1. Food deteroration-zxm课件.ppt

Food Deterioration (or/and spoilage);Main Idea;1.相关概念;1.Food deterioration includes:;1.The three general categories of food deterioration are:;SHELF LIFE AND DATING OF FOODS ;SHELF LIFE AND DATING OF FOODS ;Table 1. Useful Shelf Life at 70 F (21℃);Table 1. Useful Shelf Life at 70 F (21℃);Main Idea;The basic conditions for food spoilage 食品腐败变质的基本条件;WHAT CAUSES FOOD DETERIORATION?食品腐败变质的原因： ;（1） Food properties;（1） Food properties ---basic conditions;食品的水分活性（ Water activity Aw or aw） ;Water activity;榆供瞄按穴耻钓此邯级亥浸纫障靠恰绕恨恕据歌斟遣朴污骂撤蓬几满蜒醒1. Food deteroration-zxm课件1. Food deteroration-zxm课件; The AW of different NaCl solution NaCl% AW 0.9 0.995 1.7 0.990 3.5 0.98 7.0 0.96 10.0 0.94 16.0 0.90 30.0 0.86; The AW of different sucrose solution sucrose % AW 8.51 0.995 15.4 0.990 26.1 0.980 48.2 0.940 58.4 0.900 59.2 0.580;AW 为0.7 以下时一般霉菌不生长。 AW 为0.6以下 易保藏 ;(b) Food properties;(2) Storage conditions;Thousands of species of microorganisms exist, and a few hundred are associated with foods. Not all are bad; in fact, some are desirable in food preservation. Microorganisms are found in the soil, water and air; on animal skins, plant surfaces and digestive tracts; but they are usually not present in healthy tissue. In foods, these microorganisms attack basically all the food components -- including sugars, starches, cellulose, fats and proteins. Depending on the food and the microorganism, the action on food could be to produce acids, making the food sour, or to produce alcohol. Some microorganisms produce gas, making the food foamy, while others produce unwanted pigments or toxins. ;Microbial spoilage - yeast;Microbial spoilage – mo(u)ld; There are two type of bacteria that cause major problems in the food industry: Spoilage bacteria - responsible for the decomposition of food. Pathogenic (病原性的) bacteria 【Foodborne (食物传染)disease】 –responsible for causing illness such as dysentery （痢疾）, typhoid