Starch granules: structure and biosynthesis.

A method was developed for measuring the volume of water absorbed by starch -granules heated in excess water, based on the observation that blue dextran dye (molecular weight 2 X 106) will dissolve in supernatant and interstitial water but not in the intragranular water. Swelling curves of wheat and normal and waxy barley and maize starches, determined by measuring the swelling factor (swollen volume/initial volume of airdried starch) at various temperatures up to 850C, were characterized by an initial phase of slight swelling, a second phase of rapid swelling, and a final stage of maximum swelling (not observed with high-gelatinizing starches or if granules disintegrated). With wheat starch, swelling began at 45-500C and continued to 850C; loss of birefringence and a large decrease in gelatinization enthalpy attributed to dissociation of crystalline Gelatinization in the narrowest sense is the thermal disordering of crystalline structures in native starch granules, but in the broader sense it includes related events such as swelling of the granules and leaching of soluble polysaccharides (Atwell et al 1988). Gelatinization temperature (GT) and enthalpy (AH) are conveniently measured by differential scanning calorimetry (DSC), and this aspect has received much attention in recent years because it is experimentally convenient and precise. However, in most food systems the actual temperature at which starch gelatinizes is less important than those properties that depend on swelling, such as pasting behavior and rheological properties of the partially or fully swollen starch granules. The properties of the starch-water system will, of course, be different if the swollen granules are dispersed mechanically to give a uniform gel. Historically, starch swelling has been studied by simple methods that do not distinguish between intragranular water and intergranular or interstitial water (Leach et al 1959), and the precision of measurements was not particularly good. This paper describes an improved method for measuring only intragranular water and hence the true swelling factor at a given temperature, based on the observation that blue dextran (Mr 2 X 106) does not penetrate swollen granules. The effects of amylopectin (AP), amylose (AM), and lipids on swelling behavior were then investigated using the blue dextran method. MATERIALS AND METHODS

Swelling and gelatinization of cereal starches. I. Effects of amylopectin, amylose, and lipids

Morphological, thermal and rheological properties of starches from different botanical sources

Starch-composition, fine structure and architecture

Structures and properties of starches isolated from different botanical sources were investigated. Apparent and absolute amylose contents of starches were determined by measuring the iodine affinity of defatted whole starch and of fractionated and purified amylopectin. Branch chain-length distributions of amylopectins were analyzed quantitatively using a high-performance anion-exchange chromatography system equipped with a postcolumn enzyme reactor and a pulsed amperometric detector. Thermal and pasting properties were measured using differential scanning calorimetry and a rapid viscoanalyzer, respectively. Absolute amylose contents of most of the starches studied were lower than their apparent amylose contents. This difference correlated with the number of very long branch chains of amylopectin. Studies of amylopectin structures showed that each starch had a distinct branch chain-length distribution profile. Average degrees of polymerization (dp) of amylopectin branch chain length ranged from 18...

Effects of Amylopectin Branch Chain Length and Amylose Content on the Gelatinization and Pasting Properties of Starch

An improved colorimetric procedure for determining apparent and total amylose in cereal and other starches

Lipids in cereal starches: A review

Cereal Chem. 70:385-391. Amylose (AM) and lysophospholipid (LPL) contents were directly correlated in barley starches, but the linear regressions that described the relationships in waxy and nonwaxy starches were quite different. The data indicated that AM exists partially as lipid-complexed amylose (L.AM), with an LPL-to-L.AM ratio of 1:7 and partially as lipid-free amylose (F.AM). The [13]C-cross polarization/magic angle spinning-nuclear magnetic resonance (CP/MAS-NMR) spectra of the nonwaxy starches had a broad resonance with a chemical shift of 31.2 +/- 0.4 ppm, which is characteristic of midchain methylene carbons of fatty acids in the solid state or in V-amylose (V-AM) complexes. The extracted lipid was a viscous liquid that, when mixed with seven parts AM, did not give a discernible peak under the conditions used to acquire the solid- state spectra. However, when the lipid was complexed with AM, it gave a typical V-AM spectrum and a broad resonance at 31.8 ppm. This proves lipid complexed with L.AM existed in the native starches and was not an artifact formed subsequently from free LPL and F.AM. The intensity of the resonance was consistent with the LPL content of the starches. Independent supporting evidence was obtained by differential scanning calorimetry that showed a constant enthalpy for disordering of amylopectin, DeltaH(AP), for all waxy and nonwaxy starches, regardless of L.AM content and, hence, no exothermic formation of L.AM during starch gelatinization. Twelve waxy barley starches used in this study contained 0.8-4.0% L.AM and 0.9-6.4% F.AM; six nonwaxy starches contained 6.1-7.2% L.AM and 23.1-25.0% F.AM. All starches had essentially identical AP structures, as show by the chain lengths of debranched starches fractionated by gel-permeation chromatography and high-performance liquid chromatography. L.AM and F.AM appeared to have quite different effects on starch gelatinization behavior. Peak gelatinization temperature (Tp) of the waxy starches was p ositively correlated with L.AM content; because the Tp of the nonwaxy starches was much lower than predicted from the regression equation for the waxy starches, we concluded that F.AM lowered Tp. Swelling of starches at 80 C is essentially a property of AP content that is inhibited by LPL, but the relationship is not strictly linear. An improved equation to describe swelling properties assumed that 80% of the F.AM swelled with the AP fraction, although swelling was inhibited by L.AM0.485.

W.R. Morrison

Papers

An improved colorimetric procedure for determining apparent and total amylose in cereal and other starches

Lipids in cereal starches: A review

Swelling and gelatinization of cereal starches. IV. Some effects of lipid-complexed amylose and free amylose in waxy and normal barley starches

A relationship between the amylose and lipid contents of starches from diploid cereals

Some factors determining the thermal properties of amylose inclusion complexes with fatty acids