Ultrasonic and microwave combined treatment method for peeling walnut kernels

Abstract

The invention provides a method for efficiently peeling walnut kernels through ultrasonic-microwave combined treatment. The method comprises the following steps: (1) pretreating the walnut kernels: soaking the walnut kernels without peeling in warm water for a period of time; (2) ultrasonic treatment: performing ultrasonic treatment after soaking in warm water for a period of time; (3) high-pressure washing: putting the treated walnut kernels into peeling roller equipment, and washing the peels of the walnut kernels by means of high-pressure water generated by a high-pressure pump; (4) microwave baking: performing impurity filtration on the walnut kernels in a conveying water tank, and finally putting the obtained walnut kernels into a microwave oven for baking. According to the method, walnut kernel coats are stripped and removed by utilizing the cavitation effect and the mechanical effect of ultrasonic waves, and the peeled walnut kernels are treated by utilizing the green and efficient characteristics of microwaves, so that the drying efficiency is improved, and the walnut kernels are crisper in mouth feel. The process flow is simple, the operation is convenient, the use of chemical preparations and high-temperature steam is avoided, and the food safety is ensured on the premise of keeping the original taste and flavor of the walnut kernels and not losing nutrients.

Description

Technical Field

[0001] The invention relates to the technical field of food processing technology, in particular to a method for peeling walnut kernels based on ultrasonic and microwave combined processing. Background Art

[0002] Walnuts, one of the world's four famous dried fruits, are delicious and nutritious. Rich in protein, fat, minerals, and vitamins, they offer benefits such as tonifying the body, nourishing brain cells, preventing and combating cancer, and enhancing brain function. In recent years, walnut foods and beverages made from walnut kernels have become popular among consumers due to their natural, nutritious, and health-promoting properties. Market demand is growing, and production is expanding. Walnut kernels, the kernels of walnuts, are covered with a dense, thin, brown outer layer, also known as the walnut inner seed coat. These outer layers are rich in phenolic compounds, accounting for over 90% of the kernel's total phenolic content. When mature and dried, they develop a golden color and have a bitter, astringent taste. The main components of the walnut inner seed coat are cellulose, pectin, tannins, and pigments. Tannins, also known as tannins, are water-soluble polyphenolic compounds with protein-precipitating properties. When these polyphenols bind to salivary proteins, they cause epithelial cells in the tongue to shrink, producing an astringent taste. Tannins are primarily found in the walnut inner seed coat, comprising approximately 92% of the total tannin content. Research has shown that tannins in walnut kernels are the primary cause of bitterness and browning. Higher tannin content increases astringency, impacting the quality and stability of walnut protein. Therefore, removing the inner seed coat during walnut processing is essential. However, further processing of walnuts requires careful consideration of the removal of the thin outer skin. The walnut kernel's surface is uneven and wrinkled, and the seed coat sinks deeply into these wrinkles, making peeling difficult.

[0003] Currently, conventional methods for removing the inner husk of walnuts mainly include baking, alkali peeling, and boiling water peeling. Comprehensive analysis and comparison show that baking the walnut kernels enhances their flavor but has little effect on peeling. Boiling water peeling effectively removes the inner husk, but the high blanching temperature significantly impacts the protein quality of the kernels, hindering their comprehensive development and utilization. Furthermore, boiling the kernels with a mixture of a 0.3% dehulling agent and a 1% NaOH solution for 2 minutes yields only moderate peeling results. Furthermore, the unsaturated fatty acids in the kernels after alkali peeling are reduced, generating significant wastewater and increasing wastewater treatment costs.

[0004] Chinese patent publication number CN1023057 uses high-temperature, vigorous stirring with highly alkaline, corrosive steam and the powerful impact of high-pressure water to remove the walnut kernel's skin. However, the use of chemical reagents poses safety and environmental risks, and the high-temperature steam treatment destroys the walnut's original flavor and nutritional value.

[0005] China, with announcement number CN112075609, uses warm water soaking, high-pressure water jet washing, manual sorting, and tunnel oven baking to remove the walnut kernel skin, but the drying is not sufficient and the labor cost is too high.

