Gel casing and system and method for its production

Abstract

The invention relates to a semi-finished gel and the process for making such a semi-finished gel, suitable for use in the preparation of a gel casing for a food product, from a first natural tissue and a second natural tissue. The invention further relates to a method for making a homogenous collagen-elastin gel including a detangling treatment in an extrusion system comprising a detangler including interlocking members. The extrusion system further comprises a food dough extrusion passage and two co-operating jackets arranged coaxially about the food dough extrusion passage, at least one jacket being rotatable about the co- extrusion axis, the jackets defining an annulus therebetween having an annulus-inlet for the introduction of gel, the rotation of the at least one jacket causing orientation of the gel, thereby converting the introduced gel into an orientated gel, the annulus having an opposed annulus-outlet for discharging orientated gel; wherein discharged orientated gel is deposited onto food dough emerging from the food dough-outlet to form a food product with gel casing.

Description

[0001] Title: Gel casing and system and method for its production

[0002] The present invention relates to the preparation of a semi-finished gel suitable for use as a gel casing for a food-product from a casein and / or elastin-rich material, the semi-finished so obtained, an extrusion system and method for making a gel casing for a food product from the semi-finished gel and the food product thus obtained.

[0003] A typical method of producing a sausage includes grinding the protein and mixing the ground protein with salt, curing agents (if applicable), spices, flavors, sweeteners, extenders (such as milk solids, starch, cereal, and the like), and water prior to stuffing into a tubular gel casing.

[0004] Natural casings can be animal intestine, derived from, for example, cattle, pigs, or sheep. However, natural casings have an uneven thickness, are structurally inconsistent, and can have religious restrictions. In addition, natural casings require careful cleaning and preparation, are in short supply, and are relatively expensive.

[0005] Artificial gel casings are generally made of collagen, cellulose, and / or plastic. Artificial gel casings from animal collagen are generally edible. Collagen gel casings are mainly produced from the collagen in beef or pig hides, and the bones and tendons. It can also be derived from poultry and fish.

[0006] From US2008317915 edible gel casings for foodstuffs are known comprising collagen and a polysaccharide, and methods of manufacturing the gel casings. Collagen is a preferred fibrous protein for use in gel casing. The document also suggests to substitute another fibrous protein, such as a keratin or an elastin for the collagen, either in part or in whole.

[0007] Gels for gel casings are processed extensively. Preferably, the collagen is provided as a collagen-gel which is co-extruded with a food dough. In this context extrusion is the process of shaping a product by forcing a material through a die. The food dough is extruded via a food dough extrusion passage. The gel is extruded via an annulus provided coaxially about the food dough extrusion passage. The discharged gel is deposited onto the food dough emerging from the food dough extrusion passage to form a food product with a gel casing.

[0008] In a continuous co-extrusion process a single sausage gel casing of indefinite length is produced, which is then cut into desired lengths, usually while the co-extrusion process continues. Subsequent treatments may include dehydrating by a setting solution, e.g. using a bath, modification of the shape of the product, for example by rolling, smoking and drying. Usually the product will require drying or other steps to bring the collagen from the set but still wet condition to a stable, handleable state. The gel casing may for example be tanned using such agents as formaldehyde, liquid smoke extracts, alum and dialdehyde alginic acid. US3622353 discloses the preparation of collagen-coated sausages. During the production process the collagen is extruded in tubular form upon the foodstuff. By using a counter-rotating die, friction forces are applied to the collagen fibers that are extruded which is believed to lead to the orientation of the collagen fibers in such a way that the strength of the collagen coating or gel casing is satisfactory in all directions. To realize the required orientation of the collagen fibers this document prescribes the rotation of the jackets of the extruder with 60 to 120 r.p.m. (rotations per minute) when using dual (counterrotating jackets.

[0009] From US2016 / 0227793 a method of extruding gel casings of collagen or a collagen comprising mixture is known wherein the counter rotating jackets are rotated each with a rotation speed of 150-300 r.p.m. Due to the two rotatable and co-operating jackets the collagen (or the collagen comprising mixture) is handled such that the orientation of the fibrous collagen is influenced on a controlled way. The orientation of the fibrous collagen (which is at least a substantial component of a collagen comprising mixture) substantially influences the tissue structure of the extruded collagen gel casings (e.g. the extra-cellular matrix (ECM) morphology) which influences various mechanical properties (like strength and elasticity).

[0010] The amount of gel used in a co-extrusion process is also referred to as pickup. An extrusion process may use up to 10wt% gel in relation to the weight of the extruded food dough, in order to get acceptable characteristics. More gel means more moisture content to vaporize during further processing, resulting in increased time and costs.

[0011] The object of the present invention is to provide a collagen-elastin gel casing having improved properties, such as exhibiting the strength, appearance, regeneration characteristics (re-heating), "snap" and / or "bite" of natural gel casing food products.

[0012] This object is achieved by providing an improved semi-finished gel suitable for use in the preparation of a gel casing for a food product.

