An introduction to pectin

UNDERSTANDING YOUR FOOD<br /> the ultimate educational resource<br /> TEACHER NOTES<br /> <br /> teachers’ notes G2.1<br /> KS4<br /> science and food technology<br /> Timing- an extension exercise with<br /> some revision points; suitable as a<br /> homework<br /> Two pupil activity sheets G2<br /> accompany this activity.<br /> G2. An introduction to pectin<br /> Answers to questions on Pupil activity sheet G2:<br /> Some can be found in the text, others require research.<br /> 1. poly = many, saccharide = sugar units; a polysaccharide is a long<br /> chain carbohydrate, i.e. it consists of many sugar units joined<br /> together. Other well known plant polysaccharides are cellulose and<br /> starch.<br /> 2.<br /> Cell wall (cellulose)<br /> Middle lamella<br /> Distillation- a method of separating a mixture of liquids with different<br /> boiling points; liquids within boiling ranges are collected separately; the<br /> mixture is heated to a specific temperature so that one of the liquids<br /> boils and changes to a vapour/gas; the gas is then cooled so that it<br /> condenses, returns to a liquid and can be collected.<br /> Precipitation- exemplified by the mixing of two solutions so that a<br /> reaction takes place which produces an insoluble substance which<br /> will sink to the bottom of the reaction vessel.<br /> 7. ‘Commercially viable’ - capable of producing an actual, useful,<br /> practicable product at a profit<br /> 8. Small quantities of other fruits, such as blackcurrants, can be<br /> added to supplement the pectin (and acid) present in the<br /> 3. Cellulose<br /> 4. As fruit ripens, enzymes begin to break down the pectin; less pectin will<br /> result in a poorer set to the jam. Jam made from very ripe fruit will be<br /> difficult to set.<br /> 5. This will vary; an example is included on a separate sheet.<br /> 6.Filtration- the separation of insoluble/suspended solids from a<br /> solvent/liquid/solution by means of some sort of ‘sieve’, e.g. filter paper,<br /> strainer.<br /> Evaporation- heating a solution/liquid to remove some or all of the<br /> solvent/water by turning it into a vapour/gas so as to leave a more<br /> concentrated solution or a solid.<br /> <br /> teachers’ notes G2.2<br /> The production of pectin<br /> Fresh or dried peel<br /> 9. Powdered pectin is extremely difficult to dissolve in ordinary<br /> circumstances (last paragraph). If powdered pectin is available this<br /> could be demonstrated. It would be virtually impossible to successfully<br /> use the lumpy, very viscous mass that is produced. Pectin is very<br /> hydrophilicand is therefore water soluble but its affinity for water<br /> means that unless high speed mixing (high shear mixing) and increased<br /> temperatures are used it is difficult for it to fully hydrate without the<br /> formation of lumps.<br /> washed<br /> placed in extraction tanks<br /> 10. Pectin in a liquid state has had a quantity of water added to it. This<br /> greatly increases its mass and bulk compared to the powdered pectin<br /> alone. In the quantities used by industry this would increase<br /> transportation, storage and handling costs. This is particularly<br /> important when considering goods which are to be exported.<br /> There are other less obvious reasons as to why pectin, as a powder, is<br /> used in industry. Many more types of pectin can be produced in<br /> powdered form. Different products require pectin with different properties.<br /> For example, jams with large pieces of solid require a very quick setting<br /> pectin to ensure that the fruit pieces do not all sink to the bottom before<br /> the jam has set. Other products, which may be needed to be packed in<br /> very large quantities, require a slower set to prevent the jam setting<br /> whilst still in the machinery.<br /> The quality of performance for an industrial operation is much better<br /> when using powder rather than a liquid.<br /> Less powder needs to be used compared to liquid.<br /> Since the powdered form contains no water there is no need to preserve<br /> it in any other way.<br /> pectin dissolves in<br /> acidic solution<br /> filtration<br /> pectin<br /> solution<br /> filter again<br /> evaporation<br /> peel<br /> sold<br /> as<br /> cattle<br /> feed<br /> alcohol<br /> concentrated<br /> pectin<br /> methylated<br /> pectin<br /> precipitation<br /> dried<br /> distillation<br /> removes<br /> alcohol<br /> ground<br /> powdered<br /> pectin<br /> <br /> AN INTRODUCTION TO PECTIN pupil activity G2<br /> Pectin is used to produce a wide range of preserves, jams, jellies and spreads, that is<br /> those sweet, fruit products which need to set. Some of these products are made in<br /> the home as well as on a commercial basis.<br /> Pectin is not a single substance. The word describes a group ofpolysaccharides<br /> which are present in the cell walls, particularly near the middle lamella, of most land<br /> plants. In the intact plant, pectin is a very large molecule and is not soluble in water.<br /> Although its distribution among plants is widespread, there are only a few commercially<br /> viable sources from which pectin can be extracted. These are from thepeel of citrus<br /> fruits and apple pomace (this is a pulpy residue from apples which havebeen pressed<br /> for cider making). Both of these sources are leftovers from the fruit juiceindustry.