The influence of different pre cooling packaging o

2022-10-13
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Effects of different precooling and packaging on the fresh-keeping effect of exported cabbage (I)

Abstract: Beijing's exported cabbage accounts for a large proportion of exported vegetables, with a cultivated area of about 700hm^2, accounting for 10% of exported vegetables. The annual export volume is about 10000 tons, which has made a great contribution to Beijing's agricultural production structure adjustment, farmers' income increase and export foreign exchange earning. But at present, there are three major problems in the export of cabbage. First, the loss is large. It may be caused by untimely pre cooling, nonstandard technology, inappropriate packaging materials and methods, inadequate storage and transportation technology, etc. Second, the exit radius is small

key words: pre cooled packaged export cabbage storage

Beijing's export cabbage accounts for a large proportion of export vegetables. Its cultivated land area is about 700 HM, accounting for 10% of export vegetables. The annual export volume is about 10000 tons, which has made a great contribution to Beijing's agricultural production structure adjustment, farmers' income increase and export foreign exchange earning. But at present, there are three major problems in the export of cabbage. First, the loss is large. It may be caused by untimely pre cooling, nonstandard technology, inappropriate packaging materials and methods, inadequate storage and transportation technology, etc. Second, the exit radius is small. At present, the storage and transportation period of exported cabbage is about 10 days, so the export radius is small, and about 85% of them are exported to Hong Kong and Macao. Third, the market competitiveness is weak. Due to the unstable quality of exported cabbage, the price in Hong Kong market is often 20% - 30% lower than that in Shaoguan, Guangdong Province. It is difficult to enter Singapore, where the vegetable market management is relatively standardized. Therefore, we should select the best pre cooling method and packaging method suitable for the export of Chinese cabbage through comparative tests, so as to gradually solve the problems in the export of Chinese cabbage

I. Cai AoHong expressed his gratitude for the trust and support given by the client. Materials and methods

1. Test material

test variety (quality is not very good): 49 cabbage

the climate before the test was Sui condition. It was sunny three days before the harvest of cabbage. The highest temperature during the day was 29 ℃, and the lowest temperature at night was 18 ℃

harvesting time: the cabbage will be harvested after 8:00 a.m. (after the dew is dry). Harvest standard: the standard harvest time is when the flowering bolt of cabbage grows to the end of the leaf, and individual flowers will open but not open, which is commonly known as "Qikou flower". Generally, harvesting is carried out according to the standards of the export place, which is mainly divided into four specifications, namely, large strip, medium strip, small strip and flower turning. For example, the cabbage exported to Hong Kong requires flower turning, with a length of 8 ~ 9 cm, a stem diameter of 0.6 ~ 0.8 cm, and the flower buds are neat and large enough. The flowers are turned in a timely direction. There is no plastic material. At present, it is in a relatively low state, with large leaves, no scattered yellow flowers, no insects, no yellow leaves and no red heads

2. test method

test location: Jianhua industrial vegetable export base in Tongzhou District. The test time was from September 9 to October 12, 2004

experimental design 1: the effect of different pre cooling methods on the storage effect of cabbage

precooling methods: natural precooling in cold storage, differential pressure precooling in cold storage and vacuum precooling. Objective: to select a suitable precooling method for export cabbage. After harvesting, cabbage in foam granulator is precooled in three different ways at the same time. Natural precooling and differential pressure precooling in the cold storage use large plastic baskets, which are packaged and stored after precooling. Vacuum precooling is carried out after packing and before sealing. After precooling, ice is quickly added in the cold storage for sealing. Each precooling method treats 5 boxes, of which 3 boxes are 3 repetitions, and the other 2 boxes are used for observation. Different pre cooling methods adopt unified packaging method (foam box + wet sponge + ice bottle). The temperature and quality of vegetables were measured before and after precooling. After precooling, it shall be stored in the same cold storage (1-2 ℃) and placed randomly during stacking

experimental design 2: effect of different packaging methods on the storage effect of cabbage

packaging method: a-foam box (47 cm × 37 cm x 17 cm), b-foam box with ice, c-foam box with paper, d-carton with 0.o1 ~ 0.03 mm thick plastic. Objective: to select the suitable packaging method for export cabbage

cabbage is packaged after natural precooling in the cold storage commonly used by enterprises. Each kind of packaging is 3 boxes, which are placed randomly when stacking. As 3 repetitions, they are stored in the same cold storage (1 2 ℃, air relative humidity 90% - 95%)

3. investigation and analysis methods

after storage for 7 days, observe once every 3 days, including weight (water loss), appearance (decay, yellowing, browning, etc.). In order to reduce the influence of the investigation on the storage effect, the observation box of each treatment is investigated first each time. The treatment box is opened for observation only when the observation box begins to yellowing and rot. 20 plants are observed in each box, and the variance analysis is carried out on the investigated data

determination standard of leaf yellowing index: the area of level 1 is less than 1%, the area of level 2 is 1% - 2%, the area of level 3-yellow leaf is 2% - 5%, and the area of level 4-yellow leaf is more than 5%. The determination standard of stem knife edge decay index (here, the so-called decay refers to the depression caused by water loss in the center of the knife edge, the color is slightly darker, and there is serious slight decay): the area of level 1 is less than 5%, the area of level 2-5% - 10%, the area of level 3-10% - 15%, and the area of level 4-15%

II. Results and analysis

1. Precooling of cabbage with different precooling methods

Table 1 shows that there is no significant difference in water loss of cabbage under three different precooling methods. The natural precooling time of cold storage is the longest, and the water loss is at least 1.8%; The differential pressure precooling time is short, which is 2.5 h, and the water loss is 0.5% higher than that of the natural precooling of the cold storage; The vacuum precooling time is the shortest, 28 min, and the water loss is the same as the differential pressure precooling of the cold storage

2. Influence of different precooling methods on the storage effect of Chinese cabbage

in the test, the first yellowing phenomenon occurred in the natural precooling treatment of Chinese cabbage. When it was stored for 23 days, the naked eye could see that the leaves had yellowing and knife edge rot, the differential pressure precooling appeared yellowing at 27 days, and the vacuum precooling appeared yellowing at 32 days. See Table 2 for the specific observation results

it can be seen from table 2 that there is little mass loss during the whole storage period, such as chemical vapor deposition using methane gas or another carbon source

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