果蔬类食品预冷的意义
所谓预冷是指食品从初始温度（30℃左右）迅速降至所需要的终点温度（0℃-
-4℃）的过程。水果蔬菜采摘后由于受田间热的影响其温度比较高，加之自身的呼吸作用，在成分不断发生变化的同时，释放的热量也不断地增加，温度持续升高。而较高的温度又促使其呼吸加快，继续释放热量，水分大量蒸发，迅速萎蔫，鲜度降低，直至腐烂变质。
预冷是迅速排除田间热，抑制其呼吸作用，保持水果蔬菜的鲜度，延长货架期的有效措施。
果蔬类食品的预冷方法：
空气预冷：强制通风预冷、压差预冷。
水预冷：浸入式预冷、喷淋式预冷、喷雾式预冷。
真空预冷：真空预冷、真空喷雾预冷。
真空预冷是根据水随大气压力降低，其沸点也降低的性质，将采摘后的新鲜果蔬置于真空槽内，当压力降低至2276
Pa（17 mmhg ）时，到达闪点，水分开始蒸发，其蒸发潜热为600Kcal/kg
。压力持续下降，温度降低至4℃-0℃
预冷结束。
Vavuum
cooling is based on the principle of water evaporating
temperature against the pressure when the pressure lower to
2267Pa (17mm Hg). water begin to evaporate at it's flash
point. When the pressure lower to 800Pa (6mm Hg). water
evaporate at 4℃,
the evaporation latent heat is 600Kcal/kg. Keep lowering the
pressure, until the temperature comes to 4℃-0℃.
The meaning of fruits & vegetable
cooling.
The cooling is a processing of lowering
maerial's temperature from environment (above 30℃) to the
end (0℃-4℃). Normally, the fresh fruits &vegetable's
temperature will increase, because of its sensible heat and
breathing. The high temperature will fasten it's breathing and
releasing more heat. then the water of the fruits and
vegetable will be over-evaporated and withere, until they are
rotten.
Cooling is a processing of removing the
senaible heat, prohibiting it's breathing, then to keep the
fruit's and vegetable's fresh degree and prling it's shelr
time.
The methods of cooling for fruits and
vegetable.
Air cooling: forced draft cooling, pressure
difference cooling.
Water Cooling : water cooling, showering
cooling, spray cooling.
Vacuum cooling: Vacuum cooling, vacuum
sprey cooling.
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