Milk Quality Assessment for Adulteration and Organic Contaminants in Juja and Githurai Markets, Kiambu County

Abstract

The annual milk consumption rate in Kenya is estimated at 50-150 liters per capita. Approximately 70% of milk marketed in Kenya is sold through a largely unregulated informal market. There are concerns about the quality of milk as some cases of adulteration with water, illegal preservatives and contamination with antibiotic residues have been reported. Thus, there is need to continuously assess the quality of milk in the market to ensure its safety for consumption. This study was carried out to investigate milk quality for adulteration and presence of organic contaminants in milk marketed in Juja and Githurai markets in Kiambu County, Kenya. Milk was grouped into three categories namely raw milk sold in shops (shop milk), automated vending machine milk (AVM) and packet milk. The adulterants of interest were water and hydrogen peroxide while the organic contaminants monitored were antibiotic and pesticide residues. The analysis was based on the Kenya Bureau of Standards bench marks for milk quality and the maximum residue limits (MRLs) for antibiotics and pesticide residues set by the Codex Alimentarius Commission and the European Union. A lactometer was used to evaluate milk adulteration with water. Added water was detected in 53 %, 78 % and 70 % of shop, AVM and packet milk samples, respectively. There was a significant difference in the mean densities for shop milk obtained from Githurai and Juja (p = 0.0157) at p ≤ 0.05 significance using t-test. For AVM milk, there was no significant difference in the two mean values of densities of milk from Githurai and Juja (p = 0.365) at p ≤ 0.05 level of significance using t-test. One-way ANOVA test for the mean densities for raw, AVM and packet milk showed that there was no statistically significant difference between the three groups (p = 0.272) at p≤ 0.05 level of significance. Hydrogen peroxide in the milk was measured using Quantofix peroxide test strips. Hydrogen peroxide was detected in 4 % and 20 % of AVM and packet milk, respectively while none of the shop milk samples had detectable levels of added hydrogen peroxide. Antibiotics residues (amoxicillin, cloxacillin, tetracycline, sulfamethoxazole and trimethoprim) were analyzed using Liquid chromatography tandem mass spectrometry (LC-MS/MS). Overall, 11 % of the samples had at least one antibiotic residue at concentrations above the MRLs while 22 % of the samples had detectable antibiotic residues at levels below the MRLs. Amoxicillin, cloxacillin and tetracycline were detected at concentrations above the respective MRLs in 2 %, 8 % and 2 % of the samples, respectively, while all the samples with detectable levels of sulfamethoxazole and trimethoprim were below the MRLs. Pesticide residues (amitraz, carbaryl, chlorpyrifos, cypermethrin and deltamethrin) were analysed using LC-MS/MS and gas chromatography –mass spectrometry (GC-MS). Overall, pesticides were detected in 14 % of the samples but none of the detected pesticides exceeded the MRLs. The results of this study provide evidence of adulteration and presence of organic contaminants in some milk sold within the selected study markets. Adulteration compromises the nutritional quality of milk. Consumption of milk containing organic contaminants such as pesticides and antibiotics may lead to bioaccumulation to harmful levels over time. Thus, increased market surveillance and milk safety awareness should be conducted to deter sale of adulterated and contaminated milk.