Storage and Fresh-keeping Techniques for Peach, Plum and Apricot Fruits (Part Two)

III. Pre-storage Agricultural Measures for Peach, Plum and Apricot

1. Selection of Storage Varieties Early-maturing varieties are not tolerant of storage and transport, such as honey peach and Wuyuexian. Mid- and late-maturing varieties have better storage and transport tolerance, such as Feicheng peach, Qingzhou honey peach and Shaanxi winter peach, which are relatively tolerant of storage and transport; varieties such as Okubo, Gangshanbai and Yanhong also have good storage and transport tolerance. Clingstone varieties and soft-fleshed varieties have poor storage and transport tolerance. The storage and transport tolerance of plum and apricot is similar to that of peach; varieties such as Niuxin plum and Hebei rock sugar plum have good quality and are also tolerant of storage.

2. Pre-harvest Agricultural Technical Measures Pre-harvest agricultural technical measures have a great influence on the storability of peach, plum and apricot. Peach, plum and apricot are susceptible to microbial infection and decay during storage, which is one of the main factors making long-term storage of peach, plum and apricot difficult. There are three main diseases causing fruit decay, namely brown rot, soft rot and root rot. Among them, the fruit has already been infected by soft rot and root rot in the field; the pathogens invade the fruit through insect wounds, lenticels, etc., and multiply in large numbers when storage and transport conditions are suitable, and infect nearby fruits, causing massive decay. Therefore, strengthening pest and disease control during fruit growth can reduce the occurrence of decay during storage. The specific practice is: before germination, spray lime sulfur mixture at 5 degrees Baume; from half a month after petal fall to June, spray once every half month with 500 times 65% zineb wettable powder or 0.3 degree Baume lime sulfur mixture, either of which can prevent the occurrence of these two diseases. When fertilizing, pay attention to the reasonable combination of nitrogen, phosphorus and potassium; too much nitrogen fertilizer leads to poor fruit quality and also poor storage and transport tolerance. Orchards that apply more organic fertilizer produce fruit with good storage and transport tolerance. Irrigation should be stopped 7 days to 10 days before harvest, and ethephon must not be sprayed before harvest on fruit intended for storage and transport.

IV. Harvesting of Peach, Plum and Apricot

The harvesting of fruit is the first step in converting an agricultural product into a commodity, and it is also a relatively key step in whether fruit storage succeeds. Among these, harvest maturity is quite important; fruit intended for different purposes has different harvest maturity, short-term storage requires high maturity, and long-term storage requires low maturity. Different tree species have their own different harvest maturity requirements.

1. Points to Note When Harvesting Peach ① Peaches of different maturity have their different characteristics. Seven-ripe peach fruit has already developed fully, the ground color is green, but the fuzz is abundant and thick; eight-ripe peach has a lighter, whitish ground color, the fruit is plump, the fuzz is slightly sparse, the fruit is still somewhat hard but already has some elasticity; nine-ripe peach has milky white to light yellow skin, sparse fuzz, great elasticity, and a fragrant aroma; ten-ripe peach skin has fully displayed its characteristic skin color, and the fuzz is sparse and easily shed. The flesh of peach shows various characteristics depending on the variety; melt-fleshed varieties have soft, juicy flesh and skin that peels easily, and are not tolerant of storage. Hard-fleshed peaches can become mealy, while non-melting-fleshed peaches remain elastic. Peaches for fresh eating should be harvested at eight to nine maturity; peaches for storage can be picked somewhat earlier, generally at seven to eight maturity; ten-ripe peaches cannot be used for storage and must be @#@136@#@ nearby. ② Peaches should be harvested in the cool of early morning and evening. When picking, handle gently and place gently to prevent mechanical injury. Do not press the fruit surface with hands, do not roughly pull the fruit forcibly, and pick with the stalk attached. Generally, the capacity of each container (box, basket) should not exceed 5 kg; too much easily squeezes the fruit and causes mechanical injury.

2. Key Points for Harvesting Plum Chinese plum is the most common plum variety. Chinese plum has a thick, short stalk and generally forms an abscission layer at maturity, so it must be harvested with the stalk attached. Plum fruit has abundant bloom, and during harvest multiple handling should be avoided as much as possible to reduce the loss of bloom, which is beneficial for storage and fresh-keeping. Plums for storage must be harvested early at the right time, with seven to eight maturity being suitable. Harvesting should also be carried out in the cool of morning and evening when there is no dew, and the fruit must not be rained on after harvest, so as to avoid decay.

