OXIDATIVE STABILITY OF FRESH AND HEAT-PROCESSED DARK AND LIGHT MUSCLES OF MACKEREL (Scomber scombrus)

Oxidative stability of light and dark comminuted muscle of raw and thermally processed mackerel stored at 4C was studied over a 21 day period by monitoring changes in conjugated dienes (CD) and 2-thiobarbituric acid (TBA) values. The quantity of headspace (HS) volatiles, propanal, and hexanal as well as the ratio of aliphatic to olefinic (R_ao) or diallylmethylene (R_ad) protons in the proton nuclear magnetic resonance (¹ NMR) spectra of oils were determined. The content of CD of light and dark ground mackerel muscle samples exhibited a consistent increase over the entire storage period. Furthermore, secondary oxidation products as reflected in the TBA values and content of propanal, hexanal and HS gases, generally, showed a gradual increase in their level. The concentration of propanal, the dominant volatile of the HS gases, increased markedly up to day 6 of storage, but afterwards began to decline continuously. A similar trend was noted for hexanal, but at a lesser extent. The R_ao and R_ad values in the ¹H NMR spectra of lipids from all stored samples increased constantly during storage. In all samples, the dark ground muscle exhibited a higher degree of oxidation than its light counterpart. Furthermore, heat-processed dark comminuted muscle oxidized faster than its raw counterpart while generally an opposite trend was observed for the light ground muscle.     

ANTIOXIDATIVE ACTIVITY OF PROTEIN HYDROLYSATE FROM ROUND SCAD MUSCLE USING ALCALASE AND FLAVOURZYME

Antioxidative activity of hydrolysates from round scad (Decapterus maruadsi) muscle with degrees of hydrolysis (DH ) of 20, 40 and 60%, prepared using Alcalase (HA) or Flavourzyme (HF), was determined. At the same DH, HF exhibited a higher 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical scavenging activity and reducing power, but a lower Fe²⁺ chelating ability than HA. HF from isopropanol‐defatted muscle with 60% DH was extracted using different solvents, and hexane (E1), dichloromethane (E2), ethyl acetate (E3) and residual (R) fractions were obtained. Among all fractions, E2 and E3 exhibited the highest DPPH radical scavenging activity and reducing power. HF with 60% DH and E2 at 1,000 ppm exhibited antioxidant activity in linoleic oxidation and lecithin liposome systems, and the results were comparable to butylated hydroxytoluene (BHT) at 100 ppm. Therefore, type of proteinase, DH and defatting process prior to hydrolysis exerted an influence on the antioxidative activity of hydrolysates.     

ANTIOXIDANT ACTIVITIES OF ENZYMATIC EXTRACTS FROM AN EDIBLE SEAWEED SARGASSUM HORNERI USING ESR SPECTROMETRY

The antioxidant activity of water-soluble natural extracts from an edible seaweed , Sargassum horneri, was evaluated by examining the radical scavenging activities of the extracts of hydrolyzates from S. horneri on 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl and alkyl radicals. A spin-trapping electron spin resonance (ESR) spectrophotometer was employed and the results were compared for their ESR signal intensity. The brown seaweed S. horneri was enzymatically hydrolyzed to prepare water-soluble extracts by five carbohydrases (AMG, Celluclast, Termamyl, Ultraflo and Viscozyme) and five proteases (Alcalase, Flavourzyme, Kojizyme, Neutrase, Protamex). The extracts so prepared exhibited strong scavenging activity on DPPH, hydroxyl and alkyl radicals. The scavenging activity of the radicals increased with increased concentration of the extracts. The scavenging results were higher or similar for hydroxyl and alkyl radicals, and lower for DPPH radical compared with vitamin C as a reference. Viscozyme and Alcalase extracts were superior and scavenged radicals examined better than the extracts prepared by other carbohydrases and proteases.     

Effect of Processing on the Content of Condensed Tannins in Rapeseed Meals

The condensed tannins of rapeseed meals produced by a two-phase solvent extraction system were determined and compared with those of hexane-extracted meals. Ground seeds were extracted with absolute methanol, 95% methanol, 10% (w/w) ammonia in methanol or 10% (w/w) ammonia in 95% methanol and hexane as a second phase. Tannins were extracted with 70% (v/v) aqueous acetone and assayed by the 0.5% vanillin methodology. Methanol alone extracted only 16% of the tannins; addition of 5% (v/v) water to methanol increased the efficiency of tannin extraction to 36%. The methanol-ammonia-water/hexane, however, was the most effective solvent system for the removal of tannins. The resultant meals contained from 4% to 33% of the condensed tannins which were originally present in rapeseed meals.     

