CN110403004B - Microwave-hot air drying method for chive leaves - Google Patents

Abstract

The invention provides a microwave-assisted hot air drying method for chive leaves, which comprises the following specific steps: raw material finishing, cleaning, cutting into sections, spin-drying, microwave predrying and hot air drying. The drying method effectively solves the problem of adverse effect of single hot air drying on the quality of the chive leaves, maintains the original color, fragrance, taste and shape of the chive leaves, effectively prevents a large amount of nutritional ingredients from being damaged, simultaneously improves the drying efficiency, is healthier and safer to eat, and has wide market prospect.

Description

Microwave-hot air drying method for chive leaves

Technical Field

The invention belongs to the technical field of agricultural product processing, and particularly relates to a microwave-hot air drying method for chive leaves.

Background

China is a large country for agricultural product production, and vegetables as a very important resource in agricultural products have a great proportion in the production of China. In daily circulation, vegetables are often sold in an untreated raw state, but they are easily spoiled due to their high water content and physiological changes after harvest. Therefore, in industrial production, the moisture content of the product is reduced by processing the product in a drying mode so as to prolong the shelf life, and the dried product is convenient to package and transport and is favorable for sale.

Chive, plant of Liliaceae, allium, bulb-shaped symbiosis, rectangular oval or egg-shaped cylinder. The leaves are hollow cylinders, tapering towards the top, dark green, and often slightly whitish. Contains various saccharides such as glucose, fructose, maltose, pectin, a small amount of starch and cellulose, and various functional active ingredients such as allicin, allicin and alliin, wherein the alliin content in fresh shallot leaves is about 85.89mg/g. Modern medicine shows that: alliin has various pharmacological effects of resisting tumor, synergistically lowering blood pressure, resisting bacteria and virus, eliminating free radicals, protecting liver, resisting diabetes and the like. Has great effect on the research and development of biomedicine and is called as one of the greatest magical discoveries in the natural food and medicine field in the 21 st century by the world medical community. Therefore, the onion eaten more often can clear heat, eliminate phlegm, resist bacteria and viruses, prevent cancers and the like.

Alliin has a wide range of biological activities: the bactericidal composition has a strong killing effect on common pathogenic bacteria such as staphylococcus aureus, tubercle bacillus, meningococcus and the like, and also has a remarkable curative effect on microbial infectious diseases such as fungal infection, protozoal disease and the like; in addition, the health-care tea also has good effects on reducing blood fat, improving human immunity, resisting aging, resisting and preventing cancers and the like. At present, alliin health-care products are mainly used for preventing myocardial infarction, cerebral infarction, reducing blood fat and the like abroad.

At present, the common drying technologies for drying the chives are hot air drying and vacuum freeze drying. For example, dai Fei, etc., published a study on influencing factors in the process of freezing and drying chives (Jiangxi agricultural science, 2008, 4 th), and compared experiments were carried out on different vacuum freeze-drying conditions of chives, so as to obtain the optimal process conditions for vacuum freeze-drying of chives. Zhang Zhijiang et al published a "research on vacuum freeze-drying process of shallots" (Chinese seasoning, 2007, 6 th year), and determined corresponding pretreatment process parameters and freeze-drying process parameters through the research on pretreatment, quick-freezing, freeze-drying dehydration and rehydration performance of shallots. These all provide a theoretical basis for the freeze-drying of chives. In the patent, liu Jishun reported a method for processing dehydrated chives in 2016 (application number: 201611165680.8), lijiang san Chuan industry group Limited reported a method for freezing chives in 2014 (application number: 201410352149.6), hubei New bridge Biotechnology Limited liability company reported a method for processing dehydrated chives in 2012 (application number: 201210493434.0), and so on. However, the two drying methods have certain defects, wherein the hot air drying has the defects of long drying time, low efficiency, poor product quality and the like; vacuum freeze-drying can retain the quality of the dried product to the maximum extent but has high energy consumption and expensive drying equipment.

At present, a synergistic drying method is a research hotspot of a drying technology, so in order to solve the problems, the invention adopts a microwave synergistic hot air drying method to dry the chive leaves, and aims to provide a processing method which can prolong the shelf life of the chives and can retain the nutritional ingredients in the chive leaves.

