COATING MATERIALS FOR FOOD PRODUCTS

The present invention relates to coating materials for use in a coated food product, as well as coated food products comprising the coating material. The coating materials are particularly suitable for use in the extrusion coating of food products, such as sausages.

Synthetic coatings for food products, such as sausage casings, are well known in the art. Synthetic coatings are typically made from cellulose, though collagen and even plastics may also be used. A disadvantage of these coating materials is that they tend to confer an unnatural and unappealing texture to the outside of a food product and, in some cases, the coating is inedible. This means that synthetic coatings often have to be removed from the food product before consumption, particularly where an imperceptible coating is desirable such as with a skinless sausage. This also adds to the risk of food contamination due to added handling of the food product.

Anionic polymers have been used in synthetic food coatings, such as sausage casings, for some time. Alginate is an edible anionic polymer which is made up of two different uronic acid monomers, namely guluronic acid (G-blocks) and mannuronic acid (M-blocks). Alginate is commonly used to form sausage casings as part of a process in which a solution of alginate is extruded through a circular die around a food product and subsequently treated with calcium chloride (see e.g. WO 2016/027261 ). During this process, the alginate solution undergoes a gelification process in which matrices of cross-linked alginate chains form. The M-blocks form linear molecular chains (M-M-M-M-M), whilst the G-blocks form folded structures (G-G-G-G). Alternating regions consisting of M- and G-chains form the fundamental alginate structure, which can vary with seaweed type and seasonal climate.

Synthetic coatings are typically added to a food product by extrusion. Thus, a coating material must exhibit suitable properties for successful extrusion, such as a desirable viscosity. If the viscosity is too low, then the coating material liquifies at the extrusion interface before gelification. Machine limitations can also result in the coating being sucked into the water separator, leading to insufficient casing supply at the extrusion point. If the viscosity is too high, then the pumping efficiency of the extrusion equipment is reduced which can lead to an irregular supply of coating material to the extrusion point. Even where a regular supply is achieved, uneven coating of the food product can result in an interrupted casing. The viscosity of the coating can also have an impact on the texture and feel of the coating that is experienced by the consumer during eating. Viscosity has typically been controlled using viscosity modifying agents, such as hydrocolloids, insoluble fibres, liquid smoke and plasticisers. However, a viscosity modifying agent that is effective in a coating composition for one food product may impart an undesirable texture or flavor to another food product.

WO 2017/191312 discloses a method for preparing a coating material for a coated food product in which the viscosity of the alginate-based coating material is closely controlled by manipulation of pH levels. While the document discloses that certain components may be added to the coating material, e.g. polyol plasticisers, viscosity increasing microcrystalline cellulose or starch interrupting agents among others, the method is preferably used to prepare coating compositions without using conventional viscosity modifying additives.

Synthetic coatings must also exhibit desirable properties during processing, and when prepared by the consumer e.g. by frying or boiling. Problems that are encountered when preparing coated food products are often related to the filling composition that has been used.

Filling compositions for food products such as sausages will often comprise water in an amount of greater than 20 %, and animal matter in an amount of less than 60 % by weight of filling composition, particularly where the sausages are for production on a large economic scale. When these food products are cooked then the moisture is driven from the filling composition which can lead to the formation of bubbles under the coating material. This is particularly the case when the coated food product is cooked at high temperature e.g. by frying in oil. Bubble formation can be visually unappealing to consumers, as well as enhancing perception of the casing material during eating. In severe cases, the coating material can split, thereby damaging the structural integrity and appearance of the product.

Accordingly, there is a need for coating materials which possess a set of properties that are desirable for use in a coated food product, in particular a coated food product in which the filling composition has a high moisture content.

The present invention is based on the unexpected discovery that, by using a combination of a polyol and an interrupting agent, together with a pH in the range of from 3.4 to 4.0, a coating material may be prepared which is readily extrudable and which exhibits desirable properties on preparation and eating by the consumer. Thus, in a first aspect, the present invention provides an aqueous coating material for a coated food product, said coating material comprising an anionic polysaccharide, a plasticiser and an interrupting agent, wherein the pH of the coating material is in the range of from 3.4 to 4.0.

A method for preparing the aqueous coating material of the present invention is also provided. The method comprises: combining an anionic polysaccharide, a plasticiser and an interrupting agent in the presence of water; and adjusting the pH of the coating material so that it is in the range of from 3.4 to 4.0.

In a further aspect, the present invention provides a coated food product which comprises: a filling composition; and an aqueous coating material of the present invention.

A method for preparing a coated food product is also provided. The method comprises: applying an aqueous coating material of the present invention to a filling composition. A coated food product obtainable by said methods is also provided.

In a further aspect, the present invention provides a kit comprising: an anhydrous anionic polysaccharide, a plasticiser and an interrupting agent; and instructions for preparing a coating material or a coated food product of the present invention.

Also provided is the use of microcrystalline cellulose as an interrupting agent in a coating material for a coated food product, the use of a combination of an interrupting agent and a plasticiser for improving the cooking properties of an anionic polysaccharide-based coating material, as well as the use of a combination of an interrupting agent and a plasticiser for reducing the perception of anionic polysaccharide-based coating material during eating of a coated food product.

In a further aspect, an apparatus is provided for preparing a coated food product. The apparatus comprises a tank in which a coating material of the present invention is held; and a coating device for coating a filling composition with the coating material.

