The Diversity of Green Bean Biochemical Compounds in Robusta Coffee (Coffea canephora Pierre ex A. Froehner) as Evaluated by Near Infrared Spectroscopy

Aims: This study characterized biochemical compound variability that influence green bean quality in C. canephora as a basis for identifying heterogeneous genotypes for use in crop improvement because genetic erosion aided by climate change effects is gradually threatening the cultivation of Ugandan Robusta coffee (Coffea canephora) local races.

Study Design: Four hundred and fifty four accessions from twenty four districts were analyzed with Near Infra Red Spectroscopy (NIRS) for six biochemical compounds using calibrations developed at CIRAD, France.

Place and Duration of Study: This work was conducted at the National Coffee Resources Research Institute (NaCORRI), Uganda between January 2007 and December 2013.

Methodology: Spectrometer Nirsystem 6500 Foss- (Denmark) machine and Software ISI NIRS 2 version 4.11 (Infra Soft International, Port Matilda, USA) were used to analyze ground samples in diffuse reflectance from 400 nm to 2500 nm (2 nm steps) and predictive models were used to quantify the biochemical contents in the green beans. Data was analyzed with XLSTAT version 2011.2.05 (Addinsoft), Paris, France.

Results: Chlorogenic acid and fat concentrations of 13.26 and 13.19% dry matter respectively reported in this study were much higher than 5.88 and 9.0% dry matter respectively reported earlier. Caffeine concentrations were positively significantly correlated with cholorogenic acid but negatively significantly correlated with trigonelline, sucrose, fat and dry matter contents. Caffeine and chlorogenic acid concentrations increased with age whereas trigonelline declined as trees aged. Chlorogenic acid and trigonelline concentrations were at their lowest levels in elevations of between 1000- 1200 metres above sea level and like fat and dry matter concentrations, the compounds were at their highest levels in higher elevations of about 1500 metres above sea level. Local landraces, ‘’nganda’’ and ‘’erecta’’ had higher concentrations of chlorogenic acid, sucrose and caffeine than improved, hybrid and commercial types.

Conclusions: Ugandan C. canephora caffeine content was lower than that of West-African Robusta coffee but higher than that of Arabica coffee. Four distinct diversity groups derived from the six biochemical compounds represented the major organoleptic categories. The results reported here will be useful in defining the desirable cup qualities of Robusta coffee as demanded by world markets.

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