MICROWAVABLE COATINGS BASED ON STARCH AND CELLULOSE

Abstract: A method of producing a coated foodstuff which may be reheated by microwave irradiation comprises: (a) applying to the foodstuff a predust composition which is an admixture of at least one particulate starch and at least one particulate cellulose gum which per se gels upon heating in the presence of moisture, (b) applying a batter to the predusted foodstuff, said batter comprising a starch and a cellulose gum which per se gels upon heating in the presence of moisture, (c) frying the battered foodstuff, and (d) cooling the fried product.

Description: icro avable coatings based on starch and cellulose The present invention relates to food products provided with a microwavable coating such that the product may be heated by microwave irradiation prior to consumption. The microwave oven is now well established in both the home and in catering establishments for heating food. Microwave ovens are particularly suitable for heating food products which have been pre- prepared by a food manufacturer. Such pre-prepared products are supplied for example to shops and supermarkets and also to restaurants and so-called "fast food" establishments. The pre-prepared product need only be heated in the microwave oven so that time spent in food preparation by, for example, personnel in a catering establishment is minimised. Examples of such pre-prepared products are batter coated foodstuffs in which the basic foodstuff (e.g. meat, fish, poultry, vegetables, fruit, iced products etc) has been coated in batter, optionally subsequently coated in crumbs, and then deep fried prior to being frozen for supply to the shop, supermarket, or catering establishment. However, particular care needs to be taken in the preparation of such batter coated foodstuffs to ensure that the product (as heated by the microwave oven) has the required texture and "mouthfeel". This is because microwave heating of the foodstuff (eg from frozen to a temperature of at least about 70°C) will .cause significant moisture release from the foodstuff. Without proper formulation of the coating, this moisture release can make the coating very soggy, resulting in a poor texture and "mouthfeel" when the product is eaten. EP-A-0 155 760 discloses a procedure for forming a coating composition on a foodstuff by applying sequentially (a) a predust (b) a batter (c) low density breadcrumbs. The predust layer is a finely divided mixture of components and may, for example, comprise ' about 1 - 10% of powdered egg albumen or other food binder (eg gelatin or starch) to provide adhesion for the SUBSTITUTE SHEET components and a balance of breadcrumbs with or without flour. Seasoning may also be incorporated to the predust. The overall coating composition (i.e. comprised of (a) - (c) above) is chosen to provide an overall controlled degree of porosity to retain some moistness but to release the excess generated during reheating. WO-A-88/06007 relates particularly to a batter composition and also discloses a method by which a foodstuff may be prepared prior to coating with the batter. In particular WO-A-88/06007 discloses that the foodstuff may be predusted with a high amylose starch and alternatively or additionally a precoat of methyl cellulose may be employed. According to a first aspect of the present invention there is provided a method of producing a coated foodstuff which may be reheated by microwave irradiation, the method comprising: (a) applying to the foodstuff a predust composition which is an admixture of at least one particulate starch and at least one particulate cellulose gum which per se gels upon heating in the presence of moisture, (b) applying a batter to the predusted foodstuff, said batter comprising a starch and a cellulose gum which per se gels upon heating in the presence of moisture, (c) frying the battered foodstuff, and (d) cooling the fried product. Preferably, crumb is applied to the battered foodstuff prior to frying thereof. The fried food product may for example be chilled or frozen. If desired, the food product may be subject to further cooking or other processing steps after frying and prior to chilling or freezing. The food products produced by the method of the invention may be packaged in a suitable container, e.g. a microwavable tray, and frozen for storage. Subsequently, the products may be reheated in a microwave oven. The function of the pre-dust composition is to form a dense high viscosity surface film which acts as an oil absorption barrier and a moisture migration barrier. Furthermore, the film acts as a high temperature, freeze stable environment for any seasoning in the product composition (see below), and also as a "substrate" to which SUBSTITUTE SHEET bonding with the batter can take place. A further function of the film is to act as a cryoprotectant. The presence of the starch and cellulose gum in the batter provide a cooked batter which forms a heat stable freeze-thaw-heat barrier/surface. When the food product is reheated in a microwave oven, the batter is regenerated with steam issuing from the food product. The coating as a whole allows excess moisture to pass through as thermal gelation takes place. Subsequently, when the food cools after excess moisture is released, the coating self-crisps by absorption of free moisture. The overall result is that, in the reheated product, the texture of the coated food and the crispness of the batter are as would be expected for a freshly