3. Results and discussion
3.1. Enzyme production by A. elegans XH-22
Fungal genera involved in the traditional sufu production belong
to the Mucoraceae, including Mucor spp., Actinomucor spp., and
Rhizopus spp., which have enzyme systems with high proteolytic
activities, allowing it to grow on substrate rich in protein but poor
in carbohydrate (Han, Rombouts, & Nout, 2001). In the present
study, the fungal fermentation starter A. elegans XH-22 was usually
used for sufu production and has a very good safety record. Fungal
solid-state fermentation requires three stages, the first being the
growth of mold mycelia and partial protein hydrolysis by enzymes
excreted by mycelia, the second being salting of surimi and the
third being further protein hydrolysis by enzymes. It's important to
allow the mucor growas many mycelia as possible in the first stage
(Zhao & Zheng, 2009). A. elegans XH-22 grewvery quickly on surimi
surface during fermentation. After two days fermentation, mycelia
was found on surimi surface and a white-mycelia cover was
formed.
Proteases and a-amylase production by A. elegans XH-22 were
shown in Fig. 1. The neutral protease activity in surimi increased
rapidly (P < 0.05) during the fermentation process, and its activity
reached 66.3U/g at 48 h. Activity of a-amylase was also enhanced
with the increase of fermentation time, but significant increase
(P < 0.05) was only found between 0 h and 24 h, and no significant
difference was found among 24 h, 36 h and 48 h. This is not in
agreement with sufu fermentation process, during which both
protease and a-amylase production by the fungal fermentation
starters increased with the fermentation time (Han et al., 2003).
This difference may partly result from the high content of protein,
but low content of carbohydrate in surimi. The high protease production
can guarantee the followed enzymatic hydrolysis of the
surimi protein.