The Effect of Vacuum Pulsation Drying Temperature on the Physicochemical Properties and Microstructure of Daylily
Because the water content of fresh daylily is high,the quality of fresh daylily decreases rapidly after harvest.It is very important to explore the suitable processing methods for extending the shelf life of daylily.The effects of dif-ferent vacuum pulsating preventive technology(PVD)conditions on nutritional composition,color,flavor,rehydration rate and microstructure of daylily were investigated,so as to improve the quality of dried daylily.The effects of different dry-ing temperatures(65,70,75,80 ℃ and 85 ℃)on the quality of daylilies were studied under the conditions of vacuum holding time(10 min)and atmospheric holding time(5 min)using PVD equipment.Furthermore,principal component analysis and partial least squares method were used to discriminate the drying process,flavor composition and character-istic taste of daylily.The results showed that the content of free amino acids in naturally dried(CK)daylily was the highest,at 0.858 mg/g.The △E value was the highest,at 16.47,further indicating that the overall quality of the sample was poor.After PVD drying,daylily has a bright and vibrant color,good rehydration performance,and significantly in-creased protein and flavonoid content.When PVD was 80 ℃,the primary color retention rate was the highest(△E=7.28),and the free amino acid content was the highest(0.818 mg/g).When PVD was 75℃,the protein(7.331 g/L)and Ga(1 072.445 pg/kg)content in the sample was the highest.When PVD was 70 ℃,the proportion of β-fold and α-helix content in the daylily sample was the highest,at 35％.When PVD was 65 ℃,the flavonoid content(1.653 mg/g)and rehydration rate are the highest(3.04％),and inorganic sulfides,nitrogen oxides,and terpenoids can be well re-tained.In addition,partial least squares discriminant analysis revealed that aspartic acid,histidine,serine,glutamic acid,and alanine are characteristic taste substances of daylily.Conclusion:Different PVD drying temperatures lead to differences in the physicochemical properties and nutritional components of daylily.The research results can provide suit-able process parameters to meet different quality attribute requirements and consumer acceptance.
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