General Properties, Occurrence, and Preparation
1.2
73
residues with 5–6% α-(1→6) branch linkages, called amylopectin. Amylose has an average of
500 to 5,000 D-glucopyranose residues per molecule, depending on the source; amylopectin
is much larger and has an average of 100,000 to 1,000,000 D-glucopyranose residues per
molecule [26,27]. When at equilibrium with its surroundings, starch granules will contain
10–15% w/w water. The amylose and amylopectin molecules in the granules can be solubilized by heating the granules in water, where they swell and eventually burst, releasing the
individual molecules. Starch granules can also be dissolved in 9:1 dimethyl sulfoxide/water
solutions [28]. See > Fig. 1 in > Chap. 6.2 for the structures of segments of amylose and
amylopectin.
The amounts of amylose and amylopectin differ for starches from different botanical sources.
Most so-called normal starches have 20–30% amylose and 80–70% amylopectins, respectively [29,30]. There are mutant varieties, such as waxy maize, waxy rice, and waxy potato,
that are composed of 100% amylopectin. There also are the high amylose varieties, such as
amylomaize-V that consists of 53% amylose and 47% amylopectin and amylomaize-VII that
is 70% amylose and 30% amylopectin, just the reverse of the “normal” starches. Many of the
“normal” starches have been found to have an intermediate component that is slightly branched
amylose with 0.5–3% α-(1→6) branch linkages [26,27,29,30].
All starches can be completely converted into D-glucose by acid hydrolysis at high temperatures (100 °C) and by the action of the enzyme, glucoamylase, at lower temperatures (20–
40 °C), when the granules are solubilized. Humans and other organisms can completely convert solubilized starches into D-glucose by the combined action of several enzymes, such as
α-amylases found in saliva and in the small intestine, and α-(1→6)-glucosidase and α-(1→4)glucosidase that are secreted by special cells in the lining of the small intestines.
Starches have been chemically modified to improve their solution and gelling characteristics
for food applications. Common modifications involve the cross linking of the starch chains,
formation of esters and ethers, and partial depolymerization. Chemical modifications that have
been approved in the United States for food use, involve esterification with acetic anhydride,
succinic anhydride, mixed acid anhydrides of acetic and adipic acids, and 1-octenylsuccinic
anhydride to give low degrees of substitution (d.s.), such as 0.09 [31]. Phosphate starch esters
have been prepared by reaction with phosphorus oxychloride, sodium trimetaphosphate, and
sodium tripolyphosphate; the maximum phosphate d.s. permitted in the US is 0.002. Starch
ethers, approved for food use, have been prepared by reaction with propylene oxide to give
hydroxypropyl derivatives [31].
The solubility of the starch granules has been increased by reaction of starch granules in water
with 7% hydrochloric acid for one week at 20 °C to give “Lintner soluble starch”. Recent modifications to increase the solubility of starch granules have involved the reaction of the starch
granules with hydrochloric acid in anhydrous alcohols, such as methanol, ethanol, 2-propanol,
and 1-butanol to give a new class of limit dextrins whose average degree of polymerization
can be controlled between 1800 and 30 [32,33,34]. Enzymatic conversions of starches into
mixtures of maltodextrins are used in food preparations. Starch is the major source for the
commercial preparation of D-glucose and D-fructose. Starches have been modified to give
tertiary amino alkyl ethers, quaternary ammonium ethers, amino ethylated ethers, cyanamide
ethers, starch anthranilates, cationic dialdehyde starch, carboxymethyl ethers, and carboxy
starch for various applications in the sizing of paper, formation of coatings, sizing of textiles,
flocculation, and emulsification technologies [35].
1.2
73
residues with 5–6% α-(1→6) branch linkages, called amylopectin. Amylose has an average of
500 to 5,000 D-glucopyranose residues per molecule, depending on the source; amylopectin
is much larger and has an average of 100,000 to 1,000,000 D-glucopyranose residues per
molecule [26,27]. When at equilibrium with its surroundings, starch granules will contain
10–15% w/w water. The amylose and amylopectin molecules in the granules can be solubilized by heating the granules in water, where they swell and eventually burst, releasing the
individual molecules. Starch granules can also be dissolved in 9:1 dimethyl sulfoxide/water
solutions [28]. See > Fig. 1 in > Chap. 6.2 for the structures of segments of amylose and
amylopectin.
The amounts of amylose and amylopectin differ for starches from different botanical sources.
Most so-called normal starches have 20–30% amylose and 80–70% amylopectins, respectively [29,30]. There are mutant varieties, such as waxy maize, waxy rice, and waxy potato,
that are composed of 100% amylopectin. There also are the high amylose varieties, such as
amylomaize-V that consists of 53% amylose and 47% amylopectin and amylomaize-VII that
is 70% amylose and 30% amylopectin, just the reverse of the “normal” starches. Many of the
“normal” starches have been found to have an intermediate component that is slightly branched
amylose with 0.5–3% α-(1→6) branch linkages [26,27,29,30].
All starches can be completely converted into D-glucose by acid hydrolysis at high temperatures (100 °C) and by the action of the enzyme, glucoamylase, at lower temperatures (20–
40 °C), when the granules are solubilized. Humans and other organisms can completely convert solubilized starches into D-glucose by the combined action of several enzymes, such as
α-amylases found in saliva and in the small intestine, and α-(1→6)-glucosidase and α-(1→4)glucosidase that are secreted by special cells in the lining of the small intestines.
Starches have been chemically modified to improve their solution and gelling characteristics
for food applications. Common modifications involve the cross linking of the starch chains,
formation of esters and ethers, and partial depolymerization. Chemical modifications that have
been approved in the United States for food use, involve esterification with acetic anhydride,
succinic anhydride, mixed acid anhydrides of acetic and adipic acids, and 1-octenylsuccinic
anhydride to give low degrees of substitution (d.s.), such as 0.09 [31]. Phosphate starch esters
have been prepared by reaction with phosphorus oxychloride, sodium trimetaphosphate, and
sodium tripolyphosphate; the maximum phosphate d.s. permitted in the US is 0.002. Starch
ethers, approved for food use, have been prepared by reaction with propylene oxide to give
hydroxypropyl derivatives [31].
The solubility of the starch granules has been increased by reaction of starch granules in water
with 7% hydrochloric acid for one week at 20 °C to give “Lintner soluble starch”. Recent modifications to increase the solubility of starch granules have involved the reaction of the starch
granules with hydrochloric acid in anhydrous alcohols, such as methanol, ethanol, 2-propanol,
and 1-butanol to give a new class of limit dextrins whose average degree of polymerization
can be controlled between 1800 and 30 [32,33,34]. Enzymatic conversions of starches into
mixtures of maltodextrins are used in food preparations. Starch is the major source for the
commercial preparation of D-glucose and D-fructose. Starches have been modified to give
tertiary amino alkyl ethers, quaternary ammonium ethers, amino ethylated ethers, cyanamide
ethers, starch anthranilates, cationic dialdehyde starch, carboxymethyl ethers, and carboxy
starch for various applications in the sizing of paper, formation of coatings, sizing of textiles,
flocculation, and emulsification technologies [35].