The present invention broadly relates to the manufacture of edible proteinaceous products, in particular texturised protein products (TPPs) for human and/or animal consumption. In particular, the invention relates to a method and apparatus for the manufacture of fibrous meat analogue products using cooking-extrusion technology, as well as to a meat analogue product obtained by such method and apparatus.
The industrial manufacture of meat analogue products from protein-rich precursor materials, including plant based precursors such as cereal grain gluten (of wheat, rice, or maize; vital or with residual starch), defatted oil seed, cereal and bean flours, meals and derivatives (e.g. defatted soy flour, soy protein concentrates, wheat flour), or animal based precursors such as meat by-products obtained by mechanical separation, fish meal, dried egg white and others, alone or in combination, is nowadays well established practice. Cooking-extrusion technology is by far the most widely used one of different possible manufacturing methods to obtain such meat analogues.
The texture of such products (hereinafter also simply referred to as texturised protein products (or TPPs), whether based solely on grain or bean sourced proteins or having additional, meat-based precursors) is an especially important criteria if such product is to be used as a replacement for real meat products, as acceptance of the product, in particular if intended for human consumption, will depend on its capability to simulate existing meat as far as bite, chewiness, structure, appearance (and taste) are concerned. Whilst appearance may not seem as important where the analogue product is to be used in pet foods, either alone or mingled with real meat pieces and embedded in semi-liquid carriers (eg gravy), its structure and texture are still important factors, as these determine the suitability of the analogue product for further processing after its manufacture. For instance, the structure and texture may determine whether the analogue product may be suitable to be subjected to certain steps to obtain the end product (e.g. in retorted or hydrated form, such as in canned pet food products).
In its very basic form, manufacture of meat analogue products with a textured or fibrous structure entails the commingling of the weighted dry precursors and introducing these together with water (to obtain a desired moisture content in the mixture) into a suitable heated extruder (e.g. single or double screw extruder). Whilst passing through the extruder, which has discrete sections to perform specific mechanical operations on the mixture, the mixture is plasticised and heated to form a hot, viscous and at least partly molten mass, often referred to as a protein lava. The properties of the viscous mass at the end of the thermo-mechanical conversion process, which the precursors undergo within the extruder barrel, are dependent on the process variables (e.g. temperature in the different sections of the extruder barrel, screw speed/barrel section pressure, moisture content, precursor formulation, etc.). In order to achieve the formation of fibrous structures in the extrudate, the hot, viscous mass of proteinaceous material is pressed by the extruder screw(s) through a breaker plate having a multitude of small openings and subsequently passed through a cooling or tempering die flanged at the extruder barrel outlet opening. The cooling die is used to prevent or regulate flashing of the moisture contained in the extrudate, so as to obtain a plastically-malleable, but otherwise cohesive, non-puffed extrudate in the form of a continuous slab or ribbon of xe2x80x9cmeat analoguexe2x80x9d product (c.f. xe2x80x9cBetter Texture for Vegetable Protein Foodsxe2x80x9d, Food Engineering International Journal, September 1976).
Extrudates prepared from defatted soy flour with moderate water content (up to 35%) using single-screw, temperature controlled extruders are slightly expanded (or puffed), easily dried, and (only to a certain extent) have structure and texture features resembling animal muscle tissue. However, it is inappropriate to call them meat analogues, as they have to be rehydrated with water and/or flavoured liquids before consumption.
High moisture extrusion-cooking and texturisation (or protein fibration) is one food technology process that has been successfully employed in recent years in fibrating protein-based formulations at high moisture content, and thus texturising xe2x80x9cwetxe2x80x9d, meat-like TPPs either using solely plant protein sources (cereal and oil-seed grain protein sources such as soya flour, soy protein concentrate and vital wheat gluten, in particular) and/or animal proteins such as fish flour, egg white powder, fresh meat by-products and the like. HMEC process technology, which is particularly advantageous in the context of the present invention, is described in more detail in xe2x80x9cExtrusion cooking of high moisture protein foodsxe2x80x9d, by Akinori Noguchi in: Mercier, C., Linko, P., Harper, J. M. (ed.), Extrusion Cooking, 343-370, American Association of Cereal Chemists, St Paul, Minnesota, the contents of which, including that of the references cited there, are incorporated herein by way of short-hand cross reference. Further details on this technology are also described in xe2x80x9cHigh moisture extrusion cooking and protein fibrationxe2x80x9d, by D. Durand, J. M Bouvier and S. Le Royer, being a paper presented during the Third Annual Smart Extrusion Seminar 1998, hosted by Food Science Australia, which was held on Aug. 31 and Sep. 1, 1998, and the references cited in that paper.