[0006] In view of the problems existing in the current walnut kernel peeling process, such as poor peeling effect, great hidden dangers in the use of chemical reagents, poor drying effect, serious nutrient loss, and low production efficiency, it is urgent to develop a new walnut kernel peeling process to meet market demand. Summary of the Invention

[0007] The present invention aims to provide a method for efficiently removing the skin of walnut kernels using a combined ultrasonic and microwave treatment process. This method significantly improves the efficiency of walnut kernel removal, removes the walnut kernel skin, and preserves the kernel's color, nutritional value, and taste. This method shortens the process time and provides a new approach for efficient walnut kernel removal, thus possessing significant application value.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0009] A method for efficiently peeling walnut kernels by combined ultrasonic and microwave treatment, comprising the following steps:

[0010] (1) Walnut kernel pretreatment: Soak the unpeeled walnut kernels in warm water for a period of time;

[0011] (2) Ultrasonic treatment: Soak in warm water for a period of time and then perform ultrasonic treatment;

[0012] (3) High-pressure washing: The ultrasonically treated walnut kernels are placed in a stripping drum device and the walnut kernel skin is washed with high-pressure water generated by a high-pressure pump:

[0013] (4) Microwave baking: The walnut kernels washed with high-pressure water are filtered out in a conveying water tank, and finally the obtained walnut kernels are placed in a microwave oven for baking.

[0014] Furthermore, the walnut kernels are selected to be large, complete, plump, free of insects, mildew, and normal in taste, and their dry weight is weighed. The walnut kernels are selected and soaked in warm water at a temperature of 40-50° C. for 10-20 minutes.

[0015] Furthermore, the temperature of the ultrasonic wave and the warm water is adjusted to 40-50° C., and the walnut kernels are added to the warm water in a weight ratio of 1:3 for blanching, and the ultrasonic treatment time is 10-15 minutes.

[0016] Furthermore, the ultrasonic sound intensity is 0.2-10W / cm2.

[0017] Furthermore, after blanching with warm water, the warm water is poured out, and the walnut kernels are rinsed with high-pressure water for 10-20 minutes. The color of the peeled walnut kernels after rinsing with clean water is observed, and the taste and crispness of the peeled walnut kernels are sensory evaluated.

[0018] Furthermore, the peeled walnut kernels after being rinsed with water are placed in an oven at 60-80° C. and baked for 20-40 minutes until constant weight is achieved, and the weight is weighed to calculate the peeling rate.

[0019] Furthermore, the peeling rate calculation formula is:

[0020] Where A is the peeling rate, m is the weight of the peeled walnut kernel after blanching in warm water and drying; M is the weight of the intact unpeeled walnut kernel after drying.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention makes full use of the cavitation effect and mechanical effect of ultrasonic technology to quickly peel and remove the walnut skin. The uniform, efficient and environmentally friendly characteristics of microwave heating can quickly remove moisture from walnut kernels.

[0023] 2. The method of the present invention can achieve rapid walnut kernel stripping and quickly remove moisture from the processed walnut kernel. No chemical agents, high-temperature cooking and steam treatment are used, thus avoiding the problems of residual chemicals in the walnut kernel after chemical stripping and nutritional loss of the walnut kernel after high-temperature cooking and steam treatment. The method removes the bitter taste of the walnut kernel coat, retains the color and nutrition of the walnut kernel, and makes the walnut kernel more crispy. DETAILED DESCRIPTION

[0024] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below. This detailed description should not be considered a limitation of the present invention, but rather a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terms used herein are intended only to describe specific embodiments and are not intended to limit the present invention.

[0025] In addition, for numerical ranges in the present invention, it is understood that each intervening value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any stated value or stated range, and any other stated value or intervening value in the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention.

[0027] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0028] Example 1

[0029] A method for efficiently peeling walnut kernels by combined ultrasonic and microwave treatment, comprising the following steps:

[0030] (1) Walnut kernel pretreatment: Soak the unpeeled walnut kernels in warm water for a period of time;

[0031] (2) Ultrasonic treatment: Soak in warm water for a period of time and then perform ultrasonic treatment;

[0032] (3) High-pressure washing: The ultrasonically treated walnut kernels are placed in a stripping drum device and the walnut kernel skin is washed with high-pressure water generated by a high-pressure pump:

[0033] (4) Microwave baking: The walnut kernels washed with high-pressure water are filtered out in a conveying water tank, and finally the obtained walnut kernels are placed in a microwave oven for baking.

[0034] Furthermore, the walnut kernels were selected to be large, complete, plump, free of insects, mildew, and with a normal taste, and their dry weight was weighed. The kernels were selected and soaked in warm water at a temperature of 40° C. for 10 minutes.

[0035] Furthermore, the temperature of the ultrasonic wave and the warm water was adjusted to 40° C., and the walnut kernels were added to the warm water in a weight ratio of 1:3 for blanching, and the ultrasonic treatment time was 10 min.

[0036] Furthermore, the ultrasonic sound intensity is 0.2 W / cm2.

[0037] Furthermore, after blanching with warm water, the warm water is poured out, and the walnut kernels are rinsed with high-pressure water for 10-20 minutes. The color of the peeled walnut kernels after rinsing with clean water is observed, and the taste and crispness of the peeled walnut kernels are sensory evaluated.

