Analytica, Volume 2, Issue 1 (March 2021) – 3 articles

Acetylcholinesterase (AChE) is responsible for hydrolyzing the acetylcholine neurotransmitter, bringing an end point to cholinergic neurotransmission. Thus, AChE is the primary target of a wide spectrum of compounds used as pesticides, nerve agents or therapeutic drugs for neurodegenerative diseases such as Alzheimer’s disease (AD). This enzyme is heterogeneously distributed in the brain showing different activity depending on the nervous region. Therefore, the aim of this work is to report a novel technology that enables the simultaneous determination of tissue specific AChE activity, as well as the analysis and screening of specific inhibitors, by using cell membrane microarrays. These microarrays were composed of cell membranes, isolated from 41 tissues, organs and brain areas, that were immobilized over a slide, maintaining the functionality of membrane proteins. To validate this platform, demonstrating its usefulness in drug discovery as a high throughput screening tool, a colorimetric protocol to detect the membrane-bound AChE activity was optimized. Thus, rat cortical and striatal AChE activities were estimated in presence of increased concentrations of AChE inhibitors, and the donepezil effect was assessed simultaneously in 41 tissues and organs, demonstrating the major potential of this microarray’s technology. Full article

Soluble solids concentration (SSC) is a reference index that is typically used to quantify soluble sugars, the most abundant constituents of stone fruit flesh dry matter when approaching maturity. Dry matter concentration (DMC) is another parameter that has been often associated with fruit quality. This study investigated the relationship of SSC and DMC in fourteen stone fruit cultivars at harvest. SSC and DMC were measured at physiological maturity in peach, nectarine, plum and apricot. SSC and DMC data had similar symmetrical patterns (range, means and variability) for most of the cultivars. Mean SSC ranged between 11.6 and 19.7 °Brix, and DMC between 11.6% and 19.4% w/w across all fruit studied. High variability in SSC was observed in apricot, with an interquartile range = 5.7 °Brix. A generic linear regression model that included peach, nectarine and plum cultivars revealed a robust association between DMC and SSC (p < 0.001, R² = 0.914, n = 2800) with a DMC prediction error (RMSE) equal to 0.874% w/w. However, when a simplified DMC = SSC was used for DMC estimation, the RMSE only slightly increased and was still lower than 1.00% w/w. Similar results were observed when linear regression models were assessed in each cultivar independently, with R² > 0.75 and RMSE generated by the simplified DMC = SSC model lower than 1.00% w/w in thirteen out of fourteen stone fruit cultivars, with the exception of the apricot cultivar. These results provide empirical evidence that SSC and DMC are highly correlated fruit quality indicators in plum, peach and nectarine at harvest. Full article

Complex matrices, such as wine, provide a challenge in the quantification of compounds. There exists a high likelihood of co-elution in these matrices, thereby artificially increasing the observed concentration. This can often lead to confusing data where compounds are above aroma detection thresholds, but are not detected by olfactory analysis. Additionally, the lack of sensitivity in assays can lead to the non-detection of sub-aroma threshold concentrations and contrasting data when olfactory analysis detects these aromas. To eliminate these pitfalls and gain a better understanding of the role that methoxypyrazines impart green character to wine, a quantitative method using headspace solid-phase microextraction coupled to heart-cutting multidimensional gas chromatography mass spectrometry was developed. The method can quantitate the three common methoxypyrazines found in wine at the picogram per liter level while resolving co-eluting compounds. The proposed method was validated using model wine and wine solutions and was ultimately used for the comparative analysis of white, rosé, and red wines. Full article