Comparison of extraction methods for analysis of citrinin in red fermented rice

Development and validation of an analytical method for determination of citrinin in red rice and red yeast rice-based food supplements by ultra-high performance liquid chromatography tandem mass spectrometry

Citrinin is a hepato-nephrotoxic mycotoxin produced by fungal species. The Monascus purpureus fungus plays a crucial role in the fermentation of red rice to produce red yeast rice-based food supplements, which represent the primary source of human exposure to citrinin. In this study, a simple and sensitive analytical method was successfully developed and validated for the citrinin determination in these products. The extraction process involved a QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) step and citrinin determination by ultra high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS). The proposed method provided satisfactory linearity, percentage of recovery from 82 to 104% with relative standard deviations (RSD) lower than 14%, and limits of detection and quantification of 0.07 μg/Kg and 0.24 μg/kg, respectively. Among the 14 samples analyzed, citrinin was found in two red rice samples (0.24 and 0.46 μg/kg) and in six food supplements (from 0.44 to 87 μg/kg).

The importance and mitigation of mycotoxins and plant toxins in Southeast Asian fermented foods

Fermented foods (ffs) and beverages are widely consumed in Southeast Asia (SEA) for their nutritional balance, flavor, and food security. They serve as vehicles for beneficial microorganisms performing a significant role in human health. However, there are still major challenges concerning the safety of ffs and beverages due to the presence of natural toxins. In this review, the common toxins found in traditional ffs in SEA are discussed with special reference to mycotoxins and plant toxins. Also, mitigation measures for preventing risks associated with their consumption are outlined. Ochratoxin, citrinin, aflatoxins were reported to be major mycotoxins present in SEA ffs. In addition, soybean-based ff food products were more vulnerable to mycotoxin contaminations. Common plant toxins recorded in ffs include cyanogenic glycosides, oxalates, phytates and saponins. Combined management strategies such as pre-harvest, harvest and post-harvest control and decontamination, through the integration of different control methods such as the use of clean seeds, biological control methods, fermentation, appropriate packaging systems, and controlled processing conditions are needed for the safe consumption of indigenous ffs in SEA.

Monascus spp. and citrinin: Identification, selection of Monascus spp. isolates, occurrence, detection and reduction of citrinin during the fermentation of red fermented rice

Red fermented rice (RFR) is rice fermented using Monascus spp. This product contains monacolin K, providing health benefits including mitigation of diarrhoea and improving blood circulation. RFR can produce pigments that can act as natural colour and flavouring agents. However, Monascus spp. (a fungal starter to ferment RFR) can also produce the mycotoxin, citrinin (CIT) which is believed to have adverse effects on human health. CIT in RFR has been reported worldwide by using different methods of detection. This review focuses on the production of RFR by solid-state fermentation (SSF) and submerged fermentation (SmF), the occurrence of CIT in RFR, CIT quantification, the factors affecting the growth of Monascus spp., pigments and CIT production in RFR, and possible methods to reduce CIT in RFR. This review will help the food industries, researchers, and consumers understand the risk of consuming RFR, and the possibility of controlling CIT in RFR.

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.

Risk Assessment of RYR Food Supplements: Perception vs. Reality

Thirty-seven red yeast rice (RYR) food supplements were screened for their mycotoxin and natural statin content. Products included pure RYR capsules and multi-ingredient formulations with standardized amounts of monacolin K (MK), marketed both online and retail in the European Union. In terms of mycotoxins, citrinin (CIT) was found in all the monitored products. As CIT content ranged from 100 to 25100 μg/kg, only four products were compliant with maximum EU levels in force until April 2020, while a single product was compliant with the limit of 100 μg/kg introduced after that date. Four contaminated products were labeled as "citrinin free". In terms of natural statins, nine products had a lower content vs. label statements (from -30 to -83%), while for 24 a larger MK amount (from 10 to 266%) was noticed. Three products had a negligible MK content and only 19 offered a daily dosage exceeding 10 mg as dictated by the health claim granted by EFSA in the EU. No sample had label values compliant with pharmaceutical Good Manufacturing Practices requirements (95-105% content of active constituent). Variable, but small amounts of simvastatin (0.1-7.5 μg per daily dose) were found in 30 samples. These results suggest that limited efficacy and reported safety issues may stem from an under-regulated and undercontrolled market, weakening both effectiveness and risk assessment evaluations.

