A method for preparing instant steamed peanuts by using a steaming process

Abstract

This invention discloses a method for preparing ready-to-eat steamed peanuts using a steam-moistening process, belonging to the field of food processing technology. The method includes the following steps: pretreatment and cleaning, rehydration treatment, steam-moistening penetration, packaging, sterilization, cooling, and finished product. The steam-moistening penetration step involves heating the rehydrated peanut kernels with steam to a core temperature of 100°C, then rapidly immersing them in a seasoning and permeation liquid pre-cooled to 0°C-10°C. The peanuts are then permeated for 10-15 minutes under ultrasonic conditions at a frequency of 28kHz and a power of 300W. After ultrasonic treatment, the peanuts are soaked for another 20 minutes, then drained until the moisture content is 40%-55%. This invention utilizes the innovative principle of "high-temperature peanut kernels encountering low-temperature seasoning liquid to form an instantaneous temperature difference negative pressure," combined with ultrasonic assistance, to achieve uniform flavoring of the peanut kernels from the inside out. The finished product has a soft, chewy, and elastic texture, a dry surface, and is nutritious and healthy. After high-temperature and high-pressure sterilization, the product can be stored at room temperature for a long time, making it suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of food processing technology, and specifically relates to a method for processing peanut products, particularly a method for preparing ready-to-eat steamed peanuts using a steaming and moistening process. Background Technology

[0002] Peanuts are an important oilseed and cash crop in my country, possessing both economic value and strategic significance. my country is the world's largest producer, consumer, and importer of peanuts. According to USDA data, in 2024 / 2025, my country's peanut production accounted for 37% of the global total, and its consumption accounted for 38-46% of the global total. For 30 consecutive years, China has maintained its position as the world's leading producer and consumer of peanuts. Peanuts are rich in protein, unsaturated fatty acids, vitamins, and polyphenolic antioxidants, making them highly popular among consumers.

[0003] Currently, most commercially available ready-to-eat peanut products are processed using deep-frying, roasting, or stir-frying techniques. However, relevant studies have shown that these high-temperature processing methods have significant adverse effects on peanut quality: the content of polyunsaturated fatty acids (PUFAs) decreases while the content of saturated fatty acids (SFAs) increases; the amino acid content decreases, for example, the total free amino acids decrease by 45.1% after frying; vitamins are destroyed by high temperatures, such as vitamin B1, which decreases by 80%, and protein and dietary fiber are partially carbonized; after boiling and frying, the total phenols in peanuts are reduced by 25.5% and 5.7%, respectively. Furthermore, roasting or frying may also produce heterocyclic compounds, such as pyrazines, furan derivatives, acrylamide, and 5-hydroxymethylfurfural (HMF), which are potentially harmful components. In addition, fried products have a high residual oil content, increasing the product's fat content, and are prone to causing dry mouth and internal heat after consumption, which does not meet the modern consumer's pursuit of a low-fat, healthy diet.

[0004] While traditional boiled peanuts have a fragrant flavor and are less likely to cause internal heat, they are mostly sold in bulk, wet, and in their shells. This results in low commercialization, short shelf life, a soft and inelastic texture, excessive broth on the surface making them inconvenient to eat, and shallow flavor penetration inside, making standardized and large-scale industrial production difficult. Furthermore, the national standard GB19300-2014, "National Food Safety Standard for Nuts and Seeds," stipulates that the maximum limit for peroxide value (based on fat content) in cooked nuts and seeds is 0.50g / 100g, and moldy kernels in shelled products must meet relevant limits. This further places higher demands on the processing technology and quality control of ready-to-eat peanut products.

[0005] Therefore, there is an urgent need to develop a ready-to-eat steamed peanut product and its processing method that can preserve the natural nutrients and aroma of peanuts to the greatest extent, achieve even flavor penetration inside and out, have a soft, chewy and elastic texture, a dry surface, and be resistant to storage. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing ready-to-eat steamed peanuts using a steaming and moistening process. This method, through an innovative combination of "steam cooking and low-temperature penetration," solves the problems of traditional boiled peanuts, such as difficulty in infusing flavor, poor taste, and poor storage life, as well as the significant nutrient loss and heatiness associated with traditional roasted peanuts. The resulting ready-to-eat steamed peanuts are nutritious, healthy, uniquely flavorful, and of stable quality, making them suitable for industrial production.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing ready-to-eat steamed peanuts using a steaming and moistening process, comprising the following steps:

[0008] (1) Pretreatment and cleaning: Select shelled peanut kernels and remove unqualified kernels such as moldy, broken, and sprouted kernels; rinse the peanut kernels with a mixed aqueous solution of 1%-2% salt water and 1‰-3‰ edible alkali at room temperature to clean the surface. The edible alkali solution helps to remove any mold and insect eggs that may remain on the surface of the peanuts, while softening the kernel skin, creating favorable conditions for subsequent rehydration and flavoring.

