Around 1% of waste cooking oil (WCO) is currently recycled to make biodiesel in Brazil, mainly because used oils can acquire physicochemical characteristics that render them unsuitable as raw materials. To make biofuel production from waste oils and fats more efficient and economically feasible, it is important to develop simple, rapid, and low-cost methods for testing the quality of WCOs. With the objective of establishing the applicability of stochastic modeling of e-nose profiles in assessing the suitability of WCO for biodiesel production, the synthesized biodiesel samples from 36 pre-used frying oils, obtained from domestic and commercial premises, were analyzed regarding ester content, acidity index, density, viscosity, and iodine index. Olfactory profiles of the WCO sources were obtained using a Cyranose chemical vapor-sensing instrument and interpreted by application of stochastic modeling and quadratic discriminant analysis. The predictive model obtained by stochastic analysis exclusively from the olfactory profiles of the samples of WCO allowed the latter to be classified according to their ability to generate biodiesel that would be compliant with standard specifications and with an overall accuracy greater than 80%. Our results demonstrated that stochastic modeling is a promising tool for predicting the quality of biodiesel based only on the WCO olfactory profiles and its origin, since it allows qualitative assessments of the principal biodiesel properties and eliminates the need for complex and time-consuming laboratory tests.

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This study aims to evaluate the effects of drying in a forced-air oven or solar dryer on the drying rates, physicochemical and microbiological characteristics, and antioxidant properties of rosemary, mint, common fennel, lemon grass, and basil. The drying rates of all herbs were higher in the forced-air oven in comparison to the solar dryer. According to results obtained for herbal properties after this different drying process, mint was less affected by both drying conditions. On the other hand, regardless of the method of drying used, all dried herbs exhibited similar antioxidant properties, mainly due to the presence of total phenolics. The antioxidant activities of oven-dried herbs ranged from 19.18 to 71.55% and increased in the order common fennel < lemon grass < mint < basil < rosemary, while the activities of sun-dried samples varied from 17.73 to 58.27% and increased in the order basil < common fennel < lemon grass < mint < rosemary. The results obtained demonstrate that the process of drying can alter the quality of an herbal product, implying that standardization of post-harvest steps is essential to ensure the consistency of an herbal product.

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Purpose This study aims to describe a bibliometric analysis of recent articles addressing the applications of e- noses with particular emphasis on those dealing with fuel-related products. Documents covering the general area of e-nose research and published between 1975 and 2021 were retrieved from the Web of Science database, and peer-reviewed articles were selected and appraised according to specific descriptors and criteria. Design/methodology/approach Analyses were performed by mapping the knowledge domain using the software tools VOSviewer and RStudio. It was possible to identify the countries, research organizations, authors and disciplines that were most prolific in the area, together with the most cited articles and the most frequent keywords. A total of 3,921 articles published in peer-reviewed journals were initially retrieved but only 47 (1.19%) described fuel-related e-nose applications with original articles published in indexed journals. However, this number was reduced to 38 (0.96%) articles strictly related to the target subject. Findings Rigorous appraisal of these documents yielded 22 articles that could be classified into two groups, those aimed at predicting the values of key parameters and those dealing with the discrimination of samples. Most of these 22 selected articles (68.2%) were published between 2017 and 2021, but little evidence was apparent of international collaboration between researchers and institutions currently working on this topic. The strategy of switching energy systems away from fossil fuels towards low-carbon renewable technologies that has been adopted by many countries will generate substantial research opportunities in the prediction, discrimination and quantification of volatiles in biofuels using e-nose. Research limitations/implications It is important to highlight that the greatest difficulty in using the e-nose is the interpretation of the data generated by the equipment; most studies have so far used the maximum value of the electrical resistance signal of each e-nose sensor as the only data provided by this sensor; however, from 2019 onwards, some works began to consider the entire electrical resistance curve as a data source, extracting more information from it. Originality/value This study opens a new and promising way for the effective use of e-nose as a fuel analysis instrument, as low-cost sensors can be developed for use with the new data analysis methodology, enabling the production of portable, cheaper and more reliable equipment.