食品科学专业英语阅读练习

1、LESSON 1 NUTRITIONWhat we eat as well as how much we eat determine our nutrition status to an important extent, and influenced by a diversity of external and internal factors. The person who wants to fine the answer to the question" what should I eat for good nutrition? ”, might easily become l

2、ost in the maze of informational corridors, confused by the wealth of technical information provided by scientists or mislead by simplistic answers provided by those with products to sell.Somewhere in between is some reasonable, commonsense information that we can use to guide us our quest for sound

3、 nutrition knowledge。 To begin, we need to learn some definitions of commonly used nutrition terms and find out what sorts of guidelines are available to help us measure the quality of our diets and to develop healthful eating patterns.NUTRITION AND FOOD: DEFINITIONS  The word nutrition is ofte

4、n paired with the word food because the two go together. They are interdependent, but not interchangeable. Food might be defined as any edible substance that provides nourishment when consumed. It is made up of many natural ingredients all chemicals that have different functions such as providing od

5、or, flavor, color, and nourishment. The ingredients that give us nourishment are called nutrients. These nutrients are categorized as fats, proteins carbohydrates (sugars and starches), minerals, vitamins, and water. They are called essential nutrients because we cannot get along without them. We ne

6、ed them for energy, for building and maintaining body tissue; and for regulating body processes the three essential functions of foods in the body. Nutrition might be defined as the process whereby we obtain the essential nutrients and use them to make many other substances our bodies need, this pro

7、cess would include eating and digesting food and absorbing and using, or metabolizing, the nutrients it contains. We can obtain all of the essential nutrients from food. However, it is possible to obtain nourishment without eating and digesting food-if, for example, the nutrients are injected direct

8、ly to our veins as in intravenous feeding. Thus, it is the nutrients that are essential and the food that normally provides them. Since food is vital, we need to know the nutritive content of foods, which ones are the best sources of the various nutrients and how to combine them into a healthful die

9、t. The term good nutrition implies that we are obtaining from our food all of the essential nutrients in the amounts needed to keep our bodies functioning and to maintain optimum health. A very simplified definition of good nutrition might be" eating the right foods in the right amounts.” The w

10、ork of nutrition scientists involves finding in the body, the amount of each that we need, what happenings when we receive too much or too little and about food and died-what foods we should eat and in what amount. Yet nutrition science in its broadest sense has many more facets: the influence of se

11、nsory factors of flavor, color, and texture of food on eating behavior; the psychological, cultural, emotional, and social aspects of food intake; and even the economics of food availability and consumer behavior in the purchase of food THE NUTRIENTS  To date, nutrition scientists have identifi

12、ed some 40 to 45 substances as essential nutrients. But the list is growing as new nutrients continue to be identified; the history of nutrition science contains fascinating stories about the ways food substances have been identified as essential nutrients. In some instances, medical researchers see

13、king the cause of a particular disease found that problem was due to a single substance, and that when this substance was added to the diet, the symptoms of the disease disappeared. A number of vitamins were discovered in this way. Nutrients might be divided into two genial categories based on the a

14、mount that we need. These are the macronutrients (carbohydrates, fats, proteins, and water), which we need in relatively large amounts and the micronutrients) mineral elements and vitamins), which we need in relatively small amounts. All of the nutrients except for mineral elements and water are cla

15、ssified as organic chemicals because they contain the element carbon. Mineral elements and water are inorganic chemicals because they do not contain carbon. The vitamins are divided into two general categorizes based on their solubility in either water or fat .the fat-soluble vitamins are vitamins A

16、, D, E, and K; the water-soluble vitamins include vitamins C (ascorbic acid), niacin, thiamin, riboflavin, flacon (also called folic acid) antithetic acid, pyridoxine, vitamin B12 and biotin. The mineral elements are divided into two categories based on the quantity of them that we need. Microelemen

17、ts are those needed in relatively large amounts, while microelements are those needed in very small amounts, some example of microelements are sodium, calcium, and phosphorus. Some example of microelements is iron, iodine, manganese, zinc, and fluorine.  RECOMMENDED DIETARY ALLOWANCES  Onc

18、e a nutrient is identified, one of the principal research efforts of nutrition scientist is to determine how much of it is needed by people at various ages and stages of life. Initial studies usually are conducted with laboratory animals, but the information developed in these studies cannot be appl

19、ied directly to humans since peoples needs often are quite different from animals needs. Human nutrition studies on the other hand, are time-consuming, costly, and difficult to conduct, especially because of the problems of controlling variables and possibly causing harm to the individuals involved.