The present invention is based on the discovery that many of the problems previously encountered with synthetic casings for food products having a high moisture content may be overcome by adding a combination of a plasticiser and an interrupting agent to an aqueous coating material which comprises an anionic polymer, and maintaining the pH of the coating material in the range of from 3.4 to 4. Such coating materials display excellent extrusion and cooking properties. In particular, the formation of bubbles under the coating of a coated food product during cooking is minimised by using the coating materials of the present invention.

Plasticisers are components which soften a coating material. The plasticiser used in the aqueous coating materials of the present invention is preferably a polyol, such as a C _1-10 polyol, preferably a C _2-8 polyol, and more preferably a C _3-6 polyol. Suitable polyols include glycerol (propane-1 , 2, 3-triol), propylene glycol (also known as propane-1 , 2-diol) or sorbitol ((2S,3R,4R,5R)-hexane-1 ,2,3,4,5,6-hexol). Glycerol is particularly suitable for use in the casing materials of the present invention.

Plasticisers may be included in the coating material in an amount of at least 8 % by weight, preferably at least 12 % by weight, and more preferably at least 18 % by weight of the coating material. Plasticisers may be included in a total amount of up to 42 % by weight, preferably up to 38 % by weight, and more preferably up to 32 % by weight of the coating material. Thus, the coating material may comprise plasticisers in a total amount of from 8 to 42 % by weight, preferably from 12 to 38 % by weight, and more preferably from 18 to 32 % by weight of the coating material.

Interrupting agents disrupt the spatial orientation of the anionic polysaccharide chains in the coating material. Suitable interrupting agents for use in the aqueous coating materials of the present invention include microcrystalline polysaccharides, such as microcrystalline cellulose, and starches, such as tapioca starch, potato-derived starches and corn starch. Microcrystalline cellulose and tapioca starch are preferably used, with microcrystalline cellulose particularly effective.

Interrupting agents may be included in the coating material in an amount of at least 0.5 % by weight, preferably at least 1 % by weight, and more preferably at least 1.5 % by weight of the coating material. Interrupting agents may be included in a total amount of up to 8 % by weight, preferably up to 7 % by weight, and more preferably up to 6 % by weight of the coating material. Thus, the coating material may comprise interrupting agent in a total amount of from 0.5 to 8 % by weight, preferably from 1 to 7 % by weight, and more preferably from 1.5 to 6 % by weight of the coating material. Microcrystalline polysaccharides will preferably be used at a lower level than starches, e.g. in a totally amount of up to 2.5 % by weight, with starches preferably used in an amount of at least 4 % by weight of the coating material. Anionic polysaccharides are understood to contain functional groups which exist in an anionic form at a pH of 7. In preferred embodiments, the anionic polysaccharide used in the aqueous coating materials of the present invention comprises uronic acid monomers. Preferably, the anionic polysaccharide comprises uronic acid monomers selected from guluronic acid and mannuronic acid. More preferably, the anionic polysaccharide is alginate, i.e. a polymer comprising guluronic acid and mannuronic acid monomers.

The alginate is preferably a high-guluronic acid alginate. For instance, the ratio of guluronic acid monomers to mannuronic acid monomers in the alginate may be greater than 1 :1 , preferably greater than 1.5:1 , and more preferably greater than 2:1. The alginate preferably comprises homopolymeric blocks of guluronic acid monomers.

The anionic polysaccharide may also be a pectin (e.g. a low methoxyl pectin) or, more preferably, a combination of an alginate and a pectin.

Anionic polysaccharides may be included in the coating material in an amount of at least 2 % by weight, preferably at least 2.5 % by weight, and more preferably at least 2.8 % by weight of the coating material. Anionic polysaccharides may be included in a total amount of up to 8 % by weight, preferably up to 6 % by weight, and more preferably up to 4.5 % by weight of the coating material. Thus, the coating material may comprise anionic polysaccharides in a total amount of from 2 to 8 % by weight, preferably from 2.5 to 6 % by weight, and more preferably from 2.8 to 4.5 % by weight of the coating material. These levels of anionic polysaccharide are believed to provide a food product coating that is not overly discernible to the consumer. Where a food product is desired with a‘skinless’ feel, e.g. a skinless sausage, then anionic polysaccharides are preferably used in a total amount of less than 3.5 % by weight of the coating material.

The pH of the aqueous coating material of the present invention is in the range of from 3.4 to 4.0. For instance, the pH may be in the range of from 3.5 to 3.9, and preferably in the range of from 3.6 to 3.8. In these pH ranges, the anionic polysaccharides exist in the coating material in a partially precipitated state, thereby providing desirable levels of viscosity for extrusion of the coating compositions.

The pH level may be measured using standard methods, for instance by introducing a pH probe which is attached to a pH meter into the aqueous coating material. As is conventional in the art, pH measurements will be taken at 25 °C. The target pH level may be achieved by using an acid to lower the pH. Suitable acids include organic acids, in particular food grade acids such as citric acid, lactic acid, acetic acid, ascorbic acid and glucono-b-lactone. Citric acid is particularly suitable for controlling the pH level of the aqueous coating material. The acid will be used in an amount suitable to achieve the target pH level.

In order to assist with maintenance of the desired pH level, the coating material may comprise an acidic buffer. The acidic buffer will generally consist of an acid and a metal salt of the same acid, such as a group 1 or group 2 metal salt. Preferably, the buffer is selected from citric acid and sodium citrate; lactic acid and sodium lactate; acetic acid and sodium acetate; and ascorbic acid and sodium ascorbate.

The acidic buffer may be used in an amount of at least 0.1 % by weight, preferably at least 0.5 % by weight, and more preferably at least 1 % by weight of the coating material. The acidic buffer may be used in a total amount of up to 10 % by weight, preferably up to 5 % by weight, and more preferably up to 3 % by weight of the coating material. Thus, the acidic buffer may be used in a total amount of 0.1 to 10 % by weight, preferably from 0.5 to 5 % by weight, and more preferably from 1 to 3 % by weight of the coating material.