[0009] (2) Rehydration treatment: Place the washed peanuts in clean water and soak at room temperature for 30-40 minutes. Drain and then cover with sterilized damp gauze. Let stand at room temperature to allow the peanuts to naturally absorb water and rehydrate for at least 8 hours. This step allows the peanuts to gradually recover their moisture content to a suitable level through slow natural water absorption, avoiding cracking of the kernels caused by rapid water absorption. This lays the foundation for the formation of uniform mass transfer channels during subsequent steam cooking.

[0010] (3) Steaming and Penetration: After rehydration treatment, peanut kernels are heated with steam to a core temperature of 100°C and then quickly immersed in a seasoning and penetrating liquid pre-cooled to 0°C-10°C. The ratio of peanut kernels to the seasoning and penetrating liquid is 1:2. When hot peanuts are suddenly immersed in low-temperature seasoning and penetrating liquid, a negative pressure is formed inside the kernels due to the instantaneous temperature difference, which promotes the rapid penetration of the seasoning and penetrating liquid into the kernels. At the same time, ultrasonic treatment at a frequency of 28kHz and a power of 300W is performed for 10-15 minutes to accelerate the diffusion of the seasoning and penetrating liquid inside the kernels using the ultrasonic cavitation effect, so as to achieve uniform flavoring from the inside out. After ultrasonic treatment, the kernels are soaked in low-temperature seasoning and penetrating liquid for another 20 minutes to ensure that the flavoring is fully and evenly absorbed. Then, the kernels are removed and drained of surface water, and the moisture content of the peanut kernels is controlled at 40%-55%.

[0011] (4) Packaging: After draining, the peanut kernels are placed into high-temperature resistant composite packaging bags, and then sealed after vacuuming or degassing.

[0012] (5) Sterilization: Place the sealed packaged peanuts in a sterilizer and sterilize them at a temperature above 120°C for at least 30 minutes. Preferably, the sterilization temperature is 121°C-125°C and the maintenance time is 30-40 minutes.

[0013] (6) Cooling and finished product: After sterilization, remove the packaging and quickly cool it to room temperature by air cooling or water cooling, and blow dry the moisture on the outer surface of the packaging to obtain ready-to-eat steamed peanuts with a dry surface and soft and glutinous interior.

[0014] As a preferred option, the peanut kernels mentioned in step (1) are selected from peanut varieties with high protein and sucrose content, such as Jihua Sweet No. 1 and Silihong.

[0015] Preferably, the flavoring and infusion liquid mentioned in step (3) is an aqueous solution of natural seasonings, specifically composed of one or more of the following: spice extract, salt, and sugar, mixed with water.

[0016] Furthermore, the low temperature conditions described in step (3) are 0°C to 10°C.

[0017] Preferably, the sterilization temperature in step (5) is 121°C-125°C and the maintenance time is 30-40 minutes.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The product retains sufficient nutrients and is mild in nature: The entire process adopts the "steaming" process, which avoids the destruction of nutrients caused by high-temperature frying and baking. The product is low in fat and healthy, and will not cause dry mouth or internal heat after eating. At the same time, it is different from traditional boiling, which avoids the loss of a large amount of water-soluble nutrients.

[0020] (2) Unique flavor penetration inside and out: This invention features a unique steam-soaking and penetrating process where peanut kernels are heated to 100°C and immediately immersed in a low-temperature flavoring liquid, supplemented by ultrasound. When the high-temperature peanut kernels encounter the cold flavoring liquid, a negative pressure is created inside due to the instantaneous temperature difference, strongly absorbing the flavoring liquid; combined with the ultrasonic cavitation effect, the penetration of the liquid is accelerated, achieving uniform flavor penetration from the inside out. During the high-temperature and high-pressure sterilization process, the peanut protein undergoes moderate thermal denaturation, giving the product a unique texture that is soft and chewy with a moderate elasticity. This completely solves the problem of traditional boiled peanuts being "salty on the outside and bland on the inside," and having a soft, mushy, and dry texture.

[0021] (3) Good product form and convenient to eat: The final product surface is dry with no excess soup, no need to peel, ready to eat after opening the bag, and easy to clean.

[0022] (4) Stable quality and long shelf life: The product is sealed and sterilized under high temperature and high pressure, and can be stored at room temperature for a long time without the addition of preservatives. The quality is stable and easy to distribute and sell. The food safety indicators of the product meet the requirements of GB19300-2014 "National Food Safety Standard for Nuts and Seeds".

[0023] (5) Strong process adaptability: The parameters of each process are clear and controllable, which meets the requirements of standardized and large-scale industrial production and has good market application prospects and economic benefits. Detailed Implementation

[0025] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but these embodiments should not be construed as limiting the scope of protection of the present invention.

[0026] Example 1: A method for preparing ready-to-eat steamed peanuts using a steaming and moistening process, comprising the following steps:

[0027] (1) Pretreatment and cleaning: Select 1 kg of shelled "Jihuatian No. 1" peanut kernels and manually remove moldy, damaged and sprouted kernels. Prepare a mixed aqueous solution containing 1.5% salt and 2‰ edible alkali in the cleaning tank, and bubble and rinse the peanut kernels at room temperature for 5 minutes to thoroughly remove surface dust and impurities, and drain.

