食品添加剂 防腐剂.ppt

1、(第二章 防腐剂),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,2.5.2 Sorbic ac

2、id 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,* 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 * (

3、Questions for discussion),2.5.5other preservatives,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:,* Drying in the sun * low-temperature storage (freezi

4、ng/frozen storage)冷冻冷藏 * pickling/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 sterili

5、zation 电子辐照,(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,Atte

6、ntion:, 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,2.2 Mechanisms of preservatives,(1) Food spoilage caused by micro- organisms (three

7、 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 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(

8、), 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 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,1) Inhibit dehydrogenases involved in fatty acid ox

9、idation. 抑制脂肪氧化脱氢酶, Interfere with microbial enzymes:,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:(), Food preservatives: benzoic acid and sodium benzoate 苯甲酸（盐） sorbic acid and potassium

10、 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 monoglyceride(单辛酸甘油酯 ), Fresh-keeping

11、 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 antiomicrobial effects:,nitrites: used

12、 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 , they can be classified into-, chem

13、ical 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: most 防腐 fresh-keeping preserva

14、tives 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, natamycin synthetic pres

15、ervatives: 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.

16、, structures: page 41,General properties: water solubility,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 :, Effective against most molds, yeasts and bacteria., The undissociated for

17、m 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，它们只在酸性段有效,For example, under optimal pHs, their MIC are as low as 0.05-0.1% for mos

18、t microbes. 在最宜pH, 最多数微生物，MIC低至0.05%-0.1%,Toxicology: low toxicity Oral LD50 : 2530mg/kg for benzoic acid; 4070 mg/kg for sodium benzoate. ADI: 0-5mg/kg for both GRAS,Applications,Application standards: Table 2-3. E : 0.2-2.0 g/kg,Examples:,1) 0.1% is effective in soy sauce, vinegar, fruit juice and

19、 jams.,2) 0.05% is effective in pickles with low salt and preserved fruits.,2.5.2 Sorbic acid and potassium sorbate., source: synthetic preservatives, sorbic acid:slightly soluble (0.16g/ 100ml at 20). potassium sorbate: highly soluble (67.6/100m at 20 )., Structures: page 44., General properties: W

20、ater solubility, Antimicrobial activity (), Effective against most molds, yeasts, and aerobic bacteria but almost ineffective against anaerobic and lactic bacteria. 对霉菌，酵母，好氧菌有效，对厌氧菌和乳酸菌无效,The undissociated form of sorbic acid is the most effective antimicrobial agent. 没有离解的山梨酸抗菌效果最好, pH value of fo

21、ods affect their antimicrobial effects. They are only effective in acidic condition with optimal pH lower than 6.0 .pH影响抗菌活性，pH小于6时效果最好,Eg: at pH3, its MIC for most microbes is 0.01%, but at pH6, MIC increases to 0.2%. 例如，pH3是，MIC为0.01%，而pH6时，MIC为0.2%, ADI: 0-25mg/kg for both, Toxicology:, Sorbic ac

22、id is considered one of the least harmful antimicrobials.毒性最低的抗菌剂, Oral LD50: 7360mg/kg for sorbic acid ; 4920 mg/kg for potassium sorbate., GRAS,Applications,Application standards: Table 2-6. E: 0.2-2.0 g/kg,Examples:,1) In jams stored at 32 , when 0.05% sorbic acid was added, no spoilage was found

23、 in 12 days, but the control sample underwent spoilage in 3 days.,2) The shelf-life of beverage could extend to 1 month when 0.02% sorbic acid was added compared to the control with the shelf-life only being 3 days.,加入 山梨酸可以把饮料的货架期延长到一个月，而对照只有3天,3) At 4 and 15 , the shelf-life of the chicken carcass

24、 immersed first in boiling water for 10s then in a solution containing 6% sorbic acid for 60s was 35 and 57 times as long as that of the control respectively.,鸡肉先放进沸水处理10秒钟，然后放入含6%的山梨酸溶液中60秒可以保货架期分别演唱3-5， 到5-7倍。,2.5.3 Sodium and calcium propionates 丙酸钠和丙酸钙, source: synthetic preservatives 合成,Structu

25、res: CH3CH2COONa and (CH3CH2COO)2Ca,General properties: 一般性质 water solubility 水溶性, sodium propionate: highly soluble (100g/ 100 ml at 15); potassium propionate: highly soluble (39.9g/100ml at 20 )., Antimicrobial activity, Effective against molds, but little effective against bacteria and ineffectiv

