How does the red-outer-black-inner Wood Pulp Composite Paper protect fruit growth and improve its quality? ​

From the early stage of fruit growth, many factors in the external environment may pose a threat to it. Ultraviolet rays are a common environmental factor. Excessive exposure will destroy the DNA structure in fruit cells, interfere with the normal division and growth of cells, and affect the development process of fruits. The invasion of wind and rain should not be underestimated. Strong winds may cause fruits and branches to collide with each other, causing mechanical damage, and rainwater is easy to carry pathogens, increasing the risk of fruit infection. Dust will not only adhere to the surface of the fruit, affecting the photosynthesis of the fruit, but also may become a breeding ground for pests and diseases. The red-outer-black-inner composite paper bag is like a solid barrier. Its material has good physical barrier properties and can effectively block external ultraviolet rays, wind and rain, and dust. When ultraviolet rays hit the outer layer of the paper bag, the outer material can absorb and reflect part of the ultraviolet rays, reducing its direct damage to the fruit; in the face of wind and rain, the structure of the composite paper bag is tight, which can withstand the impact of wind and rain and prevent the fruit from being physically damaged; for dust, the surface of the paper bag is relatively smooth, and dust is difficult to adhere to, thus ensuring that the fruit grows in a relatively clean environment. ​
Pests and diseases have always been a problem that has troubled fruit farmers. They will directly damage the appearance and internal structure of the fruit and reduce the yield and quality of the fruit. The composite paper bag with red outside and black inside forms a relatively closed space to reduce the contact between the fruit and external pests and diseases. Many pests rely on vision and smell to find food. The presence of wood pulp composite paper blocks the information of the fruit, making it difficult for pests to find the fruit. The environment inside the paper bag is relatively stable, which is not conducive to the survival and reproduction of pests and diseases. Some pathogens are easy to breed in a humid and poorly ventilated environment, while the air permeability of the composite paper bag can adjust the internal humidity, maintain a relatively dry environment, and inhibit the growth of pathogens. Paper bags can also prevent some birds and small animals from pecking and biting the fruit, providing a safe environment for the growth of the fruit.​
In the late stage of fruit ripening, the unique design of the red outer and black inner composite paper bag further plays a role. The red color of the outer layer can reflect part of the light, especially during periods of strong sunlight, effectively preventing the fruit from being burned due to excessive light. Fruit burns not only affect the appearance, but also reduce the taste and nutritional value of the fruit. By reflecting light, the paper bag can control the temperature of the fruit surface within an appropriate range to ensure the normal physiological activities of the fruit. The black inner layer creates a relatively dark environment, which is of great significance for the synthesis of anthocyanins in the fruit. Anthocyanins are the key pigments that determine the color of the fruit. Sufficient anthocyanin synthesis can make the fruit appear bright in color. In a dark environment, a series of changes will occur in the physiological mechanism inside the fruit, promoting the expression of genes related to anthocyanin synthesis and increasing the content of anthocyanins. Taking apples as an example, after putting on the red outer and black inner composite paper bag, the color of the fruit is brighter and more rosy, which is more attractive in the market and can significantly improve the appearance quality and commodity value of the fruit. ​
In addition to the impact on the appearance of the fruit, the red outer and black inner composite paper bag also has a positive effect on the internal quality of the fruit. During the growth of the fruit, the stable environment created by the paper bag helps accumulate nutrients inside the fruit. Since the interference of external environmental factors is reduced, the fruit can use more energy for its own growth and nutrient synthesis. Under relatively stable temperature, humidity and light conditions, the sugar, vitamins and other nutrients in the fruit can be better accumulated, thereby improving the taste and nutritional value of the fruit. The protective effect of the paper bag reduces the physiological stress response of the fruit caused by external damage, avoids the production of excessive defensive substances inside the fruit, and ensures the purity of the fruit flavor. ​
From the perspective of actual production, the use of composite paper bags with red outside and black inside can also reduce the management costs of fruit farmers. Reducing the invasion of pests and diseases means reducing the use of pesticides, which not only reduces production costs, but also conforms to the concept of green environmental protection, and produces green agricultural products that are more popular with consumers. Due to the improvement of fruit quality, higher selling prices can be obtained in the market, increasing the economic benefits of fruit farmers. ​