Effect of roasting treatment on the micromorphology, gelatinization, structure, and digestibility of whole oat flour

Mechanistic insights into starch behavior and starch-protein interactions in whole grain oat flour: Structural and functional modifications by steam explosion treatment

This study explores the effects of steaming, roasting, and steam explosion treatment on the structural, rheological, and functional properties of whole grain oat flour, with a particular focus on starch changes and starch-protein interactions. Steam explosion treatment altered the physicochemical properties of whole grain oat flour, evidenced by changes in color parameters (L* from 70.9 to 67.4, WI from 58.6 to 54.4), degree of gelatinization (increased from 21.4 % to 89.9 %), and gel network stability. Notably, steam explosion treatment uniquely disrupted starch crystallinity and reduced amylopectin content (40.8 % to 31.1 %). Microscopic analysis (scanning electron microscopy, confocal laser scanning microscopy) and multi-scale structural characterization (infrared spectroscopy, differential scanning calorimetry) revealed that the oat starch-protein mixture exhibited a three-dimensional cellular network, with significantly increased hydrogen bonding between starch and protein. This interaction formed a cross-linked gel network structure, enhancing gel strength, water retention, and thermal stability while delaying starch retrogradation, ultimately improving the shelf life of oatmeal porridge. Mechanistic analysis revealed that steam explosion treatment enhanced water molecule binding to macromolecules, mitigating water migration and structural degradation during storage. This research provides new insights into the molecular interactions underpinning whole oat processing, offering a foundation for the development of high-quality whole oat-based products.

Nutritional, functional and rheological properties of bunya nut flour as a versatile gluten-free option

Bunya nuts are a starch-rich food that has been consumed by Indigenous communities for thousands of years. In addition to consuming fresh nuts, they were commonly processed into flour. However, their properties as a gluten-free flour are still unknown. In this study, we investigated the nutritional, functional and rheological properties of bunya flour prepared using different methods, as well as the isolated starch, and compared to wheat, rice and chestnut flours. Overall, raw bunya nut flour showed higher fibre (8.4%d.b.), lower protein (4.7%d.b.) and higher fat content (4.4%d.b.) when compared to rice and wheat flours. Its proximate composition was similar to chestnut flour. By altering the preparation method for bunya nut flour we showed that its functional properties can be altered, for example, raw and whole bunya flours showed good foam and emulsion capacity and stability, whereas roasted bunya flour had poor emulsion activity and stability but a high water absorption capacity. Raw and fermented flours showed high peak viscosity when heated in water. Bunya flours, except for the roasted one, showed a slow rate of starch hydrolysis and high resistant starch content compared to wheat and rice flours, especially considering the role of the inner coating when not removed from the nut. Bunya nut flour is a versatile option and can overcome issues found for gluten-free flours such as poor nutritional quality and sensory properties of the resultant products.

Heat-treated brown rice starch structure and effect on short-chain fatty acids and mouse intestinal microbiota

Rice with high resistant starch (RS) exhibits the potential to improve glucose metabolism, insulin sensitivity. In this study, using two rice varieties-Samgwang, a medium-amylose rice, and Dodamssal, a high-amylose rice containing RS-we analyzed the composition and molecular structural characteristics of brown rice and its starch and the effects on fasting blood glucose levels, fecal short-chain fatty acid (SCFA), and gut microbiota after 8 weeks of consumption in mice. The amylose content of heat-treated Samgwang (HS) and -Dodamssal (HD) was 21.0 ± 0.2 and 47.5 ± 0.3 %, respectively, while RS contents were 0.8 ± 0.0 and 14.7 ± 1.0 %. HD exhibited a C-type starch crystallinity with a lower proportion of short chains and a higher proportion of long chains compared to HS. HD-fed mice exhibited lower fasting blood glucose levels and the highest SCFA levels in their feces. They also had the highest abundance of Ruminococcus bromii, an RS-degrading bacterium, the highest positive correlation with Faecalicatena fissicatena (r = 0.9), and the highest negative correlation with Lachnoclostridium scindens and Lawsonibacter asaccharolyticus (r = -0.8). Overall, HD consumption can improve glucose metabolism by increasing intestinal SCFA production and can serve as a prebiotic dietary ingredient to improve obesity and diabetes.