deep-fried coated product. The predust composition used in the invention incorporates a cellulose gum which, when in the presence of water, produces a gel upon heating. Such gums are already known and are generally comprised of methylcellulose or hydroxyalkyl derivatives thereof (e.g. hydroxypropylmethylcellulose gum). We have surprisingly found that admixtures of such particulate gums and a particulate starch produce (upon heating in the presence of moisture) a gel of significantly higher viscosity than that obtained for the cellulose gum alone. The preferred cellulose gums for use in the predust composition are methylcellulose gums (and hydroxyalkyl derivatives thereof) and are most preferably those which, at 2% concentration in water and at a temperature of 50-75°C produce a viscosity of 3000 - 100,000 cP as measured using a Brookfield or similar viscometer using a No. 4 spindle or any viscosity appropriate to the predust composition. Particularly suitable cellulose gums are available from The Dow Chemical Company under the Trade Mark METHOCEL. Particularly preferred are those METHOCEL products available under the designations A4M, F4M and K4M. The starch to be used in the predust composition is preferably one having a low amylose content as this will ensure that the starch (and more particularly the- amylose) does not give the foodstuff an undesirable aftertaste. Typically the amylose content will be below 35% by weight. Starches which meet this criteria include potato, tapioca, arrowroot, corn, sorghum, rice, wheat, oat, waxy maize, waxy SUBSTITUTE SHEET sorghum, waxy rice and sago. We do not however preclude the use of starches with higher amylose contents, eg up to 70%. Typically the predust composition will comprise 10-95% by weight of the starch and 5-90% of the cellulose gum based on the total weight of the starch and gum in the predust. More preferably, the predust composition comprises 10-70% by weight of the cellulose gum, even more preferably about 30-55% of the gum on the same weight basis. The product composition may also include seasoning, e.g. in an amount up to 50% (e.g. 20-40%) by weight (of the total weight of the predust composition) of seasoning. The seasoning in the predust composition will depend on the food product being coated but may include, for example, salt, pepper, flavourings, and flavour enhancers (e.g. monosodium glutamate). It is found that bonding of the predust composition to the foodstuff ie enhanced when salt and other seasonings are present in the predust composition. We have also found that the seasoning appears to be stabilised by the predust. As a result, the full flavour of the seasoning is obtained in the final product, as compared to the case where the seasoning is applied directly to the foodstuff in which case some destabilisation of the seasoning (and hence loss of flavour) seems to occur. The predust composition may be such that it forms a gel with free surface moisture on the foodstuff prior to thermal geletation during the cooking process. Generally, the pick-up of the predust composition by the foodstuff will be about 1-2%. The cellulose gum present in the batter is preferably one which, at 2% concentration in water and at a temperature of 50-75°C, has a viscosity of 2500 to 8500 cP as measured by a Brookfield or similar viscometer using a No. 4 spindle. More preferably this viscosity is 3500 to 6000. Examples of gums which may be used in the batter include METHOCEL products available under the designations A4M, F4M, and K4M. The starch in the batter is preferably a high amylose starch. Such starches are hard granular, high gelation temperature starch. The high amylose starch may for example be that available under the name MICROCRISP from National Starch. The batter will generally also include a flour, most preferably a gluten free flour. It has been found that gluten appears to "clump" and cause a "chewiness" in the product upon reheating. The batter will be produced by admixing the powdered batter ingredients with water. Typically, the powdered batter ingredients will comprise by weight High Amylose Starch 40-50% Cellulose Gum 1-5% Flour 25-40% Ancillary Ingredients balance The above percentages are by weight of the total weight of the powdered batter ingredients. The ancillary ingredients may include D-xylose dried egg yoke, dried egg white, and/or emulsifiers etc. Typically the powdered batter ingredients will comprise The D-xylose provides a browning effect (by the Maillard reaction) to give the appearance of a "finished" product from the frying- operation. (The product from the frying operation is in fact a 'semi-finished' product with the subsequent microwave heating operation providing the 'finishing' step). Reducing sugars other than D-xylose may also be used. The Glucono-D-Lactone serves to control SUBSTITUTE SHEET the Maillard reaction due to conversion of the lactone into gluconic acid without such control. The powdered ingredients will generally be mixed with water in a ratio of one part ingredients to 2-3 parts water (most preferably about 2.5 parts water). It will be appreciated that the powdered ingredients may be admixed together, and supplied, as a 'batter mix' to be let down with water as required. Generally about 15-25% (e.g. 20%) of batter based on the weight of the food being coated is applied to the foodstuff. By increasing the viscosity of the batter (by temperature variance it is possible to increase the pick-up of batter to 40%. As mentioned