Effects of rutin and its derivatives on citrinin production by Monascus aurantiacus Li AS3.4384 in liquid fermentation using different types of media

Research on pear residue dietary fiber and Monascus pigments extracted through liquid fermentation

Pear residue, a byproduct of pear juice extraction, is rich in soluble sugar, vitamins, minerals, and cellulose. This study utilized Monascus anka in liquid fermentation to extract dietary fiber (DF) from pear residue, and the structural and functional characteristics of the DF were analyzed. Soluble DF (SDF) content was increased from 7.9/100 g to 12.6 g/100 g, with a reduction of average particle size from 532.4 to 383.0 nm by fermenting with M. anka. Scanning electron microscopy and infrared spectroscopic analysis revealed more porous and looser structures in Monascus pear residue DF (MPDF). Water-, oil-holding, and swelling capacities of MPDF were also enhanced. UV-visible spectral analysis showed that the yield of yellow pigment in Monascus pear residue fermentation broth (MPFB) was slightly higher than that in the Monascus blank control fermentation broth. The citrinin content in MPFB and M. anka seed broth was 0.90 and 0.98 ug/mL, respectively. Therefore, liquid fermentation with M. anka improved the structural and functional properties of MPDF, suggesting its potential as a functional ingredient in food.

Adding genistein or luteolin decreased the yield of citrinin and without reducing pigments in yam solid-fermentation by Monascus

BACKGROUND

Chinese yam fermented by Monascus, namely red mold dioscorea (RMD), has the potential of treating diseases. However, the production of citrinin limits the application of RMD. In the present study, the fermentation process of Monascus was optimized by adding genistein or luteolin to reduce citrinin yield.

RESULTS

The results showed that citrinin in 25 g of Huai Shan yam was reduced by 48% and 72% without affecting the pigment yield by adding 0.2 g of luteolin or genistein, respectively, to a 250-mL conical flask after fermentation for 18 days at 28 °C, whereas the addition of luteolin increased the content of yellow pigment by 1.3-fold. Under optimal conditions, citrinin in 20 g of iron bar yam decreased by 55% and 74% after adding 0.2 g of luteolin or genistein. Luteolin also increased yellow pigment content by 1.2-fold. Ultra HPLC coupled to quadrupole time-of-flight mass spectrometry was used for the preliminary analysis of Monascus fermentation products. It was found that the amino acid types in RMD are similar to those in yams, but there are fewer polysaccharides and fatty acids.

CONCLUSION

The results obtained in the present study showed that the addition of genistein or luteolin could reduce citrinin on the premise of increasing pigment yield, which laid a foundation for the better use of yams in Monascus fermentation. © 2023 Society of Chemical Industry.

Effect of Exogenous and Endogenous Ectoine on Monascus Development, Metabolism, and Pigment Stability

Monascus, a key player in fermented food production, is known for generating Monascus pigments (MPs) and monacolin K (MK), possessing bioactive properties. However, the limited stability of MPs and mycotoxin citrinin (CTN) constrain the Monascus industry. Extremolytes like ectoine, derived from bacteria, exhibit cytoprotective potential. Here, we investigated the impact of ectoine on Monascus purpureus ATCC 16365, emphasizing development and secondary metabolism. Exogenous 5 mM ectoine supplementation substantially increased the yields of MPs and MK (105%-150%) and reduced CTN production. Ectoine influenced mycelial growth, spore development, and gene expression in Monascus. Remarkably, ectoine biosynthesis was achieved in Monascus, showing comparable effects to exogenous addition. Notably, endogenous ectoine effectively enhanced the stability of MPs under diverse stress conditions. Our findings propose an innovative strategy for augmenting the production and stability of bioactive compounds while reducing CTN levels, advancing the Monascus industry.

