Effects of experimental warming on physicochemical properties of indica rice starch in a double rice cropping system

Changes in starch structure, function and enzyme activity in early-season indica rice under simulating high temperature and strong light during grain filling

Early indica rice in Southern China frequently experiences high temperatures (HT) and strong light (SL) during grain filling, which accelerates grain maturity. In this study, two indica rice cultivars with different grain qualities under control (CK), HT, and HT + SL treatments to investigate their impacts on starch structure and physicochemical properties. The results demonstrated that HT and HT + SL treatments increased the amylopectin average chain length, long chain, relative crystallinity, large granule, and protein content (40.9 %-41.6 %), while decreasing amylose content (15.4 %-21.6 %) and branching degree compared to CK. This was due to a reduction in granule-bound starch synthase, soluble starch synthase, and starch branching enzymes, along with an increase in debranching enzyme activity, which altered the starch fine structure and diminished thermal stability and gelatinization viscosity. The HT + SL treatment exhibited a more pronounced impact, increasing the amylopectin middle chain (fb1) and relative crystallinity, while decreasing the branching degree and amylopectin short-chain length, indicating that SL exacerbated the deterioration of starch structure. Nevertheless, the starch physicochemical properties of high-quality cultivar were relatively less affected by the HT + SL conditions, suggesting a potential for improved utilization of starch in high-quality early indica rice in food processing.

Translocation, Transformation, and Phytotoxicity of Sulfadiazine and N4-Acetylsulfadiazine in Rice Plants

This study investigates the uptake, biotransformation, and phytotoxicity of sulfadiazine (SDZ) and its acetyl derivative N4-acetylsulfadiazine (NASDZ) in rice. Results showed that rice was more tolerant to NASDZ, with lower malondialdehyde and reactive oxygen species levels but higher antioxidant enzyme activities (SOD, POD, and CAT). The maximum accumulations of SDZ in roots and shoots were 19.3 ± 1.0 and 3.6 ± 1.1 μg/g, while NASDZ were 18.6 ± 2.5 and 3.5 ± 1.4 μg/g, respectively. SDZ exposure generated more metabolic intermediates, including deamination, hydroxylation, glycosylation, acetylation, and formylation products, while NASDZ metabolism was documented for the first time. Key genes involved in biotransformation include cytochrome P450, acetyltransferase, glycosyltransferases, and methyltransferase. Density functional theory calculations showed structural differences affecting reactive sites and intermediates. SDZ disrupted lipid metabolism, while NASDZ altered carbohydrate and amino acid pathways, highlighting their selective effects on rice metabolism. Our data help understand sulfonamide biotransformation and phytotoxicity in rice.

Loss-of-function of SSIIa and SSIIIa confers high resistant starch content in rice endosperm

Rice (Oryza sativa L.) endosperm accumulates huge amounts of starch. Rice starch is highly digestible, potentially enhancing the occurrence of blood sugar- and intestine-related diseases such as type 2 diabetes. Resistant starch (RS) is hardly digestible in small intestine but can be converted into beneficial short-chain fatty acids in large intestine, potentially reducing the incidence of these diseases. However, it is still difficult to produce a high RS rice variety. Here, we report that simultaneous deficiency of soluble starch synthases IIa and IIIa confers high RS content in rice endosperm. The ssIIa ssIIIa exhibited higher RS content than did the ssIIIa ssIIIb, a mutant reported currently to have remarkably higher RS content than parental ssIIIa, under our experimental conditions. Loss-of-function of SSIIa and SSIIIa significantly elevated the activity of granule-bound starch synthase I and thus content of amylose. Furthermore, total lipid content increased in mutant seeds, implying that intermediate metabolites spilled out from starch biosynthesis into lipid biosynthesis. The increased amylose content and improved lipid synthesis coordinately contributed to high RS content in mutant seeds. These results further reveal the molecular mechanism of RS occurrence in rice endosperm and provide a critical genetic resource for breeding higher RS rice cultivars.

Effects of Low Field Temperature on the Physicochemical Properties and Fine Structure Stability of High-Quality Rice Starch during the Grain Filling Stage

The consumption of high-quality rice is increasing. Low temperatures during grain filling may affect the starch synthesis of high-quality rice and thus affect the quality of the rice itself. In this study, two high-quality conventional rice cultivars and two high-quality hybrid rice cultivars were selected and sown at a low temperature and normal temperature in the field. The low temperature during grain filling increased the amylose content, final viscosity, setback, short amylopectin chain ratio, and degree of amylopectin branching in four high-quality rice cultivars; meanwhile, the amylopectin content, gelatinization temperature, proportion of medium-long chain amylopectin, and the short-range order of starch decreased. Compared with the normal temperature, the alterations in the physicochemical and structural qualities of high-quality conventional rice cultivars YZX and NX42 were less significant at lower temperatures. The starch quality of high-quality conventional rice was more stable than hybrid high-quality rice.

