Abstract
Defects in coffee affect the sensory quality of finished drink. To avoid this, defective beans are usually removed after threshing, as, once the green beans have been roasted, it becomes difficult to identify the defects. Procedures have been developed to evaluate coffee samples using infrared spectroscopy to detect such defects. As such, this study evaluated infrared spectra and sensory attributes of 39 coffee samples in: commercial ground and instant coffees, medium and high roast quality coffees, and defects present in the coffee. The sensory analysis was performed by 10 judges, semi-trained by a Q-grader, and eleven attributes were assessed using a semi-structured hedonic scale. The spectra obtained from the coffee samples were processed by area normalization, first derivative, and second derivative, later followed by principle component analyses. The sensory results showed differences in the evaluated attributes, differentiating between the samples of high quality medium roast coffee from the other samples. Principal component analysis applied to IR spectra showed that when normalizing the data by area, the samples were discriminated, which explained 84% of variance; coffee defects in the samples of ground commercial coffee were separated from high quality coffee and instant coffee. Using the chemical descriptors obtained from the infrared spectra, it was possible to differentiate between high quality, commercial and instant coffee. Key words: Coffee bean defects; FTIR-ATR; principal component analysis; quality coffee.
Highlights
Quality coffee is the result of good agricultural practices and proper post-harvest handling
Given the need to establish a rapid assessment of the presence of defects and their influence on sensory quality, the purpose of this paper was to: i) evaluate and compare the sensory attributes and chemical markers of the infrared spectrum between defective and non-defective Colombian coffee samples, and ii) establish a classification of coffee samples by applying the principal component analysis (PCA) method to the data obtained from infrared spectroscopy
According to the roasting table described by Wei and Tanokura (2014), medium roasted quality coffees were classified as medium roasting and instant coffee samples as cinnamon roasted
Summary
Quality coffee is the result of good agricultural practices and proper post-harvest handling. Its intrinsic characteristics meet a requirement that may be a necessity or an expectation (ISO, 2000). In roasted and ground coffee, the addition of defective beans is a common practice, which negatively affects the sensory characteristics of the beverage (Reis; Franca; Oliveira, 2013a; 2013b). Defective beans become evident after the threshing stage, and these must be selected and eliminated by physical analysis to avoid imbalances in the coffee’s organoleptic characteristics (Puerta- Quintero, 2001). The green coffee beans are roasted, after which it becomes difficult to identify the defects (Diaz et al, 2018). Sensory evaluation is used to assess coffee quality, which is a subjective method, as it requires expert tasters and the procedures imply a considerable investment of time (Craig et al, 2018)
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