26、e against yeasts. 对霉菌有效，但对细菌和酵母无效, The undissociated form of propionic acid is the most effective antimicrobial agent.未离解的形式抗微生物效果最好, pH value of foods affect their antimicrobial effects. They are only effective in acidic condition with optimal pH lower than 5.5. pH有影响,小于5.5时才有效。 Eg: For example, at

27、 pH5.0, MIC for calcium propionate is 0.01%, while at pH5.8, the MIC rises to 0.188% .,ADI: not specified., Toxicology:, Oral LD50: 6300mg/kg for sodium salt, 3340 mg/kg for calcium salt., GRAS,Applications 应用,Application Standards: 标准,1) Sodium propionate is allowed in cake with a limit of 2.5g/kg.

28、 丙酸钠,2) Calcium propionate is allowed in wet crude flour products with a limit of 0.25 g/kg and in bread, vinegar,soy sauce, cake and soy bean products with the maximum amount of 2.5 g/kg.丙酸钙，面包，醋，酱油，蛋糕，豆制品,Examples:,1) The shelf-life of bread could be increased by 2-4 days when 0.25% calcium propio

29、nate was added in it.,加入0.25%的丙酸钙可以延长面包的货架期2-4天,2) The mooncake could be increased by 30-40 days in shelf-life with the addition of 0.25% calcium propionate.加入0.25%的丙酸钙，月饼货架期可增加30-40天,Attention: In bakery products, when chemical bulking agents such as sodium bicarbonate are used, sodium propionate i

30、s preferred. 焙烤食品中使用碳酸氢钙时使用丙酸钠较好,(2.5.4) Parabens/p-hydroxybenzoates, They are alkyl esters of p-hydroxybenzoic acid .对羟基苯甲酸的酯, Parabens used as food preservatives include:, General Structure: page 49.,methyl-p-hydroxybenzoate/ methylparaben 甲基,ethyl-p-hydroxybenzoate/ ethylparaben ( ) 乙基,propyl-p-h

31、ydroxybenzoate/ propylparaben ( ) 丙基,isopropyl -p-hydroxybenzoate/ isopropylparaben 异丙基,butyl -p-hydroxybenzoate/ butylparaben 丁基,isobutyl -p-hydroxybenzoate/ isobutylparaben 异丁基, n-heptyl-p-hydroxybenzoate/ hetylparaben 正庚基,solubility : slightly soluble in water, but highly soluble in ethanol, and

32、related to the alkyl chain length ., General properties:, source: synthetic preservatives,* but the water solubility of parabens is inversely related to the alkyl chain length.水溶性则与烷基链的长度反相关,* The solubility of parabens in ethanol increases as the alkyl chain increases.在乙醇中的溶解度随着烷基链的增长而增加, Antimicro

33、bial activity (), They are more active against molds, yeasts than against bacteria.对霉菌酵母比对细菌更有效, Against bacteria, they are more effective against gram-positive than gram-negative bacteria. Also, they are infective against lactic bacteria. 阴性菌，阳性菌，对乳酸菌无效。, The antimicrobial activity of parabens is d

34、irectly proportional to the alkyl chain length.与烷基链长度有关, The undissociated form of parabens is the most effective agent., Parabens are effective at both acidic and alkaline pH levels with the optimal pH value of 4-8 . 酸性碱性都有效，最佳pH 4-8, ?,ADI: 0-10mg/kg., Toxicology:, Low toxicity and the longer the

35、alkyl chain, the lower the toxicity., GRAS (for methyl and propyl parabens), Oral LD50: 5000mg/kg for ethyl-paraben, 6700 mg/kg for propyl-paraben.,Applications 应用,Application Standards: Table 2-9. E: 0.10-0.5 g/kg,Examples:,The mixture of methyl and propyl parabens (3:1) at the level of 0.03-0.06%

36、could be used to increase the shelf life of fruit cakes, and pie crusts .,Summarization of the above preservatives (), Toxicity and permitted maximum levels,Continuted :, Antimicrobial activity (), Application in main foods,1. Why are propionic acid and its salts suitable antimicrobials for bread?丙酸

37、及其盐,Three reasons: Firstly, propionic aid and its salts are effective against molds, and still have antimicrobial activity in breads with relatively high pHs as the dissociating constant of propionic acid is low.,Questions for Discussion,Secondly, they are effective against bacillus which easily cau

38、se rope（粘连） in bread. Thirdly, they do not have effects on yeasts, so they will not affect fermentation. 对酵母无害，不影响发酵,2. Benzoic acid and its salt are not used as preservatives in most meat products, why?,Two reasons: Firstly, the pH values of most meat products are not at the optimal pH range of ben

