Vinegar is the product of the alcoholic and subsequent acetous fermentations of carbohydrate sources under highly aerobic conditions. It is typically produced from fruits (e.g. apple), grains (e.g. rice) or alcoholic beverages (e.g. wine), but can also be produced from other fermentable materials that contain natural sugars. Those are first converted to ethanol by yeast, and then further oxidized to acetic acid by bacteria. The choice of the source material is what defines the type, quality and price of the vinegar produced as the former do not only provide different acidity and sour taste to the latter, but also play a key role in vinegar flavour as well as in its chemical composition.

The global vinegar market reached a value of over a billion USD in 2020, and is expected to keep increasing over the next years. Precisely, this increasing demand, especially of the finest vinegars, means fraudulent products can be a tempting prize. Unfortunately, there is not a specific methodology that allows the detection of such frauds with traditional methods, but current approaches rely on the quantification of certain physical properties or chemical compounds which have been reported as genuineness indicators. Consequently, the development of novel methodologies that allow to assess the authenticity and traceability of food products is of huge interest.

In this direction, the potential of a voltammetric electronic tongue (ET) to achieve the categorization and authentication of different vinegar varieties is presented herein. To this aim, a proper sensor array was selected and employed to extract the voltammetric profiles of different vinegar varieties, which along with the use of chemometric methods such as principal component analysis (PCA) and linear discriminant analysis (LDA) allowed the identification of characteristic fingerprints for each of the varieties and its discrimination.

As an analgesic and antipyretic drug, acetaminophen (AP) is widely employed in the treatment of cold, fever and relief of pain. However, AP could lead to the accumulation of its toxic metabolites in case of overdosing, which has fatal hepato- and nephro-toxic effects on health. Although there are already reported protocols for the determination of AP such as high performance liquid chromatography (HPLC), spectrophotometry or titrimetry, those processes are time-consuming and laborious. As an alternative, herein we synthesized an electropolymerized molecularly imprinted polymer (MIP) film on the surface of a graphite epoxy composite electrode for the determination of AP by electrochemical means. The electrochemical sensor exhibited superb sensitivity, selectivity, and a wide detection range towards acetaminophen.

In the environmental, industrial, and biomedical fields, pH monitorization is of the most importance. However, the most used type of pH sensors, glass pH-electrodes, still present limitations in their application in low volume samples and in cellular pH sensing, due to their size and invasive nature. Fluorescence-based sensors present a solution to such issues, providing a non-invasive solution to pH sensing [1].

Herein, we report the rational development of carbon dots (CDs) as a pH nanosensor, via an active surface preservation (ASP) method. Carbon dots (CDs) are carbon-based fluorescent nanoparticles with valuable properties such as high aqueous solubility, low cost, low toxicity, and good biocompatibility, with remarkable fluorescence performance, been increasingly used as fluorescent nanosensors [2].

By employing ASP strategies, the CDs will be prepared by using precursors with known active functional features. The ASP method allows the nanoparticles to retain the structural features of precursors, thus retaining their properties, without the need for costly and time-consuming post-synthesis functionalization procedures [2].

In this work, as proof-of-concept, the known pH-sensitivity of fluorescein is used to provide to the CDs a pH-based response. The resulting CDs presented reversible response by fluorescence enhancement in the range of pH from 4 to 12. The nanoparticles exhibited excellent photostability, in different pH solutions. The studied CDs were also unaffected by, either variation of ionic strength or the presence of interferent species, while being compatible with human cells. Finally, CDs were able to determine the pH of real samples. Thus, a selective pH fluorescent CDs-based nanosensor was developed.

Acknowledgments: Projects PTDC/QUI-QFI/2870/2020 and UIDB/00081/2020.

References:
[1] Shamsipur M, Barati A, Nematifar Z (2019). J Photochem Photobiol C Photochem Rev 39:76–141
[2] Hou P, Yang T, Liu H, et al (2017). Nanoscale 9:17334–17341

In this work, the characterization and the electroanalytical applications of antimony tin oxide (ATO) – Prussian blue (PB) screen printed electrodes (SPE) are presented. The ATO conducting particles have been used recently in the development of screen-printed electrodes due to their excellent spectroelectrochemical properties. PB is a transition metal hexacyanoferrate with high electrocatalytic properties towards various biologically active compounds like hydrogen peroxide, besides its outstanding electrochromic properties. A combination of ATO and PB ingredients into a screen-printing paste provided a versatile and cost-effective way in the development of novel electrode materials for electrochemical sensing. The ATO-PB electrode material displayed good electrochemical properties demonstrated by means of cyclic voltammetry and electrochemical impedance measurements. In addition, the PB provided a high selectivity towards potassium ions in solution due to its zeolitic structures and excellent redox behavior. The cyclic voltammetric responses recorded at the ATO-PB-SPE device in the presence of potassium ions revealed a linear dependence of the cathodic peak current and cathodic peak potential of the Prussian blue/Everitt’s salt redox system on the potassium concentrations ranging from 0.1 to 10 mM. This finding could be exploited in the development of an electrochemical sensor for electro-inactive chemical species.

