oilpalm and olives to mention just a few. Edible nuts may also come from
a botanically wide range of tree species and many of them are rich in oil
and give similar microbiological problems as oilseeds.
Seeds rich in oil, such as groundnuts, have a much lower water content
at a particular water activity than cereals, thus groundnuts with a 7.2%
water content have a water activity of about 0.65–0.7 at 25 1 C. Apart
from the problem of mycotoxin formation in moulded oilseeds, several
mould species have strong lipolytic activity leading to the contamination
of the extracted oils with free fatty acids which may in turn undergo
oxidation to form products contributing to rancidity. The most impor-
tant lipolytic moulds are species ofAspergillus, such asA. nigerand
A. tamarii, PenicilliumandPaecilomyces, while at higher water activities
species ofRhizopusmay also be important. Figure 5.8 shows the influ-
ence of moisture content, and damage on the formation of free fatty
Figure 5.8 The influence of moisture content on free fatty acid formation in groundnuts
stored for four months. 7.2% moisture content corresponds toaw0.65–0.70 at
251 C so fungal growth may occur
150 Microbiology of Primary Food Commodities