Drying Of Water Lily Flower And Storage Evaluation

Water lily（the genus Nymphaea,family Nymphaeaceae）,which is a perennial aquatic herb flower plant,exhibits various applications in water purification and horticulture.Its flower contains a variety of nutrients and bioactive compounds with high biological activity and free radical scavenging ability such as flavonoids and polyphenols,thus contributing to the reduction of blood glucose and lipids,anti-aging,anti-oxidation,and the enhancement of immunity.However,the high water content in the fresh water lily caused the difficulties in its transport and storage.Drying is an useful method to extend the shelf life and improve the utilization value of fresh flowers,but some problems such as browning and shriveling affect the sensory quality of dried flowers.In this paper,the color and shape of the air-dried petals of "El dorado" water lily flower were protected and the optimal conditions was obtained.Then,air-borne ultrasound was applied to assist the hot air drying and the changes in the quality of the petals during drying were monitored.Finally,the drying petals were stored under different conditions and the the optimal conditions was obtained by evaluating the storage stability of the petals.The results were shown as follows:1.The effects of pre-treatments on the color and shape of air-dried water lily（60℃）were studied.The results showed that color preserving reagents significantly affected the upper part of the petals,whereas the bottom part browned and exhibited severe shrinkage with the maximum L*value（69.43）showing no significant difference with the control（67.67,p>0.05）.Steam blanching for 20 s dramatically reduced the L*value of the bottom part（p<0.05）and the overall color of petals became uniform,thus dominating in the color protection.Moreover,the shrinkage rate of dried petals was significantly lower than the blank（p<0.05）.After soaking with the polysaccharide solution,the shrinkage rate of the petals decreased.Among which,sodium alginate exhibited the best effects on the shape protection.Also,the degree of browning became light.According to the the neural network model and genetic algorithm results,the optimal conditions of pre-treatment were:sodium alginate solution 0.39%,soak time 21.8 min and temperature 35.5℃.2.The effects of the combination method of air-borne ultrasound with hot air drying on the physicochemical qualities of pretreated water lily petals were studied.The combination method of air-borne ultrasound（180.1 W/dm2）with hot air drying（60℃）was applied to dry petals after color and shape protection,and the method was compared with hot air drying alone（60℃）and freeze drying.The results showed that the combination method could improve the drying rate and shorten the drying time.The drying time of fresh samples,steam blanching and soaking treatment samples by the combination method was reduced by 70.0%,20.0%and 65.7%,respectively,when compared with that of hot air drying.Five different drying models were evaluated to fit the drying process of petals,and the Midilli-Kucuk model showed the best fitting performance.Freeze drying had the highest retention rate of Vc,which reached 82.9%.The loss of Vc of fresh samples and soaking treated samples after ultrasound drying was 58.3%and 61.3%,respectively,higher than those of hot air drying alone（42.4%and 38.0%,respectively）.However,ultrasound drying can reduce the loss of Vc content of steam blanching samples,whose loss rate is 37.4%.The combination of ultrasound with hot air drying could accelerate the inactivation of polyphenol oxidase,and the combination of ultrasound with steam blanching treatment increased the content of free phenolic compounds.With the exception of gallic acid and myricetin,the content of other free phenols under ultrasonic drying was significantly higher than that under hot air drying（p<0.05）.The total free amino acid content of petals decreased from 27.02±1.05 mg/g DW to 12.51±0.81 mg/g DW after freeze-drying,which was significantly lower than that dried by hot air（17.99±1.44 mg/g DW）and ultrasound（28.17±1.26 mg/g DW）（p<0.05）.Furthermore,the total free amino acid content of steam blanching and soaking treatment samples showed no significant difference between the two drying techniques（p>0.05）.The types and contents of volatile substances decreased after drying,where alkanes and terpenes lost and aldehydes increased.No significant differences between ultrasonic hot air drying and hot air drying were observed in fresh and steam blanching samples,but the content of terpenes and aromatic hydrocarbons of soaking treatment samples after ultrasonic drying was significantly higher than that after hot air drying alone（p<0.05）.Moreover,samples dried by the combination of hot air with ultrasound showed a faster rehydration rate and a better reconstitution property compared with those dried by hot air.3.The effects of packing and storage conditions on the storage stability of dried water lily petals were studied.The dried petals were packed by using PE and vacuum packages and stored for two months at 4℃ and 25℃,respectively.The results showed that the total numbers of colony,mold,and escherichia coli of dried petals during storage were qualified.Low temperature and vacuum environment could effectively reduce water content and remain Vc and total phenol contents and their antioxidant activities.During the storage,the water content of steam blanching samples stored at 4℃ after vacuum packaging increased by 13.6%,and the Vc,total phenol contents,ABTS free radical scavenging ability and Fe2+ reducing ability decreased by 17.7%,12.0%,23.0%and 16.0%,respectively,while those of the soaking treatment samples reduced by 13.8%,18.6%,13.0%,10.0%and 17.0%,respectively.The variations of all indexes were the lowest,suggesting that this method was suitable for the long-term storage of the petals.