[0038] Furthermore, the peeled walnut kernels after rinsing with water were placed in an oven at 60° C. and baked for 20 min until constant weight was obtained and weighed to calculate the peeling rate.

[0039] Example 2

[0040] A method for efficiently peeling walnut kernels by combined ultrasonic and microwave treatment, comprising the following steps:

[0041] (1) Walnut kernel pretreatment: Soak the unpeeled walnut kernels in warm water for a period of time;

[0042] (2) Ultrasonic treatment: Soak in warm water for a period of time and then perform ultrasonic treatment;

[0043] (3) High-pressure washing: The ultrasonically treated walnut kernels are placed in a stripping drum device and the walnut kernel skin is washed with high-pressure water generated by a high-pressure pump:

[0044] (4) Microwave baking: The walnut kernels washed with high-pressure water are filtered out in a conveying water tank, and finally the obtained walnut kernels are placed in a microwave oven for baking.

[0045] Walnut kernels were selected that were large, complete, plump, free of insects, mildew, and had a normal taste. Their dry weight was weighed and the kernels were soaked in warm water at 50°C for 20 minutes.

[0046] After the temperature of ultrasonic wave and warm water was adjusted to 50°C, walnut kernels were added for blanching in a weight ratio of walnut kernels to warm water of 1:3, and the ultrasonic treatment time was 15 min.

[0047] The ultrasonic sound intensity is 10W / cm2.

[0048] After blanching with warm water, pour out the warm water and rinse the walnut kernels with high-pressure water for 20 minutes. Observe the color of the peeled walnut kernels after rinsing with clean water, and sensory evaluate the taste and crispness of the peeled walnut kernels.

[0049] Furthermore, the peeled walnut kernels after rinsing with water were placed in an oven at 80° C. and baked for 40 min until constant weight was achieved. The weight was then weighed to calculate the peeling rate.

[0050] Example 3

[0051] A method for efficiently peeling walnut kernels by combined ultrasound-microwave treatment comprises the following steps:

[0052] (1) Pretreatment of walnut kernels: Soak the unpeeled walnut kernels in 50℃ warm water for 20 minutes. The soaking temperature and time are different for walnut kernels with different fullness and humidity. Walnut kernels with full grains and high humidity require higher soaking temperature and longer soaking time. Conversely, the soaking temperature can be lower and the soaking time can be shorter, such as 40℃ and 10 minutes.

[0053] (2) Ultrasonic treatment: After the temperature of ultrasonic waves and warm water is adjusted to 50℃, walnut kernels are put into the water in a weight ratio of 1:3 for blanching. The ultrasonic treatment time is 15 minutes and the ultrasonic sound intensity is 10W / cm2.

[0054] (3) High-pressure washing: After blanching with warm water, pour out the warm water and rinse the walnut kernels with high-pressure water for 20 minutes. Observe the color of the peeled walnut kernels after rinsing with clean water, and sensory evaluate the taste and crispness of the peeled walnut kernels.

[0055] (4) Microwave baking: The peeled walnut kernels after washing with clean water are placed in an oven at 80°C and baked for 40 minutes until constant weight is reached. The weight is then weighed and the peeling rate is calculated.

[0056] Example 3

[0057] A method for efficiently peeling walnut kernels by combined ultrasonic and microwave treatment, comprising the following steps:

[0058] (1) Walnut kernel pretreatment: Soak the unpeeled walnut kernels in warm water for a period of time;

[0059] (2) Ultrasonic treatment: Soak in warm water for a period of time and then perform ultrasonic treatment;

[0060] (3) High-pressure washing: The ultrasonically treated walnut kernels are placed in a stripping drum device and the walnut kernel skin is washed with high-pressure water generated by a high-pressure pump:

[0061] (4) Microwave baking: The walnut kernels washed with high-pressure water are filtered out in a conveying water tank, and finally the obtained walnut kernels are placed in a microwave oven for baking.

[0062] Furthermore, the walnut kernels were selected to be large, complete, plump, free of insects, mildew, and with a normal taste, and their dry weights were weighed. The kernels were then soaked in warm water at a temperature of 45° C. for 15 minutes.

[0063] Furthermore, the temperature of the ultrasonic wave and the warm water was adjusted to 45° C., and the walnut kernels were added for blanching in a weight ratio of walnut kernels to warm water of 1:3, and the ultrasonic treatment time was 13 min.

[0064] Furthermore, the ultrasonic sound intensity is 5W / cm2.

