Method for obtaining dehulled corn kernels

Abstract

The present invention refers to a method for obtaining dehulled corn kernels comprising the steps of providing raw corn kernels, subjecting said kernels to an acid hydrolysis while heating, washing the hydrolyzed-pericarp corn kernels and optionally drying the dehulled corn kernels obtained to a final moisture adequate to safe storage and manufacture of the dehulled corn kernels.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of food industry. More specifically, the present invention relates to the field of corn snacks industry, in particular to a method for obtaining dehulled corn kernels.BACKGROUND

[0002] Corn (Zea mays L.) stands out as one of the most significant and widely cultivated cereals globally, covering approximately 197 million hectares of land annually. This makes it the second-largest crop worldwide, surpassed only by wheat. The popularity of this cereal is related to the nutritional and sensory properties of maize and its food-related products, especially snacks (C. A. Zugravu et al., Journal of Agroalimentary Processes and Technology, vol. 18, no. 1, pp. 8-12, 2012). According to a study described by C.A. Zugravu et al., more than 9 out of 10 adults report eating some type of salty snack regularly, at least twice a month. (D. Santiago-Ramos et al., J Cereal Sci, vol. 81, pp. 108-117, 2018).

[0003] Corn fried snack products have seen increasing popularity and demand in recent years, with corn and tortilla chips being the most popular. These snacks are typically prepared by processing corn kernels through several unit operations such as cooking, steeping, soaking, and frying. (S. Garcia-Lara, et al. 'Development and Structure of the Corn Kernel', Corn: Chemistry and Technology, Third Edition, pp. 147-163, 2019). Corn and tortilla chips are often made by transforming corn into nixtamalized dough, which is then baked, fried, or extruded to create these popular snacks. However, there is another type of corn snack that has been gaining popularity, particularly in European and North American countries that is the previously hydrated and fried / toasted corn kernels, also known as "corn nuts" or "kikos" in Spain.

[0004] Corn nuts are typically made from waxy corn kernels, as the amylose-to-amylopectin ratio in these varieties provides the desirable palatability of these snacks (J. Á. Granados-Arvizu et al., Bioresources, vol. 12, no. 4, pp. 7955-7963, 2017). These snacks are usually part of nut mix snacks or serve as the main ingredient in salty fried snacks. One of the main attractions of these products to consumers is that they have a similar appearance to whole raw kernels, whether baked or fried and, on the other hand, results in a more stable kernel. Therefore, preserving the integrity of the kernels to maintain their natural shape is a desirable attribute for consumers. In the traditional process of corn nuts, this attribute is compromised due to mechanical processes during the pericarp elimination that leads to an increased number of broken kernels, and thus turns out into a reduced yield of quality products. The pericarp, the outer layer that protects the kernels from external stress factors, also acts as a barrier to maintain kernel moisture. These carbohydrates form a hydrophobic barrier that helps the grain control moisture gradients. However, the presence of the pericarp results in undesirable properties during the corn nut preparation process. The pericarp hardens during cooking, increasing the hardness of the snacks and limiting the moisture the kernels can absorb, reducing the crunchiness of these snacks, which is often a desirable feature (Cereal Chem. 1992 | Alkali Debranning of Corn to Obtain Corn Bran).

[0005] The first step in making corn nuts is to remove the pericarp from the corn kernels, which is primarily composed of cellulose, hemicellulose, and lignin. Traditional processes use highly concentrated acids, such as sulfuric acid at 98%, to hydrolyze the glycosidic bonds in cellulose and hemicellulose (N. Parris et al., J. Agric. Food Chem., vol. 49, no. 8, pp. 3757-3760, 2001). This hydrolysis breaks down the complex carbohydrates into simpler molecules, which can then be mechanically separated through processes such as centrifugation. Broken kernels are discarded as defective products, and the acid residues must be processed in a water treatment plant to be safely disposed of without causing environmental harm. While these methods effectively remove the pericarp, they can be harsh and environmentally unfriendly. Therefore, there is a need for more sustainable and less aggressive alternatives.BRIEF DESCRIPTION OF THE INVENTION

[0006] The present application relates to a sustainable dehulling method that effectively removes the pericarp, along with zeins and sugars, from corn kernels. The inventors of the present patent application surprisingly found that high quality purified corn kernels can be obtained using lower acid concentrations in aqueous solutions, compared to traditional methods, without requiring any centrifugation step. The method of the invention significantly reduces the number of broken kernels and allows the cleaning and reutilization of the acidic aqueous solution, thereby minimizing the amount of waste generated.

