食品专业英语 LESSON 11 Food Preservation By Fermenttation

1、Microorganisms no doubt outnumber other living entities on this planet and can be found existing actively or passively wherever living organisms occ ur. While the energy for on this planet is captured by green plants in the ph otosynthetic process, microorganisms are generally responsible for the fi

2、nal d ecomposition of the photosynthetic products. Animals play a minor role in th e cycle.Inasmuch as bacteria, yeasts and molds are to be found throughout th e environment of man, it is to be anticipated that these microorganisms are i n direct competition with other living entities for the energy

3、 for life. Whenev er the conditions of nutrients and environment are favorable for microbial act ivity, it will be found.Man must compete with all other living entities on earth. In order to retain food supplies for himself, he must interfere with natural processes. Thr ough his study, and as a frui

4、t of his curiosity, man has evolved a number of control systems. One is the preservation of food by controlling, yet encouragi ngz the growth of microorganisms. Under such a condition, man may employ microorganisms to create unfavorable conditions for other microbes, yet retai n in the foodstuffs th

5、e nutrients desired.While microorganisms were not identified as the important agents in f ood spoilage until a century ago, wine making, bread baking, cheese making and salting of foods have been practiced for more than four thousand years. 统。其中之一就是通过控制（也包括促进）微生物的生长来保藏食物。在这样的情况下，人 类可以利用一些微生物去创造不利于其他

6、微生物的环境，而保存食物中必要的营养素。尽管直到一个世纪前才认定微生物是食物腐败的重要因素，而酿造葡萄酒、烘烤面 包、制作奶酪和腌制食品那么已进行了 4000年。在所有那些年代里，人类曾利用不知道的、 看不见的活性生物从事于食品保藏的实践。虽然食物保藏体系一般都抑制微生物生长，但不是所有的微生物都是有害的。事实 上，有些微生物常常被用来保藏食物。某些微生物产生的大量的酸创造了不利于其他微生物 的环境。下面用片刻时间复习一下词汇。呼吸作用是碳水化合物在有氧条件下转化为二氧化 碳和水，并放出大量能量的过程。发酵作用是碳水化合物缺氧氧化或局部缺氧氧化的过程。 腐败只作用是蛋白性物质的厌氧降解作用。氧

7、化钠在食品发酵过程中非常有用，因为它限制了腐败微生物生长，并抑制大量其 它微生物生长。然而，有些细菌能耐受高盐溶液并在其中生长。碳水化合物发酵发酵这个词本身经历了演变。在发现酵母以前，这个词被用来描述葡萄酒生产中出 现的发泡和沸腾现象。而在巴斯德的发现之后，这个词便变成与微生物活动联系起来的词来 使用，后来又与酶的活性联系起来。现今，这个词甚至被用来描述活细胞活动过程中二氧化 碳气体的放出。但是，对于无气体释放的发酵和仅由酶来完成的发酵作用来说，气体的放出 和活动细胞的存在都不是必要的。发酵作用于腐败作用有明显区别。发酵作用是对碳水化合物的一种分解作用；腐败 作用那么涉及微生物对蛋白性物质的全

8、面综合的作用。发酵过程通常不放出腐烂的气味，而且 通常产生二氧化碳。在腐败过程中，放出的物质中可能含有二氧化碳，但其特征气味是硫化 氢和含硫蛋白质的分解产物。腐败发酵作用通常即受污染的发酵作用。腐化的酸菜或泡菜是 细菌生长分解蛋白质的结果，而不是碳水化合物正常发酵产酸所致。食品保藏上重要的工业微生物微生物如果要在发酵和腌渍上有用，它必须具备三个重要特性：（1）这些微生物 必须能在适合的底物和环境中生长并容易大量培养。（2 ）这些微生物必须能够在上述条 件下保持其生理稳定性，且易于产生大量所必须的酶，以期能出现所要求的化学变化。（3 ） 为使微生物的生长和繁殖最快所必须的环境条件应相对较简单。微

9、生物在食品保藏实践上的应用必须采取积极的防护措施，以控制污染。用于发酵的微生物的显著特点是产生大量的酶。以单细胞存在的细菌、酵母和霉菌, 其单个细胞中就具有生长、繁殖、消化、吸收和修复的功能，而在生命的高等形态中，这些 功能分配给组织。因此可以预料，完全的单细胞生物体（例如酵母）具有比其它生物体更高 的产酶和发酵能力。酶是发酵作用中控制化学反响的活性物质。彳散生物的每个属、每个种实际上都是各 种酶的贮存库，以其自身特定的能力产生和分泌各种酶。人类还有待于去学会合成各种酶。干重1g具有高活性乳糖发酵酶的微生物每小时能分解10000g乳糖。这样强烈的 化学活性与微生物的简单生命过程的需求有关，与它