Since a range of different properties are desirable in a coated food product, then one or more further ingredients may be included in the coating material to help achieve these properties. Examples of one or more further ingredients include smoke derivatives, hydrocolloids and insoluble fibres. Hydrocolloids are particularly suitable for use in the casing compositions of the present invention.

Suitable smoke derivatives include liquid smoke. The use of smoke derivatives in the coating material is desirable because of the flavour that they impart on to the coating. Smoke derivatives may also catalyse hydrolysis of the alginate chains so that texture of the casing is shortened. Smoke derivatives may also be used to increase the viscosity of the coating material.

Smoke derivatives may be included in the coating material in an amount of at least 1 % by weight, preferably at least 2 % by weight, and more preferably at least 3 % by weight of the coating material. Smoke derivatives may be included in an amount of up to 10 % by weight, preferably up to 8 % by weight, and more preferably up to 5 % by weight of the coating material. Thus, the coating material may comprise smoke derivatives in an amount of from 1 to 10 % by weight, preferably from 2 to 8 % by weight, and more preferably from 3 to 5 % by weight of the coating material.

However, in many embodiments, the level of smoke derivatives is preferably limited since they may lead to an undesirable increase in viscosity in the coating material. Thus, the amount of smoke derivatives included in the coating material may be limited to less than 3.5 % by weight, preferably less than 1 % by weight, and more preferably less than 0.5 % by weight. In some embodiments, smoke derivatives may even be absent from the coating material.

Suitable hydrocolloids include hydrocolloidal vegetable gums, and preferably guar gum. Other suitable hydrocolloidal vegetable gums include tara gum and locust bean gum. Hydrocolloids may be useful for improving extrusion of the coating material.

Hydrocolloids may be included in the coating material in an amount of at least 0.1 % by weight, preferably at least 0.25 % by weight, and more preferably at least 0.4 % by weight of the coating material. Hydrocolloids may be included in an amount of up to 1 % by weight, preferably up to 0.75 % by weight, and more preferably up to 0.6 % by weight of the coating material. Thus, the coating material may comprise hydrocolloids in an amount of from 0.1 to 1 % by weight, preferably from 0.25 to 0.75 % by weight, and more preferably from 0.4 to 0.6 % by weight of the coating material.

Suitable insoluble fibres include cellulose fibres other than microcrystalline cellulose, citrus fibres and collagen. Insoluble fibres in the coating material may be useful for increasing the viscosity of the coating material.

Insoluble fibres may be included in the coating material in an amount of at least 0.5 % by weight, and preferably at least 1 % by weight of the coating material though, in preferred embodiments, insoluble fibres will not be used as preferred viscosity levels are already achieved in the coating material. Insoluble fibres may be included in an amount of up to 10 % by weight, preferably up to 5 % by weight, and more preferably up to 3 % by weight of the coating material. Thus, the coating material may comprise insoluble fibres in an amount of from 0 to 10 % by weight, preferably from 0.5 to 5 % by weight, and more preferably from 1 to 3 % by weight of the coating material. Other ingredients that may be present in the coating material include chelating agents. Suitable chelating agents include phosphates such as sodium hexametaphosphate. Colourings and flavourings, e.g. spices, may also be included in the coating material.

The coating material is in the form of an aqueous composition. Water may be used in the coating material in an amount of at least 50 % by weight, preferably at least 60 % by weight, and more preferably at least 70 % by weight of the coating material.

The aqueous coating material may have a viscosity of at least 20 Pa-s, preferably at least 25 Pa-s, and more preferably at least 30 Pa-s at 5 °C. The coating material may have a viscosity of up to 80 Pa-s, such as up to 70 Pa-s and preferably up to 60 Pa-s at 5 °C. Thus, the aqueous coating material may have a viscosity of from 20 to 80 Pa-s, such as 25 to 70 Pa-s, preferably from 30 to 60 Pa-s at 5 °C. These viscosities are preferred for extrusion of the coating material.

Viscosity is measured in Pa-s using a Brookfield R/S-CPS+ Rheometer (cone and plate) which is operated with an external temperature control system at 5 °C, with a C25-1 spindle utilizing a sample volume of 0.08 ml. The system settings are: CSR setting, with a shear time of 120 s but a measuring point at 60 s under linear point distribution with the shear rate parameter selected, with a start and end value set at 20 s ¹ , and a distribution measuring points number of 60. The measuring temperature is set to 4 °C.

The aqueous coating material of the present invention may be prepared by a method in which the anionic polysaccharide (preferably in an anhydrous form), plasticiser and interrupting agent are combined in the presence of water, and the pH of the coating material is adjusted so that it is in the range of from 3.4 to 4.0.

In some embodiments, the water is combined with components of the composition that are in liquid form (e.g. plasticisers) and subsequently combined with the dry components of the composition (e.g. powdered anionic polysaccharide and interrupting agent). Preferably, the method for preparing the coating material comprises the step of pre-mixing the dry components (e.g. anionic polysaccharide and interrupting agent) and pre-mixing the liquid components (e.g. water and plasticiser), and subsequently combining the dry and liquid components.

The step of forming the coating material may comprise the step of mixing the water, anionic surfactant, plasticiser, interrupting agent and any additional ingredients. Methods of mixing are known in the art. High shear mixing is preferably used. Suitable devices for carrying out high shear mixing are readily available.

