Model-based equipment-design for plant-based extraction processes – considering botanic and thermodynamic aspects

The growing demand for plant-based products in the food, cosmetics and pharmaceutical industry leads to the need for a systematic process and equipment-design for the potentially applicable extraction techniques. Therefore, in this article, the classification of plant-based raw materials according to their characteristics is discussed. Furthermore, physicochemical modelling via distributed plug flow approach is applied and its possible fields of application are examined. Here, especially the extraction of water from the plant-based raw material as well as the entailed effects on the equilibrium and the mass transport kinetics are concerned. In addition to that, an evaluation method for the examined and generally available equipment through spider diagram is proposed. The relation to the initially argued botanic systems is discussed in particular. The extraction of vanillin from vanilla beans serves as exemplary system for this.     

Microwave- and ultrasound-assisted extraction of vanillin and its quantification by high-performance liquid chromatography in Vanilla planifolia

Microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE) and conventional extraction of vanillin and its quantification by HPLC in pods of Vanilla planifolia is described. A range of nonpolar to polar solvents were used for the extraction of vanillin employing MAE, UAE and conventional methods. Various extraction parameters such as nature of the solvent, solvent volume, time of irradiation, microwave and ultrasound energy inputs were optimized. HPLC was performed on RP ODS column (4.6 mm ID x 250 mm, 5 microm, Waters), a photodiode array detector (Waters 2996) using gradient solvent system of ACN and ortho-phosphoric acid in water (0.001:99.999 v/v) at 25 degrees C. Regression equation revealed a linear relationship (r2 > 0.9998) between the mass of vanillin injected and the peak areas. The detection limit (S/N = 3) and limit of quantification (S/N = 10) were 0.65 and 1.2 microg/g, respectively. Recovery was achieved in the range 98.5-99.6% for vanillin. Maximum yield of vanilla extract (29.81, 29.068 and 14.31% by conventional extraction, MAE and UAE, respectively) was found in a mixture of ethanol/water (40:60 v/v). Dehydrated ethanolic extract showed the highest amount of vanillin (1.8, 1.25 and 0.99% by MAE, conventional extraction and UAE, respectively).     

Development and validation of an RP-HPLC method for quantitative determination of vanillin and related phenolic compounds in Vanilla planifolia

A simple and fast method was developed using RP-HPLC for separation and quantitative determination of vanillin and related phenolic compounds in ethanolic extract of pods of Vanilla planifolia. Ten phenolic compounds, namely 4-hydroxybenzyl alcohol, vanillyl alcohol, 3,4-dihydroxybenzaldehyde, 4-hydroxybenzoic acid, vanillic acid, 4-hydroxybenzaldehyde, vanillin, p-coumaric acid, ferulic acid, and piperonal were quantitatively determined using ACN, methanol, and 0.2% acetic acid in water as a mobile phase with a gradient elution mode. The method showed good linearity, high precision, and good recovery of compounds of interest. The present method would be useful for analytical research and for routine analysis of vanilla extracts for their quality control.     

Determination of flavour components in natural vanilla extracts and synthetic flavourings by mixed micellar electrokinetic capillary chromatography

The development of a mixed micellar electrokinetic capillary chromatography (MECC) method for the qualitative and quantitative determination of key components, including vanillin, 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, vanillic acid and 3-methoxybenzaldehyde, that contribute to vanilla flavour was investigated. The micellar phase consisted of sodium dodecyl sulfate (SDS) and sodium cholate (SC). The percent relative standard deviation (R.S.D.%) for migration time was <1 over six runs. The R.S.D.% for peak areas ranged between 0.85-1.96% over six runs. Peak efficiencies were excellent with theoretical plate numbers typically in the range of 130,000-200,000 per column (52 cm effective length). The limits of detection (LOD) were between 5-10 μg/ml. The quantitative data was verified by high performance liquid chromatography (HPLC) and gas chromatography (GC). The mixed MECC method was successfully applied to a number of natural vanilla extracts, nature identical extracts and synthetic flavourings.     

Determination of vanillin and related flavor compounds in natural vanilla extracts and vanilla-flavored foods by thin layer chromatography and automated multiple development

Summary Thin layer chromatography on silica gel high performance layers and automated multiple development was used to separate the polar aromatic flavor compounds vanillin, ethyl vanillin, 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, 4-hydroxybenzyl alcohol, vanillic acid, coumarin, piperonal, anisic acid, and anisaldehyde commonly found in extracts of natural and artificial vanilla flavors. The ratio of 4-hydroxybenzoic acid, 4-hydroxybenzaldehyde and vanillic acid to vanillin in natural vanilla extracts was used to confirm the authenticity of extracts purchased in the United States of America and the United Kingdom. Natural vanilla extracts purchased in Mexico and Puerto Rico were identified as counterfeit products based on changes in the above ratio and the presence of synthetic flavor compounds such as ethyl vanillin and coumarin. It is also demonstrated that the proposed method is suitable for the determination of natural and synthetic vanilla flavors in solvent extracts from food, beverage and confectionery products. The main advantage of thin layer chromatography for the analysis of vanilla extracts and food stuffs flavored with vanilla is its high sample throughput since sample preparation requirements are minimal and multiple samples can be separated simultaneously.     