10、们生存所需能量的获得方便有关,与它 们旺盛的生长能力和快速的繁殖速率有关，还与它们维持生命体的强大能力有关。数分钟时 间就可以产生T弋。实际上也有一定的平衡。微生物在生命活动中要消耗能量。它们活动产生的产物于 它们所赖以生长的天然物质相比是能量较低的物质。然而，以葡萄酒为例，微生物活动的产 物正是通常比生产葡萄酒的天然果汁更加受人喜爱的东西。发酵作用的顺序微生物在天然食品材料中获取可利用的碳水化合物、蛋白质、脂肪、矿物质的微量 营养素。看来，微生物首先作用于碳水化合物，然后是蛋白质，最后是脂肪。即使是碳水化 合物，也有一定的作用顺序；首先是糖类，其次是醇类，最后是酸类。由于微生物活动的第 一需

11、要是能量，所以看来最易利用的形式(按优先选择顺序)是CH2、CH、CHOH和CO OH碳键。有些键(例如CN基团)对微生物是没有用的。糖的发酵模式微生物通过完全氧化、局部氧化、酒精发酵、乳酸发酵、丁酸和其他次要发酵的活 动来发酵糖。(1)细菌和霉菌能够将糖(葡萄糖)分解为二氧化碳和水。几乎没有酵母能够完成 这一反响。(2 )最普通的发酵过程是糖发生局部氧化的发酵。在这种情况下，糖可以转化成酸。 如果允许发生，酸最终也可以氧化成二氧化碳和水。例如用某些霉菌从糖溶液生产柠檬酸。(3 )酵母是醛类变成醇类的最有效的转化者。细菌、酵母和霉菌的许多菌种能够产 生酒精。葡萄酒酵母在酒精发酵中具有很大的工业

12、重要性。这种工业用酵母产生可回收量的 酒精。虽然其他微生物也能产生酒精，但是酒精中掺杂醛、酸和脂，因而难以回收。从糖到 酒精的反响要经历许多步骤。(4浮L酸发酵在食品方面非常重要。食物中的糖可被转化成乳酸和其他终产物，转化 的量使得周围环境对别的微生物有控制作用。乳酸发酵的效率高，发酵菌的生产迅速。在自 然接种的情况下，乳酸菌在合适的环境中将占主要地位，例如牛奶变酸的情形。(5 )丁酸发酵在食品保藏中不如前面提到的那些发酵那么重要。此发酵菌是厌氧菌， 并会给食品带来令人不愉快的口味和气味。通常使人受感染生病的厌氧菌是丁酸发酵菌，二 氧化碳、氢气、醋酸和醇是丁酸的另外一些产物。（6 ）除以上所述

13、外，还有一种涉及大量气体产生的发酵。这种发酵对食品保藏有用，尽管产气有不利的方面。就能量方面而言，这种发酵产气（二氧化碳和氢气）的效率很低, 这些气体在与乳酸作比拟时所遇到的浓度下，几乎没有或完全没有保藏效力。而且，重要的 食品腐败微生物能够在这样的环境中生长。在产气发酵中糖分子转化成酸、醇和二氧化碳。 采用这种发酵形式，常常有必要引入一些别的有影响的控制措施，例如向底物添加氯化钠。（7）在食品方面还可能有许多的发酵重要，它们对处理后的食品的接受性有害。一 般来说，但凡有能力作用于诸如纤维素、半纤维素。果胶和淀粉之类高级碳水化合物的微生 物会损害被处理食品的质构、风味和品质。发酵控制方法食品是

14、天然受微生物污染的，如果不加注意，就会腐败。将要出现的微生物作用模 式取决与外界施加的条件。对某条件下最为有利的给定发酵模式，也会因控制因素的微小变 化而改变。没有照管好的肉会自然长霉并腐烂。如果加盐水或盐，完全不同的微生物就会占 优势。食品pH值是控制因素人类食用的许多天然新鲜食物是酸性的。蔬菜的pH值范 围为6.54.6。水果的pH值为4.53.0。刚宰杀的动物的肉，其pH值接近中性（7.2 ）, 但两天之内pH值将接近6.0.牛奶的pH接近6.4.由于这类食品中的两种重要的发酵作用是氧化和醇化发酵，因而，微生物的生长将 受介质酸度的控制。水果和果汁方面，酵母和霉菌将很快使自己立足。肉类方