Once the components of the coating material have been mixed, the viscosity of the coating material may increase over time. Thus, the coating material may be prepared over a period of greater than 10 minutes, preferably greater than 30 minutes, and more preferably greater than 1 hour. Whilst an increase in viscosity may be observed in these periods, it is generally preferable for the viscosity of the coating material to reach a steady state. Thus, in preferred embodiments, the coating material may be prepared over a period of greater than 3 hours, and preferably greater than 6 hours, such as 8 or 10 hours, and such as for a period of greater than 12 hours.

The coating material will generally be prepared at a temperature of from 10 to 40 °C, preferably from 15 to 30 °C, and more preferably from 20 to 25 °C.

The coating material is preferably prepared in batches.

Once the coating material has been prepared, it is preferably homogenised before it is used e.g. in an extrusion process. This is because, during the preparation of the coating material, pockets of insoluble anionic polysaccharide (in which many of the anionic moieties on the polysaccharide chain have been protonated) and soluble anionic polysaccharide (in which few of the anionic moieties on the polysaccharide chains have been protonated) may form. Homogenisation distributes protonated anionic polysaccharide in the form of insoluble particles throughout the gel. This means that the viscosity of the coating material may reduce as a result of homogenisation.

Homogenisation may be carried out by mixing the coating material, e.g. using a mechanical mixer, a bowl cutter, vacuum blending, or ultrasonification. Slow blending, e.g. for a period of at least 8 hours, may also be used. Other mixing methods will be known to the person of skill in the art and may also be used. Where vacuum blending it used, the homogenisation process may be carried out for a period of at least 10 minutes, preferably at least 20 minutes, and more preferably at least 30 minutes. Vacuum blending may be carried out at a temperature of from 1 to 8 °C, preferably from 2 to 6 °C, for instance at about 4 °C. In order to remove air, the vacuum setting is preferably set high, e.g. at its maximum.

The coating material may be used as the coating in a coated food product. The coated food product is preferably a coated moulded food product, in which the ingredients have been processed (e.g. by chopping, shredding or grinding the ingredients). Coated moulded food products include burgers, kebabs and sausages. In preferred embodiments, the coated food product is a sausage, such as a meat sausage. Skinless meat sausages are particularly preferred. Skinless meat sausages are intended to mimic the sensory attributes of traditionally prepared hotdog sausages.

The coated food product may be a raw, partially cooked or cooked food product.

The coated food product of the present invention comprises a filling composition and a coating material.

The filling composition preferably comprises animal matter. For instance, the animal matter may comprise red meat (e.g. beef, lamb, goat or bison), pork, poultry (e.g. chicken or turkey), fish or combinations thereof. In preferred embodiments, the animal matter is shredded, minced, pureed or in the form of a paste in the filling composition.

Animal matter may be used in the filling composition in an amount of at least 20 % by weight, preferably at least 25 % by weight, and more preferably at least 30 % by weight of the filling composition. Animal matter may be used in a total amount of up to 60 % by weight, preferably up to 50 % by weight, and more preferably up to 45 % by weight of the filling composition. Thus, the filling composition may comprise animal matter in a total amount of from 20 to 60 % by weight, preferably from 25 to 50 % by weight, and more preferably from 30 to 45 % by weight of the filling composition.

The coating compositions of the present invention are particularly suited to filling compositions which have a relatively high moisture content. Water may be used in filling composition in an amount of at least 30 % by weight, preferably at least 35 % by weight, and more preferably at least 40 % by weight, by weight of the filling composition. Water may be used in an amount of up to 60 % by weight, preferably up to 55 % by weight, and more preferably up to 50 % by weight of the filling composition. Thus, the filling composition may comprise water in an amount of from 30 to 60 % by weight, preferably from 35 to 55 % by weight, and more preferably from 40 to 50 % by weight of the filling composition. It will be appreciated that these amounts relate to the water that is added to the filling composition during its preparation, and do not include water that has been added to the filling composition as part of the animal matter. Preferred filling compositions comprise modified starch. The modified starch is preferably a heat-sensitive modified starch. Heat sensitive modified starches are starches in which particular properties are activated at a high temperature. In the present case, the heat- sensitive starches are preferably activated to become firmer at certain temperatures. This has the advantage that the filling composition remains soft during extrusion, but firms up on cooking. Preferably, the heat-sensitive modified starches that are used in the present invention are activated at a temperature of greater than 50 °C, preferably greater than 60 °C, and more preferably greater than 70 °C. The heat-sensitive modified starches may be activated at a temperature of lower than 120 °C, preferably lower than 110 °C, and more preferably lower than 100 °C. Thus, the heat-sensitive modified starches may be activated at a temperature in the range of from 50 to 120 °C, preferably from 60 to 110 °C, and more preferably from 70 to 100 °C.

The modified starch may be derived from potato, maize, tapioca or wheat. Modified starches derived from potato, maize (e.g. waxy maize) or tapioca are particularly suitable for use in the filling compositions of the present invention.

The modified starch may be starch in which -OH groups have been modified, e.g. esterified or etherified. It will be appreciated that modified starches typically have some, and not all, of the -OH groups modified.

-OH groups in the starch may have be esterified to give a group having the formula: - OC(0)Ri, where Ri is selected from Ci _-6 alkyl groups. Preferably, Ri is a methyl group. Esterification may be carried out using acetic anhydride or vinyl acetate.

-OH groups in the starch may have been etherified to give a group having the formula: -OR ₂ , where R ₂ is a C _1-6 alkyl group or a C _1-6 hydroxyalkyl group. Preferably, R ₂ is a hydroxy propyl group. Etherification may be carried out using propylene oxide.

