14 Introduction to Renewable Biomaterials
1.3.3 Starch Crops
Corn (Zea mays) is an annual grass that forms male terminal tassels and female cobs.
The cobs develop 8–18 rows with 25–50 maize grains in each row. Grains accumulate
starch in up to 62% of fresh matter. The rest consists of 10% protein, 5% fat, and 5% fiber,
vitamins, minerals, sugar, and water. Corn grains are at first used as starch source. Corn
grain yield reaches 10 tons per hectare. If used as feed special varieties are harvested as
whole plant biomass with a yield of up to 50 tons fresh biomass per hectare (15–20 tons
per hectare dry mass). The biggest corn grower is the United States providing about 32%
of global harvest (Table 1.15).
Potatoes (Solanum tuberosum) grow perennially and accumulate starch in tubers. The
fresh matter content is about 15% starch (79% amylopectin, a highly branched polymer
of glucose; 21% amylose, a helical polymer made of훼-d-glucose). Top yields in Germany
reach 6 tons of starch per hectare. Potato was at first grown for food, but later for
industrial purposes as well. After starch processing, the remaining potato pulp contains
hemicellulose, cellulose, protein, and pectin. It is used in enzyme production, fungi
cultivation, and as fertilizer and feed additive. A special variety depositing only amy-
lopectin for industrial markets has been bred recently by traditional breeding. A similar
variety developed by genetic engineering did not enter the European market because
of lack of public acceptance. Potato is grown in Europe, Russia, and China (Table 1.16).
Wheat, barley, and rye (Gramineae family) are grasses depositing starch (28% amy-
lose, 72% amylopectin) in the grain. Starch makes 58% of the grain (fresh matter content)
with 15% water plus cellulose, hemicellulose, and lignin of the seed hull. Up to 4 tons of
Table 1.15Most important corn-producing nations 2012
(Statista, 2014) and carbon content (43% C in sucrose assumed).
Production
(million tons)
Starch content
(million tons)
Ccontent
(million tons)
United States 274 170 75.4
China 208 129 57.3
Brazil 71 44 19.5
EU 59 37 16.2
Mexico 22 14 6.1
Table 1.16Most important potato-producing nations 2009
(Landesverband der Kartoffelkaufleute Rheinland-Westfalen, 2013).
Production
(million tons)
Starch content
(million tons)
Ccontent
(million tons)
China 69 10.3 4.6
Russia 36 5.4 2.4
India 34 5.1 2.3
Ukraine 20 3.0 1.3
United States 20 3.0 1.3
