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

Balkis Aouadi,Flora Vitalis,Istvan Kertesz,Zoltan Kovacs,Zsanett Bodor,John-Lewis Zinia Zaukuu

doi:10.3390/molecules27020388

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.

Highlights

The worldwide appeal of coffee, consumed as a functional beverage, and as a provider of unique cultural experiences, stems from its distinct organoleptic features
The efficacy of Near infrared spectroscopy (NIRS) in terms of separating the samples was based on their respective varieties, and on their provenance as the different samples came from different sources: Brazil (ARA1), Columbia (ARA2), Ethiopia (ARA3), Vietnam (ROB1), Uganda (ROB2), and India (ROB3)
This is in accordance with the findings reported by Giraudo et al [24], who proved that intra-varietal differences of coffee beans originating from different countries and continents can be traced by their respective NIR spectral patterns

Summary

Introduction

The worldwide appeal of coffee, consumed as a functional beverage, and as a provider of unique cultural experiences, stems from its distinct organoleptic features. These criteria are mostly defined by the respective geographic and varietal origin as well as the brewing processes. While genus Coffea exists under numerous varieties, Coffea arabica and Coffea canephora are the two commonly consumed ones [1]. The priciest of the two and marketed as having the higher quality grade, has been a prime target for fraud, propelled by the potential economic gains [2]. With regulations stipulating no more than 1% of foreign materials in coffee [3], this challenge becomes even more daunting

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