Preferably, the modified starch is starch which has been cross-linked, e.g. using a phosphate compound (e.g. sodium trimetaphosphate or phosphorus oxychloride) or an anhydride (e.g. adipic anhydride).

It will be appreciated that the modified starches used in the filling compositions may be modified at their -OH groups and cross-linked.

Preferred modified food starches for use in the filling composition include: • acetylated distarch adipate (EU food additive E1422, a cross-linked starch having esterified -OH groups; e.g. derived from waxy maize such as that sold under the tradename Purity™ HPC);

• acetylated starch (EU food additive E1420, a starch having esterified -OH groups; e.g. derived from tapioca starch such as that sold under the tradename Elastitex™)

• hydroxypropyl distarch phosphate (EU food additive E1442, a cross-linked starch having etherified-OH groups; e.g. derived from waxy maize such as that sold under the tradename Firm-tex™); and

• Almidon National™ 1317, a cross-linked starch.

Modified starches may be used in the filling composition in an amount of at least 3.5 % by weight, preferably at least 4 % by weight, and more preferably at least 4.5 % by weight of the filling composition. Modified starches may be used in a total amount of up to 9.5 % by weight, preferably up to 8.5 % by weight, and more preferably up to 7.5 % by weight of the filling composition. Thus, the filling composition may comprise modified starches in a total amount of from 3.5 to 9.5 % by weight, preferably from 4 to 8.5 % by weight, and more preferably from 4.5 to 7.5 % by weight of the filling composition.

The filling composition may optionally comprise unmodified starch. The unmodified starch may be derived from potato, maize, tapioca or wheat. Preferably, the unmodified starch is derived from potato. An example of a preferred unmodified starch for use in the filling composition of the present invention is a potato-derived starch sold under the tradename N- Hance®.

Unmodified starches may be used in the filling composition in an amount of at least 0.75 % by weight, and preferably at least 1.25 % by weight of the filling composition. Unmodified starches may be used in a total amount of up to 4 % by weight, preferably up to 3.5 % by weight, and more preferably up to 3 % by weight of the filling composition. Thus, the filling composition may comprise unmodified starches in a total amount of from 0 to 4 % by weight, preferably from 0.75 to 3.5 % by weight, and more preferably from 1.25 to 3 % by weight of the filling composition.

The ratio of modified starch to unmodified starch in the filling composition may be greater than 1 : 1 , preferably greater than 1.25 : 1 , and more preferably greater than 1.5 : 1. The ratio of modified starch to unmodified starch in the filling composition may be up to 10 : 1 , preferably up to 8 : 1 , and more preferably up to 5 : 1. Thus, the ratio of modified starch to unmodified starch in the filling composition may be from 1 : 1 to 10 : 1 , preferably from 1.25 : 1 to 8 : 1 , and more preferably from 1.5 : 1 to 5 : 1.

Protein extenders are also preferably used in the filling composition. Protein extenders enhance the protein content of the filling composition. The protein extender used in the filling composition may be derived from soya beans. For instance, the protein extended may be a soya isolate or a soya concentrate. As is known in the art, soya concentrate is prepared by removing the fat and water-soluble non-protein components from soya beans. Thus, soya concentrate may contain some carbohydrates and fibre. Soya isolates are prepared by removing all non-protein components from soya beans, and this are substantially carbohydrate and fibre free.

Protein extenders may be used in the filling composition an amount of at least 2 % by weight, preferably at least 2.5 % by weight, and more preferably at least 3 % by weight of the filling composition. Protein extenders may be used in the filling composition in a total amount of up to 7 % by weight, preferably up to 6 % by weight, and more preferably up to 5 % by weight of the filling composition. Thus, the filling composition may comprise protein extenders in a total amount of from 2 to 7 % by weight, preferably from 2.5 to 6 % by weight, and more preferably from 3 to 5 % by weight of the filling composition. .

Fibre is also preferably used in the filling composition of the present invention. The fibre may be derived from wheat or soya beans. Particularly preferred is fibre derived from soya beans.

Fibre may be used in the filling composition in an amount of at least 1 % by weight, preferably at least 1.5 % by weight, and more preferably at least than 2 % by weight of the filling composition. Fibre may be used in the filling composition in a total amount of up to 4.5 % by weight, preferably up to 4 % by weight, and more preferably up to 3.5 % by weight of the filling composition. Thus, the filling composition may comprise fibre in a total amount of from 1 to 4.5 % by weight, preferably from 1.5 to 4 % by weight, and more preferably from 2 to 3.5 % by weight of the filling composition.

The ratio, by weight, of protein extender to fibre may be greater than 0.8 : 1 , preferably greater than 1 : 1 , and more preferably greater than 1.2 : 1.

Without wishing to be bound by theory, it is believed that by adding modified starch to a filling composition having a high moisture content, in combination with a protein extender and fibre, a filling composition may be prepared which is readily extrudable with a synthetic casing material and which also exhibits desirable properties on eating.

Particularly preferred filling compositions comprise animal matter, water, protein extender, starch (modified and, if used, unmodified) and fibre in a combined total amount of at least 80 % by weight, preferably at least 90 % by weight, and more preferably at least 95 % by weight of the filling composition.

The filling composition will generally comprise further ingredients, such as flavourings (synthetic or natural, e.g. herbs), seasonings, breadcrumbs, oats, vegetable matter, additives etc.

In some embodiments, the filling composition may comprise a calcium compound or a phosphate compound, and preferably both. The use of these components is believed to improve binding of the coating material to the filling composition.