Experimental Warming Increased Cooked Rice Stickiness and Rice Thermal Stability in Three Major Chinese Rice Cropping Systems

Climate warming is a critical environmental issue affecting rice production. However, its effects on cooked rice texture and rice thermal properties remain unstudied in China. To address this gap, we conducted a two-year multi-site field warming experiment using free-air temperature increase facilities across three major Chinese rice cropping systems. Interestingly, warming had a minimal impact on the hardness of cooked rice, while it significantly increased stickiness by an average of 16.3% under warming conditions. Moreover, compared to control treatments, rice flour exhibited a significant increase in gelatinization enthalpy, onset, peak, and conclusion temperatures under warming conditions, with average increments of 8.7%, 1.00 °C, 1.05 °C, and 1.17 °C, respectively. In addition, warming significantly declined the amylose content, remarkedly elevated the protein content and relative crystallinity, and altered the weight distribution of the debranched starch. Correlation analysis revealed significant relationships between cooked rice stickiness, rice flour thermal properties, amylose content, protein content, and partial starch structures. Therefore, warming-induced alterations in rice composition and starch structure collectively enhanced cooked rice stickiness and rice thermal stability.

Relationship between Chalkiness and the Structural and Physicochemical Properties of Rice Starch at Different Nighttime Temperatures during the Early Grain-Filling Stage

The chalkiness, starch fine structure, and physiochemical properties of rice starch were analyzed and their correlations were investigated under different nighttime temperatures during the early grain-filling stage. Compared to MT, medium temperature (MT) and low (LNT) and high (HNT) nighttime temperatures resulted in an increased chalky grain rate (CGR) and chalkiness degree (CD). LNT mainly affected the chalkiness by increasing peak1 (short branch chains of amylopectin), the branching degree, and the proportion of small starch granules but decreasing peak2 (long branch chains of amylopectin) and peak3 (amylose branches). This altered the pasting properties, such as by increasing the peak viscosity and final viscosity. However, HNT mainly affected the chalkiness by increasing peak2 and the crystallinity degree but decreasing peak1 and peak3. Regarding the thermal properties, HNT also elevated peak and conclusion temperatures. The CGR and CD were significantly and positively correlated with the proportions of small and medium starch granules, peak1, branching degree, gelatinization enthalpy, setback viscosity, and pasting time but markedly and negatively correlated with the proportion of large starch granules, amylose content, peak3, peak viscosity, and breakdown viscosity. These findings suggest that LNT and HNT disrupted the starch structure, resulting in increased chalkiness. However, their mechanisms of action differ.

Transformation process and phytotoxicity of sulfamethoxazole and N4-acetyl-sulfamethoxazole in rice

Sulfonamide antibiotics, extensively used in human and veterinary therapy, accumulate in agroecosystem soils through livestock manure and sewage irrigation. However, the interaction between sulfonamides and rice plants remains unclear. This study investigated the transformation behavior and toxicity of sulfamethoxazole (SMX) and its main metabolite, N4-acetyl-sulfamethoxazole (NASMX) in rice. SMX and NASMX were rapidly taken up by roots and translocated acropetally. NASMX showed higher accumulating capacity, with NASMX concentrations up to 20.36 ± 1.98 μg/g (roots) and 5.62 ± 1.17 μg/g (shoots), and with SMX concentrations up to 15.97 ± 2.53 μg/g (roots) and 3.22 ± 0.789 μg/g (shoots). A total of 18 intermediate transformation products of SMX were identified by nontarget screening using Orbitrap-HRMS, revealing pathways such as deamination, hydroxylation, acetylation, formylation, and glycosylation. Notably, NASMX transformed back into SMX in rice, a novel finding. Transcriptomic analysis highlights the involvements of cytochrome P450 (CYP450), acetyltransferase (ACEs) and glycosyltransferases (GTs) in these biotransformation pathways. Moreover, exposure to SMX and NASMX disrupts TCA cycle, amino acid, linoleic acid, nucleotide metabolism, and phenylpropanoid biosynthesis pathways of rice, with NASMX exerting a stronger impact on metabolic networks. These findings elucidate the sulfonamides' metabolism, phytotoxicity mechanisms, and contribute to assessing food safety and human exposure risk amid antibiotic pollution.

