Investigation and identification of foreign turbidity particles in beverages via Raman micro-spectroscopy

Abstract Cloudiness, opalescence or a milky appearance in beverages is usually undesirable and lead the consumers to assume that the product is of lower quality. Many different types of formation and entry can lead to cloudiness and these causes can be divided into two major categories: beverage-specific, where the ingredients cause an interaction, and external influences such as process errors or particles interacting with the medium. This study considers two main sources of external influences. Raman micro-spectroscopy (RMS) was used to detect, evaluate and validate filter aids, stabilisers and various microplastic (MP) particles. A suitable sample preparation was developed, membrane filters were tested, and a filtration method for isolating the individual particles was established and implemented. To identify particles with RMS and for better representation, a few particles were selected and the results were validated using cluster analysis and the similarity matrix. The different media influences were identified by analysing the particles both dry, in water and beer. The filtration residue after membrane filtration was also analysed. A two-dimensional image scan of the particles served to determine particle homogeneity. The spectra were then recorded with single-point scans. The polyvinylpolypyrrolidone (PVPP) spectra in the different media showed similarities greater than 80%, usually greater than 95%. The cellulose spectra showed no differences between the different media, but consistently high average similarities of 94.5%. This investigation should show that foreign particles can be detected and evaluated by RMS with suitable sample preparation and recording.