Suitable calcium compounds include CaCI ₂ , calcium lactate or calcium acetate, with calcium lactate particularly preferred. Calcium compounds may be used in the filling composition in an amount of at least 0.1 % by weight, preferably at least 0.15 % by weight, and more preferably at least 0.2 % by weight of the filling composition. Calcium compounds may be used in a total amount of up to 0.5 % by weight, preferably up to 0.4 % by weight, and more preferably up to 0.3 % by weight of the filling composition. Thus, the filling composition may comprise calcium compounds in a total amount of from 0.1 to 0.5 % by weight, preferably from 0.15 to 0.4 % by weight, and more preferably from 0.2 to 0.3 % by weight of the filling composition.

Suitable phosphate compounds include sodium tripolyphosphate (STPP). Phosphate compounds may be used in the filling composition in an amount of at least 0.01 % by weight, preferably at least 0.05 % by weight, and more preferably at least 0.1 % by weight of the filling composition. Phosphate compounds may be used in a total amount of up to 0.35 % by weight, preferably up to 0.30 % by weight, and more preferably up to 0.25 % by weight of the filling composition. Thus, the filling composition may comprise phosphate compounds in a total amount of from 0.01 to 0.35 % by weight, preferably from 0.05 to 0.30 % by weight, and more preferably from 0.1 to 0.25 % by weight of the filling composition.

The ratio of calcium compounds to phosphate compounds in the filling composition is preferably greater than 1 : 1 , and more preferably greater than 1.5 : 1 by weight. The filling composition is, at least partially, covered by the coating material. Thus, the coating material may cover at least 50 %, preferably at least 70 %, and more preferably at least 90 % of the surface area of the coated food product. Most preferably, all of the surface area of the coated food product is covered with the coating material.

The coating material may have a thickness of at least 50 pm, preferably at least 100 pm, and more preferably at least 150 pm. The coating material may have a thickness of up to 300 pm, preferably up to 250 pm, and more preferably up to 200 pm. Thus, the coating material may have a thickness of from 50 to 300 pm, preferably from 100 to 250 pm, and more preferably from 150 to 200 pm.

The coating material may have a tensile strength such that the load required to rupture an extruded coating of 100 pm thickness is at least 100 g, preferably at least 150 g, and more preferably at least 200 g. The extruded coating may have a tensile strength such that the load required to rupture an extruded coating of 100 pm thickness is up to 400 g, preferably up to 350 g, and more preferably up to 300 g. Thus, the extruded coating may have a tensile strength such that the load required to rupture an extruded coating of 100 pm thickness is from 100 to 400 g, preferably from 150 to 350 g, and more preferably from 200 to 300 g.

Tensile strength may be measured using a Brookfield CT3 texture analyser which is operated with a TA18 sphere (12.7 mm in diameter) and a fixture TA-RT-KIT. The system settings are: test type set as rupture, a test target correction of 50 g, a trigger load of 5 g and a test speed of 1 mm/s.

The coated food product of the present invention may be obtained by a method in which the coating material is applied to the filling composition.

The coating material may be applied to the filling composition in an amount of at least 0.5 % by weight, preferably at least 1 % by weight, and more preferably at least 2.5 % by weight of the filling composition. The coating material may be applied to the filling composition in an amount of up to 20 % by weight, preferably up to 10 % by weight, and more preferably up to 5 % by weight of the filling composition. Thus, the coating material may be applied to the filling composition in an amount of from 0.5 to 20 % by weight, preferably from 1 to 10 % by weight, and more preferably from 2.5 to 5 % by weight of the filling composition. The coating material may be applied to the filling composition using methods that are known to the skilled person. In preferred embodiments, the coating material is extruded and applied to the filling composition.

The filling composition is preferably co-extruded with the coating material, though it will be appreciated that the coating material may be first extruded and subsequently applied to a filling composition. In some embodiments, the coating material may be extruded through a circular die which encircles the co-extruded filling composition. This is particularly preferred when the food product is a sausage, since the coating material may be extruded on to the outside surface of the sausage filling.

Extrusion may take place at a linear speed of at least 0.05 m/s, preferably at least 0.1 m/s, and more preferably at least 0.5 m/s. Extrusion may take place at a linear speed of up to 5 m/s, preferably up to 4.5 m/s, and more preferably up to 3.8 m/s. This, extrusion may take place at a linear speed of from 0.05 to 5 m/s, preferably from 0.1 to 4.5 m/s, and more preferably from 0.5 to 3.6 m/s. An advantage of the present invention is that the coating material may be extruded at relatively high speeds without compromising the integrity of the coating. Thus, in some embodiments, the coating material is extruded at a linear speed of greater than 1 m/s.

Once the filling composition has been coated, the coating may be strengthened by contacting the coated food product with group 2 metal ions. Without wishing to be bound by theory, it is believed that group 2 metal ions may act as ionic cross-linkers between the chains of the anionic polysaccharide. The group 2 metal ions are believed to interact with negatively charged groups that are present in the anionic polysaccharide. Group 2 metal ions are particularly effective at strengthening forms of alginate which comprises homopolymeric blocks of guluronic acid monomers.

The coating may be strengthened by contacting the coated food product with a solution containing group 2 metal ions, for instance by immersing the coated food product in the solution or by spraying the solution onto the coated food product.

The group 2 metal ions are preferably selected from calcium ions, barium ions and magnesium ions. Calcium ions are generally preferred due their common use in food products. Suitable solutions for strengthening the casing include calcium chloride solutions. Suitable solutions may comprise group 2 metal salts in an amount of at least 0.5 % by weight, at least 5 % by weight, and preferably at least 10 % by weight of the solution. Suitable solutions may comprise group 2 metal salts in an amount of up to 30 % by weight of the solution.