[0013] Collagen is a main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is often the most abundant protein in mammals, making up from 25% to 35% of the whole-body protein content. Collagen consists of amino acids bound together to form a triple helix of elongated fibril known as a collagen helix. It is mostly found in connective tissue such as cartilage, bones, tendons, ligaments, and skin, corneas, blood vessels, the gut and intervertebral discs. Elastin is a key component of the extracellular matrix in gnathostomes (jawed vertebrates). It is highly elastic and present in connective tissue allowing many tissues in the body to resume their shape after stretching or contracting. Elastin helps skin to return to its original position when it is poked or pinched. Elastin serves an important function in to help blood flow and is particularly abundant in large elastic blood vessels such as the aorta. Elastin is also found in the lungs, elastic ligaments, elastic cartilage, the skin, and the bladder. Typically, natural tissues such as skin, gut, casing, bladders, stomachs, arteries and veins and other organs contain collagen and elastin, albeit at different ratios. For instance, gut contains usually more collagen than elastin, whereas bladder usually contains more elastin than collagen. The ratios of collagen and elastin may vary per animal species and variety.

[0014] The present inventors have found that a gel that contains a combination of elastin and collagen can provide improved properties in casing gels for food products, in particular when the gel has been subjected to a combination of a chemical unfolding treatment and a physical treatment (detangling). The gel can be made from a first natural tissue and a second natural tissue, such as beef split and bladder. The first natural tissue is relatively rich in collagen compared to the second natural tissue. The second natural tissue is relatively rich in elastin compared to the first natural tissue.

[0015] Thus, in a first aspect, the invention pertains to a method for producing a semi-finished gel suitable for use in the preparation of a gel casing for a food product, comprising the steps of providing a first (collagen-rich) natural tissue such as beef split, and a second (elastin-rich) natural tissue such as bladder, wherein the weight ratio of the amount of collagen in the first (collagen-rich) natural tissue to the amount of collagen in the second (elastin-rich) natural tissue is more than 1 , wherein the weight ratio of the amount of elastin of the second (elastin-rich) natural tissue to the amount of elastin in the first (collagen-rich) natural tissue is more than 1 , wherein the first natural tissue and the second natural tissue are subjected to a chemical treatment to provide a first natural tissue gel and a second natural tissue gel, respectively and blending the first natural tissue gel and the second natural tissue gel or wherein a combination of the first natural tissue and the second natural tissue are subjected to a chemical treatment, to provide the semi-finished gel comprising collagen and elastin.

[0016] The “first natural tissue” can be seen as “collagen-rich ” and as used herein refers to a natural tissue such as a gut, gut ends, beef split, tendon, natural casing and other animal parts that contain collagen. Collagen-rich in this respect refers to a significant presence of collagen, such that the natural tissue can serve as an effective collagen-source for produce an collagen-rich gel. A collagen-rich tissue or product may contain a certain (minor) amount of elastin, depending on the tissue. A “first natural tissue gel ” as used herein refers to a gel that has been obtained from a first natural tissue.

[0017] The “second natural tissue” can be seen as “elastin-rich ” and as used herein refers to a natural tissue such as a skin, bladder, stomach, arteries and veins that contain elastin. Elastin-rich in this respect refers to a significant presence of elastin, such that the natural tissue can serve as an effective elastinsource for produce an elastin-rich gel. An elastin-rich tissue or product may contain a certain (minor) amount of collagen, depending on the tissue. A “second natural tissue gel ” as used herein refers to a gel that has been obtained from a second natural tissue.

[0018] The amount of collagen and / or elastin in a natural tissue or a gel can be determined by procedures know to the skilled person.

[0019] The first natural tissue differs from the second natural tissue in that the first natural tissue contains an amount of collagen (in wt.%) that is higher than the amount of collagen in the second natural tissue. Thus, the ratio of the amount of collagen of the first natural tissue to the second natural tissue is more than 1 .

[0020] The second natural tissue differs from the first natural tissue in that the second natural tissue contains an amount of elastin (in wt.%) that is higher than the amount of elastin in the first natural tissue. Thus the ratio of the amount of elastin of the first natural tissue to the second natural tissue is more than 1.

[0021] In another aspect, the invention also relates to a method for producing a semi-finished gel suitable for use in the preparation of a gel casing for a food product, comprising the steps of (A) (i) providing a collagen-rich gel by subjecting a collagen-rich feed, such as beef split, to a chemical treatment; (ii) providing an elastin-rich gel by subjecting an elastin-rich feed, such as bladder, to a chemical treatment; and (iii) blending the collagen-rich gel and the elastin-rich gel; or (B) providing a mixture of a collagen-rich feed and an elastin-rich feed and subjecting the mixture of a collagen-rich feed and an elastin-rich feed to a chemical treatment; to provide the semi-finished gel comprising collagen and elastin. A “collagen-rich feed” as used herein refers to a natural tissue such as a gut, gut ends, natural casing and other animal parts that contain collagen. “Collagen-rich” in this respect refers to the predominant presence of collagen over elastin (i.e. contains more collagen than elastin, on a weight by weight level). A collagen-rich feed or product may contain a certain (minor) amount of elastin, depending on the tissue, but the fraction of elastin is smaller than the collagen fraction. A “collagen-rich gel” as used herein refers to a gel that has been obtained from a collagen-rich feed. An “elastin-rich feed” as used refers to a natural tissue such as a skin, bladder, stomach, arteries and veins that contain elastin. Elastin - rich in this respect refers to the predominant presence of elastin over collagen (i.e. contains more elastin than collagen, on a weight by weight level). An elastin-rich feed or product may contain a certain (minor) amount of collagen, depending on the tissue, but the fraction of collagen is smaller than the elastin fraction. An “elastin-rich gel” as used herein refers to a gel that has been obtained from an elastin-rich feed.

