Principal Component Analysis of Phenolic Acid Spectra

Phenolic acids are common plant metabolites that exhibit bioactive properties and have applications in functional food and animal feed formulations. The ultraviolet (UV) and infrared (IR) spectra of four closely related phenolic acid structures were evaluated by principal component analysis (PCA) to develop spectral models for their rapid detection. Results demonstrated that UV and IR spectra could discriminate between each of the phenolic acids in overall models. Calculation of model scores and loadings showed that derivative UV spectra accounted for 99% variation with 2 principal components (PC) while derivative IR spectra required 3 PCs. Individual PCA models were developed for ferulic acid and p-coumaric acid using derivative UV spectra for detection and classification by soft independent modeling of class analogy (SIMCA). The application of this spectral technique as a classification model is expected to promote the use of agricultural residues as a source of these phenolic compounds. 1. Introduction Low molecular weight phenolic compounds such as ferulic acid and coumaric acid exhibit antioxidant and antimicrobial properties that add health benefits to foods and animal feeds [1, 2]. The bioactivities of these compounds provide functionality and extend the shelf life of formulated products. Current sources of phenolic acids include the commodity cereal grains, for example, corn, oat, and wheat. Due to the recent cost increase of these materials alternative sources such as lignocellulosic biomass offers promise as bioethanol industry develops. Switchgrass and other renewable energy crops contain significant amounts of phenolic acids that could be recovered as coproducts and improve bioethanol production [3, 4]. The development of a spectroscopic technique to rapidly detect and characterize the phenolic acid content profile could replace the more time consuming standard chromatographic analysis. Analysis times between 30 and 60 minutes are typically needed for separation of phenolic compounds by liquid chromatography. Quantitative results require replicate analysis of each sample and technical expertise to prepare samples and operate the chromatograph reproducibly. In contrast, a minimal amount of sample preparation is needed for spectroscopic methods and the instrumentation is less expensive to purchase and maintain. A modern instrument can scan a sample in less than 2 minutes and is routinely performed by operators with a small amount of training. The chemical structure of phenolic compounds, specifically the aromatic ring, produces strong