Effect Of Genetic Difference And Cultivation Locations On The Oat(Avena Sativa L.) Flavor And Microbial Flora On Oat Grains

As one of the minor grain crops in China,oat has been gaining growing recognition of its nutritional value,mainly due to the function of reducing postprandial glucose and regulating blood lipids,with increased consumption.Oat porridge and oat meal are popular oatfoods in China.One of the important reasons why people like these foods is related to its strong and unique aroma.However,little is known about the composition of its flavor and the factors affecting its flavor.In most areas of oats planting regions in China,the crop often encounters rainy season during the harvest period.The surface of the grain is prone to microbial infection,which affects the appearance and quality of the grain and subsequent product processing and flavor.In order to clarify the effects of genetic background,locations on flavor substances of oat products and microbial of grain surface,we studied the differences of flavor substances and surface microflora of grains produced in different varieties and locations.The major results are summarized as following:We compared the volatile profiles using headspace solid phase microextraction gas chromatography–mass spectrometry of oat porridge(OP)and oat meal(OM),which were of different processing and cooking methods,from different cultivars,and analyzed the effect of cultivation locations on oat volatile features.Apart from the 35 volatiles shared by OP and OM,there were 23 and 24 volatiles specific to OP and OM,respectively,with the later showing more toasting and frying-related volatiles due to the dry frying process of the grains before milling.Principle component analysis of the volatiles of OP and OM from 16 cultivars showed that they were clustered into two groups,and four cultivars were clustered together,independent of processing and cooking methods.Though genetic clustering and population genetic structure analysis,16 oat varieties can be divided into three separate subgroups.Three varieties,Bayou No.1,Bayou No.8 and Huazao No.2 showed unique flavor substances comparing with others.The unique flavor of these varieties could be that their genetic background were different from the other varieties.The oat volatile profiles of varieties grown in three regions of north China were dependent on the cultivation locations rather than cultivars,regardless of OP or OM,with those from Datong ofShanxi Province and Zhangjiakou of Hebei Province clustered together.The location effect could be due to significant less precipitation in the two regions above than the other region,Ulanqab of Inner Mongolia.Interestingly,some volatile profiles related to mold on the grain surface were detected in oat-based foods.We sampled surface microorganism of Pinyan no.2 grains planted on the hill and plain of the same region,and analysed the bacteria by sequencing the amplified 16 S V4 region.Our results showed that the bacterial flora abundance and bacterial diversity of moldy seeds from plants on the hill were higher than that of normal seeds,from the plain.Pseudomonas and Erwinia,which were dominant species,showed significant difference in abundance between normal and moldy grains.The values of their abundance on moldy grains were 1539 and 1975,whereas the values of their abundance on normal grains were 136 and182.These samples above were also analysed by fungal ITS metagenomic sequencing.Our results showed that Alternaria,Pyrenophora and Gibberella,which were dominant species,differed between grains from the hill and the plain.The values of their abundance of moldy grains were 5810,3781 and 1085,whereas the values of their abundance of grains from the hill were 1144,2260 and 124.By the isolation and molecular identification of the pathogenic fungi,we found that Alternaria might be the main pathogenic fungus on the oat grains.By culture and greenhouse inoculation of Alternaria,it was further confirmed that mould of oat grains was caused by Alternaria,which was mainly affected by environment including temperature and humidity,and fungal abundance in the environment.The surface fungal communities of 9naked oat varieties in the same area were analyzed by metagenomic sequencing.Our results showed that 37 genera were identified from the fungal communities on the grain surface of 9 naked oat cultivars.The dominant fungi included Alternaria(37.6%),Gibberella(14.8%)and Davidiella(6.5%).According to the composition characteristics and hierarchical clustering analysis,Alternaria was a dominant species in the grains of most cultivars except for 2006-2.Yanke no.2 and Baiyan no.2 showed the highest abundance,and there was significantly difference among varieties.Fungal flora on the grain surface of Bayou 13 planted in 10 ecological areas were analyzed by ITS sequence.Our results showed that the dominant fungi on the grain surface were mainly Alternaria and Davidiella.Davidiella was the dominant flora on the grains from the southern mountains of Tibet and the Haidong regions of Qinghai province,whereas Alternaria was the dominant flora on the grains from other regions.Shifting from one to the other was observed between these two fungi in different ecologicalregions,and their growth was negatively correlated.During the culture of fungi,two strains with antagonistic effects on Alternaria were identified.By inoculation and the molecular identification,Trichothecium roseum and Bacillus amyloliquefaciens subsp.Plantarum were identified as antagonistic strains against Alternaria.In conclusion,there results revealed that the unique volatile profiles from the two popular oat-based foods,and these profiles were mainly affected by the locations more than genetic background,and microorganisms on the grain surface could also lead to the production of some unique flavor substances.The characteristics of bacterial and fungal diversity,and the dominant fungal genera for moldy naked oat grain were revealed.Alternaria may be the main pathogenic fungus for moldy grains,and there was difference in the structure and abundance of surface microbials of oat grains among varieties and locations.Finally,we obtained two strains that showed antagonism effect against the dominant fungi Alternaria of grain surface in the traditional oat growing regions.Therefore,the results above could provide a theoretical foundation for the breeding of a new variety for oat processing,and for practical guidance and theoretical basis of the biological control strategy of moldy oat grains.