[0028] (2) Rehydration treatment: Put the washed peanuts into enough clean water and soak at room temperature for 35 minutes. Take them out and place them in a perforated tray to drain for 10 minutes. Take a clean gauze, boil it in boiling water for 30 minutes to sterilize it, squeeze out the water, cover the surface of the peanuts, and let it stand in a clean environment at 25°C for 10 hours to rehydrate the peanuts, so that the peanuts can fully absorb water, the texture changes from hard to soft, and the kernel volume increases.

[0029] (3) Preparation of the flavoring liquid: Take 5g of star anise, 3g of cinnamon, 2g of Sichuan pepper, and 2g of fennel seeds (the above seasoning amounts are based on 1000g of water), add 1000g of water, boil and keep simmering for 30 minutes, filter through a 200-mesh filter cloth, and collect the filtrate. After the filtrate cools to room temperature, add 15g of salt and 10g of white sugar, stir and dissolve evenly to obtain the natural flavoring liquid. Place the above flavoring liquid in a 4°C refrigerator for pre-cooling and use.

[0030] (4) Steaming and Infiltration: Place the peanuts that have been rehydrated in step (2) in a steaming tray and heat them with steam until the center temperature of the kernels reaches 100°C. Immediately immerse all the hot peanuts in the pre-cooled infiltration liquid at 4°C, with a material-to-liquid ratio of 1:2. Transfer the container to an ultrasonic device and perform ultrasonic-assisted infiltration for 15 minutes at a frequency of 28kHz, a power of 300W, and a temperature maintained at 4°C–8°C. After ultrasonic treatment, continue soaking in the low-temperature liquid for 20 minutes. Then remove the peanuts and drain the visible surface moisture on a vibrating dehydrator. The measured moisture content of the kernels is approximately 48%.

[0031] (5) Packaging: Pack the drained peanuts into high-temperature resistant aluminum foil composite retort bags in 200g bags per bag, vacuum them to 0.1MPa using a vacuum packaging machine and heat seal them.

[0032] (6) Sterilization: Place the packaged product into a high-temperature and high-pressure sterilizer, heat it to 121°C, and maintain the temperature for 35 minutes. Under these conditions, microorganisms (including heat-resistant spores) are effectively killed; peanut protein undergoes moderate heat denaturation, and the hardness of the kernels increases appropriately, forming a unique texture that is soft and glutinous with moderate elasticity.

[0033] (7) Cooling and Finished Product: After the sterilization process is completed, the back pressure cooling is turned on, and the product temperature is quickly reduced to below 30°C using circulating water. Then, the product is taken out and the surface moisture of the packaging bag is dried with strong air. After static testing, if the product has no broken bags or leakage, it is considered a finished product.

[0034] The ready-to-eat steamed peanuts prepared in this embodiment have intact kernels, dry surfaces, soft and chewy textures, and a balanced sweet and salty flavor. The aroma of the seasonings is evenly and deeply penetrated, and there is no risk of frying or causing internal heat. They can be eaten directly after opening the bag.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions and improvements made within the technical concept and essential spirit of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing ready-to-eat steamed peanuts using a steaming and moistening process, characterized in that, Includes the following steps: (1) Pretreatment and cleaning: Select shelled peanut kernels and remove unqualified kernels; rinse the peanut kernels at room temperature with a mixed aqueous solution of 1%-2% salt water and 1‰-3‰ edible alkali. (2) Rehydration treatment: Place the washed peanuts in clean water and soak at room temperature for 30-40 minutes. Take them out and drain them. Then cover them with sterilized damp gauze and let them stand at room temperature to allow the peanuts to absorb water naturally for no less than 8 hours. (3) Steaming and permeation: After rehydration treatment, the peanut kernels are heated to 100°C with steam and quickly immersed in the seasoning and permeation liquid pre-cooled to 0°C-10°C. The ratio of peanut kernels to permeation liquid is 1:

2. The peanut kernels are permeated for 10-15 minutes under ultrasonic frequency of 28kHz and power of 300W. After ultrasonic treatment, the peanut kernels are soaked for another 20 minutes. The kernels are then removed and drained to control the moisture content of the peanut kernels to 40%-55%. (4) Packaging: Pack the drained peanuts into high-temperature resistant composite packaging bags and vacuum or degas them for sealing; (5) Sterilization: Sterilize the sealed packaged peanuts at a temperature above 120°C for at least 30 minutes; (6) Cooling and finished product: After sterilization, cool quickly to room temperature and dry the outer surface of the packaging to obtain the finished product.

2. The method according to claim 1, characterized in that, The flavoring liquid mentioned in step (3) is a natural seasoning solution made by mixing one or more of the following: spice extract, salt, sugar, and water.

3. The method according to claim 1 or 3, characterized in that, The low temperature conditions mentioned in step (3) are 0°C to 10°C.

4. The method according to claim 1, characterized in that, The sterilization temperature in step (5) is 121°C-125°C and the maintenance time is 30-40 minutes.

5. The method according to claim 1, characterized in that, The high-temperature resistant composite packaging bag mentioned in step (4) is an aluminum foil composite retort bag.