No abstract

Antioxidative activities of protein hydrolysates from yellow stripe trevally (Selaroides leptolepis) prepared using Alcalase 2.4 L (HA) and Flavourzyme 500 L (HF) with the degree of hydrolysis of 15% by pH-stat method were determined. Both protein hydrolysates exhibited the antioxidative activity in a concentration dependent manner. HF generally showed the greater antioxidative activity than HA (P < 0.05) as indicated by the higher 2,2-diphenyl-1-picryhydrazyl (DPPH) radical scavenging activity, reducing power and metal chelating activity. Antioxidative activity of both hydrolysates was stable when heated at 90°C for 10 and 30 min and subjected to a wide pH range (2-12). Nevertheless, metal chelating activity decreased in very alkaline and acidic pH ranges. HA and HF at 200 ppm retarded the formation of conjugated diene and thiobarbituric acid reactive substances (TBARS) in lecithin liposome system. HF possessed the stronger antioxidative activity than HA (P < 0.05). However, a-tocopherol at 200 ppm showed the higher antioxidative activity in the system.

Hydrolysates from yellow stripe trevally meat with 15% degree of hydrolysis (DH) obtained using Alcalase (HA) and Flavourzyme (HF) following pH-stat method were characterized. Both hydrolysates, HA and HF, contained glutamic acid and glutamine as the major amino acids, while glycine was the dominant amino acid in fish flesh. Hydrolysates were also rich in aspartic acid, asparagine, alanine, lysine, and leucine. Essential amino acid/nonessential amino acid ratios were 0.55, 0.63, and 0.62 for flesh, HA, and HF, respectively. After separation on a Sephadex G-50 column, antioxidative activity of hydrolysate fractions was determined as Trolox equivalent antioxidant capacity. The fraction of HF with molecular weight (MW) of 1.77 kDa exhibited the strongest antioxidative activity, compared with other fractions. Among all fractions of HA, the one having a MW of 2.44 kDa showed the highest antioxidative activity. Thereafter, the selected Sephadex G-50 fractions from both HA and HF were further chromatographed using a Sephadex C-25 column, followed by HPLC. MW of antioxidative peptides from HA and HF determined by Maldi TOF/TOF was 656 and 617 Da, respectively. However, peptides isolated from both HA and HF possessed a lower antioxidative activity than Trolox at the same concentration (P < 0.05). HA and HF prevented DNA oxidative damage in Fenton reaction system tested by in vitro plasmid DNA relaxation assay. These results indicate that hydrolysates from yellow stripe trevally can be used as an important source of amino acids and serve as alternative natural antioxidants.

Characteristics and the use as culture media of protein hydrolysate from yellow stripe trevally (HF(25)) were determined in comparison with Bacto Peptone. HF(25) had the higher contents of ash (45.73%), lipid (0.77%), and moisture (4.34%) but lower protein content (42.11%) than did Bacto Peptone (P < 0.05). HF(25) powder was slightly darker than Bacto Peptone (P < 0.05). HF(25) contained a higher amount of essential amino acids (44.05%) than did Bacto Peptone (19.34%). HF(25) and Bacto Peptone consisted of several minerals at varying levels and had an excellent solubility over a wide pH range. At water activity (a(w)) greater than 0.75, the much higher moisture sorption was found in HF(25) (P < 0.05). HF(25) showed the higher bacterial productivity ratio than did Bacto Peptone (P < 0.05). When HF(25) and commercial Bacto Peptone were used as microbial media to determine microbial load of environmental and food samples and pathogenic bacteria, HF(25) generally exhibited similar potential in culturing those microorganisms (P > 0.05). Thus, the conversion of low market value species to fish protein hydrolysate, which can be used as the nitrogenous substrate for microbial growth, could be achieved.

Antioxidative and antimicrobial activities of extracts from Bambarra groundnut seed coat, prepared using water, ethanol and acetone as the media at various temperatures (30, 60, 90 °C) were investigated.