The application of Fourier transform infrared spectroscopy in discriminating different pomegranate juice extraction methods

This study investigated the application of Fourier transform infrared (ATR FT-MIR) spectroscopy and chemometrics for discriminating between different extraction methods used to extract pomegranate juice (‘Wonderful’). Three types of existing juice extraction methods used in the industry were assessed, and this included juice extracted without crushing the seeds (arils only) using a juice extractor (JE), juice extracted by crushing the seeds using a blender (arils plus seed) (JB) and juice extracted from half fruit using commercial hand press juicer (CH). To qualitatively discriminate between extraction methods based on physicochemical and biochemical properties, orthogonal partial least squares discriminant analysis (OPLS-DA) and principal component analysis (PCA) were used for classification. The PCA plot revealed possible grouping between spectral and chemical data sets. For instance, the JB extraction method showed a high level of juice cloudiness. The PCA score plot revealed that the extraction method CH is associated with total soluble solids, BrimA, and TSS:TA ratio. While, the extraction method JE has mainly been associated with color attributes (a*, C*, h°). The application of OPLS-DA revealed 100% discrimination between the different extraction methods. The S-line plot revealed that some of the most important wavebands within the following region (1090, 1250, 1750, and 3200 cm^‑1) are responsible for discrimination between the different extraction methods. Our results suggest that the main contributors to the discrimination of the extraction methods were total soluble solids, acidity and its ratio, color attributes, and anthocyanin concentration. The developed method using an ATR FT-MIR spectroscopy can be implemented in controlled processes for online and inline pomegranate juice grading.