[0022] As used herein “feed” refers to a raw materials such as skin, gut, casing, bladders, stomachs, arteries and veins, lungs, elastic ligaments, elastic cartilage, beef split, tendon and other organs that contain elastin and / or collagen. As these raw materials may vary in their levels of collagen and / or elastin, depending on the species or origin. As used herein “comminuted product” refers to a feed that has been comminuted into smaller pieces. As used herein “lye-treated product” refers to a product that has been subjected to a treatment with a base (lye), typically at a pH > 7.

[0023] As used herein “acid treated product” refers to a product that has been treated with an acid, typically at pH < 7.

[0024] As used herein “semi-finished gel” refers to a gel that contains elastin and / or collagen, preferably both. The semi-finished gel may be a gel obtained from an second natural tissue gel and a first natural tissue gel, via blending. The semi-finished gel may also be obtained through mixing raw materials that contain elastin and / or collagen that may have been processed as described herein elsewhere to form the semifinished gel of the invention. The semi-fished gel of the invention may also be formed by combining intermediate products that contain elastin and / or collagen, such as comminuted products, lye-treated products and / or acid-treated products.

[0025] As used herein “ homogeneous collagen-elastin gel” refers to a gel, typically the semi-finished gel, that has been subjected to a disentangling treatment to reduce fiber clumps in the gel, thereby converting the semi-finished gel into the homogeneous collagen-elastin gel.

[0026] As used herein “orientated gel” or “oriented collagen-elastin gel” refers to a gel that has been subjected to rotation of at least one of two co-operating jackets causing orientation of the gel, thereby converting the introduced gel into an orientated gel.

[0027] As used herein “gel casing” refers to a gel casing, gel casing film or gel film that has been applied to a food product (such as a sausage). The gel casing is typically subjected to drying, brining or smoking. As used herein “natural casing” refers to a casing made from natural gut, such as sheep, pig or cow.

[0028] The first natural tissue and the second natural tissue (combined or separately) are subjected to a chemical treatment to form a first natural tissue gel, a second natural tissue gel , or a gel that contains both elastin and collagen derived from the first and second natural tissue, respectively. The second natural tissue gel and the first natural tissue gel can be blended to form the semi-finished gel. In certain embodiments, the second natural tissue and the first natural tissue can be combined prior to or during the chemical treatment (as intermediate products) and result in the semi-finished gel.

[0029] As used herein, ratio’s, fractions in the semi-finished gel are calculated based on wt.% on dry matter. In embodiments where the semi-finished gel is based on a blend of second natural tissue gel and first natural tissue gel: the relative amounts of elastin and collagen are calculated based on the relative amounts of second natural tissue gel and first natural tissue gel in the semifinished gel.

[0030] In embodiments where the semi-finished gel is based on a combination of a first natural tissue and an second natural tissue: the relative amounts of elastin and collagen are calculated based on the relative amounts of second natural tissue and first natural tissue in the combination.

[0031] In certain embodiments, the amount of second natural tissue gel can exceed the amount of first natural tissue gel in the semi-finished gel. In certain embodiments, the ratio of elastin to collagen in the semifinished gel can be more than 1 (more elastin than collagen) , preferably more than 1 .2, more than 1 .3, more than 1 .5, more than 2. In certain embodiments, the ratio of second natural tissue gel to first natural tissue gel can be chosen from 100:0 (only elastin-rich) to 10:90, 80:20, 75:25, 50 / 50, 25 / 75, 90:10, 0:100 (only collagen-rich) by weight. There is a preference for 10:90, 80:20, 75:25, 50 / 50, 25 / 75, 90:10.

[0032] In certain embodiments, the second natural tissue gel is present in the semi-finished gel in more than 30 wt.%, 40 wt.%, 50 wt.%, 60 wt.%, 65 wt.%, 70 wt.%, 75 wt.%, more preferable at least 80 wt.%, 85 wt.%, 90 wt.%, calculated on the total amount of the semi-finished gel.

[0033] In certain embodiments, the second natural tissue gel is present in the semi-finished gel in an amount between 30 wt.% and 90 wt.%, 40 wt.% and 85 wt.%, 50 wt.% and 80 wt.%, 60 wt.% and 75 wt.%, 65 wt.% and 70 wt.%, calculated on the total amount of the semi-finished gel.

[0034] In certain embodiments, the first natural tissue is present in the semi-finished gel in less than 50 wt.%, 45 wt.%, 40 wt.%, 35 wt.% , 30 wt.%, more preferable less than 20 wt.%, 15 wt.%, 10 wt.%, calculated on the total amount of the mixture of the first natural tissue and the second natural tissue.

[0035] In certain embodiments, the first natural tissue gel is present in the semi-finished gel in an amount between 10 wt.% and 50 wt.%, 15 wt.% and 45 wt.%, 20 wt.% and 40 wt.%, 25 wt.% and 35 wt.%, calculated on the total amount of the semi-finished gel.