above, it is preferred to apply crumb to the battered foodstuff. One example of crumb which may be used is RHM 1004 Japanese Style (unbleached). Generally the crumb will have a particle size of 2 mm to 8 mm. Typically, the amount of predust, batter and crumb on the product will be such that, after frying, the coated foodstuff will be 30-40% (e.g. 33-37%) by weight greater than the weight of the uncoated foodstuff. In some circumstances, particularly on smaller core products, the weight increase may be just less than 100%. The batter mix, when fried, acts as a cryoprotectant to the crumb and after microwave heating causes the crumb to dry out rapidly and regain its texture. The battered foodstuff is fried using conventional techniques. Generally, the temperature of the oil in which the product is fried will be 195 - 198°C. The frying oil may be for example a blend of hydrogenated vegetable oils with dimethyl polysiloxane added as a "frying life" extender. Higher frying temperatures may be used if lower frying times are required. The frying process may be conducted either to cook the foodstuff partially or fully according to requirements. For example, the core food may be part-cooked, with the cooking to completion effected during subsequent microwaving (see infra). The increase in temperature during the frying process causes the pre-dust composition (in combination with the moisture naturally present on the surface of the foodstuff) to form a viscous gel coating SUBSTITUTE SHEET around the foodstuff. The gel formed by the predust is therefore able to take-up moisture which is thus not released into the batter. The gel produced will be stronger and more stable than that obtained by use of the cellulose gum alone and will provide a strong bond between the batter and the foodstuff. Depending on the exact predust composition, the gel coating will have a greater or lesser permeability to moisture vapour. It is therefore possible to formulate the predust composition to take into account the amount of moisture which will be released by the foodstuff during frying to ensure that a crisp batter is obtained. Upon cooling of the fried product, the gel remains but may or may not decrease in viscosity. During re-heating of the battered product in a microwave oven, the gel (formed from the cellulose gum/starch mixture predust) will again control the moisture which is released into the batter. As indicated above, the predust composition may be formulated to take into account the amount of moisture vapour which will be released into the batter during frying and microwaving to ensure that the batter does not become soggy during either of the heating stages. This will ensure that the foodstuff (when eaten) has a good "mouthfeel" as expected for the type of product being consumed. Thus the predust composition will be dependent on the moisture control which the gel (produced by heating of the predust during frying and microwaving) is required to exhibit. For example, fish products should lose water through the gel coating during the heating slips to provide an element of "dryness" within the fish flesh as is desirable for a good "mouthfeel". Conversely, meat and poultry should retain moisture during heating to ensure a desirable "mouthfeel" for the product. Other food products (eg vegetables) may require the use of predusts which provide an intermediate degree of moisture transmission. In general, the higher the content of cellulose gum in the predust the higher will be the permitted moisture loss through the gel during heating. Thus, for example, it is generally preferred to use a predust composition containing 50-70% by weight of cellulose gum (based on the total weight of the cellulose gum and starch) where higher moisture release is required, e.g. in the case of fish. SUBSTITUTE SHEET Conversely, for a product such a poultry (e.g. chicken) where there is comparatively less moisture release from the foodstuff, a lower amount of cellulose gum would be used (typically 20-30% by weight of the cellulose gum and starch. The higher the amount of cellulose gum in the predust composition the stronger will be the gel formed upon heating. A strong gel gives better stability beneath the batter leading to greater dryness. Given that the predust has been carefully formulated to provide the required degree of moisture control, it is also important that the initial moisture content of the foodstuff is correspondingly controlled for optimum results. Thus, for example, fish should be drained before application of the predust to ensure that the amount of moisture to be released is not far in excess of that for which the predust has been formulated. After frying, the product is preferably frozen under conditions such that "frost" does not adhere to the coating. The speed of freezing is important. It is essential during this process that moisture migration is avoided. Cryogenic freezing has proven to be the best means of freezing because not only is the process very rapid with the product reaching a core temperature of -30° or lower but there is the added bonus of dehydration of any surplus moisture at the surface of the product. Thus prior to packaging, the fried food product is totally dry. The product may now be packaged for distribution and sale. The packaging may for example be a microwavable bag or tray. When required for consumption, the foodstuff in heated in a conventional domestic or commercial microwave oven. During this heating the foodstuff may recover from ca - 20° to ca +80 oC in one to six minutes depending on the oven and on the weight, size and thickness of the core foodstuff. As described above, the predust composition will (during this heating) revert to a viscous gel with the required moisture transmission characteristics for the particular foodstuff to ensure good "mouthfeel" as discussed previously. This invention may be used in conjunction with a wide range of foodstuffs, eg meat, poultry, fish, vegetables and fruit. The invention may be used, for example, for producing dessert type products in which a fruit puree is coated with batter and crumbs prior to deep frying. One example of such a product is a so called "apple crumble" of the type available in fast food establishments. SUBSTITUTE SHEET

