{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,12]],"date-time":"2026-01-12T22:29:09Z","timestamp":1768256949898,"version":"3.49.0"},"reference-count":35,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2019,6,15]],"date-time":"2019-06-15T00:00:00Z","timestamp":1560556800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"FCT\/MCTES (PIDDAC)","award":["UID\/EQU\/00511\/2019"],"award-info":[{"award-number":["UID\/EQU\/00511\/2019"]}]},{"DOI":"10.13039\/501100008530","name":"European Regional Development Fund","doi-asserted-by":"publisher","award":["NORTE\u201001\u20100145\u2010FEDER\u2010000005, funded by Norte Portugal Regional Operational Programme (NORTE 2020), under PORTUGAL 2020"],"award-info":[{"award-number":["NORTE\u201001\u20100145\u2010FEDER\u2010000005, funded by Norte Portugal Regional Operational Programme (NORTE 2020), under PORTUGAL 2020"]}],"id":[{"id":"10.13039\/501100008530","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Catalysts"],"abstract":"<jats:p>Enzymatic hydroesterification is a heterogeneous catalyzed process suitable for the conversion of low-cost feedstocks in biodiesel production, namely, because of its tolerance to high free fatty acid contents. The current study describes the use of Fourier transform infrared spectroscopy (FTIR) to monitor biodiesel production using enzymatic hydroesterification and, as raw materials, acid oil from soapstock and olive pomace oil. Acid oil (~34 wt.% FFA) and olive pomace oil (~50 wt.% FFA) were first hydrolyzed (35 \u00b0C, 24 h, 200 rpm, 3 wt.% of lipase from Thermomyces lanuginosus, and 1:0.5 water:oil ratio, w:w), and then enzymatic esterification was performed (35 \u00b0C, 7 h, 200 rpm, 2 wt.% of lipase from Thermomyces lanuginosus, and 2:1 molar ratio of methanol to acid). FTIR analyses were conducted on the products using a Jasco FT\/IR-4100 with a scanning range of 4000\u2013650 cm\u22121 at 4 cm\u22121 spectral resolution and 54 scans. For free fatty acid (FFA) quantification, the C=O band at 1708 cm\u20131 was used, corresponding to the carboxylic acid, whereas for fatty acid methyl ester (FAME) quantification, the peak corresponding to C=O at 1746 cm\u22121 was considered, which corresponded to the ester. The results were calibrated using volumetric titration and gas chromatography analyses, concerning FFA and FAME quantification, respectively. The best conditions for analysis were determined, and a calibration method was established. FTIR has shown to be a simple, fast, and clean technique suitable to monitor hydroesterification of low-cost feedstocks.<\/jats:p>","DOI":"10.3390\/catal9060535","type":"journal-article","created":{"date-parts":[[2019,6,17]],"date-time":"2019-06-17T03:24:41Z","timestamp":1560741881000},"page":"535","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":18,"title":["Monitoring Enzymatic Hydroesterification of Low-Cost Feedstocks by Fourier Transform InfraRed Spectroscopy"],"prefix":"10.3390","volume":"9","author":[{"given":"Mariana","family":"Cruz","sequence":"first","affiliation":[{"name":"LEPABE, Departamento de Engenharia Metal\u00fargica e de Materiais, Faculdade de Engenharia, Universidade Do Porto, R. Dr. Roberto Frias, 4200-465 Porto, Portugal"}]},{"given":"Manuel Fonseca","family":"Almeida","sequence":"additional","affiliation":[{"name":"LEPABE, Departamento de Engenharia Metal\u00fargica e de Materiais, Faculdade de Engenharia, Universidade Do Porto, R. Dr. Roberto Frias, 4200-465 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8212-8718","authenticated-orcid":false,"given":"Maria da Concei\u00e7\u00e3o","family":"Alvim-Ferraz","sequence":"additional","affiliation":[{"name":"LEPABE, Departamento de Qu\u00edmica, Faculdade de Engenharia, Universidade Do Porto, R. Dr. Roberto Frias, 4200-465 Porto, Portugal"}]},{"given":"Joana Maia","family":"Dias","sequence":"additional","affiliation":[{"name":"LEPABE, Departamento de Engenharia Metal\u00fargica e de Materiais, Faculdade de Engenharia, Universidade Do Porto, R. Dr. Roberto Frias, 4200-465 Porto, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2019,6,15]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"417","DOI":"10.1016\/j.renene.2018.12.012","article-title":"Mass transfer and kinetic study on BEA zeolite-catalysed oil hydroesterification","volume":"135","author":"Mowla","year":"2019","journal-title":"Renew. Energy"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"4732","DOI":"10.1016\/j.rser.2011.07.079","article-title":"Production of biodiesel: A technical review","volume":"15","author":"Shahid","year":"2011","journal-title":"Renew. Sustain. Energy Rev."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"497","DOI":"10.1016\/j.rser.2017.01.001","article-title":"Production, characterization and performance of biodiesel as an alternative fuel in diesel engines\u2013A review","volume":"72","author":"Mahmudul","year":"2017","journal-title":"Renew. Sustain. 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