Pectins Introduction Manufacture. C. D. May, Consultant

Transcription

1 10 Pectins C. D. May, Consultant 10.1 Introduction Commercial pectins used as food additives are hetero-polysaccharides which contain at least 65% by weight of galacturonic acid-based units, which may be present as free acid, methyl ester or, in amidated pectins, acid amide 1 (Fig. 10.1). They form a part of the wider class of pectic substances which are one of the major cell wall polysaccharides in land plants. The commercial materials normally contain added sugar to standardise performance Manufacture Pectins are present in many fruits in variable amounts and qualities. The traditional use of pectin has been as a gelling agent, and this has largely dictated the types of fruit from which commercial grades can be manufactured. A major consideration is the availability of fruit by-products in sufficient quantity and quality. Before the development of a distinct pectin industry it was often the practice for jam makers to make a simple pectin extract from waste fruit material such as apple cores or surplus orange pith, but commercial production demands large quantities of available raw material. The history of the industry up to 1950 is described by Kertesz. 1 Since that date, there has been a geographical shift of the production of pectin, driven to a large extent by difficulties with water supply and more especially effluent disposal in areas such as southern California, so that the major US plants producing citrus pectin, who had come to dominate that market, have been closed down by the companies concerned. The largest pectin plants today are either in Europe or in Latin America, and the expectation is that more of the industry may move to citrus-producing areas in future Raw materials Today the major sources are citrus peel, the residue from the extraction of citrus juice and oil, and apple pomace, the dried residue from the extraction of apple juice. Within the

2 170 Handbook of hydrocolloids Fig Galacturonic acid, ester, and amide units found in pectins. Arrows indicate the potential for degradation by -elimination in the ester form. commercially processed types of citrus, the peel from lemons or limes is preferred for most qualities of pectin, although orange peel is available in much larger quantities, and can be used for many applications. Citrus peel may be washed free from acidity and carefully dried to preserve the pectin quality, or may be processed directly in the wet state. Wet peel processing is particularly appropriate in the case of orange peel, but does require a large and consistent source of peel very near to the pectin plant. Pectin is very susceptible to degradation either by enzymes in the wet peel or by heat during drying and subsequent processing, and such loss of quality must always be controlled as far as possible. Pectin producers devote considerable resources to ensuring both the availability and quality of raw materials, and quality has a major effect on the types of pectin which can be economically produced Production processes Although various alternative processes have been patented in recent years, most pectin is produced by the extraction of the raw material with hot aqueous mineral acid. Each manufacturer has developed conditions which suit the major type of raw material processed in their plant, but the aim is always to produce a slurry which contains solid residue which can be easily separated by the chosen technology, and a liquid phase containing as high a concentration of high molecular weight pectin as possible, without generating excessive viscosity. The liquid extract may be treated to remove impurities, and clarified by removal of particulate matter, before proceeding to isolate a solid pectin. In principle, pure pectin may be isolated in various ways. The most commonly used method is to mix the concentrated extract with an organic solvent in which pectin is insoluble, but which will permit many of the impurities to remain in solution. International food standards permit the use of only methanol, ethanol, or isopropanol as the organic solvent. In this process, the clarified pectin extract is concentrated to about

