Mould Contamination Of Camellia Oleifera Seeds During Storage And Its Effect On The Quality Of Camellia Oleifera Seeds Kernel

Camellia oleifera is an important woody economic oil crop growing in hilly areas of southern China.Camellia oleifera seed oil is rich in oleic acid and vitamin E,tea polyphenols,squalene,beta-sitosterol and other bioactive substances.It can be compared with the best woody vegetable olive oil in the world and is known as "Oriental olive oil".Camellia oleifera seeds are only harvested in autumn every year and are supplied for the whole year's Camellia oleifera seed oil extraction and processing.Camellia oleifera seeds contain various nutrients for microbial growth.It is wet and rainy in winter and spring in southern China.When Camellia oleifera seeds are stored improperly,it is easy to cause contamination of mold growth and reproduction,reduce nutritional value,and even produce mycotoxins,resulting in the hazards of Camellia oleifera seed oil quality and food safety.Therefore,it is very important to study the microbial species and their effects on the quality of Camellia oleifera seeds during storage and formulate corresponding measures to control them.The author carries out relevant research work and draws the following conclusions:(1)High throughput sequencing was used to preliminarily analyze the main fungi contaminated by Camellia oleifera seed kernel and shell during storage.The results showed that most of the fungi in the Camellia oleifera seed shell and kernel were the same.The main fungi are Aspergillus(81.38%,74.40%),Penicillium(0.46%,0.58%),Fusarium(0.07%,0.01%),Wallemia(10.63%,18.40%),and Mortierella(0.08%,0.07%).The main strains of Camellia oleifera seed kernel and shell are Aspergillus cibarius,Aspergillus penicillioides and wallemia mellicola.(2)Biolog-FF microplate technique was used to analyze the species structure of culturable fungi in the Camellia oleifera seed shell and kernel to 95 carbon sources in 8 categories.The results showed that the culturable fungi on the Camellia oleifera seeds shells could utilize the carbon sources of alcohols,carbohydrates and their derivatives,amino acids,carboxylic acids and their derivatives,and these fungi had higher utilization rates of 38 carbon sources,such as N-acetyl-D-glucosamine,D-gluconic acid,glycyl-L-glutamic acid,D-mannitol,succinamic acid.The culturable fungi on the Camellia oleifera seeds kernels have a strong ability to utilize three kinds of carbon sources: alcohols,carbohydrates and their derivatives,polymers.Among the 9 carbon sources that can be utilized by Cultured Fungi in stored camellia seed kernels,except for 6 carbon sources such as N-acetyl-D-glucosamine,i-gibberellin,beta-methyl-D-glucoside,which are the same as those available by Cultured Fungi in stored Camellia oleifera seed shell,they also exhibit unique metabolic ability to glycerol ? Adonitol and dextrin.The microbial biomass,metabolic activity,carbon source utilization ability and diversity index of culturable fungi from stored Camellia oleifera seed shell were higher than those of stored Camellia oleifera seed kernels.The number of culturable fungi in Camellia oleifera seed shell was more than that in Camellia seed kernel,and the community was more complex.(3)The effect of contaminated fungi on the quality of Camellia oleifera seeds was studied.11 strains were isolated from moldy Camellia oleifera seeds by culturable fungi isolation.By morphological characteristics and ITS sequence analysis,the 11 strains were identified as Cladosporium tenuissimum(JK4),Aspergillus tamarii(JK1,JR16),Aspergillus japonicus(JK7,JK13),Penicillium oxalicum(JK2),Penicillium expansum(JK6,XK9),Penicillium commune(JR10)and Penicillium amaliae(XR15,XK15).Eleven strains were inoculated into newly-produced shelled and undamaged Camellia oleifera seed kernels.It was found that during storage,the total sugar content of Camellia oleifera seed kernels showed a downward trend,while the acid value and peroxide value showed an upward trend.The total sugar content of Camellia oleifera seeds inoculated with JK6(Penicillium commune),JR10(Penicillium expansum)and XR15(Penicillium amaliae)decreased most rapidly,and the acid value and peroxide value increased fastest.(4)Based on the non-target metabonomics method of GC-TOF-MS,the differences of metabolites between three kinds of fungi contaminated Camellia oleifera seed kernels and non-contaminated Camellia oleifera seed kernels were studied.Through qualitative and quantitative analysis of metabolites,66 metabolites(Penicillium expansum vs CK),43(Penicillium commune vs CK)and 87(Penicillium amaliae vs CK)were identified with significant differences.Among the pathways in which fungi affect the metabolic model of Camellia oleifera seeds,the major ones are: beta-Alanine metabolism,Alanine,aspartate and glutamate metabolism,Glycine,serine and threonine metabolism,Pantothenate and CoA biosynthesis,TCA cycle,Galactose metabolism,Pentose phosphate pathway,Starch and sucrose metabolism and Glycerophospholipid metabolism.The results showed that the growth and reproduction of contaminated fungi affected TCA cycle,carbohydrate metabolism,amino acid metabolism and fatty acid catabolism.At the same time,it also destroys the structure of cell membrane and the unilateral membrane encapsulating lipids,thus exposing oil to oxidation.