Linoleic acid functions as a quorum-sensing molecule in Monascus purpureus-Saccharomyces cerevisiae co-culture

When Monascus purpureus was co-cultured with Saccharomyces cerevisiae, we noted significant changes in the secondary metabolism and morphological development of Monascus. In yeast co-culture, although the pH was not different from that of a control, the Monascus mycelial biomass increased during fermentation, and the Monacolin K yield was significantly enhanced (up to 58.87% higher). However, pigment production did not increase. Co-culture with S. cerevisiae significantly increased the expression levels of genes related to Monacolin K production (mokA-mokI), especially mokE, mokF, and mokG. Linoleic acid, that has been implicated in playing a regulating role in the secondary metabolism and morphology of Monascus, was hypothesized to be the effector. Linoleic acid was detected in the co-culture, and its levels changed during fermentation. Addition of linoleic acid increased Monacolin K production and caused similar morphological changes in Monascus spores and mycelia. Exogenous linoleic acid also significantly upregulated the transcription levels of all nine genes involved in the biosynthesis of Monacolin K (up to 69.50% higher), consistent with the enhanced Monacolin K yield. Taken together, our results showed the effect of S. cerevisiae co-culture on M. purpureus and suggested linoleic acid as a specific quorum-sensing molecule in Saccharomyces-Monascus co-culture.

Detoxification of the Mycotoxin Citrinin by a Manganese Peroxidase from Moniliophthora roreri

Citrinin (CIT) is a mycotoxin found in foods and feeds and most commonly discovered in red yeast rice, a food additive made from ordinary rice by fermentation with Monascus. Currently, no enzyme is known to be able to degrade CIT effectively. In this study, it was discovered that manganese peroxidase (MrMnP) from Moniliophthora roreri could degrade CIT. The degradation appeared to be fulfilled by a combination of direct and indirect actions of the MrMnP with the CIT. Pure CIT, at a final concentration of 10 mg/L, was completely degraded by MrMnP within 72 h. One degradation product was identified to be dihydrocitrinone. The toxicity of the CIT-degradation product decreased, as monitored by the increased survival rate of the Caco-2 cells incubated with MrMnP-treated CIT. In addition, MrMnP could degrade CIT (with a starting concentration of up to 4.6 mg/L) completely contaminated in red yeast rice. MrMnP serves as an excellent candidate enzyme for CIT detoxification.

Enhancement of functional activity and biosynthesis of exopolysaccharides in Monascus purpureus by genistein treatments

The exopolysaccharides (EPS) produced by the edible medicinal fungus Monascus purpureus (EMP) become the center of growing interest due to their techno-functional properties and their numerous applications in the food industries; however, the low EPS yields limit its application. In this study, the effect of genistein supplementation on the production, rheological and antioxidant properties of EPS by M. purpureus and its biosynthesis mechanism were explored. The results indicated that the addition of genistein (3 g/L) generated a 110% and 59% increase in the maximum mycelial biomass and EPS yield, respectively. The genistein supplementation group (G-EMP) had higher molar percentages of Xyl and Man, and significantly decreased molecule weight and particle size of EPS, which resulted in stronger antioxidant effect and cell growth promotion. Rheological analysis showed that both EMP and G-EMP demonstrated pseudoplastic fluid behavior and G-EMP exhibited strong gel-like elastic behavior (G' > G"). Furthermore, genistein not only facilitated the production of EPS by regulating cell membrane permeability, enhancing cellular respiratory metabolism and monosaccharide precursor synthesis pathways, and enhancing antioxidant enzyme activity to reduce oxidative stress damage, but also affected the composition of the monosaccharides by increasing enzyme activity in the underlying synthesis pathways. These findings expand the application of M. purpureus resources and provide a paradigm for future study of the structural and functional characteristics of EPS.

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Genistein (3 g/L) significantly stimulate yield of biomass and exopolysaccharides (EPS) from M. purpureus.

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The physicochemical and rheological properties of EPS were significantly changed.

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Their antioxidant and cytoprotective effect were compared.

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A possible mechanism for the response of genistein to increase EPS yield is proposed.