15、面，酵母的活 力不如细菌。牛奶方面，在数小时的时间内就会出现酸发酵。能量的来源一由于微生物的直接需要是能量来源，因而利用方便的可溶性碳水化 合物影响着将要占支配地位的微生物的数目。牛奶中的糖是乳糖，因此在数目上很快增值的 微生物就是乳糖发酵菌。由于微生物一般能在人类食物中获得合适的能量来源，所以除某些 例外的情况（如牛乳），能量来源通常不是限制因素。获得氧的难易程度缺氧的程度是控制发酵的主要因素。对于酵母，当有大量氧 气存在时，就促进酵母细胞的生产。如果希望产生酒精，供氧就要非常有限。霉菌是需氧的，它受缺氧的控制。基质的控制。基质中占主导地位的各种细菌的菌 数分布受各菌的需氧情况以及获得氧的难

16、易的控制。如果其他因素均为最正确，那么发酵的最终产物可以局部地受基质的氧分压控制。温度要求每一类微生物都有一最适生产温度；因此基质的温度对微生物的生产 起了积极控制的作用。为了在发酵过程中到达最大限度的操作效能，必须给微生物创造最适 的温度条件。食品存放的温度将有在一定限度内决定了微生物的种类和属性，这些微生物或者能 产生所要求的发酵作用，或者能产生腐败作用，两者必居其一。氯化钠在控制发酵方面的作用盐类是食品防腐上最重要的食品添加剂之一。在 干制方面，盐已显示出具有良好效果。在发酵方面，盐可以对允许生产的微生物起着筛选的 作用。Lesson 11detrimental伤害的损害的putrefa

17、ction腐败的，腐烂chloride氯化物putrefactive 腐败的putrid odor腐败臭气味kraut酸渍的菜warehouse 货仓lactose 乳糖oxidation氧化作用lactic乳汁的citric acid 柠檬酸inoculation接种疫苗anaerobic厌氧的pectin果胶anaerobiosis 厌氧的l)Under such a condition, many may employ microorganissms to creat unfavorable conditions for other microbes, yet retain in the

18、 foodstuffs the nut rients desired.这是一个简单句。may employ和retain是并列谓语。句中for other microbe s是作定语用的介词短语，修饰unfavorable conditionso to createmicrobes动词不 定式作状语修饰谓语may employo yet是连词,in the food stuffs是状语z the outri ents desired是宾语，desired是过去分词，作the nutrients的后置定语。While food preservation system in general inh

19、ibits the growth of microorganisms , all such organisms are not detrimeotal .While food.of microorganisms 是让步状语从句，在此 while = although。al 1 such orgaoisms are not detrimental 是局部否认结构的句子，相当于 not all su ch organisms are detrimentaloNeither gas evolution nor the presence of livioe cells is essentiaI to

20、fermentative action , however, as seen in lactic acid fermentations wher e no gas is liberated zand in fermentations accomplished solely with enzyme s .句中，as seen in.with enzymes 是 as is seen.with enzymes 的非限制性 定语从句的省略。其中as是关系代词，指整个主句，它在从句中作主语，意为如、象 那样。in lacticliberated和in fermentationsenzymes是并列的介

21、词短语，作状 语，修饰从句谓语 is seen0 where no gas isliberated 是修饰 lactic acid fermeotat ions的定语从句。Bacteria , yeasts and molds , being single cells , contain the functioo al capacities for growth , reproduction , digestion, assimilation and repairs i n a cell , that higher forms of life have distributed to tissu

22、es .句子的主语是Bacteria、yeasts和molds。being single cells是分词短语停状 语，修饰谓语contain。介词短语fo growth.repairs in a cell是修饰主句宾语the fun ctional capacities 的定语。而介词短语 in a cell 作 growthrepairs 的定语。that high er.to tissues 是修饰 growth , reproduction , digestion , assinlilation and repai rs的定语从句,其中that在从句中作宾语，即可将从句变形为highe

23、r forms of life hav e distributed that to tissltesoHowever, the product of the activity in the instance of wine is one which man generally enjoys more than the native juice from which the win e was produced .句子的主语是 the product,介词短语 in tke instance of wine 是 the activity 的定 语，由介词of与名词短语the activity i

24、n the instance of wine构成的介词短语又是t he product的定语。one是作表语的代词，其后面的which manproduced是one同 位语从句,而from whichproduced是修饰the native juice的定语从句。While other organisms are able to produce alcohol , it occurs in sue h mixture of aldehydes , acids and esters that recovery is difficult.While other.alcohol是让步状语从句。i

