Antibody- and lectin- based assays for the rapid analysis of food-grade gums and thickeners

Re-evaluation of carrageenan (E 407) and processed Eucheuma seaweed (E 407a) as food additives

The present opinion deals with the re-evaluation of the safety of food-grade carrageenan (E 407) and processes Eucheuma seaweed (E 407a) used as food additives. Because of the structural similarities, the Panel concluded that processed Eucheuma seaweed can be included in the evaluation of food-grade carrageenan. Poligeenan (average molecular weight 10-20 kDa) has not been authorised as a food additive and is not used in any food applications. In its evaluation of carrageenan (E 407) and processed Eucheuma seaweed (E 407a), the Panel noted that the ADME database was sufficient to conclude that carrageenan was not absorbed intact; in a subchronic toxicity study performed with carrageenan almost complying with the EU specification for E 407 in rats, the no-observed-adverse-effect level (NOAEL) was 3,400-3,900 mg/kg body weight (bw) per day, the highest dose tested; no adverse effects have been detected in chronic toxicity studies with carrageenan in rats up to 7,500 mg/kg bw per day, the highest dose tested; there was no concern with respect to the carcinogenicity of carrageenan; carrageenan and processed Eucheuma seaweed did not raise a concern with respect to genotoxicity; the NOAEL of sodium and calcium carrageenan for prenatal developmental dietary toxicity studies were the highest dose tested; the safety of processed Eucheuma seaweed was sufficiently covered by the toxicological evaluation of carrageenan; data were adequate for a refined exposure assessment for 41 out of 79 food categories. However, the Panel noted uncertainties as regards the chemistry, the exposure assessment and biological and toxicological data. Overall, taking into account the lack of adequate data to address these uncertainties, the Panel concluded that the existing group acceptable daily intake (ADI) for carrageenan (E 407) and processed Eucheuma seaweed (E 407a) of 75 mg/kg bw per day should be considered temporary, while the database should be improved within 5 years after publication of this opinion.

Structural characterization and antitumor and mitogenic activity of a lectin from the gill of bighead carp (Aristichthys nobilis)

In this study, we investigated the gross structure, secondary structure, and antitumor and mitogenic activity of GANL, a lectin from the gill of bighead carp (Aristichthys nobilis). We used infrared spectroscopy, β-elimination, and circular dichroism spectroscopy to determine the structure of GANL. We measured antiproliferation activity against six human tumor cell lines and mitogenic activity against murine splenocytes using the MTT assay. Based on infrared spectroscopy and β-elimination, we conclude that GANL is a glycoprotein. The protein and carbohydrate moieties are joined by O-glycosidic linkage. A circular dichroism spectroscopic analysis revealed that the secondary structure of GANL consists of α-helices (34.8 %), β-sheets (12.1 %), β-turns (24.5 %), and unordered structures (33.0 %). GANL exerted potent antitumor activity against the HeLa cell line (IC(50) = 11.86 μg/mL) and a mitogenic effect on murine splenocytes in the MTT assay. GANL, a lectin that is isolated from the gills of bighead carp, is a glycoprotein with potent antitumor and mitogenic activity.

Production and characterization of a phage-display recombinant antibody against carrageenans: evidence for the recognition of a secondary structure of carrageenan chains present in red algae tissues

We report the isolation, for the first time by phage display, of a scFv recombinant antibody called B3 directed against carrageenans, the major sulphated polysaccharides of red seaweeds. Immunoassays were used to characterize the binding of B3 antibodies toward the three main carrageenan forms (iota, kappa, and lambda) differing by their sulfonic ester content and the presence of 3,6-anhydrogalactose. In enzyme-linked immunoadsorbent assay (ELISA), B3 soluble scFv showed a high reactivity towards iota-carrageenan at any titer but, at high titer only, recognized also the highly sulfated lambda-form. Surface-adsorbed kappa-polymers were only recognized in presence of poly-L-lysine (PLL). The replacement of Na+ ions by K+ in the buffers had no effect on kappa-polymer detection but increased the binding of B3 antibodies toward both iota- and lambda-carrageenans, whereas addition of Ca2+ decreased sharply the recognition of the iota-form. In competitive assays, low titer B3 soluble scFv showed a iota>kappa>lambda selectivity and recognized a mixture of iota-oligomers with degrees of polymerization between 4 and 18 but not sub-fractions of 4 or 6 residues long. We suggest therefore that the B3 epitope could consist of a helical conformation of carrageenan chains. Immunofluorescence microscopy showed that, amongst other red algae, Chondrus gametophyte (containing iota-chains) was strongly recognized by B3 scFv whereas sporophytic tissues rich in lambda-carrageenans were not, assessing the preference of this probe for iota-carrageenans in situ. The high potential of the B3 recombinant probe is discussed.

