Discrimination between Immature and Mature Green Coffees by Attenuated Total Reflectance and Diffuse Reflectance Fourier Transform Infrared Spectroscopy

Abstract

The objective of this work was to evaluate the potential of Fourier transform infrared spectroscopy (FTIR) in the characterization and discrimination between immature and mature or ripe coffee beans. Arabica coffee beans were submitted to FTIR analysis by reflectance readings employing attenuated total reflectance (ATR) and diffuse reflectance (DR) accessories. The obtained spectra were similar, but in general higher absorbance values were observed for nondefective beans in comparison to immature ones. Multivariate statistical analysis (principal component analysis, PCA, and agglomerative hierarchical clustering, AHC) was performed in order to verify the possibility of discrimination between immature and mature coffee samples. A clear separation between immature and mature coffees was observed based on AHC and PCA analyses of the normalized spectra obtained by employing both ATR and DR accessories. Linear discriminant analysis was employed for developing classification models, with recognition and prediction abilities of 100%. Such results showed that FTIR analysis presents potential for the development of a simple routine methodology for separation of immature and mature coffee beans. Practical Application: The ultimate goal of this research is to be able to propose improvements in the way immature coffee beans are separated from graded mature beans in coffee facilities (cooperatives and other coffee producer's associations). The results obtained herein point toward FTIR as a potential tool for the aimed improvements.

Discrimination between roasted coffee, roasted corn and coffee husks by Diffuse Reflectance Infrared Fourier Transform Spectroscopy

“…Such bands have been previously reported present in spectra of roasted Arabica and Robusta coffee samples (Craig et al, 2012b;Kemsley et al, 1995) and also of crude coffee samples (Craig et al, 2011(Craig et al, , 2012a. Paradkar and Irudayaraj (2002) also reported two sharp peaks at 2882 and 2829 cm À1 in samples of caffeinated beverages such as coffee, tea and soft drinks.…”

“…In general, DRIFTS provided spectra that presented higher intensity of absorption in comparison to ATR-FTIR. Both techniques were satisfactory for discrimination between immature and mature coffees (Craig et al, 2011). However, even though DRIFTS provided complete discrimination between defective (low quality) and non-defective (high quality) coffees, ATR-FTIR could not provide complete discrimination between nondefective and sour (fermented) coffees (Craig et al, 2012a).…”

“…The specific applications were discrimination between Arabica and Robusta varieties (Kemsley et al, 1995;Suchánek et al, 1996), detection of glucose, starch or chicory as adulterants of freeze-dried instant coffees (Briandet et al, 1996), determination of caffeine content (Gallignani et al, 2008;Garrigues et al, 2000;Singh et al, 1998), evaluation of roasting conditions (Lyman et al, 2003;Wang et al, 2011), geographical discrimination (Wang et al, 2009; and separation between decaffeinated and regular roasted coffees (Ribeiro et al, 2010). A few recent studies have compared ATR-FTIR and DRIFTS for analysis of solid samples, aiming at discrimination between high and low quality coffees prior to roasting (Craig, Franca, & Oliveira, 2011;Craig, Franca, & Oliveira, 2012a). In general, DRIFTS provided spectra that presented higher intensity of absorption in comparison to ATR-FTIR.…”

Discrimination between defective and non-defective roasted coffees by diffuse reflectance infrared Fourier transform spectroscopy

“…These beans represent about 20% of the total coffee produced in Brazil and similar amounts can be expected in other producing areas around the world (Mendonça, Franca, Oliveira, & Nunes, 2008;Ramalakshmi, Kubra, & Rao, 2007). Although separated from the non-defective beans prior to commercialization in external markets, the majority of the defective beans are dumped in the Brazilian internal market and, overall, a low-grade roasted coffee is consumed in the country (Craig, Franca, & Oliveira, 2011). The negative effect that such beans have on coffee quality can be associated to specific problems that occur during harvesting and post-harvest processing operations.…”

“…Research interest on defective and low quality coffee beans has intensified over the past years, given the increasing awareness regarding the negative aspects they impart to the quality of the roasted and ground coffee used for beverage preparation and consumption (Craig et al, 2011;Craig, Franca, & Oliveira, 2012;Farah, Monteiro, Calado, Franca, & Trugo, 2006;Franca, Oliveira, Mendonça, & Silva, 2005;Mancha Agresti, Franca, Oliveira, & Augusti, 2008;Mendonça et al, 2008;Mendonça, Franca, Oliveira, & Afonso, 2009;Oliveira, Franca, Mendonça, & Barros-Junior, 2006;Ramalakshmi et al, 2007;Vasconcelos, Franca, Glória, & Mendonça, 2007). Such studies have shown that there are physical and chemical differences between defective and non-defective coffee beans prior to roasting, but only a few have attained some success regarding discrimination of defective and non-defective coffees after roasting.…”