Characterization of chlorophyll degradation in banana and plantain during ripening at high temperature

Bananas fail to fully degreen when ripening at tropical temperatures, but this abnormal symptom does not occur in plantain. To elucidate the temperature effect on banana degreening, comparison of the colour change and chlorophyll degradation pathway between banana and plantain during ripening at 20 or 30 °C was carried out. Compared to bananas ripening at 20 °C and plantains at 20 °C or 30 °C, bananas at 30 °C contained significantly higher levels of chlorophylls, chlorophyllide a and pheophorbide a at the end of the ripening process, linearly correlating to the colour scores of a^∗, b^∗ and Hue angle. Whilst higher chlorophyllase activity was recorded in both banana and plantain at 30 °C as to the fruits at 20 °C, 30 °C inhibited Mg-dechelatase activity in banana, but not in plantain. The reduction of Mg-dechelatase activity in banana peel at 30 °C may contribute to repressed chlorophyll degradation and lead to uneven degreening.     

Effects of dietary flaxseed oil on cholesterol metabolism of hamsters

High-fat/cholesterol diets (HFCD) formulated by addition of butter (BU), coconut oil (CO), or flaxseed oil (FX) enhanced (P < 0.05) serum lipids of hamsters compared to the low-fat/cholesterol diet (Control). However, FX groups showed a hypocholesterolaemic effect compared to CO and BU groups. Lower (P < 0.05) hepatic triacylglycerol and cholesterol contents were measured in FX groups than those of CO and BU groups; whereas, higher (P < 0.05) faecal triacylglycerol and cholesterol contents were observed in FX groups. HMG-CoA reductase mRNA expression was upregulated (P < 0.05) by HFCD, whilst FX groups showed no (P > 0.05) influence on LDL-receptor mRNA expression compared to that of Control groups; however, higher (P < 0.05) than those of CO and BU groups. Meanwhile, there was a tendency towards higher CYP7A1 expression in the CO or FX group than the BU group. Thus, the hypocholesterolaemic effect of FX might result from increases of LDL-receptor mRNA expression, and cholesterol catabolism/output.     

Influence of the electron acceptor on nitrite reductase gene (nir) diversity in an activated sludge community

Analyses of the nitrite reductase gene diversities (nirK and nirS) in an activated sludge community fed with both nitrite and glucose were conducted. Results suggest that the topology of nirK and nirS gene fragment-based phylogenetic trees is influenced more by the available electron acceptor than by the carbon source. A denitrification reactor was operated for 53 days and a clone library constructed when the denitrifying communities in the SBR were supplied with both nitrite and glucose. Half of the nirK and nearly all the nirS gene fragments formed a cluster that was separate from a cluster containing nirK and nirS sequences derived from other communities in nitrate-fed reactors. On the other hand, nirK and nirS fragments obtained with glucose as the carbon source were similar to those detected in communities fed with other carbon sources.     

Are the Genes nadA and norB Involved in Formation of Aflatoxin G1?

Aflatoxins, the most toxic and carcinogenic family of fungal secondary metabolites, are frequent contaminants of foods intended for human consumption. Previous studies showed that formation of G-group aflatoxins (AFs) from O-methylsterigmatocystin (OMST) by certain Aspergillus species involves oxidation by the cytochrome P450 monooxygenases, OrdA (AflQ) and CypA (AflU). However, some of the steps in the conversion have not yet been fully defined. Extracts of Aspergillus parasiticus disruption mutants of the OYE-FMN binding domain reductase-encoding gene nadA (aflY) contained a 386 Da AFG₁ precursor. A compound with this mass was predicted as the product of sequential OrdA and CypA oxidation of OMST. Increased amounts of a 362 Da alcohol, the presumptive product of NadA reduction, accumulate in extracts of fungi with disrupted aryl alcohol dehydrogenase-encoding gene norB. These results show that biosynthesis of AFG₁ involves NadA reduction and NorB oxidation.     

Surveillance of nitrite level in cubilose: Evaluation of removal method and proposed origin of contamination

The discovery of nitrite contamination aroused public concern on the safety of cubilose consumption. Here, forty-eight batches of cubilose were randomly purchased from Hong Kong market. The median nitrite content of different types of cubilose was as follows: Red cubilose (600 ppm) > Yellow cubilose (510 ppm) ;> White cubilose (100 ppm). Under a developed standardized processing method, up to 98% of nitrite was removed from cubilose; nitrite was not detected in the stewed cubilose. To search for the source of nitrite, droppings from swiftlets and water samples were collected from production sites of cubilose in Malaysia and Indonesia, and which contained a high amount of nitrate. On the other hand, the protein extract of cubilose was subjected to proteomics analysis. A microbial nitrate reductase was identified by mass spectroscopy, which converted nitrate to nitrite in cubilose. A specific inhibitor of nitrate reductase successfully abolished the nitrate reduction activity found in cubilose, which subsequently reduced the nitrite in cubilose. This phenomenon was successfully proven by the field study. Thus, the nitrite on cubilose could be a result of the contaminating nitrate reductase.     

POLYCYCLIC AROMATIC HYDROCARBON O-QUINONES MUTATE p53 IN HUMAN LUNG ADENOCARCINOMA (A549) CELLS

Human lung adenocarcinoma (A549) cells form reactive and redox active PAH-o-quinones via constitutively expressed aldo-keto reductases. To determine whether these metabolites mutate p53, A549 cells were treated with N-methyl-N-nitroso-N-nitroguanidine (MNNG an alkylating mutagen), anti-BPDE (diol-epoxide) and benzo[a]pyrene-7,8-dione (o-quinone). p53 cDNA was amplified from the treated cells and cotransfected with a gap-repair plasmid designed to express p53 in yeast. When mutant p53 is expressed, it fails to drive the expression of an ADE2 reporter, and the yeast strain yIG397 turns red. The following mutational frequencies were observed versus the solvent controls: 1 mM MNNG (24.2% red colonies p = .02), 1 μ M anti-BPDE (9.9% red colonies p = .02), and 10 μ M BP-7,8-dione (9.3% red colonies p = .03). MNNG gave a high frequency (49%) of the expected C > T (G > A) mutations (p = .25). While anti-BPDE and BP-7,8-dione gave A > G (T > C) transitions (p = .034 – p = .054). These mutations would result from stable N⁶-deoxyadenosine adducts, but not from oxidatively damaged bases.