Detecting variation in ultrafiltrated milk permeates — Infrared spectroscopy signatures and external factor orthogonalization

Ultrafiltration (UF) of milk in the dairy industry generates significant quantities of UF permeate as a by-product. In the past decade UF permeate has been utilized as a mixing ingredient in the standardization of milk. Due to the role of permeate as an ingredient, it is important that the variation in composition is known and controlled in order to ensure uniform quality of the standardized milk. In this investigation we evaluate if the composition of permeate from the ultrafiltration of milk varies between different ultrafiltration plants as assessed by infrared spectroscopy. A total of 40 permeate samples from six production sites at different geographical locations were analyzed by infrared spectroscopy. Principal component analysis of the infrared spectra showed that it was possible to classify the plant manufacturer of permeates with great accuracy. Loading spectra revealed that total solids (mainly lactose) and protein were the main sources of compositional variation between the different sites. Through an orthogonalization procedure of the infrared spectra the spectral variation due to total solid and protein content was removed. Neither the unsupervised principal component analysis nor the supervised extended canonical variate analysis could classify the permeate plant origin after orthogonalization of the infrared spectra. The result shows that, besides total solids and protein variation, permeate from the six ultrafiltration sources does not contain plant specific composition in their infrared signature. The study demonstrates how multiple external factors can be removed from the spectral data by orthogonalization.