Modulation Mechanism Of Water Activity And Temperature On Aspergillus Flavus Growth And Aflatoxin Production In Rice

Rice is the major grain crop in the world,and more than half of the population in our country eat rice.But rice is easily contaminated by Aspergillus flavus during storage and processing which can produce carcinogens-aflatoxin?AFT?.Once entering the body,it will seriously threaten the health of the human.As rice is often contaminated by Aspergillus flavus,a large amount of grain has been lost and huge economic losses have been caused to the grain industry in China.In order to reduce rice pollution and improve agricultural productivity,we studied the effects of different water activities?a_w?and temperature on Aspergillus flavus growth and toxin production in rice,and the molecular mechanism of regulating AFB₁ production.The main conclusions are as following:1.Effects of temperature on the growth and toxicity of Aspergillus flavus on paddy.The results show that the growth and toxin production of Aspergillus flavus are completely inhibited when the temperature is 20 and 25?.The growth of Aspergillus flavus is better at 28-40?,and the best growth temperature is 37?.The adaptive temperature range of the growth for Aspergillus flavus is28-37? and the optimum temperature is 37?.When the temperature is 42?,there is not aflatoxin production in rice due to the high temperature.2.Effects of water activity on the growth and toxicity of Aspergillus flavus on paddy.The results show that with the increasing of a_w,the better the growth of Aspergillus flavus.When the temperature is at 25-42?,Aspergillus flavus grow best at a_w 0.94,the growth of Aspergillus flavus in rice after a_w 0.99 is obviously weakened.3.Effect of temperature on the growth and toxicity of Aspergillus flavus on rice.The results show that the low temperature?T?20??is not suitable for the growth of Aspergillus flavus,the growth of Aspergillus flavus in low temperature conditions are almost completely inhibited,The growth of Aspergillus flavus is the most vigorous on rice at 33?.At all water activity,Aspergillus flavus is hardly grown at 42?.4.Effects of water activity on the growth and toxicity of Aspergillus flavus on rice.The results show that the different water activity of rice has different effects on the growth and toxin production of Aspergillus flavus.At the same temperature,the water activity of rice is different,and the amount of bacterias are carried by them varied significantly.At the temperature of 20-42? and a_w 0.80-0.85,the growth of Aspergillus flavus is similar,and the number of bacteria is less.In the case of low water activity,Aspergillus flavus from rice is almost no poison.When a_w gradually increase,the total AFB₁ content in rice increase firstly and then decrease.The suitable a_w was 0.90-0.96,and the best a_w was 0.96 of toxin production,while the growth of Aspergillus flavus increased firstly and then decreased,and it grew most vigorously at a_w 0.90.5.The expression of important genes controlling aflatoxin biosynthesis in rice was detected by fluorescence quantitative PCR detection technology,so as to reveal the regulation mechanism of water activity and temperature on aflatoxin related genes.The results show that the expression of toxin producing genes could be promoted when the temperature is 25?.However,Low temperature affects the activity of related proteins during gene transcription,and the aflatoxin production of Aspergillus flavus decreased.It is inhibited the expression of sporulation genes and some important structural genes when the temperature is 37?,thereby inhibiting the generation of toxin.Compared with a_w 0.96,the expression of toxin genes have decreased when the a_w is 0.90,which led to the decrease of AFB₁ synthesis.