Patterns and compound specific stable carbon isotope analysis (δ13 C) of capsaicinoids in Cayenne chilli fruits of different ripening stages.

Abstract

Capsaicinoids are alkaloids of high pungency which are exclusively formed by fruits of the genus Capsicum. Capsaicinoid content and composition of Capsicum fruits are influenced by ripening. Determination of changes in content and pattern of individual capsaicinoids in chilli pods with fruit ripening. Compound specific stable carbon isotope analysis (δ13 C values (‰), CSIA) was used for a better understanding of capsaicinoid development during fruit ripening. Cayenne chillies (Capsicum annuum) were grown in a glasshouse and harvested from different plants at four ripening stages (unripe, semi-ripe, ripe, overripe). Nine capsaicinoids (one verified by synthesis) were quantified by gas chromatography with mass spectrometry (GC-MS). For CSIA, an acetylation method for derivatising capsaicinoids was developed. Variations in the patterns of the nine capsaicinoids were not relatable to a distinct ripening stage and also total contents varied extensively from plant to plant. However, changes in total capsaicinoid concentrations were systematic. In almost all plants, maximum values were reached in unripe fruits, then decreased to semi-ripe samples and increased again in the following ripening process. Likewise, δ13 C values of individual capsaicinoids were always by ~2‰ heavier in unripe than in semi-ripe or ripe fruits. However, direction of changes in sum-δ13 C values (‰) (taking contributions of all capsaicinoids together) could not be explained by corresponding variations in capsaicinoid concentrations. Both quantification and δ13 C values (‰) verified the presence of ripening-related changes in the capsaicinoid content which may be caused by simultaneously proceeding reactions like synthesis, storage and degradation of capsaicinoids.