[0036] The first natural tissue gel and / or the second natural tissue gel can be obtained by a chemical treatment such as an chemical process that leads to the unfolding of the protein strands. The process sequence may comprise:

[0037] (a) comminuting a first natural tissue and / or an second natural tissue to provide comminuted product(s);

[0038] (b) optionally, subjecting the comminuted products of step (a) to a lye treatment to provide lye-treated products,

[0039] (c) optionally, mincing the products of step (a) or (b) to obtain minced products;

[0040] (d) optionally, acidification treatment of the products of step (a), (b) or (c) to obtain acid-treated products, and

[0041] (e) aqueous dispersion, optionally combined with a milling treatment, of the products of step (a), (b), (c), or (d), and

[0042] (f) obtaining the semi-finished gel suitable for use in the preparation of a gel casing for a food-product.

[0043] Communication of the feed serves to enhance the surface. Preferably, the comminuting step results in comminuted products having average dimensions between 0.5-3 cm. Surface enlargement is conducive for the subsequent treatment aimed at denaturation / unfolding of the protein strands. The lye treatment is a treatment using a solution of a strong base such as sodium or potassium hydroxide. Typically, a 0.1-2 Molar aqueous solution of the strong base is used. The treatment with a strong base serves to denature / unfold the proteins in the comminuted feed. The lye treatment can be at an elevated temperature and / or for a period of between 4 and 100 hours, preferably between 10 and 75, more preferably between 20 and 50 hours. Following the treatment with a strong base, the surface of the lye- treated products can be further enlarged by mincing, preferably to minced products that may have average dimensions between 0.1 and 0.4 cm. The minced products can be subjected to an acidification treatment with an aqueous acid solution, more preferably a solution of acids elected form the group consisting of lactic acid, acetic acid, hydrochloric and mixtures therefrom. Typically, a 0.1-2 Molar aqueous solution of the acid is used. The acidification treatment can be at elevated temperature and / or for a period of between 4 and 100 hours, preferably between 10 and 75, more preferably between 20 and 50 hours. Typically, the acidification restores the isoelectric point of the proteins involved. The acid-treated products may be further subjected to dispersion in an aqueous solution and optionally to milling and / or homogenization to yield the semi-finished gel.

[0044] Throughout this chemical unfolding process, the feed (first natural tissue, second natural tissue) or the intermediary products (comminuted products, lye-treated products, minced products, acid-treated products) may be processed in separate streams or streams can be combined at any stage. Thus, in embodiments wherein the first natural tissue and the second natural tissue or their ensuing intermediary products can be combined prior to one or more of the comminution step, the lye step, the mincing step, the acidification step or the dispersion step or milling step. In embodiments, between the individual steps of the process sequence, independently, one or more washing treatments can be performed. There is a preferred embodiment in which the first natural tissue gel and the second natural tissue gel are formed in separate process sequences. This allows the respective process sequence to be optimized for the specific product to enhance the quality of the resulting first natural tissue gel and / or the second natural tissue gel. The first natural tissue gel and the second natural tissue gel can be combined in an additional step in which the gels are blended or mixed. Combining the respective gels prior to obtaining the semi-finished gel, allows for adjustment of the collagen / elastin ratio to accommodate for desired variation in products or end-products such as a food casing.

[0045] Combining the first natural tissue gel and the second natural tissue gel to form the semi-finished gel is preferably by a mixing or a blending step under “relative low shear”, i.e. without the collagen or elastin protein strands being sheared or broken. Suitable machinery for the blending can be provided for instance by industrial scale low shear mixers such as obtainable form Glass Maschinenbau Germany. Indicative examples are the VSM / F and VSM / C mixing machines.

[0046] The result of the method of the invention is a semi-finished gel suitable for use in the preparation of a gel casing for a food-product.

[0047] Thus, in one aspect, the invention pertains to a semi-finished gel suitable for use as a gel casing for a food-product, preferably obtainable by the method of the invention.

[0048] The occurrence of fiber clumps in semi-finished collagen-elastin gel is a result of the composition of the gel and typically occurs upon aging. It affects the shelf-life of the semi-finished collagen-elastin gel. The dimensions of such fiber clumps generally can vary between 0,1-5 mm, in particular between 0,3 and 2 mm. fiber clumps are groups of agglomerated and intertwined or -tangled protein fibers which are undesirably large for inclusion in a gel to be deposited as a gel casing. Such fiber clumps, on a molecular level, resemble a plate of spaghetti, or tangled hair (see Fig 5 for a schematic representation). When fiber clumps are present in the gel when deposited as a gel casing onto a food dough, undesired holes and irregularities are likely to occur in the gel casing. The casing has less mechanical strength. Due to the clumps of fibers uneven color formation with liquid smoke may occur, as concentrated clumps of collagen will color darker.

[0049] The present inventors have also solved this problem by subjecting the semi-finished gel to a detangling treatment.

[0050] Thus, in a further aspect, the invention also pertains to a method for making a gel casing for a foodproduct, comprising the steps of providing a semi-finished gel and subjecting the semi-finished gel to a detangling treatment to provide a homogeneous collagen-elastin gel.

