Cathepsin B was the most active cysteine proteinase in the Pacific whiting
(Merluccius productus) fish fillet, and cathepsin L in surimi when the activities of the
most active cysteine proteinases (cathepsin L, B, and H) were compared. Cathepsin L
showed maximum activity at 55°C in both fish fillet and surimi, indicating its function
in myosin degradation during conventional cooking of fish fillet and surimi. Washing
during surimi processing removed cathepsin B and H but not cathepsin L. Autolytic
analysis of surimi proteins showed that the myosin was the primary target, while actin
and myosin light chain showed limited hydrolysis during 2 hr incubation. When
purified Pacific whiting proteinase was incubated with various component of fish
muscle, proteinase was capable of hydrolyzing purified myofibrils myosin, and native
and heat-denatured collagen. The degradation pattern of myofibrils by the proteinase
was the same as the autolytic pattern of surimi.
Inhibition by the food-grade proteinase inhibitors varied with the catalytic type
of proteinase. Beef plasma protein (BPP) had a higher percentage of papain inhibitors, followed by whey protein concentrate (WPC), potato powder (PP), and egg white
(EW). On the other hand, EW had a higher percentage of trypsin inhibitors followed
by BPP, PP, and WPC. EW inhibited trypsin activity completely at levels as low as
1%. WPC inhibited the autolytic activity of fresh surimi. Bovine serum albumin
(BSA) was not effective as WPC. WPC can be used as an inhibitor for the Pacific
whiting surimi, but high concentration is required.
A limited number of inhibitory components were found, as the components in
food-grade inhibitors were characterized by inhibitory activity staining. Both EW and
PP showed more serine proteinase inhibitors than cysteine proteinase inhibitors. PP
showed one cysteine inhibitory component while EW did not show any. BSA in both
WPC and BPP acts as an nonspecific competitive inhibitor and reduces the enzyme
activity. An unidentified high molecular weight protein (HMP) found in WPC, BPP,
and BSA functions as an alternative substrate for papain while it functions as true
inhibitor for trypsin. / Graduation date: 1995
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27070 |
| Date | 28 April 1995 |
| Creators | Weerasinghe, Vasana C. |
| Contributors | An, Haejung |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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