Dietary Supplements Based on Red Yeast Rice-A Source of Citrinin?

Citrinin (CIT) is secondary metabolite of filamentous molds. This mycotoxin has nephrotoxic, hepatotoxic, embryocidal, and fetotoxic properties. It is also produced by several species of the three genera Penicillium spp., Aspergillus spp., and Monascus spp., which are used to make red yeast rice (RYR). The material for this study consisted of 15 dietary supplements containing an extract of fermented red rice, available on the Polish market. Samples were extracted using a MeOH-H2O mixture, cleaned-up with an immunoaffinity CitriTest HPLC column, and quantified by HPLC-FLD. None of the analyzed samples contained CIT above the established limit of detection (LOD). Studies on the presence of toxic metabolites in red yeast rice show the importance of regulating this product and of clear information on the label regarding the standardized amounts of monacolin.

Characterization and inhibition of four fungi producing citrinin in various culture media

PURPOSE

This study aimed to investigate the effects of different fermentation conditions (culture medium, temperature, incubation time, pH value and additive) on citrinin production by four fungi.

RESULTS

Among the culture media, potato dextrose medium had lowest citrinin production, followed by yeast sucrose medium and monosodium glutamate medium. The lowest citrinin contents were produced by Monascus anka (M. anka) in potato dextrose medium and yeast sucrose medium, Aspergillus oryzae AS3.042 (A. oryzae) produced the lowest citrinin production in monosodium glutamate medium. The optimum fermentation temperatures for citrinin production by Aspergillus niger (A. niger) and Penicillium citrinum (P. citrinum) were at 30 °C, whereas those by M. anka and A. oryzae were at 35 °C. Citrinin synthesis by four fungi were completely inhibited with a pH value of less than 5.4. By adding ethylene diamine tetraacetic acid (EDTA) or triammonium citrate into monosodium glutamate medium, citrinin production by A. oryzae and A. niger were totally inhibited. Ammonium sulfate completely inhibited citrinin production by A. oryzae, M. anka and P. citrinum, and ammonium nitrate completely inhibited citrinin production by A. oryzae.

CONCLUSIONS

These results indicated that the suitable fermentation conditions could make considerable contributions to the reduction of citrinin production. This study provided an effective way for decreasing the citrinin production.

Citrinin in Foods and Supplements: A Review of Occurrence and Analytical Methodologies

Citrinin (CIT) deserves attention due to its known toxic effects in mammalian species and its widespread occurrence in food commodities, often along with ochratoxin A, another nephrotoxic mycotoxin. Human exposure, a key element in assessing risk related to food contaminants, depends upon mycotoxin contamination levels in food and on food consumption. Commercial supplements, commonly designated as red rice, usually used in daily diets in Asiatic countries due to their medicinal properties, may pose a health problem as a result of high CIT levels. In addition to the worldwide occurrence of CIT in foods and supplements, a wide range of several analytical and detection techniques with high sensitivity, used for evaluation of CIT, are reviewed and discussed in this manuscript. This review addresses the scientific literature regarding the presence of CIT in foods of either vegetable or animal origin, as well as in supplements. On what concerns analytical methodologies, sample extraction methods, such as shaking extraction and ultrasonic assisted extraction (UAE), clean-up methods, such as liquid-liquid extraction (LLE), solid phase extraction (SPE) and Quick, Easy, Cheap, Effective, Rugged and Safe (QuECHERS), and detection and quantification methods, such as thin layer chromatography (TLC), high performance liquid chromatography (HPLC), capillary electrophoresis (CE), biosensors, and ELISA, are also reviewed.