20、 Because of the obstacles to collecting, accurate data, our present knowledge of nutrient needs is incomplete, and the requirements of humans for many nutrients have not been established. However, the data on human and animal needs currently available are used by nutrition scientists to establish es

21、timates of the amounts of essential nutrients per day that will meet the needs of most health persons. In the United States, the most widely used nutrient guidelines are the recommended dietary allowance (RDA), which are issued by the national academy of sciences, national research council, and food

22、 and nutrition board. The RDA serves as dietary of nutritional standards for a wide range of age-weight-sex groups such as infants, children, adolescents, pregnant and lactating women, and younger and older adults. They are recommendations, not average requirements, for satisfactory levels of intake

23、 of essential nutrients of population groups of average, healthy people. They do not take account of special needs certain individuals may have due to genetic make up, metabolic disorders, chronic infections, and other abnormalities, which may result in their needing different levels of nutrients. &

24、#160;MARGIN of SAFETY ALLOWS for INDIVIDUAL DIFFERENCES  To allow for individual difference, the usually are set with a generous margin of safety. Thus, they are thought to meet the needs of 95 to 97 percent of the people within each age-sex group. In other words, the RDA exceed the requirement

25、s of most individuals to ensure that the needs of nearly all are meet. For this reason, a person who consumes a diet that provides less than the RDA for one or more essential nutrients is not necessarily getting a diet that is nutritionally inadequate. What can be concluded, however, is that the far

26、ther the intake of an essential nutrient falls below the RDA, the greater the probability of nutritional inadequacy, on the other hand, if an individual is getting all the essential nutrients at or above the RDA level of his or her age, chances are good that diet is nationally adequate. An exception

27、 is the RDA for energy or calories, which are not designed, as guides for individual caloric needs. Other variables not included in the RDA, such as body size and physical activity, are involved in an individuals caloric requirements DIFFERENCES IN NUTRIENT UTILIZATION CONSIDERED Another factor

28、 considered when the RDA are established is the availability of the nutrient and factors that affect how efficiently it is used in the body for some nutrients, such as iron, absorption or use in the body may be incomplete; so the RDA needs to be set high enough to allow for this. And because in the

29、case of certain other nutrients, substance found in carrots and other vegetables and fruits, which our bodies convert to vitamin A. On the other side of the coin, receiving too much of certain nutrients, amounts significantly above the RDA, can be just harmful as not obtaining enough certain vitamin

30、s (such as A and D) and minerals can be highly toxic if high for optimal nutrient intake from the standpoint of both maximum and minimum levels. LESSON 2 CARBOHYDRATES  The food scientist has a many-sided interest in carbohydrates. He is concerned with their amounts in various foods, availabili

31、ty (nutritional and economic), methods of extraction and analysis, commercial forms and purity, nutritional valve, physiological effects, and functional properties in foods. Understanding their functional properties in processed foods requires not only knowledge of the physical and chemical properti

32、es of isolated carbohydrates, but also knowledge of the reactions and interactions that occur in situs between carbohydrates and other food constituents and the effects of these changes upon food quality and acceptance. This is a tall order for knowledge. Because processing affects both nutritional

33、and esthetic values of food, knowledge of the changes that carbohydrates undergo during milling, cooking, dehydration, freezing, and storage is especially important. Students are advised to study the fundamental chemistry underlying useful carbohydrates properties Of service will be an understanding

34、 of the association of polar molecules through hydrogen bonding, ionic effects, substituent effects, chelation with inorganic ions, complexing with lipids and proteins, and decomposition reaction. This background will provide an understanding of properties that affect the texture and acceptance of p

35、rocessed foods (e.g., solubility, hygroscopicity, diffusion, osmosis, viscosity, plastity, and flavor production), properties that enable the formation or high quality pastries, gels, coatings, confections, and reconstitutable dehydrated and frozen foods. Ability to predict what changes in functiona

36、l properties are likely to ensue from incorporating various types of carbohydrates into processed foods is a practical goal of the food scientist.Such forecasting requires either a wealth of experience with trial-and-error methods or a deep knowledge of carbohydrate properties as related to structur

37、eperhaps both. However, scientific knowledge of cause and effect is highly respected when it shortens industrial development time  Source, Types, and Terminology   The laymans conception of carbohydrates generally involves only the sugars and starches of foodsthose that generate calories a

38、nd fat. The food chemist knows many other types that are ingested. Because most people enjoy the sweetness of sugars and the mouth feel of cooked starches, they become familiar by association with table sugar (sucrose), invert sugars hydrolyzed sucrose, corn syrup sugars (D-glucose and maltose), mil

39、k sugar (lactose), and the more starchy foods. These carbohydrates are nutritionally available; i .e., they are digested (hydrolyzed to component monosaccharides) and utilized by the human body。Carbohydrates of dietary fiber (cellulose, hemicelluse, pentosans, and pectic substances), in contrast, te

40、nd to be overlooked because they are largely unavailable. Digestive enzymes do not hydrolyze them significantly; nevertheless, they may be quite important for human health. The carbohydrates of natural and processed foods are divided into available and unavailable types. The available carbohydrates

41、vary in degrees of absorption and utilization depending upon quantities ingested, accompanying food types, and human differences in complements of defective enzymes and intestinal transport mechanisms. Malabsorption difficulties and adverse physiological effects are known for all the available carbo

42、hydrates but gelatinized starches give little or no trouble. It is important to realize that in ruminants the unavailable and most abundant polysaccharide cellulose is partially hydrolyzed to the same highly available sugar that starch provides upon digestion; i.e. D-glucose. Grazing animals do it t

