Traceability of processed animal proteins with varying texture in feed: determination with microscopic and polymerase chain reaction methods
Abstract
To test the traceability of different animal components that could enter the feed chain two methods for the determination of processed animal proteins (PAPs) in feed – classical microscopy and polymerase chain reaction (PCR)-analysis – were applied in the following study. To determine PAPs of varying but defined structure different animal meals were produced artificially and analysed after spiking to a set of 13 compound feed samples. The aims of the study were (i) to compare the capacity and the limits of both methods with respect to the determination of animal constituents of varying composition, (ii) to verify a correct interpretation of the results from each method and (iii) to determine an optimum application area for each method. Both methods complemented each other. The microscopic approach allowed a reproducible, high sensitive and quantitative determination of animal ingredients with morphological detectable structures, and in the presence of bone fragments a differentiation between fish and terrestrial animals was possible simultaneously. The PCR-analysis provided the detection of animal ingredients in feed even in absence of visible structures but fishmeal was not detected in a sufficient manner by the chosen screening setup. However, the PCR-method enabled to differentiate between animal groups or species and to identify animal species. The methods complemented each other not only in the analytical features but also regarding the results produced by the detection of two different analytical targets of PAPs, morphological structures and gene sequences, respectively. Suitable data rega rding the presence of their analytical targets were produced by each method, but a combination of both methods enabled furthermore to report correct results regarding the presence of the artificially composed PAPs in the feed samples. It was concluded that a combination of microscopy and PCR-analysis is reasonable for special application purposes to determine PAPs in feed: while microscopy provides reliable results also in highly processed feed with well- preserved morphological animal structures even with highly degraded genomic material, PCR provides applicable results in feed samples with preserved genomic animal material even after the separation of morphological structures. These specialties have to be considered for the choice of capable analytical methods and even for a correct evaluation of the results obtained from these methods in highly processed feed. An interpretation scheme based on the results of the study was proposed.