Structure of a galactoarabinoglucuronoxylan from tamarillo (Solanum betaceum), a tropical exotic fruit,and its biological activity

Tamarillo (Solanum betaceum) is a tropical exotic fruit whose polysaccharides were extracted from the ripe pulp. After various purification steps, homogeneous fractions (designated PTW, STK-1000R and PF) were analyzed by sugar composition, HPSEC, methylation and NMR spectroscopy analysis. The results showed that the fraction PTW consisted of a linear arabinan with (1 → 5)-linked α-l-arabinofuranosyl units. Fractions designated as STK-1000R and PF contained galactoarabinoglucuronoxylans, with (1 → 4)-linked β-d-Xylp residues in the backbone, carrying branches exclusively at O-2. The polysaccharide in STK-1000R is less branched than that in the PF fraction (∼20.0% and 36.5%, respectively), with side-chains formed by (1 → 5)-linked α-l-Araf residues and (1 → 4)-linked α-d-GlcpA residues and with non-reducing end units formed by α-l-Araf, β-Arap, β-d-Galp, α-d-GlcpA and 4-O-Me-α-d-GlcpA. Intraperitoneal administration of the STK-1000R fraction in mice significantly reduced the number of abdominal constrictions induced by 0.6% acetic acid and the inflammatory phase of nociception induced by 2.5% formalin, indicating that that fraction has an antinociceptive effect on inflammatory pain models.     

Characterization of glucan-producing Leuconostoc strains isolated from sourdough

Sourdough was previously demonstrated to be a fruitful biotope for isolation of lactic acid bacteria producing exopolysaccharides and more accurately diverse glycan polymers which have interesting applications as texturing agents or prebiotics. Characterization of polymers by ¹H and ¹³C NMR spectroscopy analysis demonstrated that these strains could synthesize glucans of high structural variety and containing different amounts of α-(1 → 2), α-(1 → 3) and α-(1 → 6) linkages. In this study, fifteen glucan-producing Leuconostoc mesenteroides and L. citreum strains from sourdoughs were characterized according to carbohydrate fermentation, rep-PCR fingerprinting using (GTG)₅ primers and glycansucrase activity (soluble or cell-associated). Enzyme characterization using SDS-PAGE and in situ polymer production after incubation with sucrose correlated with synthesis of classical or α-(1 → 2) branched dextrans, alternan and levan. In addition, the presence of genes coding for alternansucrase was detected by PCR and partially characterized by sequence analysis. We thus provide new information on the biodiversity of glucan production by sourdough Leuconostoc strains.     

Characterisation of a β-N-acetylhexosaminidase from a commercial papaya latex preparation

A β-N-acetylhexosaminidase (β-NAHA) (EC 3.2.1.52) with molecular mass of 64.1 kDa and isoelectric point of 5.5 was purified from a commercial papaya latex preparation. The optimum pH for p-nitrophenyl-N-acetyl-β-d-glucosaminide (pNP-β-GlcNAc) hydrolysis was five; the optimum temperature was 50 °C; the K_m was 0.18 mM, V_max was 37.6 μmol min⁻¹ mg⁻¹ and activation energy (E_a) was 10.3 kcal/mol. The enzyme was thermally stable after holding at 30–45 °C for 40 min, but its activity decreased significantly when the temperature exceeded 50 °C. Heavy metal ions, Ag⁺ and Hg²⁺, at a concentration of 0.25 mM and Zn²⁺ and Cu²⁺, at a concentration of 0.5 mM, significantly inhibited enzyme activity. The β-NAHA had only one active site for binding both pNP-β-GlcNAc and p-nitrophenyl-N-acetyl-β-d-galactosaminide (pNP-β-GalNAc). A prototropic group with pKa value of about five on the enzyme may be involved in substrate binding and transformation, as examined by Dixon–Webb plots.     

α-Glucosidase inhibitors from Chinese Yam (Dioscoreaopposita Thunb.)

