putrefacienscan grow under these conditions producing TMA and hy-
drogen sulfide to spoil the product. Work in Denmark has also demon-
strated that CO 2 tolerant marine vibrios likePhotobacterium phosphoreum
may be responsible for a non-sulfurous spoilage of these products in some
instances. This is a large (5mm diameter), almost yeast-like, bacterium
that has been isolated from the intestines of several different fish. Because
of its size it produces 10–100-fold more TMA per cell than smaller
organisms such asShewanellaand therefore can cause spoilage at lower
populations, typically around 10^7 cfu g^1 compared with 10^8 cfu g^1 for
more conventional bacteria. WhetherShewanellaorPhotobacteriumis
ultimately responsible for spoilage in MAP fish products probably de-
pends on relative numbers present initially and whether any other selec-
tive factors operate.
5.5 Plant Products
The plant kingdom provides a considerable part of human food require-
ments and, depending on the particular plant species, use is made of
every part of the plant structure from root, tuber, stem, leaves, fruit and
seeds. Plants have evolved many strategies to survive the predation of
herbivores and omnivores, including humans, and these strategies
include, not only protective mechanisms to protect vegetative parts such
as leaves, stems and roots, but also the development of rich, succulent
fruits to encourage animals to help in the dispersal of seeds.
As the human race settled down from the nomadic hunter–gatherer
state to form increasingly large stable communities so a wider range of
plants have been brought into cultivation. Plant products are grown on
Figure 5.7 Fish and fish products.Tindicates elevated temperature;Ehlow redox
potential: pH, reduced pH;aw, reducedaw, and * stored an chill temperatures
Chapter 5 145