No abstract

Hydrogen gas, which is produced during fermentation in the human colon, is either excreted in breath or metabolised by gut bacteria through a variety of pathways. These may include methanogenesis, dissimilatory sulphate reduction, and acetogenesis. To determine which of these routes predominates in the large intestine, stools were taken from 30 healthy subjects and incubated as 5% (w/v) slurries with Lintner's starch. In 23 of 30 subjects, methane production was the main method of hydrogen disposal. In the remaining seven, high rates of sulphate reduction were recorded together with raised production of H2S. All samples showed relatively low rates of hydrogen evolution and of acetate formation from CO2 and H2. Sulphate reduction and methanogenesis seem to be mutualiy exclusive in the colon and this is probably linked to sulphate availability. Sulphate reduction, methanogenesis, and acetogenesis were strongly influenced by pH. Sulphate reduction was optimal at alkaline pH values whereas methane production was maximal at a neutral pH and acetogenesis favoured acidic conditions. Faecal H2S values were related to carriage of sulphate reducing bacteria. These data show that a number of competing pathways for hydrogen disposal are possible in the large gut and that a variety of factors such as colonic pH and sulphate availability can determine which of these mechanisms predominates.

An examination is made of data on dental caries amongst 12-year-old children and sugar consumption of the total population for 90 countries. For the whole data set, DMFT score tends to rise with sugar consumption. The linear relationship between the logarithm of DMFT and sugar is estimated to have a slope of 0.021 per kg/year per head of population (P < 0.0001), and accounts for 28% of the variation in DMFT. In contrast, when data from 29 industrialised nations are analysed separately, there is no evidence of a sugar-caries relationship; the slope of the linear regression line is estimated to be -0.013, not significantly different from zero. This latter result is in agreement with the considerable evidence of a lack of strong relationship between the amount of sugar consumed and caries occurrence in Western countries. These results suggest that, in addition to sugar, other factors, such as other aspects of diet, exposure to fluoride and genetic effects, must be taken into account when seeking to explain variations in caries prevalence, and when making recommendations for caries control.

II.

A total of 160 samples of 20 Australian-sourced feed ingredients of plant origin for pigs and poultry was analysed for total phosphorus and phytate-phosphorus contents and endogenous phytase activity. The majority of total P was present as phytate-phosphorus, and these concentrations were significantly correlated in 9 feed ingredients. The endogenous phytase activity in tested feed ingredients was negligible other than for wheat, its by-products and barley. Phytate-phosphorus was determined by a standard 'ferric chloride precipitation' method, which was satisfactory for individual feed ingredients, with the exception of lupins and faba beans. It appears that phytate is more difficult to extract from these two feedstuffs, possibly because of the affinity of phytate for protein. Ferric chloride precipitation methods are not suitable for phytate-phosphorus determinations of complete feed samples containing other sources of phosphorus, which is a distinct limitation. A lesser limitation is that these methods cannot distinguish between the various esters of myo-inositol phosphate present. Given the variation of phytate contents within ingredients, particularly wheat, the desirability of determining dietary substrate levels is emphasised to take full advantage of including exogenous phytases in pig and poultry diets to reduce phosphorus excretion and abate phosphorus pollution.