[0051] By subjecting the semi-finished gel to a detangling treatment, the agglomerates and clumps are reduced to form a homogeneous collagen-elastin gel. Between the co-operating jackets the protein (collagen / elastin) strands are more orientated or straightened, forming an oriented collagen-elastin gel. The resulting has excellent properties and is particularly advantageous when used as a gel casing for a food product.

[0052] In particular it has been found that characteristics of the obtained products are better when an inventive gel casing as described above is applied, compared to known gel casings.

[0053] As the homogeneous collagen-elastin gel has a tendency to entangle upon aging, it is preferred that the detangling treatment is performed shortly before its orientation, and shortly before the oriented collagen-elastin gel is brought onto the food product. There is a preference to have a time span of not more than 2 hours, in particular less than 30 minutes, between the detangling treatment and the encasing of the food dough to produce the food product. The detangling takes place prior to the operation of the co-operating jackets, in an extrusion system for continuous production of food products with a collagen-elastin gel casing.

[0054] This object is further achieved by providing an extrusion system according to claim 16.

[0055] Advantageously, with the inventive gel and extrusion system desired product characteristics are obtained with a relatively low amount of gel casing. The inventive extrusion process may in embodiments use approximately 4-5wt.% of the inventive gel casing in relation to the extruded food dough (also referred to as “pickup”). Less gel casing means less moisture to be vaporized in process, which may lead to less time / energy and gel casing to be used.

[0056] It has been found that the inventive gel casing generates a wider range of products, i.e. besides regeneration of the sausages in hot water, roller grill or pan also barbeque is possible.

[0057] The inventive extrusion system for continuous production of food products with a collagen-elastin gel casing comprises: a food dough extrusion passage defining a co-extrusion axis, having a food dough inlet and an opposed food dough-outlet; two co-operating jackets arranged coaxially about the food dough extrusion passage, at least one jacket being rotatable about the co-extrusion axis, the jackets defining an annulus therebetween having an annulus-inlet for the introduction of gel, the rotation of the at least one jacket causing orientation of the gel, thereby converting the introduced gel into an orientated gel, the annulus having an opposed annulus-outlet for discharging orientated gel; wherein discharged orientated gel is deposited onto food dough emerging from the food dough-outlet to form a food product with gel casing; an adjacent in line upstream detangler comprising: a detangler inlet for semi-finished gel; interlocking members defining therebetween a labyrinth, at least one of the interlocking members being movable for exerting in the labyrinth a mechanical treatment onto semi-finished gel to reduce fiber clumps in the gel, thereby converting the semi-finished gel into a homogeneous collagen-elastin gel; and a detangler outlet for the homogeneous collagen-elastin gel to be introduced between the two cooperating jackets to be converted into orientated collagen-elastin gel.

[0058] The inventive detangler is provided to reduce the fiber clumps in the gel, prior to extrusion thereof, to form a homogeneous collagen-elastin gel. The semi-finished gel having fiber clumps flows through the labyrinth between the two interlocking members. The detangler comprises at least one movable interlocking member exerting a continuous mechanical treatment, in particular a high shear treatment, onto the semi-finished gel, thereby “unravelling” of the (long) collagen and elastin fibers and the knots in the gel, reducing fiber clumps in the gel and creating a homogeneous gel essentially without fiber clumps. The mechanical treatment causes dispersion of the fibrous clumps in the gel, to create a homogeneous gel essentially without fiber clumps. This results in better extrusion, better film forming capacity and better gel casing characteristics, in particular its texture e.g. resulting in higher “bite” values.

[0059] In embodiments, the interlocking members of the detangler comprise rows of projections (24, 25, 26), e.g. tooth-like projections, e.g. a serrated edge. Embodiments wherein an interlocking member has one or more, e.g. two or three rows of projections are conceivable. Such rows of interlocking tines or teeth create a detangling labyrinth improving the mechanical treatment of the semi-finished gel.

[0060] In embodiments, more than one interlocking member is movable. Advantageously, two interlocking members are relatively movable to improve the mechanical treatment of the semi-finished gel.

[0061] In embodiments, the detangler comprises interlocking members arranged coaxially about the co- extrusion axis. The movable interlocking member or both interlocking members are rotatable about the co-extrusion axis. Advantageously, the detangler comprises two relatively moving interlocking members, e.g. two counter-rotatable interlocking members. With the coaxially arranged interlocking members it is both conceivable that projections of the interlocking members are in line with, or perpendicular to, or otherwise oriented with respect to the coextrusion axis.

[0062] Adjacent and downstream of the detangler co-operating jackets are provided, the rotation of at least one jacket causing orientation of the fibers in the semi-finished gel to form the oriented collagen- elastin gel. Collagen, as well as elastin has a fibrous nature and due to the extrusion of the collagen, the collagens fibers in the resulting extruded gel casings have the tendency to orient, in particular align. Rotating jacket surface apply shear forces onto the fibers in the gel, and shearing the fibers over the jacket surfaces steers their alignment. These shear forces are less than created in the labyrinth by the interlocking members: these forces are not enough to overcome the untangling forces of the proteins and untangle the fiber clumps.

[0063] Two co-operating jackets arranged coaxially about the food dough extrusion passage, at least one jacket being rotatable about the co-extrusion axis. In embodiments, both jackets are rotatable, preferably counter-rotatable.

