Progress 09/01/02 to 08/31/05
Outputs
An understanding of the conditions leading to formation of starch spherulites has been gained through this project. Spherulites form more easily from linear starch in the absence of lipid. Starches must first be heated to temperatures above 170C, followed by a relatively rapid quench to temperature below 80C. A helix-coil transformation is thought to occur at about 170C, while a cooling rate dependent phase separation is induced at 80C. Numerous, well-developed spherulites exhibiting strong birefringence were formed of mung bean and potato starch rapidly quenched from 180C. Maize starch yielded less numerous, less well-developed, coarse spherulites. Acid-modified maize starch yielded large numbers of very round spherulites displaying moderately strong birefringence. Wheat, tapioca and arrowroot starches formed few or very poorly-developed spherulites. No spherulitic morphology was observed in oat, rice, or sorghum. Equivocal results were obtained for amaranth and yellow
pea starches. Acid-modified maize starch formed spherulites after heating to only 160C. Maize amylose (10-20% w/w) was found to form spherulites over a wide range of cooling rates (1-250C/min.). A maximum quench temperature of approximately 70C was required to produce spherulitic morphology. Quench temperatures between 70 and 110C produced a gel-like morphology. This was explained based on the relative kinetics of liquid-liquid phase separation vis-a-vis crystallization. The presence of a liquid crystalline phase was hypothesized. The enthalpy of amylose-LPC complexation and dissolution was significantly greater for the leached maize starch fraction compared with that for potato amylose, leading to erroneously high values for amylose content when potato amylose was used as the reference standard, caused by differences in degree of branching. A spherulitic morphology was observed at low LPC concentrations, but its formation was inhibited at concentrations of lipid typically used in the
LPC test. Spherulites in heated mung bean starch were obtained for a wide range of cooling rates (2.5-250C/min) provided the system was first heated to 180C and then cooled below 65C. Branched crystalline structures were also observed, as was a gel-like morphology. The dissolution temperature for spherulitic material ranged between 100 and 130C. A second dissolution endotherm was observed between 130 and 150C in systems containing gel-like material. Spherulites revealed B-type X-ray diffraction patterns. Spherulitic crystallization of starch following phase separation is proposed as a mechanism for starch granule initiation in vivo. Fractions of short chain linear starch having an approximate degree of polymerization of 125-920 have been shown to form a spherulitic morphology. The size of the spherulites formed decreases with decreasing DP. The peak dissolution temperature is seen to shift from 130 to 100C, while the enthalpy of dissolution increases fivefold (from 7.2 to 33 J/g) as
the DP decreases. WAXD shows that B-type crystallinity is present in all samples, with an increase in the crystallinity being evident as the DP decreases.
Impacts
The potential of starch spherulites to incorporate small molecular weight (less than 1000 Daltons) compounds was demonstrated during this project, which portends the development of a novel system for controlled release of flavors, fragrances or drugs. Additionally, starch spherulites have been shown to be resistant to enzymatic digestion. Consequently, they may constitute a new food ingredient with which to deliver carbohydrate with a low glycemic response, or may have prebiotic properties. Due to the size and shape of these starch particles and the presence of a hollow core, they could potentially be used as a food texturizer, simulating the mouthfeel of emulsion droplets.
Publications
- Ziegler, G.R., Creek, J.A. and Runt, J. 2005. Spherulitic crystallization in starch as a model for starch granule initiation. Biomacromolecules 6(3), 1547-1554
- Creek, J.A., Benesi, A., Runt, J. and Ziegler, G.R. 2006. Potential sources of error in the calorimetric evaluation of amylose content of starches. Progress in Food Biopolymer Research. Accepted for Publication, http://www.ppti.usm.my/pfbr/ ISSN:1823-1101
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Progress 01/01/04 to 12/31/04
Outputs
We have succeeded in preparing a significant amount of linear material of relatively high molecular weight through leaching of amylose from corn starch. We have also obtained a linear fraction of relatively low molecular weight through debranching of waxy starch followed by fractionation. These linear materials show a high propensity to form spherulites from as small as 1 micron to nearly 100 micron depending on crystallization conditions. We have demonstrated the temperature and cooling rate dependence of spherulite size for both leached linear amylose and native mung bean starch. Granules from wheat and barley were separated by size, and the spherulite forming ability of the smaller B-type granules was established. Amylose-lipid complexes were found not to be involved in spherulite formation on rapid cooling.
Impacts
Results from the mung bean, barley and wheat starch research suggest that spherulite formation is linked to granule initiation in vivo. The observations in the lpl-dsc test for amylose help resolve anomalous results in the literature. Accurate control of spherulite size will facilitate their use as encapsulation or texturizing agents.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
The conditions for starch spherulite formation in cereal starches displaying an A-type x-ray diffraction pattern were investigated using barley and wheat starch. Starch granule populations were separated based on granule size. Rapid quenching of gelatinized starch from the small granules (<10 micrometers) formed spherulites so well at cooling rates of 150C/min that the size was below the limit at which the Maltese cross extinction pattern could be easily seen (<1 micrometer). By slowing the cooling rate, nucleation density could be reduced and individual spherulites greater than 50 micrometers produced. Starch from gelatinized large granules (>10 micrometers) did not form spherulites. It is hypothesized that the small granules, with a greater percentage of hilum have a starch structure more conducive to spherulite formation. Amylose was fractionated from common corn starch by leaching at 80C. This material was characterized by 13C nmr, and no branched material was
observed. Characterization of this material by the differential scanning calorimetry method for amylose content using lysophospholecithin resulted in anomalous results. In addition to amylose-lipid complexes formed during the procedure, spherulites were observed. These spherulites melted at approximately the same temperature as the amylose-lipid complex and therefore distorted the measurement of enthalpy upon which the test is based.
Impacts
Results from the barley and wheat starch research suggest that spherulite formation is linked to granule development. This research may lead to a better understanding of the in vivo formation of the starch granule. The observations in the lpl-dsc test for amylose help resolve anomalous results in the literature.
Publications
- Ziegler, G.R., Nordmark, T.S. and Woodling, S.E. 2003. Spherulitic crystallization of starch: influence of botanical origin and extent of thermal treatment. Food Hydrocolloids 17(4):487-494
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Progress 01/01/02 to 12/31/02
Outputs
The formation of starch spherulites was found to be a general phenomenon not limited to high-amylose maize. Spherulites developed upon rapid cooling from 180C most easily from 10-20% w/w dispersions of starches exhibiting B- or C-type crystallinity. Spherulite development was favored in starches with a higher percentage of linear polymer. Acid modification may alter the average degree of polymerization to such an extent as to radically alter the crystal lamellae within the spherulite structure. Numerous well-developed spherulites exhibiting strong birefringence were formed in aqueous dispersions of mung bean and potato starch rapidly quenched from 180C. Ordinary maize starch yielded less numerous, less well-developed, coarse spherulites than did mung bean or potato. Acid-modified maize starch yielded large numbers of very round spherulites displaying moderately strong birefringence. Wheat, tapioca and arrowroot starches formed few or very poorly developed spherulites.
No spherulitic morphology was observed in oat, rice, or sorghum starch dispersions. Equivocal results were obtained for amaranth and yellow pea starches. Potato and mung bean starches required heating to at least 170C before spherulites formation was observed. Acid-modified maize starch formed spherulites after heating to only 160C and possibly as low as 150C.
Impacts
We have taken the first step towards successfully scaling up starch spherulite manufacture, with encouraging results. Novel biomaterials based on starch with commercial applications are anticipated.
Publications
- No publications reported this period
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