Carbohydrate fermentation and microbial cell growth in suspensions of pig large bowel contents

Five contrasting carbohydrate substrates were incubated anaerobically for u p to 24 hours with pig large bower contents as a source of inoculum, The pr ogress of fermentation was followed by observing changes in pH and the accu mulation of short chain fatty acids (SCFA). An attempt was made to quantify bacterial growth by measuring the incorporation of S-35 from S-35-sulphate into trichloroacetic acid-precipitable material. After 24 h incubation, th e pH was little different with crystalline cellulose as substrate than in t he absence of added substrate. However there were substantial and similar f alls in pH with starch, pectin and pea fibre but a much lower final pH with raffinose as substrate. Bacterial cell growth (as indicated by S-35-incorp oration) rose rapidly and plateaued at about 10 h with raffinose as substra te but increased throughout the period of study with the other fermentable carbohydrates. There was no simple relationship between the extent of carbo hydrate fermentation (as measured by SCFA accumulation) and bacterial growt h (indicated by S-35-incorporation) but these preliminary studies suggest t he the S-35-incorporation technique shows some promise as a means of quanti fying bacterial growth in vitro.