Importantly, the TPP slab or ribbon extrudate, after exiting the extruder, is generally subjected to further process steps in order to obtain the desired end product. So it is known to have specially designed forming dies at or within the cooling die and cutting devices to impart a specific shape on the extrudate to mimic actual animal or vegetable products such as seafood, chicken slices, beef chunks or slices, sausages, mushroom caps and the like. As indicated above, if the TPP extrudate is to be used in the manufacture of pet foods, for example, it is important that it can be appropriately portioned (e.g. into chunks, slices, etc.) and retain its texture and structural integrity during subsequent production steps which may include freezing, co-mingling as a meat extender with real meat (or meat by-products), filling into cans with aqueous liquids, thermal treatment, rehydration and/or retorting in case the moisture content of the TPP after extrusion is below desired values, and the like, which can adversely affect the fibrous structure of the TPP.
It is further known that the inherent aptness of a TPP extrudate to be subjected to further forming steps not only depends on the process parameters selected during extrusion in the screw-extruder and cooling in the forming die, but also the composition of the precursor mixture and water content. For example, inadequate dwell time or cooling of the extrudate within the flash expansion inhibiting cooling die may lead to a puffy consistency and texture of the TPP extrudate, which will negatively increase moisture absorption during subsequent manufacturing steps, and may render the finished product of mushy consistency, and not meat-like at all (compare for example U.S. Pat. No. 3,968,268 (Sair et al.)).
Similarly, formulation of the TPP (i.e. use of different protein-source precursors and relative proportions thereof in precursor mixtures), as well as presence of nutritional additives, flavouring and conservation agents, initial moisture contents and the like, affect the inner structure and texture of the extrudate and therefore its susceptibility to mimic specific types of meat. In other words, not all formulations will be useful where the end product to be mimicked is chicken meat or tuna flakes, and mixtures and formulations can only be exchanged to a certain extent for the same end product to be mimicked.
The present invention, in one of its aspects, aims at providing a method of manufacturing a texturised protein (i.e. analogue) product that mimics the appearance of flaked fish meat (in particular tuna fish flakes), shredded chicken meat or other meat products, as well as an apparatus for manufacturing such texturised protein (i.e. analogue) product.
The invention also seeks to provide a suitable formulation for a texturised protein (i.e. analogue) product that enables the TPP extrudate formed in an extrusion cooking process, in particular high moisture extrusion cooking, to be mechanically shredded into flakes that closely resemble in texture and structure a meat product, such as flaked fish meat (in particular coarsely flaked tuna fish) or shredded chicken meat (e.g. chicken breast meat).
Accordingly, in a first aspect of the present invention, there is provided a method of manufacturing a texturised proteinaceous meat analogue product, said method including:
subjecting, in a food-extruder, a mixture containing:
about 40 to 95% by weight edible proteinaceous materials selected from the group consisting of predetermined mixtures of defatted soy flour, soy meal, soy concentrate, cereal gluten in vital or starch-containing form and egg white; and
up to about 7% by weight of edible mineral binding and cross-linking compounds;
to mechanical pressure and added heat sufficient to convert the mixture into a hot, viscous protein lava;
extruding the protein lava through and from a temperature controlled cooling die which cools and reduces the viscosity of the protein lava to obtain a cohesive, texturised, extrudate slab or ribbon in which vapour-flashing is substantially inhibited; and
subjecting the solidified extrudate slab or ribbon to mechanical shredding in a hammer mill having a cage plate with a plurality of elongate discharge openings and a plurality of hammer bars hinged to discs attached to a rotating shaft, so as to obtain a plurality of extrudate shreds that resemble in consistency and texture flaked or shredded meat.
