Comprehensive characterization of pulse flour microstructure using advanced non-destructive techniques

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Date
2024-07-30
Authors
Sivakumar, Chitra
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Abstract

Milling influences flour morphology and the molecular structure of biomolecules. Such structure-function interactions are crucial in determining ingredient functionality to develop specific end-products. Laboratory scale X-ray instruments such as X-ray microtomography (µCT), small-angle X-ray scattering (SAXS), and powder X-ray diffraction (PXRD) offer limited brightness and are time-consuming when investigating the flour porosity, starch lamellar structure, and the crystallinity of pulse flours. Herein, synchrotron X-rays (SR) were employed along with laser diffraction, mid-infrared (mid-IR) spectroscopy and scanning electron microscopy (SEM) to non-invasively investigate the molecular changes in roller-milled chickpea, navy bean, green lentil, and yellow pea flours as influenced by milling configurations (termed as flour streams) and flour blending (termed as flour blends). In the realm of this thesis, flour streams comprise break and reduction streams for green lentils and yellow pea flours. However, for chickpeas and navy beans, flour streams combined byproducts streams in addition to the break and reduction streams. Flour blends are a combination of combined break, reduction, and byproduct streams in different proportions. Results indicate that there is a variation in all the measured parameters (particle size distribution (PSD), flour morphology, starch lamellar structure, starch crystallinity, flour porosity, starch and protein secondary structures) in flour streams and blends and within a pulse-type. PSD results from laser diffraction, SR-µCT and SEM revealed multi-modal curve distribution patterns with differences in measured ranges for the same sample. Flour morphology analysis through SEM showcased differences between break and reduction streams, with break streams exhibiting clustered starch granules and reduction streams displaying isolated, deformed granules. Flour blends displayed a mixture of flour morphology analogous to flour streams, reflecting blend composition effects. Interestingly, chickpea starches were porous in nature. Consistent SAXS and PXRD patterns were observed in all the flours for both flour streams and blends. Porosity analysis using SR-µCT results were correlated with the SEM results. Mid-IR spectroscopy discerned dissimilarities in carbohydrate and protein regions among all the pulse flours for both flour streams and blends. Principal component analysis effectively discriminated between flour types and streams based on spectral characteristics. Overall, this comprehensive analysis sheds light on the PSD, morphology, starch structure, and functional components of roller-milled pulse flour streams and blends, providing valuable insights for optimizing milling processes and understanding flour quality attributes.

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Synchrotron, pulse flours, scanning electron microscopy, milling, small angle X-ray scattering, powder X-ray diffraction
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