The interactions between protein and starch in the oat dough/batter system during heating are particularly important for oat-based products but are rarely understood. In this study, the gelation behaviors and digestibility of oat protein-oat starch mixtures after heat treatment and their gelling properties in the oat dough/batter model corresponding to water content ranging from 50% to 80% were determined. Under the same water content, the oat protein-starch samples exhibited higher G′ and G″ values during the gelatinization process and lower gelatinization enthalpy (ΔH) than the oat starch samples. At low water content (oat dough system), competitive hydration between oat protein and starch played a dominant role, and protein inhibited the retrogradation behavior of starch. When the water content increased to 80% (oat batter system), the protein significantly promoted starch retrogradation behavior with ΔH values increasing from 0.54 to 1.71 J/g. The addition of protein weakened the tight binding between starch and water molecules and enhanced the mobility of water in the system. The interaction between oat protein and starch inhibited the enzymatic hydrolysis and slowed starch digestion, which was mainly related to the formation of resistant starch in the oat protein-starch gels system.
Summary Size reduction by milling of endosperm granules produces flour and prompts the heterogeneous distribution of nutrients, changing its properties. The effects of impact milling and frictional milling on the breakage of endosperm granules were evaluated. Comparison of both methods showed that frictional milling initially squeezed larger starch granules out of the endosperm granules, and the flour particles were smaller and exhibited decreased relative crystallinity. Meanwhile, impact milling peeled the protein off the surface of endosperm granules, and the surface of the flour particles had higher S and N contents. Moreover, the content of random coils decreased, and the V‐shaped peak disappeared. The weight loss rate of the ground samples and the maximum thermal cracking temperature of the impact‐milled samples increased significantly as processing progressed. Different milling mechanical forces can be used in combination to obtain the desired flour.
Roasting is the traditional heat treatment of oat kernels before milling in China. The effects of roasting and milling methods on the physicochemical properties of oat flour and the quality of the steamed oat cake have not been explored. Roasting treatment caused a looser structure of the oat grain, which made the oat grain easier to crush. Stone milling induced severe damage (92 g/kg) and aggregation of starch granules, resulting in the highest total starch hydrolysis rate of oat flour and the highest total gas volume of raw oat batter. However, the pore expansion capacity was restricted, resulting in the minimum specific volume and the highest hardness of steamed oat cake. Ultrafine milling produced a more uniformly particle size distribution of raw and roasted oat flour and the steamed oat cake prepared with ultrafine-milled raw oat flour had the maximum specific volume and minimum hardness, 2.75 mL/g and 6.01 N. Pulverizer milling resulted in the lowest solubility index and the lowest starch hydrolysis rate of raw and roasted oat flour. Raw whole oat flour prepared by ultrafine milling or pulverizer milling gave softer steamed oat cakes with higher volume or slower starch degradation, respectively.
The effect of frozen storage on the quality of fast-frozen steamed bread has not been explored. Meanwhile, gluten, as a key component of wheat, can be used as a quality improver for fast-frozen steamed bread due to its functional characteristics. Therefore, the effects of different gluten contents (0%, 0.5%, 1.0%, 1.5% on flour weight) and glutenin/gliadin (glu/gli) ratios (1:1, 1:2, and 2:1) on the quality of fast-frozen steamed bread were investigated, and the influence mechanism on its quality was also analyzed. Frozen storage induced the amount of SDS-soluble protein and freezable water increased, which further resulted in the reduction of specific volume, the increase of hardness and the destruction of microstructure. The results further indicated that 1.0%-1:1 gluten addition resulted in steamed bread with supreme specific volume and minimum hardness during frozen storage. By analyzing the mechanism of quality improvement, we determined that the SDS-soluble protein and freezable water content of steamed bread frozen for 60 d decreased by 8.45% and 9.63% following 1%-1:1 gluten addition, respectively. Adequate elasticity and extensibility of dough (specific alveograph index: P = 62, L = 55, P/L = 1.08) with 1.0%-1:1 of gluten addition resulted in the best quality and freeze stability of the fast-frozen steamed bread.
Nutritional constituents, hydration, pasting, and thermal properties of oat flour sieve fractions (74–180 μm) and the relationship between composition and characteristics were studied. Starch constituents, protein components (except for albumins), and saturated fatty acids (SFA) were mostly distributed in small particle fractions, while total protein, albumin, dietary fiber (DF), lipids, and unsaturated fatty acids (UFA) were abundant in large particle fractions. Amino acids (except for Tyr and Gly) of group Ⅰ, Ⅱ, and Ⅲ were significantly lacking in S2 (150–180 μm), and Cys decreased from 2.51% to 1.50% with the decrease in sieving particle sizes. The largest particles showed the highest water solubility index (WSI, 9.90%), the medium particles (100–132 μm) exhibited the highest pasting viscosities (final viscosity of 4148 cP), and the smallest particles had the maximum gelatinization enthalpy (ΔH, 3.2 J/g). Correlation analysis demonstrated that except for the basic components, Glu, Cys, Iso, Phe, C16:0, C18:0, and C18:2n6c also significantly affected the WSI and pasting properties of oat flour, while amylose, Gly, Ala, Val, Met, and C20:1 were highly correlated with thermal properties. The results are useful for oat processing and the development of oat-based products with specific particle size range to achieve desirable characteristics.
Summary Wheat ( Triticum aestivum L.) is one of the most important food grains worldwide, mainly consumed in the form of wheat flour or flour‐based foods. Milling reduces the particle size of wheat grains or wheat endosperm, which strongly affected the physical and chemical properties of wheat flour and subsequent product characteristics. In this paper, the differences in physical and chemical properties of wheat flour due to its particle size distribution, the sources of the differences and the applicability of flour products were reviewed. Furthermore, the modern wheat milling process, the mathematical modelling, and mechanical modification of wheat milling process in recent years were introduced. The research prospect of the influence of milling process on the formation of particle size and quality of wheat flour was put forward.
The aim of this study was to explore the effect of biochar on N2O emissions in soils with different pH levels. Soils with five pH levels (4.0, 5.1, 5.8, 6.6, and 7.2) were incubated in two conditions, with 0% biochar (CK) and 1% biochar (BC), for 23 days. N2O emissions were measured at nine time points, and soil chemical properties, AOA-amoA, AOB-amoA, nirK, nirS, and nosZ, were analyzed. Partial least squares path modelling (PLS-PM) was used to assess the effect of nitrification and denitrification pathways on potential N2O emissions. The results showed that biochar reduced N2O emissions in highly acidic soil (pH 4.0) but increased emissions in soils with pH values ranging from 5.1 to 7.2. In highly acidic soils, decreased N2O emission was associated with increased soil pH (p < 0.05) and decreased dissolved organic carbon content (p < 0.05), leading to higher nosZ gene abundance (p < 0.05). Meanwhile, in acidic to neutral soils, biochar application increased soil pH (6.6–11.7%), dissolved organic nitrogen (5.9–29.5%), dissolved organic carbon (8.6–41.0%), stimulated AOB-amoA, nirK, nirS gene abundance (p < 0.05), and thus increased N2O emissions. The results verified the influence of nitrification and denitrification genes on N2O production in soils with different pH values. In conclusion, biochar had different effects on N2O emissions based on soil pH, highlighting the need to consider pH when using biochar to mitigate N2O emissions in subtropical citrus orchards.
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