Storage characteristics and fresh-keeping Technology of Pear

Pear is one of the three major fruits in China, and its output ranks first among the three major fruits. The amount of deep processing is limited and the decay rate is high. In order to prolong the market supply, combined with its variety characteristics to do a good job of storage and preservation, reduce urban biological waste, and provide a guarantee for the income of the pear industry.

I. Biological characteristics

A pear consists of fruit, core and seed. The growth process of pear fruit is an S-shaped growth curve, which is mainly cell division and embryo growth in the early stage, the volume increases slowly, and the fruit grows rapidly in the later stage. The growth of 40-50 days before harvest is about 10 times of the previous growth.

Pear fruit can be divided into two types: hard meat type and soft meat type according to the soft and hard meat after ripening. Hard meat varieties such as Yali pear, ci pear, Xuehua pear, Dangshan pear, Korla fragrant pear and so on, this kind of fruit has no obvious respiratory transition period from ripening to senescence, and always keeps the fruit crisp, tender and juicy, and is more resistant to storage. Soft-meat fruits, such as Ba pear, Jiuwu pear, Jingbai pear, Zimu pear, Hongxiao pear, etc., when harvested, the pulp is thick and hard, the taste is light or sour, but the fruit softens after ripening, and this kind of fruit has an obvious respiratory transition period. After pre-cooling, it should be stored at about 0 ℃ immediately.

Second, storage characteristics

1. Tolerance to low temperature storage: experiments show that low temperature cold storage is an effective measure for pear preservation, which can reduce respiratory intensity, reduce the loss of sugar and vitamin C, and delay ripening. At the same time, low temperature slowed down the harm of bacteria and provided basic conditions for maintaining the crisp quality of pear fruit. The storage temperature required by different varieties of pears is different. The temperature of long-term storage is about-1 ~ 2 ℃. Most pears should not be less than-1 ℃, otherwise chilling injury will occur. For example, the apple pear lost its edible value when stored at 20 ℃ for 4 months. If it was stored at about 0 ℃, the storage period was as long as 9 months and the quality was good.

2. Tolerance to high humidity storage: the water content of pears is generally about 90%. Due to the underdeveloped epidermis, pears lose water and wilt quickly in the natural state after harvest. High relative humidity is a necessary condition for pear preservation. The speed of water loss of each variety of pear is also related to the number of stomata and tension of its own fruit, the thickness of wax layer and the amount of pectin. In general, the relative humidity of the storage should be kept at 90%-95%, and the cold storage should be kept at 85-95%.

3. Gas composition: pears are sensitive to carbon dioxide, high concentration of carbon dioxide will cause physiological metabolic disorders of pears and physiological diseases, resulting in pulp browning. For example, when the concentration of carbon dioxide is more than 2.81%, the apple pear is prone to carbon dioxide poisoning (that is, the skin and flesh are brown and smooth); when the oxygen content is insufficient (less than 13.5%), it is easy to get honey disease, so during controlled atmosphere storage, be sure to control the concentration of carbon dioxide and oxygen in the bag or in the room. Most of them are suitable for storage gas when the oxygen content is 1215% and the carbon dioxide content is less than 1%. There are individual pears, the situation is more special, such as Yali pear in 5% to 7% oxygen and carbon dioxide environment, can effectively inhibit and reduce the incidence of black heart disease, the storage effect is better.

Third, storage and fresh-keeping technology

The main results are as follows: 1. The suitable harvest time for timely and harmless harvest can be determined according to the characteristics of varieties and the length of storage period. Harvested too early, the fruit is not yet ripe, the sugar and acid content is low, and there are few ingredients for respiratory consumption, so it is not resistant to storage; if harvested too late, the pulp cells have become senescent, the senescence process of the fruit is accelerated, and it is not resistant to storage. Only by accurately judging the harvest time of pear fruit can it be stored for a long time. For the varieties of white pear and sand pear system, it is better to harvest when the fruit surface shows inherent color, the pulp changes from hard to brittle, the seed color changes to brown, and the fruit stalk is easy to fall off from the fruit platform; for the varieties of western pear and Qiuzi pear system, they have obvious post-ripening changes and can be picked early, that is, when the fruit size has been basically shaped, the fruit surface green gradually fades, the seed has not yet browned, and the fruit stalk is easy to fall off from the fruit platform.

It is required to avoid scraping, bumping, pressing, stabbing, smashing and other injuries in picking, loading, unloading and transportation, reduce the number of baskets (boxes) and replacement, and handle them gently. Some pears are required to be harvested with a stalk. Harvest time is best in cool weather or every morning.