Recent advances in analytical methods for the determination of citrinin in food matrices

Citrinin is a toxic small organic molecule produced as a secondary metabolite by fungi types Penicillium, Monascus and Aspergillus and is known to contaminate various food commodities during postharvest stages of food production. During the last 10 years, most reported methods for citrinin analysis employed enzyme-linked immunosorbent assays or high-performance liquid chromatography. Over this same time period, liquid extraction, solid-phase extraction, dispersive liquid-liquid microextraction and QuEChERS were the most cited sample preparation and clean-up methods. In this review the advantages and disadvantages of the various sample preparation, separation and detection methods for citrinin analysis over the last decade are evaluated. Furthermore, current trends, emerging technologies and the future prospects of these methods are discussed.

Comparative transcriptomic analysis reveals the regulatory effects of inorganic nitrogen on the biosynthesis of Monascus pigments and citrinin

Monascus spp. and its secondary metabolites have been widely applied in foods and medicines for thousands of years in eastern Asia. Nitrogen sources are essential nutrients for the growth and metabolism of Monascus spp. Our previous study found that inorganic nitrogen sources (especially NH₄Cl and NH₄NO₃) promoted the biosynthesis of Monascus pigments (MPs) and inhibited the production of citrinin. The objective of the present study was to investigate the regulatory mechanism of inorganic nitrogen on the biosynthesis of MPs and citrinin by the comparative transcriptional approach (RNA sequencing combined with RT-qPCR). Results indicated that the submerged fermentation of M. purpureus M3103 with NH₄Cl or NH₄NO₃ as the sole nitrogen source can significantly increase the yields of MPs (especially for Monascus orange and red pigments) and decrease citrinin production, compared with the organic nitrogen source (peptone group). Comparative transcriptomic profiling by RNA sequencing found that the numbers of differentially expressed genes (DEGs) between different experimental groups—M group (peptone group) vs. ML group (NH₄Cl group), and M group (peptone group) vs. MX group (NH₄NO₃ group), were 722 and 1287, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that genes involved in carbon and nitrogen metabolism, biosynthesis of amino acids were up-regulated by NH₄Cl and NH₄NO₃, which would produce more biosynthetic precursors for MPs. Whereas, the inorganic nitrogen source (both of NH₄Cl and NH₄NO₃) down-regulated the expression levels of genes involved in tyrosine metabolism. In addition, NR analysis indicated that the essential genes and transcription factors involved in the biosynthesis pathway of citrinin were down-regulated by NH₄Cl and NH₄NO₃. These results indicated that NH₄Cl or NH₄NO₃ as a nitrogen source for M. purpureus M3103 can significantly promote the precursor synthesis of Monascus pigments, but reduce the transcription of polyketide synthase for citrinin, and therefore significantly increase Monascus pigments production and decrease citrinin formation. These findings will facilitate a comprehensive understanding of the regulatory mechanisms of inorganic nitrogen in the biosynthesis of secondary metabolites in M. purpureus, and would benefit the application of M. purpureus in the production of MPs.

Comparative transcriptional approach (RNA sequencing combined with RT-qPCR) was used to investigate the regulatory mechanism of inorganic nitrogen on the biosynthesis of MPs and citrinin.

Lovastatin in lactone and hydroxy acid forms and citrinin in red yeast rice powders analyzed by HPTLC-UV/FLD

