The use of capillary electrophoresis with contactless conductivity detection for sensitive determination of stevioside and rebaudioside A in foods and beverages

Nine high-intensity sweeteners in beverages in a single LC-MS/MS analysis

With the increasing demand for reduced sugar or sugar-free products by consumers with chronic non-communicable diseases and individuals seeking weight control, foods and beverages with high-intensity sweeteners (HIS) tend to become more common in the market. Therefore, monitoring HIS concentrations added to industrialised products is an important issue. Thus, an analytical method using LC-MS/MS was established and validated in order to allow the simultaneous determination of nine of these compounds in beverages marketed in Brazil. HIS levels were determined in 132 commercial samples of beverages like nectar-type juices, powdered juices, and soft drinks. The results obtained during validation showed coefficients of variation (CV%) for precision lower than 14.9% and accuracies between 88.5% and 109.9%, with all samples below the maximum limits as set by the Brazilian legislation.

Capillary and microchip electrophoresis with contactless conductivity detection for analysis of foodstuffs and beverages

The paper provides a comprehensive survey of the use of capillary and microchip electrophoresis in combination with contactless conductivity detection (C⁴D) for the analysis of drinking water, beverages and foodstuffs. The introduction sets forth the fundamentals of conductivity detection anddescribes an axialC⁴Dversion. There is also a detailed discussion of the determination of inorganic ions, organic acids, fatty acids, amino acids, amines, carbohydrates, foreign substances and poisons from the standpoint of separation conditions, sample treatment and detection limits. Special attention is paid to the analysis of foodstuffs at microchips with emphasis on the employed material and connection of the microchip with the C⁴D. The review attempts to draw attention to modern trends, such as dual-opposite injection, field-enhanced sample injection, electromembrane extraction and on-line combination of microdialysis with CE. CE/C⁴D is characterised by high universality, high speed of analysis, simple sample preparation, small consumption of sample and other chemicals.

HI-HPTLC-UV/Vis/FLD-HESI-HRMS and bioprofiling of steviol glycosides, steviol, and isosteviol in Stevia leaves and foods

Food products and botanicals on the global market need to be investigated in a more comprehensive way to detect effects, falsifications or adulterations. This is especially true for such ones containing Stevia leaves, Stevia extracts, or steviol glycosides. A multi-imaging profiling was developed exploiting hydrophilic interaction liquid chromatography (HILIC). A minimalistic sample preparation, different mixtures of acetonitrile and water/buffer on the silica gel phase as well as derivatization reagents and optional hyphenation with high-resolution mass spectrometry were exploited. The hydrophilic interaction high-performance thin-layer chromatography (HI-HPTLC) development took 10 min for 48 analyses. It was used to screen Stevia leaf extracts and 20 different food products. For the first time, the biological and biochemical profiling of Stevia leaf products by HI-HPTLC-UV/Vis/FLD-assay pointed to 19 different bioactive compound bands found in the more natural multicomponent Stevia leaf extracts, whereas most of these activities were not existent for the steviol glycosides. The chemically isolated, purified, and EU-regulated steviol glycosides ease risk assessment and food product development. However, multipotent botanicals may have subtle impact on homeostasis via several metabolic pathways, providing benefits for the consumer's health. Analyzed side by side by means of the effect-directed profiling, their individual activity profiles were visualized as image and individual substances of importance were pointed out. Multi-imaging (comprehensive detection) plus non-targeted bioprofiling (focus on known and unknown bioactivity) allows for a fast detection of questionable product changes that occur along the global food chain and are particularly related to food safety. Graphical abstract.

Simple and Efficient Green Extraction of Steviol Glycosides from Stevia rebaudiana Leaves

The food industry has currently shown great interest in alternative sweeteners to sugars with the aim of producing healthier products. In light of this, steviol glycosides are natural low-caloric sweeteners present in Stevia rebaudiana, which have additionally been described as bioactive components with potential therapeutic properties. In this work, a green method for the extraction of steviol glycosides from stevia leaves was optimized by applying a factorial screening design of five variables (time, temperature, agitation, grinding, and sample-solvent ratio) and the subsequent response surface design of Box-Behnken. The optimized extraction method allows for the recovery of stevia sweeteners in a simple and efficient manner by using tap water as the extractant, without the application of an auxiliary energy source to reduce costs, thus representing an interesting strategy for their industrial-scale production.

Highly specific sophorose β-glucosidase from Sphingomonas elodea ATCC 31461 for the efficient conversion of stevioside to rubusoside

Enzyme specificity and particularity is needed not only in enzymatic separation methods, but also in enzymatic determination methods for plant compound extraction. Stevioside, rubusoside, and rebaudioside A are natural sweet compounds from plants. These compounds have the same skeleton and only contain different side-chain glucosyl groups, making them difficult to separate. However, enzymes that target diterpenoid compounds and show specific activity for side-chain glucosyl groups are rare. Herein, we report the identification and characterization of an enzyme that can target both diterpenoid compounds and sophorose, namely, β-glucosidase SPBGL1 from Sphingomonas elodea ATCC 31461. SPBGL1 displayed high specificity toward sophorose, and activity toward stevioside, but not rebaudioside A. The stevioside conversion rate was 98%. SPBGL1 also operated at high substrate concentrations, such as in 50% crude steviol glycoside extract. Glucose liberated from stevioside was easy to quantify using the glucose oxidase method, allowing the stevioside content to be determined.

