Polyphenols Changes In Tea Fermentation And The Inhibitory Effect On Aflatoxin Production

China’s tea planting area and output all rank first in the world. In recent years, excessiveheavy metal and pesticide residue in tea product increase harshly due to environmentalpollution and lack of standardized processing technology, which results in severe food safetyproblem. Aflatoxin is the most toxic and cancer-causing carcinogen in human beings, and itis classified as Class IA (extremely hazardous) by the International Agency for Research onCancer. Current research shows that tea is also faced with the risk of contamination from thetoxin. At present, the key point of aflatoxin contamination in tea is unclear. In this project, weused green tea collected in summer from Xinyang city as the research object to explore thepolyphenols change in the non-fermentation and microbial fermentation tea process, screenedthe active polyphenols related to Aspergillus flavus contamination, and studied the molecularmechanisms for aflatoxin production inhibition.1. Facing the problem of “false positive” in the diagnosis of AFB1-polluted teaproducts, we constructed a one-step indirect competitive ELISA protocol based on thepolyclonal antibodies (pAbs) against AFB1. The linear range of this protocol for the AFB1inthe PBS buffer is between0.14and126ng/mL, and it’s values of IC50and LOD were3.85ng/mL and0.06ng/mL respectively. This immunoassay was a promising alternative for fastand convenient detection on large batch samples, and remained the high assay accuracy bycomparison with the results by UPLC-MS/MS. This protocol was then utilized to detect theAFB1existence in the tea products on sale, and the results confirmed the existence of AFB1-contamination potential in tea products.2. The results showed that polyphenols contained in green tea are mainly gallic acid,epicatechin, epigallocatechin gallate and epicatechin gallate epicatechin gallate and so on.When green tea was inoculated with fungi and yeast, polyphenol content decreased withfermentation extension. When inoculated with Aspergillus niger with yeast, the polyphenolscontent decreased from31.16%to5.32%. Epigallocatechin gallate content in green reached26.59mg/g, but decreased rapidly after7d of fermentation, and its amount reduced to0.27mg/g. Quercetin and kaempferol content in green tea were low and their content fluctuatedduring fermentation. 3. The total free amino content in green was79.03mg/g. As natural and artificialinoculation fermentation proceeded, the amino acid increased at first and then decreased. Inthe natural fermentation process, the total amino acid content reached its highest level of80.78mg/g after7d.4. The results showed that most polyphenol monomer could inhibit aflatoxin B1production, but their activity concentration was different. Quercetin and gallic acid had higherinhibitory activity than other catechin polyphenols. But non-ester type catechin derivativeshad better cytotoxic activity than ester catechin. Except for quercetin, polyphenols could notinhibit Aspergillus flavus growth even at the highest concentration. The inhibition of teapolyphenols on AFB1might have relationship with antioxidant activity. However, theantioxidant capacity of various monomers and their ability to inhibit the toxin was notconsistent.5. So we aimed the antioxidant system of Aspergillus flavus and studied the toxin genesexpress after quercetin treatment. The results confirmed that quercetin treatment couldalleviate the oxidative stress of Aspergillus flavus. Quercetin was able to activate thetranscription factor Yap1in antioxidant system to increase antioxidant enzyme activity. Thisinduction was likely to be key factor for quercetin inhibition AFB1. The quercetin not onlydecreased AflR, but also AflS expression. And AflS could regulate toxin production bycombining AflR expression gene, thus inhibiting AflR was likely to be the key effect forquercetin inhibited AFB1, which was also associated with activation of antioxidant systems ineasing the fungi oxidative stress in vivo. In the case of AflR downward, the toxin geneexpression was inhibited. Hence, quercetin can be employed to be an efficient aflatoxinsynthesis inhibitor and incubate great potential.6. The death rate arising from stroke by SAH arrives at12%approximately, andmitochondrial misfunction is the early characteristic of SAH. In this study neuro-protectiveeffects of tea polyphenols were explored in a SAH model by monitoring the changes ofmitochondrial membrane potential, ATP content and cytochrome c (cyt c) at3h,6h,12h,24h and72h post the combination with oxyhemoglobin. The results showed that tea polyphenolscould enhance neuroprotective effects by inhibiting polarization of mitochondrial membranepotential, increasing ATP content, and blocking cyt c release.