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.

Molecular, Structural, and Rheological Characterization of Camel Skin Gelatin Extracted Using Different Pretreatment Conditions.

Optimum conditions for high-quality gelatin recovery from camel skin and its molecular, structural, and rheological characterization were carried out in this study. Increased yield and gel strength were recorded, with an increase in camel skin pretreatment times of 6 to 42 h and 0.50 and 0.75 M-NaOH. Gelatin from skin pretreated with 0.75 and 0.5 M-NaOH for 42 h showed the highest yield (22.60%) and gel strength (365.5 g), respectively. Structural characterization by Fourier transformation infrared spectra, X-ray diffraction, and nuclear magnetic resonance indicated that all gelatins possessed major peaks in the amide region, and diffraction peaks around 22° were basically amorphous. The temperatures for gelling and melting ranged from 20.9 °C to 25.8 °C and 27.34 °C to 30.49 °C. Microstructure revealed loose network with more voids in gelatin from skin pretreated with 0.5 and 0.75 M-NaOH for 6 h, while a highly cross-linked network and less voids were observed in those pretreated with 0.75 M-NaOH for 24 h and 0.5 M-NaOH for 42 h. The results reveal that great potential exists in producing halal gelatin with excellent quality and functionality from camel skin.

Antioxidant activities of lead (Leucaena leucocephala) seed as affected by extraction solvent, prior dechlorophyllisation and drying methods.

Extracts of brown lead (Leucaena leucocephala) seed prepared using different extraction solvents were determined for antioxidative activities using different assays. The highest yield (3.4-4.0%) was obtained when water was used as an extraction solvent, compared with all ethanolic extracts used (1.2-2.0 %) (P < 0.05). Much lower chlorophyll content was found in the water extract. When hot water was used, the resulting extract contained lower total phenolic and mimosine contents (P < 0.05). In general, 60-80 % ethanolic extracts had higher 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activities, ferric reducing antioxidant power (FRAP) and metal chelating activity than water extracts (P < 0.05). When brown lead seed was dechlorophyllised prior to extraction, the water extract had slightly increased yield with lower chlorophyll content. Nevertheless, prior chlorophyll removal resulted in the increase in antioxidative activities but lower total phenolic and mimosine contents (P < 0.05). Generally, phenolic compounds and mimosine were more released when water was used as the extraction solvent, while the lower amount of chlorophyll was extracted. Oven-drying exhibited the negative effect on antioxidative activities and mimosine content. The higher antioxidative activities with concomitant higher total phenolic and mimosine contents were found in water extract dried by freeze drying. Thus, extraction solvent, dechlorophyllisation and drying methods directly influenced the yield and antioxidative activity of lead seed extract.

Antioxidant activity and inhibitory effects of lead (Leucaena leucocephala) seed extracts against lipid oxidation in model systems.

Antioxidant activity of brown lead (Leucaena leucocephala) seed extracts with and without prior chlorophyll removal was studied in comparison with mimosine. Both extracts showed similar hydroxyl radical (HO(•)) scavenging activity, hydrogen peroxide (H2O2) scavenging activity, singlet oxygen inhibition and hypochlorous acid (HOCl) scavenging capacity (p > 0.05). Nevertheless, the extract without prior chlorophyll removal had higher oxygen radical absorbance capacity than that with prior chlorophyll removal (p < 0.05). Generally, lead seed extracts with and without prior chlorophyll removal possessed a lower antioxidant activity, compared with mimosine. When lead seed extract without prior chlorophyll removal (100 and 200 ppm) was used in different lipid oxidation model systems, including ß-carotene-linoleic acid and lecithin liposome systems, the preventive effect toward lipid oxidation was dose-dependent. At the same level of use, mimosine exhibited a higher efficacy in prevention of lipid oxidation in both systems as indicated by the lower increases in thiobarbituric acid reactive substances. A similar result was obtained in minced mackerel. Therefore, lead seed extract containing mimosine could act as a natural antioxidant to prevent lipid oxidation in foods.

Gelatin hydrolysate from blacktip shark skin prepared using papaya latex enzyme: Antioxidant activity and its potential in model systems.

Antioxidant activities of gelatin hydrolysates from blacktip shark skin prepared using papaya latex enzyme with different degrees of hydrolysis (DHs: 10%, 20%, 30% and 40%) were evaluated. All antioxidant activity indices of hydrolysates increased with increasing DH (P<0.05). When gelatin hydrolysate with 40%DH was determined for its pH and thermal stability, ORAC and chelating activity remained constant or slightly increased in a wide pH range (1-9) and during heating (100°C) for 240min. It was also stable in simulated gastrointestinal tract model system. Moreover, gelatin hydrolysate at a level of 500 and 1000ppm could inhibit lipid oxidation in both ß-carotene linoleate and cooked comminuted pork model systems. Therefore, gelatin hydrolysate from blacktip shark skin (40%DH) can potentially be used as an alternative source of natural antioxidants.