39、zoate activity. Secondly, benzoic acid is not effective against C. botulinum.肉毒杆菌,3. Why can sorbic acid and potassium sorbate be used in most foods?,Two reasons: Firstly, they are effective against most microorganisms. Secondly, they are effective in wide pH range. Its optimal pH is below 6, but it

40、 still has antiomicrobial activity when pH is up to 6.,4. Though parabens have many advantages compared to other compounds, they are seldom used in most foods, why? 优点多，却少用，为什么？,Two reasons: Firstly, low water solubillity. Secondly, astringent taste（涩味）.,(5) Other preservatives,structure: Nisin is a

41、 peptide consisting of 34 amino acids produced by lactococcus lactis with the molecular weight being 3500. 肽，氨基酸，分子量,1) Nisin,Properties:,Applications,Application Standards: Nisin is permitted in canned foods, vegetable protein beverages with a limit of 0.2g/kg; is permitted in milk products, meat p

42、roducts with the maximum level of 0.5g/kg. 罐藏，植物蛋白饮料,Examples:,1) 1-10mg/kg of nisin was suggested to milk products such as cheeses, pasteurized milk, and flavored milk.奶酪，巴氏奶，风味奶,2) 2-2.5 mg/kg of nisin was suggested to canned vegetable products such as canned pineapple, cherry, apple and tomato ja

43、m.菠萝，樱桃，苹果，西红柿酱,3) 150-200 mg/kg of nisin was suggested as an adjunct to nitrite in cured meats for the purpose of preventing the growth of clostridia（与亚硝酸盐并用，腌肉，梭状菌）.,2) Fresh-keeping preservaties for fruits and vegetables 保鲜,Preservatives used for surface treatment for integral fruits and vegetabl

44、es during their storage.,They are usually alkaline substances including sec-butylamine, -phenyl phenol, and thiabendazole etc., Antimicrobial activity, sec-butylamine: oral LD50 is 660 mg /kg., -phenyl phenol: oral LD50 is 2430-3000mg /kg; ADI is 0-0.2 mg/kg., toxicology:, thiabendazole: oral LD50 i

45、s 3600 mg /kg; ADI is 0-0.1mg/kg., They should not be added into final foods but used as preservatives for fruits and vegetables during their storage. Their maximum levels and residues should be restricted according to GB2760-1996. 不用于最终产品，用于果蔬储运，最大量按国家标准, Application,For example: according to GB276

46、0-1996, the maximum level of thiabendazole is 0.02g/kg, and its residue should be lower than 0.002g/kg. 残留量, They are usually compounded to solutions to soak fruits or vegetables or be sprayed into the surface of the products. 浸或者喷, They can also be added into wax to coat fruits and vegetables . 加入涂

47、覆蜡中, sec-butylamine and thiabendazole can also be compounded into fumigant to fumigate fruits and vegetables because of their property of sublimation. 仲丁胺和塞苯咪唑可以升华，可以加入熏剂,6. Attention to the application of food preservatives,(1) Factors to be considered in selecting a food antimicrobial agent., The

48、antimicrobial spectrum of the compound to be used must be known along with knowledge of the bioburden of the food products., The chemical and physical properties of both the antimicrobial and the food product must be known., The conditions of storage of the product and interactions with other proces

49、ses must be evaluated to ensure that the antimicrobial will remain functional over time., A food must be of the highest microbiological quality initially if an antimicrobial is to be expected to contribute to its shelf life., The safety and legality of the compound must be known.,(2) Factors affecti

50、ng the antimicro-bial effects of preservatives., pH value: most preservatives function in the undissociated form, so pH affects their activity.,For exampe, benzoic acid and its sodium salt, sorbic acid and potassium salt, propionic acid and its sodium and calcium salts, and nisin., Degree of dissolu

51、tion or distribution:,Generally only when a preservative dissolves or distributes uniformly in a food can it exert its full activity.,For example, nisin is usually dissolved in the solution of HCl (0.02mol/L) before it is added into a food product.,Another example, parabens are slightly soluble in w

52、ater, so they are usually dissolved in the solution of NaOH, acetic acid or ethanol before it is added into a food product.,7. Development tendency of food preservatives,For example, preservatives in combination with gas package or with heat treatment.,(1). Development of comprehensive preserving systems.,(2). Development of new, effective, economical, and safe preservatives.,Questions for discussion,1. what is the definition of food preservatives?,Answer: substances which can kill microorganisms or prevent the growth of microorganisms.,A.