3 Pectins 171 2% pectin, and mixed with sufficient alcohol to give a precipitate firm enough to be handled with the separation technology chosen by the manufacturer concerned, which may be either filtration or centrifugation. The pectin is separated as completely as possible from the mother liquor, and washed once or several times with further aqueous alcohol to remove salts and other impurities. The washing liquor may include sufficient food grade alkali to adjust the solution ph of the final pectin to the desired range. An alternative method, which is gradually going out of use, is based on the fact that basic aluminium salts form charge-transfer complexes with anionic polymers such as pectin. The aluminium chemistry involved is in fact complex, and involves the formation of polymerised aluminium oxy-ions which interact with the negatively charged pectin molecule, and careful control of all the conditions is required. The presence of excess citrate ion from a citrus raw material competes with the pectin and should be removed by washing the peel before the pectin is extracted. An advantage is that the pectin extract does not require concentration, and if conditions are right the precipitate flocculates and can be separated easily from the large volume of liquor. At this stage the precipitate is a greenish yellow due to the interaction of the aluminium ions with impurities present. The yellow mass can then be pressed to a low moisture content, before being treated with a limited volume of aqueous alcoholic acid which leaches out the aluminium leaving purified pectin. Once the pectin isolated by either process has been separated from as much alcohol as possible, it is dried and ground to a fine powder. The pectin produced in this way will have a varying gelling power depending on the nature and quality of the raw material, and it will make a rapidly-setting gel under traditional jam-making conditions. The variable gel strength can be adjusted by blending one or more batches with sufficient sugar to give a standard performance. Other, more subtle, variations are minimised by selection of initial batches for cross-blending at this stage to ensure consistent performance. This pectin can be sold as such, or further modified to make it suitable for a wide range of applications The chemical nature of pectin Pectins as defined for use in food are high molecular weight heteropolymers containing a majority (at least 65% by weight) of galacturonic acid units. The acid group may be free (or as a simple salt with sodium, potassium, calcium or ammonium) or naturally esterified with methanol. However, pectins are derived from the breakdown of more complex protopectins which are present in the plant tissue, and also contain a range of neutral sugars, including rhamnose, galactose, arabinose and lesser amounts of other sugars. These sugar units are present in a non-random structure, which consists of blocks of differing character retaining fragments of the original plant cell wall structure. The use of purified enzymes has shown that pectin extracted under very mild conditions contains both linear blocks (smooth regions) consisting of homopolygalacturonic acid, and highly branched blocks (hairy regions) which themselves contain several types of structures. Figure 10.2 illustrates the results of studies by the Wageningen group initiated by Prof. Walter Pilnik, and including Voragen, de Vries, Schols, and others. This work was summarised in the Pilnik Lecture delivered by Schols in It is not at present clear exactly how this complex structure and its variations influence the functional performance of commercial pectins, but the practical implications of certain basic aspects of structure are better understood.

4 172 Handbook of hydrocolloids Fig Hypothetical structure of apple pectin showing I xylogalacturonan region, II region with arabinan side chains, III rhamnogalacturonan region making up the hairy region. (From H. Schols et al. Structural Features of Native and Commercially Extracted Pectins, ingums and Stabilisers for the Food Industry 9 ed P. A. Williams and G. O. Phillips, RSC Cambridge, 1998, by permission of the authors.) The regions of the pectin molecule which contain largely galacturonic acid units consist of a mixture of methyl ester, free acid and salt derivatives of the carboxyl group of the acid. Because commercial pectins are extracted under hot acidic conditions, many of the regions containing a high proportion of neutral sugars are hydrolysed, leaving mostly the more acid-stable galacturonate blocks. In certain pectins, such as those from sugar beet and potato, a proportion of the hydroxyl groups will also be acetylated. It has been known for a long time that the properties of pectin are dependent on ph, and on the percentage of acid group present in the form of ester (degree of esterification) Commercial pectin: properties, modification and function The pectin described above is normally from around 67 73% esterified. Apple pectin can, with great care, be extracted with up to 80% esterification. Pectin is readily degraded by a -elimination mechanism at ambient temperature or above at neutral or alkaline ph values. The ester groups can be hydrolysed under either alkaline or acidic conditions, or by pectin esterases. Commercially, acidic treatment is most commonly used, producing pectins with around 60% of ester groups which are slow setting. Under identical conditions of 65% total sugar solids by refractometry and a ph of say 3.1, the gel will take much longer to set. The setting of these gels is both time and temperature dependent,

5 Pectins 173 and the setting temperature depends on the rate of cooling. Slow-setting pectins permit gels to be prepared at higher sugar contents, valuable for sugar confectionery, biscuit jams, and so on. Because of the higher charge density on the slow-set pectin molecules, there is also a change in the ph requirements for gelation towards a lower ph in gels of otherwise similar composition. Further de-esterification to below 50% esterification produces a range of low methoxyl pectins. These show a markedly greater reactivity towards calcium ions, which will cause gelation under suitable conditions of soluble solids and ph. Conditions for effective gelation depend on a balance of several factors, including soluble solids content, ph, calcium and pectin concentrations, and the presence of sequestrants. Amidated pectins (mostly of the low methoxyl type) are produced by reaction of suitable high methoxyl pectins with ammonia. The reaction is normally carried out in an aqueous alcohol slurry of the pectin at ambient or lower temperature. The process requires careful control of the relative rates of de-esterification and amidation, whilst minimising the rate of polymer chain degradation Gelation properties of pectins Because pectin is a charged hydrocolloid, it is sensitive to variations in ph and to a greater or lesser extent to the nature and quantity of cations present in the system. Gelation may be considered as a state between solubility and precipitation of a polymer, and therefore the nature of the solvent is also significant. Gelation of high methoxyl pectins High methoxyl pectins will gel only in the presence of sugars or other co-solutes, and at a sufficiently low ph, so that the acid groups in the polymer are not completely ionised. Both gel strength and setting temperature are influenced by these factors. In a system with sucrose as the sweetener, at around 65% soluble solids, typical of high sugar jams and preserves, high methoxyl pectins gel at up to ph3.4 (rapid set pectin) or 3.2 (slow set pectin). As the ph is reduced, gel strength and setting temperature will increase (Fig. 10.3) up to the point at which the setting temperature approaches the temperature at which the gel is deposited. Below this ph, pectin tends to pre-gel, and the resulting nonhomogeneous gel is weaker and more subject to syneresis. However, if the gel mixture is prepared at higher ph, and acidified immediately before or on depositing, the gel strength is maintained to low ph values. The gelation of high methoxyl pectins is also time-dependent, and setting temperatures will therefore depend on the rate of cooling, being higher with slower cooling. Very rapid cooling under shear can be used to produce a thick heavy texture useful in some industrial applications of fruit products. Changing the nature of the sugars present has a noticeable effect on the performance of pectin. For example, the replacement of a substantial amount of sugar by glucose syrup leads to increased setting temperature with a corresponding increase in the optimum ph for gelation, but some loss in maximum gel strength. Other sugars such as maltose may show a similar effect. Increasing the concentration of sugars increases both setting temperature and optimum ph. In making confectionery jellies, at 75 80% soluble solids, a slow set pectin would be used at a ph of to give a suitable depositing time, enabling a batch to be deposited over minutes or more.

