ABSTRACT
Millstream flours, bran, pollard, and germ fractions were prepared from two Australian and two New Zealand wheat cultivars using a pilot-scale roller mill. The distribution of six redox enzymes in milling fractions and the relationship of the enzymes to baking parameters were investigated. Lipoxygenase (LOX), dehydroascorbate reductase (DAR), and protein disulfide isomerase (PDI) tended to be higher in the tail-end fractions of break and reduction flour streams, but the highest levels were in the bran, pollard, and germ fractions. These enzymes had moderate to strong correlations with ash content of flour. These results indicated that a considerable amount of these enzymes in the tail-end flour streams were likely to be derived from contamination with bran, aleurone, or germ components of grain. Peroxidase (POX) tended to be higher in the break flours, but polyphenol oxidase (PPO) and ascorbate oxidase (AOX) tended to be evenly distributed in the millstream flours. These three enzymes generally had poor correlations with ash and baking parameters. LOX and DAR had a negative correlation with the baking quality of bread made in the absence of ascorbic acid (AA) but a poor correlation with improvement of bread quality made with AA. The negative correlation probably reflects the high content of ash (hence trichomes), glutathione, and protein thiols in those fractions that have high LOX and DAR, and these high-reducing-power components and trichomes in flour may be the actual cause of poor quality bread. PDI generally had a poor correlation with bread quality in the absence of AA but a significant positive correlation with improvement in the quality of bread made with AA. It thus seems that the endogenous levels of these six enzymes were not a limiting factor in the breadmaking process, except for PDI, the levels of which may have positively influenced breadmaking in the presence of AA.
