Quantitative evaluation of the defects of roasted coffee by means of spectroscopy techniques
Today, the analysis of the chemical composition and the sensory evaluation are the methods mostly used for the quality control of roasted and ground coffee. As a result, the sector’s industry is more and more interested in finding faster methods. In this respect, a recent study conducted by a group of international researchers (Dias et al., 2018) proposed the use of Infrared photo-acoustic spectroscopy (FTIR-PAS) to assess, in a quantitative way; the presence of defects in roasted and ground coffee.
Therefore, beans characterized by specific defects were mixed with undamaged beans belonging to the variety Coffea Arabica (Arabic) and Coffea canephora (Robust). The mixtures thus obtained were then subjected to medium roasting (corresponding to a weight loss of 17%, and a brightness value, L*, comprised between 22 and 26) and grinding.
The results show that by applying the multivaried statistical analysis (PCA methods, Principal Components Analysis, and PLS-DA, minimum partial squares) to FTIR-PAS spectra a satisfactory differentiation of samples is obtained. In particular, it has been possible to classify 100% of the products in four different classes, in function of the presence of defects. In conclusion, the authors argue that the proposed method is conveniently used to characterize different coffee mixtures since it is accurate, quick and easy, as well as more environmentally friendly than traditional methods.
Classification of coffee using a colorimetric sensor
The aromatic properties of coffee are influenced by several factors, such as the variety and the processing conditions. The analytical methods that are commonly used to determine the aromatic profile of this product are based on gas-chromatography or mass-spectrometry. These methods are considered to be reliable, but since they are expensive and involve long analytical times, they are not particularly suitable for the development of a fast sample classification method.
In this respect, a recent study conducted by a group of Korean researchers (Kim & Kang, 2018) presents an innovative methodology based on the use of a colorimetric sensor for the differentiation of different types of coffee. The system is based on a hydrophobic membrane onto which twelve sensors were printed with selective sensitivity toward the main aromatic compounds of coffee. The experiment was performed using samples belonging to the varieties Arabica and Robusta, subjected to different degrees of roasting.
The results demonstrate that the colorimetric profiles of the products, supplied by the instrument, are easily differentiable to the naked eye, without applying any statistical method. However, the PCA (Principal Components Analysis) and the analysis of the groups was applied to classify samples of roasted coffee, espresso and coffee aeropress in function of the variety, of the degree of roasting, and the preparation procedure. The results confirm that the proposed system is potentially usable for the rapid discrimination of coffee-based products since it was able to classify correctly 57 out of 60 samples.
References
R.C.E. Dias et al., Food Chemistry, 255, 2018, 132-138
S.-Y. Kim & B.-S. Kang, Sensors & Actuators: B. Chemical, 275, 2018, 277-