Comparative Transcriptomic and Metabolomic Analyses Reveal the Regulatory Effect and Mechanism of Tea Extracts on the Biosynthesis of Monascus Pigments

Monascus pigments (MPs) are natural edible pigments with high safety and strong function, which have been widely used in food and health products. In this study, different types of tea extracts (rich in polyphenols) were used to regulate the biosynthesis of MPs. The results showed that 15% ethanol extract of pu-erh tea (T11) could significantly increase MPs production in liquid fermentation of Monaco’s purpureus M3. Comparative transcriptomic and metabolomic analyses combined with reverse transcription-quantitative polymerase chain reaction (RT-qPCR) were used to further explore the regulatory mechanism of T11 on the biosynthesis of MPs. Comparative transcriptomic analysis showed that there were 1503 differentially expressed genes (DEGs) between the Con group and the T11 group, which were mainly distributed in carbohydrate metabolism, amino acid metabolism, energy metabolism, lipid metabolism, metabolism of terpenoids and polyketides, etc. A total of 115 differential metabolites (DMs) identified by metabolomics between the Con and T11 groups were mainly enriched in glutathione metabolism, starch and sucrose metabolism, alanine, aspartic acid and glutamate metabolism and glycine, serine and threonine metabolism, etc. The results of metabolomics were basically consistent with those of gene transcriptomics, indicating that the regulatory effect of T11 on the biosynthesis of MPs is mainly achieved through affecting the primary metabolic pathway, providing sufficient energy and more biosynthetic precursors for secondary metabolism. In this study, tea extracts with low economic value and easy access were used as promoters of MPs biosynthesis, which may be conducive to the application of MPs in large-scale industrial production. At the same time, a more systematic understanding of the molecular regulatory mechanism of Monascus metabolism was obtained through multi-omics analysis.

Effect of γ-Heptalactone on the Morphology and Production of Monascus Pigments and Monacolin K in Monascus purpureus

Monascus is used widely in Asian countries and produces various biologically active metabolites, such as Monascus pigments (MPs) and monacolin K (MK). In this study, the effect of γ-heptalactone on secondary metabolites and mycelial growth during Monascus purpureus M1 fermentation was investigated. After the addition of 50 μM γ-heptalactone, the yields of MPs (yellow, orange, and red) reached maxima, increased by 115.70, 141.52, and 100.88%, respectively. The 25 μM γ-heptalactone groups showed the highest yield of MK was increased by 62.38% compared with that of the control. Gene expression analysis showed that the relative expression levels of MPs synthesis genes (MpPKS5, MpFasA2, mppB, mppC, mppD, mppG, mpp7, and mppR1/R2) were significantly upregulated after γ-heptalactone treatment. The relative expression levels of MK synthesis genes (mokA, mokC, mokE, mokH, and mokI) were significantly affected. The mycelium samples treated with γ-heptalactone exhibited more folds and swelling than that in the samples of the control group. This study confirmed that the addition of γ-heptalactone has the potential to induce yields of MPs and MK, and promote the expression of biosynthesis genes, which may be related to the transformation of mycelial morphology in M. purpureus.

Citrinin Mycotoxin Contamination in Food and Feed: Impact on Agriculture, Human Health, and Detection and Management Strategies

Citrinin (CIT) is a mycotoxin produced by different species of Aspergillus, Penicillium, and Monascus. CIT can contaminate a wide range of foods and feeds at any time during the pre-harvest, harvest, and post-harvest stages. CIT can be usually found in beans, fruits, fruit and vegetable juices, herbs and spices, and dairy products, as well as red mold rice. CIT exerts nephrotoxic and genotoxic effects in both humans and animals, thereby raising concerns regarding the consumption of CIT-contaminated food and feed. Hence, to minimize the risk of CIT contamination in food and feed, understanding the incidence of CIT occurrence, its sources, and biosynthetic pathways could assist in the effective implementation of detection and mitigation measures. Therefore, this review aims to shed light on sources of CIT, its prevalence in food and feed, biosynthetic pathways, and genes involved, with a major focus on detection and management strategies to ensure the safety and security of food and feed.

