Assessment of raw milk quality and water adulteration across milk value chain in West Hararghe Zone, Eastern Ethiopia

Water adulteration is one of the most common forms of milk fraud, reducing nutritional quality and compromising consumer safety. However, information on the extent of milk adulteration along milk chain value in the West Hararghe Zone of Eastern Ethiopia is limited. Therefore, this study evaluated the chemical composition and water adulteration of raw milk collected from different milk chain actors in Chiro, Hirna, and Mieso districts. A total of 108 raw milk samples were randomly collected from producers, collectors, and service providers and analyzed using a MilkoScan instrument. Fat, protein, lactose, solids-not-fat (SNF), and the extent of added water were determined, while starch and skimmed milk powder were assessed qualitatively. Producer milk samples exhibited significantly higher fat (4.28%), protein (3.28%), and SNF (8.36%) contents than samples obtained from collectors and service providers. The highest lactose content (4.11%) was recorded in Hirna district, whereas the greatest water adulteration (13.2%) occurred in service provider samples from Mieso district. Pearson correlation analysis demonstrated strong negative associations between water adulteration and milk composition, with correlation coefficients of −0.95 for fat, −0.91 for SNF, −0.89 for protein, and −0.83 for lactose (all P ≤ 0.002), indicating that increasing water adulteration was associated with progressive reductions in milk solids. Starch and skimmed milk powder were not detected in any sample, but water adulteration was observed throughout the supply chain, increasing from producers to service providers. Although most producer and collector samples complied with Ethiopian standards for raw cow milk, deterioration in chemical composition was evident with increasing water adulteration. These findings highlight the need for routine milk quality monitoring, stronger regulatory enforcement, and awareness programs to minimize adulteration and protect consumer health. Graphical Abstract