Phytate degradation in soaked and fermented liquid feed—effect of diet, time of soaking, heat treatment, phytase activity, pH and temperature

An in vitro trial was performed in order to study phytate degradation in fermented liquid feed comprising mainly barley or wheat. The influence of heat treatment, microbial counts, temperature of soaking, time of soaking, pH as well as phytase activity was studied. The diets were soaked and fermented with water (1:2.75) in 1-l fermentors. The temperature was held constant at 10, 20 or 38 °C, respectively. Samples were taken at 0, 4, 8, 12, 24, 48 and 72 h (10 and 20 °C) or 2, 4, 6, 8, 10, 12 and 24 h (38 °C). The experiment comprised of four diets based on heat-treated or non-heat-treated barley or wheat. The diets were either supplemented or not supplemented with microbial phytase. Between 17 and 79% of total phytate in the diets was degraded within the first 8 h of soaking when the temperature was held at 10 or 20 °C, with the greatest degradation rate at 20 °C. When the temperature was held at 38 °C, it took only 2 h to degrade comparable amounts. The degradation was improved when endogenous phytase or microbial phytase was available. When the soaking temperature was 20 °C, the endogenous phytase was degraded during the soaking period, whereas the microbial phytase remained intact over time. At 10 °C, the endogenous phytase also remained intact during the soaking and fermentation period. In heat-treated cereals, natural phytase activity was reduced considerably and hence the rate of phytate degradation was slower. To check the quality of fermentation the microbial counts of lactic acid bacteria, coliform bacteria, yeast and moulds were determined. The results revealed no interactions between microbial counts and phytate degradation.