How to Store and Preserve Peaches, Plums and Apricots for Freshness? A Detailed Guide to Practical Techniques

Peach, plum and apricot (including cherry) fruits all contain a hard stone and belong to the stone fruit category, sharing common characteristics in fruit development and postharvest physiology. It is precisely because the fruit contains a hard stone that a double-S growth curve appears during growth. Peach, plum and apricot fruits have high respiration intensity; all exhibit a respiration peak, so they all belong to the climacteric type of fruit, which determines that they share basically similar storage, transport and freshness-preservation technical measures. However, as tree species and cultivars differ, the storage, transport and freshness-preservation techniques adopted also differ. Peaches, plums

They are generally divided into early-, mid- and late-maturing cultivars, and the difference between early- and late-maturing cultivars is very large. The early-maturing Chunlei peach ripens in early May in Shandong, while the late-maturing winter peach does not ripen until November. Early-maturing plums ripen in early June in Shandong, while Black Gem ripens at the end of October. However, the ripening periods of other fine peach and plum cultivars are relatively concentrated between July and August. The difference between early- and late-maturing apricots and cherries is relatively small, and their ripening periods are relatively concentrated, so the phenomenon of "rot in peak season, shortage in off season" inevitably occurs, which requires

raising the storage, transport and freshness-preservation technical level of various cultivars, extending the market supply period, and increasing fruit growers' income.

1. Postharvest Physiology and Storage Characteristics of Peach, Plum and Apricot

After peach fruit harvest, the activities of pectinase, cellulase and amylase in the fruit tissue are very strong, which is the main reason why peaches soften and spoil very easily at room temperature after harvest. Especially for honey peaches, respiration intensity rises rapidly after harvest, 1 to 2 times higher than that of apples, and they soften within 1 to 2 days under room temperature conditions. Low temperature, low oxygen or high carbon dioxide can inhibit the activity of these enzymes, so harvested fruit should be cooled immediately and promptly enter a controlled atmosphere state to maintain its firmness and quality.

Peaches are more sensitive to temperature than any other fruit. After harvest, peach respiration intensity is strongly inhibited under low temperature conditions, but chilling injury readily occurs. The freezing point of peaches is -1.5°C, and long-term storage below 0°C readily causes chilling injury. The timing and degree of chilling injury are related to temperature. Research shows that peaches sometimes suffer chilling injury at 7%, with 3°C to 4°C being the peak of chilling injury occurrence, while near 0°C it is instead minor. In peach fruits that suffer chilling injury, the cells all thicken, the fruit becomes corky, the flavor becomes bland, the flesh hardens, the flesh or vascular bundles turn brown, and the peach stone cracks; some cultivars become bitter or develop off-flavors after chilling injury, but the chilling injury symptoms differ among cultivars.

Peach fruit is very sensitive to carbon dioxide, and carbon dioxide injury occurs when the carbon dioxide concentration is higher than 5%. The symptoms of carbon dioxide injury are brown spots and decay on the peel, browning of the flesh and vascular bundles, little juice in the fruit, hard flesh and abnormal flavor, so suitable gas indicators should be maintained during storage.

The surface of peach fruit is covered with fuzz. Most of the fuzz connects with the stomata or lenticels of the epidermis, which increases the transpiration surface of peaches by more than ten times or even a hundred times, so peaches lose water very rapidly after harvest under exposed conditions. Generally, under conditions of 70% relative humidity and 20°C, when left exposed for 7 to 10 days, the fruit's water loss exceeds 50%. After water loss, the fruit shrivels and softens, and in severe cases loses its commercial value.

The postharvest physiological characteristics of stone fruits such as plums and apricots are similar to those of peaches.

2. Storage Conditions for Peach, Plum and Apricot

1. Storage temperature {The suitable storage temperature for peach, plum and apricot is 0°C to 1°C, but long-term storage at 0°C readily causes chilling injury. At present there are several methods for controlling chilling injury. One method is the intermittent warming method, that is, peaches are first stored at -0.5°C to 0°C for 15 days, then warmed to 18°C for 2 days, then transferred to low-temperature storage, and this is repeated. Another method is to treat harvested fruit with two temperatures, first storing at 0°C for 2 weeks, then storing at 5°C (in the United States, to prevent chilling injury in peaches, the gas concentrations are controlled at 0°C with O2 at 1% and CO2 at 5%. During controlled atmosphere storage, every 3 weeks or 6 weeks the controlled atmosphere peaches are warmed once, then returned to 0°C; after 9 weeks of storage at 0°C they are taken out of storage, placed at 18°C to 20°C to ripen, and then sold. This method extends storage life by 2 to 3 times compared with ordinary refrigeration). Intermittent warming can reduce peach respiration intensity, lower ethylene release and alleviate chilling injury; at the same time, the temperature increase also favors the volatilization and metabolism of other harmful gases.

2. Storage environment humidity {When storing peach, plum, apricot and cherry, the relative humidity should be controlled within the range of 90% to 95%. If humidity is too high, it readily causes rot and aggravates the symptoms of chilling injury; if humidity is too low, it causes excessive water loss and weight loss, affecting marketability and thus causing undue economic losses.

3. Gas composition {Under controlled atmosphere conditions with an O2 concentration of 1% and a CO2 concentration of 5%, the storage period of peaches can be doubled (under the same temperature, humidity and other conditions). For plums, an O2 concentration of 3% to 5% and a CO2 concentration of 5% are the suitable controlled atmosphere state. However, it is generally believed that plums are extremely sensitive to CO2, and long-term high CO2 increases the rate of fruit apex cracking. The most suitable gas composition for controlled atmosphere storage of apricots is an O2 concentration of 2% to 3% and a CO2 concentration of 2% to 3%. The suitable controlled atmosphere gas composition for cherries is an O2 concentration of 3% to 5% and a CO2 concentration of 10% to 25%. Cherries tolerate high CO2 concentrations, so high CO2 treatment is also used during transport to inhibit their respiration intensity and maintain freshness.

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