NIRS and Aquaphotomics Trace Robusta-to-Arabica Ratio in Liquid Coffee Blends

Abstract

Coffee is both a vastly consumed beverage and a chemically complex matrix. For a long time, an arduous chemical analysis was necessary to resolve coffee authentication issues. Despite their demonstrated efficacy, such techniques tend to rely on reference methods or resort to elaborate extraction steps. Near infrared spectroscopy (NIRS) and the aquaphotomics approach, on the other hand, reportedly offer a rapid, reliable, and holistic compositional overview of varying analytes but with little focus on low concentration mixtures of Robusta-to-Arabica coffee. Our study aimed for a comparative assessment of ground coffee adulteration using NIRS and liquid coffee adulteration using the aquaphotomics approach. The aim was to demonstrate the potential of monitoring ground and liquid coffee quality as they are commercially the most available coffee forms. Chemometrics spectra analysis proved capable of distinguishing between the studied samples and efficiently estimating the added Robusta concentrations. An accuracy of 100% was obtained for the varietal discrimination of pure Arabica and Robusta, both in ground and liquid form. Robusta-to-Arabica ratio was predicted with R2CV values of 0.99 and 0.9 in ground and liquid form respectively. Aquagrams results accentuated the peculiarities of the two coffee varieties and their respective blends by designating different water conformations depending on the coffee variety and assigning a particular water absorption spectral pattern (WASP) depending on the blending ratio. Marked spectral features attributed to high hydrogen bonded water characterized Arabica-rich coffee, while those with the higher Robusta content showed an abundance of free water structures. Collectively, the obtained results ascertain the adequacy of NIRS and aquaphotomics as promising alternative tools for the authentication of liquid coffee that can correlate the water-related fingerprint to the Robusta-to-Arabica ratio.

Aquaphotomics—Exploring Water Molecular Systems in Nature

“…Out of the 21 published articles, 3 were reviews [ 2 , 3 , 4 ] and 18 were original research papers [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ], that can be roughly separated into 6 categories ( Figure 3 ).…”

“…The majority of the articles, approximately one third, belongs to the field of applications in agriculture and food science [ 8 , 9 , 12 , 13 , 14 , 21 , 22 ], a field from which aquaphotomics originated, and probably the reason why this category is still at the forefront of aquaphotomics development. Following this category are the preprocessing and chemometrics [ 2 , 4 , 15 , 18 ] and fundamental studies [ 5 , 6 , 10 , 17 ].…”

“…In the agricultural sector, aquaphotomics development in the area of food adulteration seem to be increasingly popular. Three papers in the Special Issue tackled challenges in food adulteration, specifically honey [ 8 , 21 ] and coffee [ 14 ]. While honey adulteration was a subject of investigations in several previous publications [ 33 , 34 , 35 ], the current ones contain two novelties.…”

“…While honey adulteration was a subject of investigations in several previous publications [ 33 , 34 , 35 ], the current ones contain two novelties. First, a study by Bodor et al [ 14 ] for the first time reports the aquaphotomics results in the detection of honey adulteration by heat processing. Their results prove that even at a low temperature treatment (40 °C), measurable changes occur in the spectra of the honey, as demonstrated in aquagrams of three types of honey (sunflower, bastard indigo, and acacia), and that these spectral changes are mainly related to the transformation of the highly bonded water to less-bonded water or free water.…”

“…Another important contribution of this paper is in the assignments and interpretation of the absorbance bands found to be important for honey adulteration, and their importance from the standpoint of honey functionality. The coffee adulteration work by Balkis et al [ 14 ] is another achievement in food adulteration detection, a particular research topic for which the group of Prof. Kovacs from Hungary is becoming increasingly recognized for. The coffee adulteration work was able to accurately determine the ratio of coffees Robusta (less expensive and easier to cultivate; therefore, commonly used as adulterant in higher-price coffee blends [ 36 , 37 ]) to Arabica in both ground and liquid forms.…”