6 174 Handbook of hydrocolloids Fig (a) Variation of gel strength of high methoxyl pectins with ph in a 65% sucrose gel (relative values) (b) Variation of gel setting temperature in the same system. Gelation of low methoxyl pectins The gelation of low methoxyl pectins is governed mainly by the interaction between the pectin and calcium ions. For this reason, the availability of calcium ions is important, and this is commonly governed by sequestrants either naturally present (e.g. citrate and other organic acid ions from fruit or milk) or added (commonly food grade di- or polyphosphates). Reactivity to calcium is governed by the proportion and arrangement of carboxyl groups in the pectin chain. Reactivity increases with decreasing degree of esterification, and is greater but less controllable if the arrangement of acid groups is Fig Variation of relative gel strength of low methoxyl pectin gels (conventional and amidated) with added calcium at 30% added sucrose and ph 3.0 with a citric acid/sodium citrate buffer system.

7 Pectins 175 Fig The range of commercial non-amidated pectins with some typical applications. less random, with blocks of de-esterified galacturonate units. Amide groups have a moderating influence, and permit gelation over a wider range of calcium concentrations (Fig. 10.4). Gelation is favoured by increased soluble solids, but decreased by increasing ph, or by increasing the level of sequestrant. However, a certain level of a sequestrant such as citrate is essential to produce a practically workable gel system. With correct formulation, low methoxyl pectins can gel over a wide range of soluble solids (10 80%), and in either acidic or less acid-tasting products, at a ph of 3.0 to above Availability of pectin types Pectin manufacturers generally offer a wide range of pectin types for different applications (Fig. 10.5) Nutritional and safety aspects Manufacturers will provide detailed nutrition data for labelling purposes on request. Pure pectin is essentially a soluble dietary fibre, but the commercial product will contain limited amounts of protein, sodium and calcium, and sugar or dextrose for standardisation. The amount of carbohydrate to be declared in nutrition labelling depends on national legislation, as soluble fibre may be either included, or totally excluded. This also affects the declaration of energy value. Pectins may contain 1 2% of protein, but if legislation requires that protein is declared as N 6.25 (or other factor) it is arguable whether the amide nitrogen should be included in the calculation. The levels of most other nutrients are not significant when the use level of pectin in the final product is considered, except in the case of blends with, e.g., sodium, potassium or calcium salts.