Combined effect of heat moisture and ultrasound treatment on the physicochemical, thermal and structural properties of new variety of purple rice starch

The advantages of physically modifying starch are evident: minimal environmental impact, no by-products, and straightforward control. The impact of dual modification on starch properties is contingent upon modification conditions and starch type. Herein, we subjected purple rice starch (PRS) to heat-moisture treatment (HMT, 110 °C, 4 h) with varying moisture content, ultrasound treatment (UT, 50 Hz, 30 min) with different ultrasonic power, and a combination of HMT and UT. Our findings reveal that UT following HMT dispersed starch granules initially aggregated by HMT and resulted in a rougher granule surface. Rheological analysis showcased a synergistic effect of HMT and UT, enhancing the fluidity of PRS and reinforcing its resistance to deformation in paste form. The absorbance ratio R1047/1015 indicates that increased moisture content during HMT and high ultrasound power for UT reduced the short-range order degree (1.69). However, the combined HMT-UT exhibited an increased R1047/1015 (1.38-1.64) compared to HMT alone (1.29-1.45), likely due to short-chain rearrangement. Notably, the A-type structure of PRS remained unaltered, but overall crystallinity significantly decreased (23.01 %-28.56 %), consistent with DSC results. In summary, physical modifications exerted significant effects on PRS, shedding light on the mechanisms governing the transformation of structural properties during HMT-UT.

Long-term straw return improves cooked indica rice texture by altering starch structural, physicochemical properties in South China

Straw return can improve rice eating quality by modifying starch formation from long-term field trials, whereas the relevant mechanisms are still unknown. A long-term field experiment, including straw removal (CK), straw burning return (SBR), and straw return (SR) was conducted to investigate the starch structure, physicochemical properties, and cooked rice textures of indica early- and late-rice. Compared with CK, SBR and SR enhanced relative crystallinity, amylopectin long chains in both rice seasons, and gelatinization temperatures in late rice. Compared to SBR, SR decreased protein content and amylopectin short chains but increased starch branching degree, breakdown, and stickiness, ultimately contributing to improved starch thermal and pasting properties. Meanwhile, SR decreased hardness, cohesiveness, and chewiness, resulting in cooked texture meliorated, which was mainly attributed to amylopectin chain length and starch granule size. The results suggest that SR increased cooked texture of indica rice by altering starch structural and physicochemical properties.

Starch multiscale structure and physicochemical property alterations in high-quality indica rice quality and cooked rice texture under different nitrogen panicle fertilizer applications

The starch multiscale structure, physiochemical properties, grain quality and cooked rice texture of high-quality early and late indica were analyzed under nitrogen panicle fertilizer (low panicle fertilizer, LPF; middle panicle fertilizer, MPF; high panicle fertilizer, HPF) treatments and their internal relations were investigated. Compared to the MPF treatment, the starch granules in HPF and LPF had more surface-proteins and irregular voids for high-quality early and late indica rice cultivars, respectively. Nitrogen panicle fertilization application increased amylopectin medium and long chains as well as protein content, resulting in higher relative crystallinity and gelatinization temperatures. Moderate changes in starch multistructures and physicochemical properties such as branching degree, amylopectin medium chain, and pasting viscosities derived from MPF treatment significantly improved processing, appearance qualities and cooked rice texture. Additionally, the decrease in starch branching, gelatinization temperatures, and granule uniformity along with an increase in large granules, breakdown, and △Hgel under MPF treatment were the main reasons for improving rice textural properties.

Cultivation pattern affects starch structure and physicochemical properties of yam (Dioscorea persimilis)

Yam (Dioscorea spp.) is a major food source in many countries due to its tuber rich in starch (60 %-89 % of the dry weight) and various important micronutrients. Orientation Supergene Cultivation (OSC) pattern is a simple and efficient cultivation mode developed in China in recent years. However, little is known about its effect on yam tuber starch. In this study, the starchy tuber yield, starch structure and physicochemical properties were compared and analyzed in detail between OSC and Traditional Vertical Cultivation (TVC) with Dioscorea persimilis "zhugaoshu", a widely cultivated variety. The results proved that OSC significantly increased tuber yield (23.76 %-31.86 %) and commodity quality (more smooth skin) compared with TVC in three consecutive years of field experiments. Moreover, OSC increased amylopectin content, resistant starch content, granule average diameter and average degree of crystallinity by 2.7 %, 5.8 %, 14.7 % and 9.5 %, respectively, while OSC decreased starch molecular weight (Mw). These traits resulted in starch with lower thermal properties (To, Tp, Tc, ΔH_gel), but higher pasting properties (PV, TV). Our results indicated that cultivation pattern affected the yam production and starch physicochemical properties. It would not only provide a practical basis for OSC promotion, but also provide valuable information on how to guide the yam starch end use in food and non-food industries.

