Study On The Volatile Flavor Compositions Of Chlorella Pyrenoidosa

Chlorella pyrenoidosa is a very important and common edible microalgae.When C.pyrenoidosa is used as food or aquatic feed,it will directly or indirectly bring undesirable odors to food and aquatic products fed on it,and directly impact food acceptability.In this research,C.pyrenoidosa was cultured for study of main research object.Firstly,electronic nose and headspace solid-phase microextraction-gas chromatography-mass spectrometry(HS-SPME-GC-MS)techniques were applied to identify volatile compounds and analysis the volatile profiles of C.pyrenoidosa and other four common edible(feeding)microalgae and the key unfavorable components were screened.Then,by changing the culture conditions of C.pyrenoidosa,the changes of volatile components in the growth process were explored,and the key undesirable volatile components that changed the most during the growth process were determined.A preliminary study on the formation mechanism of bad flavor was carried out by binary simulation and transcriptome sequencing.The main contents and results of this study were as follows:(1)The volatile compounds of C.pyrenoidosa and four common food(feeding)microalgae were extracted,and the volatile profiles were detected by electronic nose technology and headspace solid-phase microextraction-gas chromatography-mass spectrometry.The results showed that aldehydes,alcohols,and ketones were the main volatile compounds in the five microalgae,and these compounds with low olfactory thresholds played a major role in flavor and constituted their characteristic flavor profile.Among them,hexanal,1-octen-3-ol,(E,Z)-2,4-decadienal and hexanol were the main unpleasant flavor compounds,which were ubiquitously present in five microalgae and endowed the microalgae with fat,fishy,and grassy odors.(2)The changes of volatile components during the growth of continuousilluminated-autotrophic culture,photoperiodic-autotrophic cycle light culture,continuous-illuminated mixtrophic culture,photoperiodic-mixtrophic culture and heterotrophic culture of C.pyrenoidosa were analyzed.Through PCA analysis and significance analysis,it was determined that aldehydes and alcohols were the main causes of flavor changes,among which hexanal and hexanol were the substances with the highest content and the greatest impact on flavor.(3)A binary simulation system was established to study the formation pathways of hexanal and hexanol,the key undesirable flavor compounds in C.pyrenoidosa.The fatty acid composition and related enzyme activities of C.pyrenoidosa from two culture patterns were determined,which were continuous-illuminated-autotrophic culture and continuous-illuminated-autotrophic plus followed dark for 12 h or24 h culture.A crude enzyme solution was then extracted from the cultured algal mass to simulate the enzymatic oxidation reaction of linoleic acid to analyze its products.The results showed that the composition and content of fatty acids 、hexanal and hexanol in C.pyrenoidosa changed after the dark incubation,and the enzyme activity did not change significantly with the change of illumination.The enzymatic oxidation of linoleic acid generated volatile compounds such as hexanal,(E)-2-heptenal,(E)-2-hexenal,and hexanol,which have an important effect on flavor.In addition,changes in illumination exhibited an impact on the generation of volatile compounds,and also caused an important impact on flavor.(4)The transcriptomes of C.pyrenoidosa cultured in the previous mentioned,three culture conditions were determined.The differential gene KEGG analysis showed that the change of illumination caused changes in the oxidative phosphorylation pathway and peroxidase pathway of photosynthesis,and the genes related to photosynthesis had significantly up-regulated or down-regulated,thereby affecting the synthesis of organic compounds,fatty acids and the expression of enzymes related to the metabolic pathways,which in turn affect the flavor of C.pyrenoidosa.