8 176 Handbook of hydrocolloids If fibre is to be declared, the figure will depend on the analytical method accepted locally. Where the AOAC method is specified, the content of pure pectin, after deducting moisture and ash contents, can be taken as fibre. The Englyst method gives lower results, typically around 65% of the AOAC value Health and safety characteristics Pectin is a fine organic powder, and like flour, starch, and similar carbohydrate materials, has the potential to cause a dust explosion. It is therefore important to observe good housekeeping practices such as collecting up spilled material, and minimising dusting by careful handling. A lesser but more common hazard is spillage of pectin solution or of powder pectin onto a wet floor, creating the risk of slips and falls. Pectin is not a particular environmental hazard, but does have a significant BOD, and large spillages should be contained and disposed of carefully. Pectin is a component of the normal diet, and an approved food additive, and ingestion of pectin at reasonable levels is safe. As with any water-soluble gum, it is inadvisable to consume large amounts of dry pectin which could swell and possibly risk obstruction of the gullet Uses and applications In all pectin applications, the action of the pectin is very dependent on the exact conditions in the product, ph, ionic strength and composition, the proportion of sweeteners and their nature, and, where fruit is present, the amount and nature of the pectin provided by the fruit. It is therefore always wise to test any change in formulation, including a new season or source of fruit, on a small (saucepan) scale before embarking on full-scale manufacture Dissolving pectin In most pectin applications it is essential to ensure that the pectin is dissolved before gelling conditions are reached. Pectin will not dissolve when near gelling conditions, and high methoxyl pectins in particular will not dissolve in sugar solutions of more than 20 25%. As with most gums, it is vital to disperse the solid particles before they partially dissolve and stick together. This may be achieved either with a high shear mixing system (batch or in line) or by mixing the pectin with several times its weight of sugar, and stirring vigorously. Occasionally, the pectin may be dispersed in a sugar syrup and the mixture diluted with stirring to achieve a similar result Optimising pectin formulations Pectin formulations will typically require adjusting to particular production conditions. The factors described above which influence gelation must always be kept in mind. In most practical situations, the soluble solids level and fruit content (if any) are established as part of a product brief, and cannot be modified. There is always an optimum set of conditions between lack of set on the one hand and pre-gelation on the other, but it is possible to mistake some pre-gel conditions for lack of set because processing may result

9 Pectins 177 in a smooth syrup rather than a broken gel. If a gel is not obtained, and neither lowering the ph nor increasing the pectin content causes gelation to occur, this should be suspected, especially if the pectin level is already high. If small changes in pectin content or ph do not result in improved performance, changing the pectin for a slightly different type should be considered. If this is not effective, it is wise to consult the pectin supplier who should be able to advise, and will treat detailed information in confidence if requested. There are many different pectin types, and selection for a particular application requires considerable experience High sugar jams and preserves The earliest application for pectin was in fruit jams with 60 70% total soluble solids and a ph in the range For this application, a high methoxyl pectin can be used. The composition of jams is often closely regulated, and the relevant regulations should be checked. In Europe, there are also specific labelling requirements in addition to the general Food Labelling Regulations. Depending on the nature of the fruit, the fruit content, and the desired soluble solids content, differing amounts and types of pectin will be required. Table 10.1 gives an indication of the proportion of pectin required for a jam at around 65% total soluble solids as measured by refractometer. The type of pectin will be determined by the type of product and the process to be used. Jams made by the traditional open pan cooking method will require a rapid setting pectin, whilst those made by vacuum cooking at a lower temperature require a slower setting pectin to avoid pre-setting. Clear jellies are usually made with a slow or extra slow set pectin, to allow any small bubbles of air to rise before the gel sets in the final container. If there is a problem with floating fruit, it may be useful to use a proportion of low methoxyl pectin to increase hot viscosity. A typical traditional jam recipe is given in Formulation The recipe for orange marmalade in Formulation 10.2 illustrates the use of a mixture of high and low methoxyl pectins to prevent fruit floating and give a soft, spreadable, texture. Table 10.1 Typical pectin requirement for traditional jam at 65% soluble solids Fruit content % Fruit type Low pectin e.g. strawberry, peach, % % % raspberry, pineapple Medium pectin e.g. apricot, blackberry, % % % marmalade High pectin e.g. apple, damson, gooseberry, % % % plum, quince, redcurrant

10 178 Handbook of hydrocolloids Formulation 10.1 Traditional raspberry jam A Rapid set pectin 2.2 Sucrose 10 B Water 50 C Raspberries 450 Sucrose 610 Water 50 ph (50% solution at 20ºC) Soluble solids (approximately) 67% 1. Dry mix ingredients A and dissolve in water B, using a suitable high shear/speed mixer. 2. Heat ingredients C to the boil while stirring. 3. Add the pectin solution and boil down to 1015g. 4. Cool to 85ºC and deposit into jars. Note: The ph should be maintained in the range Depending on the type of fruit it may be necessary to add a dilute solution of citric acid. If this is required it should be added slowly with vigorous mixing at the end of the boiling process to avoid pre-gelation. Formulation 10.2 Soft set orange marmalade A Rapid set pectin 1.0 Low methoxyl pectin 0.5 Sucrose 10 B Water 100 C Orange pulp and peel 200 Sucrose 640 Water 150 D Citric acid monohydrate (50% weight/vol.) 1.5 ml ph (50% solution at 20ºC) Soluble solids (approximately) 67% 1. Dry mix ingredients A and dissolve in water B, using a suitable high shear/speed mixer. 2. Heat ingredients C to the boil while stirring. 3. Add the pectin solution and boil down to 1015g. 4. While stirring add ingredients D, cool to 85ºC and deposit into jars Low sugar jams and jellies Low sugar jams and jellies cannot be made with high methoxyl pectins, and are usually best prepared with amidated low methoxyl pectins. However, in Europe, only nonamidated pectins may be used if an organic claim is to be made for the product. With

