甚麼是防腐劑呢？其原理是甚麼呢？

防腐劑就是可以減慢微生物生長(eg. 霉菌)或化學變化(eg. 蘋果切開後變啡)引起的腐壞。

減慢微生物生長的原理: 改變生長環境，令微生物生長減慢，甚至死亡(eg.改變pH)，或利用對微生物有害的物質(eg. SO2)直接使微生物死亡

減慢化學變化的原理: 通常是減慢食物中的酶與空氣產生化學反應的速度(eg. 醋能減少蘋果的酶與空氣反應)

天然防腐劑: 就是非人造的防腐劑(eg. 醋、鹽、糖)

The green persevatives are salt , sugar & vinegar . Take vinegar for example , it is the high content of acetic acid inhibit the growth of bacteria so when any germs try to colony on the food , the acetic acid just stop the multipication of the bacteria . In this way the food can be kept for a long time . As for sugar or salt , they are hygroscopic that they can absorb water even from the cells of plants & animals . For a dry peice of meat , it can kept for a long time just like a salted fish or egg . Water is required for breeding living things !