[0007] Conventional acid hydrolysis performed to dehulling corn kernels uses highly concentrated acid aqueous solutions, up to 98% v / v. In contrast, the method disclosed herein combines the acid hydrolysis employing a much less concentrated acid aqueous solution and heat with the performance of an ulterior wash with alkaline aqueous solution. This incorporation of heat to the acid treatment and the ulterior wash with alkaline aqueous solution allows that, in spite of using a low concentrated acid aqueous solution, a high quality dehulled corn kernel is obtained without requiring any centrifugation step.

[0008] Therefore, in a first aspect, the invention relates to a method for obtaining dehulled corn kernels, comprising the steps of: a) providing raw corn kernels b) subjecting the corn kernels of step a) to hydrolysis with an acid aqueous solution at an acid concentration between 15 and 50% v / v while heating at a temperature comprised between 40 °C and 90 °C to obtain hydrolyzed-pericarp corn kernels and a waste acid aqueous solution, c) washing the hydrolyzed-pericarp corn kernels obtained in step b) with an alkaline aqueous solution to obtain dehulled corn kernels, d) optionally, drying the dehulled corn kernels obtained in step c) to obtain dehulled corn kernels having a final moisture content equal to or below 15%. FIGURES

[0009] Figure 1. Final appearance of dehulled corn kernels obtained by the method of the invention. Figure 2. Fried dehulled corn kernels exhibiting incomplete removal of zeins and sugars exposed on the surface of the vitreous endosperm of the hydrolyzed-pericarp corn kernels. Figure 3. Fried dehulled corn kernels exhibiting complete removal of zeins and sugars exposed on the surface of the vitreous endosperm of the hydrolyzed-pericarp corn kernels. Figure 4. Corn nuts prepared using dehulled corn kernels obtained by the method of the invention, soaked overnight in a 3% ammonia carbonate aqueous solution (hydrated) and fried. DETAILED DESCRIPTION OF THE INVENTION

[0010] In the context of the invention, the expression "hydrolyzed-pericarp corn kernels" refers to the corn kernels obtained after the performance of the acid hydrolysis. The pericarp is composed of complex carbohydrates such as cellulose, hemicellulose and lignin. During said acid hydrolysis step, the glyosidic bonds of these pericarp components are broken and released in the form of carbohydrates or simple sugars. Therefore, the "hydrolyzed-pericarp corn kernels" of the invention are substantially free of pericarp.

[0011] In the context of the invention, the expression "dehulled corn kernels" refers to the corn kernels obtained after the removal of the pericarp by the treatment with the acid aqueous solution and the ulterior wash with the alkaline aqueous solution to remove zeins and sugars exposed on the surface of the vitreous endosperm of the "hydrolyzed-pericarp corn kernels".

[0012] Throughout the present specification, when a numeric range is indicated herein, both the lower limit and the upper limit are meant to be included in said range.

[0013] Throughout the present specification, the unit "m / v" refers to the ratio of mass / volume solution, commonly expressed as grams of solute per 100 mL of solution.

[0014] Throughout the present specification, the unit "v / v" refers to the ratio of volume / volume solution, that is, the number of milliliters of solute dissolved per 100 mL of solution.

[0015] As previously mentioned, in a first aspect the invention relates to a method for obtaining dehulled corn kernels, comprising the steps of: a) providing raw corn kernels, b) subjecting the corn kernels of step a) to hydrolysis with an acid aqueous solution at an acid concentration between 15 and 50% v / v while heating at a temperature comprised between 40 °C and 90 °C to obtain hydrolyzed-pericarp corn kernels and a waste acid aqueous solution, c) washing the hydrolyzed-pericarp corn kernels obtained in step b) with an alkaline aqueous solution to obtain dehulled corn kernels, d) optionally, drying the dehulled corn kernels obtained in step c) to obtain dehulled corn kernels having a final moisture content equal to or below 15%.

[0016] The method disclosed herein uses a combination of acid and temperature to perform the successful removal of the pericarp. The concentration of the acid aqueous solution used herein is significantly lower than the concentration of the acid aqueous solutions used in traditional methods for pericarp removal.

[0017] Therefore, in step b) the acid concentration of the acid aqueous solution is between 15 and 50% v / v, preferably between 20 and 40 % v / v, even more preferably between 25 and 38 % v / v.