Flaking of millets and its impact on bioactivity, pasting, digestibility, structural and thermal properties

Five different millets (foxtail, little, barnyard, kodo and browntop) with and without sprouting were subjected to flaking. Phytic acid and phenolic content tends to decrease significantly, whereas antioxidant activity increased up to 77.32% on flaking of millets. A significant decrease in peak and final viscosity was observed in millet flakes. A-type diffraction pattern was predominant for unsprouted millets whereas the flaked millets showed V-type crystallinity. The protein digestibility significantly increased up to 37.77% in flakes made from sprouted millets. The mineral bioavailability upon flaking of millets increased, especially Ca (88.22% for little), Fe (43.04% for barnyard) and Zn (61.77% for kodo), which is attributed to the reduction in phytic acid. Flaking, however, led to an increase in rapidly and slowly digestible starch with a corresponding decrease in resistant starch. Among the unsprouted and sprouted millet flakes, foxtail received the highest sensory scores for overall acceptability.

The impact of addition of pearl millet starch-germ complex in white bread on nutritional, textural, structural, and glycaemic response: Single blinded randomized controlled trial in healthy and pre-diabetic participants

The rise of pre-diabetes at the global level has created a significant interest in developing low glycaemic index food products. The pearl millet is a cheaper source of starch and its germ contains significant amount of protein and fat. The complexing of pearl millet starch and germ by dry heat treatment (PMSGH) resulted an increase in the resistant starch content upto 45.09 % due to formation of amylose-glutelin-linoleic acid complex. The resulting pearl millet starch germ complex was incorporated into wheat bread at 20, 25, and 30 %. The PMSGH incorporated into bread at 30 % reduced the glycaemic index to 52.31. The PMSGH incorporated bread had significantly (p < 0.05)increased in the hardness with a reduction in springiness and cohesiveness. The structural attributes of the 30 % PMSGH incorporated bread revealed a significant (p < 0.05)increase in 1040/1020 cm-1 ratio and relative crystallinity. The consumption of functional bread incorporated with pearl millet starch germ complex reduced blood glucose levels and in vivo glycaemic index in healthy and pre-diabetic participants when compared to white bread. Hence, the study showed that the incorporation of pearl millet starch-germ complex into food products could be a potential new and healthier approach for improving dietary options in pre-diabetes care.

Structural modification of starch and protein: From the perspective of gelatinization degree of oat flour

To clarify the relationship between gelatinization degree and structure characteristics, oat kernels were roasted to different gelatinization degree of 15 %-90 % based on tempering water content of 22.5 %-35 %, and the structure characteristics of starch and protein were evaluated. The results showed that the increased gelatinization degree dependent on tempering water content promoted protein aggregation on the surface of starch particles, forming larger aggregates with molecular weight >100 kDa. Oat kernels presented a dense starch gel network structure induced by gelatinized starch. Partial gelatinization of starch led to a decrease in pasting viscosities (setback viscosity, 3.91 Pa·s-1.59 Pa·s) and enthalpy (5.12 J/g-0.11 J/g). With the increase of gelatinization degree, the starch crystal structure conversed from A + V type to V type, accompanied by the formation of starch-lipid complexes and a decrease of relative crystallinity (22.28 %-8.72 %). Moreover, 50 % gelatinized oat flour possessed the highest β-sheet structure (38.04 %), but a decrease in surface hydrophobicity and an increase in endogenous fluorescence intensity were found in oat flour of gelatinization degree >50 %. This study provided a theoretical reference for the application of oat flour with different gelatinization degrees to match suitable products.

Influence of Supercritical Carbon Dioxide on the Activity and Conformational Changes of α-Amylase, Lipase, and Peroxidase in the Solid State Using White Wheat Flour as an Example

