Fresh-keeping and Storage Technology of Bamboo shoot

Bamboo shoots are the buds of bamboo, also known as shoots. Bamboo is a perennial evergreen herb, the edible part is primary, tender fat, short and strong buds or whips. Bamboo is native to China with many types, strong adaptability and wide distribution. There are 30 genera and 550 species in the world, which are abundant in tropical, subtropical and temperate regions. China is one of the most bamboo-producing countries in the world, with 22 genera and more than 200 species, distributed all over the country, with the most in the Pearl River Basin and the Yangtze River Basin. There are only a few dwarf bamboos growing in the north of Qinling Mountains. The growth habits of bamboo shoots the underground stems of scattered bamboo species such as Phyllostachys pubescens and Zaozhu are deeply embedded in the soil, and the bamboo whips and shoot buds are protected by the soil layer, so they are not easy to suffer frost damage in winter, and the shooting period is mainly in spring. The underground stems of tufted bamboo species such as Phyllostachys pubescens and green bamboos are shallow in the soil, and the shoot buds are often exposed to the soil, which are easy to be damaged by freezing in winter, and the shooting period is mainly in summer and autumn. Bamboo is native to the tropics and subtropics. It likes temperature and is afraid of cold. It is mainly distributed in the area of annual rainfall 1000~2000mm. The optimum temperature for the growth of Phyllostachys pubescens is 16-17 ℃ per year, less than 30 ℃ in summer and 4 ℃ in winter. Dendrocalamus latiflorus and Phyllostachys pubescens require an average annual temperature of 18-20 ℃, and the average temperature in January is above 10 ℃. Therefore, bamboo forests are luxuriant in southern China, while bamboo forests are rare in the north of Qinling-Huaihe River. Bamboo needs a soil with deep soil layer, loose, fertile, moist, drained and well ventilated soil, and the soil pH value is 4. 5%. 5-7 is appropriate.

Bamboo shoots are delicious, often eaten as vegetables, but also have a certain medicinal value. Bamboo shoots taste sweet, slightly cold, non-toxic, and have the effects of relieving thirst, diuresis, clearing lungs, resolving phlegm and so on. The cellulose contained in bamboo shoots can promote intestinal wall peristalsis, enhance digestive gland secretion, facilitate digestion and excretion, reduce the stagnation of harmful substances in the intestinal tract, and play a role in the prevention and treatment of intestinal cancer. Therefore, bamboo shoots have become a favorite traditional food in people's daily life because of their rich nutrition.

Lignification is easy to occur in bamboo shoots at room temperature, which greatly affects the nutrition and quality of bamboo shoots. Bamboo shoots were stored at room temperature for 24 hours, that is, 60% of the bamboo shoots were lignified, and almost lost their edible value after 48 hours. As bamboo shoots are mostly produced in mountainous areas or hills with inconvenient transportation, it often takes a period of time from picking to selling areas, which aggravates the Lignification of green bamboo shoots. The annual output of bamboo shoots in China is 2.1 million tons, ranking first in the world, and the output is on the rise. It is predicted that the output of bamboo shoots in China will reach 3-3.2 million tons in 2010. Therefore, it is of great significance to study how to keep green bamboo shoots fresh. The commonly used fresh-keeping technologies in China are:

(1) coating treatment. After removing the shell, bottom and root of bamboo shoots, a film was coated on the surface of bamboo shoots to slow down the respiratory intensity of bamboo shoots and slow down the loss of nutrients in the body. The main coating films are chitosan film and konjac glucomannan film. The general process of coating film is as follows:

Bamboo shoots → cleaning → removing roots and bottom bamboo shell → color protection (8 minutes) → green → coating → drying → plastic packaging → weighing → storage.

When coating, the chitosan film is about 1.5%, and the konjac glucomannan film is about 0.2%. The specific concentration should be based on the composition of the coating solution and the coating process.

In the above film treatment, the anti-green process is involved, and its main purpose may be to passivate the enzymes at the bottom of bamboo shoots and kill microorganisms. In general, the higher the temperature and the longer the time is, the more thoroughly the enzyme is inactivated and the microorganism is inhibited. However, after the enzyme was killed by high temperature for a long time, some bamboo shoots were steamed and softened during storage, which caused the loss of bamboo shoot juice and shortened the storage time of bamboo shoots. Therefore, the temperature and time of killing green will vary with different varieties of bamboo shoots. According to the report, the temperature adopted when killing the green is about 60 ℃ and the time is 30-60 seconds.

(2) fresh-keeping with chemical reagents. There are mainly two kinds of chemical reagents for preservation: ⑴ is added with chemical reagents that can release sulfur dioxide and carbon dioxide. The released carbon dioxide increases the concentration of carbon dioxide in the packaging system, thus inhibiting the respiratory intensity of bamboo shoots. Sulfur dioxide is used to inhibit microorganisms and enzymes, so as to achieve the purpose of fresh-keeping. The commonly used sulfur reagents are sodium sulfite, sodium pyrosulfite, sodium bisulfite and so on. ⑵ preservative. Mainly using sodium benzoate, potassium sorbate, sodium chloride and so on, such as Xuping in Simao area of Yunnan Province, using sodium benzoate and sodium pyrosulfite as chemical additives to keep bamboo shoots fresh, and achieved success (national patent 90109091). However, due to the increasing demand for food, the use of preservatives has been controlled to a certain extent. Therefore, when using preservatives, we must pay attention to the scope of use of different preservatives and their maximum use.

(3) low temperature cold storage. The treated bamboo shoots are placed in a breathable plastic basket and placed in a cold storage. the temperature is generally controlled at 3-6 ℃ and the humidity is 85-95%. Proper cooling can effectively reduce the respiratory intensity of bamboo shoots, delay the emergence of respiratory peak, and greatly delay the decomposition of protein, fat, starch and other substances in bamboo shoots.

(4) Film packaging. The bamboo shoots are packed in plastic bags and then sealed and preserved. Vacuum sealed packaging is also used. The commonly used plastic bags are mainly PE bags. However, this treatment can easily lead to anaerobic respiration of bamboo shoots, thus deteriorating the quality of bamboo shoots. Therefore, this method is often combined with other methods, such as low temperature storage, solid buffer releasing agent which can release sulfur dioxide and carbon dioxide, activated carbon and so on.

Storage of bamboo shoots:

Optimum storage temperature: 0 ℃

Relative humidity: above 95%RH

The tenderness of bamboo shoot tissue is an important factor to determine its commodity value. When the plant was just cut off, the metabolic rate of tissue was very high, and the formation of fiber was very rapid. Therefore, rapid precooling to reduce the product temperature after harvest is an important key to maintain the good quality of bamboo shoots. Use water cooling to reduce the temperature of bamboo shoots, preferably below 5 ℃. The storage and transportation within a day must be reduced to at least 15 ℃, and the fiber formation can be obviously delayed. If you want to prolong the storage period after storage and transportation, it is best to store it below 5 ℃, close to 0 ℃, and keep the relative humidity of the environment at 95-100%RH. After the bamboo shoots are harvested, if the storage and transportation temperature is high, do not be stuffed in a plastic bag, otherwise it will produce a peculiar smell due to anaerobic breathing and reduce the quality.

Storage temperature (℃) 051015 room temperature (25 ℃)

Storage period (days) within 20-3014-20311 days