Claims: CLAIMS 1. A method of producing a coated foodstuff which may be reheated by microwave irradiation, the method comprising: (a) applying to the foodstuff a predust composition which is an admixture of at least one particulate starch and at least one particulate cellulose gum which per se gels upon heating in the presence of moisture, (b) applying a batter to the predusted foodstuff, said batter comprising a starch and a cellulose gum which per se gels upon heating in the presence of moisture, (c) frying the battered foodstuff, and (d) cooling the fried product. 2. A method as claimed in claim 1 wherein the predust composition comprises 10-95% by weight of said at least one particulate starch and 5-90% by weight of said at least one particulate cellulose gum, the percentages being based on the total weight of said cellulose gum and said starch in the predust composition. 3. A method as claimed in claim 2 wherein the predust composition comprises 10-70% by weight of said at least one particulate cellulose gum and 30-90% of said at least one starch based on the total weight of said cellulose gum and said starch in the predust composition. 4. A method as claimed in claim 3, wherein the predust comprises 30-55% by weight of said at least one particulate cellulose gum and 45-70% by weight of said at least one starch based on the total weight of said cellulose gum and said starch in the predust composition. 5. A method as claimed in any one of claims 1 to 4, wherein the cellulose gum present in the predust composition is one which at 2% concentration in water and at a temperature of 50-70°C, has a viscosity of 3000 to 100,000 cP. 6. A method as claimed in any one of claims 1 to 5, wherein the starch in the predust composition has an amylose content below 35% by weight. 7. A method as claimed in claim 6, wherein the starch in the predust composition is a potato, tapioca, arrowroot, corn, sorghum, rice, wheat, oat, waxy maize, waxy sorghum, waxy rice or sago starch. SUBSTITUTE SHEET 8. A method as claimed in any one of claims 1 to 7, wherein the predust composition contains seasoning. 9. A method as claimed in claim 8, wherein the predust composition contains 1-50% by weight of the seasoning. 10. A method as claimed in any one of claims 1 to 7, wherein the amount of the predust composition applied to the foodstuff is 1- 2% by weight of the foodstuff. 11. A method as claimed in any one of claims 1 to 10 wherein the cellulose gum used in the batter is one which at 2% concentration in water and at a temperature of 50-75°C has a viscosity of 2500 to 8000 cP. 12. A method as claimed in claim 11, wherein the cellulose gum used in the batter is one which at 2% concentration in water and at a temperature of 50-75°C has a viscosity of 3500 to 6000 Cp. 13. A method as claimed in any one of claims 1 to 13, wherein the starch in the batter is other than a dextrinised starch. 14. A method as claimed in any one of claims 1 to 13, wherein the starch in the batter is a high amylose starch. 15. A method as claimed in any one of claims 1 to 14, wherein the batter contains a gluten free flour. 16. A method as claimed in any one of claims 1 to 15 wherein the batter contains D-xylose. 17. A method as claimed in any one of claims 1 to 16 wherein crumb is applied to the battered foodstuff prior to frying. 18. A predust composition comprising a mixture of 10-95% by weight of at least one particulate starch and 5-90% by weight of at least one particulate cellulose gum which per se gels upon heating in the presence of moisture, said percentage being based on the total weight of the starch and cellulose gum in the composition. 19. A powdered batter mix comprising at least one cellulose gum which per se gels upon heating in the presence of moisture and, at 2% concentration in water and at a temperature of 50-75°C, has a viscosity of 2500 to 8500 cP, gluten free flour, and starch other than dextrinised starch. 20. A batter mix as claimed in claim 19, wherein the starch is a high amylose starch. SUBSTITUTE SHEET 21. A batter mix as claimed in claim 20, wherein the high amylose starch is present in the batter mix in an amount of 40-50% by weight. 22. A batter mix as claimed in any one of claims 19 to 21 wherein the cellulose gum is present in an amount of 1-5% by weight. 23. A batter mix as claimed in any one of claims 19 to 22 wherein the flour is present in an amount of 25-40% by weight. 24. A batter mix as claimed in any one of claims 19 to 23, additionally comprising D-xylose. SUBSTITUTE SHEET

Inventors: PICKFORD KEITH GRAHAM, PICKFORD, KEITH, GRAHAM
Applicants: NOVUS INVESTMENTS LTD, NOVUS INVESTMENTS LIMITED
Application year: 1992
Main classification: A23P1
IPC codes: A23L1, A23P1