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1、Chapter 2 PreservativesContents: 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 food2.5.1Benzoic acid and its sodium salt*苯甲酸2.5.2 Sorbic acid and its potass
2、ium 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* 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 discuss
3、ion)2.5.5other preservativesExamples of foods which easily undergo spoilage as the result of microbial action meat productscheesebreadspicesFruit juiceaquatic productsMethods for preserving foods (1) Physical methods:* Drying in the sun* low-temperature storage (freezing/frozen storage)冷冻冷藏* picklin
4、g/salting, sugaring 腌制* soaking with wine 腌制、浸酒* fermentation 发酵Traditional physical methods： New Physical Methods: * Canning packaging 罐藏* vacuum/gas packaging 真空、气体* high hydrostatic pressure (sterilization) 高压* irradiation sterilization 辐照* electron sterilization 电子辐照(2) Chemical Methods：preserva
5、tives 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Attention: spices such as sugar, vinegar, and s
6、alt, 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2.2 Mechanisms of preservatives(1) Food spoilage caused by micro- organisms (three types) 食品腐败三种形式 Food spoilage caused by the
7、action of bacteria. 细菌的作用 Food spoilage caused by the action of molds 霉菌的作用* alcohol fermentation, 酒精* acetic acid fermentation,醋酸* lactic acid fermentation,乳酸* butylic acid fermentation.丁酸 Food fermentation: 发酵(2) Mechanisms of food preservatives() Destroy the structure or change the permeability o
8、f microbial cell membrane 破坏或改变微生物细胞膜的通透性 Interfere with microbial enzyme 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 acid1) Inhibit dehydrogenases involved in fatty acid oxidation. 抑制脂肪氧化脱氢酶 Interfere with microbial Interfere wit
9、h microbial enzymes:enzymes:2) Inhibit sulfhydryl enzymes. 抑制巯基酶2.3 Varieties of preservatives(1) Varieties(1) Varieties: : about 50 in USA, 40 in about 50 in USA, 40 in Japan, and 32 in China.Japan, and 32 in China.(2) Preservatives in China:() Food preservatives: benzoic acid and sodium benzoate 苯
10、甲酸（盐盐） sorbic acid and potassium sorbate 山梨酸 propionic acid , sodium and calcium propionate 丙酸 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 mon
11、oglyceride(单辛酸甘油酯 ) Fresh-keeping preservatives for fruits and vegetables : sec- butylamine（仲丁胺） -phenyl phenol （邻苯基苯酚） thiabendazole （噻苯咪唑） ethoxyquin（乙氧基喹） cinnamaldehyde（桂醛,肉桂醛） chlorine dioxide（ClO2） glutaraldehyde （戊二醛） sodium o-phenylphenolate（2-苯基苯酚钠） The following substances also have antiom
12、icrobial 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 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 , th
13、ey can be classified into- chemical preservatives:化学* organic preservatives: most 有机防腐剂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 food perservatives: mos
14、t 防腐 fresh-keeping preservatives for fruits and vegetables 保鲜(2) According to their application range, they can be classified into- (3) According to their sources, they can be classified into- 来源(4) According to their antimicrobial effect , they can be classified into- natural preservatives: nisin,
15、natamycin synthetic preservatives: most bacteriostatic: substances which can only prevent the growth of microbe.抑制 bactericidic: substances which can kill microorganisms. 杀菌剂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 solubilityWater solubility :benzoic acid: slightly soluble in water (0.34g/ 100ml at 25). sodium benzoate: highly soluble in water(50g/100ml at 25 ). Antimicrobial activity : Effective against most molds, yeasts and bacteria. T
