Mesoscopic modelling and simulation of espresso coffee extraction

A mesoscopic model for the simulation of espresso extraction based on the Smoothed Particle Hydrodynamics method is presented. The model incorporates some essential features such as bimodal granulometry (fines-coarses) of the coffee bed, double (liquid/intra-granular) molecular diffusion and solid-liquid release mechanism. The porous structures ('coarses') are modelled as stationary solid regions whereas the migration of cellular fragments ('fines') is described by single-particles advected by the flow. The boundary filter is modelled as a buffer region where fines are immobilized while entering it, therefore providing a transient flow impedance. The model captures well the transient permeability of the coffee bed under direct-inverse discharge observed in experiments, showing the importance of fines migration on the hydrodynamics of the extraction. The concentration kinetics for different molecular compounds (i.e caffeine, trigonelline and chlorogenic acid) are compared to experimental data for a traditional espresso extraction, showing excellent results. The present work lays down the basis for the virtual analysis of coffee flavors by monitoring the hydrodynamic and microstructural effects on the balance of extracted key-odorant or taste-actives compounds in the beverage.Project RTI2018-094595-B-I00 funded by (AEI/FEDER, UE) and acronym “VIRHACOST

Simulation of espresso coffee extraction using smoothed particle hydrodynamics

A mesoscopic model for the simulation of espresso extraction based on the Smoothed Particle Hydrodynamics method is presented. The model incorporates some essential features such as bimodal granulometry (fines-coarses) of the coffee bed, double (liquid/intra-granular) molecular diffusion and solid-liquid release mechanism. The porous structures (’coarses’) are modelled as stationary solid regions whereas the migration of cellular fragments (’fines’) is described by single-particles advected by the flow. The boundary filter is modelled as a buffer region where fines are immobilized while entering it, therefore providing a transient flow impedance. The model captures well the transient permeability of the coffee bed under direct-inverse discharge observed in experiments, showing the importance of fines migration on the hydrodynamics of the extraction. The concentration kinetics for different molecular compounds are also studied. The present work lays down the basis for the virtual analysis of coffee flavors by monitoring the hydrodynamic and microstructural effects on the balance of extracted key-odorant or taste-actives compounds in the beverage

Dermoscopy of Pitted Keratolysis

Irritated hyperhidrotic soles with multiple small pits are pathognomonic for pitted keratolysis (PK). Here we show the dermatoscopic view of typical pits that can ensure the diagnosis. PK is a plantar infection caused by Gram-positive bacteria, particularly Corynebacterium. Increases in skin surface pH, hyperhidrosis, and prolonged occlusion allow these bacteria to proliferate. The diagnosis is fundamentally clinical and treatment generally consists of a combination of hygienic measures, correcting plantar hyperhidrosis and topical antimicrobials

Modeling the effect of flow-induced mechanical erosion during coffee filtration

The espresso extraction process involves a complex transport inside a geometry-changing porous medium. Large solid grains forming the majority of the porous medium can migrate, swell, and consolidate, and they can also morphologically change during flow, i.e., being mechanically eroded by hydrodynamic forces. These processes can, in turn, have a significant back-effect on the flow and the related coffee extraction profiles. In this article, we devise a bottom–up erosion model in the framework of smoothed dissipative particle dynamics to consider flow-induced morphological changes of the coffee grains. We assume that the coffee grains are not completely wetted and remain brittle. We found that heterogeneity in both the filtration direction and the transverse direction can be induced. The former is controlled by the angle of internal friction while the latter is controlled by both the cohesion parameter and the angle of internal friction. Not restricted to the modeling of espresso extraction, our model can also be applied to other eroding porous media. Our results suggest that, under ideal porous flow conditions, we can control the heterogeneity (in both the pressure drop direction and the transverse direction) of an eroding medium by tuning the yield characteristics of the eroding material

Bare carbon electrodes as simple and efficient sensors for the quantification of caffeine in commercial beverages

This work has been supported by the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 642014 (IPCOS). Ĺ.Š. would like to acknowledge the Grant Agency of the Slovak Republic (grant no. 1/0489/16)

NMR quantification of 16-O-methylcafestol and kahweol in Coffea canephora var. robusta beans from different geographical origins

Diterpenes have recently received a great deal of interest as tools to investigate the botanical origin of coffee. Specifically, kahweol has been proposed as a marker of Coffea arabica while 16-O-methylcafestol (16-OMC) is a Coffea canephora specific marker and its detection and quantification allow the authenticity of pure C. arabica roasted coffee blends to be assessed. In this study, we evaluated the possibility of the industrial use of the quantification of these diterpenes to assess the relative amounts of the two coffee species in blends. The content of 16-OMC and kahweol was determined in 78 samples (i.e., 39 green and the corresponding 39 roasted beans) of C. canephora from different geographical origins using a recently published NMR approach. Our results show a small natural variability in 16-OMC content for the Asian samples (average content = 1837 \ub1 113 mg/kg) while a much larger spread was found for the African samples (average content = 1744 \ub1 322 mg/kg). This large variability prevents the use of 16-OMC to quantify C. canephora in unknown roasted coffee blends. We also show that kahweol cannot be considered a specific C. arabica marker since it was detected almost all coffees and quantified in about 30% of the C. canephora samples