Electronic noses are bioinspired instruments that mimic the biological sense of smell. They are based on the use of gas sensors combined with pattern recognition methods. The analysis of patients’ breath odors has had a long history of application for the detection of various human diseases. Due to an increase in awareness that the early detection of diseases greatly increases the chances for successful treatment, there is an urge in demand for inexpensive, non-invasive, simple, and fast early qualitative diagnosis of diseases. The study is aimed to emphasize on the possibilities of combining an electronic nose device based on five tin oxide (SnO₂) sensors with a pattern recognition method to discriminate between healthy controls (HC), patients with liver cirrhosis (LCi), and gastric cancer (GCa). Breath samples were collected from 36 volunteers, including 13 HC, 15 LCi patients, and 8 GCa patients. For this purpose, pattern recognition techniques such as principal component analysis (PCA), discriminant function analysis (DFA), and support vector machines (SVM) are utilized for data processing of multivariable responses generated by the sensor array. The chemometrics results showed good discrimination between the data points of breath samples related to the three groups. The PCA score accounted 96.42% of the total variance, while scores of 100% were obtained using DFA and SVM for the recognition of the analyzed groups, respectively. This pilot study reveals that e-nose technology based on exhaled breath analysis could be an effective and promising non-invasive way to distinguish LCi and GCa patients from HC.

A conductometric transducer is proposed for the first time for the detection of ethanol vapor. This ethanol microsensor is prepared by encapsulation of alcohol dehydrogenase (ADH) in chitosan. The electrodeposition of chitosan allows the addressing of the chitosan film on the microconductometric devices and to encapsulate ADH and nicotinamide adenine nucleotide (NAD⁺), which was monitored by IRTF. The analytical performance of the ethanol microsensor was determined in gaseous methanol, ethanol and acetone samples, collected from the head space above aqueous solutions of known concentration. The response time (t₉₀) of the sensor varies from 9 s to 46 s from lower concentrations to higher concentrations. The detection limit is 0.12v/v % in the gas phase, corresponding to 0.22 M in the liquid phase. The relative standard deviation for the same sensor is from 12% for lower concentrations to 2% for higher concentrations. ethanol sensor presents a 2.6 times lower sensitivity for methanol and 28.3 times lower sensitivity for acetone. A detection of ethanol in a red wine sample was performed.

Marine macroalgae are gaining importance in the diet due to their nutritional composition and potential health benefits. Many of these beneficial properties are motivated by the presence of antioxidant compounds, responsible for the improvement of product preservation, and their therapeutic effects in the prevention of various diseases. Among all the marketed algae, one of the most consumed is Himanthalia elongata, known as sea spaghetti. However, despite such high consumption, there are only few studies focused on its chemical characterization. Therefore, different studies are required to optimize the extraction and characterization of its bioactive compounds, specially polyphenols with antioxidant activity. This study is aimed at optimizing of the extraction of antioxidants from H. elongata by ultrasound-assisted extraction (UAE). This system was chosen as it is an emerging green technique with which good results are achieved in plant matrices, as supported by several studies. The process was optimized by response surface methodology (RSM) using a five-level central composite design, combining the independent variables of processing time (t, 15-45 min), power (P, 0-100%) and solvent (S, 0-100 % ethanol, v/v) [1]. Specifically, RSM was performed to optimize different responses associated with polyphenol production and antioxidant activity determination: total phenolic content, total flavonoids, antioxidant capacity, in terms of sequestering capacity of the diphenyl-2-picryl-hydrazyl radical (DPPH), Trolox equivalent antioxidant capacity (TEAC) and β-carotene discoloration method (BC), and extraction yield. The theoretical models were fitted to the experimental data, statistically validated, and used in the prediction and optimization steps. The best yields of fucoxanthin, a compound with antioxidant activity typical of brown algae, were obtained at 44.9 min, 418.9 W and 86.8% ethanol. The analysis presented provides important data that allows the comparison between different extraction conditions, in terms of efficiency, and consequent related decision making. Overall, it can be concluded that ultrasounds assisted extraction can be an efficient and green technique to revalorize algae of common uses as Himanthalia elongata into potent antioxidant phenolic for their further application in food and nutraceutical industries.

Nowadays, anthocyanins have gained attention in the scientific and industrial fields, due not only to their biological activities but also to their coloring properties. In this sense, the use of anthocyanins for developing new nutraceutical foods has been proposed, both to substitute synthetic additives and also as ingredients with added-value. These compounds appear naturally in several plant sources, such as fruits and flowers, being part of plant secondary metabolites. Then, the extraction of anthocyanins is usually carried out from vegetal matrices. As the range of application of these compounds increase, it is necessary to design efficient extraction methods, with better yields, and also to develop suitable analytical methods for the identification and quantification of anthocyanins. The aim of this study was to evaluate the current data about the identification and quantification techniques employed and also the validation process of such methods. Our results showed that anthocyanins have been identified by different methods, including Nuclear Magnetic Resonance and chromatographic-based techniques (e.g. High Performance Liquid Chromatography coupled to Diode Array Detector or Mass Spectroscopy). When validating methods, several issues have been described, but most reports showed positive results on validation parameters, suggesting that the current analytical technology offers a successful identification and quantification of anthocyanins, with the capability of being applied for both research and industrial purposes.

