The mineral levels were assessed in crushed and homogenized
samples prepared by organic wet digestion in accordance with
the methodology described by Salinas and Garcia (1985). For organic
digestion, the samples were treated with a mixture of concentrated
nitric and perchloric acids at a high temperature. The
macro- and microelements were solubilized, subjected to different
treatments and diluted for further quantitative evaluation. The
quantification of elements was performed by spectrophotometry
using a standard curve for each mineral. To determine the concentration
of calcium, iron and manganese, we used an atomic absorption
spectrophotometer and acetylene. A flame photometer was
used to determine potassium (768 nm), and a visible-light spectrophotometer
was used to determine phosphorus (420 nm).