| With the improvement of living standards,people have an increasing demand for maintaining the flavor and nutrition of fruits and vegetables.The development of cold chain logistics provides technical support for the preservation and transportation of harvested vegetables.However,the use of cold storage technology in cold chain logistics still causes problems such as insufficient cold capacity and "disconnected circulation" in cold chain logistics.Therefore,the improvement and development of cold storage technology is still a current research hotspot.The advancement of cold storage technology needs the promotion of cold storage materials.Therefore,the research and development of high-performance cold storage materials is a key measure to solve the insufficiency and low efficiency of cold chain logistics.Choosing a cold storage material with suitable phase change temperature and higher latent heat of phase change can ensure that the storage environment of fruits and vegetables is always maintained within a certain temperature range,which is essential for extending the shelf life of the product and reducing the loss before consumption.Based on this,the main research contents of this study are as follows:(1)An environmentally degradable starch grafted acrylic superabsorbent resin(SAR)is prepared.The graft polymerization of potato starch and acrylic acid is completed by inverse suspension polymerization.The SAR preparation conditions are determined by single factor combined with response surface optimization experiment: the water absorption rate of the product prepared under optimal conditions(dispersant 4.38%,crosslinking agent 0.06%,initiator 0.9%,starch addition amount 10%,neutralization degree 75%,monomer mass ratio 0.1,reaction temperature 65°C)is 573 g/g.Fourier infrared spectroscopy shows that starch and acrylic acid are successfully grafted.Different starch additions have certain influence on the water absorption,water retention,and gel strength of SAR,and its degradability is nearly 6 times higher than that of non-starch additives,more than 60% within 75 days.It shows that the material not only optimizes water absorption and water retention through starch grafting,but also has a good degradation rate in the natural environment.(2)The cold storage characteristics of the water-absorbing resin used as a phase change cold storage material after absorbing water have been studied.Differential scanning calorimetry analysis shows that the latent heat of phase change of the cold storage material is 330.4 J/g,which is about 11% higher than non-starch SAR,and the phase change temperature is about-2～-3℃,which meets the low temperature transportation requirements of fruits and vegetables.20 repeated freezing and thawing cycle experiments show that the prepared cold storage material has good temperature stability,and there is basically no phenomenon of supercooling and phase separation.Combining with the cold storage characteristics,the cold storage material amount is calculated by the heat balance method.Determined the optimal amount of cold storage material: Lentinus edodes = 1:3.Then,the temperature changes and distribution in the insulation system through the ANSYS finite element analysis method is qualitatively simulated,which provides a certain reference value for the placement of cold storage materials.(3)The effect of the prepared degradable phase change cold storage material is analyzed and verified through the mushroom storage application experiment.The storage experiment results show that the material could maintain the low temperature environment in the incubator for a longer period of time compared with the commercially available cold storage materials.The experimental group with the degradable phase change cold storage material basically maintained a low temperature environment below 10℃ within 12 hours.Sensory quality(color,weightlessness,odor,rot,etc.)played a better role in maintaining the weight loss rate and BI value of Lentinus edodes by 21% and 16%,5.6% and 7.2%respectively compared with the control group and the commercially available material group.It can delay the change process of malondialdehyde content and relative conductivity during the storage of Lentinus edodes and maintain high antioxidant enzyme(SOD,POD,CAT)activity.This indicates that the prepared degradable phase change cold storage material has a higher latent heat of phase change,which improves the ability to maintain a lower temperature requirement in the storage environment,thereby improving the preservation effect,and can be widely used in the logistics storage and transportation of fruits and vegetables. |