Macroalge are regarded as a helathy food due to their composition and nutritional properties [1]. In this work, nutritional composition of two green (Ulva rigida, Codium tomentosum) and two red (Palmaria palmata, Porphyra purpurea) edible seaweed species widely distributed in Atlantic shores were studied using a variety of analytical methods. Total lipids were measured gravimetrically as evaporated mass after petroleum-ether Soxhlet extraction of samples. In addition, fatty acid profile was determined by gas chromatography coupled to a flame ionization detector (GC-FID). Results showed that all studied species were accounted for very low levels of lipids (>1% DW), but levels of unsaturated fatty acids oleic, linoleic and linolenic acids were present at high concentrations, with P. palmata displaying the highest quantities (>200 mg C18:1 / g extract). In parallel, proteins were quantified following the macro-Kjedahl method in which the nitrogen content is converted to protein using a conversion factor of 6.25. In this analysis, red algae, specially P. purpurea showed signficant protein content up to 30% DW. Total organic acids were determined by ultra-filtration liquid-chromatography coupled to an amperometric detector (UFLC-PAD) after an acid extraction, being P. purpurea the algae with the higher organic acid content (10.61 % DW), half of which was determined as citrate. Minerals were idenfitied and quantified by inductively coupled plasma atomic emission spectroscopy (ICP-OES), suggesting that both algae groups are rich in K and Mg (>15 g / kg), but U. rigida also displayed a remarkable iron content (>1 g Fe / kg). Finally, hydrocarbons were determined as the difference of the rest of components, following AOAC guidelines. Altogether, results corroborate that these edible algae are a good source of nutrients in accordance with literature.

References.

1. Martínez–Hernández, G.B.; Castillejo, N.; Carrión–Monteagudo, M. del M.; Artés, F.; Artés-Hernández, F. Nutritional and bioactive compounds of commercialized algae powders used as food supplements. Food Sci. Technol. Int. 2018, 24, 172–182, doi:10.1177/1082013217740000.

Acknowledgements

The research leading to these results was supported by MICINN supporting the Ramón y Cajal grant for M.A. Prieto (RYC-2017-22891) and the FPU grant for A. Carreira-Casais (FPU2016/06135); by Xunta de Galicia for supporting the program EXCELENCIA-ED431F 2020/12, the post-doctoral grant of M. Fraga-Corral (ED481B-2019/096), the program BENEFICIOS DO CONSUMO DAS ESPECIES TINTORERA- CO-0019-2021 that supports the work of F. Chamorro and the program Grupos de Referencia Competitiva that supports the work of J. Echave (GRUPO AA1-GRC 2018); by the Bio Based Industries Joint Undertaking (JU) under grant agreement No 888003 UP4HEALTH Project (H2020-BBI-JTI-2019) that supports the work of P. Otero, P. Garcia-Perez and C. Lourenço-Lopes; and by Ibero-American Program on Science and Technology (CYTED—AQUA-CIBUS, P317RT0003). The JU receives support from the European Union’s Horizon 2020 research and innovation program and the Bio Based Industries Consortium. The project SYSTEMIC Knowledge hub on Nutrition and Food Security, has received funding from national research funding parties in Belgium (FWO), France (INRA), Germany (BLE), Italy (MIPAAF), Latvia (IZM), Norway (RCN), Portugal (FCT), and Spain (AEI) in a joint action of JPI HDHL, JPI-OCEANS and FACCE-JPI launched in 2019 under the ERA-NET ERA-HDHL (n° 696295). The authors are grateful to AlgaMar enterprise (www.algamar.com) for the collaboration and algae material provision.

Cortisol is a major glucocorticoid that can affect physiological activities in the human body. Besides, it is also a biomarker that can reflect the stress state of the body. Therefore, in order to monitor stress states in a sensitive and non-invasive manner, an ultra-sensitive aptamer-antibody sandwich sensor modified with multi-walled carbon nanotubes, ordered mesoporous carbon CMK-3, and silver nanoparticles (MWCNTs/CMK-3/AgNPs) was proposed for noninvasive monitoring of cortisol in saliva. The MWCNTs/CMK-3/AgNPs nanocomposite was fixed on the surface of the glassy carbon electrodes (GCEs) as the material for the first signal amplification, and secondary signal amplification was realized by conjugating cortisol antibodies with gold nanoparticles (AuNPs). Finally, the aptamer-antibody sandwich pattern was used to specifically recognize and bind cortisol. The concentration response range for this aptamer-antibody sandwich sensor is 0.1 pg/mL-10 ng/mL, and the limit of detection (LOD) is 0.09 pg/mL. Heretofore, the LOD of this sensor has been relatively low, showing its good sensitivity, selectivity, stability, and reproducibility. Furthermore, it has been successfully applied to detect cortisol in saliva samples to compare the stress states of postgraduates and undergraduates.