11 Pectins 179 Formulation 10.3 Reduced sugar strawberry jam A Amidated pectin, medium set 6 Sucrose 30 B Water 250 C Strawberries 550 Sucrose 325 D Citric acid monohydrate (50% w/v) 4 ml E Potassium sorbate (20% w/v) 5 ml ph (as is at 20ºC) Soluble solids (approximately) 43% 1. Dry mix ingredients A and dissolve in water B using a suitable high shear/speed mixer. 2. Gently heat ingredients C to the boil. Add the pectin solution and boil down to 1020g. 3. With stirring add the citric acid D, followed by the potassium sorbate E. 4. Cool to 85ºC and deposit. low sugar products, it is particularly important to use good quality fruit in generous quantity to provide an acceptable product. The type of pectin used should be matched to the product, and, in general, lower solids require the use of a high reactivity or fast setting low methoxyl pectin. The recipe in Formulation 10.3 illustrates a typical middle of the road reduced sugar jam. Local regulations and requirements will dictate the preservative to be used, if any Industrial fruit products This heading covers a varied and expanding range of products, from traditional bakery and biscuit jams to a range of fruit bases and toppings many of which have to be tailored to a specific end use. For example, fruit bases prepared specifically for fruit yoghurts need to be easy to handle in bulk without fruit separation, but may either be required to mix with the yoghurt, or to be deposited as a separate layer without forming a skin at the interface. In some cases there may be a requirement for the pectin to add extra body to the finished mixed yoghurt Bakery products For bakery jams various special properties may be required, but bake stability is one of the common requirements. For example, in open jam tarts baked with the filling, the jam must flow to give a smooth glossy surface but must not boil out of the pastry case. In such a complex field it is not possible to give more than a few typical recipes, and pectin manufacturers expect to provide technical assistance in formulating recipes for specific requirements. The following recipes (Formulations ) provide a few illustrations of the many possibilities for pectins in this area.

12 180 Handbook of hydrocolloids Formulation 10.4 Bake resistant jam A Medium rapid set pectin 5 Sucrose 20 B Water 230 C Strawberries DE glucose syrup 250 (82% soluble solids) Sucrose 340 D Citric acid monohydrate 1 ml (50% weight/volume) ph (50% solution at 20ºC) Soluble solids (approximately) 60% 1. Dry mix ingredients A and dissolve in water B using a suitable high shear/speed mixer. 2. Heat ingredients C to the boil, add the pectin solution and return to the boil and boil down to 1020g while stirring. 3. Add the citric acid D, while stirring. 4. Cool with gentle stirring to 70ºC and deposit as required. Note: A bakery jam that will withstand baking and is suitable as a pie or tart filling, can be produced using medium rapid set pectin. Formulation 10.5 Heat-reversible biscuit or wafer filling A Phosphate-buffered amidated pectin 17 Sucrose 50 B Water (70ºC) 350 Citric acid monohydrate 1.3 C Sucrose DE glucose syrup (82% soluble solids) 535 D Colour and flavour As required ph (50% solution at 20ºC) Soluble solids (approximately) 84% 1. Dry mix ingredients A and dissolve in hot water B using a suitable high shear/speed mixer. 2. Heat the pectin solution and ingredients C to the boil and boil down to 1020g. 3. Add colour and flavour if required. 4. Cool to 70ºC. Depending on the type of equipment used, spread the filling between 60 70ºC. Note: This filling may be packed into suitable containers and melted as required by heating to 70 75ºC.

