Food is the material basis for human survival. With the improvement of people's living standards and quality of life, the quality of food is becoming more and more demanding. To ensure the quality of food, it is necessary to deal with the packaging and storage of food. About 20% of China's grain is invented by the state, 80% of the grain is stored by the farmers themselves. Most of the farmers' grain is in simple bag form. These plastic woven bags can only play a role in the grain. It is impossible to meet the requirements of dustproof, insect proof and rodent prevention, let alone any preservation. In the process of circulation, sale and consumption, some of the commodity grain is also unable to achieve the desired effect due to some problems in packaging.
1. Current status of rice sales and packaging in China
At present, China's rice sales packaging from the packaging materials, mainly using plastic woven bags, composite plastic bags as packaging containers, and these bags in the transportation, loading and unloading, retail and other links have many problems to be solved. The use of plastic woven bags to package food, the phenomenon of waste is more serious, generally only 1-2 times, the relative cost is relatively high. Moreover, the packaging method is simple, and it is difficult to re-seal after opening, which is not conducive to long-term preservation, and the pest and mildew phenomenon are more serious. The packaging material has poor moisture resistance and poor barrier property, and the grain is easy to be oxidized and mildewed. The plastic composite bag is made up of high-barrier packaging materials, which can solve the problem of mildew, insect and fresh-keeping of food to a certain extent, but the post-treatment is difficult. Because it is not easy to be degraded, the use is also restricted.
Domestic rice sales packaging From the packaging technology point of view, there are basically two kinds of packaging forms, one is ordinary packaging, using polypropylene plastic woven bags to package rice, no packaging technology is applied during the packaging process, this packaging for rice The anti-insect, anti-mildew and fresh-keeping effect is poor; the other vacuum-packaging technology is used to vacuum the packaging bag, and the vacuum packaging technology has a good preservation effect on the storage of rice, but due to the shape of the rice itself and the choice of vacuum degree. Inappropriate, the vacuum degree of vacuum packaging currently used in rice is generally between -0.07 and -0.09 kPa. As long as the vacuum is within this range, the factory is a qualified product. Due to the large degree of vacuum, the packaging material tightly wraps the rice. Since the ends of the rice are sharper, the packaging bag is easily punctured by the rice grains, forming a pinhole, so that the packaging bag will leak, causing the vacuum packaging to fail. Tests have shown that the rice bag with a vacuum of -0.094 MPa is placed at rest and not stacked. The leak rate of the bag is 16% within 20 days, so the high vacuum will inevitably result in a high bag breaking rate. . In addition, the friction, collision and drop between the bag and the bag during the circulation of the bag can easily cause the bag to be broken. According to statistics, the bag breaking rate of vacuum packaging in the circulation process reaches 30%. The problem of vacuum packaging has caused waste of rice, causing losses and troubles for consumers and businesses. Therefore, in order to preserve the packaging of rice, it must be combined with the circulation environment, in order to achieve good results.
2, the food quality of rice
2.1 The taste of rice
At present, domestic and international evaluation of rice quality focuses on four aspects, namely: process quality, appearance quality, food quality (cooking performance and taste), nutritional quality. The quality of the taste can not only make people enjoy the senses, but also directly affect the digestion and absorption of rice. Therefore, the quality of rice is mainly determined by the taste of rice.
The taste of rice is not the taste of rice, but the comprehensive reflection of the sense of smell and taste and visual impression brought by the cooked rice. The chemical composition of the food and its structure are closely related to the taste, so different foods have a special taste due to the chemical composition of their food and their tissue structure. The same is true of rice. The taste of rice has a lot to do with the origin, variety, cultivation, harvesting, storage, processing and cooking methods and processes of rice. If a certain link is not handled well, it will affect the taste of rice. It is important to objectively evaluate the taste of rice in the fields of rice production, distribution, sales and scientific research. China has stipulated the cooking method for rice taste evaluation, see GB/T15682-1995.
2.2 Quality changes of rice during storage
The rice is shelled to obtain brown rice, and the brown rice is crushed to peel and the embryo becomes rice. Because the rice is not protected by the husk, the endosperm is directly exposed to the space and is susceptible to external factors. Therefore, the storage stability of rice is poor. The main factors affecting rice deterioration are the three main factors such as rice moisture content, storage temperature and gas composition in contact with it.
The content of lipids in rice ranges from 0.6% to 3.9%. The lipid content directly affects the edible quality of rice. The higher the fat, the better the gloss of rice. The aroma of rice is related to the unsaturated fatty acids contained in the rice grains. The fat in rice is most likely to change. It is decomposed into glycerol and fatty acid by the catalytic action of esterase, so that the free fatty acid is increased. The free fatty acid is contained in the spiral structure of the linear component of starch, making it difficult to pass the water required for gelatinization. The strength of the starch granules increases to cause an increase in the hardness of the rice. At the same time, fatty acids can be further decomposed into lower aldehydes, ketone compounds and acids to reduce the eating quality of rice. Therefore, in rice storage, the fatty acid value is often used as a sensitive indicator to determine the free fatty acid content in rice as an indicator of food deterioration. The newly harvested food fatty acid value is generally within 15 (mgKOH/100g), which will gradually increase during storage and increase rapidly under high temperature and high humidity.
