Quality assessment of raw and pasteurized milk sold through different marketing channels

Abstract:

Nearly 52% of the liquid milk consumed in urban Nakuru County still passes through informal marketing routes, yet systematic quality data for these channels are scarce. This research examined 150 milk samples drawn between March and October 2023 from five marketing channels operating in and around Nakuru: organised raw, pasteurised packaged, unorganised vendors, direct farmer delivery, and dairy cooperatives. Samples were evaluated for fat, solids-not-fat, protein, titratable acidity, total plate count, coliform count, methylene blue reduction time, and common adulterants. Pasteurised packaged milk returned the best mean profile, with fat at 3.72 ± 0.11%, SNF at 8.61 ± 0.09%, total plate count of 3.48 ± 0.24 log CFU/mL, and no detectable coliforms in 93% of samples. Unorganised vendor samples performed worst across every parameter, with adulteration indicators (added water, detergent residue, or starch) in 37% of units. Cooperative samples clustered closer to the pasteurised category, while farmer-direct raw samples showed acceptable composition but high microbial load. Principal component analysis separated the five channels into three distinct quality clusters. The findings point to the pasteurisation step and cold-chain discipline, rather than the milk source itself, as the main determinant of retail quality, and they reinforce the case for extending organised channels into semi-urban markets where informal supply still dominates.