Long kidney bean is a vegetable variety that combines nutrition, deliciousness and health care. It contains a large number of high-quality protein, dietary fiber, carbohydrates and multivitamins and trace elements that are easily absorbed by the body. Chinese medicine believes that cowpea is sweet and has the effect of strengthening the spleen and tonifying the kidney. Regular eating kidney beans can help digestion and improve the body's immunity. Phospholipids in cowpea have the effect of promoting insulin secretion and participating in glucose metabolism, and are ideal food for diabetics. The fresh pods of cowpea are tender, crisp, and fragrant. They can be fried and can be mixed with cold; the dried long bean can be made into a vegetarian dish that is refreshing and refreshing. To this end, cowpeas, whether they are fresh pods or dried products, are well received by consumers.

1. Market potential of long kidney beans

Long kidney beans can be grown in the south of China for two seasons. The first season of open field cultivation is from March to July, when the climate is mild, the most suitable for the growth and development of long kidney beans, the least application, the highest yield and the best quality. However, at this time, the area south of the Yangtze River is in a rainy season, and a large number of fresh pea pods are on the market. As fresh food, it is difficult to be fully digested by the market and cannot be dried. Therefore, for a long time, the early season of the first season of long bean production was higher, the medium-term price was flat, and the late price was extremely low. Most of the long bean produced in the second season is used for drying. In the past, the economic income of growing long kidney beans was not high, and it did not exert its economic potential well. Through investigation and analysis, we carried out research and development of key technologies for dehydrated long kidney beans, and produced high-quality artificial dehydrated cowpea products, which greatly improved the grade of the products, so that the long kidney beans had a good price during the whole picking period. Farmers increase production and income. Breakthroughs in key technologies have spurred the enthusiasm of farmers for planting. At present, long kidney beans have become the main cultivated economic crops in the Bihu Basin, forming a stable situation in which fresh and dry complement each other and production and sales are booming. Lishui City, Zhejiang Province has also become the country's largest production base for dehydrated long kidney beans, with an annual economic income of more than 100 million yuan.

2. Dehydrated long kidney bean processing technology

According to the production process and product characteristics, dehydrated long kidney beans can be divided into hot air dehydration products and vacuum freeze-dried products. Due to the huge investment in vacuum freeze-drying equipment and high drying cost, there are not many applications in production. Domestic dehydrated cowpeas are mainly hot air dehydrated products. The process of dehydration processing of long kidney bean is: raw material recovery → pretreatment (exclusion, cleaning, head removal, cutting, etc.) → blanching → cooling → dehydration → homogenization → secondary dehydration → post-treatment (sorting, packaging , storage, etc.). The blanching and dewatering process is the key to the entire process.

3. Operating points

The fresh pods of long kidney beans planted in the first season of mid-June are used as raw materials, and immediately after the mining, boiled and boiled. When blanching, add 25kg of tap water in the pot. After the water is boiled, put 10kg of cowpea each time, so that the water in the pot is submerged in the cowpea. When blanching, it should be turned upside down to make the maturity consistent. The blanching time is preferably after the water temperature of the cowpea is raised to 100 ° C and then kept for 3 minutes. After the greening, the cowpeas should be evenly spread on the baking grid, try not to overlap, and then put on the drying room and bake. When the moisture of cowpea is reduced to about 30%, it should be observed and turned frequently to avoid baking; when the moisture of cowpea is reduced to 6%, it is taken out of the drying room and placed in a closed plastic film bag to be wet and soft. After softening, a sample of 0.5 kg was randomly sampled, and each treatment was numbered, and then the panel was evaluated by the judges.

Rehydration test: Weigh a certain amount of dehydrated long kidney beans and soak them in clear water. The water temperature is 17 ° C, and the ratio of material to water is 1:30. Then, the weighing quality was taken every 30 minutes, and 80% of the dehydrated cowpea was immersed as the rehydration time. The ratio of the mass and the quality of the raw material after rehydration for 3 hours was the rehydration rate.

4. Long cowpea dehydration test

Each batch was tested with 200 kg of long kidney beans and divided equally into 5 parts, ie 40 kg per parallel test. The dehydration treatment is designed as: dehydration time 1h, 2h, 3h, 3.5h, 4h, 5h, 7h. The dehydration rates of long kidney beans with different dehydration time are shown in Table 1. The effect of dehydration time on the quality of long bean products is shown in Table 2.

5. Results and analysis

It can be seen from Table 2 that as the dehydration time is prolonged, the color of the product gradually darkens from the emerald green to the yellowish brown color, which may be caused by the excessive dehydration time, the high humidity in the drying room, and the decrease of chlorophyll oxidation, resulting in yellow leaf The increase is related. The effect of dehydration time on product rehydration rate and rehydration time may be related to the movement of water from the inside to the surface during dehydration, the degree of damage to the cells by temperature and the degree of keratinization of the cowpea surface after dehydration. The dried products of dehydration treatment for 1h, 2h and 3h have the best taste, brittle and sweet taste; when treated for more than 3.5h, the taste is not good, the taste is tough and has astringency.

For large and medium-sized enterprises with excellent mechanical equipment, dewatering process can be used for 1h or 2h treatment, which can produce high-quality dehydrated products. For small-scale production enterprises, it is better to use dehydration treatment for 3h. This process is suitable for small dehydration. equipment. In order to produce high-quality dehydrated cowpea products, it is necessary to master the blanching operation, and the dehydration treatment should be dried out within 3 hours. Otherwise, the product quality will gradually decrease with the prolonged dehydration time, especially the dehydration time cannot be extended to more than 5h.

This experiment only studies the dehydration time, which is the key factor affecting the quality of dehydrated cowpea. Further trials are needed for the time of blanching. For the production of high-quality convenient dehydrated cowpea products, it is best to combine cooking techniques, adding seasonings or nutrients before blanching or blanching into the drying room to produce high-quality, long-flavored bean products with special flavors. Enrich the market.

Table 1 % dehydration rate of long kidney beans with different dehydration time

Dehydration time / h sample 1 sample 2 sample 3 sample 4 sample 5 average

1 9.875 9.925 10.075 9.900 10.050 9.965

2 9.900 9.975 9.775 ― 10.050 9.925

3 9.925 10.025 10.025 9.725 9.875 9.915

3.5 9.800 10.250 9.800 9.875 9.925 9.930

4 10.025 9.875 10.050 9.875 9.875 9.940

5 9.775 10.075 9.800 10.075 9.975 9.940

7 10.025 10.050 9.925 9.250 ― 9.813

Table 2 Effect of different dehydration time on the quality of long bean products

Dehydration time / h color yield /% rehydration rate / double rehydration time / min taste

1 Fresh green 9.965 5.76 50 Crisp, sweet taste

2 emerald 9.925 5.77 55 crisp, sweet taste

3 Fresh Green 9.915 5.75 60 Crisp, sweet taste

3.5 Dark Green 9.930 5.69 70 Crisp, tasteless

4 Dark Green 9.940 5.65 78 Crisp, tasteless

5 yellow brown green 9.940 5.53 95 tough, slightly astringent

7 yellow brown 9.813 4.98 110 tough, astringent taste