Increased Extracellular Saponin Production after the Addition of Rutin in Truffle Liquid Fermentation and Its Antioxidant Activities

Saponins possess a variety of pharmacological effects and exhibit great potential in the food industry as bioactive substances. In this study, extracellular saponin production via the liquid fermentation of Tuber melanosporum occurred with the addition of rutin. For this purpose, medium composition and culture conditions were optimized using single-factor experiments and an orthogonal experiment design. The optimal medium consisted of glucose (43.5 g/L), peptone (6 g/L), KH2PO4 (1.15 g/L), NaCl (0.2 g/L), vitamin B2 (0.082 g/L), vitamin B6 (0.1 g/L), vitamin C (0.02 g/L), and rutin (4.8 g/L). The culture conditions were as follows: 12.5% (v/v) inoculation, medium volume of 50 mL/250 mL flask, culture temperature of 24 °C, shaker speed of 190 rpm, initial pH of 5.7, and culture time of 96 h. Finally, a maximal extracellular saponin content of 0.413 g/L was obtained, which was 134.7% higher than that in the base medium. Rutin proved to be an excellent promoter, because the saponin production was increased by 50.2% compared to that in the optimized medium without rutin. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity, hydroxyl radical scavenging activity, and ferric reducing antioxidant power of truffle saponins reached 94.13%, 79.26%, and 42.22 mM, respectively. This study provides a useful strategy for fungal bioactive saponin production by liquid fermentation with the addition of flavonoid compounds.

Volatile Organic Compound-Mediated Antifungal Activity of Pichia spp. and Its Effect on the Metabolic Profiles of Fermentation Communities

Volatile organic compounds (VOCs) are chemicals responsible for antagonistic activity between microorganisms. The impact of VOCs on microbial community succession of fermentation is not well understood. In this study, Pichia spp. were evaluated for VOC production as a part of antifungal activity during baijiu fermentation. The results showed that the abundance of Pichia in the defect group (agglomerated fermented grains) was lower than that in control group, and a negative interaction between Pichia and Monascus was determined (P < 0.05). In addition, the disruption of fungi was significantly related to the differences of metabolic profiles in fermented grains. To determine production of VOCs from Pichia and its effect on Monascus purpureus, a double-dish system was assessed, and the incidence of M. purpureus reduction was 39.22% after 7 days. As to antifungal volatile compounds, 2-phenylethanol was identified to have an antifungal effect on M. purpureus through contact and noncontact. To further confirm the antifungal activity of 2-phenylethanol, scanning electron microscopy showed that 2-phenylethanol widely and significantly inhibited conidium germination and mycelial growth of filamentous fungi. Metatranscriptomic analysis revealed that the Ehrlich pathway is the metabolic path of 2-phenylethanol in Pichia and identified potential antifungal mechanisms, including protein synthesis and DNA damage. This study demonstrated the role of volatile compound-mediated microbial interaction in microbiome assembly and discovered a plausible scenario in which Pichia antagonized fungal blooms. The results may improve the niche establishment and growth of the functional yeast that enhances the flavor of baijiu.IMPORTANCE Fermentation of food occurs within communities of interacting species. The importance of microbial interactions in shaping microbial structure and metabolic performance to optimize the traditional fermentation process has long been emphasized, but the interaction mechanisms remain unclear. This study applied metabolome analysis and amplicon sequencing along with metatranscriptomic analysis to examine the volatile organic compound-mediated antifungal activity of Pichia and its effect on the metabolism of ethanol during baijiu fermentation, potentially enhancing the establishment of the fermentation niche and improving ethanol metabolism.

Agro-industrial residues for the production of red biopigment by Monascus ruber: rice flour and sugarcane molasses

Three culture media were studied for red pigment production by Monascus ruber in submerged cultivation: rice flour (20 g L^-1), sugarcane molasses (30 g L^-1), and, finally, molasses + rice flour (10 g L^-1+10 g L^-1); all culture media were added of 5 g L^-1 glycine as nitrogen source. Rice flour showed pigment production of 7.05 UA_510nm and molasses 5.08 UA_510nm, and the mixture of rice flour and molasses showed the best result of 16.38 UA_510nm. Molasses culture presented good results for cell biomass production of 11.09 g L^-1. With these results, it was observed that one substrate presented good pigment production (rice flour) and another attained better results for cell biomass growth (molasses), and a third medium containing 10 g L^-1 of rice flour + 10 g L^-1 of molasses was formulated. The results for this mixture showed satisfactory results, with global pigment productivity of 0.097 UA_510nm h^-1 and maximum productivity rate of 0.17 UA_510nm h^-1. The high production and productivity obtained for the mixture of rice flour and molasses indicated that the production of red pigment by submerged fermentation, using the mixture of these low-cost culture media, may be promising in terms of commercial production.

