Abstract
Fish processing waste can be used to produce commercially valuable by-products, such as pepsinogen, which has application in food, manufacturing industries, collagen extraction, gelatin extraction, and in regulating digestibility.An important acidic protease, pepsin, is synthesized and secreted in the gastric membrane in an inactive state called pepsinogen (PG). In the present study, the purification of pepsinogen from the stomach of red perch, using aqueous two phase systems (ATPS) formed by polyethylene glycol (PEG) and salt at 4°C, was optimized.The effects of PEG molecular weight (PEG 1000, 1500, 3000 and 4000) and concentration (16, 18, 20, 22 and 24%) on the partitioning of PG were studied, and parameters including total volume (TV), volume ratio (VR), total enzyme activity (AE), protein content (Cp), specific enzyme activity (SA), partition coefficient (Kp), purification fold (PF), and recovery yield (RY) were evaluated. PEG molecular weight and PEG concentration also had significant effects on each parameter. TV and VR decreased with increased salt concentration, since salt formed hydrogen bonds with water molecules and formed a more compact and ordered water structure. PG partitioned predominantly in the PEG-rich top phase due to its negative charge. AE, CP, SA, PF and RY increased with increased salt concentration and then decreased, while KP had an opposite pattern. The PEG 3000 (20%), PEG 1000 (24%), PEG 4000 (16%) and PEG 1000 (18%) concentrations gave the highest TV, VR, CP and KP, respectively. PEG 1500 with 18% concentration gave the highest AE, SA, PF and RY (86.2%). As PEG 1500 at 18% concentration gave the highest RY (86.2%). It was selected as the optimum PEG molecular weight and PEG concentration. (NH4)2SO4 at 15%, which gave the highest RY (71.7%), was selected as the optimum salt type and salt concentration. 15% (NH4)2SO418% PEG 1500 was the optimal ATPS combination, and presented a better partition. The values of SA and PF and RY obtained with ATPS method were much higher (2 fold in case of SA and PF, and 1.2 fold in case of RY), than those obtained with the Ammonium Sulphate Fractionation (ASF) method.
Highlights
Atlantic Canada has 15% (40,000 km) of the Canada’s coastline and 42% of the Canada’s fresh water (320,000 km2)
The results of the extraction of crude PG from the stomach (35 g) of red perch are summarized in table 1
Zhou et al [31] homogenized stomach samples using a homogenizer with phosphate buffer, centrifuged the homogenate to collect the crude enzymes from sea bream, and reported decreases in the AE, CP and recovery yield (RY) of 35%, 55% and 36%, and increases in the specific enzyme activity (SA) and purification fold (PF) of 42% and 40% during extraction steps, respectively
Summary
Atlantic Canada has 15% (40,000 km) of the Canada’s coastline and 42% of the Canada’s fresh water (320,000 km). A large portion of the fish (80%) landed in Atlantic Canada is processed [2]. There are three major common steps in fish processing: (a) removing the viscera, (b) removing the head, tail, fins and skin, and (c) removing the frame and producing fillets. A large fraction (30-80%) of fish (flesh, heads, bones, fins, skin, tails and viscera) is generated as waste during fish processing [3,4]. Fish wastes are usually disposed of in landfills or poured directly into the sea, which results in high disposal cost and causes environmental problems. About 56% of the fish landing in Canada is converted into waste; of which 13% is disposed in the ocean [5]. Conventional disposal of fish wastes underscores the need for a more reasonable utilization approach of fish wastes, as well as effective recovery of valuable ingredients from these wastes
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