PHYSICOCHEMICAL AND BIOCHEMICAL CHANGES IN WHOLE LIZARDFISH (SAURIDA MICROPECTORALIS) MUSCLES AND FILLETS DURING FROZEN STORAGE

The physicochemical and biochemical changes in whole lizardfish (Saurida micropectoralis) muscles and its fillets kept in air and under vacuum during frozen storage at ?20C for 24 weeks were investigated. The formaldehyde (FA) and dimethylamine contents increased with a concomitant decrease in trimethylamine‐ N‐oxide (TMAO) content as the storage time increased (P < 0.05). The Ca²⁺–adenosine 5′‐triphosphatase activity continuously decreased with a coincidental decrease in salt‐soluble fraction. The disulfide bonds were increasingly formed throughout the storage (P < 0.05). The surface hydrophobicity increased and reached the maximum at week 12 with a subsequent decrease up to the end of storage. In general, the higher changes were observed in samples kept under vacuum than those kept in air. With the same atmosphere used, the whole fish showed slightly higher changes than the fillets. A marked increase in TMAO demethylase (TMAOase) activities was observed up to 12 weeks, followed by the continuous decrease up to 24 weeks of storage. The produced FA might play an important role in inducing protein denaturation and/or aggregation in lizardfish. The TMAOase activity as well as the FA formation could be reduced to some extent with the removal of internal organs and storage in the presence of oxygen. However, a detrimental effect of oxygen, especially on the promotion of lipid oxidation, would be an obstacle.     

EXTRACTION OF CAROTENOPROTEIN FROM BLACK TIGER SHRIMP SHELLS WITH THE AID OF BLUEFISH TRYPSIN

The effect of bluefish (Pomatomus saltatrix) trypsin on the recovery and characteristics of carotenoprotein from black tiger shrimp (Penaeus monodon) shells was investigated. Trypsin concentration and reaction time both affected the hydrolysis and the recovery of carotenoproteins ( P <  0.05). The recovery of carotenoproteins from shrimp shells was maximized by the hydrolysis of shrimp shells using 1.2 trypsin units/g shrimp shells for 1 h at 25C. Freeze-dried carotenoprotein recovered contained 70.20% protein, 19.76% lipid, 6.57% ash, 1.50% chitin, and 87.91 µg total astaxanthin/g sample, indicating a substantial reduction in the levels of antinutrients associated with shrimp waste, while enriching the product in carotenoid pigments and valuable essential nutrients (proteins and lipids). Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of the recovered carotenoprotein revealed that protein with molecular weight of 45 kDa was the major constituent. When hydrolytic activities of bluefish and bovine trypsins toward carotenoproteins in black tiger shrimp shells were compared, the recovery efficacy of protein and pigment by bluefish trypsin was similar to that achieved by trypsin from bovine pancreas. Therefore, bluefish trypsin could be used as an alternative cheap proteinase for extraction of carotenoproteins from black tiger shrimp shells.

PRACTICAL APPLICATIONS

Carotenoproteins from black tiger shells, the byproduct of shrimp processing, can be recovered with the aid of fish trypsin. This product can be used for both food and feed applications. Additionally, the fish trypsin can be used instead of bovine trypsin. As a whole, the utilization of fish and shellfish processing wastes can be maximized.     

EFFECT OF CHICKEN PLASMA PROTEIN AND SOME PROTEIN ADDITIVES ON PROTEOLYSIS AND GEL-FORMING ABILITY OF SARDINE (SARDINELLA GIBBOSA) SURIMI

The effect of chicken plasma protein (CPP) and various protein additives on autolysis and gel‐forming ability of sardine (Sardinella gibbosa) surimi was investigated. CPP and other protein additives showed inhibitory activity toward autolysis of sardine surimi incubated at 70C in a concentration‐dependent manner. Porcine plasma protein (PPP) and egg white (EW) were more effective in proteolysis prevention than CPP and other protein additives. Breaking force and deformation of both modori and kamaboko gels increased when CPP and other protein additives were added at levels up to 2% (P < 0.05). Nevertheless, PPP and EW showed a greater gel‐strengthening effect than CPP and other protein additives (P < 0.05). Addition of CPP and other plasma proteins resulted in decreased whiteness, especially with increasing amount (P < 0.05). However, no change in whiteness was observed with gels containing EW and soy protein isolate (SPI) (P > 0.05). Proteolysis of sardine surimi can be retarded by the addition of CPP and protein additives, leading to increased gel‐forming ability.     

INHIBITION OF GEL WEAKENING OF THREADFIN BREAM SURIMI USING THAI LEGUME SEED PROTEINASE INHIBITORS

Partially purified proteinase inhibitors from cowpea (Vigna unguiculata (L) Wasp), pigeon pea (Cajanus cajan (L.) Millsp.) and bdmbara groundnuts (Voandzeia subterranea (L.) Thou) effectively inhibited sarcoplasmic modori‐inducing proteinase extracted from threadfin bream muscle in a concentration dependent manner. Incorporation of these proteinase inhibitors into threadfin bream surimi partially inhibited autolytic degradation and increased the gel force and deformation. Combination of setting and incorporating proteinase inhibitors from cowpea and bambara groundnut var. HY at the level of 30 Kcunits/g resulted in an increase in gel force and deformation by 60% and 26%, respectively. However, the lightness and whiteness of surimi gels decreased slightly when the proteinase inhibitor was added at a level of 30 kunits/g.     

PORCINE PLASMA PROTEINS AS GEL ENHANCER IN BIGEYE SNAPPER (PRIACANTHUS TAYENUS) SURIMI

Cohn's fraction I‐S from porcine plasma showed the highest transglutaminase activity, compared to fractions I. 11+III, IV, IV‐l. The optimum temperature for incorporating monodancylcadaverine into dimethylated casein was 45C. Plasma transglutaminase in fraction I‐S was activated by calcium chloride but was inhibited by N‐ethylmaleimide, ethylenediaminetetraacetic acid, and ammonium chloride. The addition of fraction I‐S into bigeye snapper surimi resulted in a substantial increase in gel breaking force and deformation, particularly in the presence of calcium chloride and thrombin. No changes in whiteness and water holding capacity were observed in surimi gel with the addition of 0–0.5% of fraction I‐S. Fraction I‐S was found to catalyze nondisulfide covalent cross‐linking of myosin heavy chain. The combination of endogenous and plasma transglutaminase enhanced surimi gelation.     

PROPERTIES OF CYSTEINE PROTEINASE INHIBITORS FROM BLACK GRAM AND RICE BEAN

Cysteine proteinase inhibitors (CPI) were purified to 59 and 54 fold from black gram (Vignaraungo (L.) Hepper) and rice bean (Vignaumbellata Thunb.), respectively, by using heal treatment, followed by chromatography on a carboxymethyl (CM)‐papain‐Sepharose affinity column. The purified inhibitors were highly inhibitory to papain and Pacific whiting cathepsin L in a concentration dependent manner. They were detected as a dark band on tricine‐SDS‐PAGE gel stained for inhibitory activity. The apparent molecular weights of purified CPI from black gram and rice bean seeds were estimated to be 12, 000 daltons. The purified inhibitors were thermostable up to 90C and active in the neutral and alkaline pH ranges.