Analysis of benzoate and sorbate in soft drinks

Soft drinks have been part of our global lifestyle since the nineteenth century and many of the soft drinks we consume today are the same as those first enjoyed centuries ago.

A preservative is a substance, such as sodium benzoate or potassium sorbate, that enables soft drink products to have a longer shelf life by inhibiting or arresting the growth of micro-organisms such as yeasts, moulds and bacteria.

Ion chromatography represents a robust, precise quantitative technique for the analysis of the preservatives benzoate and sorbate in a variety of different sample matrices that include soft drink beverages with an ion exclusion separation column.

In recent years the cost of ion chromatography instruments have fallen and they now represent a cost effective analytical solution to alternative techniques.

The use of preservatives in soft drinks.

Not all soft drinks contain preservatives; their need is dependant upon the type of product and the processing used.

The presence of carbon dioxide prevents mould growth and the high levels of acidity and carbonation help to inhibit the growth of yeasts and lactic acid bacteria. Conversely those beverages that contain fruit or fruit juices provide additional nutrients that may enable organisms to grow despite the levels of acidity and carbonation.

The soft drink products most likely to ferment are mildly acidic types with low carbonation containing fruit juice and in these instances a preservative is added to prevent micro-biological spoilage.

The most common preservatives used in soft drinks are sodium benzoate and potassium sorbate and they may be used in tandem.

Sodium benzoate is the salt of benzoic acid and occurs naturally in the lingon berry, while potassium sorbate is found in the rowan berry.

Sodium benzoate is effective against yeasts and moulds but can be difficult to dissolve and can impart a slight flavour at high levels.

Potassium sorbate meanwhile is more effective at lower acidities than sodium benzoate but is much more expensive and less effective against certain strains of bacteria.

In cold conditions its solubility is reduced and it can suppress the flavour of the drink.

The use of preservatives in soft drinks throughout Europe is governed by the EU Directive on food additives other than colours and sweeteners, transposed to a national level for implementation by the individual member states.

In the United Kingdom, the legislation is covered under the Miscellaneous Food Additive Regulations 95.

The ingredients in soft drinks.

The ingredients used in soft drink beverages are approved and closely regulated by bodies such as the US Food and Drug Administration or the Food Standards Agency in the UK.

There are an enormous number of soft drinks that are formulated to different recipes and not all the ingredients are found in all soft drink products.

Most regular soft drinks contain around 90% of water from a pure source, while diet variants may comprise up to 99% of water.

Drinking water can contain trace amounts of different minerals that can affect its taste and so bottling and manufacturing plants use sophisticated filtering and treatment equipment, to help remove residual impurities to standardise the quality of water used to produce the beverage, to ensure the same taste whether the drink is produced in the UK or Germany.

Carbon dioxide is an essential ingredient present in all carbonated beverages and imparts a unique taste when dissolved in water.

In the early days of soft drink manufacturing, carbon dioxide was derived from sodium salts giving rise to the term soda or soda water.

Today, carbon dioxide gas is absorbed into the flavoured soft drink with a carbonation machine just before the container is sealed.

While under pressure and chilled, the soft drink can absorb up to four times the beverage's volume of carbon dioxide.

When the soft drink container is opened, the 'pop' heard and 'fizz' observed is the rapid escape of carbon dioxide caused by the sudden release of pressure on the product.

Many soft drink producers mix many individual flavours to create a uniform, unique taste.

Natural flavours come from spices, oils and natural extracts while fruit flavoured beverages may contain natural fruit extracts.

Artificial flavourings are used when nature does not produce enough of certain flavours to satisfy the global demand and some natural flavours may be limited to geographical locations as well as seasonal fluctuations.

Colourings are an important factor in taste perception as it affects our psychological impression of food and these may originate from both natural and synthetic sources.

Caffeine is a naturally occurring substance that is added to certain soft drink beverages (particularly colas) as part of the flavour profile as its bitter taste enhances other flavours.

Acidity regulators add tartness to soft drinks and help act as a preservative and beverages may contain small amounts of either phosphoric acid or citric acid.

Soft drinks should not normally spoil because of their acidity and carbonation but storage conditions and time can impact the taste and flavour.

For this reason, some beverages contain small amounts of preservatives.

Most of the sodium and potassium present in soft drink products are derived from the water used in production as well as trace amounts from other ingredients present.

Regular soft drink beverages are sweetened with sucrose or fructose and diet formulations with intensely sweet substances such as aspartame or saccharin.

Manufacture of soft drinks.

The production of soft drink beverages begins by forming a sugar and water syrup while around the same time an extract made up of fruit juice, aromatic substances and acids is produced.

The components are thoroughly mixed into a soft drink concentrate to give a syrup mixture.