Effect of Sulfanilamide on the TBA Values of Cured Meats

The effect of sulfanilamide addition on the TBA numbers of meats cured with 0 - 200 ppm levels of sodium nitrite has been investigated. Results indicate that the TBA numbers of meats cured with 100 - 200 ppm level were always larger when sulfanilamide was present than in its absence. However, at low levels of 0 - 50 ppm sodium nitrite the TBA values were always lower in the presence of sulfanilamide. This effect is substantial and has apparently not been observed before. A possible explanation has been put forward. In all cases a distillation method was employed to evaluate TBA numbers.     

STABILIZATION OF MEAT LIPIDS WITH GROUND SPICES

The antioxidant efficacy of ground clove, ginger, oregano, rosemary, sage, and thyme was investigated in comminuted pork systems. Spices at 200–2000 ppm levels of addition inhibited the formation of the 2-thiobarbituric acid (TBA) reactive substances (TBARS) by 12–96% over 21-days of storage at 4C. The anti-oxidative effect of spices was concentration-dependent; but close followed by sage and then rosemary was most effective. Ginger and thyme exerted the least effect in prevention of oxidation of meat lipids.     

STRUCTURED LIPIDS: ACIDOLYSIS OF GAMMA-LINOLENIC ACID-RICH OILS WITH n-3 POLYUNSATURATED FATTY ACIDS

Structured lipids were synthesized by acidolysis of γ-linolenic acid-rich oils and n-3 polyunsaturated fatty acids (PUFA), namely eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), using different lipases. Lipase PS-30 from Pseudomonas sp. was chosen over the other enzymes to catalyze the acidolysis reaction owing to higher incorporation of n-3 PUFA. Effects of mole ratio, reaction time, incubation temperature, enzyme load, and solvent type on acidolysis reactions were studied. At 250 enzyme activity units, incorporation of n-3 PUFA reached optimal values of 29.9 and 30.7% for the reactions with borage and evening primrose oils, respectively. For the time course reaction, incorporation of n-3 PUFA increased up to 34.1 and 31.5% (in 30 h), in borage and evening primrose oils, respectively. After 24 h incubation in hexane, n-3 PUFA (EPA+DHA) incorporated into borage and evening primrose oils was 31.8 and 32.7%, respectively. The highest n-3 PUFA incorporation in both oils occurred at a mole ratio of 1:2:2 (oil/EPA/DHA). Among the solvents tested, n-hexane was found to be highly effective; total n-3 PUFA incorporation of 33.3 and 27.8% in borage and evening primrose oils, respectively, was achieved in hexane. However, the solvent-free reaction afforded products with a total of 23.4–28.8% n-3 fatty acids (EPA and DHA).     

LIPID AND LIPID SOLUBLE COMPONENTS OF GONADS OF GREEN SEA URCHIN (STRONGYLOCENTROTUS DROEBACHIENSIS)

Seasonal changes in the lipid and lipid soluble components of gonads of green sea urchin (Strongylocentrotus droebachiensis) were investigated. The lipid content was highest in the spring while it was lowest in the winter. The composition of nonpolar and polar lipid classes of sea urchin gonads were not affected qualitatively, but there were significant (P<0.05) quantitative variations. Major nonpolar lipid classes were triacylglycerols (TAG), free fatty acids (FFA) and sterols (ST) while dominant polar lipid components were phosphatidylcholine (PC) and phosphatidylethanolamine (PE). The fatty acids 16:0 and 14:0 were the major saturated fatty acids (SFA) consistently present in total, nonpolar and polar lipids of sea urchin gonads. The 5-olefinic acid 20:1 n-15 was the dominant monounsaturated fatty acid (MUFA) while 20:4 n-6 and 20:5 n-3 were the major polyunsaturated fatty acids (PUFA) present. The content of PUFA increased during cold climatic conditions with a simultaneous decrease in the content of SFA. These changes were reversed during warm seasons. Total carotenoid content was highest in the spring. Echininone was the major carotenoid present and its relative content varied significantly (P<0.05) with the season; being highest in the spring and lowest in the summer. In addition, β-carotene was present in each season. Thus, the importance of seasonal variations on the lipid and lipid soluble components of sea urchin gonads is evident.