A rapid technique for determination of nitrate and nitric acid by acid reduction and diazotization at elevated temperature

Nitrate content in a collection of higher mushrooms

BACKGROUND

Data of mushroom nitrate content from scientific studies is limited. There have been two such recent investigations (mainly regarding certain cultivated species). To obtain comparable analytical data, we analyzed 134 samples of 54 taxa gathered and prepared by our department.

RESULTS

The mushroom species were evaluated according to their nutritional types: saprotrophic, mycorrhizal and wood-decaying groups. Low and relatively invariable contents were found in the mycorrhizal (216.5 mg kg(-1) dry matter (DM) and wood-decaying groups (228.6 mg kg(-1) DM), but in the saprotrophic group we observed a wide variability (151.4-12 715 mg kg(-1) DM).

CONCLUSION

A considerable nitrate content was found in samples of seven 'accumulator' species (Clitocybe nebularis, C. odora, Lepista nuda, L. personata, L. irina, Macrolepiota rachodes and M. procera). The toxicological relevance of daily uptake of acceptable nitrate content via mushrooms only is not presumable, but the 'accumulator' saprotrophic species can be 'contributors' to our nitrate intake in foods.

Effect of Sodium Nitrate and Nitrate Reducing Bacteria on In vitro Methane Production and Fermentation with Buffalo Rumen Liquor

Nitrate can serve as a terminal electron acceptor in place of carbon dioxide and inhibit methane emission in the rumen and nitrate reducing bacteria might help enhance the reduction of nitrate/nitrite, which depends on the type of feed offered to animals. In this study the effects of three levels of sodium nitrate (0, 5, 10 mM) on fermentation of three diets varying in their wheat straw to concentrate ratio (700:300, low concentrate, LC; 500:500, medium concentrate, MC and 300:700, high concentrate, HC diet) were investigated in vitro using buffalo rumen liquor as inoculum. Nitrate reducing bacteria, isolated from the rumen of buffalo were tested as a probiotic to study if it could help in enhancing methane inhibition in vitro. Inclusion of sodium nitrate at 5 or 10 mM reduced (p<0.01) methane production (9.56, 7.93 vs. 21.76 ml/g DM; 12.20, 10.42 vs. 25.76 ml/g DM; 15.49, 12.33 vs. 26.86 ml/g DM) in LC, MC and HC diets, respectively. Inclusion of nitrate at both 5 and 10 mM also reduced (p<0.01) gas production in all the diets, but in vitro true digestibility (IVTD) of feed reduced (p<0.05) only in LC and MC diets. In the medium at 10 mM sodium nitrate level, there was 0.76 to 1.18 mM of residual nitrate and nitrite (p<0.01) also accumulated. In an attempt to eliminate residual nitrate and nitrite in the medium, the nitrate reducing bacteria were isolated from buffalo adapted to nitrate feeding and introduced individually (3 ml containing 1.2 to 2.3×10⁶ cfu/ml) into in vitro incubations containing the MC diet with 10 mM sodium nitrate. Addition of live culture of NRBB 57 resulted in complete removal of nitrate and nitrite from the medium with a further reduction in methane and no effect on IVTD compared to the control treatments containing nitrate with autoclaved cultures or nitrate without any culture. The data revealed that nitrate reducing bacteria can be used as probiotic to prevent the accumulation of nitrite when sodium nitrate is used to reduce in vitro methane emissions.