The inhibitory activities of crude extracts and purified constituents from the fresh tuberous rhizomes of Chinese Yam (Dioscorea opposita Thunb.), which is commonly called Huai Shan Yao in Chinese, were evaluated against yeast α-glucosidase in order to search for the active principals for treatment of diabetes. Bioassay-guiding isolation gave four compounds: trans-N-p-coumaroyltyramine (1) (IC₅₀ = 0.40 μM), 1,7-bis(4-hydroxyphenyl)heptane-3,5-diol (2) (IC₅₀ = 0.38 mM), 6-hydroxy-2,4,7-trimethoxyphenanthrene (3) (IC₅₀ = 0.77 mM) as α-glucosidase inhibitors, and cis-N-p-coumaroyltyramine (4), an isomer of compound 1, which showed no inhibitory activity against α-glucosidase. Furthermore, the separation and purification of compound 3 from Chinese Yam (Huai Shan Yao) was conducted by high-speed counter-current chromatography (HSCCC) using hexane–ethyl acetate–methanol–water (1:1:1:1, v/v/v/v). Compound 1, 2 and 4 were isolated from or detected in the Dioscoreaceae family for the first time.     

Cooking quality of faba bean after storage at high temperature and the role of lignins and other phenolics in bean hardening

Selected physical and chemical characteristics of faba beans (Vicia faba L.) cv. Fiesta were studied after 12 months storage at 5, 15, 25, 37, 45 or 50 °C (±2 °C) in relation to the hard-to-cook phenomenon. In comparison with control (seeds stored at 5 °C), seeds stored at 15 and 25 °C demonstrated non-significant (p?0.05) changes in most of the physical and chemical characteristics including hydration and swelling coefficients, acid detergent fibre, lignin and tannin contents, whereas seeds stored at ?37 °C demonstrated significant changes (p?0.05). Solutes and electrolytes leaching after 18 h soaking substantially increased with increased temperature. Faba bean hardness tested by the hard-to-cook test also increased substantially with increased storage temperature. After 8 h soaking followed by 2 h cooking, the puncture force required for seeds stored at 5 °C was 3.3 N seed⁻¹ whereas seeds stored at 50 °C required a much higher puncture force of 15.2 N seed⁻¹. There was a high negative correlation (r²=0.98) between storage temperature and cooking ability of faba bean. Substantial increases in acid detergent fibre and lignin contents occurred with increased storage temperatures. There was a three-fold increase in lignin content of faba bean stored at 50 °C compared to those stored at 5 °C and it was correlated with bean hardness (r²=0.98). Storage at high temperatures for 12 months led to a substantial reduction in total free phenolics especially in the testa and there was a greater reduction with increasing storage temperature. Reduction in free phenolics was negatively correlated (r²=0.75) with bean hardness.     

Influence of fermentation on some quality characteristics of trifoliate yam (Dioscorea dumetorum) hardened tubers

Processing of Dioscorea dumetorum tubers into flour could be a means of adding a longer-term value to this tropical plant with a high nutritional potential but which possesses a post-harvest hardening problem, characterised by a hard-to-cook defect. In an attempt to investigate the changes leading to fermentation of hardened tubers, CIE L^∗a^∗b^∗ parameters and some physicochemical properties of the yams were monitored. Four fermentation periods (0, 2, 4, 7 and 14 days) under ambient temperature (23 ± 5 °C) in the presence and absence of oxygen were studied. The results showed that fermentation significantly (p ? 0.05) increased a^∗ and b^∗ parameters, and decreased L^∗ parameter. However, browning affected more tubers fermented in the presence of oxygen. All the anti-nutrients evaluated (total phenols, phytic acid, oxalates, trypsin inhibitors and α-amylase inhibitors) decreased by significant levels (p ? 0.05) within 14 days of fermentation. However, the rates of anti-nutrient losses varied for each constituent and followed first-order reaction kinetics.     

