Biomedical Engineering Reference
In-Depth Information
Grain sorghum contains a number of bioactive compounds, including phenolic
compounds, phytosterols and policosanols. Benzoic and cinnamic acid derivatives, tannins
and anthocynanins are the major phenolic acids and flavonoids in sorghum (Hahn
et al
.,
1983 ; Waniska
et al
., 1989; Krueger
et al
., 2003 ; Awika and Rooney, 2004 ). These
compounds are secondary metabolites which play an important role in plant defense
mechanism. Some sorghum cultivars that are commonly known as “bitter”, “bird proof”,
“bird resistant” or “brown”, are rich in condensed tannins (proanthocyanins) which protect
the plants against pests, insects and diseases. Based on its tannin content sorghum is
categorized as type I (no significant amount of tannins that are extractable with acidified
methanol) and type II (contains tannins that are extractable with acidified methanol but not
with pure methanol) and type III (contains tannins that are extracted with either methanol or
acidified methanol) (Dykes and Rooney, 2006). The difference between type II and III
sorghums is the location of tannins in the grain structure. Tannins in type II sorghums are
deposited in the vesicles within the testa layer, whereas in type III sorghum tannins are
deposited along the cell walls of the testa and some are present in the pericarp. In type II
sorghums acid is needed to break up the structure of vesicles to release tannins (Earp
et al
.,
2004). Examples of sorghum cultivars within this classification are: Type I, TX2911 (red
perocarp), Type II, Early Hegari and type III, Early Sumac (Price
et al
., 1978 ; Awika and
Rooney, 2004). Sorghum is also classified based on the color of the grain and total extractable
phenol content. White sorghum, also referred to as food-type, contains no detectable amount
of tannins or anthocyanins and has a very low level of total extractable phenol. Red sorghum
does not contain tannins but has a red pericarp with significant amount of extractable
phenols. As the name implies, black sorghum has a black pericarp and contains very high
levels of anthocyanins. Brown sorghum contains considerable amount of tannins and has a
pigmented testa (seed coat) and pericarp with varying degrees of pigmentation (Awika and
Rooney, 2004). Currently 99% of the sorghum grown in United States is tannin free. A small
amount of tannin sorghum grown in the United States is identity preserved seed stock.
The United Nations (UN) World Health Organization (WHO) identified iron (Fe), zinc
(Zn) and pro-vitamin A (
-carotene) as limiting micronutrients in human diet. Deficiency of
these micronutrients is highest in South and Southeast Asia and sub-Saharan Africa (SSA),
where sorghum is consumed as a staple food by millions of people (Reddy
et al
., 2005 ). In
2004, the HarvestPlus Challenge Program was launched with the objective of developing
biofortified crops (HarvestPlus, 2011). Within this program 84 sorghum lines were analyzed
for their micronutrient contents. Significant differences in iron (20.1-37.0 ppm), zinc (13.4-
31.0 ppm) and phytate (3.8-13.5 mg/g) contents were found among the sorghum samples
examined. There were also variations in
β
β
-carotene content among the samples. Only a trace
amount of
-carotene was present in non-yellow lines while lines with yellow endosperm
contained 0.56-1.13 ppm
β
-carotene. The information about the variations in chemical
composition among sorghum lines is valuable to plant breeders because this information can
be used to increase the micronutrient content of sorghum. Furthermore, data on the chemical
composition of sorghum lines is also important for choosing the right feedstock for specific
sorghum applications.
β
1.2.4.3
Utilization
Food applications of sorghum have been reviewed extensively (Taylor and Dewar, 2001;
Taylor
et al
., 2006 ; O'Kennedy
et al
., 2006). White food sorghum grain is milled into flour
and incorporated into snacks, cookies (biscuits), bread and ethnic foods. In the United States
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