1H NMR-based metabolomic study of the effects of flavonoids on citrinin production by Monascus

Monascus comprises purple-red molds. Various compounds can be obtained from these species, including statins and food-safe yellow, red, and orange pigments. However, the secondary metabolite citrinin, a mycotoxin, is produced during the late stages of growth. Citrinin biosynthesis should be reduced to apply Monascus pigments safely. Fortunately, this can be achieved by the addition of flavonoids (genistein, daidzein, apigenin, and kaempferol). However, the effects of these flavonoids on other metabolites remain unknown. Here, we report a ¹H NMR-based multivariate metabolomic analysis of the effects of flavonoids on mycotoxin citrinin production by Monascus. Fifteen metabolites involved in lysine and arginine biosynthesis and alanine, aspartate, glutamate, biotin, arginine, proline, and glutathione metabolism were detected. The reduction in glutamate, aspartate, biotin, and 2-phosphoglycerate content suggested their association with the citrinin reduction mechanism. This study identifies the citrinin production pathway in Monascus and will aid in the development of citrinin-control methods.

Addition of genistein to the fermentation process reduces citrinin production by Monascus via changes at the transcription level

Monascus, which is traditionally used in various Asian industries, produces several secondary metabolites during the fermentation process, including citrinin, a toxin whose impact limits the development of the Monascus industry. We have previously found that the addition of 2.0 g/L genistein to Monascus medium reduces citrinin production by approximately 80%. Here, we explored the molecular mechanisms whereby genistein affects citrinin production. We sequenced the Monascus genome and performed transcriptome analysis on genistein-treated and -untreated groups. Comparison between the two groups showed 378 downregulated and 564 upregulated genes. Among the latter, we further examined the genes related to citrinin biosynthesis and quantified them using quantitative real-time polymerase chain reaction (qRT-PCR). Genes orf5, pksCT, orf3, orf1, orf6, and ctnE were significantly downregulated, demonstrating that genistein addition indeed affects citrinin synthesis. Our results may lay the groundwork for substantial improvements in the Monascus fermentation industry.

The ctnF gene is involved in citrinin and pigment synthesis in Monascus aurantiacus

The application of Monascus is restricted by citrinin. So, it is important to explore the synthetic pathway of citrinin to completely inhibit the production of citrinin. In our previous study, we found that the protein encoded by the ctnF gene has a significant similarity to fructose-2,6-bisphosphatase (F26BPase). It is generally known that the bifunctional enzyme F26BPase regulates the glycolytic flux. So, we speculated that the CtnF protein strengthens carbon flux towards acetyl-CoA and malonyl-CoA which are precursor compounds in citrinin and pigment synthesis. In this study, the ctnF gene-targeting vector pctnF-HPH was constructed and transformed into Monascus aurantiacus. A ctnF-deficient strain was selected by four sets of primers and polymerase chain reaction amplification. Compared with the wild-type strain, citrinin content in the deficient strain was reduced by 34%, and the pigment production was decreased by 72%. These results indicate that the ctnF gene is involved in the common synthesis of citrinin and pigment, which is consistent with previous speculations.

Production and characterization of okara dietary fiber produced by fermentation with Monascus anka

Okara dietary fiber was prepared by liquid fermentation with Monascus anka (M. anka). Infrared spectra results indicated that there were more oligosaccharides because of the hydrogen bond cleavage of the polysaccharides in okara Monascus dietary fiber (OMDF). Scanning electron microscopy and X-ray analyses showed that the structures of OMDF were altered as compared to that of the control. The UV-visible spectrum of the M. anka seed broth (MSB) contained three absorption peaks corresponding to red, orange, and yellow pigments, which were present in equal quantities. The concentration of citrinin in MSB and Monascus okara fermentation broth was 0.980 ppm and 0.940 ppm, respectively. After fermentation, the soluble OMDF content in OMDF was 7.7 g/100 g, which was 1.79 times of that in the control. Further, the water holding capacity, oil holding capacity, and swelling capacity of OMDF increased significantly, while the water retaining capacity decreased slightly. HYPOTHESIS: This study was aimed at investigating the effect of liquid fermentation of M. anka on okara. After fermentation, the dietary fiber structure may change and the functional properties may be improved.