[0018] The reduction of the concentration of acid required when compared with traditional processes is possible due to the effect of the temperature employed. In step b) the hydrolysis is performed at a temperature comprised between 40 °C and 90 °C, preferably between 50 °C and 90 °C, even more preferably between 60 °C and 90 °C.

[0019] The hydrolysis described in step b) of the method is performed during a certain time, to be determined considering the acid concentration as well as the temperature. One skilled in the art would know that if this hydrolysis is performed for too long, the hydrolysis could have negative consequences on the integrity of the grain. Therefore, in an embodiment, step b) is performed during a time equal to or of less than 15 minutes.

[0020] In another embodiment, step b) is performed during a time comprised between 1 and 15 minutes (both included), comprised between 3 and 15 minutes, comprised between 5 and 15 minutes, comprised between 7 and 15 minutes, comprised between 9 and 15 minutes, comprised between 11 and 15 minutes, or comprised between 13 and 15 minutes.

[0021] In a most preferred embodiment, the hydrolysis of step b) is performed with an acid aqueous solution at an acid concentration comprised between 25 and 38% v / v, while heating at a temperature comprised between 60 and 90 °C during a time comprised between 3 and 15 minutes.

[0022] In a preferred embodiment, the hydrolysis of step b) is performed by stirring, preferably gently stirred, even more preferably by mechanical stirring. Non-limiting examples of mechanical stirring methods are blade stirring, turbine stirring, magnetic stirring or recirculation using vacuum-based pumps.

[0023] The hydrolysis of the method of the invention can be performed using any acid known in the state of the art. In an embodiment, the acid of the acid aqueous solution of step b) is selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, acetic acid and mixtures thereof. In a preferred embodiment, the acid of the acid aqueous solution of step b) is sulfuric acid.

[0024] In an embodiment, the corn kernel:acid aqueous solution ratio of step b) is comprised between 1:1 and 1:5 m / v, preferably between 1:1 and 1:2 m / v, even more preferably 1:2 m / v.

[0025] In a preferred embodiment, after the acid hydrolysis of step b), and before the washing with the alkaline aqueous solution of step c), the hydrolyzed-pericarp corn kernels obtained in step b) are treated with water, in order to eliminate fragments of hydrolyzed pericarp which can be adhered to the hydrolyzed-pericarp corn kernels.

[0026] After the acid hydrolysis of step b), and after optionally performing the treatment with water, a color test can be performed as a quality control check to ensure that the hydrolyzed-pericarp corn kernels obtained in step b) are substantially free of pericarp.

[0027] This test is carried out taking into account that the bright yellow color is the one that the hydrolyzed-pericarp corn kernels acquire once the pericarp has been hydrolyzed. This test uses the CIELAB color space, or CIE 1976 L* a* b* color system, which represents quantitative relationship of colors on three axes: L* value indicates lightness, and a* and b* are chromaticity coordinates.

[0028] The CIELAB color space was proposed by the International Commission on Illumination (CIE by its acronym in French). The three parameters in the CIELAB represent the color luminosity: parameter L*=0 black, whereas L*=100 represents white; parameter a* determines the position of the color between red and green: a* negative values represent green, while positive values represent red; and parameter b* determines the position of the color between yellow and blue: b* negative values represent blue, while positive values represent yellow. The colorimetric CIELAB analysis has been broadly used in food industry, in characterization as well as in determination of quality in different food matrices (Cairone, F., Carradori, S., Locatelli, M. et al. Eur Food Res Technol vol. 246, pp. 259-272, 2020).

[0029] To ensure the proper hydrolysis of the pericarp an experimental test can be performed as described next. Firstly, the inventors determined the L*, a* and b* values by taking high-definition photographs of the hydrolyzed-pericarp corn kernels obtained in step b) and by treating said high-definition photographs with any suitable software which allows the performance of a color analysis in the CIELAB color space. Examples of said software are Adobe Photoshop ®< , MATLAB ®< or any other software which allows to perform said color analysis.

[0030] After this color analysis, the inventors determined that the suitable hydrolyzed-pericarp corn kernels show an L* value greater than 200, an a* value lower than 127, and a b* value greater than 185. These reference values were obtained by comparison of the hydrolyzed-pericarp corn kernels obtained by the method of the invention with hydrolyzed-pericarp corn kernels obtained by traditional methods.

