Study On Preservation Effect Of Different Coatings On Fresh Grape After Vibration

The grapes,belongs to the Vitis L.(Vitaceae)family and is one of the world's most productive fruits.The area of viticulture in the world has exceeded 10 million hm~2.The annual output is about 65 million tons,accounting for 20%of the world's total fruit production.Second only to citrus,ranking second in the world.In recent years,grape cultivation has developed rapidly in China,and is ranked as China's top five fruits with apples,citrus,pears,and bananas.China's annual output is about 3 million tons,of which 70%is used for fresh food.Grape skin is thin and juicy,with soft fruit,and contains various nutrients such as sugar,organic acids,protein,minerals and vitamins.It has high nutritional and therapeutic value and is deeply loved by consumers.The phenomenon of threshing,rotting,stemming,and browning are prone to occur in the course of storage,transportation,and marketing.This has brought difficulties to the market expansion of grapevines and prolonged sales,which has seriously affected the economic benefits.Each year,due to technical reasons such as harvesting,packaging,and storage,the rot decay of grapes accounts for more than 20%of the total output.By studying the fresh-keeping effect of three different coating treatments including1%chitosan(m/v),2%carboxymethyl chitosan(m/v)and 1%sodium alginate(m/v)on fresh grapes after vibration stress(vibration intensity 5 Hz,maximum amplitude 5cm,vibration time 12 h)during storage(10 d)at room temperature(25±1°C),the quality indicators(weight loss rate,rot rate,hardness,soluble solids),respiratory intensity,Vc content,total phenolic content,titratable acid content and relative conductivity were determined.The results showed that during the storage period,the three different coating treatments(1%chitosan(m/v),2%carboxymethyl chitosan(m/v),and 1%sodium alginate(m/v))can improve the fresh-keeping effect of fresh grapes to varying degrees,which is mainly reflected in the reduction loss of moisture in table grapes,reduced weight loss rate(up to 48.19%compared to the control group),eased the softening of table grapes during storage(the hardness of the coating groups on the 10th day was 303.2,327.0,311.1 kg/cm~2,respectively,the control group was280.2 kg/cm~2),reducing respiratory intensity,reducing nutrient Vc(up to 26.02%)and alleviating the decrease in titratable acid.At the same time,it was found that the 2%carboxymethyl chitosan(m/v)coating had the best preservation effect.After being stored at room temperature for 10 days,the weight loss rate was 17.14%,the hardness was 327.0 kg/cm~2,the Vc content was reduced by 36.99%,and the total phenolic content was decreased by 8.66%.The titratable acid decreased by 35%and the relative conductivity increased by 347%.Besides,in order to study the effect of Konjac Glucomannan(KGM)on the freshness of table grapes after vibrating stress,three different concentrations of konjac glucomannan(1,2,3 g/L)were used to coat the grapes after vibration(vibration intensity 5 Hz,maximum amplitude 5 cm,vibration time 12 h).The freshness of the table grapes with distilled water and the freshness of the table grapes treated with different concentrations of Konjac Glucomannan in the storage period(10 days)at room temperature(25±1?)was compared,mainly determined by measuring the quality index(weight loss rate,decay rate,hardness,soluble solids),respiration intensity,Vc content,total phenol content,titratable acid content and relative conductivity performance.The results showed that different concentrations of Konjac Glucomannan coating could improve the freshness of table grapes in different degrees,mainly in reducing the loss of water and reducing the weight loss rate(compared with the control group,the maximum can reduce 35.19%),slowing the storage process of softening and decay(highest decay rate decreased 29.78%),reducing the respiratory strength,reducing the consumption of VC and total phenol(the highest was reduced53.02%and 68.97%separately).At the same time,it was found that 2 g/L concentration of Konjac Glucomannan has the best freshness effect,after 10 days,the weight loss rate,decay rate and hardness were 21.44%,49.35%,323.53 kg/cm~2 respectively,Vc content,total phenol content and titratable acid content reduced 23.45%,17%and 22.5%respectively and the relative conductivity increased by 131%.This provides the theoretical basis for the freshness of table grapes in the future.