Pineapple aroma contains more than fruity compounds. It also includes compounds described on their own as reminiscent of meat or onions. A 2012 study compared Tainong No. 4 and Tainong No. 6 grown in China, showing that even cultivars developed from the same parental cross differed in the compounds likely to contribute to their aroma.
Sweet, caramel-like furaneol in Tainong No. 4 and fruity ethyl 2-methylbutyrate in Tainong No. 6 had particularly high values on an index calculated from concentration and odor detectability. Sulfur-containing esters were also important candidates common to both cultivars.
Examining two cultivars with the same method
The aim was to identify the compounds responsible for each cultivar’s characteristic aroma and explain the differences. The researchers used three fruits per cultivar obtained from a research institution in Guangdong, China, and also measured peel and flesh color and soluble solids.
For aroma analysis, they used 10 g of peeled, crushed flesh. While stirring it in a container, they collected compounds released from the flesh into the air for 40 minutes at 25°C and analyzed them by gas chromatography–mass spectrometry. Compounds were compared with standards and databases, and amounts were determined using an internal standard.
The measurements therefore concern volatile compounds recoverable from crushed flesh under these conditions. The purpose differs from directly evaluating preference while eating or the strength of the aroma of an intact fruit.
Abundant compounds are not necessarily the most readily smelled
Esters dominated the measured amounts in both cultivars. The most abundant compound in Tainong No. 4 was methyl 3-(methylthio)propanoate, a sulfur-containing ester. In Tainong No. 6, its ethyl counterpart was detected in the largest amount.
However, the most abundant compound does not necessarily make the greatest contribution to aroma. The researchers therefore calculated an index called the odor activity value, or OAV. This divides a compound’s concentration by the concentration at which its odor first becomes detectable. A compound detectable at a small amount can have a high OAV.
The study used odor thresholds in water reported in earlier literature. Compounds with OAVs greater than 1 were selected as candidates likely to contribute to aroma. A key point is that this value does not directly measure a compound’s actual contribution within the mixture of substances in fruit flesh.
Sweet notes stood out in No. 4, fruity compounds in No. 6
In Tainong No. 4, furaneol had the highest OAV, at 2,549. The paper describes its odor as sweet and reminiscent of pineapple and caramel. The next highest was δ-octalactone, described as coconut-like. The methyl and ethyl sulfur-containing esters also exceeded 1, making four candidate contributors to the cultivar’s characteristic aroma.
In Tainong No. 6, fruity ethyl 2-methylbutyrate had the highest value, at about 3,707, and apple-like methyl 2-methylbutyrate was also high. Together with decanal, ethyl hexanoate, and the ethyl sulfur-containing ester, five compounds were selected.
The authors suggested that this combination of fruity compounds might explain why Tainong No. 6 is called apple pineapple. An OAV of about 3,707 does not mean that the fruit smells 3,707 times stronger. It is the ratio of the concentration to the selected odor threshold.
An onion-like compound can be part of a fruit aroma
For the two sulfur-containing esters, the paper’s odor-description table includes meaty and onion-like descriptors. The same table states that at low concentrations, the methyl compound can also smell fruity and the ethyl compound pineapple-like. Assigning just one odor to each compound overlooks these concentration-dependent differences in character.
The ethyl compound had an OAV above 1 in both cultivars. The methyl compound, meanwhile, had an OAV of 3.46 in Tainong No. 4 and 0.18 in Tainong No. 6. It was present in No. 6 too, but the calculation using the selected threshold gave it less weight as an individual candidate contributor.
The authors considered pineapple aroma to arise from combinations of esters, sulfur-containing compounds, terpenes, and other substances. However, this study did not reconstruct the fruit aroma by remixing compounds or test changes after omitting one ingredient. Given that only three fruits per cultivar were sampled, the findings are best read as chemical clues to the differences between cultivars.
Summary
The two pineapple cultivars differed not only in compound amounts but also in their leading candidates when odor thresholds were taken into account. Sweet furaneol and a coconut-like lactone stood out in Tainong No. 4, while fruity esters stood out in Tainong No. 6. The ethyl sulfur-containing ester was common to both.
Understanding what makes pineapple smell like pineapple means looking beyond sweet fruit notes to compounds that can have meaty, onion-like, or fruity characters depending on concentration. Combining abundance with detectability makes these aroma differences more concrete.
The research was supported by public-interest agricultural research funding from China’s Ministry of Agriculture, the Hainan Provincial Natural Science Foundation, basic research funding for central research institutions, and research grants from Yunnan’s education authorities. The authors declared no competing interests.
Reference
Zheng LY, Sun GM, Liu YG, et al. Aroma Volatile Compounds from Two Fresh Pineapple Varieties in China. International Journal of Molecular Sciences. 2012;13:7383–7392. Original paper
