Pre cooling I, an important part of the hottest pr

Pre cooling is an important link in Fresh-keeping Technology (I)

preface

China is a large country producing fruits and vegetables. In 2000, the output of fruits reached 62 million tons, accounting for 14% of the world's output of fruits, and the per capita output of fruits was nearly 50 kg. In 2001, China's vegetable planting area reached 13 million Hm2, and the output reached 440 million tons, accounting for 66% of the world's total output. The annual per capita share of vegetables was 338 kg, three times that of the world's per capita of 102 kg. However, in terms of fruit and vegetable preservation technology and means, China is still at a low level, which also makes the fruit and vegetable market one of the most impacted markets after China's entry into WTO

in the United States, 30% of the total agricultural investment is used for pre harvest and 70% for post harvest. Compared with the natural output value at harvest, the output value after delivery is 3.7:1 in the United States, 2.2:1 in Japan, and only 0.38:1 in China. At present, although most farmers and operators in China have improved their awareness of preservation and storage, most people still only pay attention to pre harvest planting and pest control, do not pay attention to post harvest treatment and storage, and only pursue yield in terms of input, but do not pay much attention to quality. Therefore, every year, the loss rate of fruit and vegetable storage accuracy: ± 0.5% in storage and preservation reaches 25%-30%, about 75billion yuan. This is also the main reason for the increase in output of fruits and vegetables, unsalable market, falling prices and declining agricultural benefits. The serious losses caused by the harvest of fruits and vegetables make producers and operators have to bear huge economic risks. Therefore, the development of fresh-keeping technology and equipment suitable for China's national conditions is an important means to reduce business risks and improve economic benefits. It is a very important event related to people's livelihood. The Ministry of Agriculture plans that by 2010, the postpartum treatment rate of agricultural products in China will reach 45% - 55% of the production time. If the consumption of fruits and vegetables in China is reduced by 3%-5%, the consumption of fruits and vegetables can be reduced by more than 2 million tons and more than 10 million tons each year. When the storage and preservation amount accounts for 15% - 20% of the total output, the output value of fruits and vegetables in China will increase by billion yuan. Therefore, the fruit and vegetable preservation industry will become one of the most potential industries in the development of modern agriculture

fruit calculation shows that the physiological changes of non-zero vegetables after harvest

fruits and vegetables after harvest are still living organisms in the storage, transportation and sales system under the promotion of national policies, and they are still carrying out metabolic activities as before harvest. Physiological and biochemical changes in fruit and vegetable cells are, to a large extent, the continuation of metabolic processes during the growth of these organisms

postharvest fruits and vegetables no longer absorb water and nutrients from the soil, and basically no longer carry out photosynthesis. Postharvest life activities are metabolic processes dominated by respiration, which are characterized by physiological and biochemical changes in the maturity and aging of fruits and vegetables, resulting in changes in quality and quantity. However, such changes after harvest generally do not meet people's requirements, and effective measures need to be taken to control and adjust them

fruits and vegetables are prone to decay, weight loss and wilting during storage, transportation and marketing. The reasons are summarized in three aspects: first, environmental factors such as temperature, humidity, gas and light cause physiological disorders and aging of fruit and vegetable tissues; Second, the infection of pathogenic microorganisms; The third is the infection of bacteria caused by mechanical damage and pest damage. It is of great economic significance for the storage, transportation and marketing of fruits and vegetables to study the causes of decay and deterioration from a physiological point of view, take measures to delay aging, and re adjust the curve after the experiment, so as to enhance the disease resistance and immunity of fruits and vegetables and reduce the loss of decay and deterioration

as food and commodities, consumers and customers are most concerned about the nutritional value, edible quality and commodity quality of fresh fruits and vegetables. The purpose of fresh-keeping is to maintain the quality and quality of fruits and vegetables at the time of harvest to the greatest extent. However, during the storage, transportation and marketing of fruits and vegetables, due to changes in the environment and their own physiological factors, their appearance, color, flavor, texture, smell and nutritional components will inevitably change, and their weight will gradually decline. In order to achieve the purpose of delaying this change, the importance of adopting applicable fresh-keeping technology and advanced fresh-keeping means is more apparent

various technical measures for post harvest commercialization, storage and preservation of fruits and vegetables are based on post harvest physiology of fruits and vegetables. The purpose of keeping fresh is to maintain this normal physiological activity and to minimize the process of maturation and aging

several reference indicators of freshness

to achieve freshness, what kind of condition is fresh? The concept of freshness in the field of preservation is relatively wide, and the country has not yet formulated a unified standard. However, generally speaking, it is mainly summarized from the following aspects:

first, quality

is divided into internal quality and external quality

the technical parameters of external quality mainly include: the appearance, size, shape, color, flavor, texture, smell, nutritional composition, uniformity, etc. of fruits and vegetables. Through the determination of these technical parameters, we can judge the freshness and quality of fruits and vegetables. Generally, it is judged by direct observation

the technical parameters of internal quality include sugar content, minerals, vitamins, flavor substances and other nutritional components. Generally, it is judged by instrument detection, such as nondestructive sugar content and acidity measuring device

second, character

the reference value of character is the storage resistance and disease resistance of fruits and vegetables

III. quality control indicators

mainly include: variety, specification, color, maturity, packaging, storage and equipment of fruits and vegetables. Quality control index is an important price reference value for exported fruits and vegetables

IV. indicators for determining the freshness and maturity of fruits and vegetables

total sugar

chlorophyll

acidity

several key factors in the storage and preservation of fruits and vegetables

to study the preservation technology, we must understand the preservation environment. In other words, we should make clear the factors that lead to the decay, deterioration, yellowing and wilting of fruits and vegetables after harvest. By controlling the changes of these factors, the fresh-keeping effect can be achieved

what material factors will affect the fresh-keeping environment of fruits and vegetables

research shows that the main reason for the decline of fruit and vegetable quality is affected by six plant hormones, Its production sequence is:

1) methionine (inducer)

2) ethylene (aging and ripening)

3) ethylene oxide (metabolite)

4) acetaldehyde (aging and fermentation)

5) ethyl acetate (aroma)

ethanol (fermentation and corruption)

we will introduce it step by step from the following aspects:

respiration

photosynthesis basically stops after fruits and vegetables are harvested, Respiration has become the leading process of postharvest life activities, which is closely related to various physiological changes after harvest. Controlling the respiration of fruits and vegetables after harvest can control the quality changes, physiological disorders, storage life, microbial infection, commercialization and shelf life of fruits and vegetables

fruit and vegetable products belong to various organs of plants. Like general plants, different kinds and varieties of fruits and vegetables have different respiratory metabolism levels, which is a genetic characteristic formed by various fruits and vegetables under the long-term influence of external environmental conditions. Even for the same variety, there are great differences in respiratory level due to different physiological age and reproductive status at the time of harvest. Usually, the respiratory level of young and tender organs is higher than that of slow growth and aging organs

as for fruits, the respiratory level of nuts, citrus and grapes is low, that of drupes is medium, and that of berries is the highest; The respiration level of fruits matured in summer was higher than that in autumn and winter; The respiration level of fruits grown in tropical and subtropical regions is higher than that in temperate and cold regions. For fruits of different varieties in the same category, the respiration level of varieties with long growth and development period is lower than that of varieties with short growth and development period

among all kinds of vegetables, leaf vegetables (loose leaf type) usually have the highest respiratory level, followed by fruit vegetables and cauliflower, and rhizome vegetables have the lowest respiratory level