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Some temperature concepts related to fruit refrigeration

Fruits freezing point

Fruit freezing point is the temperature at which the water in the fruit begins to form ice crystals (freezing). Because the fruit contains sugar, organic acids and other substances dissolved in water, the freezing point of pears and other fruits are below 0 ℃ (Figure 2). Pear fruit freezing point mainly depends on its soluble solids content, generally in -1.5 ℃ or so, the higher the soluble solids content of the fruit, the lower its freezing point temperature. Such as duck pear soluble solids content of 9.2% to 12.4%, fruit freezing point -1.8 ~ -1.1 ℃, yellow crown pear soluble solids content of 8.2% to 12.1%, freezing point -1.6 ~ -0.9 ℃.

Lethal temperature

The freezing temperature that leads to the physiological freezing of the tissue of the cold storage products (such as pears, apples, etc., Figure 3) and accompanied by tissue death, for pear fruit, that is, the freezing point and the temperature below the freezing point. But some varieties of fruit slightly frozen, slow return to temperature can still return to normal.
 Note: touch crush injury, stalk prick injury, insect rot and low soluble solids content of the part first freeze, kulle balsam pear fruit freezing point is generally lower than -1.8 ℃.

Critical temperature

Generally refers to the temperature that can cause the fruit (such as banana, avocado, etc.) peel or internal browning, tissue texture changes and other physiological disorders during the specified storage period.

Optimal temperature for long-term storage

The temperature at which the cold storage product is maintained in good quality under normal or controlled air conditions until the cold storage product is sold. In long-term storage, the temperature of the product must be higher than the lethal temperature and, if necessary, higher than the critical temperature. Therefore, the optimal temperature for long-term storage of fruit is: lethal temperature plus a safety factor, or critical temperature plus a safety factor.

Depot fixed temperature

The air temperature measured at a defined location within the cold storage.

Actual average temperature

The average of the maximum and minimum temperatures in a cold storage room during the period when the temperature is stable. In the case of long-term storage, the actual temperature of the cold storage products is related to the temperature of the surrounding air, the characteristics of the cold storage products, the packaging, the loading of the cold storage and the flow of the cold storage atmosphere circulation.

Fruit temperature

Internal temperature of the fruit. The fruit temperature changes very little during the storage temperature stabilization period, and even less if film bags are used for packing.

Cold storage cold spot

The location point of the lowest air temperature in the cold storage. The cold point in air-cooled cold storage is usually in the area near the evaporator.

Cold Storage Hotspots

The location point of the highest air temperature in the cold storage. The hot spot in air-cooled cold storage is usually at the farthest point from the evaporator or air supply duct, where the cold air cannot blow at the dead end.