[0031] However, one skilled in the art would know that values of L*, a* and b* parameters for suitable hydrolyzed-pericarp corn kernels may vary depending on the natural color of the corn variety.

[0032] After the performance of the hydrolysis described in step b) it is necessary to wash the hydrolyzed-pericarp corn kernels with an alkaline aqueous solution to eliminate the zeins and sugars that are exposed on the surface of the vitreous endosperm of the hydrolyzed-pericarp corn kernels. Without wanting to be bounded to a particular theory, it is believed that, due to the partial hydrolysis of the outer layers of the vitreous endosperm caused by the treatment with the acid aqueous solution, zeins and sugars get exposed on the surface of said vitreous endosperm of the hydrolyzed-pericarp corn kernels.

[0033] It is important to ensure the proper elimination of the zeins and sugars that get exposed on the surface of the vitreous endosperm after the treatment with the acid aqueous solution, since the presence of these substances in the dehulled corn kernels can lead to unwanted effects caused by the frying of said dehulled corn kernels, for instance, the creation of a shiny, plastic film-like surface on the fried corn kernels or a diminished ability to absorb moisture, which is crucial for achieving the desired texture and crunchiness in corn nuts.

[0034] Step c) of the method of the invention relates to the washing of the hydrolyzed-pericarp corn kernels obtained in step b) with an alkaline aqueous solution to obtain dehulled corn kernels. The alkaline agent of the alkaline aqueous solution of step c) can be any base known in the state of the art. Any suitable metal hydroxide, metal carbonate or mixtures thereof can be used for the purposes of the invention.

[0035] In an embodiment, the alkaline aqueous solution of step c) is a mixture of a metal hydroxide aqueous solution and a metal carbonate aqueous solution.

[0036] In a preferred embodiment, the metal hydroxide of the metal hydroxide aqueous solution is selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide and mixtures thereof. In a most preferred embodiment, the metal hydroxide of the hydroxide aqueous solution is sodium hydroxide.

[0037] In a preferred embodiment, the concentration of the metal hydroxide aqueous solution of step c) is comprised between 0.5-10% m / v, between 0.5-5% m / v, preferably between 0.5-4% m / v, even more preferably between 0.5-3% m / v. In the most preferred embodiment, the concentration of the metal hydroxide aqueous solution of step c) is 1% m / v.

[0038] In a further preferred embodiment, the metal carbonate of the metal aqueous carbonate solution is selected from the group consisting of sodium carbonate, potassium carbonate, calcium carbonate, magnesium carbonate and mixtures thereof. In a most preferred embodiment, the metal carbonate of the carbonate aqueous solution is potassium carbonate.

[0039] In a further embodiment, the concentration of the metal carbonate aqueous solution of step c) is comprised between 1-15% m / v, between 2-15% m / v, preferably between 3-15% m / v, even more preferably between 3-10% m / v. In the most preferred embodiment, the concentration of the metal carbonate aqueous solution of step c) is 6% m / v In a preferred embodiment, the alkaline aqueous solution of c) is a mixture of a metal hydroxide aqueous solution at 0.5-3% m / v and a metal carbonate aqueous solution at 3-10% m / v, even more preferably a mixture of a metal hydroxide aqueous solution at 1% m / v and a metal carbonate aqueous solution at 6% m / v.

[0040] In a preferred embodiment, the alkaline aqueous solution of c) is a mixture of sodium hydroxide and potassium carbonate.

[0041] In a more preferred embodiment, the alkaline aqueous solution of c) is a mixture of a sodium hydroxide aqueous solution at 0.5-3% m / v and a potassium carbonate aqueous solution at 3-10% m / v.

[0042] In step c), the washing of the hydrolyzed-pericarp corn kernels is preferably performed by stirring them with the alkaline aqueous solution, more preferably gently stirred, using methods selected from low-shear paddle agitation, gentle recirculation, or magnetic stirring. The goal is to facilitate the detachment of the remaining zeins and sugars from the surface of the hydrolyzed-pericarp corn kernels, allowing said zeins and sugars to dissolve into the washing alkaline aqueous solution.

[0043] In an embodiment, the hydrolyzed-pericarp corn kernels:alkaline aqueous solution ratio is comprised between 1:1 to 1:5 m / v ratio, preferably between 1:1 to 1:2 m / v ratio.

