Short communication
Simultaneous determination of salicylic, 3-methyl salicylic, 4-methyl salicylic, acetylsalicylic and benzoic acids in fruit, vegetables and derived beverages by SPME–LC–UV/DAD

“Dedicated to Professor Pier Giorgio Zambonin (Bari, Italy) on the occasion of his 80th birthday”
https://doi.org/10.1016/j.jpba.2015.12.016Get rights and content

Highlights

  • A new SPME–HPLC/UV(DAD) method is proposed.

  • Salicylates and benzoic acid are determined simultaneously in fruits and vegetables.

  • Overall, the proposed method is easy and cost-efficient.

  • We believe that it could be potentially applied to other food commodities.

Abstract

Salicylic and benzoic acid are phenolic acids occurring in plant cells, thus they can be present in fruit and vegetables at various levels. They possess anti-inflammatory and antimicrobial properties, however they may induce symptoms and health problems in a small percentage of the population. Therefore, a low phenolic acid diet may be of clinical benefit to such individuals. In order to achieve this goal, the concentration of these substances in different food and beverages should be assessed. The present work describes for the first time a new method, based on solid phase microextraction (polydimethylsiloxane–divinylbenzene fiber) coupled to liquid chromatography with UV diode array detection, for the simultaneous determination of salicylic acid, 3-methyl salicylic acid, 4-methyl salicylic acid, acetylsalicylic acid and benzoic acid in selected fruit, vegetables and beverages.

All the aspects influencing fiber adsorption (time, temperature, pH, salt addition) and desorption (desorption and injection time, desorption solvent mixture composition) of the analytes have been investigated. An isocratic separation was performed using an acetonitrile-phosphate buffer (pH 2.8; 2 mM) mixture (70:30, v/v) as the mobile phase. The estimated LOD and LOQ values (μg/mL) were in the range 0.002–0.028 and 0.007–0.095. The within-day and day-to-day precision values (RSD%) were between 4.7–6.1 and 6.6–9.4, respectively.

The method has been successfully applied to the analysis of fava beans, blueberries, kiwi, tangerines, lemons, oranges and fruit juice (lemon and blueberry) samples. The major advantage of the method is that it only requires simple homogenization and/or centrifugation and dilution steps prior to SPME and injection in the LC system.

Introduction

Phenolic compounds are the largest and most widely distributed group of secondary metabolites in plants [1], [2]. Therefore, variable amounts of them can be found in fruits and vegetables even at high levels.They are used by plants for growth and development processes, as well as photosynthesis, transpiration, ion uptake, and transport [3], [4], [5]. In particular, salicylic acid (SA), its methyl- and acetyl-esters (denominated salicylates) and its glycoside derivatives are present at different concentrations in plant tissues [6], [7]: blackberries and blueberries; cantaloupes, dates, raisins, kiwis, guavas, apricots, green peppers, olives, tomatoes, radish and chicory mushrooms, some herbs and spices, legumes, seeds, nuts, cereals, almonds, water chestnuts [2], [8], [9], [10], [11], [12].

In the past few years, these natural compounds have received increasing interest concerning several controversial issues [13], [14], [15]. The medicinal properties of salycilates have been known for a long time [7], [16], [17], [18], [19], [20], [21], [22]. Acetylsalicylic acid (ASA) is a well known drug (aspirin) used as an antipyretic, analgesic and antithrombotic agent [16], [17]. In addition, anticarcinogenic and antidiabetic effects have been recognized for ASA [18], [19]. It is a prodrug of SA which suppresses the activity of cyclooxygenase (COX) thus blocking prostaglandin synthesis [18], [20]. SA is also known to stimulate the adenosine monophosphate-activated protein kinase (AMPK) with consequent anticancer and antidiabetic effects [7], [21], [22]. Although a diet rich in salicylates might have positive effects on human health, there is a small percent of the population for which even a small dose of these compounds may be a problem. Some adults and children may develop symptoms and health problems from salicylates, which are dose-related. This is called ‘Salicylate Sensitivity’ or ‘Salicylate Intolerance’, which produces urticaria, angioedema, rhinitis, bronchial asthma and/or recurrent nasal polyps [23], [24].

The chronic nature of some of these clinical presentations may suggest an underlying etiology related to dietary salicylates. Thus, a low salicylate diet may be of clinical benefit to individuals affected by the above intolerance. This cannot be established, however, until the total salicylate content in food, that includes the contribution of SA and other salicylates, mainly methyl esters and glucosides of SA, is known. Thus, methods for their determinations in fruit, vegetables and related beverages are extremely useful.

Existing papers on this topic require complicated sample pre-treatment approaches and have been based on UV and fluorescence spectroscopy [25], [26], chromatographic techniques [2], [27], [28], [29], flow injection atomic absorption spectrometry [30] and electrochemistry [31], [32]. Furthermore, derivatives of salicylic acid have never been considered, thus making the assessment of the real dietary exposure to salycilates virtually impossible.

Very few data have also been reported to date [33], [34] on the simultaneous determination of SA and benzoic acids (BA), an active metabolite occurring in plants, which is a precursor of SA in the biosynthetic pathway [35]. It is widely used as a fungicidal and antimicrobial agent, and also in pharmaceutical preparations to help drug uptake and delivery after administration [36], [37], [38], [39]. However, despite its widespread use, it could be very toxic since it can lead to benzene formation through a decarboxylation reaction [40], [41], [42]. Liquid chromatography with ultraviolet detection (LC–UV) methods have been reported [41], [43], [44], [45] for the determination of benzoic acid in fruits and derived products that required complex sample clean-up with organic solvents or solid-phase extraction The present work describes for the first time a new method. based on the solventless extraction technique known as solid phase microextraction (SPME) [46] coupled to LC–UV diode array (DAD), for the simultaneous determination of SA, some of its derivatives (3-methyl salicylic acid, 4-methyl salicylic acid, acetylsalicylic acid) and BA (see Fig. 1) in fava beans, blueberries, kiwi, tangerines, lemons, oranges and fruit juice (lemon and blueberry) samples.

Section snippets

Chemicals

Salicylic acid, 3-methyl salicylic acid, 4-methyl salicylic acid, acetyl salicylic acid and benzoic acid were supplied by Sigma–Aldrich s.r.l. (MI, Italy).

Stock solutions (10 mg/mL) were prepared in ethanol and stored in the dark at +4 °C. Working solutions (concentration range 0.001–3 μg/mL) were prepared in water just before use in the presence of HCl (pH 2.0; 10 mM) with NaCl (0.3 g/mL).

All chemicals and organic solvents used (Sigma–Aldrich) were LC grade. The mobile phase was filtered through a

SPME–LC optimization

Firstly, all the parameters relevant to the resolution of the analytes under study, i.e. stationary phase, mobile phase composition and flow rate, were carefully considered and optimized. The ideal conditions are reported in the Section 2.3.

Then, all the factors affecting adsorption of the analytes on the SPME fiber (time, temperature, pH, ionic strength) and their desorption in the SPME–LC interface (desorption mode and desorption mixture composition) were investigated. Fig. 2a reports the

Conclusions

The simultaneous determination of SA, some of its derivatives (3-methyl salicylic acid, 4-methyl salicylic acid, acetylsalicylic acid) and BA by SPME–LC–UV/DAD was accomplished for the first time. The LC separation of the target compounds was achieved working in isocratic conditions.

All SPME parameters, (i.e. extraction time, temperature, pH, salt addition, desorption and injection time, desorption solvent mixture composition) have been carefully studied.

The potential of the described procedure

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