Study On The Formation Regularity Of Volatile Compounds In Sea Cucumber Peptide Powders (SCPPs) Induced By Moisture Absorption And The Establishment Of Its Fingerprints

The study belongs to the general project of the national natural science foundation of China(31772018).The sea cucumber peptide powders(SCPPs)is commonly used in the products development with high quality and value in the form of nutrition compatibility as basic material powder.However,during processing and storage the peptide powders has metamorphosing phenomenon such as moisture absorption,sticky,getting agglomeration,and off-flavor forming,resulting in loss of functionality and lowered quality.At present,there are few studies on the hygroscopic problems of sea cucumber protein peptide powder at home and abroad.In this study,the effects of hygroscopic behavior on SCPPs were investigated using a variety of detection techniques.(1)The water migration rules of SCPPs during storage under different conditions were analyzed by DVS,LF-NMR and MRI technology.The hygroscopicity of SCPPs can be decreased in low temperature and low humidity environment.The moisture in SCPPs was in three states: bound water,immobilized warer and free water.Water vapor in the initial storage environment was gradually absorbed into the peptide powders and mainly as the form of bound water and immobilized warer.The internal binding water and immobilized warer migrated and converted each other.With the extension of storage time,water vapor is mainly transformed into bound water.And part of immobilized warer also gradually migrated to the bound water until bound water reached adsorption saturation.Then immobilized warer and free water also become saturated after slowly increasing.The water in SCPPs stored at 25? and 75% RH reached saturation after 15 days,and the distribution of three kinds of water become stable state.According to the above results,we established the hygroscopic kinetic model of SCPPs during storage under the storage environment with high humidity(25? / 75% RH).(2)The influence of moisture absorption behavior on structures of SCPPs stored at 25? and 75% RH was analyzed by EPR,SEM,XRD,CD,HPLC,FL,UV-Vis and FT-IR technologies.With the prolongation of storage time,the antioxidant activity of SCPPs gradually decreased and the regular spherical crystallization deformed and even collapsed.And the secondary structure also gradually changed.The ?-sheet of peptide molecules gradually changed to random coil and ?-helix.After 90 days of storage,most functional groups of SCPPs changed significantly and new functional groups were produced.In addition,the contents of most amino acids except histidine and tryptophan increased gradually during the hygroscopic process and reached the maximum at 15 days.(3)The characteristic fingerprints of typical hygroscopic behavior of SCPPs was constructed by HS-GC-IMS technology.It was found that the moisture absorption behavior could induce the change of volatile substances of SCPPs.The characteristic fingerprints of SCPPs stored in four environments(high hygroscopic and airtight,high hygroscopic and aseptic,low hygroscopic and airtight,low hygroscopic and aseptic)were constructed.it was illustrated that aseptic and dry environment could effectively control the influence of hygroscopic behavior of SCPPs.(4)The relationship between the hygroscopic behavior and microbial community in SCPPs was investigated by 16 S r DNA sequencing technique.The hygroscopic behavior of SCPPs stored at 25? and 75% RH can induce the aggregation of Firmicutes,Proteobacteria and Bacteroidetes,as well as inhibit the growth of Cyanobacteria.The storage environment with low humidity can inhibit the growth of Firmicutes and Proteobacteria.The metamorphism of SCPPs in high humidity storage environment was related to Firmicutes and Proteobacteria,mainly including Bacillus,Psychrobacter and Atopobium.Therefore,the dry environment with humidity low can effectively reduce the metamorphism of SCPPs by inhibiting the growth of Firmicutes and Proteobacteria.(5)The variation of volatile compounds content induced by hygroscopic behavior of SCPPs was investigated by P&T-GC-MS technique.When the SCPPs were stored at 25? and 75% RH for 5 days,the types and contents of volatile compounds increased significantly.After 15 days of moisture absorption,the concentration of volatile compounds reached the maximum.The concentration of aldehydes,heterocyclic compounds(2-pentyl furans),alcohols and esters increased significantly during the hygroscopicity process.There were some new compounds produced after 15 days of moisture absorption,such as(Z)-3,5-dimethyl-2-(1-propenyl)-pyrazine and diisobutyl phthalate.These volatile compounds with large concentration were as the main off-flavor.The formation of off-flavor was mainly related to Maillard reaction,esterification reaction,fat oxidation and microbial metabolism.