Simultaneous quantification of antioxidants paraxanthine and caffeine in human saliva by electrochemical sensing for CYP1A2 phenotyping

The enzyme CYP1A2 is responsible for the metabolism of numerous antioxidants in the body, including caffeine, which is transformed into paraxanthine, its main primary metabolite. Both molecules are known for their antioxidant and pro-oxidant characteristics, and the paraxanthine-to-caffeine molar ratio is a widely accepted metric for CYP1A2 phenotyping, to optimize dose\u2013 response effects in individual patients. We developed a simple, cheap and fast electrochemical based method for the simultaneous quantification of paraxanthine and caffeine in human saliva, by differential pulse voltammetry, using an anodically pretreated glassy carbon electrode. Cyclic voltammetry experiments revealed for the first time that the oxidation of paraxanthine is diffusion controlled with an irreversible peak at ca. +1.24 V (vs. Ag/AgCl) in a 0.1 M H2 SO4 solution, and that the mechanism occurs via the transfer of two electrons and two protons. The simultaneous quantification of paraxanthine and caffeine was demonstrated in 0.1 M H2 SO4 and spiked human saliva samples. In the latter case, limits of detection of 2.89 \ub5M for paraxanthine and 5.80 \ub5M for caffeine were obtained, respectively. The sensor is reliable, providing a relative standard deviation within 7% (n = 6). Potential applicability of the sensing platform was demonstrated by running a small scale trial on five healthy volunteers, with simultaneous quantification by differential pulse voltammetry (DPV) of paraxanthine and caffeine in saliva samples collected at 1, 3 and 6 h postdose administration. The results were validated by ultra-high pressure liquid chromatography and shown to have a high correlation factor (r = 0.994)

Hepatic PPARs: their role in liver physiology, fibrosis and treatment

Complex molecular and cellular mechanisms are involved in the pathway of liver fibrosis. Activation and transformation of hepatic stellate cells (HSCs) are considered the two main reasons for the cause and development of liver fibrosis. The peroxisome proliferator-activated receptors (PPARs) belonging to the family of ligand-activated transcription factors play a key role in liver homeostasis, regulating adipogenesis and inhibiting fibrogenesis in HSCs. Normal transcriptional function of PPARs contributes to maintain HSCs in quiescent phase. A reduced expression of PPARs in HSCs greatly induces a progression of liver fibrosis and an increased production of collagen. Here, we discuss role and function of PPARs and we take into consideration molecular factors able to reduce PPARs activity in HSCs. Finally, although further validations are needed, we illustrate novel strategies available from in vitro and animal studies on how some PPARs-agonists have been proved effective as antifibrotic substances in liver disease

Phospholipase activities in green coffee beans (Coffea arabica L.) harvested in different countries

Triacylglycerols (TAGs) are accumulated in specialised organelles called \u201coil bodies\u201d, which are enclosed in a phospholipid monolayer embedded with some unique proteins. Upon germination, such membranes are modified to allow the availability of TAGs as an energy source during early stages of seedling growth in oilseeds. This process occurs by the sequential and/or collective action of many hydrolytic enzymes, such as phospholipases, lipoxygenases and lipases that are associated to oil body membranes. In contrast, during seed storage, oilseed lipids may undergo lipolytic degradation processes leading to a wide range of metabolites potentially harmful for seed viability. In particular, green coffee endosperm consist of approx. 99% of the mature seed mass and contains many polyunsaturated fatty acids whose degradation leads to volatile compound formation through the oxylipin pathway. In spite of this, the enzymes involved in TAGs degradation (particularly lipases) are poorly studied. Therefore, the aim of this work was to evaluate the involvement of phospholipase activity in oil body membrane degradation during storage of green coffee (Coffea arabica L.) and to determine the correlations between storage lipid mobilization and maintenance of seed viability in beans harvested in different countries (Ethiopia, India, Kenya and Tanzania). Green coffee beans were frozen and powdered in liquid nitrogen and oil bodies were extracted with cold acetone. Phospholipase A1 and A2 activities were assayed in crude extracts by a fluorimetric method, using different probes. Such activities were just partially stimulated by free Ca2+, in contrast with what reported by others. Furthermore, PLA2 activity was assayed in a wide range of pH, evidencing two peaks of pH optimum. These results suggests that green coffee bean presents at least two isoforms of PLA2. Phospholipase profiles (PLA2 and total) were correlated with the provenience of the beans, showing a higher activity in those harvested in Ethiopia, while the lower was associated to beans from India