2.2.2 Changes in reducing sugar
Rice contains a small amount of low molecular sugars, such as glucose, maltose, etc., because these sugar molecules contain free reducing groups, thus affecting the redness of rice, easy to be oxidized under appropriate conditions, seriously affecting the quality of rice. Compared with rice stored at low temperature, Chenmi has about 50% more reducing sugar, so the change of reducing sugar in rice also reflects the change of rice quality.
2.2.3 Changes in water content
The adsorption of water molecules by rice is mainly caused by the interaction of polar groups contained in rice with water molecules. The moisture on the surface of rice is mainly caused by adsorption, and the internal moisture is mainly caused by the diffusion of the surface of the rice to the inside. Therefore, the water content of grain has a great relationship with the environmental humidity. Measuring the water content in rice can also measure the quality of rice.
Based on the above, the determination of some components in rice can be used to analyze changes in rice quality. The main indicators tested after rice storage are: fatty acid content, reducing sugar content and moisture content.
3. Circulation characteristics of vacuum packed rice
The ability to measure the resistance of a package during its circulation is generally based on the 'brittle value' parameter. In the National Standard for Cushion Packaging Design Method, the brittle value is defined as "the maximum acceleration that the product can withstand without physical or functional damage", generally expressed as a multiple G of the gravitational acceleration. The larger the G value, the stronger the ability of the product to withstand external forces. As an indicator of the inherent characteristics of the product, the brittle value is a comprehensive manifestation of the product's ability to withstand impact. Rice with different vacuum degree can draw on the theory and measurement method of embrittlement value of electromechanical products, and use the drop experiment to study. The maximum acceleration of the rice bag before the bag is broken is the crispness of rice vacuum packaging under the vacuum. value.
4. Research method for optimal vacuum degree of rice vacuum packaging
4.1 Rice vacuum packaging storage simulation experiment
In order to study the effect of vacuum vacuum packaging on the storage quality of rice, the storage simulation test of rice vacuum packaging was carried out. In actual production, rice is packaged, transported, and sold in the hands of the consumer, and the intermediate time is about 40-60 days. Therefore, the storage time in the storage simulation test is determined to be 60 days.
The production and sale of rice is carried out in any season. The temperature and humidity of the environment vary greatly throughout the year, and the climate difference between different geographical locations is also very large. In the simulation test, based on the most severe storage conditions, Take Zhengzhou's summer as an example, the average temperature is 35 ° C, and the average relative humidity is 75%. China's supermarkets or retailers are in the process of storing goods without refrigeration, and the conditions for storage of goods are consistent with the external environment. Therefore, the environment of the storage experiment was set to a temperature of 35 ° C and an average relative humidity of 75%.
The metered rice is packaged by a multifunctional vacuum air-packing machine, and the degree of vacuum is controlled by the time of vacuuming. The reading of the vacuum gauge is recorded during the vacuuming process. In the choice of vacuum degree, the vacuum degree used by the company is -0.å®--0.09MPa, with reference to the vacuum degree used by the company, the vacuum degree can be selected to be -0.09MPa, -0.07MPa, -006MPa, -0.05MPa, -0.04MPa and OMPa. Put the packaged rice on the test bench for half a day to one day, check whether the bag is leaking, and select the packaged rice into a constant temperature and humidity chamber for storage experiment.
It is taken out every 10 days to check the credit quality of rice. The method of inspection can be used to test the quality of rice by cooking experiment. At the same time, the chemical composition of rice can be tested to evaluate the quality of rice. The test is to be tested according to national standards: GB/T15682-1995; fatty acids were determined according to GB5510-85 method; reducing sugars were determined according to GB5513-85 method; water content was determined according to GB5497 name 5 method.
4.2 Rice vacuum packaging circulation simulation experiment
In line with the actual vacuum-packed rice, in the circulation simulation experiment, the vacuum packaging with a packaging weight of 2.5 kg of rice was packaged in the same manner as in the storage test. The drop tester was used to detect the brittleness value of different vacuum rice packages to study the rice packaging with different vacuum degrees and the resistance to impact external force during circulation. At the same time, in the circulation, considering the damage caused by vibration on the package, the vibration test bench is used to detect the "vibration brittleness value" or "vibration resistance" of the rice package with different vacuum degrees.
4.3 Optimized design of vacuum degree of rice vacuum packaging
In order to study the combination of the circulation environment and the optimal vacuum of rice vacuum packaging, an optimized mathematical model needs to be established, and MATLAB software can be used in the establishment. In storage simulation experiments, a functional relationship between vacuum and rice quality, vacuum and fatty acid, vacuum and reducing sugar, and vacuum and water content can be established. A functional relationship between vacuum and brittleness can be established in a flow simulation experiment. Because the brittle value and the taste value of rice are both dimensionless quantities, the sum of the two can be used as the objective function in the mathematical model of optimization design; the degree of vacuum and fatty acid, vacuum and reducing sugar and vacuum degree The function between the water content is used as a constraint condition, and the optimal vacuum degree of the vacuum packaging of the rice in combination with the circulation environment is solved by a modern optimization design method.
5 Conclusion
Combining packaging technology and circulation environment to study rice vacuum packaging has great practical significance. The vacuum degree researched by this method can not only maintain the eating quality of rice during the price period, but also reduce the circulation process. waste.
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