Volatile off‐flavour compounds in desiccated coconut

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Abstract
Aliphatic methyl ketones and secondary alcohols have been isolated from desiccated coconut and shown to be responsible for the rancid off‐flavour. Two series of compounds have been isolated. The series with an odd number of carbon atoms (C5,7,9,11) comprising pentan‐2‐one, pentan‐2‐ol, heptan‐2‐one, heptan‐2‐ol, nonan‐2‐one, nonan‐2‐ol and undecan‐2‐one is derived from even chain fatty acids one carbon atom longer, present in the coconut oil by a modified β‐oxidation due to growth of moulds. Heptan‐2‐one and nonan‐2‐one were present in the greatest concentration in the rancid coconut. These compounds gave an odour reminiscent of rancid almonds and turpentine respectively while heptan‐2‐ol and nonan‐2‐ol gave an odour similar to rancid coconut as well as a musty, stale odour. This type of off‐flavour has been called ketonic rancidity and is an oxidative variation of the hydrolytic type of rancidity. The presence and origin of the even numbered series (C6,8), hexan‐2‐one, hexan‐2‐ol and octan‐2‐one is discussed. The increase in C5,6,7,8,9,11 oxidation products in the rancid samples occurred at the expense of C8,10,12 short chain fatty acids.