Preparation method of low-purine white kidney bean product

Abstract

The invention discloses a preparation method of a low-purine white kidney bean product, relates to a preparation method of a white kidney bean product, and belongs to the technical field of food processing. The invention aims to solve the problems of low purine degradation rate, large nutrient loss, long process period and poor flavor in the prior art. The preparation method comprises the following steps: mixing bean flour with water, adjusting the pH value, adding pullulanase and beta-amylase, carrying out enzymolysis and enzyme deactivation, and cooling to room temperature to obtain an enzymatic hydrolysate; inoculating a mixed bacterial solution of lactobacillus plantarum and saccharomycetes into the enzymatic hydrolysate, fermenting, sterilizing, centrifuging, and drying to obtain the product. Through the innovative biological synergistic effect, namely, the dual effect of enzymolysis release and microbial degradation, the total purine content in the white kidney bean product is reduced by 40% or above, the balance of nutrition retention and function enhancement is achieved, the sensory quality of the product is actively improved, and the processing period is remarkably shortened to 24-48 hours.

Description

Technical Field

[0001] This invention relates to a method for preparing white kidney bean products, belonging to the field of food processing technology. Background Technology

[0002] Legumes and their products are important sources of high-quality plant protein and various bioactive components, occupying a vital position in global healthy dietary systems. White kidney beans, as an important category, are not only high in protein but also possess unique value in weight management and blood sugar regulation due to their content of components such as α-amylase inhibitors. However, some legumes, represented by white kidney beans, have high purine content (for example, some dried beans can contain 1500-2200 mg / kg of purine), becoming a major limiting factor in dietary intake for people with hyperuricemia and gout. In clinical nutrition management, limiting exogenous purine intake is one of the core intervention methods, but completely avoiding legumes can lead to insufficient intake of beneficial nutrients such as plant protein and dietary fiber, creating a contradiction between "nutrition and risk." Therefore, developing processing technologies that can significantly reduce purine content while maximizing or even enhancing their inherent nutritional and functional properties has become a key issue that urgently needs to be addressed in the fields of food science and nutrition engineering. Current purine reduction methods and their limitations are as follows:

[0003] Physical removal methods (such as steaming, boiling, and discarding the broth after soaking): This method is based on the water solubility of purines, achieving removal by boiling and then discarding the broth. Its core problem lies in its extremely low removal rate and poor selectivity. The purine removal rate is low (usually below 10%), and because most purines exist in a bound form inside cells, simple boiling is insufficient for effective release. More seriously, this process leads to the significant loss of water-soluble vitamins (such as B vitamins), minerals (such as potassium and magnesium), oligosaccharides, and some proteins, resulting in severe nutritional depletion—a truly counterproductive process.

[0004] Single-enzyme hydrolysis: This method utilizes specific enzymes (such as nucleases and proteases) to directly degrade purine substances or uses cell wall degrading enzymes (such as cellulase) to destroy their structure. Its core problems lie in the limited target and efficiency bottleneck. Enzymes that directly target purines are often expensive and highly specific, resulting in incomplete degradation of various purine derivatives in complex food matrices. Furthermore, using a single cell wall degrading enzyme (such as cellulase or amylase alone) is insufficient to completely destroy the dense structure of legume cells composed of cellulose, hemicellulose, and starch, leading to inadequate release of bound purines and hindering subsequent degradation.

[0005] Traditional fermentation methods primarily rely on natural microbial communities or inoculation with a single probiotic (such as lactic acid bacteria) to ferment purines through microbial metabolism. The core problems are its long cycle, unstable efficiency, and uncontrollable flavor. Natural fermentation takes 3-5 days, is susceptible to contamination by other microorganisms, and results in significant quality fluctuations. Single-strain fermentation, due to its limited metabolic pathways, degrades purines slowly and to a low degree, and often produces overly sour flavors or other unpleasant odors due to the single metabolic product (such as excessive acid production), requiring additional acidification and flavoring processes.

