Field of the Invention

This invention relates to a pectinaceous gelling agent which has good gelling properties, to a process for its production, and to foodstuffs containing it.

Background to the Invention

Pectins are commonly used as gelling agents in foodstuffs. Gels are tri- dimensional networks formed by the gelling agent and that contain a liquid phase. Pectin gels are formed by hydrated pectins, after physical or chemical changes that decrease the solubility of the pectins. Pectins are found in nature in the middle lamella and primary cell walls of plant tissue. They are primarily straight-chained polymers of D-galacturonic acid in which the D-galacturonic acid units are linked by l->4 glycosidic linkages. Neutral sugars such as galactose, glucose, rhamnose, arabinose and xylose may also be present; usually in the range of 5 to 10% by weight of the galacturonic acid. The rhamnose is often in the polymer as an interruption of the polygalacturonate sequences. The other sugars are usually found as side chains or as contaminating polysaccharides.

The functional group at the sixth carbon of each galacturonic acid unit may exist as a methyl ester or as a free carbonyl group. Two types of pectins are commonly distinguished on the basis of the extent of esterification of this functional group. One type is low methoxy pectins which have a degree of esterification (DE) of less than 50%; that is less than 50% of the total number of functional groups exist in the methyl ester form. The other type is high methoxy pectins which have a degree of esterification (DE) of greater than 50%. High methoxy pectins form gels in an acidic environment and in the presence of sucrose. Low methoxy pectins form gels in the presence of alkaline earth metals; especially calcium. In the gels, the galacturonic acid units making up the polymer chain are cross-linked by divalent calcium ions. However, in both cases, gelation and the properties of the gel however depend upon many factors including pH, temperature, the degree of esterification, molecular weight, sugar content, calcium content and pectin content.

The main sources of commercial pectin products are citrus peels and apple pomace. Lemon and orange peels are one of the riches sources. However, many vegetable materials which form wastes and by products contain pectin. Therefore there has been some interest in using these vegetable materials as commercial sources of pectin. For example, Sosulski, F et al; 1980; Przemysl Fermentacyjny i Owocowo-Warzywny. 24(3), 19-21 describe a process for the purification of pectin from sunflower stalks and flowers. Also, sugar beet pulp has been identified as a possible source of pectin since it contains about 20% by weight of pectin and is widely available. Unfortunately, the pectins in sugar beet pulp have a high degree of esterification and, to date, have shown to have poor gelling properties. Some attempts have been made to improve the gelling properties of pectins obtained from sugar beet but these have all involved structurally modifying the pectins. This results in complicated processing and a product which is too expensive for commercial application. Accordingly there is a need for pectinaceous gelling agents which have low degrees of esterification and which may be obtained from vegetable matter having a high degree of esterification.

Summary of the invention

Accordingly, in one aspect, this invention provides a pectinaceous gelling agent obtained from vegetable matter containing pectinaceous substances that have a degree of esterification of greater than about 50%, the gelling agent comprising about 30% to about 55% by weight of galacturonic acid and having a degree of esterification of about 5% to about 20%.

Surprisingly, it has been found that excellent gelling agents may be prepared from vegetable matter containing pectinaceous substances that have a degree of esterification of greater than about 50% by keeping the galacturonic acid content to below about 55% by weight. Traditionally, efforts have been directed to obtaining extremely pure pectin products; for example with galacturonic acid contents above 80% by weight. Further the gelling agents of the invention contain pectinaceous substances having very low degrees of esterification; often less than a third of the degree of esterification of the pectinaceous substances in the vegetable matter itself. The vegetable matter may be sugar beet pulp. The pectin content of sugar beet pulp is about 20% by weight on a dry basis and the degree of esterification is

about 53%. Preferably, when the vegetable matter is sugar beet pulp, the gelling agent contains about 40% to about 50% by weight of galacturonic acid and has a degree of esterification of about 6% to about 15%. Consequently gels produced using the gelling agents have excellent properties. In another aspect, this invention provides a process for the production of a pectinaceous gelling agent from vegetable matter that contains pectinaceous substances having a degree of esterification of greater than about 50%, the process comprising: subjecting comminuted vegetable matter to an alkaline extraction at a temperature of about 15 to about 50°C for providing a pectinaceous extract; separating the extract from the vegetable matter; and neutralizing the extract to provide a pectinaceous gelling agent containing about 30% to about 55% by weight of galacturonic acid and having a degree of esterification of about 5% to about 20%. The alkaline extraction may be carried out by suspending the comminuted vegetable matter in an aqueous alkaline solution at a pH of about 8 to about 12.