The water is de-aerated to avoid oxidation reactions that can destroy the aromatic substances.

For carbonated drinks, carbon dioxide is dissolved into the water at low temperatures under high pressures.

It is important that all the air has been removed otherwise the beverage will froth over when the container is opened.

The syrup and carbonated water are then mixed in the correct proportions according to their formulation prior to bottling, storage and then transportation of the finished soft drink product to the consumer.

Good for teeth? A group of scientist have claimed that the preservative benzoate found in soft drinks, ice cream and other foods may help prevent tooth decay.

The preservatives when combined with fluoride help prevented tooth cavities in a study conducted by the University of Rochester Medical Center, New York state.

Research was conducted on four groups of laboratory rats giving them doses of fluoride, benzoate, both fluoride and benzoate or neither.

Those rats receiving neither fluoride nor benzoate had an average of 16 cavities on their teeth after three weeks.

Those given fluoride had two cavities and those rats given fluoride and a high dose of benzoate had no cavities at all.

Work presented by Professor Bowen to the International Association of Dental Research said that the use of fluoride in water supplies was the main reason for falling rates of tooth decay in the past few decades, but during the same period, there had been a huge increase in the use of food preservatives which pretty much mirrored the decline in tooth decay.

A spokesperson for the British Dental Association added that the use of additives were helping fluoride but were not a substitute for their sole use instead of fluoride.

What is ion chromatography? Chromatography is a method for separating mixtures of substances using two phases, one of which is stationary and the other mobile moving in a particular direction. Chromatography techniques are divided up according to the physical states of the two participating phases.

The term ion exchange chromatography or ion chromatography (IC) is a subdivision of high performance liquid chromatography (HPLC).

A general definition of ion chromatography can be applied as follows: "ion chromatography includes all rapid liquid chromatography separations of ions in columns coupled online with detection and quantification in a flow-through detector".

In ion exclusion chromatography, a completely sulphonated cation exchanger with neutral sulphonic acids groups using protons as the counter ions is often adopted as the packing material.

In an aqueous environment the functional groups are hydrated.

The hydrate shell is limited by a negatively charged membrane known as a Donnan membrane.

The membrane is passable only by uncharged, non dissociated molecules such as water.

Organic carboxylic acids can be separated if strong mineral acids (like sulphuric acid) are used as the mobile phase.

Carboxylic acids have a low acid dissociation constant and are present in a fully non dissociated form in a strongly acidic eluent and can pass through the Donnan membrane before adsorption at the stationary phase.

The sulphate ions of the completely dissociated sulphuric acid are excluded. Method for the determination of benzoate and sorbate in soft drinks.

The soft drink was opened and a sample representative of the bulk was degassed using an ultrasonic bath.

100mg of the sample was weighed accurately into a 100ml volumetric flask and then diluted up to the mark with dilute sulphuric acid.

The diluted sample was injected directly into the Metrohm 761 Compact IC and the response for the peaks recorded using a sulphuric acid/acetone mobile phase with the Metrosep organic acids separation column.

The calculation was carried out automatically using integration software IC Net 2.3 against a previously prepared calibration plot.

There are no external displays or switches on the instrument, all the hardware is fully controlled via a single RS232 connection between the IC and the PC.

All the instrument parameters can be called upon with a click of the mouse.

The 761 Compact IC comprises a low-pulsation dual-piston pump, pulsation dampner, electromagnetic injection valve, two-channel peristaltic pump suppressor module, conductivity detector, eluent organiser as well as a data recording and processing module.

All the components that come into contact with the eluent and sample are metal-free.

The detector is the heart of every ion chromatography instrument.

The Metrohm detector's temperature varies by less than 0.01deg C and can be optimally adapted to the ambient conditions.

This outstanding temperature stability reduces interference and allows exact conductivity measurements.

The benzoate and sorbate content present in the soft drink beverage analysed were both found to be approximately 20mg l-1.

Conclusion.

Ion chromatography as an analytical technique has seen an enormous surge in popularity, due partly to the simplicity of many of the methods as well as other factors such as market forces driving down the expenditure costs of the equipment and an improved instrument power.

Ion chromatography is a precise technique that requires only a very small amount of sample for the analysis and the quantified results obtained within a matter of minutes.

The low running costs of ion chromatography with Metrohm instruments are surprisingly low requiring only the acquisition of chemicals required for the eluent and chemical suppression as well as a clean, reliable source of deionised water for preparation of the standards and samples.

Ion chromatography is a clean technique in that all the reagents are enclosed, its robustness and reliability are assured demonstrating precisely the reason why it is rapidly becoming the method of choice for many analysts in a plethora of different industries and is eminently suited to the analysis of benzoate and sorbate in soft drink beverages.