GB2496604A - Production of nuts and legumes - Google Patents

Abstract

immersing at least one of nut kernels and legume kernels in an aqueous liquid thereby hydrating at least a portion of the kernel by marination; and b) cooking the hydrated kernel at an elevated cooking temperature, the cooking causing at least partial dehydration of the hydrated portion. The nuts or legumes may be peanuts, cashews, beans or chickpeas. Step a) may comprise immersing kernels in water for 5-120 minutes at a temperature from 15-100°C. Step b) may comprise roasting the hydrated kernels. The aqueous liquid may comprise water and a humectant such as salt or sugar. A texturised peanut or cashew product comprising whole kernels having partly separated and partly connected kernel halves and an outer layer being crispier than an inner portion is also described. A texturised nut or legume product having blisters of the nut or legume meat on an outer surface of nut or legume kernels is disclosed.

Description

Production of enhanced nuts an4jgumes The present invention i-elates to a method of producing at least one of nuts and legumes, a method of texturizing a peanut or cashew nut product, a method of texturizing a nut or legume product, It is well known to produce snack foods from nuts and legumes.

Typical known production processes for nuts, such as peanuts, cashew nuts and almonds, and legumes, such as beans and chickpeas, include blanching of the nuts/legumes, removal of ay skin, coating of the nuts/legumes with a flavour coating, and then frying or oven roasting, and possibly final flavour addition. Accordingly, all added value to the nut/legume product is dependent upon the selection of the applied flavouring or coating, or the selection of the nut or legume grade.

In one aspect, the present invention aims to provide a process that can add value to the nuts/legumes themselves, in particular peanuts, by modi'ing the properties of the meat of the nut/legume during thc production process. The present invention aims to provide a nut/legume product which modifies the texture or other properties of the nut/legume kernel over and above conventional coating technologies which can provide a product with a unique texture, and optionally appearance, and further optionally flavour, to the consumer as compared to conventional nut/'egume products.

Currently, there are known technologies which can be used to add flavour and/or colour to nuts, in particular peanuts, almonds and cashews. These teclmologies include application of flavour/colour components to the nuts: 1. Topically using dry ingredients such as: salt, seasonings, etc.; 2. Through spray systems, using flavoured oils, sugar, salt or gum solutions, etc.; and 3. By coating those using dry mixes of starch, flours, etc. For the technologies mentioned above, the final product flavour is mainly produced by the added ingredients in each technology. These ingredients coat the outer surface of the nut. In contrast the nut itself, within the body of the kernel, only has its characteristic nut flavour and colour profile, the flavour ranging from bland to strong, and the colour ranging from light to dark, depending on the cooking process to which the nut was subjected, for example frying or roasting. I'he cooking process may he before or subsequent to the application of the flavour/colour components.

In one aspect, the present invention aims to enhance the flavour and/or colour profile of the nut or legume meat, so that not only a surface but also a portion of the kernel has an enhanced flavour profile or a changed colour.

The present invention provides a method of producing at least one of nuts and legumes, the method comprising the steps of: (a) immersing at least one of nut kernels and legume kernels in an aqueous liquid thereby hydrating at least a portion of the kernel by niarination; and (b) cooking the hydrated kernel at an elevated cooking temperature, the cooking causing at least partial dehydration of the hydrated portion.

l'he present invention also provides a method of texturizing a peanut or cashew nut product by partly separating kernel halves of whole peanut or cashew nut kernels, the method comprising the steps of: (a) immersing peanut or cashew nut kernels in water for a time period of from 10 to 90 minutes and at a temperature of from 15 to 30 °C thereby hydrating at least a part of an outer layer of the kernel by marination; and (b) roasting the hydrated kernels for a period of from 2 to 20 minutes at a temperature of from to 160 °C to dehydrate the kernel to a total moisture content of from Ito 4 wt%.

The present invention further provides a method of texturizing a nut or legume product by enhancing the crispiness of nut or legume kernels, the method comprising the steps of (a) immersing nut or legume kernels, or a mixture thereof, in an aqueous liquid, which liquid includes a humectant for controlling hydration of the kernel, for a time period of from to 120 minutes and at a temperature of from 15 to 100 °C thereby hydrating a maj or portion of the kernel by marination; and (b) roasting the hydrated kernels for a period of from 2 to 20 minutes at a temperature of from to 160°C to dehydrate the kernel to a total moisture content of from 1 to 4 wt°A.

