Novel approach for screening milk based on fast and environmentally friendly determination of protein and fat

Abstract

Milk is very vulnerable to fraud and is generally priced by the protein and fat content, but most analytical alternatives available for quantifying these components are limited in terms of technical aspects or instrument availability. Therefore, a novel, fast, and green analytical alternative for screening milk samples based on the protein and fat content is proposed herein. The procedure relies on the effect of ethanol in milk, which induces protein precipitation (chaotropic effect) and promotes fat extraction. The analytical measurements are based on the precipitated mass (protein content) and the amount of water needed to induce turbidity in the ethanolic extract (fat determination). The amount of water was determined by microtitration of the extract, giving values of (64 ± 5) μL for whole milk (3 % m/v fat) and (104 ± 5) μL for skim milk (1 % m/v fat), whereas the mass of precipitate (from 0.1036 ± 0.0072 to 0.1134 ± 0.0068 g) did not differ significantly for these milk types because the protein content is standardized to ca. 3.0 % m/v. Quality control charts were used for sample screening, achieving specificity and sensitivity rates of 100 % for fat and 100 % and 75 % for protein, respectively. Ethanol (800 μL of 92.8 % v/v solution per determination) was the only reagent needed, demonstrating the environmental friendliness of the approach. The proposed procedure is suitable for fast and cost-effective screening of milk samples, with the aim of detecting non-conformities in the most important quality parameters of bovine milk at different stages of the production chain.