13 Pectins 181 Formulation 10.6 Flan glazing jelly (without fruit pulp) A Phosphate-buffered amidated pectin 15 Sucrose 50 B Water (70ºC) 350 C Water 50 Citric acid monohydrate (50% weight/volume) 4.5 ml Sucrose DE glucose syrup (82% soluble solids) 200 D Colour and flavour As required ph (on 50% solution) Soluble solids (approximately) 63% Setting temperature (approximately) 40ºC 1. Dry mix ingredients A and dissolve in water B, using a suitable high shear/speed mixer. 2. Heat together ingredients C and boil down to 75 76% soluble solids (refractometer). 3. Stirring thoroughly, pour the hot pectin solution into the boiling batch. 4. Boil down to 1010g and remove from heat. 5. Stirring slowly, cool to 65 70ºC, and add required colour and flavour. 6. Fill into containers and cool to at least 40 45ºC. If the glaze is to be used in an undiluted form, gently mash and liquefy the glaze by heating to 95ºC. The glaze may then be applied at any temperature down to 60ºC. If the glaze is to be used in a dilute form, gently mash the glaze with up to 60% water and heat to 95ºC. The diluted glaze may then be applied at any temperature down to 30ºC. Any unused glaze can be kept and melted back when required without any loss in quality. In contrast to the non-melting behaviour of the recipe in Formulation 10.4, it is equally possible to use a pectin system to make fully themally reversible gels at a range of soluble solids levels, as in Formulation 10.6 for a glazing jelly based on an amidated pectin combined with phosphate salts which control both the availability of calcium and the ph of the gel. The use of pectin in bakery applications is not restricted to high sugar products, and the recipe (Formulation 10.7) for a bakery pie filling illustrates how resistance to baking can be maintained down to only 30% soluble solids Fruit bases The requirements for pumpability and absence of fruit separation require a degree of restructuring after shear, usually best provided by an (amidated) low methoxyl pectin. The exact properties of these bases need to be tailored to the equipment and systems in use by both the fruit processor and the end user, as well as those demanded by the final

14 182 Handbook of hydrocolloids Formulation 10.7 Apple pie filling A Pectin type Sucrose 40 B Water (70ºC) 250 C Diced apple 500 Sucrose 200 D Calcium lactate pentahydrate 1.5 Water (100ºC) 50 ph (as is at 20ºC) Soluble solids (approximately) 30% 1. Dry mix ingredients A and dissolve in hot water B using a suitable high shear/speed mixer. To aid dissolving place the mixer so as to obtain maximum turbulence. Gradually add the dry mix ensuring addition is complete before thickening slows agitation. 2. Heat the pectin solution, add ingredients C and bring to the boil. 3. Prepare the hot calcium lactate solution and add to the boiling mix while stirring continuously. 4. Reduce to 1010g, remove from the heat and cool to 85ºC and deposit as required. Formulation 10.8 Low sugar fruit base A Pectin (low methoxyl or amidated) 9 Sucrose 40 B Water 300 C Strawberries 500 Sucrose 210 Water 70 Citric acid monohydrate (50% weight/volume) As required Sodium citrate dihydrate (20% weight/volume) As required ph (as is at 20ºC) Soluble solids (approximately) 31% Filling temperature (approximately) 30ºC 1. Dry mix ingredients A and dissolve in hot water B using a suitable high shear/speed mixer. 2. Weigh ingredients C and the pectin solution into a pan and heat to 90ºC. 3. Maintain temperature at 90ºC for 10 minutes to pasteurise, or heat until the batch weight has been reduced to 1020g. 4. Cool the fruit preparation while stirring to 30ºC to obtain a thickened rather than a gelled texture. This may be achieved by in line cooling under shear.

15 Pectins 183 product, and recipes can only be a guide to what is possible fruit contents, soluble solids levels, and flow properties can be adjusted to meet a wide range of requirements but in some cases a custom blend of pectin with other additives may be required. This may contain a pectin, one or more phosphate sequestrants, and a calcium source such as a calcium orthophosphate. In order to obtain the correct characteristics, a number of factors can be adjusted. The amount of total citrate will control both the acid taste and the binding of the calcium ion present. An increase will increase the perceived acidity, but reduce the body of the base. The ph can be adjusted by altering the balance of these ingredients. If the base is too liquid, either a faster setting, more reactive, pectin can be used, or calcium can be added as a dilute solution of calcium chloride or lactate to the finished product before cooling. Various modifications to the formulation are possible to produce a base for layer desserts or to add extra thickness to a mixed fruit yoghurt (post-dosage thickening) by interaction between the pectin from the fruit base and the calcium in the yoghurt. Similar formulations may be used as toppings for gateaux and cheesecakes, including also caramel, butterscotch and other non-acid flavours Dairy products Pectin can have two distinct functions in dairy products and dairy analogues such as those prepared from soya. High methoxyl pectins can act as protein dispersion stabilisers at reduced ph as in yoghurt or milk/fruit juice drinks. Low methoxyl pectins behave quite differently, and can gel either milk or more acid products by interaction with calcium. Acid milk stabilisation Pectin is an effective protective colloid for casein particles at a ph of , typical of yoghurt. It is important to homogenise the yoghurt to break up protein aggregates in the presence of the pectin, before heat treatment is carried out. The amount of pectin required will be a function of the amount of homogenisation carried out, and this will also affect the product viscosity. Surplus pectin over the amount required for stabilisation of the dispersion will increase the viscosity of the final product, which may or may not be desirable. Typically, about 0.4% of a specially selected and standardised pectin will be added either as a solution or dispersed in sugar or a syrup, and the product then homogenised. Heat treatment may, in some cases, be followed by further homogenisation, often at a lower pressure, to ensure maximum stability. The resulting drink is free from chalkiness and sedimentation. Similar advantages are possible for blends of milk and fruit juices, enabling a milkbased fruit drink with a true fruit flavour and acidity. Either liquid milk or milk powder can be used, as in Formulation The principle can be extended to carbonated milk drinks, and other products, including drinks based on whey, which can be stabilised against precipitation of the soluble whey proteins. Milk gels and desserts Low methoxyl amidated pectins can be used to gel milk by directly dispersing pectin powder, preferably mixed with several times its weight of sugar, in cold milk, and heating with stirring to boiling to dissolve the pectin. The amount of pectin required will be from