25、t是主句的形式主语，真正的主语是that r ecovery is difficult ix一主语从句。The most favoreble to e given type of fermentation under one con dition will be altered by slight changes in a controling factor .The most favorable 是句子的主语，二 the most favorable type of action (type of action 是上句提至I的概念)。介词短语 to a given type of ferme

26、ntion under one condition 是 the most favorable 的定语。under one condition 又是 a given type of fermentation 的定语。The temperature at which a food is held will determine within certai n limits the nature of the organisms capable of either yielding the desired f ermentation or spoilage z whichever the case m

27、ay be .主句的主语是The tenlperature , at which a food is held是修饰主语的定语从句。 主句的谓语是will determine ,宾语是the nature.spoilage ,其中，形容词短语capab Ie of either yielding the desired fermentation or spoilage 是the organisms的定 语，of the organisms.spoilage 是 the nature 的定语，whichever the case may b e是非限制性定语从句，修饰fermentation和s

28、poilage ,其中关系代词whichever又是这一从句中的表语。For all those years mankind practiced food preservation using unknown, invisi blez active, living organisms.While food preservation system in general inhibits the growth of microor ganisms, all such organisms are not detrimental. In fact some are commonly utilized

29、in food preservation. The production of substantial amounts of acid b y certain organisms creates unfavorable conditions for others.To review terms for a moment, respiration is that process whereby carbo hydrates are converted aerobically into carbon dioxide and water with the re I ease of large amo

30、unts of energy. Fermentation is a process of anaerobic, or partially anaerobic, oxidation of carbohydrates. Putrefaction is the anaerobic d egradation of proteinaceous materials.Sodium chloride is useful in a fermentation process of foods by limiting the growth of putrefactive organisms and by inhib

31、iting the growth of large n umbers of other organisms. Yet some bacteria tolerate and grow in substanti al amounts of salt in solution.Fermentation of CarbohydratesThe word fermentation has undergone evolution itself. The term was em plyed to describe the bubbling or boiling condition seen in the pr

32、oduction ofwine. prior to the time that yeasts were discovered. However, after Paste urs discovery, the word became used with microbial activity, and later with e nzyme activity. Currently the term is used even to describe the evolution of c arbon dioxide gas during the action of living cells. Neith

33、er gas evolution nor the presence of living cells is essential to fermentations where no gas is liber ated, and in fermentations accomplished solely with enz3mes. s)There is a clear difference between fermentation and putrefaction. Fer mentation is a decomposition action on carbohydrate materials; p

34、utrefaction r elates to the general action of microorganisms on proteinaceous materials. Fe rmentation processes usually do not evolve putrid odors, and carbon dioxide is usually produced. In putrefaction the evolved materials may contain carbon dioxide, but the characteristic odors are hydrogen sul

35、fide and sulfur-containi ng protein decomposition products. A putrid fermentation is usually a contam inated fermentation. Putrid kraut or pickles result from microbial growths dec omposing protein, rather than the normal fermentation of carbohydrates to p roduce acid.Industially Important Organisms

36、 In Food PreservationThere are three important characteristics microorganisms should have if t hey are to be useful in fermentation and pickling. (1) The microorganisms mu st be able to grow rapidly in a stuiable substrate and environment, and be e asily cultivated in large quantity. (2) The organis

37、m must have the ability to m aintain physiological constancy under the above conditions, and yield the esse ntial enzymes easily and abundantly in order that the desired chemical chang es can occur. (3) The environmental conditions required for maximum growthand reproduction should be comparatively

38、simple.The application of microorganisms to food preservation practices mus t be such that a positive protection is available to control contamination.The microorganisms used in fermentations are notable in that they pr oduce large amounts of enzymes. Bacteria, yeasts and molds, being single cel Is,

39、 contain the functional capacities for growth reproduction, digestion, assimil ation and repairs in a cell, that higher forms of life have distributed to tissue s Therefore, it is to be anticipated that single cell complete living entities(suc h as yeasts) have a higher enzyme productivity and ferme

40、ntative capacity tha n found with other living creatures.Enzymes are the active substances which control chemical reactions in fermentation. The microorganisms of each genus and species are actually a warehouse of enzymes, with its own special capacity to produce and secrete enzymes. Man has yet to

41、learn to synthesize them.A dry gram of an organism endowed with high activity lactose ferme nting enzymes is capable of breaking down 10,000 g of lactose per hour. Thi s great chemical activity is associated with the single life-process requirement s of the organisms, the ease with which they obtain

42、 energy for life, their gre at growth capacity and reproduction rate, and their great capacity for mainte nance of the living entity. One generation may occur in a matter o minutes.But there is a balance in effect. In living, the organisms consume ene rgy. The product of their actions is a substrate