The present invention still fui-ther provides a method of texturizing a nut or legume product by forming blisters on an outer surface of nut or legume kernels, the method comprising the steps of: (a) inmersing nut or legume kernels, or a mixture thereof, in water for a time period of from to 1 20 minutes and at a temperature of from 1 5 to 100 °C thereby hydrating at least an outer layer of the kernel by marination, and leaving free water within the kernel; and (b) cooking the hydrated kernel at an elevated cooking temperature to cause the free water to evaporate and blistering ol' the nut or legume meat on the outer surface of the kernel.

more typically from 65 to 70%, of the distance of the outer surface to a centre of the kernel.

[he present invention also provides a texturized peanut or cashew nut product comprising whole peanut or cashew nut kernels having partly separated and partly connected kernel halves, and an outer layer of the kernel being crispier than an inner portion of the kernel.

The present invention provides a texturized nut or legume product having blisters of the nut or legume meat on an outer surface of nut or legume kernels.

For all of these aspects of the invention, further preferred features are defined in the dependent claims.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is an illustration of a longitudinal cross-section through a peanut with a hydrated outer layer produced according to a first embodiment of the present invention; Figure 2 is a photomicrograph of a side view of two of the peanuts of Figure 1 after cooking, illustrating a partly separated kernel structure of the peanut; Figure 3 is a photomierograph of a side view of two peanuts produced according to a second embodiment of the present invention, illustrating a crispy, crunchy peanut; and Figure 4 is a photomierograph of a transverse cross-section of two peanuts produced according to a third embodiment of the present invention, illustrating a blistered surface of the peanuts.

In accordance with the present invention, there is provided a method of producing at least one of nuts and legumes.

In a first step of the method, at least one of nut kernels and legume kernels are immersed in an aqueous liquid for a period sufficient to hydrate at least a portion of the kernel by marination. Thereafter the hydrated kernel is cooked at an elevated cooking temperature, the cooking causing at least partial dehydration of the hydrated portion.

Marination has been found to provide significant changes in texture by making the nuts or legumes crispier and crunchier. In addition, as discussed further below, the marination step can also be employed to provide flavour and colour to the nuts or legumes.

The present invention is at least partly predicated on the finding by the inventors that marination provides an aqueous environment in which one or more reactions within the nut or legume may take place. The reactions may impart changes in, for example, texture, flavour and/or appearance, and may modify the mechanical properties and! or the chemical composition of the nut or legume. The reactions may occur during marination, or provide changes which are completed during subsequent processing; for example the inarination may rnodifj the Maillard reaction which occurs subsequently during cooking at elevated temperature.

It is postulated, without being bound by any theory, that the absorption of water by the nut or legume during the marination process increases water activity within the kernel, which in turn may increase molecular mobility, and in turn may provide increased kinetics during subsequent chemical reactions and molecular changes to biopolymers such as proteins and carbohydrates within the nut of legume. Hydration may cause unfolding of protein and/or carbohydrate molecules, which may lower the glass transition temperature of these molecules, and increase the plastic nature of these molecules. The resultant hydrated kernel may he more rubbery and may deform under hydration conditions.

Since many nuts and legumes contain significant amount of oil, for example peanuts contain greater than 40 wt% oil, the absorption of water into the meat of the kernel maybe slow. The absorption rate is enhanced at higher marination temperatures. The hydration rate can be used as a processing variable to modify the texture and appearance of the resultant nut or legume product.

Also, some raw nuts and legumes have a low water activity, for example raw peanut exhibiting a water activity of less than 0.4, and so these low water activity products tend to exhibit slow reaction Icineties. The hydration achieved during the marination process can increase water activity within the nut or legume kernels, and consequently increase reaction kinetics, When the niarination is controlled to he carried out for a relatively short time in an aqueous environment, in particular at relatively low niarination temperatures, only the outer layers of the kernel are hydrated, optionally as well as any germ which may be present. The cells within the hydrated portion of the kernel are distorted, whereas the cells in the unhydrated portion remain intact. This increases the malleability of the hydrated material, and causes a moisture content gradient which can cause bending of the kernel.

