Analysis of industry-generated data. Part 2: Risk-based sampling plan for efficient self-control of aflatoxin M_1 contamination in raw milk

摘要

Aflatoxin M_1 (AFM1) contamination in 21 969 milk samples taken in Italy during 2005-08 and 2010 provided the basis for designing an early warning self-control plan. Additionally, 4148 AFM1 data points from the mycotoxin crisis (2003-04) represented the worst case. No parametric function provided a good fit for the skewed and scattered AFM1 concentrations. The acceptable reference values, reflecting the combined uncertainty of AFM1 measured in consignments consisting of milk from one to six farms, ranged from 40 to 16.7 ng kg~(-1), respectively. Asymmetric control charts with these reference values, 40 and 50 ng kg~(-1) warning and action limits are recommended to assess immediately the distribution of AFM1 concentration in incoming consignments. The moving window method, presented as a worked example including 5 days with five samples/day, enabled verification of compliance of production with the legal limit in 98% of the consignments at a 94% probability level. The sampling plan developed assumes consecutive analyses of samples taken from individual farms, which makes early detection of contamination possible and also immediate corrective actions if the AFM1 concentration in a consignment exceeds the reference value. In the latter case different control plans with increased sampling frequency should be applied depending on the level and frequency of contamination. As aflatoxin B_1 increases in feed at about the same time, therefore a coordinated sampling programme performed by the milk processing plants operating in a confined geographic area is more effective and economical then the individual ones. The applicability of the sample size calculation based on binomial theorem and the fast response rate resulting from the recommended sampling plan were verified by taking 1000-10 000 random samples with replacement from the experimental databases representing the normal, moderately and highly contaminated periods. The efficiency of the control plan could be substantially enhanced if the dairy farms used feed with a tolerable level of AFB1.