3. Results and discussion
3.1. Feasibility study
The aim of the study was to find a suitable approach to produce
homogeneous cheese powder materials. Three processing schemes
were tested called I, II and III (Table 1). Process I aimed to mimic
the laboratory scale processing procedure used at Anses for provid-
ing samples in proficiency testing rounds (Hennekinne et al., 2003).
Process II focussed on the inclusion of cryogenic milling to prepare
cheese powders. Cryogenic milling, which produces finely ground
powders with reproducible particle size distributions, is often
applied at our premises for processing various types of reference
materials. However, a prerequisite for a suitable material is that
it must behave similarly to a real sample in the analytical process.
Hence, the aim was to verify that cryogenic milling has no adverse
effect on the material. Finally, procedure III was carried out with
the aim to investigate whether cheese can be efficiently freeze-
dried, and if mixtures of such cheese powders with powders pro-
duced by freeze-drying of spiked cheese slurries behave similarly
when compared to materials A and B (basically evaluated by the
recovery calculation). Procedure III was considered preferential in
terms of minimizing contamination of processing equipment,
equipment cleaning and workload, which is important seen the
large amounts of cheese that are needed to be manipulated for
the candidate RM batches: only a small amount of cheese had to
be spiked with toxin (higher concentration) with subsequent
freeze-drying of the homogenised spiked cheese slurry, whereas
the vast majority of the cheese could be directly lyophilised,
thereby avoiding producing large amounts of non-spiked cheese
slurry as an intermediate product.