[0064] In embodiments, a single drive is provided to control the rotation speed of a rotatable jacket and to control movement of the at least one movable interlocking member of the detangler. Advantageously, two drives are provided: one drive to control the rotation speed of one of the rotatable jackets as well as to control movement of one of two movable interlocking members of the detangler; a second drive to control the rotation speed of the other one of the rotatable jackets as well as to control movement of the other one of two movable interlocking members of the detangler.

[0065] In embodiments, at least one of the interlocking members of the detangler is formed integral with a jacket, upstream of the annulus-inlet wherein the homogeneous collagen-elastin gel is introduced. In such embodiments at least one of the jackets has an upstream interlocking member of the upstream detangler of the extrusion system, and a downstream part defining the annulus. Preferably both of the interlocking members of the detangler are formed integral with the jackets, upstream of the annulusinlet.

[0066] Projections of such integrally formed interlocking member(s) can be arranged coaxially about the food dough extrusion passage, or perpendicular thereto.

[0067] In embodiments, the jackets have a conical shaped part defining part of the annulus, such that the annulus includes a sharp angle of 30-60° with the co-extrusion axis. This creates a longer path for the gel than for the food dough. This is advantageous in embodiments wherein time is needed to create orientated collagen-elastin gel in the annulus. In embodiments, the jackets comprise a cylindrical shaped part defining part of the annulus, such that the annulus is parallel with the co-extrusion axis. It is conceivable that the jackets have a conical shaped part at the annulus-inlet and a downstream cylindrical part at the annulus-outlet.

[0068] In embodiments, at least one of the jackets has a profiled surface part in the annulus. For instance the surface structure and roughness may have effect on the shear forces transferred to the gel. In embodiments a flow guiding profile is provided, with raised and lowered jacket surface parts, also having effect on the gel flow and the resulting gel casing.

[0069] In embodiments, at least one of the jackets is interchangeable. By changing the jackets the contact surface of the inner and / or outer jacket may be changed while the different contact surfaces will also have a different effect on the gel fluid flowing along the surfaces.

[0070] Example

[0071] A collagen-rich gel is prepared by comminuting thawed and rinsed short casing ends, 0.3 M NaOH treatment for 40 hours, washing, mincing to an average size of 2 mm, acid treatment for 48 hours with lactic acid followed by colloid milling to obtain a dispersion. An elastin-rich gel is prepared in a similar way starting from cut bladders.

[0072] The blended gels and blends thereof are extruded on a food dough using an extrusion system wherein the gel is subjected to a detangling treatment. The resulting encased food product is brined, dried and smoked using a standardized protocol, e.g. as disclosed in WO2021096358. It has been found that the food product characteristics of a food product after thermal treatment with a gel casing according to the invention are better than products with a known gel casing.

[0073] The invention is further elucidated in relation to the drawings, in which:

[0074] Fig. 1 is a side view of an inventive extrusion system;

[0075] Figs. 2a, 2b are detailed views of the extrusion system of fig. 1 ;

[0076] Figs. 3a, 3b are detailed view of the interlocking members of the extrusion system of figs. 1 and 2;

[0077] Fig. 4 is a further detailed cross-sectional view of the extrusion system of figs. 1-3;

[0078] Figs. 5a - 5c are schematical representations of a semi-finished gel, a homogeneous collagen- elastin gel and an orientated collagen-elastin gel.

[0079] Figure 1 schematically shows an extrusion system 1 according to the invention for continuous production of food products with a collagen-elastin gel casing, schematically indicated with reference numeral ‘10’ at the right-hand side of fig. 1 . A coextruded food product 10 emerging from the inventive extrusion system 1 is further transported. In a following process e.g. crosslinking takes place to form a solid protective layer. The system in particular suitable for manufacturing coextruded food products, in particular sausages.

[0080] The extrusion system 1 comprises a co-extruder for forming a continuous food dough strand 3 on the outside of which is provided a gel layer 4 distributed substantially uniformly over the strand 3. Food dough 3, e.g. a meat dough or sausage dough, is fed into a food dough inlet 5a of a food dough extrusion passage 5 as indicated by an arrow at the left-hand part of the drawing. The food dough extrusion passage 5 defines a co-extrusion axis A, as shown in figs. 2 and 4. The food dough extrusion passage 5 has an opposed food dough outlet 5b.

[0081] Two co-operating jackets 28, 29, as shown in figs. 2 and 4, are arranged coaxially about the food dough extrusion passage 5. At least one jacket 28, 29 is rotatable about the co-extrusion axis A. The jackets define an annulus 41 therebetween having an annulus-inlet 41a for the introduction of a liquid coating material, here a gel E2. The rotation of the at least one jacket causes orientation of the gel, thereby converting the introduced gel, such as gel E2 as depicted in fig. 5b, into an orientated gel E3, as depicted in fig. 5c. In particular, the rotation creates shear forces onto the fibers in the gel to orient them. In embodiments having counter- rotating jackets, the shear forces at the outer region of the gel create an alignment opposite to the fibers in an inner region of the gel, creating a network of oriented fibers. The annulus has an opposed annulus-outlet 41 b for discharging orientated gel as a thin layer to the continuous strand 3, which is deposited onto food dough 3 emerging from the food dough-outlet 5b to form a food product with gel casing.