In some embodiments, the method for preparing a coated food product comprises cooking the coated food product, preferably after it has been strengthened using group 2 metal ions. For instance, the coated food product may be steamed, boiled, fried, or smoked. Preferably, the food product is cooked at a temperature of greater than 50 °C, and more preferably greater than 60 °C. The food product may be partially cooked, or fully cooked.

The coated food product, optionally once cooked, may be further processed by at least one of drying, chilling (e.g. at a temperature of between 1 and 10 °C), and freezing (e.g. at a temperature of less than -5 °C).

Once the coated food product has been prepared, it may be packaged. In some embodiments, the coated food product will be packaged as a single article. Generally, however, at least two, preferably at least four, and more preferably at least six coated food products will be included in a package.

Thus, a coated food product of the present invention may be in a dried, chilled, frozen and/or packaged form.

The present invention provides kits which may conveniently be used for preparing the coating material and the coated food products disclosed herein.

In an embodiment, the kit may comprise: an anionic polysaccharide, a plasticiser and an interrupting agent; and instructions for preparing a coating material or a coated food product of the present invention. The kit may comprise one or more further ingredients as described herein, such as an acid or guar gum. In preferred embodiments, the anionic polysaccharide is provided in the kit in anhydrous form.

As mentioned above, the present invention is based in part on the discovery that a combination of an interrupting agent and plasticiser may be used to improve the cooking properties of an anionic polysaccharide-based coating material. Improved cooking properties may observed as a reduction in the formation of bubbles during cooking, e.g. frying. This may be measured by assessing the proportion of surface area that is covered with bubbles on the coated food product. Since bubble formation can also lead to enhanced perception of the coating material during eating, a combination of an interrupting agent and plasticiser may also be used to reduce the perception of anionic polysaccharide-based coating material during eating of a coated food product.

The present invention also provides the use of microcrystalline cellulose as an interrupting agent in a coating material for a coated food product.

The coated food product of the present invention may be prepared using an apparatus which comprises: a tank in which the coating material is held; and a coating device in which a filling composition, e.g. as described herein, is coated with the coating material.

The tank may have a volume of greater than 1 L, preferably greater than 5 L, and more preferably greater than 10 L. A tank of this size enables batch-wise production of the coating material.

In preferred embodiments, the coating material of the present invention may be prepared in the tank. Thus, the apparatus may further comprise a storage area containing an anhydrous anionic polysaccharide. This storage area is adapted to provide the tank with said anhydrous anionic polysaccharide.

A water inlet may also be present on the tank. Water may be provided through the water inlet to the tank in order to hydrate the anhydrous anionic polysaccharide.

The apparatus may further comprise a homogeniser. The homogeniser may be used to mix the components of the coating material. The homogeniser may be introduced into the tank to mix the coating material. Alternatively, the tank may be coupled to a homogeniser and the coating material passed from the tank to the homogeniser.

The apparatus further comprises a coating device, such as an extruder. The coating device is used to coat the filling composition with the coating material preferably using a method disclosed herein.

The apparatus may further comprise a strengthening station, in which the coating of the coated food product is strengthened by contacting the coated food product with group 2 metal ions preferably as described herein. The present invention will now be illustrated by way of the following examples and with reference to the following figures in which:

Figures 1 a and b are photographs of coated food products of the present invention that have been fried. Specifically, Figure 1a is a photograph of a fried sausage in which microcrystalline cellulose is used as the interrupting agent in the coating material, and Figure 1 b is a photograph of a fried sausage in which tapioca starch is used as the interrupting agent in the coating material.

Examples

Example 1 : Screening of casing materials

17 aqueous alginate-based casing materials were prepared on a small scale. The casing materials comprised guar gum (0.5 %), water (to 100 %) and varying quantities tapioca starch (0 to 5 %), soy isolate (0 to 1 %), microcrystalline cellulose (0 to 2 %) and glycerol (0 to 20 %).

The pH and viscosity of the casing materials were measured. The pH was measured at 25 °C using a Hanna Edge meter with food probe (model FC2020). Viscosity was measured at 4 °C using a Brookfield R/S plus Rheometer, cone spindle model 50.3.250 02 C25-1 , 3357.

The casing materials were then tested so as to determine the puncture force, breaking distance and work required to puncture the casings.

Test samples were prepared using the following method.

1. Film preparation and setting

(i) An 18 cm piece of dialysis membrane tubing is cut and placed into 200 ml of deionized water for 10 minutes. Suitable dialysis tubing along with suitable dialysis membrane tubing closures (such as closures 50 mm in size) may be obtained from Sigma Aldrich or Spectrum Labs.

(ii) Fully hydrated sodium gel is placed in a plastic bag and placed under vacuum three times so as to remove air bubbles.

(iii) A small incision is made on a corner of the plastic bag containing the gel. The gel is piped into the back of a 5 ml syringe. The plunger of the syringe is then put back on the syringe.

(iv) A few drops of sodium gel and deionized water are dropped and spread over a glass surface and elcometer® film thickness gauge surface so as to wet and lubricate the surfaces. The elcometer® is a Baker Film Applicator with a 250 pm gap and 100 mm width. (v) The dialysis tubing is removed from the deionized water and one end is carefully opened so that the opening of the syringe can be inserted into it. Approximately 2 ml of sodium gel is then slowly pushed into the top of the open membrane. The gel in the membrane is slightly compressed to level it out.

(vii) The gel-loaded tubing is then placed on the wet glass surface.

