Determination of Ochratoxin A in Bread: Evaluation of Microwave-Assisted Extraction Using an Orthogonal Composite Design Coupled with Response Surface Methodology

Abstract

An analytical method using microwave-assisted extraction (MAE) and liquid chromatography (LC) with fluorescence detection (FD) for the determination of ochra-toxin A (OTA) in bread samples is described. A 2 4 orthogonal composite design coupled with response surface methodology was used to study the influence of MAE parameters (extraction time, temperature, solvent volume, and stirring speed) in order to maximize OTA recovery. The optimized MAE conditions were the following: 25 mL of acetonitrile, 10 min of extraction, at 80 °C, and maximum stirring speed. Validation of the overall methodology was performed by spiking assays at five levels (0.1-3.00 ng/g). The quantification limit was 0.005 ng/g. The established method was then applied to 64 bread samples (wheat, maize, and wheat/maize bread) collected in Oporto region (Northern Portugal). OTA was detected in 84 % of the samples with a maximum value of 2.87 ng/g below the European maximum limit established for OTA in cereal products of 3 ng/g.

Microwave‐assisted extraction of phenolic compounds from Morus nigra leaves: optimization and characterization of the antioxidant activity and phenolic composition

“…This physical–chemical characteristic of the solvent expresses its capability to absorb microwave radiation and convert it to thermal energy . Bearing this in mind, and based also on previous studies, different pure solvents, i.e. water, methanol and ethanol, and mixtures of these solvents in several ratios (1:4, 1:1, 4:1 v/v; organic solvent:water) were tested using a sample weight of 0.50 g and a solvent volume of 20 mL at 100 °C for 20 min.…”

“…The additional MAE conditions were kept constant, namely, 20 min extraction time, 20 mL of extraction solvent, and medium stirring. The selection of these conditions was established based on our previous experience with MAE and on data from the literature . For the extraction temperature, the range tested in the present study was chosen bearing in mind that an increase in temperature results in higher desorption of analytes from the sample and in their easier solubilization within the solvent, improving the extraction efficiency.…”

“…The selection of these conditions was established based on our previous experience with MAE and on data from the literature. [19][20][21]40 For the extraction temperature, the range tested in the present study was chosen bearing in mind that an increase in temperature results in higher desorption of analytes from the sample and in their easier solubilization within the solvent, improving the extraction efficiency. However, when extracting thermolabile compounds, such as phenolic compounds, high temperatures may lead to their degradation decreasing the extraction yield.…”

“…The development of an optimum extraction process for phenolics can be challenging due to the different possible structures and their antioxidant activity that can lead to fast reaction with other matrix components . Over the last decade, microwave‐assisted extraction (MAE) has stood out due to its intrinsic benefits over traditional techniques, such as maceration, Soxhlet and ultrasound enhanced extraction, originating environment‐friendly processes with energy‐, time‐ and cost‐savings and production of high quality extracts . Also, extraction in closed vessels can be accomplished at high temperatures, which increases the mass transfer of the analyte from the sample matrix, allowing rapid processes without deterioration of thermally unstable compounds .…”

“…17,18 Over the last decade, microwave-assisted extraction (MAE) has stood out due to its intrinsic benefits over traditional techniques, such as maceration, Soxhlet and ultrasound enhanced extraction, originating environment-friendly processes with energy-, timeand cost-savings and production of high quality extracts. 1,2,[19][20][21] Also, extraction in closed vessels can be accomplished at high temperatures, which increases the mass transfer of the analyte from the sample matrix, allowing rapid processes without deterioration of thermally unstable compounds. 19 Supercritical CO 2 extraction is also a novel technique that has been explored for extraction of valuable compounds, which may be of importance for food and pharmaceutical industries, due to the several advantages (non-toxic and non-explosive properties, readily-available and easy removable from the products) of using CO 2 as solvent.…”