3. Harvesting of Apricot and Cherry The ripening period of apricot and cherry is relatively concentrated, and after full ripening they can hardly be stored and transported, so they must be harvested appropriately early according to different uses. Both apricot and cherry must be harvested with the stalk attached. To prevent the stalk from falling off during storage and transport, calcium can be sprayed before harvest, or calcium can be soaked after harvest. The commonly used calcium salt is calcium chloride, at a concentration of 1%-8%, with a soaking time of 5 minutes-60 minutes. The concentration and time must be well coordinated; a high concentration allows a shorter time, and a low concentration allows a longer soaking time. Spraying cherry with calcium chloride solution regularly before harvest can significantly reduce fruit decay, stalk drop rate and browning index during storage and transport. The packaging of apricot and cherry should be controlled within 2 kg-2.5 kg, and ventilation holes should be left on the packaging.

V. Post-harvest Handling of Peach, Plum, Apricot and Cherry.

1. Sorting Remove products infected by pests and diseases and products with mechanical injury. Because injured products are extremely susceptible to pathogen infection and decay, and at the same time infected products release large amounts of pathogens, infecting surrounding healthy products, so sorting is necessary.

Sorting generally uses manual methods. When the quantity is small, the method of transferring packaging can be used; when the quantity is large and the processing time is required to be short, a dedicated conveyor belt with manual sorting can be used. Operators must wear gloves, and during the sorting process handle gently to avoid causing new mechanical injury. Generally, the sorting process is often combined with grading, packaging and other processes to save manpower and reduce costs.

2. Pre-cooling The purpose of pre-cooling is to rapidly lower the product temperature, reduce respiration intensity, and reduce consumption, while enabling the fruit product temperature to reach the optimal storage and transport temperature as quickly as possible, so as to facilitate the early use of plastic film packaging for controlled atmosphere storage without condensation. If the fruit product temperature is high and the storage temperature is low, with a difference of more than 3°C, condensation is likely to form. Condensation easily causes fruit decay. Several pre-cooling methods are introduced below: ① Air cooling method. A cold fan with a mechanical refrigeration system circulates cold air, cooling the fruit by means of heat conduction and latent heat of evaporation. During air cooling, the larger the contact area between the fruit and the cold air, the faster the cooling rate; the greater the wind speed, the faster the temperature drop. ② Ice cooling method. Bringing ice into direct contact with the fruit can cool the fruit. For each kilogram of ice melted, 80 kilocalories of heat can be taken from inside the fruit, and the thermal conductivity of ice is greater than that of water and air, while using crushed ice can increase the contact area and raise the cooling rate. ③ Water cooling method. Also called ice water cooling method, this is because when cooling fruit with water, crushed ice is often added or a ice machine is used to cool the water. The simple water cooling method is to immerse the fruit in cold water; if the cold water is still, its cooling efficiency is low, so flowing water is generally used, and the method of floating, spraying or a combination of immersion and spraying gives better results. ④ Vacuum pre-cooling method. Vacuum pre-cooling is to place the fruit in a vacuum pre-cooling chamber and draw a vacuum; under reduced pressure, the moisture on the fruit surface evaporates rapidly, absorbing a large amount of heat and thereby cooling the fruit.

For the pre-cooling of peach, plum, apricot and cherry, the air cooling method and water cooling method are generally preferred. For water cooling, 0°C water can be used, and a certain concentration of fungicide can be added to the water; after the fruit is cooled to 0°C, drain off the water. The vacuum pre-cooling method is not suitable for pre-cooling peach.

The suitable pre-cooling temperature for peach, plum, apricot and cherry for storage is 0°C, and it should not be too low, so as to avoid chilling injury.

4. Anti-corrosion and Fresh-keeping Treatment Peach, plum and apricot are prone to decay during storage, and low-temperature and controlled atmosphere storage can inhibit the occurrence of diseases. Low temperature and controlled atmosphere plus anti-corrosion and fresh-keeping agents give even better storage results.