Molecular characterization of native and processed waxy maize starch in relation to the recrystallization behavior of model systems and starch microspheres

• The recrystallization behavior of five starch materials, native waxy maize starch, and starches modified by acid hydrolysis and mechanical treatments, were investigated by DSC (differential scanning calorimetry) and electron microscopy (SEM). The starches were known to vary significantly in molecular weights but not in the degree of branching. Microspheres manufactured from one of these starches were also studied by both methods. The acid hydrolysis did not produce major breakdown of the granular structure of starch as evidenced by SEK or the amount of crystalline amylopectin, as measured by DSC, but broadened the melting temperature range compared to native starch. No crystallinity could be detected in the material after the mechanical treatment, which also seemed to destroy the granular structure. The crystallinity was regained after the material had been dispersed in 70 % water during heating followed by 20 hour storage at 6 degreesC, called as one-step temperature treatment, while within the set of samples stored at 20 degreesC only one of the starches showed presence of regained crystallinity. No significant differences could be observed with regard to endothermic transition temperature or temperature range between the samples of native starch and both the acid hydrolysed and the mechanically treated samples, as measured by DSC. Apparently from the enthalpy values and presence of endothermic transitions, amylopectin molecular weight and modification method seemed to affect the amount of starch crystallites formed and/or the recrystallization rates, with acid hydrolysed samples showing higher enthalpy values compared to mechanically treated samples. The same conclusion, as for one-step temperature treatment of starch materials, was done for a two-steps temperature treatment of the starch materials, regarding transitions temperatures within the set of experiment. The two-steps treatment with nucleation at a lower temperature and crystal growth and perfection at a higher temperature resulted in an increase in the melting temperatures and narrower melting intervals. This treatment is also similar to the actual microsphere manufacture process. DSC thermogram of placebo starch microspheres revealed that the crystallites, obtained in production process of the microspheres, melted at temperatures similar to melting temperatures of the starch dispersion after 14 days/6 degreesC- storage but showed higher enthalpy value and smaller melting interval.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Annan teknik -- Livsmedelsteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Other Engineering and Technologies -- Food Engineering (hsv//eng)

Nyckelord

starch microspheres

SEM

recrystallization

DSC

waxy maize starch

Publikations- och innehållstyp

kon (ämneskategori)

ref (ämneskategori)