[0006] Existing technologies generally suffer from problems such as incomplete purine reduction, significant nutrient loss, long processing cycles, or unsatisfactory product flavor. Therefore, there is an urgent need for a new method for processing soy products that can efficiently reduce purines while preserving or improving the nutritional and flavor quality of the product. Summary of the Invention

[0007] The purpose of this invention is to solve the technical problems of low purine degradation rate, large nutrient loss, long processing cycle and poor flavor in the prior art, and to provide a method for preparing low-purine white kidney bean products.

[0008] The preparation method of low-purine white kidney bean products is as follows:

[0009] I. Raw material pretreatment: After washing the white kidney beans, soak them in water at 25-40℃ for 6-12 hours, drain, crush, and pass through a 60-100 mesh sieve to obtain bean flour;

[0010] II. Compound enzymatic hydrolysis:

[0011] Mix soybean flour and water at a ratio of 1g:10mL, adjust the pH to 5.0-6.5, add pullulanase and β-amylase, and hydrolyze at 50-65℃ for 4-10 hours. After hydrolysis, inactivate the enzyme at 90℃ for 10 minutes, cool to room temperature, and obtain the hydrolysate.

[0012] The total amount of pullulanase and β-amylase added is 0.5%-2.0% of the soybean flour mass, and the mass ratio of β-amylase to pullulanase is 1:1-1:3.

[0013] III. Co-fermentation:

[0014] Inoculate the enzymatic hydrolysate with a mixed culture of Lactobacillus plantarum and yeast, and ferment at 24-40℃ for 12-72 hours. Stir for 5-10 minutes every 6-12 hours during fermentation. After fermentation, sterilize the product at 80-95℃ for 10-20 minutes, centrifuge to obtain the supernatant or whole pulp, and dry to obtain low-purine white kidney bean product.

[0015] The total inoculation volume of the mixed culture of *Lactobacillus plantarum* and yeast is 3-10% of the volume of the enzymatic hydrolysate.

[0016] The ratio of live Lactobacillus plantarum to live yeast in the mixed bacterial solution is 1:1 to 3:1.

[0017] The pullulanase activity described in step two is ≥1×10⁻⁶. 5 U / g.

[0018] The β-amylase activity described in step two is ≥700,000 U / g.

[0019] The *Lactobacillus plantarum* mentioned in step three has a viable count ≥ 1 × 10⁻⁶. 10 CFU / g.

[0020] The yeast used in step three is *Saccharomyces cerevisiae*, with a viable count ≥ 1 × 10⁻⁶. 9 CFU / g.

[0021] The drying process described in step three is either spray drying or vacuum freeze drying.

[0022] The research and development path of this invention is as follows:

[0023] 1) Addressing the issue of "incomplete release": An innovative combined enzymatic hydrolysis system of pullulanase and β-amylase is introduced. Unlike single-enzyme action, this combination synergistically hydrolyzes the key starch scaffold in legume cell walls—pululanase precisely cleaves the α-1,6-glycosidic bonds of amylopectin, while β-amylase efficiently hydrolyzes the α-1,4-glycosidic bonds of amylose. The synergistic effect of both maximizes the disintegration of the starch structure encapsulating purines, fully releasing the bound purines and providing sufficient substrate for subsequent microbial degradation. This step solves the key problem of "difficult release of bound purines."

[0024] 2) Addressing the issues of "low conversion efficiency and poor flavor": A symbiotic fermentation system of *Lactobacillus plantarum* and yeast was designed and constructed. This system is not a simple superposition, but rather based on the principle of metabolic complementarity: *Lactobacillus plantarum*, as the main force in purine degradation, possesses a highly efficient purine absorption and metabolic enzyme system, enabling efficient utilization of free purines; yeast not only contributes additional purine decomposition pathways, but also promotes the activity of *Lactobacillus plantarum* by consuming lactic acid and providing growth factors, and metabolizes to produce abundant esters, higher alcohols, and other flavor substances. The complementary metabolism of the two bacteria accelerates the entire process of purine degradation, while simultaneously generating organic acids, esters, and other flavor substances, improving the product's taste and flavor. The symbiosis between the two forms a virtuous cycle of "degradation-flavor generation," simultaneously solving the dual challenges of efficient purine conversion and flavor quality improvement.