Disclosure of Invention

The invention aims to provide a synergistic drying method for drying the chive leaves, improve the drying efficiency of the chive leaves, obtain high-quality chive leaf dried products and provide theoretical basis and technical support for industrial production of chive leaf dehydration.

In order to achieve the aim, the invention provides a high-efficiency drying method for guaranteeing the quality of chive leaves by microwave and hot air, which comprises the steps of raw material finishing, cleaning, water refreshing, cutting, water throwing, microwave predrying and hot air drying; wherein the microwave power in the microwave drying is 2000W-3000W, and the scallion leaves are taken out and then are dried by hot air when the moisture content of the wet base of the scallion leaves is 50% -70%.

Preferably, the raw material arrangement is to select fresh chives, remove yellow leaves and rotten leaves, separate the leaves and petioles, and reserve the leaves for later use.

The microwave predrying is to place the water-spun chive leaves on a material belt of tunnel type microwave drying equipment for drying.

Preferably, the microwave pre-drying time is 10-20 min.

The hot air drying temperature of the chive leaves is 55-75 ℃, and the moisture content of the wet base is below 6% at the end of drying. Preferably, the moisture content of the wet base at the drying end is 5-6%, and the hot air drying time is 10-15min.

The cleaning is carried out by flowing clear water, and the refreshing degree is that the surface of the detergent does not have excessive moisture.

Preferably, the cutting is to cut the chive leaves into small sections with the length of 8 mm-10 mm.

The method for efficiently drying the chive leaves by microwave and hot air in a synergistic manner for quality guarantee comprises the following specific steps:

s1, raw material arrangement: selecting fresh chives to remove yellow leaves and rotten leaves, separating the leaves from leaf stalks, and keeping the leaves for later use;

s2, cleaning and refreshing: cleaning the chive leaves and putting the chive leaves on a clean filter screen for cooling;

s3, cutting into sections and throwing water: cutting the spare chive leaves in the step S2 into sections, and throwing water for later use;

s4, microwave predrying: uniformly placing the chive leaves cut for later use in the step S3 on a material belt of tunnel type microwave drying equipment for drying, taking out the chive leaves when the moisture content of the wet base of the chive leaves is reduced to 50% -70%, and stopping microwave drying; the microwave power in the microwave drying is 2000W-3000W;

s5, hot air drying: and (5) placing the chive leaves prepared in the step (S4) in a forced air drying oven for hot air drying, and taking out the chive leaves when the moisture content of the wet base of the chive leaves is below 6% to obtain the chive leaf dried product.

The invention is further illustrated by the following experiments:

1. aiming at the influence of microwave power on the drying rate of the chive leaves and the product quality: the microwave power was adjusted and the product quality was checked as per the method of example 1:

TABLE 1 influence of microwave power on the drying rate of chive leaves and product quality

As can be seen from table 1, the microwave power has a significant effect on the drying rate of the chive leaves, and as the microwave power increases, the drying rate of the chive leaves also gradually increases.

The degree of the original fresh state of the dry product after rehydration is an important index for measuring the quality of the dry product, namely the rehydration ratio. When the microwave power is 2000W and 3000W, the rehydration ratio of the chive leaves has no obvious difference, but both the rehydration ratios are obviously larger than the rehydration ratio of the chive leaves when the microwave power is 1000W, because the chive leaves shrink seriously due to long drying time when the microwave power is lower (1000W), and the rehydration ratio is reduced, thereby affecting the product quality. The microwave power had no significant effect on the Δ Ε value and the chlorophyll retention rate.

Alliin is an important active ingredient in the chives and is an important index for testing the quality of the dry chive leaves. As can be seen from Table 1, the alliin retention of the dried product of chive leaves at a microwave power of 3000W is significantly higher than the retention at powers of 1000W and 2000W.