Autolysis-assisted production of fish protein hydrolysates with antioxidant properties from Pacific hake (Merluccius productus)

Fish protein hydrolysates (FPH) with antioxidative properties were prepared using Pacific hake fish with high endogenous proteolytic activity from Kudoa paniformis parasitic infection. Infection level of ∼10⁷K. paniformis spores/g fish mince or higher yielded FPH with high antioxidant potential by autolysis and/or Validase^® BNP or Flavourzyme^® 500L. Autolyzing fish mince containing 30 × 10⁶ spores/g for 1 h at 52 °C and pH 5.50 produced FPH (named E-1h) with Trolox equivalent antioxidant capacity (TEAC) in the 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) radical assay of 262 ± 2 μmol/g and oxygen radical absorbing capacity (ORAC) of 225 ± 17 μmol Trolox equivalents/g freeze-dried sample. E-1h FPH also exhibited a marked concentration-dependent scavenging activity on 1,1-diphenyl-2-picrylhydrazyl radical. Antioxidant activity of E-1h FPH was higher (p < 0.05) than BHA and α-tocopherol in a linoleic acid peroxidation system over prolonged storage (∼162 h). Antioxidative FPH from Pacific hake may be useful ingredients in food and nutraceutical applications.     

Development of a solid-state fermentation process for production of an alpha amylase with potentially interesting properties

Ca-independency with potential activity and stability at low pH are among the most interesting characteristics of α-amylase in starch industry. In this attempt the synergetic effect of low pH on activity of crude Ca-independent α-amylase isolated from a native Bacillus sp. KR-8104 in solid-state fermentation (SSF) was studied using wheat bran (WB) as a substrate. The effects of different parameters including moisturizing agents, solid substrate to moisture ratio, particle size, incubation temperature and period, inoculum (v/w) and supplementation with 1% (w/w) different carbon and nitrogen sources on enzyme production were investigated. Maximum enzyme production of 140 U/g dry fermented substrate was obtained from wheat bran moistened with tap water at a ratio of 1:1.5 and supplemented with 1% (w/w) NH₄NO₃ and 1% (w/w) lactose after 48 h incubation at 37 °C. Even though the production of α-amylase was lower at 40 and 45 °C, the viable cell count was higher. In addition response surface methodology (RSM) was applied to find optimum conditions of temperature and pH on crude amylase activity. Using central composite design (CCD) a quadratic mathematical model equation was derived for the prediction of enzyme activity. The results showed that the model was in good agreement with experimental results, with R² = 0.90 (p < 0.0001) and the low pH has a synergetic effect on enzyme activity at higher temperature.     

Chemical and microbiological quality of grass carp (Ctenopharyngodon idella) slaughtered by different methods

The effect of two slaughter methods (immersion in ice-water slurry and electrical stunning followed by ice slurry asphyxiation) on chemical and microbiological parameters of grass carp (Ctenopharyngodon idella) stored in ice for 20 days was evaluated. No differences in total volatile basic nitrogen (TVB-N), pH, carbohydrate or protein content of mucus were observed between the slaughter methods. Ice-slaughtered fish had lower bacteria counts at the beginning of storage, but higher counts than fish slaughtered by electricity at the end of storage (p < 0.05). However, no significant differences in the shelf life were observed between the slaughter methods evaluated (limit of acceptability – counts > 3 × 10⁶ CFU g⁻¹ – attained after 13–16 days). Results indicated that the chemical parameters evaluated have a limited applicability to assess the shelf life of grass carp stored in ice, since pH limit (6.8) was exceeded after 4 days, while TVB-N limit (30 mg%) was not attained after 20 days of storage.     

Isolation and characterisation of an α-glucosidase inhibitory substance from fructose–tyrosine Maillard reaction products

An α-glucosidase inhibitory substance was isolated and characterised from fructose–tyrosine Maillard reaction products (MRPs) and the inhibition mode of the active substance determined. The ethyl acetate fraction of fructose–tyrosine MRPs showed strong α-glucosidase inhibitory activity; this fraction was isolated and purified using silica gel column chromatography and semi-preparative RP-HPLC. The structure of the purified compound was determined using spectroscopic methods. The isolated compound was identified as 2,4-bis (p-hydroxyphenyl)-2-butenal (C₁₆H₁₄O₃, HPB242). This is the first report of baker’s yeast α-glucosidase inhibitory activity of HPB242 isolated from fructose–tyrosine MRPs. The IC₅₀ value of HPB242 on α-glucosidase inhibition was 4.00 ± 0.09 μg/ml. Kinetic data revealed that HPB242 inhibits the p-NPG hydrolysing activity of baker’s yeast α-glucosidase noncompetitively with a K_i value of 0.870 mM.