with 40% whole wheat; B: corn recipe; C: corn recipe in 3D rendering (carrot cut in the extruded ball).
Adapted from (Chanvrier et al. 2014).
Figure 1.7 Microstructure of rye crisp bread. A1 and A2: Reconstructed X‐ray micro‐CT cross‐sections and 3‐D structure of extruded rye crispbread (Gondek et al. 2013). A3: Scanning electron micrograph of extruded rye crispbread (Marzec et al. 2007). B1–C3: bright field (B1 and C1) and confocal (B2, B3, C2, C3) micrographs of non‐fermented and fermented (yeast leavened) rye crisp bread before and after in vitro digestion. Amylose in blue, amylopectin in purple, protein in yellow, β‐glucan in green fluorescence. Images from B1 to C3 kindly provided by Daniel Johansson
(Source: Department of Molecular Sciences, SLU, Uppsala).
As suggested by Johansson et al. (2018), factors related to the microstructure of cereal products can influence the digestive process and the release and absorption of nutrients, with possible later implications for the postprandial responses in vivo. Some microstructural differences between whipped (non‐fermented) and leavened (fermented) rye crispbread can be observed under confocal microscopy (Figure 1.7). Due to the inability of rye proteins to properly develop gluten, both types of crispbread present a continuous starch network consisting of highly swollen starch granules with some leaked amylose that encapsulates the protein (Figures 1.7 B1 and 1.7 C1). Visualization of the β‐glucans by using immunolabeling and confocal microscopy show that β‐glucans (green fluorescence) appear to be more degraded or solubilized in fermented rye crispbread (Figure 1.7 C2) compared to non‐fermented rye crispbread (Figure 1.7 B2). This has also been confirmed by analysis of the calcofluor average molecular weight of β‐glucans in these products (Johansson et al. 2018). Yeast fermentation has been shown to decrease the molecular weight of β‐glucans (Andersson et al. 2004; Tiwari and Cummins 2009; Rakha et al. 2010). In the same way, digested samples of non‐fermented rye crispbread show less degraded β‐glucans than the leavened one (Figures 1.7 B3 and 1.7 C3). Lower degradation of fibres could contribute to higher viscosity of the digesta and slower diffusion rates of enzymes, which has been related to later glucose peaks registered in in vitro experiments and lower insulin responses in human trials for non‐fermented rye crispbread compared to leavened rye crispbread (Johansson et al. 2015, 2018).
1.9 Conclusions
Cereal products constitute complex systems and lack of understanding of the mechanisms involved in the generation of cereal product structures may result in detrimental changes in texture and functionality. Microstructural characteristics of cereal products help define and predict their physical and health properties. The wide range of microscopy techniques available in combination with other analytical tools make it possible to increase the knowledge on structure‐functionality relationship of cereal products.
1.10 References
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