Incoming wheat provides a prime contamination source for end products. The modal (m) aerobic mesophilic count was 105cfu/g, with 55% of samples containing counts greater than or equal to 104 cfu/g, up to a maximum of 107 (Fig. 1). Bacillus spp. (m=104cfu/g), yeasts and moulds (m=103 cfu/g for both) constitute a significant proportion of the microbial population of incoming wheat(Table 2). Thermophiles and coliforms, although higher in wheat than in subsequent milling samples (m=101 cfu/g), were of minor importance. Most Bacillus spp. entered the milling process on incoming wheat as vegetative cells, as mesophilic aerobic spore numbers were generally three to four log units lower (Table 2). Mesophilic aerobic spore counts (m=10 cfu/g) were low on wheat before conditioning compared with other spoilage organisms. Mould genera entering the milling system on wheat most frequently comprised Aspergillus, Cladosporium,Penicillium and Aureobasidium (Table 5).
E. coli and B. cereus were detected at their minimum detection level or one log unit higher in the majority of samples. Modal E. coli (1 MPN/g) and B. cereus (1 MPN/g) counts were low on wheat before conditioning. Salmonella was not detected on wheat before conditioning (Table 2).
Wheat quality is of high importance to flour quality. A comparison of the milling of high and low microbiological quality wheats and their respective end product flour showed wheat of low microbiological quality yields flour with high microbial loads and vice versa(Table 4). There was also considerable variation in the quality of incoming wheat from different geographical areas, with wheat from hotter, wetter areas generally carrying the highest microbial loads (data not shown).