The deprotenisation of the shrimp shells was brought
about by the activity of the neutral protease of B. subtilis.
13,18 Yang et al.14 found that the optimum activity
of the protease produced by Bacillus subtilis took place
at 30 C and pH of 6. In the present work also the protease
showed maximum proteolytic activity of 10.6875 g
tyrosine/g protein after 48 h of fermentation when the
pH of the liquor was 5.9. The proteolytic activity remained
fairly constant for 5–6 days during fermentation
(Fig. 2). These changes are clearly supported by the
reports of Allagheny et al.26 and Sarkar et al.19
During fermentation, when the available carbohydrate
source was utilized by the microorganisms for
their growth, acid was released and this was responsible for calcium solubilization from the shrimp shell.12 As
the calcium ion concentration increased in the fermenting
media, proteolytic activity showed a decreasing
trend. Tsuru et al.27 reported that calcium is recognized
to prevent protease autolysis.