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| Author(s): |
Mariana Souza Costa
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São José do Rio Preto. 2017-07-04. |
| Institution: | Universidade Estadual Paulista (Unesp). Instituto de Biociências Letras e Ciências Exatas. São José do Rio Preto |
| Defense date: | 2017-06-07 |
| Advisor: | Célia Maria Landi Franco; Maria Victória Eiras Grossmann |
| Abstract | |
The effect of the crystalline pattern of starch on the obtainment and on the morphology, structural, molecular and physicochemical characteristics of starch nanocrystals (SNC) and their application in biofilms have been studied. The cassava, corn and potato starches were isolated and characterized. Suspensions of starch (14.7% w/v) in 3.16 M H2SO4 were hydrolyzed for 1, 3, 5 and 7 days at 40 °C. The amylodextrins obtained were characterized regarding amylose content (potentiometric titration), attenuated total reflectance vibration spectroscopy (FTIR-ATR), crystalline pattern and relative crystallinity (X-ray diffraction), thermal properties (DSC), thermogravimetric analysis, distribution of amylodextrins chains in high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD), morphology (SEM and TEM) and size (zetasizer). Cassava starch was the most susceptible to hydrolysis due to imperfections in its crystalline structure. The crystalline patterns of amylodextrins kept unchanged and crystallinity and peak temperature increased with hydrolysis time, while thermal degradation temperature decreased, independently of treatment time and starch source. A-type amylodextrins (cassava and corn starches) were structurally and thermally more stable than B-amylodextrins (potato starch), but their particles had a greater tendency to agglomeration. SNC were observed by TEM from the third day of hydrolysis in cassava amylodextrins, while corn and potato amylodextrins displayed SNC only on the fifth day. The amylodextrins were formed by two structures: micro- (crystalline particles) and nano- (organization of double helices). A-type SNC displayed platelet shapes, while B-type SNC were rounded. SNC were fractionated in column of Bio-Gel P6 and the fractions of the high and low molecular weight were collected. Fractions I and III were treated enzymatically (a: β-amylase followed by isoamylase and pullulanase; b: debranching enzymes followed by β-amylase) and analyzed by HPAEC-PAD. SNC were formed by two populations of dextrins compound by linear chains (degree of polymerization - DP 11-15) and single branched (DP 22-25). A-type SNC contained inner longer chains linked to the branching points, which were protected during acid action. SNC, regardless the crystalline pattern, were compound by stable double helices formed by chains with DP 10-15, but with distinct characteristics: while SNC A-type contained a greater amount of branches located mainly in the reducing end of their structure, SNC B-type had fewer branches, which were located at the non-reducing end. The location of the branching points in the crystalline structure influenced the shape of the SNC. Potato SNC obtained after 5 and 7 days (PO5 and PO7) and cassava and corn SNC obtained after 3 (CA3 and CO3), 5 (CA5 and CO5) and 7 (CA7 and CO7) days of hydrolysis were added in biofilms of cassava starch in different proportions (0, 1, 3 and 5%) and were characterized. The films added of the SNC had lower moisture content and higher solubility, regardless the crystalline type and concentration of SNC, except for those added with CO3 SNC. The addition of SNC of PO5, PO7, CA3, CA5, CO3 and CO5, regardless concentration, reduced the water vapour permeability (WPV) of the biofilms by improving the barrier properties, while the CA7 and CO7 SNC caused increase in the WPV due to particle agglomeration. Principal component analysis allowed to group the samples into four groups according to the mechanical properties. Films added by SNC 3%PO5, 5%PO7, 3%CA5, 1%CO3 and 5%CO3 were distinguished the other SNC for presenting better barrier and mechanical properties. The morphology of the SNC did not influence the mechanical properties, but the dispersion of the particles in the polymer matrix and the stability of the crystal surfaces improved the tensile forces. The CO3 SNC at 1% concentration was the most suitable to be applied in starch-based films. (AU) | |
| FAPESP's process: | 13/01500-7 - Production and characterization of nanocrystals from different sources of starch and its application in biofilms |
| Grantee: | Mariana Souza Costa |
| Support Opportunities: | Scholarships in Brazil - Doctorate |