[0044] In an embodiment, step c) is performed during a time equal to or less than 15 minutes, preferably during a time equal to or less than 10 minutes, even more preferably during a time equal to or less than 5 minutes. According to another embodiment, step c) is performed until the alkaline aqueous solution has reached color saturation, meaning that the solution has reached an orange color, and this color remains invariable with time, which means that zeins and sugars that get exposed on the surface of the vitreous endosperm after the treatment with the acid aqueous solution have been fully transferred to the solution.

[0045] In the most preferred embodiment, step c) is performed with a sodium hydroxide aqueous solution at 0.5-3% m / v, during a time comprised between 30 and 120 seconds, preferably during 90 seconds.

[0046] In an embodiment, the dehulled corn kernels obtained in step c) are separated from the alkaline aqueous solution by draining, decantation, filtration, gravitational settling, or sieving, preferably by draining. These techniques ensure an efficient separation without the need for centrifugation. Therefore, these techniques allow for a simple and effective removal of the washing solution while maintaining the integrity of the kernels.

[0047] In a preferred embodiment, after the washing step c) an additional treatment with an alcohol aqueous solution can be performed, if there is any uncertainty about the elimination of the zeins and sugars that get exposed on the surface of the vitreous endosperm after the treatment with the acid aqueous solution.

[0048] In this optional treatment, the alcohol of the alcohol aqueous solution can be any alcohol suitable known in the state of the art. Non-limiting examples of alcohols are ethanol, butanol or tert-butanol. In a preferred embodiment, the alcohol is ethanol.

[0049] The person skilled in the art would know that when a toxic alcohol is used in this optional step, said toxic alcohol must be completely removed in ulterior stages, such as in the drying step.

[0050] Said alcohol aqueous solution can have different concentrations. In an embodiment, the alcohol aqueous solution is an ethanol solution at 50-90% v / v, preferably at 60-90% v / v, even more preferably at 70-90% v / v.

[0051] Said alcohol aqueous solution can further comprise a color protecting agent, such as ascorbic acid.

[0052] In an embodiment, the treatment with an alcohol aqueous solution is performed at a temperature comprised between 30 and 80 °C, preferably between 40 and 70 °C.

[0053] In order to maximize the contact between the hydrolyzed-pericarp corn kernels with the alcohol aqueous solution the contact can be performed by ultrasonic treatment and / or by constant stirring.

[0054] In an embodiment, the contact with the alcohol aqueous solution is performed by ultrasonic treatment at 40 KHz, during a time comprised between 5 and 20 minutes.

[0055] In another embodiment, the contact with the alcohol aqueous solution is performed by constant stirring, preferably during a time comprised between 10 and 30 minutes.

[0056] In another embodiment, the contact with the alcohol aqueous solution is performed by a combination of ultrasonic treatment at 40 kHz and constant stirring during a time comprised between 5 and 30 minutes.

[0057] After the washing of step c), a color test using the CIELAB color space can be performed as a quality control check to ensure that the dehulled corn kernels obtained in step c) are free of the zeins and sugars that come from the partial degradation of the outer layers of the vitreous endosperm.

[0058] To perform this test it is necessary to fry the dehulled corn kernels obtained in step c) before the performance of the control test, since the dehulled corn kernels obtained in step c) do not show any appreciable difference of color when comparing with the hydrolyzed-pericarp corn kernels obtained in step b).

[0059] To ensure the proper elimination of the zeins and sugars that get exposed on the surface of the vitreous endosperm after the treatment with the acid aqueous solution, the inventors determined that the suitable dehulled corn kernels show a value of L* comprised between 110 and 155, a value of a* comprised between 130 and 147, and a value of b* greater than 140. These reference values were obtained by the same procedure than the color analysis performed after the acid hydrolysis, that is, taking high-definition photographs and processing said photographs with a suitable software for color analysis, and by comparison of the values obtained in the dehulled corn kernels obtained by the method of the invention with dehulled corn kernels obtained by traditional methods.

[0060] Step d) of the invention is related with an optional drying, preferably performed by convective drying, of the dehulled corn kernels obtained in the previous step, to obtain a final moisture content equal to or below 15%, preferably equal to or below 14%. One skilled in the art would know that achieving a proper final moisture content is necessary to avoid microbiological issues during the corn storing and manufacturing. A proper moisture content ensures quality and safety of the final product.

[0061] In an embodiment, the drying step d) is performed during a time comprised between 1 to 3 hours.