When the marination is controlled to be carried out for a relatively long time in an aqueous enviromnent, or a shorter time at higher marination temperatures, the kernel may be substantially fully hydrated. The marination process may be controlled so as to avoid the presence of free water within the kernel, so that the hydrated portion of the kernel is substantially homogeneous. A humectant within the aqueous environment during marination can he used to avoid the presence of such free water. It is believed that proteins and hydrocolloids may unfold and bind to the cell walls during such hydration. After the subsequent cooking process, the cell walls are strengthened, the cell interior is more amorphous, and the vacuoles may shrink, resulting in a crunchier and crispier kernel. This effect is not thermally reversible, indicating that the hydration and cooking have introduced some chemical reactions, for example the formation of covalent bonds, during the marination and cooking, which affect the texture of the final product. The increased water activity is believed to provide faster reaction kinetics and reactions such as cross-linking, which in turn can increase the crunchiness and crispiness of the resultant cooked product. In addition, the enhanced crunchiness and crispiness of the resultant cooked kernel may still be present even if the product is heated to an elevated temperature, such as 70 C. In contrast, conventional peanuts, for example, become softer when heated to such an elevated temperature.

When the marination is controlled as described above so that, the kernel may be substantially fully hydrated, the marination process may be controlled so as to provide the presence of free water within the kernel, so that the hydrated portion of the kernel is substantially

S

heterogeneous. This is achieved by using water as the aqueous environment without the presence of a humectant. A low osmotic potential in the aqueous environment, for example by using water without any salt (such as brine) or other humectant, increases the moisture content of the marinated kernel, and some of that water is present as free water. This provides that the full hydration causes pooling of free water within the meat of the kernel. Upon rapid heat transfer during the subsequent cooking step, the free water evaporates, causing a build-up of steam pressure within the kcrncl. This causes blistering of the surface layers of the kernel, and the presence of voids in the final product.

The marination step can be performcd at room temperature. However at higher temperatures, typically up to 100 °C, the marinating solution penetratcs morc quickly into thc nuts or tcgumes, reducing marination processing times to achieve the desired hydration of the nuts/legumes.

Thc marination step may be carried out in a batch process, for example in a kettle, or in a continuous process. In a continuous process, the marination equipment may comprise an elongate reservoir that has a conveyor comprising a rotatable elongate endless belt with a plurality of mutually spaced pedals mounted thereon. Alternatively, a helical screw conveyor may be used, The reservoir is filed with an aqueous liquid. The nuts and/or legumes are inputted at an upstream end of the reservoir and outputted at the downstream cnd. The convcyor rnixcs thc nuts/legumes in the aqueous liquid and conveys the product at a controlled rate and residence time through the length of the equipment. Typically the reservoir and conveyor are made of stainless steel. When the marination step is to be carried out at a temperature higher than room temperature, the reservoir is at least partly sun'ounded by a hollow jacket which is connected to a source of heat, for example a steamer which provides steam, which can raise the temperature of the aqueous liquid in the reservoir to a desired temperature required for the particular marination process.

The reservoir is heated up to the desired temperature, and then the peanuts/legumes are added at the upstream end and conveyed through the marinating liquid. The temperature of the nuts/legumes is raised in the presence of the liquid. The liquid soaks into the meat of the kernels. The marination produces a tenderizing effect on the nuts/legumes, allowing the solution to start penetrating the outer layers of the nuts/legumes. With increased residence time, the nuts/legumes absorb progressively more solution into the layers. The degree of hydration is controlled by controlling the combination of temperature and residence time, and may range from partial hydration, iii which only a thin outer layer is hydrated, or full hydration, in which the nut/legume is hydrated to the centre of the kernel.

The processing parameters, in particular temperature and residence time, may readily be varied, and are selected to achieve the desired texture, flavour and/or colour profile in the particular nuts and/or legumes which are being processed. These parameters may readily he determined by reasonable trial and error.

