| Aflatoxins （AFs） are the secondary metabolites produced mainly by Aspergillus flavusand Aspergillus parasiticus.Up to the present, the aflatoxins are one of the most acutely toxicand carcinogenic compounds. They were identified as the Classâ… carcinogens by Food andAgriculture Organization of the United Nations （FAO） and Word Health Organization（WHO）, which severely contaminate agricultural commodities and thus pose serious healthhazards to both humans and domestic animals. Although most countries in the world nowhave limitations for the maximum tolerated levels of aflatoxins in food, the contamination ofthese compounds is still a problem.Fungal β-glucans have established a close relationship with aflatoxin, which provides anew perspective to control the aflatoxin contamination. In this paper, various kinds of glucanswere investigated for their inhibitory effects on the aflatoxin product. The results showedlentinan exhibited the highest inhibitory activity. At the same time, we made some structuralmodifications to lentinans, and expected to achieve products with different inhibitory effectsto understand some information of lentinan associated with AF biosynthesis. The resultsshowed as follows:1. Various kinds of glucans were investigated for their inhibitory effects on the aflatoxinproduction, including lentinan, pustulan, oat β-glucan, peanut shell cellulose, chitosan andpectin. The results showed not all the β-glucans could inhibit AF biosynthesis. The resultsshowed lentinan at the concentration of200μg·mL-1exhibited the highest inhibitory activity（complete inhibition）, and deviating from this concentration its activity actually decreased.The inhibitory rate of600μg·mL-1lentinan on AFB1production dropped to18%.2. Derivatives of lentinan were prepared by structural modifications includingcarboxymethylation, sulfation, and phosphorylation, and FT-IR spectra analysis wasperformed to confirm these structural modifications. All the derivatives of lentinan in thisstudy still held the β-linkage in structure, whereas they exhibited different inhibition modesagainst AF formation. The results showed that lentinan and its derivatives did not show anysignificant inhibition against hypha growth. During the3derivatives analyzed, all of them displayed antiviral capability against AF and2derivatives were much stronger than lentinan.The lowest completely-inhibitory concentration of the carboxymethylated derivatives to AFproduction was200μg·mL-1, and notably this inhibition kept stable with the increasingconcentration.3. Further RT-PCR was performed to understand the effects of lentinan and itscarboxymethylated derivatives on some genes transcriptions associated with AF biosynthesis.It was surprised to find that both lentinan and its carboxymethylated derivatives promoted thetranscription of aflS and aflR in the A. flavus at an AF-production-inhibitory state, which wasfar different from the down-regulation of aflR transcription in A. parasiticus by β-glucanextract from Lentinula edodes culture. Exposure of lentinan or its carboxymethylatedderivatives could lead to a higher transcription level of yapA in A. Flavus, which seemed toanswer their inhibition to AF formation well. Moreover, lentinan could delay the transcriptionof aflQ, but its carboxymethylated derivatives promoted the transcriptions of all the testedgenes, which suggested a post-transcriptional regulation resulted in this inhibition to A. flavusby carboxymethylated lentinan. |