[0062] In another embodiment, the drying step d) is performed at a temperature comprised between 45 and 60 °C.

[0063] In a preferred embodiment, the drying step d) is performed during a time comprised between 1 to 3 hours at a temperature comprised between 45 and 60 °C. Therefore, in an embodiment, the final moisture content of the dehulled corn kernels is equal to or below 15%. In another embodiment, the final moisture content is comprised between 12% and 15%.

[0064] In a particular embodiment, the method of the present invention further comprises the frying of the dehulled corn kernels obtained in step d) In another particular embodiment, the dehulled corn kernels obtained in step d) are first soaked with water or with a water solution and then fried.

[0065] In a preferred embodiment, the dehulled corn kernels obtained in step d) are fried at a temperature comprised between 180 and 200 °C, preferably at 190 °C.

[0066] In a preferred embodiment, the dehulled corn kernels obtained in step d) are fried using a vegetable oil selected from the group consisting of fractionated palm oil, corn oil, sunflower oil, canola oil and olive oil, preferably fractionated palm oil.

[0067] In a preferred embodiment, the dehulled corn kernels obtained in step d) are fried for less than 10 minutes, preferably for less than 5 minutes.

[0068] In a preferred embodiment, the dehulled corn kernels obtained in step d) are first hydrated, that is, are soaked with water or with an aqueous solution before being fried, preferably with an ammonia carbonate aqueous solution. In a more preferred embodiment, the concentration of the ammonia carbonate aqueous solution is comprised between 1% and 5% m / v, preferably 3% m / v.

[0069] In an embodiment, this hydration process is performed to increase the moisture of the dehulled corn kernels up to a moisture content comprised between 40% and 50%, before being fried.

[0070] In a more preferred embodiment, the dehulled corn kernels obtained in step d) are soaked in water or in an aqueous solution, preferably in an ammonia carbonate aqueous solution, for 24 hours, preferably 12 hours, before being fried.

[0071] In another embodiment the method of the invention further comprises either first soaking with water or with an aqueous solution and then frying the dehulled corn kernels obtained in step c) in the same conditions as recited above for the dehulled corn kernels obtained in step d).

[0072] The reduced concentration of the acid used in the method of the invention allows the easier cleaning and reutilization of the acidic solution, minimizing thus the amount of waste generated in comparison with traditional methods, which require the treatment of the waste acid solution, particularly sulfuric acid solutions up to 98% v / v, in water treatment plants, with the concomitant environmental and economical negative impact.

[0073] Therefore, in an embodiment, the method of the invention further comprises the purification of the waste acid aqueous solution obtained in step b) with a resin. This waste acid comprises the carbohydrates and simple sugars that come from the hydrolysis of the complex carbohydrates of the pericarp.

[0074] In a preferred embodiment, this purification is performed with a separation column packed with SEPABEADS resins (S. Neifar et al., Food Chem, vol. 309, p. 125710, 2020). These resins effectively retain most of the sugars and low molecular weight compounds that have affinity for the resin's chemical structure, and which have been generated during the acid hydrolysis of the method.

[0075] Once the waste acid aqueous solution is purified it can be reused in the acid hydrolysis step of the process, whereas the resin column can be washed with NaOH and ethanol solutions, allowing the resins to be reloaded with sugars from a new batch. Therefore, in an embodiment, the method of the invention further comprises the recirculation of the purified waste acid aqueous solution.

[0076] The present invention will be described in further detail with reference to the following examples. These examples are for illustrative purposes only and are not intended to limit the scope of the present invention.EXAMPLES Example 1. Pericarp hydrolysis

[0077] Example 1a: 250 g of raw corn kernels are mixed with 500 mL of H 2 SO 4 at 25% v / v while heating at a temperature of 70 °C for 15 minutes.

[0078] Example 1b: 250 g of raw corn kernels are mixed with 500 mL of H 2 SO 4 at 30% v / v, while heating at a temperature of 75 °C for 12 minutes.

[0079] Example 1c: 250 g of raw corn kernels are mixed with 500 mL of H 2 SO 4 at 38% v / v, while heating at a temperature of 80 °C for 8 minutes.

[0080] After the acid hydrolysis, a color test was performed to confirm the full removal of the pericarp in the hydrolyzed-pericarp corn kernels. In this test, the bright yellow color that the corn kernel acquires one the pericarp is removed is considered. After imagen analysis, the hydrolyzed-pericarp corn kernels accomplish the requirements shown in table 1.