Preferably, the extrudate shreds resemble in consistency and texture flaked fish meat, shredded chicken meat or shredded red meat (such as beef or lamb).
Preferably, the above method includes the addition of some real meat product or meat by-product. This addition may occur prior to, during or after the step of subjecting the mixture to mechanical pressure and heat. Preferably, the addition of the meat product or meat by-product occurs during the extrusion step. This real meat or meat by product may be obtained from fish, poultry or from livestock (such as cattle or sheep).
Advantageously, the extrudate is transferred directly after leaving the cooling die to the hammer mill for shredding, as optimum shredding to obtain extrudate shreds or flakes is achieved whilst the extrudate slab is still warm. Therefore, typically, the time between extrusion and cutting should not exceed 5 minutes.
Preferably, the mixture referred to above has a total moisture content of between about 40 and about 60%. However, during the manufacturing process, moisture is lost especially after the extrudate slab or ribbon exits the cooling die. Therefore, since the preferred moisture content of the extrudate slab or ribbon is between about 40 to 60% water is generally added as some point(s) in the process.
Preferably, tempered water is sprayed onto the extrudate slab after it exits the cooling die and whilst being conveyed towards the hammer mill. This step increases densification of the solidified extrudate and has a positive effect on the actual shredding operation. However, tempering should be moderate, as warm cutting of the extrudate slab renders a better end product than shredding a fully cooled slab.
It will be understood that the extrudate can be conveyed as a continuous band or ribbon directly into the hammer mill, or it may be conveyed in shorter lengths or discontinuous portions.
A preferred formulation in the manufacture of the extrudate shreds includes, (in % by weight of materials that make up the mixture before addition of water), about 40-55% detatted soy flour, soy meal or soy concentrate, about 35-45% vital wheat gluten, egg white powder, a mixture of vital wheat gluten and maize gluten or a mixture of vital wheat gluten and wheat flour, 0.1-7.0% of non-leaching mineral compound(s) that bind in the protein matrix and enhance protein cross-linking (including for example 0.08 to 0.3% sulphur), optionally 0-5% nutritional fiber additives, in particular cellulose or beet pulp, 0.1-0.3% vitamins, 0-3.0% flavouring agents and 0.01-3.0% colouring agents. The moisture content of such a dry ingredients mixture is typically within a range of 6-15% by weight, and water in an appropriate amount is added to the dry mixture itself or into the extruder at a point downstream of the feeding entry for the dry material mixture so as to obtain a total moisture content of the extrudate within a range of 35 to 60%.
A particularly preferred formulation, which results in extrudate shreds that substantially mimic tuna fish flakes and which can be further processed together with real fish chunks and gravy into a fish-based, canned pet food product, consists of a dry ingredient mixture of about 51.5% defatted soy flour, about 42% vital wheat gluten, 5% dicalcium phosphate, 0.1% sulphur, 0.18% nutritional vitamin supplements, 0.2% nutritional mineral supplements, 1.0% flavouring agents and 0.002% colouring agents (all weight %), water being added to the mixture before or after being metered into the extruder in an amount to obtain an extrudate overall moisture content by weight of about 48-52%.
In accordance with the invention, it has been unexpectedly found that a conventional hammer mill, which is generally employed to grind, particulate or pulverise dry, soft materials such as coal, grains, seeds and similar dry materials, can be employed to shred the proteinaceous, plasto-elastically-resilient, and moisture-rich extrudate slab or ribbon into chunks or pieces that closely resemble in appearance those of shredded tuna fish meat or chicken meat, without otherwise adversely affecting the structure and texturisation of the TPP shreds.
