Development of Yellow Discoloration in Sawai (Pangasianodon hypophthalmus) Muscle due to Lipid Oxidation.

In this study, we investigated the impact of lipid oxidation on the discoloration of Sawai (Pangasianodon hypophthalmus) lipids and proteins. Sawai microsomes, liposomes, and salt-soluble myofibrillar proteins were prepared and subjected to lipid oxidation process. The results revealed that the levels of thiobarbituric acid-reactive substances, yellowness (as indicated by b* values), and pyrrole compounds increased when Sawai liposomes and microsomes were oxidized using iron and ascorbate. Meanwhile, the levels of free amines decreased, particularly as the iron content (25∼100 µM) and incubation time (0∼20 h) increased. The impact of oxidized liposomes at different levels (1, 2, and 5%) on the salt-soluble Sawai myofibrillar proteins was also evaluated. The findings revealed that lipid oxidation products reduced the sulfhydryl content and increased the surface hydrophobicity and carbonyl content of the salt-soluble Sawai myofibrillar proteins. These results imply that the formation of yellow discoloration in Sawai muscle could be due to nonenzymatic browning reactions occurring between lipid oxidation products and amines in the muscle protein.

Extraction and Physico-Chemical Characterization of Chitosan from Mantis Shrimp (Oratosquilla nepa) Shell and the Development of Bio-Composite Film with Agarose.

Mantis shrimp (Oratosquilla nepa) exoskeleton, a leftover generated after processing, was used as a starting material for chitosan (CS) production. CS was extracted with different deacetylation times (2, 3 and 4 h), termed CS−2, CS−3 and CS−4, respectively, and their characteristics and antimicrobial and film properties with agarose (AG) were investigated. Prolonged deacetylation time increased the degree of deacetylation (DDA: 73.56 ± 0.09−75.56 ± 0.09%), while extraction yield (15.79 ± 0.19−14.13 ± 0.09%), intrinsic viscosity (η: 3.58 ± 0.09−2.97 ± 0.16 dL/g) and average molecular weight (Mν: 1.4 ± 0.05−1.12 ± 0.08 (×106 Da)) decreased (p < 0.05). FTIR spectra of extracted CS were similar to that of commercial CS. Among all the CS samples prepared, CS−3 had the best yield, DDA, Mν and antimicrobial activity. Therefore, it was chosen for the development of composite films with AG at different ratios (CS−3/AG; 100/0, 75/25, 50/50, 25/75 and 0/100). As the proportion of AG increased, the tensile strength (29.96 ± 1.80−89.70 ± 5.08 MPa) of the composite films increased, while thickness (0.056 ± 0.012−0.024 ± 0.001 mm), elongation at break (36.52 ± 1.12−25.32 ± 1.23%) and water vapor permeability (3.56 ± 0.10−1.55 ± 0.02 (×10−7 g m m−2 s−1 Pa−1)) decreased (p < 0.05). Moreover, lightness of the films increased and yellowness decreased. CS−3/AG (50/50) composite film exhibited high mechanical and barrier properties and excellent compatibility according to FTIR and SEM analyses. According to these finding, mantis shrimp exoskeleton could be used to produce CS. The developed bio-composite film based on an appropriate ratio (50/50) of CS−3 and AG has potential for being used as food packaging material.

Comparative study on antioxidant activity of hydrolysates from splendid squid (Loligo formosana) gelatin and protein isolate prepared using protease from hepatopancreas of Pacific white shrimp (Litopenaeus vannamei).

Antioxidative activities of splendid squid gelatin hydrolysate (SGH) and squid mantle protein isolate hydrolysate (SMPIH) with different DHs (10-50 %) prepared using crude protease from hepatopancreas of Pacific white shrimp were comparatively studied. At the same DH, SGH had higher FRAP and metal chelating activity and SMPIH showed higher ABTS radical scavenging activities. However, SMPIH had higher ABTS radical scavenging activity than SGH at all DHs tested. SMPIH showed higher DPPH radical scavenging activities than SGH when DHs were up to 30 % DH. However, the former had the lower activity as DHs were 40 and 50 %. ABTS radical scavenging activity of SGH and SMPIH with 50 % DH in gastrointestinal model system increased in the duodenal condition, while SGH showed higher activity in stomach condition than SMPIH. SGH and SMPIH (500, 1000 and 2000 mg/L) could retard lipid oxidation in a lecithin liposome system in a dose dependent manner. Based on Sephadex G-25 column chromatography, the fraction with ABTS radical scavenging activity had MW of 283 and 1381 Da, respectively. Therefore, both hydrolysates from squid gelatin and mantle protein isolate could be used as the alternative natural antioxidants.

Impact of enzymatic method using crude protease from Pacific white shrimp hepatopancreas on the extraction efficiency and compositions of lipids.

Lipids from striped catfish muscle were extracted with the aid of crude protease extract (CPE) from hepatopancrease of Pacific white shrimp at different levels (5-15 unit/g protein) for various hydrolysis times (0-180 min) at 60 °C. Yield of lipids increased within the first 30 min and was in agreement with increasing degree of hydrolysis. The increases in phospholipid and free fatty acid content were observed with hydrolysis times up to 30 min (p<0.05). Yield of lipid increased when 50mM CaCl2 was combined with CPE. CPE exhibited similar extraction efficiency to Alcalase. However, the lower yield was obtained in comparison with the solvent extraction. Higher oxidation and hydrolysis were found in lipids extracted with the aid of CPE and Alcalase, compared with those found in lipid extracted using solvents (p<0.05). All lipid samples had triglyceride as the major component and were rich in palmitic acid and oleic acid.

Compositions and yield of lipids extracted from hepatopancreas of Pacific white shrimp (Litopenaeus vannamei) as affected by prior autolysis.

Compositions and yield of lipids extracted from hepatopancreas of Pacific white shrimp (Litopenaeus vannamei) subjected to autolysis at 60°C for different times (0, 30, 60, 90 120 and 150 min) were investigated. Extraction yield increased from 7.4% to 8.8% as autolysis time increased from 0 to 150 min. Coincidental increase in total carotenoid content was obtained with increasing autolysis time (p<0.05). The increases in thiobarbituric acid-reactive substances (TBARS) and p-anisidine value (AV) of lipids were noticeable when autolysis time increased (p<0.05). However, no changes in free fatty acid (FFA) content were observed within the first 60 min of autolysis (p>0.05), but subsequently increased up to 150 min. (p<0.05). No differences in fatty acid profiles of lipids extracted from hepatopancreas without and with 60 min prior autolysis were observed. Lipids extracted contained docosahexaenoic acid (DHA; C22:6(n-3)) as the most abundant fatty acid, followed by eicosapentaenoic acid (EPA; C20:5(n-3)). Therefore, prior autolysis at 60°C for 60 min increased the extraction yield without negative effect on lipid quality.