43、hrough the celluloses generated by the microorganisms of their rumen. Cellulose is, therefore, a contributing source of voluble animal protein. Food chemists probably can improve upon the efficiency and economics of the ruminants conversion of cellulose to nutrients. Development of celluloses that a

44、re stable outside the cells of microorganisms enables the culturing of fungi and with yeasts on cellulose hydrolyzates. Fungi (e.g., mushrooms) can produce protein with the biological value of animal protein. The conversion of cellulose wastes to animal feed and human food is an intriguing prospect

45、for limiting environmental pollution and for feeding the world expending population. Carbohydrates were first named according to their natural sources; e.g., beet sugar, cane sugar, grape sugar, malt sugar, milk sugar, cornstarch, liver glycogen, and sweet corn glycogen. Trivial names were then form

46、ed, in English terminology, often from a prefix related to the source followed by the suffix “-ose” to denote carbohydrate. Names arising in this way, for example, are fructose, maltose, lactose, xylose, and cellulose. These short, well-established names are still commonly used. They furnish no info

47、rmation on the chemical structures however, so a definitive carbohydrate nomenclature has been developed. From the definitive names, structural formulas can be written. Some of the terms involved in the definitive nomenclature are explained in the following paragraphs. The simple sugars (monosacchar

48、ides0 are basically aliphatic polyhydroxy aldehydes and ketones: HOCH2- (CHOH) n-CHO and HOCH2- (CHOOH) n-1-C-O-Ch2OH, called “aldoses” and “ketoses,” respectively. However, it must be understood that cyclic hemiacetals of those open-chain forms prevail I solids and at equilibrium in solutions. In t

49、he definitive nomenclature, the suffix “ose” is appended to prefixes denoting the number of carbon atoms in the nomosaccaride; e.g. trioses (n=1), tetroses (n=2), pentoses (n=3), hexoses (n=4) to distinguish aldoses from ketoses, ketoses are designated as”-uloses.” Thus, the simplest ketose, HOCH2-C

50、:O-CH2OH, is a triulose; the most common ketose, D-fructose (levulose), is a hexlose. To designate the configurations of hydroxyl groups on the asymmetric carbon atoms of monosaccharides, the prefixes D and L are used together with prefixes derived from the trivial sugar names (e.g., D-glycero-, L-a

51、rabino-, D-xylo-) followed by pentose, hexose hexulose, etc. As open-chain hydroxy aldehydes and hydroxyl ketenes, the monosaccharides are very reactive. They readly enolize in alkaline soluions to reduce ions such as Cu2+ and Fe(CN)63-. Therefore, they are called “reducing sugars”. Plants protect t

52、he reactive monosaccharides for transport and storage by condensing them with loss of water, into less reactive sugars, e.g., D-glucose and D-fructose, are condensing in such a way that their reactive functions are lost to form the disaccharide no reducing sugar, sucrose. The less reactive sucrose i

53、s then transported to all parts of the plant for enzymin syntheses of oligo-and polysaccharides. From thousands or more D-glucose moieties of sucrose the glucans, starch and cellulose, are built. From the D-fructose moiety of sucrose, fructans such as inulin are assembled. Other polysaccharides are

54、formed from other sugar, which rose by enzymic transformations of phosphorylated hexoes and sugar nucleotides.The prefix “glyc,” is used in a generic sense to designate sugars and their derivatives; e.g., glycoses, glycosides, glycosans, glyconic glyceric, and glycuronic acids. The generic name for

55、polysaccharides is “glycan”homoglycansare composed of single monosaccharide; for example, the D-glucans, cellulose and starch, release only D-glucose by hydrolysis. Other homoglycans (e.g., the hexcsans, D-galactan and D-manan, and the pentosans, L-arabinan and D-xy-lan) are uncommon in nature. Hete

56、roglycans, composed of two or more different monosaccharides, are widely distributed than the homoglycans that are not glucans. Galactomnnans, glucomammans, arabinogalactans, and arabinoxylans are common diheteroglycans(composed of two sugars).the glycant vail over free glycoses in natural foods. Th

57、e reducing sugars are readily oxidized. mild oxidation of aldoses yields aldonic acids, HOCH2-(CHOH)n-COOH; e.g., gluconic acid(n=4).oxidation of both ends of the aldose molecule yields aldaric acids, HOOC-(CHOH)n-COOH; e.g., tartaric acid(n=2). Oxidation of the terminal CH2OH group of hexoses witho

58、ut oxidation of the reducing function (protected) produces hexuronic acids, HOOC-(CHOH)-CHO. The hexuronic acids are common monosaccharide constituents of many heteroglycans .for example, they are found in acidic hemicelluloses, pectic substances, alginpl and exudate gumes, and the mucopolysaccharid

59、es of mammalian tissues. Penturonic acids have not been found in nature. Reduction of aldoses or ketoses yield sugar alcohols ,properly called alditols,” HOCH2-(CHOH)n-CH2OH.the suffix “-itol “ is applied to the trivial prefixes to denote different alditols; e.g., D-glucitol, D-manniitol, xylitol. The triitol