Undesirable Enzymatic Browning in Crustaceans: Causative Effects and Its Inhibition by Phenolic Compounds

Undesirable enzymatic browning mediated by polyphenol oxidase (E.C. 1.14.18.1) on the surface of seafood from crustaceans have been a great concern to food processors, causing quality losses of seafood products. Seafoods especially from crustaceans are worldwide consumed due to their delicacy and nutritional value. However, black spot formation (melanosis) is the major problem occurring in crustaceans during postmortem handling and refrigerated storage induce deleterious changes in organoleptic properties and, therefore, decreases commercial value. Polyphenoloxidase (PPO), the copper-containing metalloprotein involved in oxidation of phenol to quinone is the major biochemical reaction of melanosis formation. This enzymatic mechanism causes unappealing blackening in postharvest crustaceans. To alleviate the melanosis formation in crustaceans, use of phenolic compounds from plant extract can serve as antimelanotics and appears to be a good alternative to the conventional sulfites which are associated with health-related disorders. In this review, we focuses on the unique features about the structure, distribution, and properties of PPO as well as mechanism of melanosis formation and provide a comprehensive deeper insight on the factors affecting melanosis formation and its inhibition by various antimelanotics including newly discovered plant phenolic compounds.     

Physicochemical properties, α-amylase and α-glucosidase inhibitory effects of the polysaccharide from leaves of Morus alba L. under simulated gastro-intestinal digestion and its fermentation capability in vitro by human gut microbiota

The investigation aimed at determining the impact of sequential simulated digestion on the physicochemical properties and digestive enzymes inhibitory effects of the polysaccharides fraction (MLP-2) of Morus alba L. leaves as well as its in vitro fermentation behaviours. After artificial salivary, gastric and intestinal digestions, the chemical components and microstructure of MLP-2 were altered with significantly (P < 0.05) decreased molecular weight. The α-amylase and α-glucosidase inhibitory activities of MLP-2 were significantly (P < 0.05) improved throughout simulated digestion. MLP-2I, the intestinal digested fraction of MLP-2, could significantly (P < 0.05) decrease the pH value of fermented culture and increase the short-chain fatty acids (SCFA) concentrations, especially acetic, propionic and butyric acids. In conclusion, MLP-2 could be gradually degraded under simulated digestion with altered physicochemical properties and enhanced α-amylase and α-glucosidase inhibitory effects, and further utilised by human gut microbiota to decrease pH value and promote SCFA production.     

Antibacterial activity of Thai edible plants against gastrointestinal pathogenic bacteria and isolation of a new broad spectrum antibacterial polyisoprenylated benzophenone,chamuangone

Twenty-two edible plant extracts were subjected to evaluation of their antibacterial activity against some gastrointestinal pathogenic bacteria, including Escherichiacoli, Salmonella typhimurium, Salmonella typhi, Shigella sonnei and Helicobacter pylori using the disc diffusion and broth microdilution methods. Sixteen of the plant extracts exhibited antibacterial activity against one or more tested bacteria. Only Garcinia cowa leaf extracts exhibited antibacterial activity against all tested bacteria. Purification of the ethyl acetate extract of G. cowa leaves using an antimicrobial assay-guided isolation afforded a new polyprenylated benzophenone, chamuangone, that exhibited satisfactory antibacterial activity against Streptococcus pyogenes (minimum inhibitory concentration (MIC) 7.8 μg/ml), Streptococcus viridans and H. pylori (MICs 15.6 μg/ml), and Staphylococcus aureus, Bacillus subtilis and Enterococcus sp. (MICs 31.2 μg/ml).     

Antibacterial,anti-inflammatory and anti-allergic activities of standardised pomegranate rind extract

Antibacterial, anti-inflammatory and anti-allergic activities of standardised pomegranate rind extract (SPRE) containing 13% w/w ellagic acid were studied in vitro. The antibacterial activity of SPRE was determined using the disc diffusion and broth microdilution methods. SPRE exhibited a potent bacteriostatic effect against Propionibacterium acnes, a Gram-positive anaerobe, with a MIC of 15.6 μg/ml, and Gram-positive facultative anaerobic bacteria, Staphylococcus aureus and Staphylococcus epidermidis, with MICs of 7.8–15.6 μg/ml. Anti-inflammatory activity of SPRE was evaluated by measuring the inhibition of nitric oxide (NO) production by murine macrophage-like RAW264.7 cells. SPRE exhibited a potent NO inhibitory effect, with an IC₅₀ of 10.7 μg/ml. Evaluation of the anti-allergic activity showed that SPRE inhibited the release of β-hexosaminidase from antigen-stimulated rat basophilic leukemia (RBL-2H3) cells with an IC₅₀ of 20.9 μg/ml. In addition, SPRE exhibited only moderate cytotoxicity on human keratinocyte cells, with CC₅₀ of 33.6 μg/ml. These findings support the potential use of SPRE as a nutraceutical for antibacterial, anti-inflammatory and anti-allergic proposes.     

Ultrafiltration isolation,physicochemical characterization,and antidiabetic activities analysis of polysaccharides from green tea,oolong tea,and black tea

Both fermentation degree and preparation method of polysaccharides could influence the bioactivity of tea polysaccharides. The aim of this study was to compare the physicochemical characterization and biological activities of the polysaccharides isolated by ultrafiltration method from three kinds of tea (green tea, oolong tea, and black tea). The bioactivities of tea polysaccharide fractions were compared from four aspects, including antioxidant activities, antiglycation activities, α-glucosidase inhibitory capability, and hypoglycemic effects on L6 myotubes. Results showed that six polysaccharides (GTPS1, GTPS2, OTPS1, OTPS2, BTPS1, and BTPS2) had different contents of neutral sugar and uronic acid, and they showed different morphologies. Six polysaccharides were composed of the seven monosaccharides with different molar ratios. BTPS1 exhibited the highest DPPH scavenging activity and hydroxyl radical scavenging activity (P < 0.05), and BTPS1 also showed the strongest antiglycation inhibitory effects (P < 0.05). BTPS1 and BTPS2 showed strong inhibitory capacity on α-glucosidase and hypoglycemic effects in L6 skeletal muscle cells. The result suggested that the degree of fermentation of tea could improve their bioactivities (BTPS > OTPS >GTPS), and TPS1 with smaller molecular weight distribution showed higher bioactivities than TPS2. This study can provide a scientific foundation for the application of tea polysaccharides and related functional products.