High salinity reduces the content of a highly abundant 23-kDa protein of the mangrove Bruguiera parviflora

A significant decrease in the amount of a protein, whose migration in two-dimensional gel electrophoresis corresponds to an apparent molecular mass of 23 kDa and pI = 6.5, was observed in leaves of NaCl-treated Bruguiera parviflora (Roxb.) Wt. & Arn. ex Griff. seedlings. This particular salt-sensitive protein, designated as SSP-23, almost disappeared after 45 days of treatment in 400 mM NaCl as compared to untreated seedlings (0 mM NaCl) where the presence of the protein was significant. A polyclonal antibody raised against the 23-kDa protein was used to determine the subcellular localization of this protein in leaves by cross-reaction with proteins from isolated chloroplasts, mitochondria, peroxisomes and cytosol fractions on Western blots. SSP-23 was confirmed to be localized in the cytosol by immunoblotting. The disappearance of SSP-23 as a result of high NaCl treatment suggests that this protein is salt-sensitive and has a possible role in salt adaptation.

The development of immunoassays to identify and quantify species source of gum arabic

Gum arabic from Acacia senegal is commonly used as an additive in foodstuffs. Adulteration of gum arabic by other gums is a potential problem for reasons of safety and quality. This study aimed to develop and evaluate the use of enzyme-linked immunosorbent assays (ELISAs) for the detection of potential adulterants of gum arabic. Indirect competitive ELISAs (IC-ELISAs) were developed using the monoclonal antibodies SY CC7 (A. senegal), SY HH3 (Acacia seyal), and SY J1A1 (Combretum erythrophyllum). All IC-ELISAs had a working range of 0.005-10 mg/mL. The antibodies used were tested using the IC-ELISAs for cross-reactivity with other Acacia species and other gums. The antibodies were very specific for their respective antigens. Significant cross-reactivity was found for SY CC7 (between A. senegal and A. melliferae) and SY J1A1 (between C. erythrophyllum and A. seyal). The IC-ELISA was adapted further to test confectionery samples for the presence of gum arabic, which was successful, although recovery rates were reduced. Both IC- and plate trapped antigen ELISA (PTA-ELISA) formats were able to distinguish an adulterated sample of gum arabic when blended with either A. seyal or C. erythrophyllum. The PTA-ELISA was more sensitive for A. seyal than the IC-ELISA, but both were equally sensitive for C. erythrophyllum. The results suggest that the antibodies SY CC7, SY HH3, and SY J1A1 could be used in combination with each other for the detection of potential adulterants of A. senegal and the detection of gum arabic in foodstuffs.

Novel mode of resistance to Fusarium infection by a mild dose pre-exposure of cadmium in wheat

Exposure of healthy wheat seeds (Triticum aestivum var Sonalika) to mild dose of cadmium (Cd(2+)) given as 50 microM CdCl(2) for 48 h and then washed off Cd(2+) offered resistance to the subsequent infection by Fusarium oxysporum inoculum. Seven days old seedlings having two primary leaves were aseptically inoculated with fungus, F. oxysporum (1 x 10(6)) spores. The seedlings pre-exposed to low level of Cd(2+) survived the Fusarium infection, while plantlets without Cd(2+) stress wilted and then perished due to Fusarium infection. The stress associated proteins induced by Cd(2+) (50 microM), F. oxysporum and by the co-stress (50 microM Cd(2+) and then with F. oxysporum) treatments were observed to be of same molecular weight (51 kDa). Antibody was raised against the purified Cd(2+)-stress associated protein (CSAP). Immuno-gold labeling of wheat seedling root tissue showed the presence of this CSAP in Cd(2+) pre-exposed and in co-stressed tissues and to be located predominantly on the inner linings of the cell membranes. We also observed that the anti-CSAP-antibody also labeled the root tissue of only Fusarium inoculated seedlings and the gold labeling was intensely located on the membrane. This cross-reaction of anti-CSAP suggests that Fusarium-induced stress protein (FISP) possibly has close homology to CSAP. We thus show for the first time the over expression of a high molecular mass protein by mild dose of Cd(2+) pre-exposure to wheat seeds which subsequently provided protection against Fusarium infection. This mode of resistance developed by an abiotic stress-causing agent against pathogen infection is novel.

Use of an enzyme-linked lectinsorbent assay to monitor the shift in polysaccharide composition in bacterial biofilms

An enzyme-linked lectinsorbent assay (ELLA) was developed for quantification and characterization of extracellular polysaccharides produced by 1- and 4-day biofilms of 10 bacterial strains isolated from food industry premises. Peroxidase-labeled concanavalin A (ConA) and wheat germ agglutinin (WGA) were used, as they specifically bind to saccharide residues most frequently encountered in biofilms matrices: D-glucose or D-mannose for ConA and N-acetyl-D-glucosamine or N-acetylneuraminic acid for WGA. The ELLA applied to 1- and 4-day biofilms colonizing wells of microtiter plates was able to detect that for Stenotrophomonas maltophilia and to a lesser extent Staphylococcus sciuri, the increase in production of exopolysaccharides over time was not the same for sugars binding with ConA and those binding with WGA. Differences in extracellular polysaccharides produced were observed among strains belonging to the same species. These results demonstrate that ELLA is a useful tool not only for rapid characterization of biofilm extracellular polysaccharides but also, in studies of individual strains, for detection of changes over time in the proportion of the exopolysaccharidic component within the polymeric matrix.