[0025] 3) Process Integration and Optimization: The above-mentioned enzymatic pretreatment and dual-strain fermentation are organically integrated, and key parameters such as the material-to-liquid ratio, pH, temperature, time, enzyme ratio, and strain ratio are systematically optimized. While ensuring efficient purine reduction, a complete, efficient, and controllable process scheme is formed, significantly improving production efficiency and maximizing nutrient retention. This scheme represents a technological leap from "passive leaching" to "active enzymatic decomposition and release + microbial transformation," which is the core innovation of this invention.

[0026] This invention aims to provide a low-purine white kidney bean product and its preparation method. Through an integrated process of compound enzymatic hydrolysis and dual-strain synergistic fermentation, it solves the problems of low purine degradation rate, significant nutrient loss, long processing cycle, and poor flavor in existing technologies, achieving the following objectives:

[0027] 1) Fundamentally improves purine removal efficiency: This invention reduces the total purine content in white kidney bean products by more than 40% through innovative biological synergy, namely the dual action of enzymatic decomposition and microbial degradation, far exceeding the level of existing physical or single biological methods.

[0028] 2) Achieving a balance between nutrient retention and functional enhancement: While effectively reducing purines, it fully retains core nutrients such as dietary fiber and resistant starch, and generates beneficial metabolites such as prebiotics and short-chain fatty acids through the fermentation process, thereby enhancing the health value of the product.

[0029] 3) Proactively improve the sensory quality of the product: Through targeted fermentation control, the organic acids, esters and other substances produced by fermentation effectively mask the beany smell, and the product has a natural fermented aroma (naturally produced pleasant flavor substances), which effectively masks or eliminates the beany smell, reduces the dependence on exogenous flavorings, and eliminates the need to add flavorings.

[0030] 4) Optimize production process: Enzymatic pretreatment accelerates substrate release, significantly shortens the processing cycle to 24-48 hours, which is much shorter than traditional natural fermentation (3-5 days), improves production efficiency and process controllability, provides a feasible solution for large-scale and standardized production, and is conducive to continuous industrial production. Detailed Implementation

[0031] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0032] Specific Implementation Method 1: The preparation method of the low-purine white kidney bean product in this implementation method is as follows:

[0033] I. Raw material pretreatment: After washing the white kidney beans, soak them in water at 25-40℃ for 6-12 hours, drain, crush, and pass through a 60-100 mesh sieve to obtain bean flour;

[0034] II. Compound enzymatic hydrolysis:

[0035] Mix soybean flour and water at a ratio of 1g:10mL, adjust the pH to 5.0-6.5, add pullulanase and β-amylase, and hydrolyze at 50-65℃ for 4-10 hours. After hydrolysis, inactivate the enzyme at 90℃ for 10 minutes, cool to room temperature, and obtain the hydrolysate.

[0036] The total amount of pullulanase and β-amylase added is 0.5%-2.0% of the soybean flour mass, and the mass ratio of β-amylase to pullulanase is 1:1-1:3.

[0037] III. Co-fermentation:

[0038] Inoculate the enzymatic hydrolysate with a mixed culture of Lactobacillus plantarum and yeast, and ferment at 24-40℃ for 12-72 hours. Stir for 5-10 minutes every 6-12 hours during fermentation. After fermentation, sterilize the product at 80-95℃ for 10-20 minutes, centrifuge to obtain the supernatant or whole pulp, and dry to obtain low-purine white kidney bean product.

[0039] The total inoculation volume of the mixed culture of *Lactobacillus plantarum* and yeast is 3-10% of the volume of the enzymatic hydrolysate.

[0040] The ratio of live Lactobacillus plantarum to live yeast in the mixed bacterial solution is 1:1 to 3:1.

