Citation: Dima, S , .-O.; Constantinescu-Aruxandei, D.; Tritean, N.; Ghiurea, M.; Capr˘ a, L.; Nicolae, C.-A.; Faraon, V.; Neamt , u, C.; Oancea, F. Spectroscopic Analyses Highlight Plant Biostimulant Effects of Baker’s Yeast Vinasse and Selenium on Cabbage through Foliar Fertilization. Plants 2023, 12, 3016. https://doi.org/10.3390/ plants12163016 Academic Editors: Ioan Grozescu, Maria Iorizzi and Adina-Elena Segneanu Received: 26 June 2023 Revised: 12 August 2023 Accepted: 17 August 2023 Published: 21 August 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). plants Article Spectroscopic Analyses Highlight Plant Biostimulant Effects of Baker’s Yeast Vinasse and Selenium on Cabbage through Foliar Fertilization S , tefan-Ovidiu Dima 1 , Diana Constantinescu-Aruxandei 1, * , Naomi Tritean 1,2 , Marius Ghiurea 1 , Luiza Capră 1 , Cristian-Andi Nicolae 1 , Victor Faraon 1 , Constantin Neamt , u 1 and Florin Oancea 1,3, * 1 Polymers and Bioresources Departments, National Institute for Research & Development in Chemistry and Petrochemistry—ICECHIM, Splaiul Independent , ei nr. 202, Sector 6, 060021 Bucharest, Romania; ovidiu.dima@icechim.ro (S , .-O.D.); naomi.tritean@icechim.ro (N.T.); marius.ghiurea@icechim.ro (M.G.); luiza.capra@icechim.ro (L.C.); cristian.nicolae@icechim.ro (C.-A.N.); victor.faraon@icechim.ro (V.F.); titi.neamtu@icechim.ro (C.N.) 2 Faculty of Biology, University of Bucharest, Splaiul Independent , ei nr. 91-95, Sector 5, 050095 Bucharest, Romania 3 Faculty of Biotechnologies, University of Agronomic Sciences and Veterinary Medicine of Bucharest, Bd. Mărăs , ti nr. 59, Sector 1, 011464 Bucharest, Romania * Correspondence: diana.constantinescu@icechim.ro (D.C.-A.); florin.oancea@icechim.ro (F.O.); Tel.: +40-21-316-3071 (F.O.) Abstract: The main aim of this study is to find relevant analytic fingerprints for plants’ structural characterization using spectroscopic techniques and thermogravimetric analyses (TGAs) as alternative methods, particularized on cabbage treated with selenium–baker’s yeast vinasse formulation (Se- VF) included in a foliar fertilizer formula. The hypothesis investigated is that Se-VF will induce significant structural changes compared with the control, analytically confirming the biofortification of selenium-enriched cabbage as a nutritive vegetable, and particularly the plant biostimulant effects of the applied Se-VF formulation on cabbage grown in the field. The TGA evidenced a structural transformation of the molecular building blocks in the treated cabbage leaves. The ash residues increased after treatment, suggesting increased mineral accumulation in leaves. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) evidenced a pectin–Iα-cellulose structure of cabbage that correlated with each other in terms of leaf crystallinity. FTIR analysis suggested the accumulation of unesterified pectin and possibly (seleno) glucosinolates and an increased network of hydrogen bonds. The treatment with Se-VF formulation induced a significant increase in the soluble fibers of the inner leaves, accompanied by a decrease in the insoluble fibers. The ratio of soluble/insoluble fibers correlated with the crystallinity determined by XRD and with the FTIR data. The employed analytic techniques can find practical applications as fast methods in studies of the effects of new agrotechnical practices, while in our particular case study, they revealed effects specific to plant biostimulants of the Se-VF formulation treatment: enhanced mineral utilization and improved quality traits. Keywords: plant cell wall; plant response; glycine betaine; molecular fingerprints; spectroscopic techniques; Fourier-transform infrared spectroscopy—FTIR; X-ray diffraction—XRD; thermo-gravimetric analyses—TGAs; soluble and insoluble fibers 1. Introduction The plant cell wall is constantly monitored and remodeled by a complex network of cellular pathways—signaling cascades that respond to external and internal cues and regulate biodegrading and biosynthetic pathways [1,2]. Changes in the composition and architecture of plant cell walls occur as a plant cell response to various stresses [3–6]. These structural and compositional changes could represent an indicator of plant growing conditions, especially Plants 2023, 12, 3016. https://doi.org/10.3390/plants12163016 https://www.mdpi.com/journal/plants