Effect of cereals milling on the contents of phytic acid and digestibility of minerals and protein

Abstract

Introduction. The aim of the study was to the examination of effects of the milling process which were applied differently to cereals for commercially flour production, on the phytic acid, microelement, and in-vitro digestibility. Materials and methods. The nutritional consequences of the milling processes of the cereals (wheat, barley, rye, oat, paddy) were evaluated by examining protein, ash, phytic acid, mineral contents, and protein/mineral digestibility rates. Mineral contents were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES), protein content by Kjeldahl method, and mineral digestibility and phytic acid were determined by in-vitro assays. Results and discussion. The dehulling/debranning process increased the protein digestibility rate over to 65% and decreased phytic acid content significantly (p<0.05) of the cereal grains except for rye. The mineral digestibility raised for all grain samples, but it was evaluated statistically insignificant (p>0.05). The rice flour was the sample that had the lowest phytic acid content (921.87 mg/100g) and the highest mineral digestibility rate (58.35%). Although the contents of total ash and some of the minerals (Na, Ca, K, Mg, Zn, Fe, Ba, and P) decreased in flours especially in wheat and paddy, the rate of some minerals (Na, Mg, Zn, Fe, and Al) increased due to their distribution and localization in the grain layers, especially in rye and oat. The result of the study has shown that the level of the minerals changed depending on the bran/hull content of the grains, and the milling process was more effective on phytic acid content and on protein digestibility than on the mineral digestibility. While the phytic acid content was located on the outer layer of the grain, it was decreased in the kernel. Conclusions. Although the phytic acid content which affects the digestibility of the cereals were reduced by the milling process, the combination of different treatments such as soaking, fermentation could be suggested for improving the nutritional quality of the cereal.