[0081] L*, a* and b* parameters were obtained by taking high definition photographs and treating said photographs with an adequate software to perform color analysis using color values in the CIELAB space. Examples of suitable software are Adobe Photoshop ®< , MATLAB ®< or any other software which allows to perform said color analysis. Table 1: Color parameters of the hydrolyzed pericarp corn kernels obtained by the method of the invention.ParameterRequired valueExperimental valueL*More than 200204.33a*Less than 127124.64b*More than 185185.77 Example 2. Washing procedure

[0082] After pericarp removal under acidic conditions, the kernels are treated with a NaOH / K 2 CO 3 aqueous solution at 1% and 6% m / v, respectively for the elimination of zeins and sugars. They are gently agitated in a 1:2 kernels-solution ratio for up to 5 minutes, or until the solution reaches color saturation. After this step, the alkaline aqueous solution is drained from the dehulled corn kernels.

[0083] After washing with the NaOH / K 2 CO 3 aqueous solution and draining the solution from the dehulled corn kernels, the corn kernels were dried at 60 °C for 1.5 hours. The appearance of washed and dry kernels is depicted in Figure 1.Example 3. Comparison between dehulled corn kernels obtained by the method of the invention and dehulled corn kernels commercially provided.

[0084] Control tests were performed to confirm the completion of the washing step.

[0085] Incomplete elimination of zeins and other components as sugars can be assessed by frying dehulled corn kernels at 190°C for 30 seconds with fractionated palm oil.

[0086] The incomplete elimination of zeins and other components as sugars can be produced as a consequence of not carrying out properly the acid hydrolysis, the alkaline washing or both of them. This scenario can occur, for example, if the acid hydrolysis is performed at a temperature not high enough, when the acid aqueous solution is not enough concentrated or when the corn kernels:acid aqueous solution ratio is not adequate for allowing a proper contact of the acid aqueous solution with the corn kernels. This scenario can also occur, for example, if the washing step with an alkaline solution is performed with an alkaline solution not concentrated enough, or if the hydrolyzed-pericarp corn kernels:acid aqueous solution ratio is not adequate for allowing a proper contact of the alkaline solution with the hydrolyzed-pericarp corn kernels.

[0087] Figure 2 shows an example of incomplete elimination, indicated by darkened or "burned" areas after frying, which suggests the presence of zeins and sugars.

[0088] Conversely, as shown in Figure 3, complete elimination results in dehulled fried corn kernels that are pale yellow and free of a bright, plastic film-like surface.

[0089] Additionally, values of L*, a* and b* of fried dehulled corn kernels were measured. Table 2 shows the values obtained in dehulled corn kernels obtained by the method of the invention along with values obtained in dehulled corn kernels obtained by traditional methods. Table 2: Comparison of L*, a* and b* values of dehulled corn kernels obtained by the method of the invention vs the values of corn kernels obtained by reference methods (traditional methods, using sulfuric acid at 98% v / v).ParameterDehulled fried corn kernel of the inventionDehulled fried reference corn kernel 1Dehulled fried reference corn kernel 2L*118.78141.12126.55a*146.56139.10138.73b*150.63153.09148.72

[0090] The L*, a* and b* values of the fried dehulled corn kernels obtained by the method of the invention were compared with the L*, a* and b* values of fried dehulled corn kernels commercially available, obtained by traditional methods.

[0091] After the determination of the L*, a* and b* values of the fried dehulled corn kernels commercially available, the inventors established that suitable values of L* are comprised between 110 and 155, suitable values of a* are comprised between 130 and 147, and suitable values of b* are above 140.

[0092] However, the main parameter to be considered is b*, since it is related with the color scale from blue to yellow. The fried dehulled corn kernels obtained by the method of the invention shows a parameter b* very close to the one shown by fried dehulled corn kernels obtained by traditional method. Therefore, the dehulled corn kernels obtained by the method of the invention meets the criteria for using the dehulled corn kernels as raw material for corn nuts production.Example 4. Confirmation of the industrial criteria

[0093] In order to confirm that the process meets the criteria, dehulled corn kernels obtained by means of the method of the invention were soaked (hydrated) and fried, and the final appearance and taste of the snacks were evaluated.