[0041] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the pullulanase activity in step two is ≥1×10⁻⁶. 5 U / g. Everything else is the same as in Specific Implementation Method 1.

[0042] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the β-amylase activity in step 2 is ≥700,000 U / g. Everything else is the same as in Specific Implementation Method 1 or 2.

[0043] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the viable count of *Lactobacillus plantarum* in step three is ≥1×10⁻⁶. 10 CFU / g. Other details are the same as in any of the specific embodiments one to three.

[0044] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the yeast used in step three is *Saccharomyces cerevisiae*, with a viable count ≥ 1 × 10⁻⁶. 9 CFU / g. Other details are the same as in any of the specific implementation methods one through four.

[0045] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the drying in step three is spray drying or vacuum freeze drying. Everything else is the same as in Specific Implementation Methods One to Five.

[0046] The effects of the present invention are verified using the following embodiments:

[0047] Example 1

[0048] The preparation method of low-purine white kidney bean products is as follows:

[0049] I. Raw material pretreatment: After washing the white kidney beans, soak them in 40℃ water for 6 hours, drain them, crush them, and pass them through a 100-mesh sieve to obtain bean flour;

[0050] II. Compound enzymatic hydrolysis:

[0051] Mix soybean flour and water at a ratio of 1g:10mL, adjust the pH to 6.0, add pullulanase and β-amylase, and enzymatically hydrolyze at 60℃ for 9 hours. After enzymatic hydrolysis, inactivate the enzyme at 90℃ for 10 minutes, and cool to room temperature to obtain the enzymatic hydrolysate.

[0052] The total amount of pullulanase and β-amylase added was 1.0% of the soybean flour mass, and the mass ratio of β-amylase to pullulanase was 1:3.

[0053] III. Co-fermentation:

[0054] A mixed culture of Lactobacillus plantarum and yeast was inoculated into the enzymatic hydrolysate and fermented at 32°C for 48 hours. During fermentation, the mixture was stirred for 5 minutes every 6 hours. After fermentation, the product was sterilized at 80°C for 10 minutes, centrifuged, and the supernatant was dried to obtain a low-purine white kidney bean product.

[0055] The total inoculation volume of the mixed culture of *Lactobacillus plantarum* and yeast is 4% of the volume of the enzymatic hydrolysate.

[0056] The ratio of live Lactobacillus plantarum to live yeast in the mixed bacterial solution is 1:1.

[0057] The total purine content of the low-purine white kidney bean product was reduced from 599.9 mg / kg in the raw white kidney beans to 358.8 mg / kg, a reduction rate of 40.2%. The product has a fermented aroma and no beany smell.

[0058] Example 2

[0059] The preparation method of low-purine white kidney bean products is as follows:

[0060] I. Raw material pretreatment: After washing the white kidney beans, soak them in 40℃ water for 6 hours, drain them, crush them, and pass them through a 100-mesh sieve to obtain bean flour;

[0061] II. Compound enzymatic hydrolysis:

[0062] Mix soybean flour and water at a ratio of 1g:10mL, adjust the pH to 6.0, add pullulanase and β-amylase, and enzymatically hydrolyze at 55℃ for 6 hours. After enzymatic hydrolysis, inactivate the enzyme at 90℃ for 10 minutes, and cool to room temperature to obtain the enzymatic hydrolysate.

[0063] The total amount of pullulanase and β-amylase added was 0.8% of the soybean flour mass, and the mass ratio of β-amylase to pullulanase was 1:2.

[0064] III. Co-fermentation:

[0065] A mixed bacterial culture of Lactobacillus plantarum and yeast was inoculated into the enzymatic hydrolysate and fermented at 30°C for 36 hours. During the fermentation, the mixture was stirred for 5 minutes every 6 hours. After the fermentation was completed, the product was sterilized at 80°C for 10 minutes, centrifuged to collect the supernatant, and dried to obtain a low-purine white kidney bean product.