For the analysis of pigment-rich red yeast rice products, a fast quantitative high-performance thin-layer chromatography (HPTLC) method was newly developed and validated. The active ingredient lovastatin, present in lactone (LL) and hydroxy acid forms (LH), as well as the mycotoxin citrinin were analyzed in 19 red yeast rice products, including powders, dietary supplements, and Chinese proprietary medicines (Xuezhikang and Zhibituo). The HPTLC method including sample preparation allows a high throughput of matrix-rich samples (10 min per analysis) and is highly cost-efficient (running costs of 0.5 Euro per analysis). For a fast protocol, application volumes up to 10 μL were selected although higher application volumes will lower still the LODs, which were 30 mg/kg for LL and LH as well as 4 mg/kg for citrinin. Thanks to the minimalistic sample preparation, the overall mean recovery rate was good (109.9% ± 5.9%; repeated measurements of the three analytes per fresh sample preparation at three spike levels). Repeated calibrations (five per analyte) in the red yeast rice matrix showed highly satisfying determination coefficients (≥ 0.9991; mean 0.9996). For three analytes at three concentration levels, the obtained mean intermediate precisions in red yeast rice matrix analyzed over the whole procedure including sample preparation were highly satisfying (≤ 2.6%). Citrinin was not detectable in the samples down to the given LOD of 4.0 mg/kg for the 10-μL sample volume applied. The mean content of lovastatin in 15 RYR powders was 8.7 g/kg, with a rang of 1.5-26.2 g/kg. The content of lovastatin in Zhibituo tablets and Xuezhikang capsules was determined to be 2.7 and 11.1 g/kg, respectively. The two commercially available RYR dietary supplement samples showed the highest lovastatin contents of 40.7 and 41.4 g/kg. By these figures of merit, the HPTLC method was proven to be suited for the control of such matrix-rich, fermented food. Graphical abstract.

Metabolic Effects of the pksCT Gene on Monascus aurantiacus Li As3.4384 Using Gas Chromatography--Time-of-Flight Mass Spectrometry-Based Metabolomics

Monascus spp. have been used for the production of natural pigments and bioactive compounds in China for several centuries. Monascus can also produce the mycotoxin citrinin, restricting its use. Disruption of the pksCT gene in Monascus aurantiacus Li AS3.4384 reduces citrinin production capacity of this strain (Monascus PHDS26) by over 98%. However, it is unclear how other metabolites of M. aurantiacus Li AS3.4384 (the wild-type strain) are affected by the pksCT gene. Here, we used metabolomic analyses to compare red yeast rice (RYR) metabolite profiles of the wild-type strain and Monascus PHDS26 at different stages of solid-state fermentation. A total of 18 metabolites forming components within the glycolysis, acetyl-CoA, amino acid, and tricarboxylic acid (TCA) cycle metabolic processes were found to be altered between the wild-type strain and Monascus PHDS26 at different stages of solid-state fermentation. Thus, these findings provide important insights into the metabolic pathways affected by the pksCT gene in M. aurantiacus.

Citrinin Determination in Red Fermented Rice Products by Optimized Extraction Method Coupled to Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)

A rapid and sensitive method was developed and validated for citrinin determination in red fermented rice products by liquid chromatography tandem mass spectrometry (LC-MS/MS) under the selected reaction monitoring mode. Sample preparation was especially focused, and the quantitative methods of LC-MS/MS and high-performance liquid chromatography with fluorescence detection (HPLC-FLD) were compared. In red fermented rice samples, the limit of detection was 1.0 μg/kg for LC-MS/MS compared to 250 μg/kg for HPLC-FLD, the limit of quantification was 3.0 μg/kg for LC-MS/MS compared to 825 μg/kg for HPLC-FLD. High correlation coefficient was obtained (R(2) = 0.999) within the linear range (0.1 to 100 μg/L) in the MS method. The recoveries ranging from 80.9% to 106.5% were obtained in different spiking concentrations. The average intra- and inter-day accuracy ranged from 75.4% to 103.1%, and the intra- and inter-day precisions were from 3.3% to 7.9%. The developed method was applied to 12 commercial red fermented rice products, and citrinin was found in 10 samples ranging from 0.14 to 44.24 mg/kg. Compared to traditional qualitative and quantitative methods, the newly developed LC-MS/MS method for citrinin determination includes the merits of using a small amount of extraction solvent, simple preparation steps, and high sensitivity.