[0082] In the shown embodiment, the jackets 28, 29 have a conical shaped part defining an angled part of the annulus 41’, such that the angled part of the annulus includes a sharp angle of 30-60° with the co- extrusion axis. Adjacent the annulus-outlet 41 b the jackets have a parallel part such defining an annulus part 41” parallel to the co-extrusion axis A.

[0083] The inventive extrusion system 1 further comprises a detangler 9. In the shown embodiment the detangler 9 is provided adjacent, in-line and upstream of the co-operating jackets 28, 29.

[0084] In figs. 2a and 2b it is visible that the extrusion system 1 is provided with feed apertures 21 for supplying gel, here a semi-finished gel E1 as shown in fig. 5a. Due to the composition of the gel, entanglement of the fibers takes place over time, in particular during shelf-life. In the disclosed embodiment shown in Figure 2b, it can be seen that behind the apertures 21 , a detangler inlet 19a is provided for the semi-finished gel. Two rings 22, 23 are positioned essentially concentrically about central axis A. In operation, the rings are for example arranged to rotate in opposite directions. The rotation rates may be, for example, on the order of 200 rotations per minute.

[0085] The rings 22, 23 are shown detached in a perspective manner in Figures 3a and 3b. Visible are interlocking members 24, 25, 26 implemented in the form of teeth falling over each other, and a rim 27. Here the teeth are embodied as rectangular protrusions resembling battlements. Other configurations are also conceivable, e.g. crenellated edges with triangular protrusions and / or gaps. The interlocking members 24, 25, 26 define therebetween a labyrinth 40. In the shown embodiment, the rings 22, 23 are detachably coupled with jackets 28, 29. In embodiments, the jackets rotate in opposite directions, with the jacket 28 (shown shaded in Figure 2b) rotating in the first direction, and with the jacket 29 (shown chequered in Figure 2b) rotating in the opposite direction. The jackets 28, 29 are driven by external drive means (not shown), and rotate within the housing 30. Preferably, the device is made of stainless steel.

[0086] Figure 4 shows an enlarged section of the extrusion system 1 shown in Figure 2b in cross-section. This shows how gel E1 is supplied via a channel 6 and the feed openings 21 into the detangler inlet 9a, and is fed via labyrinth 40 formed between the interlocking members of the counter- rotating rings 22, 23, each fitted with teeth 24, 25, 26, to the annulus-inlet between the co-operating jackets. Movement of at least one of the interlocking members exert in the labyrinth a mechanical treatment onto semi-finished gel E1 to reduce fiber clumps FC in the gel, thereby converting the semi-finished gel into a homogeneous collagen-elastin gel E2 as shown in fig. 5b. The mechanical treatment includes very high shear forces causing the untangling. These shear forces exceed the forces of the jackets causing orientation of the fibers in the gel.

[0087] In the annulus 41’, 41 ” the introduced homogeneous collagen-elastin gel E2 is converted into an orientated collagen-elastin gel E3. The orientated collagen-elastin gel is discharged via annulus outlet 41 b and deposited onto food dough 3 emerging from the food dough-outlet to form a food product with gel casing.

[0088] A typical size of the annulus 41 is about 0.35 mm, however, this depends on the desired thickness of the manufactured layer of coating material.

Claims

C L A I M S1 . Method for producing a semi-finished gel suitable for use in the preparation of a gel casing for a food product, comprising the steps of providing a first (collagen-rich) natural tissue such as beef split, and a second (elastin-rich) natural tissue such as bladder, wherein the weight ratio of the amount of collagen in the first (collagen-rich) natural tissue to the amount of collagen in the second (elastin-rich) natural tissue is more than 1 , wherein the weight ratio of the amount of elastin of the second (elastin-rich) natural tissue to the amount of elastin in the first (collagen-rich) natural tissue is more than 1 , wherein the first natural tissue and the second natural tissue are subjected to a chemical treatment to provide a first natural tissue gel and a second natural tissue gel, respectively and blending the first natural tissue gel and the second natural tissue gel, or wherein a combination of the first natural tissue and the second natural tissue are subjected to a chemical treatment, to provide the semi-finished gel comprising collagen and elastin.

2. Method according to claim 1 , further comprising a physical disentanglement treatment to provide a homogeneous collagen-elastin gel.

3. Method according to any of the preceding claims, wherein the ratio second natural tissue gel to first natural tissue gel when blending or the ratio of second natural tissue to first natural tissue can be chosen from 100:0 to 10:90, 80:20, 75:25.

4. Method according to any of the preceding claims, wherein in(A) the second natural tissue gel is present in more than 50 wt.%, 60 wt.%, 65 wt.%, 70 wt.% , 75 wt.%, more preferable at least 80 wt.%, 85 wt.%, 90 wt.%, calculated on the total amount of the semi-finished gel;(B) the second natural tissue is present in more than 50 wt.%, 60 wt.%, 65 wt.%, 70 wt.% , 75 wt.%, more preferable at least 80 wt.%, 85 wt.%, 90 wt.%, calculated on the total amount of the combination of the first natural tissue and the second natural tissue.