The extract is preferably neutralized by suspending it in an aqueous solution at a pH of about 6 to about 7.5. Alcohol may then be added to the suspension for precipitating the pectinaceous gelling agent. The suspension may be a water suspension. The alcohol is preferably ethanol and the suspension preferably contains about 50% by weight of ethanol.

The invention also provides the gelling agent obtainable by the process defined above.

In another aspect, this invention provides a gelled emulsion product containing protein, lipid, carbohydrate and a binder, the binder comprising a gelling agent as defined above. Preferably the gelled emulsion product is a pet food.

Detailed description of the preferred embodiments

This invention provides a gelling agent which contains pectin. The gelling agent may be produced from waste vegetable matter which contains pectinaceous substances having a degree of esterification of greater than 50%. Any suitable vegetable matter which is a source of high methoxy pectins may be used; for example the sugar beet pulp, tomato, and pumpkin.

The vegetable matter is preferably comminuted prior to processing; for example by subjecting it to grinding or shredding. The comminuted vegetable matter may then be dried. To inactivate enzymes, the vegetable matter is preferably subjected to heat treatment. This may be accomplished by washing in hot water; for example at a temperature of about 70°C to about 90°C and for a time of about 10 to 30 minutes. Washing has the additional advantage of removing by-products.

The washed vegetable matter is then subjected to extraction under alkaline conditions. Extraction may be carried out in any suitable manner. For example, the vegetable matter may be suspended in the appropriate solution in a stirred tank reactor. Alternatively, the extraction solution may be caused to flow through a fixed bed of the vegetable matter. Continuous extraction techniques may also be used.

The extraction solution is an aqueous alkaline solution at a pH of about 8 to 12. The temperature is held at about 15 to 50°C; for example at room temperature. Any suitable alkaline may be used; especially alkaline metal hydroxides and carbonates or alkaline-earth metal hydroxides and carbonates. For example, the alkaline may be sodium hydroxide. Suitable NaOH strengths are 0.02 to 0.2 M; for example 0.05 M NaOH which is at a pH of about 12. The extraction time needed depends upon the mode of extraction. However extraction times of about 5 minutes to about 180 minutes may be used.

The extract is then separated off from the residual solid matter. This may be carried out by any suitable solid-liquid separation technique. Centrifugation is preferred. Pectinaceous matter is then caused to precipitate from the extract. This may be accomplished by adding an acid to the extract to lower the pH to a neutral pH of about 6.0 to about 7.5 and then adding a suitable alcohol. The precipitation is conveniently carried out at room temperature. Ethanol is a suitable alcohol. Typically, sufficient ethanol is added such that ethanol makes up at least about 50% by weight of the solution. If desired, sodium chloride may be added to the solution prior to the addition of the ethanol. Any suitable acid may be used for the neutralization; for example HC1.

The precipitate is then separated from the liquid. Again any suitable solid- liquid separation technique may be used. Centrifugation is preferred.

The precipitate may then be recovered, washed and dried to provide the gelling agent. Washing is preferably carried out with ethanol; for example in three stages using successively increasing concentrations. Concentrations of

70%, 80% and 95% are suitable. The drying may be carried out under vacuum at room temperature.

The gelling agent obtained comprises about 30% to about 55% by weight of galacturonic acid; which is a relatively low concentration since most pectin-based gelling agents contain above 68% by weight of galacturonic acid. However the pectinaceous substances in the gelling agent have a degree of esterification of about 5% to about 20% which provides the gelling agent with excellent gelling properties. Further the gelling agent is safe to use in food stuffs and hence may be used as a gelling agent for food stuffs. Suitable food stuffs include pet foods, gelled meat products, jellies, jams, and gelled dairy products. The gelling agent may also be used as a thickener or stabilizer in ice creams, juices and beverages.