The hammer mill requires for this purpose modification of the shape of the generally circular cage plate openings into suitable shapes, such as oblong slits or rectangular holes. Conventionally, intermeshing rotatable knife blades would have been the expected choice for shredding the extrudate. However, the resultant pieces lack the desirable flaky texture observed in many fish meats. Whilst no detailed analysis has been conducted on this, it is believed that the hammer bars interact with the slit-like openings in a manner so as to tear or rip the extrudate slab apart at interfaces between the fibres formed in the cooling die extrusion process, thereby imparting a shredded, flaky appearance as compared to clean cutting surfaces as obtained with rotary knifes.
The cage plate openings are preferably of uniform shape and area thereby to obtain extrudate shreds in which the individual shreds have a weight within a narrow range of possible weights, and have a randomly uniform appearance to the eye.
The process of this invention may include additional steps. For example, after the shredding operation, the extrudate shreds may undergo further processing which can include freezing, dehydration and canning.
In applications where the meat analogue extrudate shreds are to serve as meat extenders in canned pet food products, the extrudate shreds can be metered directly from the hammer mill into mixing vessels where the shreds may be commingled with appropriate real meat pieces (eg fish, chicken, lamb or beef pieces), gravy and nutritional additives. This may be desirable as the shelf life of the (uncanned) extrudate after shredding is relatively short, (eg 4 to 7 hrs), xe2x80x94the texture and structure of the untreated, moisture-rich shreds being stable for thermal and mechanical processing during that period. However, once further processed, for example in a canned product, the extrudate shreds maintain their body structure and appearance. Similarly, the dehydrated extrudate shreds can be hydrated using known processes without negatively affecting the structure and integrity of the rehydrated product.
In a second aspect of the present invention there is provided a shredded meat analogue product manufactured in accordance with the process described above using the formulation of materials referred to above.
In a third aspect of the present invention there is provided a production line for the manufacture of texturised proteinaceous meat analogue products, according to the method of the first aspect of the invention, including:
a food extruder with a plurality of temperature-controlled barrel sections and having at least one feed opening adapted for receiving the mixture of the first aspect of this invention, and a discharge opening adapted for discharging a hot, viscous protein lava;
a temperature-controlled cooling die located at the discharge opening and adapted for receiving the hot protein lava and for cooling the same to such an extent that an at least surface-solidified, proteinaceous extrudate slab or ribbon exits the cooling die substantially without vapour flashing taking place in the extrudate;
a hammer mill having a cage plate with a plurality of elongate discharge openings and a plurality of hammer bars hinged to discs attached to a rotating shaft; and
conveyor means adapted to receive and convey the extrudate slab or ribbon from the cooling die to a feeding chute of the hammer mill.
Advantageously, a volumetric or mass flow dry material feeder is disposed in communication with the feed opening of the extruder, a separate means for metering water into the extruder being located at a point downstream of the dry material feeding opening. Water steam injection into the extruder barrels could also be used in known ways.
A water spraying unit is advantageously associated with the conveyor means, which preferably incorporates an endless conveyor rack, such as to direct fine sprays of tempered water on to the surface of the extrudate slab or ribbon as it travels on the conveyor rack toward the hammer mill chute, to effect additional densification of the surface of the extrudate slab or ribbon after it exits the cooling die.
The cooling die may be adapted so as to form the extrudate slab or ribbon having any suitable cross-section (e.g. rectangular or circular). The cooling die is preferably a multi-channel cooling die.
The production line is arranged such that continuous manufacturing of shredded TPP extrudate is achieved from metering of the dry ingredients and water into the extruder to metering the extrudate shreds into appropriate vessels for further processing. Alternatively, a further conveyor means can be disposed underneath the hammer mill discharge chute for conveying the meat analogue shreds towards further processing units of an integrated food production line, (e.g. a canning station or the like).
The extruder is preferably a twin conveyor and pressurising screw extruder with 4 to 8 barrel sections that are individually temperature controlled, each section having a length to diameter ratio of approximately 4, as used in high moisture extrusion cooking. Temperature settings at the individual barrel sections during the manufacturing process will vary between 60 and 120xc2x0 C. and internal pressure between 3 and 8 MPa, at screw speeds of between 200 to 350 rpm.