Various embodiments of the invention may be carried out. These embodiments may vary the marination conditions, in particular the time and/or temperature of marination. The varied marination conditions can affect the degree and depth of hydration of the kernel.

Furthermore, the marination may be carried out in water, without any additives thereto, or in an aqueous liquid in which one or more additives have been added to water. These additives may affect the degree, depth andior nature of the hydration of the kernel, andlor may provide the nut or legume product with at least one of flavour and colour, Flavoured hut colourless solutions provide only flavour to the final nuts/legumes, and may comprise, for example, water and table salt (sodium chloride), while flavour and coloured solutions provide flavour and additionally taint the final nuts/legumes, and may comprise, for example, water and soluble coffee.

In the various embodiments of the invention described below, prior to the immersion step the kernels may optionally be blanched. Furthermore, the kernels may be with or without skin.

The second step of the process reduces the product moisture up to the desired final value.

After the immersion and marination of the kernels to hydrate them, the subsequent cooking step may typically comprise roasting or frying. The cooking may in particular comprise roasting in a high velocity oven or frying in oil at a temperature of at least 150 °C, most pam-ticularly when a blistered product is to he made which, as discussed below, requires rapid evaporation of flee water from within the kernel.

The cooking step may typically comprise dry roasting for a period of from 2 to 20 minutes at a temperature of from 125 to 160 °C, more typically for a period of from 5 to 15 minutes at a temperature of from 140 to 150 °C.

The cooking step dehydrates the kernel to a total moisture content typically of from I to 4 wt%, optionally from 2 to 3 wt%, based on the total weight of the cooked kernel.

In the embodiments of the invention, in particular those described below, the nut is a ground nut or a tree nut or a mixture thereof The nut is selected from any one of a peanut, an aimond a cashew nut, a brazil nut, or any mixture of two or more of these nuts. Additionally or alternatively the legume is a bean or a chickpea or a mixture thereof The soaking and hydration of the kernels tends to produce a slightly blander flavour to the kernels as compared to kernels which have not been subjected to marination. 1-lowever, after subsequent roasting or frying, to dehydrate the hydrated portions and achieve a final product moisture of from 1 to 4 w% based on the weight of the cooked kernel, produces a crispier or crunchier texture of the kernel, and a different visual appearance associated with the change in texture. As described below, the change in appearance may comprise a partial splitting of the kernel for peanuts or cashew nuts, or blistering of the outer surface of thc kernel for a variety of different nuts and legumes. The blistering is provided by small pockets of air in the outer layers of the kcrncl. Thc cooking time for thc hydrated nut/kerncl may bc cxtended as conipared to the cooking of a conventional unhydrated product, in order to reduce the total moisture content to the same final value (for example 2 wt%), and the extended cooking time may enhance the crispiness and crunchiness of thc kcrnel and may shrink the volume of the kernel.

In a first embodiment of the invention, a peanut or cashew nut product is texturized by partly separating kernel halves of whole peanut or cashew nut kernels. In the immersing step, the peanut or cashew nut kernels are marinated in water for a time period of from 10 to 90 minutes and at a temperature of from 15 to 30 °C. Optionally, the immersing step is carried out for a time period of from 20 to 30 minutes and at a temperature of from 20 to 25 °C. The water immersion hydrates at least a part of an outer layer of the kernel by a marination mechanism.

Typically, the hydrated outcr layer has a depth which is from 5 to 20%, typically from 8 to 15%, more typically about 10%, of the distance from the outer surface to a centre of the kernel, For example, the hydrated outer layer has a depth of from 0.1 to 0,5mm, typically from 0.2 to 0.4mm.

In the immersing step (a) the hydrated outer layer applies a deilectional force to the kernel.

This force causes warping of the kernel during the immersing step. The hydration may lower the glass transition temperature of the nut meat, lowering the strength of the peanut or cashew nut meat and assisting the deflection of the kernel. The warping results in at least some, typically a majority, of the nut kernels comprising a whole kernel having connected kernel halves, with the kernel halves being only partly connected together at one end of the kernel, by a germ within the kernel, and unconnected at another end of the kernel, A typical hydrated peanut structure following immersion and marination is illustrated in Figure 1. The peanut 2 includes a kernel 4, otherwise called a cotyledon, comprising two kernel halves 6, 8, and a germ 10. The marination causes hydration of outer layers 12 of the kernel 4.

