Characterization of Polysaccharides from Wild Edible Mushrooms from Thailand and Their Antioxidant, Antidiabetic, and Antihypertensive Activities.

Bioactive polysaccharides from three wild edible mushrooms (Rugibolutus extremiorientalis, Russula emetica, and Phleobopus portentosus) extracted by conventional refluxing extraction (RFE) and ultrasound-assisted extraction (UAE) were investigated. The result indicated that the PS of R. extremiorientalis extracted by RFE exhibited the greatest antioxidant activities on ABTS cation free radical scavenging (153.0 mg TEAC/g of the extract), DPPH radical scavenging (9.91 mg TEAC/g of the extract), and also reducing power capacity (10.2 mg TEAC/g of the extract). Whereas, those of R. emetica extracted by UAE have the highest antidiabetic and antihypertensive activities (56.3% and 70.5% inhibition, respectively). All crude PS extracts were composed mainly of carbohydrate and protein plus a small proportion of phenolic compounds of which glucose was the prevalent monosaccharide of all polysaccharides. PS of both R. extremiorientalis and R. emetica contained of ß-glycosidic conformation, while those of Ph. portentosus contained both α- and ß-glycosidic conformations.

Identification of bioactive peptide from Oreochromis niloticus skin gelatin.

Fish skin, one type of wastes generated from Nile tilapia processing, is still a good source of collagen and gelatin. Bioactive peptides can be obtained from Nile tilapia skin gelatin by trypsin digestion. Trypsin hydrolysate was subsequently purified by gel filtration chromatography. Trypsin A fraction showed the greatest reducing power (5.138 ± 1.060 µM trolox/mg peptide) among all hydrolysate fractions, while trypsin B fraction from gel filtration column was found to exhibit the best radical scavenging and angiotensin-I-converting enzyme (ACE) inhibitory activities 8.16 ± 2.18 µg trolox/mg peptide and 59.32 ± 9.97 % inhibition, respectively. The most active fraction was subjected to MALDI-TOF/TOF MS/MS. After annotation by Mascot sequence matching software (Matrix Science) with Ludwig NR Database, two peptide sequences were identified; GPEGPAGAR (MW 810.87 Da) and GETGPAGPAGAAGPAGPR (MW 1490.61 Da). The docking analysis suggested that the shape of the shorter peptide may be slightly more proper, to fit into the binding cleft of the ACE. However, the binding affinities calculated from the docking showed no significant difference between the two peptides. In good agreement with the in silico data, results from the in vitro ACE inhibitory activity with synthetic peptides also showed no significant difference. Both peptides are thus interesting novel candidates suitable for further development as ACE inhibitory and antioxidant agents from the natural source.

Antioxidant and antihypertensive activity of gelatin hydrolysate from Nile tilapia skin.

Fish skin, a by-product from fish processing industries, still contains a significant amount of protein-rich material. Gelatin was extracted from Nile tilapia skin with the yield 20.77 ± 0.80 % wet weight. Gelatin was then separately hydrolyzed by proteases, including bromelain, papain, trypsin, flavourzyme, alcalase and neutrase. Low molecular weight gelatin hydrolysate (<10 kDa) has a great potential as an antioxidant agent. Flavourzyme hydrolysate has potent activity on ABTS radical scavenging (1,413.61 ± 88.74 µg trolox/mg protein) and also inhibits the oxidation of linoleic acid at a high level (59.74 ± 16.57 % inhibition). The greatest reducing power is in alcalase hydrolysate (4.951 ± 1.577 mM trolox/mg protein). While, bromelain hydrolysate has the highest ferrous ion chelating activity (86.895 ± 0.061 %). Evaluation of the angiotensin-I-converting enzyme's inhibitory activity indicates that all hydrolysates have great potency as an antihypertensive agent. All studied tilapia skin gelatin hydrolysates contain potent antioxidant and anti-hypertensive effects.