Note that the data of the total P by the wet chemistry method
(Table 3) were significantly lower (p < 0.05) than data of the element
P by the ICP method (Table 1), even though the two methods
measured the same compounds. However, in barley samples, the
two methods gave similar P values (Liu et al., 2007). Apparently,
the complex matrix of DDGS might prevent complete extraction
of total P by the wet method used. Since the present study focused
on changing patterns during the process, and since the difference
between the two methods for total P were systematic, using data
of total P by the wet method in Table 3 did not change any conclusion
of the present study.
Noureddini et al. (2009) measured total P in several stream
products of the dry-grind process, including whole corn, milled
corn, whole stillage, wet grains, syrup (condensed distillers solubles),
distillers wet grains with solubles, and DDGS. They found
that syrup contained the highest total P concentration (1.34%,
dry matter). The present study showed that syrup contained very
high concentrations of total P, with an average value of three
plants as 1.88% (dry matter) for three plants, but thin stillage
had the highest total P concentration (1.98%). Noureddini et al.
(2009) further showed that about 59% of total P in whole stillage
was phosphate P, and attributed the remainder of P in whole stillage
(41%) as phytate P. They did not, however, consider the contribution
by the rest of P defined in this study. Furthermore, their
HPLC analysis of this stream and its two centrifuged fractions did
not reveal the presence of phytate. In contrast, the present study
showed that about 48% of total P in whole stillage was phytate P
and that phosphate P toward total P in whole stillage was only
25.19%. The remaining 26.82% was contribution by the rest of P.
When the sum of contribution by both phosphate P and the rest
of P is collectively considered as nonphytate P contribution toward
total P, the present study showed that in DDGS the nonphytate P
was 56.30% (Table 3). This value matches well with 54% reported
by NRC (1994).
Moreover, in the study of Noureddini et al. (2009), several
stream products, including cooked slurry, liquefied mash, fermented
mash, and thin stillage, were not collected for analysis of
total P. The levels of phosphate P and phytate P were measured
only in whole stillage, its liquid and solid fractions after laboratory
centrifugation. The contribution by the rest of P was not accounted
for in the stream and its fractions. Therefore, the present study is
considered to be the first to document changes in all four forms
of P during the entire dry-grind process from corn.