will occur. The sensitivity of Huangjin pear fruit to carbon dioxide injury is closely related to its fruit maturity, and unsuitable low temperatures can also aggravate the incidence of carbon dioxide injury.

The method for controlling high carbon dioxide injury and low oxygen injury is to strictly control the gas concentration in the storage environment, maintaining the carbon dioxide concentration below 3%, and carbon dioxide between 5% and 8%.

2.2 Chilling injury and freezing injury Experimental studies show that the freezing point of Huangjin pear is -2.9 to -3.1°C, and during storage it can tolerate a low temperature of 0°C. If the temperature is lower still, or below -5°C during transport, the water inside the fruit will gradually freeze. Rapid cooling at the time of storage easily causes black heart in the fruit, which is also a type of chilling injury.

2.3 Peel browning The peel of Huangjin pear is thin and crisp; its phenolic substance content and polyphenol oxidase (PPO) activity are both higher than in other parts. During the storage and transport of Huangjin pear, browning at the lenticels gradually deepens and expands. Peel dehydration and membrane lipid peroxidation leading to increased tissue membrane permeability and destruction of compartmentalized distribution are the main causes of peel browning in Huangjin pear.

To control peel browning in Huangjin pear, the following points should be noted: ① Harvest appropriately late to increase fruit maturity; ② Store at low temperature to reduce peel moisture loss; ③ Spray calcium before harvest or dip in calcium after harvest; ④ Bag the fruit in the field before harvest, and store after harvest with single-fruit film bag packaging; ⑤ Avoid friction damage from branches and leaves, bag friction damage, and mechanical injury.