In the subsequent cooking step, the hydrated kernels are roasted for a period of from 2 to 20 minutes at a temperature of from 125 to 160 °C to dehydrate the kernel to a total moisture content of from 1 to 4 wt%. In the cooking step, the warped kernel shape is rigidly set at an elevated cooking temperature.

In the final cooked peanut or cashew nut product, the texturized peanut or cashew nut product comprises whole peanut or cashew nut kernels having partly separated and partly connected kernel halves, and an outer layer of the kernel being crispier than an inner portion of the kernel. In at least some, typically a majority, of the peanut or cashew nut kernels the kernel halves are connected at one end of the kernel and unconnected at another end of the kernel.

Typically, the kernel halves are connected by a germ within the kernel. In addition to the visible separation of the kernel halves, the outer layer is crispier than the inner portion of the texturized peanut or cashew nut. Typically, the crispier outer layer has a depth which is from to 20%, typically from 8 to 15%, more typically about 10%, of the distance from the outer surface to a centre of the kernel. For example, the crispier outer layer has a depth of from 0.1 to 0.5mm, typically from 0.2 to 0,4mm.

A typical resultant peanut structure is illustrated in Figure 2. The kernel halves 6, 8 are separated at one end of the kernel 4 to form an open gap 14 therebetween. Typically, the gap 14 has a transverse width W at the edge of the kernel of from 0.2 to 5 mm, optionally from 0.5 to 2' mm, This embodiment provides a unique and distinctive visual appearance to the peanuts or cashew nuts, which makes them more appealing to the consumer.

In a second embodiment of the invention, in the immersing step the aqueous liquid includes a hmeetant for controlling hydration of the kernel. The immersing step hydrates at least an outer portion of the kernel comprising a major portion of the kernel. The kernel may be substantially ifilly hydrated. The hydration may increase water activity in the kernel. The humeetant provides that the kernel is substantially uniformly hydrated without free water being trapped as pools within the mierostrueture of the kernel, although one or more inner portions of the kernel may remain unhydrated. Typically, the humeetant is selected from an edible ionic salt compound, for example sodium chloride, and/or a compound enhancing the osmotic pressure of the marinating liquid on the kernel, for example a sugar, such as glucose.

The huniectant binds to free water and prevents water pools for being present in the kernel, so that hydrated portions of the kernels are substantially homogeneous, The immersing step is typically carried out for a time period of from 5 to 120 minutes and at a temperature of from 15 to 100 °C. Optionally, the immersing step is carried out for a time period of from 80 to 100 minutes and at a temperature of from 20 to 25 DC.

The hydrated outer layer has a depth which is from 50 to 100%, typically from 60 to 90%, more typically from 65 to 70%, of the distance from the outer surface to a centre of the kernel, The hydrated outer layer may have a depth of from I to 3mm, typically from 1.5 to 2mm, In this embodiment, the cooking step may comprise roasting the hydrated kernels for a period of from 2 to 20 minutes at a temperature of from 125 to 160 °C to dehydrate the kernel to a total moisture content of from Ito 4 wt%.

In the cooking step (b) the hydrated portion of the kernel is made crispier and crunchier than an inner unhydrated portion of the kernel. It has been found that the cooked kernel may exhibit substantially constant crunchiness and crispiness over a range of temperature of from to 70°C.

A typical e resultant structure in the embodiment of a peanut is illustrated in Figure 3. The peanut kernel halves 6, 8 are substantially filly connected.

This embodiment produces nuts or legumes having enhanced crispiness as compared to conventional fried or roasted nuts or legumes. The embodiment therefore texturizes the kernel to provide the property of enhanced crispiness. The nut may he a ground nut or a tree nut, or a mixture of nuts may he produced. The nut may he selected from any one of a peanut, an almond a cashew nut, a brazil nut, or any mixture of two or more of these nuts. The legume may be a bean or a chickpea or a mixture of legumes may be produced. This embodiment may n particular produce peanuts of enhanced crispiness wherein at least some of the kernels comprise a whole kernel having connected kernel halves, and in the final cooked peanut the kernel halves are substantially fully connected together as a result of the substantial hydration of the peanut.

