No abstract

In this study, the odour-active volatile compounds present in a coffee aroma concentrate obtained from a soluble coffee extract in an industrial aroma recovery system based on distillation and evaporation were characterized by solid-phase microextraction coupled to gas chromatography with mass spectrometry and olfactometric detection technique. This analysis allowed the identification of 58 compounds, of which 15 pyrazines, 9 furans, 6 aldehydes, 4 ketones, 4 esters, 4 pyrroles, 4 sulphur compounds, 3 pyridines, 3 phenols, 3 alcohols, an oxazole, and a pyran are highlighted. From these families, the following compounds presented the highest sensory activities (%MF = 100): 2-methylbutanal, 2-methyl-2-butenal, 2-furancarboxaldehyde, furfural, and methyl phenyl acetate. These compounds can be considered as quality markers in the process control on the aroma recovery system.Caracterización de compuestos de aroma presentes en un concentrado de recuperación industrial de aromas de café. RESUMEN PALABRAS CLAVE proceso de recuperación de aromas; compuestos aromáticos; SPME-GC-O-MS; aroma de café; café instantáneo (soluble) CONTACT Julián Zapata

Concentrated liquid coffees (CLCs) refer to stored extracts stable at environmental temperature, used as ingredients in the retail market. Their low chemical stability affects the sensory profile. This study was performed in two CLCs, one without additives (BIB) and another with a mix of sodium benzoate and potassium sorbate additives (SD), stored at 25 °C for one year. Quantitative-Descriptive (QDA) and discriminant analyses permitted identifying the critical sensory attributes and their evolution over time. The concentrate without additives presented an acceptance limit of 196 days (evaluated at a 50% acceptance ratio), while the additives increased the shelf life up to 226 days (38.9% improvement). The rejection was related to a decreased aroma, increased acidity, and reduced bitterness. A bootstrapped feature selection version of Partial Least Square analysis further demonstrated that reactions of 5-caffeoylquinic acid (5CQA) and 3,5-dicaffeoylquinic acid (3,5diCQA) could cause changes in the aroma at the first degradation stage. In the following stages, changes in fructose and stearic acid contents, a key indicator of acceptance for both extracts possibly related to non-enzymatic reactions involving fructose and other compounds, might affect the bitterness and acidity. These results provided valuable information to understand flavor degradation in CLCs.

In this study, we aimed to apply an untargeted LC/QTOF-MS analysis for the identification of compounds that positively and negatively affect the acceptance of coffee beverages from liquid coffee concentrates (CLCs) before and after storage. The metabolomic results were integrated with physicochemical and sensory parameters, such as color, pH, titratable acidity, and oxygen contents, by a bootstrapped version of partial least squares discriminant analysis (PLS-DA) to select and classify the most relevant variables regarding the rejection or acceptance of CLC beverages. The OPLS-DA models for metabolite selection discriminated between the percent sensory acceptance (the Accepted group) and rejection (the Rejected group). Eighty-two molecular features were considered statistically significant. Our data suggest that coffee sample rejection is associated with chlorogenic acid hydrolysis to produce ferulic and quinic acids, consequently generating methoxybenzaldehydes that impact the perceived acidity and aroma. Furthermore, acceptance was correlated with higher global scores and sweetness, as with lactones such as feruloyl-quinolactone, caffeoyl quinolactone, and 4-caffeoyl-1,5-quinolactone, and significant oxygen levels in the headspace.

BACKGROUND:The main by-product of the coffee industry is spent coffee grounds (SCG). To the best of our knowledge, this is the first occasion where industrial SCG has been used to build a batch-valorization line combining barrel coffee roasters as an innovative drying process and ultrasound-assisted extraction technology under the biorefinery concept, seeking to extract chlorogenic acids (CGA).RESULTS: A Probat Sample Barrel Roaster were used to determine the optimal temperature, volume flow of fan, and time for a novel drying method. Drying optimization was carried out in order to reach 5.0% moisture content, reduce water activity and maximize total CGA content. Optimal conditions of 140 °C, 160.0 m 3 h −1 and 11.43 min for temperature, volume flow of fan, and time, respectively, were obtained with a desirability of 70%. Likewise, the optimal temperature, power and frequency settings for an ultrasonic extraction procedure of CGA from dried SCG were evaluated. To maximize the total CGA content, the ultrasonic technique was optimized. Temperature 50 °C, frequency 37 kHz and power 100 W with a desirability of 80% were necessary for optimality. The study was completed with a kinetic analysis using a second-order rate model, Peleg's kinetic model and the phenomenological model. CONCLUSION: Industrial coffee by-products can be processed and valorizing using barrel coffee roasters as a novel technique. For process design, the kinetic parameters of ultrasound-assisted extraction are a helpful tool. A new mathematical model is presented that takes into account the impact of changing temperature on the ultrasonic process.