Liyan Ma

Comparison of Polyphenol Profile and Inhibitory Activities Against Oxidation and α-Glucosidase in Mulberry (Genus Morus) Cultivars from China

UNLABELLED Mulberry (genus Morus) is a significant source of polyphenols, which can promote positive effects on human health. China has various mulberry cultivars, however, many Chinese mulberry cultivars have been only minimally studied. To solve this lack of research, 8 mulberry cultivars (Da10, Tang10, Yueshen74, Yuefenshen, Longsang, Ningxia1hao, Taiwanguosang, and Baiyuwang) from 4 regions of China were assessed to determine their polyphenol profiles using HPLC-MS/MS and then tested for their antioxidant and anti-α-glucosidase activities in vitro. A total of 18 nonanthocyanins and 4 anthocyanins were quantified in mulberry cultivars; among these polyphenols, chlorogenic acid, quercetin 3-O-rutinoside, and cyanidin 3-O-glucoside were confirmed as the major phenolic acid, flavonol derivative, and anthocyanin, respectively. Two types of stilbene compounds, piceid, and piceatannol, were detected for the 1st time in all mulberry cultivars. Moreover, the methanolic extracts of different mulberry cultivars showed disparate antioxidant and α-glucosidase inhibitory activities, and this discrepancy was mainly attributed to varying the anthocyanin content. Based on our results, Taiwanguosang is proposed to be a good candidate suitable for further process due to its high level of anthocyanins. PRACTICAL APPLICATION The polyphenols of mulberry cultivars are vital for human health and are relevant to the further development of mulberry-based products. China has a wide range of mulberry cultivar resources, and many of these cultivars have not yet been studied. Our research concentrated on the polyphenol profiles, antioxidant, and α-glucosidase inhibitory activities of various mulberry cultivars from different regions of China to provide basic information for mulberry cultivar selection and mulberry-based food production.

Development and validation of a simple and fast method for simultaneous determination of aflatoxin B1 and sterigmatocystin in grains

In this study, a simple, fast, sensitive and reliable method was developed for the simultaneous determination of aflatoxin B1 (AFB1) and sterigmatocystin (STC) in rice, wheat, maize, oat, rye and barley grains based on a modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) method and liquid chromatography-tandem mass spectrometry (LC-MS/MS). AFB1 and STC were extracted using 95% acetonitrile in water and cleaned up using N-Propylethane-1,2-diamine (PSA). The method was validated according to the SANCO/12571/2013 regulation of the European Union (EU). Recoveries at three spiked levels of 0.5, 2.5 and 5.0μg/kg ranged from 77.7% to 119.7% and the relative standard deviations (RSDs) were between 1.3% and 12.8%. Limits of detection (LOD) were 0.03 and 0.02μg/kg for AFB1 and STC, respectively. The limit of quantification (LOQ) was 0.5μg/kg for both AFB1 and STC. The proposed method was successfully applied to determine AFB1 and STC levels in ten non-processed rice samples from Guangdong province in China.

Ochratoxin A in dried vine fruits from Chinese markets

A total of 56 dried vine fruits, including 31 sultanas and 25 currants, were selected from Chinese markets in 2012. All samples were analysed for Ochratoxin A (OTA) using solid-phase extraction and high-performance liquid chromatography (HPLC) with fluorescence detection. It turned out that 58.9% of the samples were positive and the OTA amount ranged from <0.07 to 12.83 μg/kg, with a mean level of 0.99 μg/kg. Only one sample exceeded the European Union (EU) maximum level of 10 μg/kg. Meanwhile, it was shown that OTA contamination increased among north-western, northern and southern China, which showed OTA means of 0.08, 0.99 and 2.01 μg/kg, respectively. Moreover, in samples of products sold in sealed plastic bags, i.e. consumer-size packages (n = 19, mean = 0.30 μg/kg) less OTA was detected when compared with sampled bulk packages (n = 37, mean = 1.67 μg/kg). In addition, sultanas (mean = 0.92 μg/kg) had less OTA contamination than currants (mean = 1.22 μg/kg).