Therefore, 2000W-3000W is preferably used as the microwave power in the chive leaf drying process

2. Aiming at the influence of the water content of the conversion point on the drying rate of the chive leaves and the product quality: according to the method of the embodiment 1, the water content of the conversion point is adjusted, and the product quality is detected:

TABLE 2 influence of moisture content at transition point on the drying rate of chive leaves and product quality

As can be seen from Table 2, the moisture content at the transition point has a significant effect on the drying rate of the chive leaves, and the microwave drying time is longer and the drying rate is higher when the moisture content at the transition point is low. And as for the rehydration ratio, the rehydration ratio of the chive leaves is the lowest when the water content at the conversion point is 40%, and the rehydration ratios of other conversion points have no obvious difference. The water content of the conversion point has no obvious influence on the chlorophyll retention rate of the chive leaves.

For alliin, the water content of the switching point is 40%, 50%, 60% and 70%, and the water content is significantly different from that of the switching point of 30%. When the water content of the transition point is 30%, the microwave drying time is longer, and the microwave drying temperature is higher than the hot air temperature, so that the alliin loss in the chive leaves is larger, and the retention rate is obviously reduced compared with the water content of other transition points. Therefore, the water content at the transition point is preferably 50% to 70%.

3. Influence of hot air temperature on the drying rate of the chive leaves and the product quality: the hot air temperature was adjusted and the product quality was checked as in example 1:

TABLE 3 influence of the temperature of the hot air on the drying rate of the chive leaves and the quality of the product

As can be seen from table 3, the temperature of the hot air has a significant effect on the drying rate of the chive leaves, which increases significantly with the increase in the temperature of the hot air. Although the temperature of the hot air has certain influence on the rehydration ratio of the dried chive leaf products, the difference is not obvious. The rehydration rate of the dried product of the chive leaves is higher when the hot air temperature is 55-75 ℃, the rehydration rate of the dried product of the chive leaves is lower when the hot air temperature is 85 ℃, probably because the drying temperature is too high when the hot air temperature is 85 ℃, the chive leaves are easy to be burnt when the drying temperature is too high, and the rehydration performance of the chive leaves is reduced. When the temperature of the hot air is 55-85 ℃, the chlorophyll retention rate of the chive leaves has no obvious difference, but the difference is obvious compared with that of the chive leaves at 45 ℃. Probably because the drying rate of the chive leaves is lower when the temperature of the hot air is 45 ℃, the time required by drying is longer, and the chlorophyll loss in the drying process is obvious. The temperature of the hot air has obvious influence on the retention rate of alliin in the scallion leaves, and the retention rate is obviously reduced along with the increase of the temperature. Mainly because alliin is relatively sensitive to heat, its retention rate decreases when the temperature of hot air increases. Therefore, the hot air temperature is preferably 55 to 75 ℃.

The invention has the advantages that:

1. the invention provides a method for drying and dehydrating chive leaves, aiming at the performance of chives, the invention adopts microwave and hot air to dry the chive leaves to prepare a chive leaf dried product, thereby effectively maintaining the original color, fragrance, taste and shape of the chive leaves and avoiding the great damage of nutrient components;

2. the invention is a cooperative drying technology, overcomes the defect of damaging the product quality in the traditional hot air drying technology, and simultaneously improves the drying efficiency. Compared with vacuum freeze drying, the energy consumption is low, and because the price of drying equipment is relatively low, the drying technology is convenient to popularize, and theoretical basis and technical support can be provided for enterprise production;

3. the dry product of the chive leaves overcomes the defect of slightly scorched flavor caused by hot air drying, has slightly lighter flavor compared with fresh chives, and basically keeps the original flavor of the chives;

4. the dried product of the chive leaves prepared by the invention has good rehydration performance, stable shape, convenient eating and prolonged shelf life.

Detailed Description

The invention is further illustrated by the following specific examples:

example 1: microwave-assisted hot air drying method for chive leaves

(1) Finishing raw material

Taking fresh chives purchased from the market, removing yellow leaves and rotten leaves of the chives, separating the leaves from leaf stalks, and keeping the leaves for later use.

(2) Cleaning and refreshing water

And (3) cleaning the treated chive leaves with flowing clear water, and placing the cleaned leaves on a filter screen for refreshing until no excess water is left on the surfaces of the leaves.

