Impact of harvest seasons on the volatile and non-volatile chemical composition of conilon coffee

Abstract

To obtain specialty coffees with superior sensory quality, researchers seek to understand the relationship between pre and post-harvest factors, with particular attention to the harvest timing. This study aims to determine chemical markers of two harvest periods of Coffea canephora (conilon) in june and august 2023 from a single plantation. The samples were processed using the washed method and evaluated sensorially by R-grader assessors. GC-MS was used to assess volatile compounds, and NMR was used for mainly non-volatile compounds. GC-MS employed solid-phase microextraction by headspace, and NMR was conducted on a 400 MHz spectrometer for 1H. Principal Component Analysis (PCA) was used to investigate separation trends based on the chemical differences between the harvest periods. Volatile compounds showed higher concentrations in the first harvest, highlighting chemical markers such as pyrrole, 2,3-dimethylpyrazine, 2,6-dimethylpyrazine, 2-methyl-5-ethylpyrazine, 2-ethyl-6-methylpyrazine, and methylpyrazine. Non-volatile compounds exhibited higher concentrations in the second harvest, with the presence of lactates, γ-butyrolactone, citrate, malate, caffeine, sugars (with caffeine signature), formic acid, N-methylpyridinium, trigonelline, and 5-hydroxymethylfurfural. Slow maturation tends to favor the formation and accumulation of chemical compounds that contribute to the complexity and superior quality of the beverage, which may be related to regional climatic conditions. The second harvest had higher sensory scores, consistent with the highlighted non-volatile chemical markers. Thus, it was possible to assess the effects of the harvest periods and their respective influences, suggesting when the harvest will result in a higher-quality beverage.

Keywords: Chemical composition; Coffee; Conilon; GC–MS; Harvest time; NMR.