High-performance liquid chromatography-tandem mass spectrometry method for simultaneous detection of ochratoxin A and relative metabolites in Aspergillus species and dried vine fruits

ABSTRACT A simple, sensitive and reliable quantification and identification method was developed for simultaneous analysis of ochratoxin A (OTA) and its related metabolites ochratoxin alpha (OTα), ochratoxin B (OTB) and mellein. The method was assessed by spiking analytes into blank culture media and dried vine fruits. Performance was tested in terms of accuracy, selectivity and repeatability. The method involves an ultrasonic extraction step for culture samples using methanol aqueous solution (7:3, v/v); the mycotoxin is quantified by high-performance liquid chromatography coupled with electrospray ionisation and triple quadrupole mass spectrometry (LC-ESI-MS/MS). The recoveries were 74.5–108.8%, with relative standard deviations (RSDs) of 0.4–8.4% for fungal culture. The limits of detection (LODs) were in the range of 0.03–0.87 μg l–1, and the limits of quantification (LOQs) ranged from 0.07 to 2.90 μg l–1. In addition, the extraction solutions and clean-up columns were optimised specifically for dried vine fruit samples to improve the performance of the method. Methanol–1% sodium bicarbonate extraction solution (6:4, v/v) was determined to be the most efficient. Solid-phase extraction (SPE) was performed as a clean-up step prior to HPLC-MS/MS analysis to reduce matrix effects. Recoveries ranged from 80.1% to 110.8%. RSDs ranged from 0.1% to 3.6%. LODs and LOQs ranged from 0.06 to 0.40 μg kg–1 and from 0.19 to 1.20 μg kg–1, respectively. The analytical method was established and used to identify and quantify OTA and related compounds from Aspergillus carbonarius and Aspergillus ochraceus in cultures and dried vine fruits. The results showed that A. carbonarius produced OTα, OTB and OTA, whereas A. ochraceus produced OTB, OTA and mellein after 7 days of cultivation. Of 30 commercial samples analysed, 10 were contaminated with ochratoxins; OTB, OTα and mellein were also detected in different samples. GRAPHICAL ABSTRACT

Effect of Different Solvents on the Measurement of Phenolics and the Antioxidant Activity of Mulberry (Morus atropurpurea Roxb.) with Accelerated Solvent Extraction

The effects of 9 different solvents on the measurement of the total phenolics and antioxidant activities of mulberry fruits were studied using accelerated solvent extraction (ASE). Sixteen to 22 types of phenolics (flavonols, flavan-3-ols, flavanol, hydroxycinnamic acids, hydroxybenzoic acids, and stilbenes) from different mulberry extracts were characterized and quantified using HPLC-MS/MS. The principal component analysis (PCA) was used to determine the suitable solvents to distinguish between different classes of phenolics. Additionally, the phenolic extraction abilities of ASE and ultrasound-assisted extraction (UAE) were compared. The highest extraction efficiency could be achieved by using 50% acidified methanol (50MA) as ASE solvents with 15.14 mg/gallic acid equivalents g dry weight of mulberry fruit. The PCA results revealed that the 50MA followed by 50% acidified acetone (50AA) was the most efficient solvent for the extraction of phenolics, particularly flavonols (627.12 and 510.31 μg/g dry weight, respectively), while water (W) was not beneficial to the extraction of all categories of phenolics. Besides, the results of 3 antioxidant capability assays (DPPH, ABTS free radical-scavenging assay, and ferric-reducing antioxidant power assay) showed that water-based organic solvents increased the antioxidant capabilities of the extracts compared with water or pure organic solvents. ASE was more suitable for the extraction of phenolics than UAE.

Aflatoxin B1 and sterigmatocystin survey in beer sold in China

ABSTRACT A total of 101 samples of beer from the Chinese market were analysed for the presence of aflatoxin B1 (AFB1) and sterigmatocystin (STC), using methods based on liquid chromatography–tandem mass spectrometry. The limit of quantification and the limit of detection in beer were 0.1 and 0.03 µg/kg, respectively. Recoveries of AFB1 and STC from spiked beer samples were 97.8–103.6% and 92.7–102.1%, respectively. None of the beer purchased samples were contaminated with AFB1 or STC.

Ochratoxin A in Chinese dried jujube: method development and survey.