16 184 Handbook of hydrocolloids Formulation 10.9 Milk/fruit juice drink A Pectin (dairy stabiliser grade) 4 Sucrose 10 B Water 152 C Skim milk powder 25 Sucrose 80 D Water 615 E Fruit Juice 100 Sucrose 10 Citric acid monohydrate (50% w/v) 4 ml ph (as is at 20ºC) Soluble solids (approximately) 15% 1. Dry mix ingredients A and dissolve in water B using a suitable high shear/speed mixer. 2. Dry mix ingredients C and dissolve in water D. 3. Mix the pectin solution into the milk solution for 2 3 minutes using a suitable high shear/speed mixer. 4. With continuous mixing add ingredients E, and continue mixing for a further minute. Homogenise as required. 5. Pasteurise as necessary. Note: The ph must be in the range to obtain stability to heat treatment, outside this range the stability will not be as great and more pectin will be required. The ph can be adjusted by altering the level of fruit juice or by adding a dilute solution of acid or citrate as required %, and the texture of the gel can range from firm and brittle to very soft and creamy, depending on the pectin type chosen. It is also possible to formulate a fruit syrup which, on adding to cold milk, will produce a lightly gelled fruit dessert (Formulation 10.10) Other dessert products Pectin gels can be used as an alternative to gelatine in fruit desserts and trifles (Formulation 10.11). Pectin gels can be deposited and set very rapidly so that other components such as sponge or cream can be added after a short cooling stage, enabling the complete dessert to be assembled on line. They give an attractive light texture with excellent flavour release. Whipped cream or protein whipping agents can be added to produce mousse-type products (Formulation 10.12) Sugar confectionery Pectin confectionery jellies can be divided into two types: tender, fruity jellies made with high methoxyl pectin (Formulation 10.13), and elastic jellies based on low methoxyl

17 Pectins 185 Formulation Syrup for milk dessert A Amidated pectin 15 Sucrose 80 B Water 400 C Raspberries 200 Water 300 Citric acid monohydrate (50% w/v) 4 ml Sodium citrate dihydrate (20% w/v) 20 ml Sucrose 80 ph (as is at 20ºC) Soluble solids (approximately) 20% 1. Dry mix ingredients A and dissolve in water B using a suitable high shear/speed mixer. To aid dissolving, place the mixer so as to obtain maximum turbulence. Gradually add the dry mix ensuring addition is complete before thickening slows agitation. 2. Warm ingredients C, add the pectin solution and heat to the boil while stirring. 3. Boil down to 1020g, remove from the heat, cool and deposit. 4. To prepare the dessert, take equal parts of fruit syrup and milk. Mix the milk into the fruit syrup for seconds. The dessert may be eaten within 5 minutes of preparation or may be stored in the fridge until required. Note: It may be necessary to adjust the amount of citric acid or sodium citrate used. Formulation Water-based dessert jelly A Pectin type Sucrose 40 B Water 600 Citric acid monohydrate 2.5 C Sucrose 240 D Water (100ºC) 200 Calcium lactate pentahydrate 1.8 E Colour and flavour As required ph (as is at 20ºC) Soluble solids (approximately) 30% 1. Dry mix ingredients A and dissolve in water B using a suitable high shear/speed mixer. 2. Heat the pectin solution to the boil and add the sucrose C.

