Fourier Transform Infrared (FT-IR) Spectroscopy as a Possible Rapid Tool to Evaluate Abiotic Stress Effects on Pineapple By-Products  
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1 LEAF, Linking Landscape, Environment, Agriculture and Food, Instituto Superior de Agronomia, Universidade de Lisboa, Tapada da Ajuda, 1349-017 Lisboa, Portugal; [EMAIL_ADDRESS]  
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2 CEREA, Centro de Estudos em Recurso Naturais e Ambiente, Instituto Superior Tecnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal; [EMAIL_ADDRESS] (M.J.N.C. ); [EMAIL_ADDRESS] (M.M.M.) [PERSON]  
2 CEREA, Centro de Estudos em Recurso Naturais e Ambiente, Instituto Superior Tecnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal; [EMAIL_ADDRESS] (M.J.N.C. ); [EMAIL_ADDRESS] (M.M.M.) [PERSON]  
4 CRES, Centro de Engenharia Biologica, Universidade de Minho, Campus de Gualtar, 4710-057 Braga, Portugal; [EMAIL_ADDRESS]. may be influenced by more than one analyte in chemically complicated matrices [3]. Therefore, these spectroscopic analytical techniques are widely used in association with multivariate data analysis for the qualitative and quantitative analysis of complex matrices. Qualitative assessment of the spectra can be accomplished by principal components analysis (PCA), while partial least squares (PLS) regression permits the enhancement of calibration models between spectral and analytical data. Fresh-cut fruit consumption is increasing because of the rising awareness of its benefits [4]. The fresh-cut fruit industries generate large amounts of by-products that are traditionally undervalued, and the removal of these materials is a problem exacerbated by legal restrictions [5]. The by-products normally correspond to more than 25-35% of the fruits. The shell is the predominant by-product and represents around 10% of the weight of the fruit [5; 6]. Pineapple wastes have potential as raw materials or, after biological treatment, as a high-added-value product to be used as an ingredient in the food or feed industries [7; 8]. It has been reported that pineapple by-products are an abundant source of antioxidant polyphenols, which could be recovered for food or cosmetic applications with advantages in terms of economic and environmental sustainability [9; 10; 11]. As these by-products are living tissues, still physiologically active and capable of synthetizing phenolic and carotenoid compounds, they can be used as biofacories of secondary metabolite compounds with pharmaceutical and nutraceutical applications. Postharvest abiotic stresses can change the secondary metabolite synthesis in crop tissues, participating in the biosynthesis of the three main groups of secondary metabolites: terpen, phenolics, and nitrogen-containing compounds [12]. Numerous biochemical pathways are susceptible to being implicated in responses to abiotic stresses, like the accumulation of phenolic compounds caused by a change in phenylalanine ammonia lyase activity (PAL) [13]. Increased PAL activity promotes the accumulation of different phenolic compounds (chlorogenic acid, dicaffeoyl tartaric acid, and isochlorogenic acid) and tissue browning [14]. The wound-induced accumulation of phenolic compounds can be influenced by the submission to an extra abiotic stress in the wounded tissue, involving changes in the total quantity and type of phenolic compounds amassed [15]. Bioactive compound synthesis can be increased by abiotic stresses like heat treatment, UV-C radiation, and wounding, increasing phenolic and carotenoid contents [16; 17]. Heat treatments, in addition to controlling postharvest deterioration and enhancing the storage quality of fruits, have been investigated as abiotic stresses able to promote bioactive synthesis by living plant tissues. For instance, by-products of the minimally processed fruits industry are used to produce natural additives that can be used in the dietary supplements industry, enhancing the extractable yields of particular active compounds that have nutraceutical or additional functional properties [12].