Water solubility :
benzoic acid: slightly soluble in water (0.34g/ 100ml at 25℃). sodium benzoate: highly soluble in water(50g/100ml at 25 ℃).
Antimicrobial activity :
parabens (ethyl and propyl ~)对羟基苯甲酸酯（
乙酯，丙酯）
dehydroacetic acid and sodium dehydroacetate, sodium diacetate, 脱氢醋酸（
盐）
carbon dioxide CO2 nisin (尼生素，乳酸链球菌素) hydrogen peroxide H2O2 natamycin (纳它霉素） capryl monoglyceride(单辛酸甘油酯 )
Attention:
spices such as sugar, vinegar, and salt, which also have anti-microbial effect, are not included .调味品如糖、醋
、盐有抗菌效果，没有包括
Disinfectants used for sterilizing food containers are not included either. 用于容器的消毒剂也不包含在内
(2) Chemical Methods：preservatives
1. Definition()
Food preservatives may be defined as substances which can kill microorganisms or prevent the growth of microorganisms. 抑制或杀死微生物的物质 Or in simple words, preservatives are substances used in foods which have antimicrobial effects. 抗菌效果
Food preservatives:
benzoic acid and sodium benzoate 苯甲酸（盐）
sorbic acid and potassium sorbate 山梨酸
propionic acid , sodium and calcium propionate 丙酸
2.5.2 Sorbic acid and its potassium salt**山梨酸
2.5.3Sodium and calcium propionate**丙酸 2.5.4Parabens/p-hydroxybenzoates ** (sum)
对羟基苯甲酸酯
2.5.5other preservatives
(2) According to their application range, they can be classified into--- food perservatives: most 防腐
fresh-keeping preservatives for fruits and vegetables 保鲜
Chapter 2 Preservatives
Contents:
2.1 Definition of preservatives**
2.2 Mechanisms of preservatives**机理 2.3 Varieties of preservatives**种类 2.4 Classification of preservatives **分类 2.5 Introduction to the preservatives used often in food 2.5.1Benzoic acid and its sodium salt**苯甲酸
(2) Mechanisms of food preservatives()
Destroy the structure or change
the permeability of microbial cell membrane 破坏或改变微生物细胞膜的通透性
Interfere with microbial enzyme
2) Inhibit sulfhydryl enzymes. 抑制巯基酶
2.3 Varieties of preservatives
(1) Varieties: about 50 in USA, 40 in Japan, and 32 in China. (2) Preservatives in China:()
Examples of foods which easily undergo spoilage as the result of microbial action
meat products
cheese
bread
spices
Fruit juice
aquatic products
Methods for preserving foods (1) Physical methods: Traditional physical methods： * Drying in the sun * low-temperature storage (freezing/frozen storage)冷冻冷藏 * pickling/salting, sugaring 腌制 * soaking with wine 腌制、浸酒
2. 5. Introduction to the preservatives commonly used in foods ()
2.5.1 Benzoic acid and sodium benzoate.
苯甲酸和苯甲酸钠
source: synthetic preservatives. structures: page 41 General properties: water solubility
sucrose esters （蔗糖酯）: used as emulsifiers . 乳化剂 glucono--lactone:used as a coagulator凝固剂
2.4.Classification of preservatives
(1) According to their components , they can be classified into--- chemical preservatives:化学 * organic preservatives: most 有机防腐剂
The following substances also
have antiomicrobial effects: nitrites: used as color fixatives 发色剂
short-chain organic acids:used as acids 短
链有机酸
sulfites:used as bleaching agents漂白
Effective against most molds, yeasts and bacteria.
The undissociated form of benzoic acid is the most effective antimicrobial agent.没离解的苯甲酸抗菌效果最好
pH values of foods affect their antimicrobial effects. They are only effective in acidic conditions with the optimal pH of 2.5-4.0 . pH影响抗菌效果，它
2.2 Mechanisms of preservatives (1) Food spoilage caused by microorganisms (three types) 食品腐败三种形式
Food spoilage caused by the action of bacteria. 细菌的作用 Food spoilage caused by the
*
Nisin ** 乳酸链球菌素
* fresh-keeping preservatives for fruits and vegetables **
2. 6 Attention to the application of food preservatives **
2. 7 Development tendency of food preservatives ** (Questions for discussion)
systems 干扰微生物酶系统
Other effects: cause the
denaturation of microbial proteins
微生物蛋白失活
Example: mechanisms of sorbic acid
Interfere with microbial enzymes: 1) Inhibit dehydrogenases involved in fatty acid oxidation. 抑制脂肪氧化脱氢酶
Eg: benzoic acid and sodium benzoate, sorbic acid and
potassium sorbate. 苯甲酸，山梨酸（盐）
* inorganic preservatives: nitrite, sulfite无机
biological preservatives: nisin, natamycin. 生物防腐，乳酸链球菌素，纳塔霉素
Fresh-keeping preservatives for fruits and vegetables : sec- butylamine（仲丁胺）