REDUCTION IN THE LEVELS OF PHYTATE DURING WHOLEMEAL BREAD-MAKING - EFFECT OF YEAST AND WHEAT PHYTASES

No difference in wheat phytase activity was observed when different ty pes of acid were used to adjust the pH of wholemeal wheal flour suspen sions to pH 5.0, the optimum for wheat phytase. When whole wheat bread was made without additives or after adjustment of the dough pH with a cetic acid or lingonberry (traditional ingredients in bread making in Sweden), 64%, 96% and 83%, respectively, of the initial phytate was hy drolysed. a small but significant difference between breads with and w ithout yeast or with deactivated yeast was found, indicating that yeas t contributed some phytase activity under the conditions of bread maki ng (pH 5.3-5.8 and 30-37 degrees C). The optimum pH of yeast phytase w as found to be 3.5. The isomers of IP5 formed with purified wheat phyt ase or yeast phytase were studied using sodium phytate as substrate. W heat phytase formed 1,2,3,4,5-IP5 whereas yeast phytase formed 1,2,4,5 ,6-IP5. Determination of the isomers of inositol pentaphosphate demons trated that the reduction in phytate levels in bread compared with who lemeal flour resulted from both wheat and yeast phytase activities. (C ) 1996 Academic Press Limited