18 186 Handbook of hydrocolloids 3. Pre-dissolve the calcium lactate in the hot water D, and stir into the pectin solution, while maintaining a full rolling boil. 4. Boil down to 1020g and remove from the heat and stir in ingredients E. 5. Deposit as required. Notes 1. The texture of the jelly can be altered by changing the pectin/calcium ratio, i.e. a high pectin to a low calcium level will result in an elastic gel, whereas if more calcium is added the resultant gel will become more brittle. 2. It is important to add the calcium lactate as a hot dilute solution and with efficient agitation to avoid the formation of jelly lumps (fisheyes). Formulation Chocolate mousse Chocolate base A Pectin type Sucrose 50 B Water (70ºC) 330 C Cocoa powder (5% lecithin) 20 Sucrose 100 Cream base D Double cream (47% fat) 500 ph (as is at 20ºC) Soluble solids (approximately) 15% 1. Dry mix ingredients A and dissolve in water B using a suitable high shear/speed mixer. 2. Add ingredients C to the pectin solution with efficient mixing, and continue mixing until the sucrose has dissolved. 3. Whip the cream D until aerated and firm, or the desired over run. 4. Gently mix the cream and chocolate syrup together until homogenous and deposit as required. pectins blended with sequestering phosphate buffers, suitable for traditional turkish delight flavours, and also mint and other non-acid flavours (Formulation 10.14). The latter approach can also be used to add structure and thixotropy to caramel and similar fillings. It is essential to include a proportion of glucose syrup to prevent crystallisation of the sugar Other food applications Many of the above formulations may be adapted to produce condiment jellies, glazes and marinades for chilled and frozen recipe dishes, and for other similar uses. Pectin/sugar solutions can be used to coat confectionery items, either chocolate or sugar coated, by standard panning techniques.

19 Pectins 187 Formulation Fruit-flavoured confectionery jelly A Pectin (Slow set) 8.8 Sucrose 40 B Water (70ºC) 325 Citric acid monohydrate (50% weight/volume) 2.8 ml Potassium citrate monohydrate (40% weight/volume) 6.25 ml C Sucrose DE glucose syrup (82% soluble solids) 300 D Citric acid monohydrate (50% weight/volume) 6 ml E Colour and flavour As required ph (50% solution at 20ºC) Soluble solids (approximately) 78% 1. Dry mix ingredients A and dissolve in hot ingredients B using a suitable high shear/speed mixer. 2. Bring the pectin solution to the boil and add ingredients C (the sucrose followed by the glucose syrup). 3. Boil rapidly to 1020g, and thoroughly mix in the citric acid D. 4. Remove from the heat, mix in the colour and flavour and deposit into moulds. Depositing must be completed before the batch begins to set if it is held at 90ºC within 20 minutes of adding the acid. Formulation Turkish delight jelly A Phosphate-buffered amidated pectin 20 Sucrose 60 B Water (70ºC) 300 Citric acid monohydrate (50% weight/volume) 0.5 ml C 42DE glucose syrup (82% soluble solids) 300 D Sucrose 440 E Colour and flavour As required ph (10% solution at 20ºC) Soluble solids (approximately) 76%

20 188 Handbook of hydrocolloids 1. Dry mix ingredients A and dissolve in ingredients B using a suitable high shear/speed mixer. 2. Heat the pectin solution to the boil. 3. Add the glucose syrup C and return to the boil, followed by the sucrose D. Continue boiling until the weight has been reduced to 1020g. Add colour and flavour, if required, and pour into moulds. Notes: This formulation will set at about 50ºC. Slight reformulation will reduce the setting temperature sufficiently to permit depositing into pre-formed chocolate shells at around 30ºC. It may also be used for other non-acid flavours Legal status Pectin is generally regarded as one of the safest and most acceptable of food additives, and this is recognised by Acceptable Daily Intake (ADI) levels of not specified by both the Joint Food Experts Committee (JECFA) for Codex Alimentarius purposes, and the Scientific Committee for Food (SCF) in the European Union, and by Generally Regarded as Safe (GRAS) status in United States legislation. Similar status has been awarded in most other jurisdictions. In general, there are few restrictions on the use of pectin in most foods, but most authorities prescribe restricted lists or the absence of food additives in a limited number of basic food categories, and pectin may or may not be listed in these cases. The Codex and US specifications include both amidated and non-amidated pectins. In the EU, there are separate specifications for E440(ii) and E440(i) respectively, but permitted uses are similar except in organic foods, where only E440(i), non-amidated pectin, is permitted References 1. KERTESZ, Z. I. (1951) The Pectic Substances, New York, Interscience Publishers Inc. 2. SCHOLS, H. A., ROS, J. M., DASS, P. J. H., BAKX, E. J. and VORAGEN, A. G. J. (1998) Structural Features of Native and Commercially Extrcated Pectins, Gums and Stabilisers for the Food Industry 9, Wrexham, The Royal Society of Chemistry.