[0066] The total inoculation volume of the mixed culture of *Lactobacillus plantarum* and yeast is 3% of the volume of the enzymatic hydrolysate.

[0067] The ratio of live Lactobacillus plantarum to live yeast in the mixed bacterial solution is 2:1.

[0068] The total purine content of the low-purine white kidney bean product was measured to decrease from 599.9 mg / kg in the raw white kidney beans to 541 mg / kg, a reduction rate of 9.8%.

[0069] Example 3

[0070] The preparation method of low-purine white kidney bean products is as follows:

[0071] I. Raw material pretreatment: After washing the white kidney beans, soak them in 40℃ water for 6 hours, drain them, crush them, and pass them through a 100-mesh sieve to obtain bean flour;

[0072] II. Compound enzymatic hydrolysis:

[0073] Mix soybean flour and water at a ratio of 1g:10mL, adjust the pH to 6.0, add pullulanase and β-amylase, and enzymatically hydrolyze at 50℃ for 10 hours. After enzymatic hydrolysis, inactivate the enzyme at 90℃ for 10 minutes, and cool to room temperature to obtain the enzymatic hydrolysate.

[0074] The total amount of pullulanase and β-amylase added was 2.0% of the soybean flour mass, and the mass ratio of β-amylase to pullulanase was 1:3.

[0075] III. Co-fermentation:

[0076] A mixed bacterial culture of Lactobacillus plantarum and yeast was inoculated into the enzymatic hydrolysate and fermented at 40°C for 24 hours. During the fermentation, the mixture was stirred for 5 minutes every 6 hours. After the fermentation was completed, the product was sterilized at 80°C for 10 minutes, centrifuged to collect the supernatant, and dried to obtain a low-purine white kidney bean product.

[0077] The total inoculation volume of the mixed culture of *Lactobacillus plantarum* and yeast is 8% of the volume of the enzymatic hydrolysate.

[0078] The ratio of live Lactobacillus plantarum to live yeast in the mixed bacterial solution is 3:1.

[0079] The total purine content of the low-purine white kidney bean product was measured to decrease from 599.9 mg / kg in the raw white kidney beans to 452.1 mg / kg, a reduction rate of 15.4%.

[0080] Comparative Example 1 (Microwave-Atmospheric Pressure Cooking):

[0081] Microwave pretreatment: Whole or broken white kidney beans are moistened with a small amount of water and microwaved at medium to high power for 2 minutes.

[0082] Boiling: Add enough water (bean-to-water ratio ≥ 1:5), boil at normal pressure for 15-20 minutes.

[0083] Separate: Discard all the broth.

[0084] Results: The total purine content of white kidney bean products decreased from 599.9 mg / kg in the raw white kidney beans to 593.1 mg / kg, a reduction rate of 1.1%.

[0085] Comparative Example 2 (Microwave-Pressure Cooking):

[0086] Microwave pretreatment: Whole or broken white kidney beans are moistened with a small amount of water and microwaved at medium to high power for 2 minutes.

[0087] High-pressure cooking: Microwave-treated beans and water (bean-to-water mass ratio ≥ 1:5) are cooked together under high pressure at a bean-to-water mass ratio of 1:2.25, a temperature of 121℃, and a time of 30 minutes.

[0088] Separate: Discard all the broth.

[0089] Results: The total purine content of white kidney bean products decreased from 599.9 mg / kg in the raw white kidney beans to 534.2 mg / kg, a reduction rate of 11.0%.

[0090] Comparative Example 3 (Single Enzyme Digestion)

[0091] Enzymatic pretreatment:

[0092] Mix soybean flour and water at a ratio of 1g:10mL, adjust the pH to 6.0, add pullulanase and β-amylase, and enzymatically hydrolyze at 60℃ for 9 hours. After enzymatic hydrolysis, inactivate the enzyme at 90℃ for 10 minutes, and cool to room temperature to obtain the enzymatic hydrolysate.

[0093] The total amount of pullulanase and β-amylase added was 1.0% of the soybean flour mass, and the mass ratio of β-amylase to pullulanase was 1:3.