2. The pears harvested by grading, bagging and packaging should carry out primary selection, grading, removal of cracked fruit, diseased and rotten fruit, deformed fruit, prickly fruit and overripe fruit, so as to achieve homogeneity, same price and commodity standardization.

Pear fruit generally does not use film single fruit packaging or carton lined film packaging, because this will make the volume of carbon dioxide gas is too high and easy to cause pulp, core browning. Generally using 0.01~0.02mm thick polyethylene bag single fruit packaging, not only can play an obvious fresh-keeping effect, but also will not cause carbon dioxide damage to pear fruit, its natural loss rate and decay rate are low. It is a simple, economical and practical treatment measure. The pear fruit after single fruit packaging is put into the cardboard box, evenly placed in two layers, separated by thin cardboard in the middle, or cardboard grid is placed in the cardboard box, one grid for each fruit, two layers above and below, the middle separation effect is better. And punch holes in the side of the carton to achieve the effect of ventilation and fresh-keeping.

3. The pre-cooled pear fruit still has the function of exuberant respiration, evaporation, decomposition and consumption after harvesting. At the same time, the pear fruit also releases a large amount of field heat after harvest, which will rapidly increase the ambient temperature around the picked pear fruit and accelerate ripening and senescence. Freshness and quality decreased significantly. Therefore, the pear fruit must be cooled to 3-4 ℃ in a short time after harvest. The harvested pears are transported to the pre-cooling room where the temperature has been thoroughly sterilized and the storage temperature has dropped to the required temperature as soon as possible, and placed according to batches and grades. The pre-cooling temperature is set at 0: 3 ℃, and the pre-cooling can be achieved after 1-2 days. However, for individual pears, the precooling temperature should not be too fast. For example, Yali pear is sensitive to temperature. After harvest, it should be precooled at 10: 12 ℃ and slowly cooled to 0: 3 ℃ for storage. If stored at 0 ℃ immediately after harvest, physiological damage will occur, resulting in core and pulp browning.

4. Storage management

4.1 stable low temperature management can effectively inhibit the respiratory intensity of pear fruit and minimize metabolism, thus delaying senescence. At the same time, low temperature slowed down the harm of bacteria and provided basic conditions for maintaining the crisp quality of pear fruit. In order to better grasp the temperature of each part of the library, thermometers should be placed in different representative places. During storage, try to keep the storage temperature stable and reduce the great change of temperature. The temperature of cold storage should be kept at 0 ±1 ℃. In general, the fluctuation range of temperature in cold storage is less than 2 ℃, and the range of fruit temperature is less than 0.5 ℃.

4.2 humidity management pear fruit has more water content, which determines its relative humidity during storage. Stable and suitable humidity can keep pear fruit crisp and tender for a long time. In order to maintain or increase the humidity in the warehouse, it can be solved by sprinkling water on the ground, laying wet sawdust or wet gunny bags. If the humidity is too high, put dry sawdust, quicklime or window ventilation in the library to solve the problem, and place hygrometers in different locations in the library in order to accurately grasp the changes of humidity and do a good job in humidity regulation and control.

4.3 Gas composition management when using controlled atmosphere storage, we must pay attention to the concentration of oxygen and carbon dioxide, especially the concentration of carbon dioxide is less than 2%, and the concentration of oxygen is 12-15%. In non-controlled atmosphere storage, polyethylene film with 0.01~0.02mm thickness was used for airtight packaging of single fruit, or regular ventilation was used to adjust the gas composition and concentration in the storage to prevent the occurrence of carbon dioxide poisoning of pear fruit.

4.4 proper ventilation, whether it is cold storage or natural ventilation storage, adequate ventilation is necessary, it can take away the heat load in the storage, eliminate ethylene, ethanol and carbon dioxide gas produced in the process of fruit physiological metabolism, and supplement appropriate oxygen. And it can prevent the uneven temperature and adjust the humidity in the library. However, during ventilation, we should pay attention to the level of the external air temperature to determine the ventilation time, and weaken the wind speed to prevent the substantial change of the temperature range in the reservoir.

4.5 normal inspection normal inspection of pear fruit color, aroma, taste, shape changes, whether there is no peculiar smell, deterioration, decay, disease, rodent damage and so on. Do a good job in cleaning the warehouse, recording the temperature and humidity, and opening the door and window for ventilation.