Journal of Film Preservation - FIAF

macromolecular chains. In a second step, the enzymes called
peptidases give small polypeptides segments and amino acids. The
fragmentation is of a “terminal” type giving low molecular weight
units. Such types of mechanisms are illustrated in figure 13.
Figure 13: Different types of proteolytic enzymes acting on the gelatine structure
There are several types of micro-organisms which possess these
proteolytic enzymes i.e. Bacillus, Clostridium, Aeromas, Staphylococcus,
Micrococcus, Serratia, Pseudomonas, Penicillium, Aspergillus .
Stickley29 , from Kodak, published some results of the degradation of
gelatine solution by Bacillus and Pseudomonas. The biodegradation
activity of these micro-organisms was evaluated by measuring the
viscosity decay of photographic gelatine solutions over 24 hours at 37
ºC. Bacillus exhibits an initial lag phase showing a little decrease in
viscosity. In this phase the bacillus spores germinate and the cells grow.
After this period, and between 8 and 16 hours Bacillus exhibits an
exponential growth phase which is seen as a sharp drop in viscosity.
After this drastic decay, viscosity remains constant as bacterial growth
slows down due to the food supply becoming limited. With
Pseudomonas the viscosity starts dropping almost immediately, no
spore germination phase is detected, but the cells continue to grow.
The viscosity loss occurs in one steady drop until a levelling off is
achieved when the food supply becomes a limiting growth factor.
In this study, the most important fungus found to liquefy and degrade
gelatine products was Aureobasidium sp. although the number of fungi
present in the water supply would not normally cause problems.
The profiles of gelatine viscosity decay versus time with both microorganisms
are shown in figures 14.
During their manufacturing processes, gelatines can be contaminated
by different types of micro-organisms. De Clerck and De Vos30 published a study of the diversity of contaminants isolated from
samples taken in five important points along two different gelatine
production lines and from water supplies used for extraction and
cooling. Apart from members of the genus Bacillus and related
endospore forming genera, other micro-organisms have been isolated,
50 Journal of Film Preservation / 67 / 2004