[0094] High-pressure cooking: The enzymatically hydrolyzed soybeans and water (soybean-to-water mass ratio ≥ 1:5) are cooked together under high pressure until the soybean-to-water mass ratio is 1:2.25, at a temperature of 121℃ for 30 minutes.

[0095] Separate: Discard all the broth.

[0096] Results: The total purine content of white kidney bean products decreased from 599.9 mg / kg in the raw white kidney beans to 518.6 mg / kg, a reduction rate of 12.6%.

[0097] Comparative Example 4 (Single Fermentation)

[0098] Fermentation pretreatment: Inoculate the mixture of white kidney beans and water with a mixed bacterial culture of Lactobacillus plantarum and yeast, and ferment at 32°C for 48 hours, stirring for 5 minutes every 6 hours during fermentation;

[0099] The total inoculation volume of the mixed culture of *Lactobacillus plantarum* and yeast is 4% of the volume of the enzymatic hydrolysate.

[0100] The ratio of live Lactobacillus plantarum to yeast in the mixed bacterial solution is 1:1.

[0101] High-pressure cooking: Fermented soybeans and water (soybean-to-water mass ratio ≥ 1:5) are cooked together under high pressure at a mass ratio of 1:2.25, a temperature of 121℃, and a time of 30 minutes.

[0102] Separate: Discard all the broth.

[0103] Results: The total purine content of white kidney bean products decreased from 599.9 mg / kg in the raw white kidney beans to 523.6 mg / kg, a reduction rate of 12.7%.

Claims

1. A method for preparing low-purine white kidney bean products, characterized in that... The preparation method of the low-purine white kidney bean product is as follows: I. Raw material pretreatment: After washing the white kidney beans, soak them in water at 25-40℃ for 6-12 hours, drain, crush, and pass through a 60-100 mesh sieve to obtain bean flour; II. Compound enzymatic hydrolysis: Mix soybean flour and water at a ratio of 1g:10mL, adjust the pH to 5.0-6.5, add pullulanase and β-amylase, and hydrolyze at 50-65℃ for 4-10 hours. After hydrolysis, inactivate the enzyme at 90℃ for 10 minutes, cool to room temperature, and obtain the hydrolysate. The total amount of pullulanase and β-amylase added is 0.5%-2.0% of the soybean flour mass, and the mass ratio of β-amylase to pullulanase is 1:1-1:

3. III. Co-fermentation: Inoculate the enzymatic hydrolysate with a mixed culture of Lactobacillus plantarum and yeast, and ferment at 24-40℃ for 12-72 hours. Stir for 5-10 minutes every 6-12 hours during fermentation. After fermentation, sterilize the product at 80-95℃ for 10-20 minutes, centrifuge to obtain the supernatant or whole pulp, and dry to obtain low-purine white kidney bean product. The total inoculation volume of the mixed culture of *Lactobacillus plantarum* and yeast is 3-10% of the volume of the enzymatic hydrolysate. The ratio of live Lactobacillus plantarum to live yeast in the mixed bacterial solution is 1:1 to 3:

1.

2. The method for preparing the low-purine white kidney bean product according to claim 1, characterized in that... The pullulanase activity described in step two is ≥1×10⁻⁶. 5 U / g.

3. The method for preparing the low-purine white kidney bean product according to claim 1, characterized in that... The β-amylase activity described in step two is ≥700,000 U / g.

4. The method for preparing the low-purine white kidney bean product according to claim 1, characterized in that... Step 3 requires a live Lactobacillus plantarum count ≥ 1 × 10⁻⁶. 10 CFU / g.

5. The method for preparing the low-purine white kidney bean product according to claim 1, characterized in that... The yeast used in step three is *Saccharomyces cerevisiae*, with a viable count ≥ 1 × 10⁻⁶. 9 CFU / g.

6. The method for preparing the low-purine white kidney bean product according to claim 1, characterized in that... The drying process described in step three is either spray drying or vacuum freeze drying.