Troxerutin attenuates oxygen‑glucose deprivation and reoxygenation‑induced oxidative stress and inflammation by enhancing the PI3K/AKT/HIF‑1α signaling pathway in H9C2 cardiomyocytes

Myocardial ischemia-reperfusion (MI/R) injury is a complex pathological process that occurs when tissues are reperfused following a prolonged period of ischemia. Troxerutin has been reported to have cardioprotective functions. However, the underlying mechanism by which troxerutin protects against MI/R injury has not been fully elucidated. The aim of the present study was to explore whether troxerutin-mediated protection against oxygen-glucose deprivation/reoxygenation (OGD/R)-induced H9C2 cell injury was associated with the inhibition of oxidative stress and the inflammatory response by regulating the PI3K/AKT/hypoxia-inducible factor-1α (HIF-1α) signaling pathway. The results of the present study suggested that troxerutin pretreatment prevented the OGD/R-induced reduction in cell viability, and the increase in lactate dehydrogenase activity and apoptosis. Troxerutin reversed OGD/R-induced the inhibition of the PI3K/AKT/HIF-1α signaling pathway as demonstrated by the increased expression of PI3K and HIF-1α, and the increased ratio of phosphorylated AKT/AKT. LY294002, a selective PI3K inhibitor, inhibited the PI3K/AKT/HIF-1α signaling pathway and further attenuated the protective effect of troxerutin against OGD/R-induced H9C2 cell damage. Furthermore, small interfering (si)RNA-mediated knockdown of HIF-1α reduced troxerutin-induced protection against OGD/R injury. Troxerutin pretreatment alleviated OGD/R-induced oxidative stress, as demonstrated by the reduced generation of reactive oxygen species and malonaldehyde content, and the increased activities of superoxide dismutase and glutathione peroxidase, which were reduced by HIF-1α-siRNA. Troxerutin-induced decreases in the levels of interleukin (IL)-1β, IL-6 and tumor necrosis factor-α in OGD/R conditions were also reduced by HIF-1α-siRNA. The results from the present study indicated that troxerutin aggravated OGD/R-induced H9C2 cell injury by inhibiting oxidative stress and the inflammatory response. The primary underlying protective mechanism of troxerutin was mediated by the activation of the PI3K/AKT/HIF-1α signaling pathway.

Evaluation of tyrosol and farnesol as inducer in pigment production by Monascus purpureus ATCC16365

This study focused on investigating the effect of exogenously applied two quorum sensing molecules (tyrosol and farnesol) on the synthesis of bioactive metabolites (pigments, lactic acid, ethanol, and citric acid) in Monascus purpureus ATCC16365. None of the tested concentrations (62.5, 125, 250, and 500 µl/L) of farnesol affected the synthesis of metabolites as well as cell growth. As with farnesol application, none of the tested concentrations (3.45, 6.9, 13.8, and 27.6 mg/L) of tyrosol caused a significant change in the synthesis of lactic acid and citric acid as well as cell growth. Conversely, all of the tested concentrations of tyrosol increased pigment synthesis but reduced ethanol synthesis, compared with the control. Maximum increases (3.16-, 2.68-, and 2.87-fold increase, respectively) in yellow, orange, and red pigment production were achieved, especially when 6.9-mg/L tyrosol was added to the culture on day 3. On the contrary, 6.9-mg/L tyrosol reduced the content of citrinin by approximately 51.5%. This is the first report on the effect of tyrosol and farnesol on the synthesis of Monascus metabolites. Due to potential properties, such as low price, nonhuman toxicity, promotion of pigment synthesis, and reduction in citrinin synthesis, tyrosol can be used as a novel inducer in the fermentative production of Monascus pigments.

