1, changes in respiratory intensity
Vacuum precooling can significantly reduce the respiratory intensity of Chinese cabbage, and slowly weaken during storage, which is beneficial to reduce the nutrient loss of Chinese cabbage and maintain its storage quality.
2, changes in moisture content
The water content of the sample before the pre-cooling treatment was 93.21%. After vacuum pre-cooling treatment, the water content was 92.95%, only 0.26%, and the appearance was still very fresh. However, with the extension of storage time, it will gradually sluggish, and the water content will also decrease. It has been observed that wilting occurs when the water content of the vegetable heart drops below 91%. Therefore, in the vacuum cooling of the vegetable heart, the pressure or temperature of the pre-cooling chamber and the pre-cooling time should be controlled to control the degree of dehydration. In addition, proper humidifying and humidifying of vegetables prior to pre-cooling can effectively avoid water loss after vegetables are pre-cooled. The pre-cooling process maintains the moisture content of the cabbage at more than 91% and keeps the appearance fresh.
3, changes in vitamin C content
The contents of vitamin C in the cabbage after vacuum precooling were stored in the cold storage at 8～10°C for 24h and 38h. Vacuum precooling has an effect on the vitamin C content in Chinese cabbage.
4, changes in quality
The principle of vacuum precooling determines that the quality of leaf vegetables after pre-cooling will be reduced, which is the deficiency of vacuum pre-cooling technology. Under normal circumstances, vacuum precooling of 1% water per evaporated vegetable mass can reduce the product temperature by approximately 6°C. In this experiment, the average mass loss rate of Chinese cabbage was only 2.3%, which is consistent with the result that the moisture content in the pre-cooling process only decreased by 0.26%. The reason for this is that the amount of processing is only about 1/4 of the rated capacity, the filling rate is small, the amount of water to be evaporated is less, the cooling rate is faster, so that the required pre-cooling time is shortened, and the shortening of the pre-cooling time leads to the cauliflower The cooling of leaves and stems was uneven, and the average final temperature of the leaves fell to 3.1°C, while the average final temperature of the stems only dropped to 10.4°C. The stems evaporate less water, resulting in less total mass loss.
5. Changes in appearance quality during storage
The appearance quality of Chinese cabbage will gradually deteriorate during its storage, mainly characterized by wilting, yellowing, softening and rotting. Compared with the samples stored in the same cold storage without vacuum pre-cooling, the appearance of the cauliflower after vacuum pre-cooling was slow during storage, and the control samples were yellowed after 68 hours of storage, and were pre-cooled by vacuum. After storage for 92 h, the cabbage was still green and the effective storage life could be extended by more than 2 days.
conclusion and discussion
1) Use VC-1000 vacuum precooler to conduct small batch (120kg/time) vacuum vacuum cooling test of the Chinese cabbage, the whole process takes about 15min, pre-cooling start 12min will make the temperature of vegetable leaves fall below 6°C. The evacuation phase, cooling phase, and recompression phase lasted 59%, 33%, and 8%, respectively, and efforts should be made to reduce the vacuum phase to increase productivity. It may be considered to open one more vacuum pump during the vacuum phase and close it after entering the cooling phase, or use a double pre-cooling chamber to alternate pre-cooling and a parallel vacuum pre-cooling device configured with multiple vacuum pumps.
2) The quality loss of Chinese cabbage was mainly occurred in the cooling stage. The quality loss rate in the cooling stage was positively correlated with the cooling time S and negatively correlated with the leaf temperature T. The linear regression equation obtained from the test data was: $W= 16.38 21.705S-7.7T.3) After precooling in vacuum, the respiration intensity of Chinese cabbage was significantly reduced, the appearance quality was slowed down, and the effective storage life was prolonged; the moisture content was slightly reduced but did not affect the shelf life; the content of vitamin C was slightly increased. Reduced, with an average mass loss rate of 2.3%.
The use of VC-1000 vacuum precooler to treat small batches of Chinese cabbage can shorten the cooling time, reduce the rate of mass loss, and significantly reduce the cooling rate between the leaves and the stem. It is difficult to achieve uniform cooling in a short precooling time.
Our Wind Power Lighting Pole, Solar Street Lights Pole are made from quality sheet through bending, forming, automatic welding and hot galvanization. We can reach one-run machining length of 14m and can bend sheet of thickness up to 45mm. We adopt advanced welding procedures, automatically weld main joints and reach rank-II welding quality.
We have supplied our Wind Power Lighting Pole,Solar Street Lights Pole to Australia, Columbia, England, Kuwait, Iraq, Philippines, Pakistan and etc.
Wind Power Pole, Solar Lighting Pole, Solar Street Lights Pole, Wind and Solar Lighting Poles
Jiangsu Xinjinlei Steel Industry Co., Ltd. , http://www.steel-pole.com