Correlations between capsaicin, dihydrocapsaicin and phenolic content in habanero chillies

Australia is a minor producer of chilli, with the industry producing around 2500 tonnes of chillies per year. Due to the small size of the industry, there is currently limited research on the typical levels of capsaicinoids in the Australian crop and the relationship between these constituents and other agronomic and nutritional factors. This study applied a rapid, maceration-based extraction protocol with end-over-end shaking, coupled with a HPLC-DAD method for the analysis of capsaicin and dihydrocapsaicin in 20 Habanero chilli samples from Queensland, Australia. All samples were from the same growing season (2020) but were taken from different within-field locations to ensure that all of the variability within the growing site was sampled. In addition to the capsaicinoid measurements, the total phenolic content was measured using the Folin-Ciocalteu assay, while antioxidant activity was measured using the Ferric Reducing Antioxidant Power (FRAP) method. The capsaicin concentration of the samples ranged from 1474–3916 mg/kg, while the dihydrocapsaicin content ranged between 638–1757 mg/kg, giving total pungencies of approximately 32,000 to 83,000 Scoville Heat Units. Similarly, the total phenolic content varied from 1000–1608 mg gallic acid equivalents/100 g, while the antioxidant activity ranged from 301 to 455 mg Trolox equivalents/100 g. Pearson linear correlation analysis revealed that the capsaicin and dihydrocapsaicin contents were strongly positively correlated with one another (R2 = 0.73; p < 0.001), with a mean capsaicin: dihydrocapsaicin ratio of 2.4:1. Furthermore, there was a moderate positive correlation between the total capsaicinoid content and total phenolic content of the samples (R2 = 0.58; p < 0.01), as well as a strong correlation between the total capsaicinoid content and FRAP (R2 = 0.81; p < 0.001). However, dry matter content was not significantly correlated with capsaicinoid content, total phenolic content or antioxidant activity (p > 0.05 for all). These results may be used to inform future breeding programs for high-capsaicin chilli varieties and support further research into the agronomic and genetic factors driving capsaicin and dihydrocapsaicin content.