Effect of temperature and steeping time on calcium and phosphorus content in nixtamalized corn flours obtained by traditional nixtamalization process.

摘要

Effects of temp. (72, 82 and 92 degrees C) on Ca and P contents in nixtamalized corn flours obtained by the traditional nixtamalization process (NCF) during the cooking stage and steeping time (0, 1, 3, 5, 7, 9, 11, 13 and 15 hr) were determined. In addition, Ca and P contents in industrial nixtamalized corn flours were analysed for comparative purposes. AAS and UV-vis spectroscopy were used to study Ca and P contents as well as the Ca2+/P ratio in NCF and industrial nixtamalized corn flours. Additionally, deposition and identification of Ca compounds in nixtamalized corn pericarp were analysed by low-vacuum SEM, energy dispersive spectrometry and X-ray diffraction techniques. DM loss in NCF is also reported. As temp. increased, Ca2+ content was enhanced, while P content decreased with statistical differences (P <= 0.05) between thermal treatments. Ca2+ content in industrial nixtamalized corn flours was significantly lower (P <= 0.05) than that of NCF. On the other hand, no statistical differences (P <= 0.05) were found between P content in commercial nixtamalized corn flours and NCF. Ca compounds, identified as calcite, were detected in corn pericarp. Statistical differences (P <= 0.05) were observed in P content in NCF obtained at different cooking temp. In addition, a decrease in P levels significantly correlated with steeping time at 92 degrees C (r = -0.91). At 72, 82 and 92 degrees C, average Ca2+/P ratio in NCF was 0.45 +or- 0.03, 0.61 +or- 0.05 and 0.82 +or- 0.05, respectively, indicating a correlation between this parameter and cooking temp. However, no correlation was found between Ca2+/P ratio and steeping time. This behaviour was attributed to Ca attached to the corn kernel. In commercial nixtamalized corn flours, Ca2+/P ratio was significantly lower (P <= 0.05) than that of NCF. There was a significant correlation (P <= 0.01) between DM loss and steeping time (r = 0.99) in NCF; this fact influenced the Ca2+/P ratio due to Ca attached to the pericarp. At 82 and 92 degrees C, max. values of Ca2+/P ratio were detected in NCF at 7 hr of steeping time and at 9 hr at 72 degrees C. It is suggested that these results could be used for industrial purposes to assess a max. Ca-to-P ratio, and at the same time to avoid loss of pericarp to increase the functional properties of NCF.