However, due to the excellent gelling properties of the gelling agent, it is most suitably used in products which undergo retorting and sterilization; especially in the pet food industry. Examples of suitable products include gelled emulsion products such as gelled loaf products and gelled chunk-type products. The gelled emulsion products typically contain protein, lipid, carbohydrate and a binder. The protein may be provided in the form of a meat material, animal or dairy proteins, and vegetable proteins, or mixtures of these proteins. Any suitable type of meat material may be used, for example, muscular or skeletal meat, meat by-products such as heart, liver, kidney, lung, or a mixture of meat and meat by-products. Further, the material may be obtained from any suitable source such as from livestock, poultry, and fish. Also, the meat material may be in the form of meat meals such as poultry meal, fish meal, red meat meal and mixtures thereof. Suitable animal or dairy proteins which may be used include egg proteins, gelatin, blood, and whey, or mixtures of these proteins. Suitable vegetable proteins which may be used include wheat gluten, soy flour, soy protein concentrates, soy protein isolates, pea protein isolates, etc, or mixtures of these proteins. The exact choice of protein used will depend upon factors such as availability, cost and palatability. Typically, the protein suitably comprises about 5 % to about 15% by weight of the gelled emulsion product.

The lipid may be provided in the form of suitable animal or vegetable fats and oils, or both. If the protein is provided in the form of a meat material, the meat material may well provide the desired amount of lipids and hence addition of further lipid may not be necessary. If it is necessary to add lipids, suitable examples of animal fats are tallow, chicken fats, pork fats, beef fats, and the like. Suitable examples of vegetable fats and oils are hydrogenated palm oil, corn oil,

sunflower oil, rapeseed oil, and the like. Typically the emulsion product contains a maximum lipid level of about 25% by weight. Conveniently, the amount of lipid in the emulsion is in the range of about 2% to 15% by weight; more preferably about 5% to about 12% by weight. If it is necessary to add carbohydrate, the carbohydrate is preferably provided in the form of a starch or flour. Suitable carbohydrate sources are wheat starch, potato starch, corn starch, wheat flour, corn flour, oat flour, rye flour, rice flour, and the like. Sugars may also be added. Typically, for chunk products, the carbohydrate, in the form of starch or flour, comprises about 3% to about 15% by weight of the gelled emulsion product.

Additional ingredients such as salts, spices, seasonings, flavoring agents, minerals, and the like may also be included in the emulsion product. The amount of additional ingredients used is preferably such that they make up about 0.5% to about 5% by weight of the emulsion product. The emulsion product may be prepared by emulsifying the protein, carbohydrates and lipids to provide a primary emulsion. The additional ingredients such as salts, spices, seasonings, flavoring agents, minerals, and the like may be added at this time. Water may also be included in the primary emulsion to provide from about 50% to about 90% by weight of the primary emulsion. If sufficient moisture is present in the protein, especially if the protein is provided as a meat material, water need not be added. A high speed emulsifier or homogeniser is particularly suitable for preparing the primary emulsion. The gelling agent is then added to the primary emulsion; preferably in solution. Usually between about 0.5 % and about 5% by weight of the gelling agent is suitable. If necessary a calcium source is also added; for example calcium carbonate or calcium sulfate. Preferably calcium is present in an amount of about 40 to about 150 mg/g of gelling agent used. The primary emulsion is then subjected to further mixing or emulsification. The primary emulsion is then heated to a temperature above about 65°C; for example in a mixer-cooker. Steam may be injected into the primary emulsion if desired.

If it is desired to produce chunks, the heated emulsion may then be extruded, cooled and cut into chunks. The chunks may then be mixed with a suitable gravy or jelly and filled into cans or other containers. However, if it desired to produce a loaf type product, the heated emulsion may be filled directly into cans or other containers. The cans or other containers are then sealed and

sterilized. Sterilization usually takes place at a temperature above about 120°C and for a period of at least about 15 minutes.

The gelled emulsion product obtained undergoes much less cook out of fats and starches giving a product with an excellent appearance. Further, the gelled emulsion product has a firm, relatively elastic texture.

Specific examples are now described for further illustration.

Example 1 - Extraction from Sugar Beet Pulp

Sugar beet pulp having a dry matter content of 20% to 30% by weight is used. The sugar beet pulp is dried in an oven at 45°C and then ground to a size of 0.5 mm to 60 mesh. An amount of 500 g of the ground pulp is dispersed in 12.5 1 of water at 85°C for 20 minutes. The water is removed using a centrifuge and the solid matter is suspended in 10 1 of a 50 mM NaOH solution. The pH is 12. The solution stirred for 2 hours at room temperature. The extract is then recovered using a centrifuge.