(vii) Two fingers are then placed on the end of the dialysis membrane to hold it down while the Elcometer® is placed between the fingers and the gel until it is level with the glass surface.

(viii) The Elcometer® is then placed on top of the membrane and pushed across the full length of the membrane in one swift movement.

(ix) The Elcometer® is then pulled back to the starting end in one swift movement, ensuring all excess gel is worked out of the open ends of the membrane.

(x) The Elcometer® is then pushed a final third time over the gel-filled membrane.

(xi) The flat end of a spatula is then used to carefully lift the one end of the membrane off the glass surface, with the least amount of disturbance to the membrane as possible. A membrane clip is then clamped over the end, interrupting the least amount of membrane possible.

(xii) This is repeated for the other end of the membrane.

(xiii) The clipped, gel-filled membrane is carefully picked up and lowered into a fixation bath container at room temperature, keeping the membrane as horizontal as possible.

(xiv) The films are allowed to set for 2 hours (at minimum) without any disturbances to the fixation bath.

(xv) The above steps are repeated so as to produce four separate membranes which are allowed to set in the fixation bath.

2. Fixation bath preparation The fixation bath referred to in steps (xiii) and (xiv) above was prepared by the following method.

(i) 40.0 g of calcium chloride powder is weighed out and added to 1960 g of water before stirring in a beaker.

(ii) This 2.0 % w/w calcium chloride solution is mixed for an hour and allowed to equilibrate to room temperature.

(iii) This fixation solution is then transferred to a 20 kg gel bucket and the lid is closed.

3. Texture analyser set up and film measurements

(i) The membrane is removed from the fixation bath and the clips are cut off with the scissors on a clean, flat surface.

(ii) Scissors are used to cut a thin (< 1 mm) piece of the side of the membrane so that the casing film can be removed and the thickness can be measured with a micrometer. The micrometer is a digital thickness gauge: 0 to 1000 pm, 1.0 pm resolution, +/- 5.0 p accuracy. (Insize, code 2871 - 101 ). The cutting is done on 10 parts of the film and the readings are averaged to obtain this measurement that is needed for the sample size section of the texture analyser.

(iii) The next membrane is removed from the bath and cut into 40 mm long pieces with 25 mm widths. Each film thus provides three puncture samples. The samples are now ready for analysis.

(iv) A thin (< 1 mm) piece of the closed side of the membrane is cut with scissors so that the casing film can be removed and placed in the middle of the open puncture box, covering the opening. Utmost care must be taken when handling the membrane that it is not damaged or stretched in any way.

(v) The lid of the puncture box is carefully placed on and the screws are fastened, ensuring that the film cannot move. The film is now prepared for puncture analysis. The puncture box is custom made by DEKS Engineering from hard plastic. (vi) The texture analyser set up parameters are shown in the table below. The texture analyser is a CT3™ texture analyser available from BROOKFIELD AMETEX).

(vii) The puncture box is placed in the middle of the texture analyser platform and the platform is adjusted to the desired height. The box is positioned so that the probe can travel through the film-covered opening without any obstruction. The run is started and the probe travels to sample surface and instrument measurement is triggered at set load.

(viii) The probe then compresses the sample until a distance of 20 mm is covered; recording the data and a graph of force (g) versus distance (mm) is simultaneously plotted. This includes the film puncture data which usually occurs < 15 mm of distance. If the film does not puncture at this distance, the settings are adjusted for a longer distance and the experiment is repeated with a new sample.

(ix) The raw data, graph and resultant report parameters are all exported and saved for further processing and analytic interpretation.

Based on the results of the initial screening, five casing materials were selected for further investigation. Each of these casing formulations exhibited the following properties: pH in the range of from 3.73 - 4.02

Viscosity in the range of from 15.5 to 46.7 Pa-s

Puncture force in the range of from 196.2 to 414.0 g

Breaking distance in the range of from 6.1 to 9.5 mm

Work required to puncture in the range of from 5.2 to 13.3 mJ Example 2: Cooking properties of casing materials

The five casing materials identified in Example 1 were made in 20 kg batches. The pH and viscosity of the casing materials were measured. The casing materials were extruded onto the outside of a filling material with a relatively high moisture content, and then immersed in a strengthening solution comprising from 5 to 15 % by weight calcium chloride. The coated sausages were then deep fried. The cooking properties of the coated sausages were assessed based on the degree of bubble formation under the coating.

It can be seen that the use of an interrupting agent, specifically tapioca starch or microcrystalline cellulose, and a pH in the range of from 3.4 to 4.0 enables the casing material to be successfully extruded. The addition of a plasticiser, specifically glycerol, significantly improves the cooking properties of the sausages.

Photographs of deep fried sausages covered in coatings 11 and 17 are shown in Figures 1a and b, respectively. Minimal bubble formation is observed under the coating of the sausages, particularly where microcrystalline cellulose was used as the interrupting agent.

Further coating materials comprising guar gum (0.5 %), water (to 100 %) and varying amounts of alginate, tapioca starch, microcrystalline cellulose and glycerol were prepared and tested in a similar manner.

All of the casing materials exhibited good properties when deep fried, as well as a pleasing skinless texture on eating. It can be seen that the use of a combination of microcrystalline cellulose and glycerol in the coating materials leads to particularly good cooking properties. Although casing material 19 exhibited the best cooking ( i.e . lowest amount of bubble formation), it was perceived to be slightly less stable during processing than casing 11 , containing a slightly lower proportion of glycerol.

Slight differences in the pH and viscosities of the casing materials between experiments is due to the use of different batches of alginate, and different sources of water.