Effects of some flavonoids on the mycotoxin citrinin reduction by Monascus aurantiacus Li AS3.4384 during liquid-state fermentation

Monascus can produce many beneficial metabolites; however, it can simultaneously also produce citrinin, which seriously limits its application. Therefore, reducing the production of citrinin is of great interest. Herein, Monascus aurantiacus Li AS3.4384 (MAL) was used to optimize the liquid-state fermentation process and investigate the effects of genistein and other flavonoids on citrinin, pigments, and biomass of MAL. Results showed that citrinin decreased by 80%, pigments and biomass increased by approximately 20% in 12 days with addition of 20.0 g/L rice powder as a carbon source and 2.0 g/L genistein during shaking liquid-state fermentation. Further, genistein, daidzein, luteolin, apigenin, quercetin, baicalein, kaempferol myricetin, and genistin exerted different effects on citrinin production by MAL, with genistein causing the highest reduction in citrinin production during liquid-state fermentation, possibly due to the presence of C5-OH, C4′-OH, and C7-OH. Therefore, genistein can be added to the fermentation process of Monascus to reduce citrinin.

Development of Real-Time Immuno-PCR Based on Phage Displayed an Anti-Idiotypic Nanobody for Quantitative Determination of Citrinin in Monascus

Citrinin (CIT) is a mycotoxin that has been detected in agricultural products, feedstuff, and Monascus products. At present, research has been performed to develop methods for CIT detection, mainly through TLC, HPLC, biosensor, and immunoassay. The immunoassay method is popular with researchers because of its speed, economy, simplicity, and ease of control. However, mycotoxins are inevitably introduced during the determination. Immunoassays require the use of toxins coupled to carrier proteins or enzymes to make competitive antigens. In this study, anti-idiotypic nanobody X27 as CIT mimetic antigen was used as non-toxic surrogate reagents in immunoassay. Therefore, the X27-based real-time immuno-PCR (rtIPCR) method had been established after optimal experiments of annealing temperature and amplification efficiency of real-time PCR, concentration of coating antibody, phage X27, and methyl alcohol. The IC₅₀ value of the established method in the present study is 9.86 ± 2.52 ng/mL, which is nearly equivalent to the traditional phage ELISA method. However, the linear range is of 0.1-1000 ng/mL, which has been broadened 10-fold compared to the phage ELISA method. Besides, the X27-based rtIPCR method has no cross-reactivity to the common mycotoxins, like aflatoxin B₁ (AFB₁), deoxynivalenol (DON), ochratoxin A (OTA), and zearalenone (ZEN). The method has also been applied to the determination of CIT in rice flour and flour samples, and the recovery was found to be in the range of 90.0-104.6% and 75.8-110.0% respectively. There was no significant difference in the results between the rtIPCR and UPLC-MS. The anti-idiotypic nanobody as a non-toxic surrogate of CIT makes rtIPCR a promising method for actual CIT analysis in Monascus products.

Soybean isoflavones reduce citrinin production by Monascus aurantiacus Li AS3.4384 in liquid state fermentation using different media

BACKGROUND

Monascus, a filamentous fungus, produces many bioactive substances. However, in the process of fermentation, Monascus also produces the mycotoxin citrinin. Owing to the presence of citrinin, the safety of Monascus products has been questioned and their wide application limited. Using soybean isoflavones (SI) as exogenous additives, alterations in citrinin production by Monascus aurantiacus Li AS3.4384 (MALA) in different media used for liquid state fermentation were investigated.

RESULTS

Results showed that the citrinin concentration was 95.98% lower than that of the control group after 16-days fermentation when 20.0 g L-1 SI were added to rice powder and inorganic salt medium. Citrinin production was reduced by 97.24% after 12-days fermentation with 10.0 g L-1 SI in starch inorganic salt medium; 82.52% after 20-days fermentation with 20.0 g L-1 SI in starch peptone medium with high starch content; 45.07% after 14-days fermentation with 5.0 g L-1 SI in starch peptone medium with low starch content; and 82.21% after 14-days fermentation with 20.0 g L-1 SI in yeast extract sucrose medium.

CONCLUSION

The developed method of removing citrinin is simple, safe, and effective, and it can be applied to reduce the citrinin content of Monascus products. © 2019 Society of Chemical Industry.