Variation in short chain fatty acid and ethanol concentration resulting from the natural fermentation of wheat and barley for inclusion in liquid diets for pigs

Fifty-six samples of wheat and 44 samples of barley were taken, at harvest, from locations across the UK. Lactic acid bacteria (LAB) and yeasts were enumerated before the samples were ground. Following grinding, triplicate 30-g samples of each cereal were mixed with sterile distilled water and incubated at 30, 35 or 40degreesC. Samples were taken immediately after mixing and at 24-h intervals for analysis of short-chain fatty acids (SCFA) and ethanol by isocratic ion-exclusion liquid chromatography. The number of LAB and yeasts present in samples ranged from 0 to 5.0 (mean 2.25 +/- 1.31) and 3.30 to 6.25 (mean 4.96 +/- 0.74) log(10) colony-forming units (cfu) ml(-1) respectively. At 30degreesC the mean concentrations (mmol l(-1)) of SCFAs and ethanol were, lactic acid 59.6 +/- 40.0 (range 0.14-134.9), acetic acid 23.2 +/- 11.1 (range 2.9-51.4), butyric acid 17.2 +/- 16.8 (range 0.0-62.2) and ethanol 15.0 +/- 9.0 (range 4.6-53.7) respectively. After fermentation for 24h only 9 of 300 fermentations produced more than 75 mmol l(-1) lactic acid, which has previously been demonstrated to prevent the growth of Salmonella in liquid pig feed. Fermenting at 35 or 40degreesC had no effect on lactic acid concentration but significantly (p < 0.001) increased the concentrations of acetic and butyric acids and ethanol. These results indicate that natural fermentation cannot be relied upon to produce levels of SCFAs that will prevent the proliferation of enteropathogens. © 2004 Society of Chemical Industry.