43、 of lower energy than that nati ve material upon which they were planted. However, the product of the activi ty in the instance of wine is one which man generally enjoys more than the native juice from which the wine was produced.Order of FermentationMicroorganisms have available carbohydrates, prot

44、eins, fats, minerals a nd minor nutrients in native food materials. It appears that microorganisms fir st attack carbohydrates, then proteins, then fats. There is an order of attack e ven with carbohydrates; first the sugars, then alcohols, then acids. Since the fi rst requirement for microbial acti

45、vity is energy, it appears that the most avail able forms, in order of preference, are the CH2, CH, CHOH, and COOH carbo n linkages. Some linkages such as CN radicals are useless to microorganisms.Types ,of Fermentations of SugarMicroorganisms are used to ferment sugar by complete oxidation, par tia

46、l oxidation, alcoholic fermentation , lactic acid fermentation, butyric ferment ation and other minor fermentative actions.Bacteria and molds are able to break down sugar (glucose) to carb on dioxide and water. Few yeasts can accomplish this action.The most common fermentation is one in which a part

47、ial oxidatio n of sugar occurs. In this case, sugar may be converted to an acid. The acid finallymay be oxidized to yield carbon dioxide and Water, if permitted to o ccur. For example, some molds are used in the production of citric acid fromsugar solutions.Yeasts are the most efficient converters o

48、f aldehydes to alcohols.Many species of bacteria, yeasts and molds are able to yield alcohol. The yea st, Saccharomyces ellipsoideus. is of great industrial importance in alcoholic fe rmentatioas. The industrial yeasts yield alcohol in recoverable quantities. While other organisms are able to produc

49、e alcohol, it occurs in such mixtures of al dehydes, acids and esters that recovery is difficult. The reaction from sugar to alcohol is many stepped.Lactic acid fermentation are of great importance in food preservati on. The sugar in foodstuff may be converted to lactic acid and other end pro ducts,

50、 and in such amounts that the environment is controlling over other or ganisms. Lactic acid fermentation is efficient, and the fermenting organisms ra pid in growth. Natural inoculations are such that in a suitable environment th e. lactic acid bacteria will dominate, as in souring of milk.Butyric f

51、ermentations are less useful in food preservation than thos e noted previously. The organisms are anaerobic and impart undesirable flavo rs and odors to foods. The anaerobic organisms capable of infecting man cau sing disease are commonly butyric fermenters. Carbon dioxide, hydrogen, acet ic acid an

52、d alcohols are some of the other fermentation products.In addition to the above there is a fermentation which involves mu ch gas production. It is useful ;n food preservation, although gas production has disadvantages. Energy-wise it is less efficient to produce gases (carbon di oxide and hydrogen)

53、which have little or no preserving power in concentratio ns found in comparison with lactic acid. Also, the important food spoilage or ganisms are capable of growing in such environments. In gassy fermentations sugar molecules are altered to form acids, alcohols and carbon dioxide. It is usually nec

54、essary to include some other controlling influence, such as adding sodium chloride to a substrate, with this form of fermentation.There are many fermentative actions possible in foods which are d etrimental to the acceptability of treated foods. Generally the organisms capa ble of attacking higher c

55、arbohydrates such as cellulose, hemicelluloses, pectin, and starch will injure the texture, flavor and quality of treated foods.Fermentation ControlsFoods are contaminated naturally with microorganisms and will spoil i f untended. The type of action which will develop is dependent upon the con ditio

56、ns which are imposed. The most favorable to a given type of fermentatio n under one condition will be altered by slight changes in a controlling facto r. Untended meat will naturally mold and putrefy. If brine or salt added, entir ely different organisms will take over.The pH Value of Food is a Cont

57、rolling Factor-Most foods in native, fr esh form which man consumes as food are acid. Vegetables range in pH valu e from 6.5 to 4.8. Fruits range from 4.5 down to 3.0. Animal flesh when kille d is approximately neutral (7.2) but within two days the pH value will be app roximately 6.0. Milk has a pH

58、value near 6.4.In as much as the two important fermentation in such foods are oxida tive and alcoholic, the growth of organisms will be controlled by the acidity of the medium. In fruits and fruit juices, yeasts and molds will quickly establis h themselves. In meats yeasts are less active than bacteria. In milk, an acid fe rmentation is established in the matter of a few hours.Source of Energy-Inasmuch as the immediate need of microorganisms is a source of energy, the soluble, readily available carbohydrates influence t he microbial populatio