Determination of steviol glycosides in commercial extracts of Stevia rebaudiana and sweeteners by ultra-high performance liquid chromatography Orbitrap mass spectrometry

Stevia rebaudiana extracts are used as sweeteners in several countries worldwide. Several extracts of diverse composition are available on the market, and their taste depends on the contents of the various steviol glycosides. This study presents an accurate method for the qualitative and quantitative determination of steviol glycosides in 40 Stevia extracts, 7 sweeteners and 3 Stevia-sweetened beverages by a UHPLC coupled to an Orbitrap mass spectrometer. The sub-2 μm amide column provided the separation of all the target analytes in a run time of 30 min with high resolution. The effect of different eluent compositions on the ionisation efficiency of the steviol glycosides was studied. The optimal ionisation conditions were achieved in negative mode using 0.05% formic acid. Under this condition, adducts were not found, [M-H]^- were the main ions and the spontaneous loss of a glucose residue at C19 was reduced. The %RSD for intra- and inter-day precision for all eleven analytes varied from 2.1 to 4.2% and 3.0-5.1%, respectively. The recoveries from spiked Stevia extract samples were greater than 95% for all analytes. Rebaudioside A was the most abundant, ranging from 23 to 102%. Nine Stevia extracts and one drink were not compliant with the European Regulation. Isosteviol was under the LOD in all samples and steviol was found in four samples in quantities in the range 0.01-0.03%.

Contactless conductivity detection for analytical techniques: Developments from 2016 to 2018

The publications concerning capacitively coupled contactless conductivity detection for the 2-year period from mid-2016 to mid-2018 are covered in this update to the earlier reviews of the series. Relatively few reports on fundamental investigations or new designs have appeared in the literature in this time interval, but the development of new applications with the detection method has continued strongly. Most often, contactless conductivity measurements have been employed for the detection of inorganic or small organic ions in conventional capillary electrophoresis, less often in microchip electrophoresis. A number of other uses, such as detection in chromatography or the gauging of bubbles in streams have also been reported.

Optimization of a capillary zone electrophoresis-contactless conductivity detection method for the determination of nisin

Determination of natural preservatives using electrophoretic or chromatographic techniques in fermented milk products is a complex task due to the following reasons: (i) the concentrations of the analytes can be below the detection limits, (ii) complex matrix and comigrating/coeluting compounds in the sample can interfere with the analytes of the interest, (iii) low recovery of the analytes, and (iv) the necessity of complex sample preparation. The aim of this study was to apply capillary zone electrophoresis coupled with contactless conductivity detection for the separation and determination of nisin in fermented milk products. In this work, separation and determination of natural preservative-nisin in fermented milk products is described. Optimized conditions using capillary zone electrophoresis coupled with capacitance-to-digital technology based contactless conductivity detector and data conditioning, which filter the noise of the electropherogram adaptively to the peak migration time, allowed precise, accurate, sensitive (limit of quantification: 0.02 μg/mL), and most importantly requiring very minute sample preparation, determination of nisin. Sample preparation includes following steps: (i) extraction/dilution and (ii) centrifugation. This method was applied for the determination of nisin in real samples, i.e. fermented milk products. The values of different nisin forms were ranging from 0.056 ± 0.003 μg/mL to 9.307 ± 0.437 μg/g.

Estimation of steviol glycosides in food matrices by high performance liquid chromatography

Steviol glycosides (SGs) are non-caloric, natural sweetener obtained from plant Stevia rebaudiana and are used as sugar substitute in foods. The level of SGs in foods should not exceed maximum permissible limit defined by regulatory agencies. Thus analytical methods are required for assay of stevioside (Stev) and rebaudioside A (Reb A), which are two major constituents of SGs, in foods. A method for extraction of Stev and Reb A from dairy viz., flavoured milk, flavoured yoghurt and non-dairy foods viz., carbonated water, jam, chewing gum and estimation of these by HPLC has been described. Extraction of SGs from dairy samples was achieved by treating samples with 20% acetonitrile in presence of Carrez solutions while these can be simply extracted with water from non-dairy samples. Separation and estimation of these two glycosides was achieved on C18 column (length: 4.6 × 250 mm, particle size: 5 μm) using isocratic mobile phase prepared by mixing of acetonitrile and 10 mM sodium phosphate buffer (pH 2.6) in ratio of 32:68 (v/v). Recovery of two SGs was quantitative. Separation and estimation of SGs by HPLC was robust. Limit of detection and limit of quantitation for Reb A in different food was in range from 1.057-1.834 to 3.525-6.114 mg kg^-1 while that of Stev was from 1.679-2.912 to 5.596-9.707 mg kg^-1, respectively. Neotame, an artificial sweetener can be used as internal standard for separation of SGs.