[0094] To perform this test, standard procedures to fry cereal puffed snacks were followed, such as corn nuts. In that sense, the kernels were soaked in a 3% ammonia carbonate aqueous solution overnight (hydrated) and fried at 190°C for 4 minutes in fractionated palm oil. The obtained corn nuts are displayed in Figure 4.

[0095] The corn nuts obtained were further evaluated in a food tasting made by people of the food industry sector, concluding that the fried final product showed an adequate final appearance and good flavor.

[0096] In another evaluation, the dehulled corn kernels obtained by the method of the invention were processed by an external manufacturer, which confirmed that the fried corn snack has the same final appearance and taste as other fried corn snacks obtained by frying dehulled corn kernels obtained by traditional methods.

[0097] Furthermore, the process of the invention led to a 2.18% of broken corn-kernels and to a 1.30% of pieces of kernel, which are close to the specification of raw corn kernels, meaning that throughout the different steps of the method of the invention barely any corn kernel get broken or cracked.

[0098] Furthermore, the method of the invention allows for the production of 1 kg of dehulled corn kernels starting from 1.1 kg of raw corn kernels. This leads to a loss percentage of raw corn kernels of approximately 10% or less. In comparison, traditional methods result in a loss percentage of raw corn kernels of about 20-30% due to the need to process 1.3-1.5 kg of raw corn kernels to obtain 1 kg of dehulled corn kernels.

Claims

1. A method for obtaining dehulled corn kernels, comprising the steps of: a) providing raw corn kernels, b) subjecting the corn kernels of step a) to hydrolysis with an acid aqueous solution at an acid concentration between 15 and 50% v / v while heating at a temperature comprised between 40 °C and 90 °C to obtain hydrolyzed-pericarp corn kernels and a waste acid aqueous solution, c) washing the hydrolyzed-pericarp corn kernels obtained step b) with an alkaline aqueous solution to obtain dehulled corn kernels, d) optionally, drying the dehulled corn kernels obtained in step c) to obtain dehulled corn kernels having a final moisture content equal to or below 15%.

2. The method of claim 1, wherein the heating of step b) is performed at a temperature comprised between 60 °C and 90 °C.

3. The method according to any one of claims 1 to 2 wherein the acid concentration of the acid aqueous solution of step b) is between 20 and 40 % v / v.

4. The method according to any one of claims 1 to 3, wherein step b) is performed during a time equal to or less than 15 minutes.

5. The method according to any one of claims 1 to 4, wherein the acid of the acid aqueous solution of step b) is selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, acetic acid and mixtures thereof.

6. The method according to any one of claims 1 to 5 wherein the corn kernels:acid aqueous solution ratio is comprised between 1:1 and 1:5 m / v, preferably between 1:1 and 1:2 m / v.

7. The method according to any one of claims 1 to 6, wherein the hydrolysis of step b) is performed with an acid aqueous solution at a concentration comprised between 25 and 38% v / v, while heating at a temperature comprised between 60 and 90 °C during a time comprised between 3 and less than 15 minutes.

8. The method according to any one of claims 1 to 7, wherein the washing of step c) further comprises contacting the hydrolyzed-pericarp corn kernels obtained with an alcohol aqueous solution.

9. The method according to any one of claims 1 to 8, wherein the hydrolyzed-pericarp corn kernels:alkaline aqueous solution ratio is comprised between 1:1 to 1:5 m / v ratio, preferably between 1:1 to 1:2 m / v ratio.

10. The method according to any one of claims 1 to 9, wherein the alkaline aqueous solution of step c) is a metal hydroxide aqueous solution at 0.5-3% m / v.

11. The method according to any one of claims 1 to 9, wherein the alkaline aqueous solution of step c) is a metal carbonate aqueous solution at 3-10% m / v.

12. The method according to any one of claims 1 to 10, wherein step c) is performed with a sodium hydroxide aqueous solution at 0.5-3% m / v, during a time comprised between 30 and 120 seconds, preferably during 90 seconds.

13. The method according to any one of claims 1 to 13, further comprising the purification of the waste acid aqueous solution obtained in step b) with a resin.

14. The method according to any one of claims 1 to 14, further comprising the recirculation of the purified waste acid aqueous solution obtained according to claim 14.

15. The method according to any one of claims 1 to 14, further comprising either first soaking with water or with an aqueous solution and then frying the dehulled corn kernels obtained in step c), or first soaking with water or with an aqueous solution and then frying the dehulled corn kernels obtained in step d).

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