<br /> Ripe fruit is used in the fruit juice industry. However, when ripening begins, enzymes in<br /> the fruit begin to break down pectin and it becomes soluble. This process decreases<br /> the quantity and quality of pectin obtainable from the fruit. Therefore, it is important<br /> for the pectin manufacturer to process the fruit obtained from the fruit juice industry as<br /> quickly as possible.<br /> Like all natural materials, the molecules of pectin, within the same plant and between<br /> different plants, vary considerably. The major constituent of pectin isgalacturonic<br /> acid.<br /> Acid group{<br /> OH<br /> C=O<br /> OH<br /> H<br /> H<br /> OH<br /> O<br /> H<br /> H<br /> OH<br /> galacturonic acid<br /> H OH<br /> Several hundred of these units are linked together to form a long chained molecule of<br /> polygalacturonicacid. A certain number of the acid groups, –COOH, are<br /> methylated, i.e. contain a methyl group, –CH<br /> 3. It is the number of these methyl<br /> groups which strongly influences the performance of the pectin in practical situations.<br /> The production of pectin<br /> Fresh or dried fruit peel is washed with water. It is then put into a series of extraction<br /> tanks. The conditions inside the tanks are carefully controlled with respect to acidity<br /> and temperature. The peel softens and swells due to the break down of the cell walls.<br /> The pectin is released and dissolves into the acidic solution. The peel is separatedfrom<br /> the pectin extract by filtration. It is washed and sold as cattle feed.<br /> The solution of pectin is filtered again in a special way to make a clearer solution. Some<br /> of the liquid is then evaporated so that the product is more concentrated. Toproduce<br /> a pectin with many methyl groups attached, the pectin liquid passes into the<br /> precipitation stage. In this, the pectin extract is mixed with alcohol. Pectin is insolublein<br /> alcohol and so is precipitated. The alcohol is then recovered by distillation.Following<br /> precipitation, the pectin is dried and then ground or milled to a powder before the final<br /> stage of blending.<br /> <br /> pupil activity G2 AN INTRODUCTION TO PECTIN<br /> The use of pectin<br /> Long before the development of chemical preservatives and the invention of the<br /> refrigerator, we had been using high concentrations of sugar to improve the keeping<br /> qualities of seasonal fruits. The boiling of fruit with added sugar forms the basis of all<br /> commercial jam making. This type of industry can be found in nearly every country in<br /> the world.<br /> Home-made jam and marmalade making is still quite popular despite the readily<br /> available products from the supermarket shelves. As any home jam maker will tell<br /> you, it is easier to make jams and marmalades from fruits such as blackcurrants,<br /> damsons, gooseberries, plums, lemons and bitter oranges than it is from cherries,<br /> pears, peaches or strawberries. This is because the former contain large amounts of<br /> pectin and the conditions inside the fruit are acidic. Both of these are important<br /> factors in the production of a set. Liquid pectin, which can be bought from shops<br /> and supermarkets, can be used to assist in jam making, particularly when using the<br /> latter fruits.<br /> In large scale commercial jam making, pectin is used in addition to the pectinalready<br /> present in the fruit. The manufacturer is able to manipulate the production conditions<br /> so that a huge variety of different preserves can be made according tofruit type,<br /> desired set strength, quantity of product, quantity of sugar, type of sugar and many<br /> other factors. Most of the pectin used commercially is in the form of a powder rather<br /> than a liquid.<br /> It is extremely difficult, using ordinary methods, to dissolve powdered pectin in water.<br /> Industry makes use of high speed mixers and raised temperatures in order to dissolve<br /> it. A powder form is preferable in industry where very large quantities of pectin are<br /> used.<br /> Questions<br /> 1.What is meant by a polysaccharide? Name two other polysaccharides, apart<br /> from pectin, that are found in plants.<br /> 2.Draw a diagram of three or four simple plant cells to show the position of the cell<br /> wall and the middle lamella.<br /> 3.What material makes up the greatest proportion of plant cell walls?<br /> 4.Jam recipes always advise that fruit to be used in jam making should be only just<br /> ripe. Use the information in the third paragraph to explain this.<br /> 5.Using the information in ‘The production of pectin’ section, draw a flow chartwhich<br /> shows the stages in pectin production.<br /> 6.Explain the scientific processes of filtration, evaporation, distillation and<br /> precipitation.<br /> 7.Explain what is meant by ‘commercially viable’.<br /> 8. Liquid pectin is readily available in shops so that making a jam such as strawberry<br /> at home now presents few problems. How else can a strawberry jam be<br /> produced without the use of liquid pectin?<br /> 9.Why would powdered pectin be unsuitable to use in home jam making?<br /> 10.Industry uses large quantities of powdered pectin. Suggest some reasons why<br /> industry does not use liquid pectin.