In a third embodiment of the invention, thc nut or legume kernels, or a mixture thereof, are immersed in water for a time period of from 5 to 120 minutes and at a temperature of from to 100 °C. Thc immersion hydrates at least an outer layer of the kernel by marination, and leaves free water within the kernel. Optionally, the immersing step is carried out for a time period of from 80 to 100 minutes and at a temperature of from 20 to 25 °C. In contrast to when a humectant is employed to hind to free water in the kernel, the high level of local hydration of the kernel in water without a humectant causes water pools to be present in the kernel, so that hydrated portions of the kernels are substantially heterogeneous, with hydrated meat and water pools co-existing in the hydrated portions of the kernels.

Typically, the hydrated outer layer has a depth which is from 25 to 100%, typically from 60 to 90%, more typically from 65 to 70%, of the distance of the outer surface to a centre of the kernel, l'he hydrated outer layer may have a depth of from Ito 3mm, typically from 1.5 to 2mm.

In the subsequent cooking step, the hydrated kernel is cooked at an elevated cooking temperature to cause the free water to evaporate. The water evaporates rapidly, causing blistering of the nut or legume meat on the outer surface of the kernel. The cooking step may be carried out with a high heat transfer coefficient to cause rapid evaporation of the free water and steam pressure sufficient to cause blistering of the outer surface. The resultant product is a texturized nut or legume product having blisters formed on an outer surface of the nut or legume kernels. In addition, in the cooking step the outer hydrated layer of the kernel is made crispier than an inner unhydrated portion of the kernel.

The cooking step typically comprises roasting the hydrated kernels for a period of from 2 to minutes at a temperature of from 125 to 160 °C to dehydrate the kernel to a total moisture content of from 1 to 4 wt%. In the cooking step, the blistered surface is rigidly set at the elevated cooking temperature.

The resultant structure in the embodiment of a peanut is illustrated in Figure 4. The outer surface 14 of the kernel 4 has blisters 16 formed by voids 18 in outer layers of the kernel 4.

In addition, similar to the first embodiment, the peanut kernel halves 6, 8 may be separated at one end of the kernel 4 to form an open gap (not shown) therebetween.

In this embodiment the nut may he a ground nut or a tree nut or a mixture thereof, and the nut may be selected from any one of a peanut, an almond a cashew nut, a brazil nut, or any mixture of two or more of these nuts. When producing peanuts, at least some of the kernels comprise a whole kernel having connected kernel halves, and after the cooking step (h) the kernel halves may be substantially filly connected together or may he partly separated as discussed above. Alternatively, the legume may be a bean or a chickpea or a mixture thereof.

A mixture of any nut and legume combination may be employed in this embodiment, According to this embodiment, a unique and distinctive visual appearance is imparted to nuts and/or legumes, which makes them more appealing to the consumer. In addition, this embodiment produces nuts or legumes having enhanced crispiness as compared to conventional fried or roasted nuts or legumes. The embodiment therefore texturizes the kernel to provide the property of enhanced crispiness as well as an enhanced visual appearance.

In a further emhodiment of the invention, in the immersing step (a) the aqueous liquid includes at least one additive selected from a flavouring, a colorant, a precursor of a flavour forming reaction, a precursor of a colour forming reaction, a precursor of a Maillard reaction and a mixture thereof For example, the at least one additive may comprise a salt, for example sodium chloride, a spice, a herb, a sweetener, or a flavouring such as coffee, or any mixture thereof.

The immersing step may be carried out for a time period of from 5 to 120 minutes and at a temperature of from 15 to 100 °C, optionally for a time period of from 20 to 30 minutes and at a temperature of from 75 to 95°C.

The use of such an additive may he combined with the immersion conditions of any previous embodiment, to provide a nut or legume product which has uiique texture and unique colour and/or flavour.

Further modifications to the inventions and the various embodiments disclosed herein will he readily apparent to those skilled in the art and are encompassed within the present invention as defined in the appended claims.