5. Method according to any of the preceding claims, wherein the chemical treatment is a process sequence comprising:(a) comminuting a first natural tissue and / or an second natural tissue to provide comminuted product(s);(b) optionally, subjecting the comminuted products of step (a) to a lye treatment to provide lye-treated products,(c) optionally, mincing the products of step (a) or (b) to obtain minced products;(d) optionally, acidification treatment of the products of step (a), (b) or (c) to obtain acid-treated products, and(e) providing an aqueous dispersion of the products of step (a), (b), (c), (d), and(f) obtaining the semi-finished gel suitable for use in the preparation of a gel casing for a food-product.

6. Method according to any of the preceding claims, wherein step (a) results in comminuted products having average dimensions between 0.1 and 5 cm, preferably between 0.5 and 3 cm.

7. Method according to any of the preceding claims, wherein step (b) is in an aqueous solution of a strong base, preferably 0.1-1 .0 M strong base.

8. Method according to claim 7, wherein step (b) is in an aqueous solution of a strong base for a period between 4 and 100 hours.

9. Method according to any of the preceding claims, wherein step (c) provides minced products having average dimensions between 0.1 and 0.4 cm.

10. Method according to any of the preceding claims, wherein step(d) uses an acid that is selected from the group consisting of lactic acid, acetic acid, hydrochloric acid and mixtures therefrom.11 . Method according to any of the preceding claims, wherein step (c) the dispersed products are subjected to milling and / or homogenization.

12. Method according to any of the preceding claims, wherein the first natural tissue gel and the second natural tissue gel are formed in separate process sequences.

13. Method according to any of the preceding claims, wherein the first natural tissue gel and the second natural tissue gel are combined to form the semi-finished gel.

14. Semi-finished gel suitable for use as a gel casing for a food-product obtainable by the method of claims 1-13.

15. Method for making an oriented collagen-elastin gel suitable to form food products with gel casing, comprising the steps of providing a semi-finished gel as defined in claim 15, subjecting the semi-finished gel to a detangling treatment in an extrusion system (1) according to claim 16 to provide an orientated collagen-elastin gel (E3).

16. Extrusion system (1) for continuous production of food products with a collagen-elastin gel casing (10), comprising:a food dough extrusion passage (5) defining a co-extrusion axis (A), having a food dough inlet (5a) and an opposed food dough-outlet (5b); two co-operating jackets (28, 29) arranged coaxially about the food dough extrusion passage (5), at least one jacket being rotatable about the co-extrusion axis, the jackets defining an annulus (41 ’, 41 ”) therebetween having an annulus-inlet (41 a) for the introduction of gel (E2), the rotation of the at least one jacket causing orientation of the gel, thereby converting the introduced gel into an orientated gel (E3), the annulus having an opposed annulus-outlet (41 b) for discharging orientated gel; wherein discharged orientated gel is deposited onto food dough (3) emerging from the food dough-outlet to form a food product with gel casing; characterized in that the system further comprises adjacent and in line with the co-operating jackets an upstream detangler (9) comprising: a detangler inlet (19a) for semi-finished gel (E1); interlocking members (24, 25, 26) defining therebetween a labyrinth (40), at least one of the interlocking members being movable for exerting in the labyrinth a mechanical treatment onto semi-finished gel (E1) to reduce fiber clumps (FC) in the gel, thereby converting the semi-finished gel into a homogeneous collagen-elastin gel (E2); a detangler outlet (19b) for the homogeneous collagen-elastin gel to be introduced between the two co-operating jackets to be converted into orientated collagen-elastin gel (E3).

17. System according to claim 16, wherein the interlocking members of the detangler comprise rows of projections (24, 25, 26), e.g. tooth-like projections, e.g. a serrated edge.

18. System according to claim 16 or 17, wherein the interlocking members (24, 25, 26) are arranged coaxially about the co-extrusion axis, the interlocking members) being rotatable, e.g. counterrotatable, about the co-extrusion axis.

19. System according to any of the preceding claims 16-18, wherein the interlocking members (24, 25, 26) of the detangler (9) are formed integral with the jackets (28, 29), upstream of the annulus-inlet (41 a).

20. System according to any of the preceding claims 16-19, wherein the jackets have a conical shaped part defining an angled part of the annulus (41 ’), such that the angled part of the annulus includes a sharp angle of 30-60° with the co-extrusion axis.

21. Method for continuous production of food products with a gel casing wherein use is made of an extrusion system of claim 16, the method comprising the steps of: introducing a semi-finished gel into the detangler; the movable interlocking member of the detangler exerting a continuous mechanical treatment onto the semi-finished gel, thereby reducing fiber clumps in the semi-finished gel and converting the semi-finished gel to a homogeneous collagen-elastin gel; introducing a food dough into the food dough inlet;introducing the homogeneous collagen-elastin gel into the annulus-inlet when leaving the outlet of the detangler; orienting the homogeneous collagen-elastin gel in the annulus between the jackets to convert the introduced homogeneous collagen-elastin gel into an orientated collagen-elastin gel, - discharging the orientated collagen-elastin gel onto the food dough emerging from the food doughoutlet to form a food product with a collagen-elastin gel casing.

22. Food product comprising a co-extruded food dough and a collagen-elastin gel casing produced in a system according to claim 16.

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