Green technologies using renewable and alternative sources, including supercritical carbon dioxide (sc-CO2), are becoming a priority for researchers in a variety of fields, including the control of enzyme activity which, among other applications, is extremely important in the food industry. Namely, extending shelf life of e.g., flour could be reached by tuning the present enzymes activity. In this study, the effect of different sc-CO2 conditions such as temperature (35-50 °C), pressure (200 bar and 300 bar), and exposure time (1-6 h) on the inactivation and structural changes of α-amylase, lipase, and horseradish peroxidase (POD) from white wheat flour and native enzymes was investigated. The total protein (TPC) content and residual activities of the enzymes were determined by standard spectrophotometric methods, while the changes in the secondary structures of the enzymes were determined by circular dichroism spectrometry (CD). The present work is therefore concerned for the first time with the study of the stability and structural changes of the enzyme molecules dominant in white wheat flour under sc-CO2 conditions at different pressures and temperatures. In addition, the changes in aggregation or dissociation of the enzyme molecules were investigated based on the changes in particle size distribution and ζ-potential. The results of the activity assays showed a decrease in the activity of native POD and lipase under optimal exposure conditions (6 h and 50 °C; and 1 h and 50 °C) by 22% and 16%, respectively. In contrast, no significant changes were observed in α-amylase activity. Consequently, analysis of the CD spectra of POD and lipase confirmed a significant effect on secondary structure damage (changes in α-helix, β-sheet, and β-turn content), whereas the secondary structure of α-amylase retained its original configuration. Moreover, the changes in particle size distribution and ζ-potential showed a significant effect of sc-CO2 treatment on the aggregation and dissociation of the selected enzymes. The results of this study confirm that sc-CO2 technology can be effectively used as an environmentally friendly technology to control the activity of major flour enzymes by altering their structures.

The Impact of Food Processing on the Structure and Hypoglycemic Effect of Oat β-glucan

The impact of food processing including baking, steaming and bread making, on the structure and hypoglycemic effect of oat β-glucan was studied. The structural analysis revealed the β-D-glucopyranosyl units of β-glucan was unchanged in aforementioned processing. The baking processing endowed β-glucan with increased molecular weight (Mw) and viscosity, which enhanced the capacity of β-glucan to delay starch digestion in vitro, such as the rapidly-digestible starch content decreased, the slowly-digestible and resistant starch content increased, and the glycemic index (GI) value decreased. Meanwhile, the inhibitory activity of β-glucan against α-glucosidase and α-amylase was enhanced by baking processing. By contrast, during steaming and bread making processing, β-glucan showed decreased Mw and viscosity, which accelerated starch digestion in vitro and reduced the inhibitory activity of β-glucan against α-glucosidase and α-amylase. Apart from that, baking processing promoted the physiological and antioxidant properties of β-glucan, but the properties decreased during steaming and bread making processing. The results suggest that oat raw materials can be treated with dry heat and high temperature, avoiding moist heat and fermentation treatments to maximize the hypoglycemic effect of β-glucan.

Effect of Heat–Moisture Treatment on the Physicochemical Properties, Structure, Morphology, and Starch Digestibility of Highland Barley (Hordeum vulgare L. var. nudum Hook. f) Flour

This study modified native highland barley (HB) flour by heat–moisture treatment (HMT) at different temperatures (90, 110, and 130 °C) and moisture contents (15%, 25%, and 35%). The effects of the treatment on the pasting, thermal, rheological, structural, and morphological properties of the native and HMT HB flour were evaluated. The results showed that HMT at 90 °C and 25% moisture content induced the highest pasting viscosity (3626–5147 cPa) and final viscosity (3734–5384 cPa). In all conditions HMT increased gelatinization temperature (T_o, 55.77–73.72 °C; T_p, 60.47–80.69 °C; T_c, 66.16–91.71 °C) but decreased gelatinization enthalpy (6.41–0.43 J/g) in the HMT HB flour compared with that in the native HB flour. The HB flour treated at 15% moisture content had a higher storage modulus and loss modulus than native HB flour, indicating that HMT (moisture content, 15%, 25%, and 35%) favored the strengthening of the HB flour gels. X-ray diffraction and Fourier-transform infrared spectroscopy results showed that HMT HB flour retained the characteristics of an A-type crystal structure with an increased orderly structure of starch, while the relative crystallinity could be increased from 28.52% to 41.32%. The aggregation of starch granules and the denaturation of proteins were observed after HMT, with additional breakage of the starch granule surface as the moisture content increased. HMT could increase the resistant starch content from 24.77% to 33.40%, but it also led to an increase in the rapidly digestible starch content to 85.30% with the increase in moisture content and heating temperature. These results might promote the application of HMT technology in modifying HB flour.