A method was developed for the determination of the mycotoxin ochratoxin A in dried jujube (Zizyphus jujuba Miller) using alkaline methanolic extraction, immunoaffinity column clean-up (IAC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) determination. The limit of detection (LOD) was 0.01 μg kg–1 and limit of quantification (LOQ) was 0.03 μg kg–1. The average recoveries were 82%, 98% and 115% at 5, 0.5 and 0.1 μg kg–1 spiked levels with relative standard deviations (RSD) of 2.9%, 5.2% and 9.2% accordingly. The method showed good linearity for both solvent standard calibration and matrix-matched standard calibration with correlation coefficients of 0.9998 and 0.9997 respectively. The intra-day precision RSD was 3.3% and the inter-day precision RSD was 4.0%. In addition, there was almost no matrix interference in LC-MS/MS detection after the IAC clean-up process. The proposed analytical set-up was successfully used to test 20 samples that were collected from local markets and stores. The results showed that all the samples were positive and the amount of OTA ranged from < 0.01 to 0.18 μg kg–1, with a mean level of 0.14 μg kg–1. In spite of the high positive rate, samples with this level would not cause significant health effects after consumption.

A study on accumulation of volatile organic compounds during ochratoxin a biosynthesis and characterization of the correlation in Aspergillus carbonarius isolated from grape and dried vine fruit

Volatile organic compounds (VOCs) and ochratoxin A (OTA) were detected in Aspergillus carbonarius strains (AF, SD26 and SD27) during a 7-day growing period, using HS-SPME-GC-MS and HPLC-MS/MS, respectively. Results showed that 33 VOCs were detected in these strains. The AF strain showed the different sesquiterpene profile compared with the other strains. Principal component analysis revealed that the AF strain was segregated from the other two strains regarding the VOC profile, especially the sesquiterpene profile. Ester metabolites were produced more at the beginning of the strain growth period, whereas extension of the strain incubation resulted in an intense accumulation of hydrocarbon compounds. The prediction models on the correlation between OTA and VOCs were established using partial least squares regression analysis. This analysis indicated that C-8 alcohols, ketones, and trans-nerolidol showed a close relation with the OTA synthesis.

Chemometric Analysis of the Volatile Compounds Generated by Aspergillus carbonarius Strains Isolated from Grapes and Dried Vine Fruits

Ochratoxin A (OTA) contamination in grape production is an important problem worldwide. Microbial volatile organic compounds (MVOCs) have been demonstrated as useful tools to identify different toxigenic strains. In this study, Aspergillus carbonarius strains were classified into two groups, moderate toxigenic strains (MT) and high toxigenic strains (HT), according to OTA-forming ability. The MVOCs were analyzed by GC-MS and the data processing was based on untargeted profiling using XCMS Online software. Orthogonal projection to latent structures discriminant analysis (OPLS-DA) was performed using extract ion chromatogram GC-MS datasets. For contrast, quantitative analysis was also performed. Results demonstrated that the performance of the OPLS-DA model of untargeted profiling was better than the quantitative method. Potential markers were successfully discovered by variable importance on projection (VIP) and t-test. (E)-2-octen-1-ol, octanal, 1-octen-3-one, styrene, limonene, methyl-2-phenylacetate and 3 unknown compounds were selected as potential markers for the MT group. Cuparene, (Z)-thujopsene, methyl octanoate and 1 unknown compound were identified as potential markers for the HT groups. Finally, the selected markers were used to construct a supported vector machine classification (SVM-C) model to check classification ability. The models showed good performance with the accuracy of cross-validation and test prediction of 87.93% and 92.00%, respectively.

The effect of dipping pretreatment on ochratoxin A accumulation in sultanas and currants

The dipping pretreatment on the occurrence of ochratoxin A (OTA) in sultanas and currants was investigated. Grape samples were divided into two groups before a drying process. One group was dipped with potassium carbonate-ethyl oleate, and the other group was left without treatment (the control). OTA were detected using solid-phase extraction clean-up and a high-performance liquid chromatography fluorescence detector. Results showed that OTA content was below the limit of detection in the fresh grapes of both varieties. OTA were not detected in dried vine fruits before storage. However, a real naturally environmental storage revealed that the dipping pretreated samples were contaminated with OTA earlier and to a greater extent than the control. The OTA concentration in the treated and control samples after one-year storage was 0.22 and 0.19 μg/kg for sultanas and 0.34 and 0.21 μg/kg for currants, respectively. These results indicated that dipping pretreatment might increase the toxin contamination and safety risk.