Quantitation of the main constituents of vanilla by reverse phase HPLC and ultra‐high‐pressure‐liquid‐chromatography with UV detection: Method validation and performance comparison

Vanilla's main constituents, i. e., vanillin, para‐hydroxybenzaldehyde, and their corresponding acids, can be easily quantified by RP LC with UV detection and external calibration. This paper describes two methods that were developed using HPLC and ultra‐high‐pressure LC (UHPLC), respectively, and validated according to the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) [1]. Both methods were highly specific, exhibited good linearities with high precision, and achieved good accuracies of quantitative results. The UHPLC method was more sensitive, five times shorter, and gave better peak resolutions than the HPLC alternative.     

Ultrafast UPLC‐ESI‐MS and HPLC with monolithic column for determination of principal flavor compounds in vanilla pods

In this study, two novel chromatographic methods based on monolithic column high‐performance liquid chromatography (HPLC) and ultra‐performance liquid chromatography (UPLC) were developed for the ultrafast determination of principal flavor compounds namely vanillin, vanillic acid, p‐hydroxybenzoic acid, and p‐hydroxybenzaldehyde in ethanolic extracts of Vanilla planifolia pods. Good separation was achieved within 2.5 min using Chromolith RP18e column (100 mm×4.6 mm) for HPLC and Acquity BEH C‐18 (100 mm×2.1 mm, 1.7 μm) column for UPLC. Both methods were compared in terms of total analysis time, mobile phase consumption, sensitivity, and validation parameters like precision, accuracy, LOD, and LOQ. Further, system suitability test data including resolution, capacity factor, theoretical plates, and tailing factor was determined for both the methods by ten replicate injections. Monolithic column based HPLC gave better results for most of the selected parameters while UPLC was found to be more eco‐friendly with low mobile phase consumption and better sensitivity. Both methods may be used conveniently for the high throughput analysis of large number of samples in comparison to traditional particulate column.     

RP-HPTLC densitometric determination and validation of vanillin and related phenolic compounds in accelerated solvent extract of Vanilla planifolia*

A simple, fast and sensitive RP-HPTLC method is developed for simultaneous quantitative determination of vanillin and related phenolic compounds in ethanolic extracts of Vanilla planifolia pods. In addition to this, the applicability of accelerated solvent extraction (ASE) as an alternative to microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE) and Soxhlet extraction was also explored for the rapid extraction of phenolic compounds in vanilla pods. Good separation was achieved on aluminium plates precoated with silica gel RP-18 F(254S) in the mobile phase of methanol/water/isopropanol/acetic acid (30:65:2:3, by volume). The method showed good linearity, high precision and good recovery of compounds of interest. ASE showed good extraction efficiency in less time as compared to other techniques for all the phenolic compounds. The present method would be useful for analytical research and for routine analysis of vanilla extracts for their quality control.     

A disposable electrochemical sensor for vanillin detection

A disposable electrochemical sensor was developed for the detection of vanillin in vanilla extracts and in commercial products. An analytical procedure based on square-wave voltammetry (SWV) was optimised and a detection limit of 0.4 μM for vanillin was found. A relative standard deviation of 2% was calculated for a vanillin concentration of 100 μM. The method was applied to the determination of vanillin in natural concentrated vanilla extracts and in final products such as yoghurt and compote. The obtained results were compared with those provided by a reference method based on HPLC. The electrochemical behaviour of other compounds (vanillic acid, p-hydroxybenzaldehyde, p-hydroxybenzoic acid, etc.), generally present in natural oleoresins, were also studied, to check for interferences with respect to the vanillin voltammetric signal.     

Preparation and Recognition Properties of Vanillin‐Imprinted Polymers

Some new molecularly imprinted polymers (MIPs) were prepared by different protocols involving vanillin as the imprinted molecule, methacrylic acid (= 2‐methylprop‐2‐enoic acid; MAA) as the functional monomer, and ethylene glycol dimethacrylate (EGDMA = 2‐methylprop‐2‐enoic acid ethane‐1,2‐diyl ester) as the cross‐linking agent. The adsorption property of the imprinted polymers was studied by UV spectrophotometry and HPLC. The results indicated that the porogen solvent had a certain influence on the adsorption performance of the polymer. The vanillin‐imprinted polymer MIP₁ prepared with MeOH as porogen, exhibited advantageous characteristics, i.e., a high binding activity, a good selectivity, and a rapid adsorption equilibrium. The binding parameters studied by Scatchard analysis established that there are two types of binding sites in MIP₁. Finally, by packing an SPE column (SPE = solid‐phase extraction) with the polymer MIP₁, the vanillin was separated and enriched successfully by this sorbent from the samples of Vanilla fragrans and beer.