| Grape,as a kind of berry,has delicious taste and high nutritional value,and is deeply loved by people.The cultivation of grapes in our country is very extensive.You can see the grapes growing from south to north and from east to west.Grapes are mostly used for fresh food in China,and the demand for fresh grapes is increasing every year.With the rapid development of China's grape growing area,yield and quality,China has become a major grape producer in the world.The main source of grapes in China is self-produced.As of 2018,China's grape output reached 13.667 million tons,with an import volume of 231,700 tons and an export volume of 277,200 tons.There are also some problems behind the growing grape market.For example,grapes are very difficult to store,and it is easy to cause the loss of nutritional quality due to infection,decay,browning and dehydration of pathogenic bacteria during the storage,transportation,and sales of grapes,which seriously affects the development of the grape industry.With the continuous development of the economy and society,people have higher requirements for the quality and nutrition of grapes.Therefore,how to maintain the freshness of grapes at room temperature has become the key to the current development of the grape industry.After the grapes are picked,they must be transported,stored,and sold to reach consumers.The loss of grape nutrition quality during this process has greatly affected the development of the grape market.A bacteriostatic agent is combined with a substrate resin to produce a packaging film with bacteriostatic effect through granulation and casting under certain conditions.Such packaging can well solve the preservation of fruits and vegetables at normal temperature,and is safe and practical.This kind of packaging film with a certain bacteriostatic effect has also become the focus of fruit and vegetable packaging research.In this study,masterbatch was prepared by melt blending nano-zinc oxide,modified T resin and modified b resin with low density polyethylene substrate with antibacterial effect,and then modified film was prepared by casting equipment.The performance of the modified film was tested,and films suitable for grape freshness preservation experiment were screened out.The effect of the modified film on the freshness preservation of grapes at room temperature was studied.The results are as follows:(1)Based on low-density polyethylene,modified T resin and modified nano-zinc oxide were added to it,and a modified polyethylene film was prepared by melt blending using a twin-screw pelletizer and a caster,and researched Effects of the content of modified T resin and modified nano zinc oxide on the antibacterial effect,water vapor transmission,oxygen transmission,mechanical properties,microstructure,infrared spectrum and ultraviolet transmittance of polyethylene film.The results show that when the 1.5% modified nano-zinc oxide is added,the antibacterial properties of the film become more significant with the increasing content of the modified T resin,and the trend of the change in the UV transmittance is to decrease first and then increase.When the mass fraction of the modified nano zinc oxide is 1.5% and the mass fraction of the modified T resin is 1%,the water vapor transmission amount and the oxygen transmission amount are the smallest,and the tensile strength and the elongation at break are the largest.In a comprehensive comparison,when the mass fraction of modified nano zinc oxide is 1.5% and the mass fraction of T resin is 1%,the performance of the film is the best.However,by observing the surface of the film,it can be seen that there are some tiny pores.(2)The low-density polyethylene resin is modified with nano zinc oxide and b resin,and a modified film is prepared through melt blending and extrusion casting.Then the mechanical,optical,barrier and antibacterial properties of the films were measured.The results showed that the addition of nano zinc oxide significantly improved the antibacterial effect,mechanical properties and UV blocking effect of the film,and the optical properties and blocking performance of the film decreased accordingly.As the content of b resin continues to increase,the optical and mechanical properties of the film continue to decrease;the barrier properties and UV blocking effect increase first and then decrease.When the amount of nano zinc oxide and b resin is 1.5% and 3%,the comprehensive properties of the modified film are the best.At this time,the water vapor transmission and oxygen transmission of the modified film are reduced by 5.3% and 27.5%respectively.The UV transmittance was reduced by 29.8%,and the antibacterial effect was greatly improved.Observing the surface of the nano-zinc oxide-b resin modified composite film,there are no obvious pores,which is more suitable for making bags into grapes for preservation.(3)Using nano zinc oxide and b resin as bacteriostatic agents,they were added to low-density polyethylene substrate resin,and three modified films with bacteriostatic effects were obtained through extrusion casting process.Under normal temperature conditions,the three modified films and pure low-density polyethylene film were used to package the grapes,and the grape weight loss rate,good fruit rate,hardness,soluble solids,total acid,ascorbic acid and other indicators Measurements were made to analyze the freshness-preserving effect of different modified films on grape packaging.The results showed that the grapes packaged with nano-zinc oxide-b resin modified composite film prepared with 1.5% nano-zinc oxide and 2% b-resin had a good fruit rate of 74% after 15 days of storage,and the soluble solids decreased by 0.67 %,The titratable acid content was reduced by 0.188%,and the VC content was decreased by 12.6%.Compared with the other three kinds of packaging films,the nano-zinc oxide-b resin modified composite film has the best fresh-keeping effect,which can effectively extend the fresh-keeping period of grapes at room temperature. |
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