(3) Cutting and throwing water

And (4) cutting the scallion leaves after being watered, wherein the length of the scallion leaves is 8-10 mm, and throwing water for later use.

(4) Microwave predrying

Uniformly spreading 150g of the cut chive leaves on a material conveying belt of tunnel type microwave drying equipment, setting the microwave power to be 3000W, stopping drying until the moisture content of the wet base of the chive leaves is 50%, taking out the chive leaves, and pre-drying for 10min by microwave.

(5) Drying with hot air

And (5) placing the chive leaves prepared in the step (4) into a forced air drying oven for hot air drying, wherein the hot air temperature is 75 ℃, and when the moisture content of the wet base is 6%, stopping drying to obtain a chive leaf dried product, wherein the hot air drying time is 14min.

The dried product of chive leaves prepared in this example had a drying rate of 37.62 g/g.min, a rehydration ratio of 4.44, a chlorophyll retention of 79.37%, an alliin retention of 76.88%, and a color difference Δ E value of 6.90. Compared with hot air drying, the drying rate of the chive leaves subjected to microwave synergistic hot air drying in the embodiment is improved by 16.72%, the chlorophyll retention rate is improved by 28.78%, and the alliin retention rate is improved by 34.26%.

Example 2: microwave-assisted hot air drying method for chive leaves

(1) Finishing raw material

Taking fresh chives purchased from the market, removing yellow leaves of the chives, separating leaves from leaf stalks, and keeping the leaves for later use.

(2) Cleaning and refreshing water

And (3) cleaning the treated chive leaves with flowing clear water, and placing the cleaned chive leaves on a filter screen for cooling until no excess water is on the surfaces of the chive leaves.

(3) Cutting and throwing water

And (4) cutting the scallion leaves after being watered, wherein the length of the scallion leaves is 8-10 mm, and throwing water for later use.

(4) Microwave predrying

Taking 150g of the cut chive leaves, uniformly paving the cut chive leaves on a material conveying belt of tunnel type microwave drying equipment, setting the microwave power to be 2000W, stopping drying when the moisture content of the wet base of the chive leaves is 50%, taking out the chive leaves, and pre-drying for 16min.

(5) Drying with hot air

And (5) placing the chive leaves prepared in the step (4) into a forced air drying oven for hot air drying, wherein the hot air temperature is 75 ℃, and when the moisture content of the wet base is 5%, stopping drying to obtain a chive leaf dried product, wherein the hot air drying time is 14min.

The dried product of chive leaves obtained in this example had a drying rate of 34.43 g/g.min, a rehydration ratio of 3.89, a chlorophyll retention of 77.97%, an alliin retention of 63.14%, and a color difference Δ E of 5.93. Compared with hot air drying, the drying rate of the chive leaves subjected to microwave synergistic hot air drying in the embodiment is improved by 6.83%, the chlorophyll retention rate is improved by 26.51%, and the alliin retention rate is improved by 10.27%.

Comparative example 1 chive leaf microwave drying method used alone

(1) Finishing raw material

Taking fresh shallot, removing yellow leaf, separating leaf and petiole, and keeping leaf for use.

(2) Cleaning and refreshing water

And (3) cleaning the treated chive leaves with flowing clear water, and placing the cleaned chive leaves on a filter screen for cooling until no excess water is on the surfaces of the chive leaves.

(3) Cutting and throwing water

And (4) cutting the scallion leaves after being watered, wherein the length of the scallion leaves is 8-10 mm, and throwing water for later use.

(4) Microwave drying

Uniformly spreading 150g of the cut chive leaves on a material conveying belt of tunnel type microwave drying equipment, setting the microwave power to be 2000W, stopping drying until the moisture content of the wet base of the chive leaves is 6%, and taking out the chive leaves, wherein the drying time is 36min.

The drying rate of the chive leaves obtained under the microwave drying condition is 26.78 g/g.min, the rehydration ratio is 3.22, the retention rate of chlorophyll is 69.59%, the retention rate of alliin is 71.41%, and the color difference delta E value is 5.37. Compared with the shallot leaves dried by microwave and hot air, the drying speed of the shallot leaves is obviously improved, and the rehydration ratio, the chlorophyll retention rate and the color difference delta E value are also improved.

