The chemistry of Banana, smell and flavor

Technical Knowledge 🔎
Written by Fulvio Ciccolo
banana smell rose Scentspiracy

Banana is one of the clearest examples of how a handful of esters can suggest a fruit, while the real fruit remains far more complex. The first banana flavors relied mainly on amyl and isoamyl esters; analytical studies later revealed a wider mix of esters, alcohols, aldehydes and ketones that changes with cultivar and ripeness (Jordan et al., 2001; Zhu et al., 2018). This article follows that path, from early formulas to the compounds identified in the fruit.

Banana flavor in the '20s

Imitating banana flavor worked reasonably well from the start. Amyl and isoamyl acetate, as well as amyl butyrate, have been shown to occur in nature and proved excellent ingredients for a fairly faithful formulation (Fenaroli, n.d.). Isoamyl acetate was one of the first compounds used in artificial flavors to be confirmed in the real fruit as well (Mayer, 2017). The names amyl acetate and isoamyl acetate refer to closely related compounds that were used almost interchangeably in commercial practice (Mayer, 2017).

Artificial banana flavor is older than the 1920s: flavor historian Nadia Berenstein traced American formulas for banana flavoring to the 1860s and advertisements for banana “fruit essences” to the early 1850s (Mayer, 2017).

In perfumery terms, the note of these esters is completed by a green, woody facet and by a more volatile fruity facet; amyl butyrate in particular has a ripe fruity note.

The formulas of the 1920s

Formulators sought better results by adding other esters, citrus essential oils and vanillin. Formulas from around 1920, intended for flavoring hard candy at an approximate yield of 1 × 3000, were made up for about 50% of amyl acetate and amyl butyrate, generally in a 2:3 ratio, and for about another 20% of amyl valerate (Fenaroli, n.d.).

Other esters were used in smaller proportions, such as caprylate and ethyl nitrate. Citrus essential oils together with vanillin accounted for a maximum of 10% (Fenaroli, n.d.).

In formulations without essential oils, the ester proportions increased, reaching (Fenaroli, n.d.):

  • 44% amyl butyrate

  • 43% amyl acetate

  • 8% ethyl butyrate

  • 4% vanillin

  • 1% geranyl propionate

Some formulators proposed about 10% acetaldehyde (acetic aldehyde) in formulas built on more than 50% amyl acetate, but containing strong floral notes of rose and violet, as well as coumarin, vanilla and heliotropin (piperonal), altogether about 10% (Fenaroli, n.d.).

Early imitations of the banana aroma were therefore rather elementary, and the range of constituents was very narrow. This fits the wider history of synthetic fruit flavors: early chemists rarely analyzed the fruit itself, because aroma compounds occur in tiny amounts, and instead relied on sensory resemblances between available synthetic esters and fruit (Mayer, 2017).

Mid-modern times

From a perfumer’s point of view, today’s banana accords have not moved far from these early schemes. The substantial qualitative improvement came when esters of high purity became available.

A more rounded banana note can be built on amyl acetate, isoamyl acetate and isoamyl butyrate, then developed with materials such as:

  • benzyl butyrate

  • 2-ethylbutyl acetate

  • methyl heptenone

  • isopropyl benzyl carbinol

  • methyl amyl ketone (2-heptanone) (The Good Scents Company, n.d.-a)

  • ethyl enanthate (ethyl heptanoate) (The Good Scents Company, n.d.-c)

  • ethyl valerate

  • hexyl acetate

  • cyclohexanol esters (isovalerate, butyrate and propionate)

Not all of these materials have been identified among the constituents of natural banana flavor, so their use may be subject to limitations depending on the application and market.

The use of acetate and butyl butyrate may also be interesting (Fenaroli, n.d.).

Volatile compounds identified in banana

There have been many studies on the formation of banana flavor, most of them since 1950 (Fenaroli, n.d.). Bananas from different cultivars and at different degrees of ripeness have been studied: as expected, the usual constituents recur, but their proportions vary widely. Comparing two cultivars, Zhu et al. (2018) found that C6 aldehydes such as hexanal and trans-2-hexenal, together with 1-hexanol, dominated the volatile profile of mature-green fruit. As ripening progressed, esters such as isoamyl acetate and isoamyl butyrate increased sharply, while unsaturated aldehydes and alcohols decreased.

Fenaroli (n.d.) reports the presence of the following compounds in banana; many of them have also been found in more recent analyses (Jordan et al., 2001; Zhu et al., 2018):

  • ethyl acetate

  • ethyl alcohol

  • 2-pentanone

  • 1-propanol

  • isobutyl acetate

  • 2-butanol

  • n-butyl acetate

  • 2-pentanol acetate (2-pentyl acetate) (The Good Scents Company, n.d.-b)

  • 1-butanol

  • isoamyl acetate

  • isoamyl alcohol (3-methyl-1-butanol)

  • amyl acetate

  • trans-2-hexenal

  • 2-pentenyl butyrate

  • n-hexyl acetate

  • isoamyl butyrate

  • 1-hexanol

  • 1-hexanyl acetate

Detection is not the same as odor contribution. In a GC-olfactometry study of Cavendish banana essence, 2-pentanone, 2-pentanol and butanol were among the most concentrated compounds without being key odorants, whereas isoamyl acetate, 2-pentanol acetate, 2-methyl-1-propanol, 3-methyl-1-butanol, 3-methylbutanal, acetal, hexanal, ethyl butyrate, 2-heptanol and butyl butyrate were perceived by all panelists in every replicate (Jordan et al., 2001).

Why alcohols matter

The presence of alcohols is particularly interesting. These components had generally not been given much consideration in banana formulas, yet they can be very effective in recreating the slightly musty, woody note that often accompanies the green facet of many natural banana flavors (Fenaroli, n.d.). Analytical data point the same way: in the banana essence analyzed by Jordan et al. (2001), 3-methyl-1-butanol (isoamyl alcohol) was the most concentrated compound, and both 3-methyl-1-butanol and 2-methyl-1-propanol were among the odorants recognized by every panelist.

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References

Fulvio Ciccolo
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