[0065] After blanching, the warm water was discarded and the walnut kernels were rinsed with high-pressure water for 15 minutes. The color of the peeled walnut kernels after rinsing with clean water was observed, and the flavor and crispness of the peeled walnut kernels were sensory evaluated. Furthermore, the peeled walnut kernels after rinsing with clean water were baked in an oven at 70°C for 30 minutes until constant weight was reached. The peeled walnut kernels were then weighed and the peeling rate was calculated.

[0066] In summary:

[0067] (1) Walnut kernel pretreatment: For walnut kernels with different fullness and humidity, the soaking temperature and time are different. Walnut kernels with full grains and high humidity require higher soaking temperature and longer soaking time. Conversely, the soaking temperature can be lower and the soaking time can be shorter.

[0068] (2) Ultrasonic treatment: The sound intensity and duration of ultrasonic treatment are also related to the fullness and humidity of the walnut kernel. The fuller the walnut kernel particles and the greater the humidity, the stronger the ultrasonic sound intensity and the longer the ultrasonic treatment time. Conversely, the ultrasonic sound intensity is weakened and the treatment time is shorter.

[0069] (3) High-pressure washing: The ultrasonically treated walnut kernels are placed in a peeling drum device and washed with high-pressure water generated by a high-pressure pump. The washing time and water pressure can be adjusted according to the ultrasonic peeling effect. If the walnut kernel skin has been mostly peeled off after ultrasonic treatment, the water pressure can be reduced and the washing time can be shortened.

[0070] (4) Microwave baking: After high-pressure washing, the walnut kernels are filtered for debris in a conveying water pool, and finally the obtained walnut kernels are placed in a microwave oven for baking. The baking time is also related to the fullness and humidity of the walnut kernels. The fuller the walnut kernels and the higher the humidity, the higher the drying temperature and the longer the drying time required.

[0071] In a specific implementation, the ultrasonic generating device can be placed on the ultrasonic horn on the upper part of the immersion tank, and multiple ultrasonic generating devices can be used and respectively set at different positions.

[0072] By adopting this process, walnut kernels can be quickly peeled with a peeling rate of more than 98%, and the moisture of the walnut kernels after peeling can be quickly removed without adding any chemical reagents or high-temperature steam treatment. The bitter taste of the walnut skin is removed, and the color and nutrition of the walnut kernel are retained, making the walnut kernel taste more crispy.

[0073] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and its clear concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for efficiently peeling walnut kernels by combined ultrasonic and microwave treatment, comprising the following steps: (1) Walnut kernel pretreatment: Soak the unpeeled walnut kernels in warm water for a period of time; (2) Ultrasonic treatment: Soak in warm water for a period of time and then perform ultrasonic treatment; (3) High-pressure washing: The ultrasonically treated walnut kernels are placed in a stripping drum device and the walnut kernel skin is washed with high-pressure water generated by a high-pressure pump: (4) Microwave baking: The walnut kernels washed with high-pressure water are filtered out in a conveying water tank, and finally the obtained walnut kernels are placed in a microwave oven for baking.

2. The method for efficiently peeling walnut kernels by combined ultrasonic and microwave treatment according to claim 1, characterized in that: Walnut kernels are selected to be large, complete, plump, free of insects, mildew, and with normal taste. Their dry weight is weighed and the kernels are soaked in warm water at a temperature of 40-50°C for 10-20 minutes.

3. The method for efficiently peeling walnut kernels by combined ultrasonic and microwave treatment according to claim 1, wherein the ultrasonic wave and warm water temperature are adjusted to 40-50°C, and the walnut kernels are placed in a weight ratio of 1:3 of walnut kernels to warm water for blanching, and the ultrasonic treatment time is 10-15 minutes.

4. The method for efficiently peeling walnut kernels by combined ultrasonic and microwave treatment according to claim 1 or 3, wherein the ultrasonic sound intensity is 0.2-10 W / cm2.

5. The method for efficiently peeling walnut kernels by ultrasonic and microwave combined treatment according to claim 1, wherein after blanching with warm water, the warm water is poured out, the walnut kernels are rinsed with high-pressure water for 10-20 minutes, and the color of the peeled walnut kernels after rinsing with clean water is observed.

6. The method for efficiently peeling walnut kernels by ultrasonic and microwave combined treatment according to claim 5, wherein the peeled walnut kernels after rinsing with clean water are placed in an oven at 60-80°C for 20-40 minutes, baked to a constant weight and weighed to calculate the peeling rate.

7. The method for efficiently peeling walnut kernels by ultrasonic and microwave combined treatment according to claim 6, wherein the peeling rate is calculated as follows: Where A is the peeling rate, m is the weight of the peeled walnut kernel after blanching in warm water and drying; M is the weight of the intact unpeeled walnut kernel after drying.

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