Study On Occurrence Mechanism Of Internally Moldy Sunflower Seeds And Nondestructive Detection Method By Near-infrared Spectroscopy

Food safety issues caused by mold contamination have received widespread attention worldwide.However,research on nut crops,such as sunflower seeds,has been relatively rare.Sunflower seeds are prone to internal mildew after a worrisome level of fungi contamination under suitable environment.Most internally moldy seeds which have a normal-looking shell cannot be recognized by the appearance.For this reason,accidental ingestion is frequent,negatively affecting human health,consumer experience and the development of sunflower-seed industry.In view of the problems such as the unclear internal mildew occurrence mechanism as well as the lack of methods to control internal mildew,the sunflower seeds from the main producing areas in China were used to analyze the relationship between fungal community change and internal mildew occurrence at different stages throughout the production cycle by using high-throughput sequencing,to analyze internal mildew occurrence mechanism from the relationship among host,microorganism and environment and to develop a nondestructive mildew grade discrimination method based on near infrared spectroscopy(NIRS).The main research results are as follows:(1)Clarifying the main internal mildew occurrence mechanism of the sunflower seeds.High-throughput sequencing was used to accurately characterize the fungal communities of the sunflower-seed kernels in the main producing area for three consecutive years.The results indicated that almost all of the fungal genera identified represent a total of eight genera and five phyla.Alternaria had proven to be the predominant fungi as well as mildew-causing pathogenic fungi.Additionally,sequencing showed that the fungal genera and the relative abundance in the mildewed seed kernels pre-storage are similar to those in the mildewed seed kernels post-storage,indicating that the sunflower seeds are most vulnerable to internal mildew during the field-planting stage with Alternaria as the main source.And most sunflower-seed kernels have been infected by the mould during the field-planting stage,however,which abundance are not enough to form visible mildew.Our research also found that that internal mildewing did not significantly alter the composition of the fungal community of sunflower seed kernels,with fungal community characteristics different from common crops with external mildew.(2)Exploring the environment mechanism determining the occurrence of internal mildew during storage stage and large-scale internal mildew controlling method.The relationship between fungal community and environmental factors was further studied by using high-throughput sequencing and β-diversity analysis method based on artificial simulation storage conditions.After storing below the critical threshold(normal-temperature warehouse,relative humidity(RH)67%),the microbial community hardly changed over six-month storage.When RH exceeded the critical threshold,internal mildew signs appeared with the change of fungal community and the mildew occurrence rate increased with the extension of storage time.So,when the storage humidity is higher than the critical threshold,it is necessary to explore largescale mildew controlling method.When the irradiation dose exceeded 4 kGy,the mildew occurrence rate in artificially simulated high-humidity environment can be significantly reduced from 26%(2 kGy)to 7%,with acid value and peroxide value significantly increasing.For maintaining the original edible quality to the maximum extent.So,4 kGy can be used as the lowest effective radiation dose.(3)Studying on metabolites of internal mildew.Liquid Chromatograph-Mass Spectrometer(LC-MS)non-targeted metabonomics was used to further study internal mildew mechanism from the metabolite level by analyzing the component changes during mildew.Fatty acids,amino acids and other substances were found to be the main components related to mildew based on the joint use of metabonomics and mid-infrared spectroscopy,with great potential to discriminate mildew grade as important markers.(4)Establishing nondestructive internal mildew degree discrimination method based on NIRS.For internal mildew from the field stage is not easily avoided by current technology,non-destructive testing technology could be a key technology for quality control during storage and processing.However,The difference of metabolites among different mildew degrees provides the possibility to non-destructively discriminate the internal mildew grades of shelled sunflower seeds based on NIRS.And this method was realized by near-infrared diffuse reflectance&near-infrared diffuse transmission(NIRr-NIRt)fusion spectra coupled with one-dimensional convolution neural network(1D-CNN).The fusion spectral model based on 1D-CNN yielded a prediction accuracy(PA)of 97.60%and 94.04%,respectively for the training and the test set.which are superior to those of the single spectra.Overall,the paper analyze the occurrence mechanism of internal mildew from the relationship among host,microorganism and environment,proposes large-scale mildew-controlling method during storage and develop a nondestructive internal mildew degree discrimination method based on NIRS,providing theoretical and technical support for studying internal mildew problems of sunflower seeds and other nuts.