The pH of the extract is adjusted to about 6.5 to 7.0 using 6 N HC1. An amount of 100 g of NaCl is added and 10 1 of 95% ethanol is added. The mixture is stirred for 10 minutes and then stored overnight at 4°C. The precipitate which forms is recovered by centrifuging at 5000 φm for 15 minutes. The precipitate is then washed three times; once with 70%,ethanol, once with 80% ethanol and once with 95% ethanol. The washed precipitate is dried in a vacuum oven at room temperature to provide a gelling agent.

Example 2 - Characterization of the gelling agent

Samples of the gelling agent of example are subjected to the following analysis:

- the Weibull-Stoldt method to determine fat content. - the Kjeldahl method to determine protein content.

- hydrolysis of a 50 mg sample in 12N H ₂ SO ₄ for 60 minutes at 30 °C and then in 0.4N H ₂ SO ₄ for 75 minutes at 130°C. Monosaccharides are then determined using high performance anion exchange chromatography and pulsed amperometric detection. - decarboxylation and measurement of the carbon dioxide produced to determine the galacturonic acid content.

- saponification and measurement by gas chromatography of the methanol release to determine the degree of methoxylation.

- drying in an oven for 4 hours at 104°C and the moisture content measured;

- roasting at 550°C for 12 hours and ash content then measured. The fat and protein contents of each gelling agent are determined from further samples using the Weibull-Stoldt and Kjeldahl methods respectively.

The results are as follows:

Example 3 - Gel preparation and rheological measurements

A sample of the gelling agent of example 1 is dispersed in water to provide a concentration of about 2% by weight of gelling agent. The pH of the solution is 7.4. In each case, the suspension is stirred at a temperature of 25°C for about 2 hours. A selected amount of a solution containing 2.9 % by weight of

CaSO ₄ .2H ₂ O is then added to obtain a desired calcium concentration. The solution is then stirred for about 1 minute, poured into a mold, and stored at 4°C for 24 hours. The gelled product is then removed and subjected to analysis.

The process is repeated except with the following changes:

- the gelling agent is dissolved in the presence of increasing concentrations of a citrate buffer;

- the gelling agent is hydrated at pH's in the range of about 4.2 to about 7.4 in the presence of sodium citrate buffer;

- the concentration of calcium is varied between 40 and 100 mg/g of gelling agent; and

- the temperature at which the gelling agent is hydrated is varied.

In each case, the elastic modulus E, which is a measure of gel firmness, is determined for each gelled product using a Micro System TA-XT2 Texture Analyzer. The strain applied during the measurement is 10% and the plate speed is 0.8 mm/s. Certain of the results are as follows:

The results indicate that increasing the presence of sodium citrate decreases the elastic modulus of the gelled products. Further, the results indicate that increasing the amount of calcium present in general increases the elastic modulus of all gelled products. Also, the elastic modulus decreases with increasing hydration temperature leading to an optimum hydration temperature of about room temperature (about 20°C to about 30°C). The optimum hydration pH is about 4.5 to about 6.5.

These results indicate that the gel firmness may be readily adjusted by varying parameters such as calcium content, pH, hydration temperature, sodium citrate presence, etc, to achieve a desired level.

Example 4 - Production of a pet food

Frozen beef is comminuted and emulsified with beef fat in a homogenizer. Carbohydrate, in the form of wheat starch, and salt are added and the mixture mixed at low speed. Water containing CaSO ₄ .2H ₂ O is added and the mixture emulsified at high speed.

A sample of a gelling agent of example 1 and calcium sulfate is added to the mixture. The mixture is heated treated at 78°C for 30 minutes and then allowed to cool to form gelled emulsion products. The gelled emulsion products are cut into chunks and filled into cans with water. The cans are sealed and sterilized at 121°C for 20 minutes. The cans are then allowed to cool.

The cans are opened and the contents visually inspected. The chunks are well-formed and little or no cook out of fat or starch is noticeable. Further the chunks retain their shape and have a firm texture.

Example 5 - Production of a pet food loaf

Frozen liver, lungs, and kidneys are comminuted and mixed at low speed with water and salts, including CaSO ₄ .2H ₂ O. The mixture is then emulsified at high speed and heated to 35°C. A gelling agent of example 1 is added to water and hydrated at 30°C for 15 minutes at a pH of 6. The gelling agent solution is then added to a separate emulsion. The mixtures are then filled into cans, the cans are sealed and retorted at 121°C for 20 minutes. The cans are opened and the contents visually inspected. The meat matrix is gellified, retains its shape and has a firm texture.