Comparative example 2 method for drying chive leaves with hot air alone

(1) Finishing raw material

Taking fresh chives purchased from the market, removing yellow leaves of the chives, separating leaves from leaf stalks, and keeping the leaves for later use.

(2) Cleaning and refreshing water

And (3) cleaning the treated chive leaves with flowing clear water, and placing the cleaned leaves on a filter screen for refreshing until no excess water is left on the surfaces of the leaves.

(3) Cutting and throwing water

And (3) cutting the water-cooled chive leaves into sections with the length of 8-10 mm, and throwing water for later use.

(4) Drying with hot air

And (3) placing the chive leaves in a forced air drying oven for hot air drying, wherein the hot air temperature is 75 ℃, and stopping drying when the moisture content of the wet base is below 6%, so as to obtain the chive leaf dried product, wherein the drying time is 40min.

The drying rate of the chive leaves obtained by drying at the hot air temperature of 75 ℃ is 32.23 g/g.min, the rehydration ratio is 4.39, the retention rate of chlorophyll is 61.63%, the retention rate of alliin is 57.26%, and the color difference delta E value is 4.16. And the chlorophyll retention rate and the alliin retention rate of the chive leaves obtained by microwave and hot air drying are obviously improved.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be able to cover the technical solutions and the inventive concepts of the present invention within the technical scope of the present invention.

Claims (7)

1. A microwave-assisted hot air drying method for chive leaves is characterized by comprising the steps of raw material finishing, cleaning, water refreshing, cutting, water throwing, microwave predrying and hot air drying; wherein the microwave power in the microwave drying is 2000W to 3000W, and the green onion is taken out and then dried by hot air when the moisture content of the green base of the green onion is 50 to 70 percent; the microwave pre-drying time is 10-20 min; the hot air drying temperature of the chive blades is 55-75 ℃, and the hot air drying time is 10-15 min; the microwave predrying is to place the water-spun chive leaves on a material belt of tunnel type microwave drying equipment for drying.

2. The microwave-assisted hot air drying method for the chive leaves as claimed in claim 1, wherein the raw material preparation comprises selecting fresh chives, removing yellow leaves and rotten leaves, separating the leaves from the petioles, and keeping the leaves for later use.

3. The microwave-assisted hot air drying method for the chive leaves according to claim 1, wherein the moisture content of the wet base of the chive leaves at the hot air drying end point is below 6%.

4. The microwave-assisted hot air drying method for the chive leaves according to claim 1, wherein the moisture content of a wet base at the end of drying is 5% -6%.

5. The method for drying chive blades by microwave-assisted hot air according to claim 1, wherein the cleaning is carried out by flowing clear water, and the degree of refreshing water is that the surface of the chive blades is free from excessive moisture.

6. The microwave-assisted hot air drying method for the onion leaves as claimed in claim 1, wherein the cutting is to cut the onion leaves into small sections with the length of 8mm to 10 mm.

7. The microwave-assisted hot air drying method for the chive blades as claimed in claim 1, which is characterized by comprising the following specific steps of:

s1, raw material arrangement: selecting fresh chives to remove yellow leaves and rotten leaves, separating the leaves from leaf stalks, and keeping the leaves for later use;

s2, cleaning and refreshing: cleaning the chive leaves and putting the chive leaves on a clean filter screen for cooling;

s3, cutting into sections and throwing water: cutting the spare chive leaves in the step S2 into sections, and throwing water for later use;

s4, microwave predrying: uniformly placing the chive leaves cut for later use in the step S3 on a material belt of tunnel type microwave drying equipment for drying, taking out the chive leaves when the moisture content of the wet base of the chive leaves is reduced to 50-70%, and stopping microwave drying; in the microwave drying, the microwave power is 2000W to 3000W;

s5, hot air drying: and (5) placing the chive leaves prepared in the step (S4) in a forced air drying oven for hot air drying, and taking out the chive leaves when the moisture content of the wet base of the chive leaves is below 6% to obtain the chive leaf dried product.