Solving the recent orange juice off-flavour mystery

 A research team from the Leibniz Institute for Food Systems Biology at the Technical University of Munich has solved the mystery of a novel clove-like off-flavour in orange juice, the cause of which was previously unknown. The study proves for the first time that the undesirable flavour note is due to the odorant 5-vinylguaiacol. As the results of the study show, the substance is mainly produced during the pasteurisation process when residues of a cleaning agent react with a natural orange juice component under the influence of heat.

This is not the first time the orange juice industry has had to contend with clove odour. So far, 4-vinylguaiacol has been considered the main cause of this undesirable flavour note, which is particularly abundant in orange juices that have been stored for a long time. The quantitative determination of this odorant has therefore long been an established part of routine quality controls.

However, according to Eva Bauersachs, a PhD student at the Leibniz Institute in Freising and first author of the study, there have been recent reports of orange juice samples that had a pronounced clove odour and low concentrations of 4-vinylguaiacol. “We therefore asked ourselves which other odorants contribute to this undesirable off-flavour,” Bauersachs said.

To investigate this, the research group, led by Martin Steinhaus, head of the Food Metabolome Chemistry research group at the Leibniz Institute, carried out investigations to identify odorants that cause the off-flavour and their origins. The research was in cooperation with the Professorship of Functional Phytometabolomics and the Chair of Food Chemistry and Molecular Sensory Science at the Technical University of Munich.

Using techniques such as gas chromatography-olfactometry and aroma extract dilution analysis, the team was able to identify 5-vinylguaiacol as the source of the off-flavour. Compared to 4-vinylguaiacol, it even proved to be more odour-active in five out of six commercially available orange juices with a clove-like off-flavour.

Further studies suggested that 5-vinylguaiacol is formed during pasteurisation, when the orange juice component hesperidin reacts with peracetic acid, which is commonly used as a cleaning agent for cleaning-in-place (CIP) in the fruit juice industry.

“Inadequate rinsing of the machines after the CIP process could therefore have led to contamination of the orange juice with peracetic acid and caused the formation of 5-vinylguaiacol during further processing,” Steinhaus said. Based on the new scientific findings, the team recommends that orange juice processing companies should no longer use peracetic acid as a cleaning agent.

There are other odorants that may be the cause of off-flavours in orange juice, for example, heating orange juice may produce cabbage-like smell dimethyl sulfide. Prolonged storage of the juice can also lead to chemical reactions that produce α-terpineol, which smells like turpentine. This odorant is formed under the influence of acid from the compounds limonene and linalool, which are present in high concentrations in orange juice. Oxidation reactions during storage may also lead to the formation of (S)-carvone from limonene, which smells like caraway.

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