After being harvested, fruits and vegetables are still organic organisms, and they will also perform complex life activities such as dormancy, water evaporation, and respiration, and still consume oxygen and discharge. Water is an important factor in maintaining the freshness of fruits and vegetables. Therefore, the preservation of fruits and vegetables after harvest is also extremely important. PBS film has barrier properties and can maintain the oxygen and carbon dioxide concentrations in the environment where fruits and vegetables are located, thereby controlling the decomposition of chlorophyll. The application of PBS film in the preservation of fruits and vegetables is mainly achieved through the modification technology of PBS film. The following analyzes the effect of modified PBS film on fruits and vegetables after harvest.
1. Barrier properties of PBS/PBAT blended film
The modified PBS film has good barrier properties. Compared with pure PBS, the increase in gas permeability of the blended film with PBAT added is mainly due to the good permeability of PBAT itself to CO2 and O2. The respiration and transpiration of fruits and vegetables themselves will also release a large amount of water vapor. Good moisture permeability can emit some unnecessary moisture to prevent problems such as fruit and vegetable sourness and microbial growth caused by condensation.
2. Changes in gas composition in modified PBS packaging bags
The key to spontaneous modified atmosphere packaging is to maintain a more suitable gas composition in the packaging bag, thereby inhibiting the strong respiratory metabolism of fruits and vegetables and delaying their maturation and aging process. During the preservation period of fruits and vegetables, the CO2 content in the packaging bag is more suitable at 1% to 5% and the O2 content is more suitable at 3% to 5%.
3. Changes in weight loss rate of fruits and vegetables during preservation
The weight loss of fruits and vegetables is mainly caused by water loss and nutrient metabolism. The water content in fruits and vegetables is relatively high, accounting for 75% to 80% of the total weight. The loss of water will cause the peel to wilt, the tissue to loosen and the freshness to decrease, seriously affecting its commercial value. The 150g packaging bag has a lower weight loss rate in the early stage of storage due to its high quality, but in the later stage, due to anaerobic respiration, the cell tissue is destroyed by ethanol and the juice is lost. This shows that the modified PBS packaging bag can effectively solve the problem of water loss caused by respiration of fruits and vegetables, but the quality of fruits and vegetables in the packaging bag must be moderate to maintain a certain water retention and freshness of the fruit.
4. Changes in the hardness of fruits and vegetables during preservation
The change in the hardness of fruits and vegetables is one of the important indicators to characterize their transition from maturity to aging. Normal fruits and vegetables undergo anaerobic respiration in the later stage, produce a large amount of ethanol, and the cell tissue is softened by ethanol damage, resulting in a rapid decrease in their hardness. However, fruits and vegetables packaged with modified PBS film can still remain firm after harvesting. This is because the suitable atmospheric conditions delay the aging and softening of the fruit tissue, thereby maintaining a good hardness.
5. Changes in the soluble solids content (TSS) of fruits and vegetables during preservation
The total amount of soluble solids in fruits and vegetables is the sum of all compounds that can be dissolved in water, which can be used to characterize the maturity of fruits and vegetables. The change of TSS content mainly reflects the aging of fruits, while the permeability of gas and water vapor in the packaging bag directly affects the respiratory metabolism of fruits and vegetables, and thus inhibits the reduction of soluble solids content to a certain extent.
6. Changes in VC content of fruits and vegetables during preservation
Vitamin C is one of the vitamins most closely related to the human body. VC mainly participates in redox reactions in the human body and plays a role in electron transfer in material metabolism. About 98% of the vitamin C required by the human body comes from fruits and vegetables.
Lei Qiao et al. found that increasing the CO2 concentration while appropriately reducing the O2 concentration can effectively reduce the oxidation of VC. Therefore, the VC content in the late storage period is significantly higher than that of fruits and vegetables in ordinary packaging bags. Compared with normal packaging bags, the modified PBS film has a 30-fold increase in its elongation at break, and the permeability of CO2, O2 and water vapor has been appropriately improved. The modified PBS film has good gas permeability, which keeps the oxygen and carbon dioxide concentrations in the PBS film in a stable atmosphere, thereby inhibiting the corruption of fruits and vegetables.
The moisture permeability of PBS/PBAT film reached 1803cm3/(m2·d), and the good moisture permeability prevented the condensation in the bag. The storage period of the packaging group was nearly twice that of the blank group, and the shelf life was extended to more than 31 days. From the perspective of economic value, weight loss rate, hypoxia damage, etc., the modified PBS film packaging bag has a better effect on the quality of fruits and vegetables.