Grain yield and quality performances of different late-season rice cultivars in response to experimental warming in subtropical China

Introduction

Climate warming has pronounced effects on rice production in China. However, late-seasons rice cultivars are diverse in double rice cropping systems, and the actual responses in grain yield and quality of different late-season rice cultivars to climate warming are still unclear.

Methods

A two-year field warming experiment was conducted by using free-air temperature increase facilities with three widely-planted late-season rice cultivars, including Taiyou398 (TY, short growth duration indica hybrid rice), Jiuxiangnian (JXN, long growth duration indica inbred rice), and Yongyou1538 (YY, long growth duration indica-japonica hybrid rice) in a double rice cropping system in subtropical China.

Results

Warming (1.9-2.0°C) had no significant effects on the grain yields of TY and JXN, but significantly decreased that of YY by 4.8% relative to ambient treatment due to a reduction of spikelet number. Compared to ambient treatment, the head rice yields of TY and YY did not change while that of JXN increased by 6.3% under warming conditions. Warming significantly increased the head rice rates of JXN and YY by 6.6% and 7.8%, and the chalky grain rates of TY, JXN, and YY by 79.1%, 21.6%, and 7.6%, respectively. Under warming conditions, the amylose content of JXN and YY decreased significantly by 7.5% and 8.8%, and the setback of three cultivars decreased significantly by an average of 41.5%.

Conclusion

Warming could improve the milling and eating qualities of long growth duration late-season rice (JXN and YY) and increase or maintain their head rice yield, even though decreased the grain yield of indica-japonica hybrid rice (YY). These results will provide a better understanding for the selection of suitable late-season rice cultivars under future climate warming conditions.

Generating waxy rice starch with target type of amylopectin fine structure and gelatinization temperature by waxy gene editing

Waxy rice, which lacks amylose, is an important variant in rice, and its starches have been widely used. New waxy rice varieties generated via the CRISPR/Cas9 gene-editing system is described. Herein, four waxy rice starches with different physicochemical properties were successfully obtained by the CRISPR/Cas9 editing Waxy (Wx) gene. The results showed that the amylose content (AC) of wx mutant starches ranged from 0.26 to 1.78 %, and CZBwx1 starches had the best gel consistency and highest water solubility among all wx mutants. Mutations of Wx^b allele produced more short-chains (degree of chain polymerization (DP) 6-11), and less medium- and long-chains (DP12-70) than that of Wx^a, while the AC of Wx^a allele mutants was higher than the mutations of Wx^b allele. The gelatinization temperature (GT) of wx^a mutant starches was higher than that of wx^b mutant starches. Moreover, we found that the GT and amylopectin fine structure type of waxy rice starch did not change after Wx gene editing. Based on these findings, it is possible to produce waxy rice starch with different physicochemical properties, containing target GT and chain length distributions of amylopectin.

Influence of accelerating storage of foxtail millet on the edible and cooking quality of its porridge: An insight into the structural alteration of the in-situ protein and starch and physicochemical properties

This study aimed to elucidate the effect of the accelerating storage (40 °C, 10 weeks) of foxtail millet on the edible and cooking quality of its porridge. The structural alteration of the in-situ protein and starch in foxtail millet, as well as the physicochemical properties were investigated. Both the homogeneity and palatability of millet porridge were significantly improved after 8-week storage of millet, while its proximate compositions remained unchanged. Meanwhile, the accelerating storage increased the water absorption and swelling of millet by 20 % and 22 %, respectively. The morphological studies (using the SEM, CLSM and TEM) revealed that the starch granules in the stored millet became easier to swell and melt, leading to better gelatinization with a higher coverage extension in protein bodies. FTIR results showed that the protein hydrogen bonds in the stored millet became stronger and the starch ordered degree was reduced. Compared to the native foxtail millet, the peak, trough, final, and setback viscosity of the stored sample increased by 27 %, 76 %, 115 % and 143 %, respectively, while the onset, peak, and conclusion temperature increased by 0.80, 1.10 and 0.80 °C, respectively. Besides, the G' and G″ of the stored foxtail millet were significantly higher than its native counterpart.

Pho1 cooperates with DPE1 to control short maltooligosaccharide mobilization during starch synthesis initiation in rice endosperm

Plastidial α-glucan phosphorylase is a key factor that cooperates with plastidial disproportionating enzyme to control short maltooligosaccharide mobilization during the initiation process of starch molecule synthesis in developing rice endosperm. Storage starch synthesis is essential for grain filling. However, little is known about how cereal endosperm controls starch synthesis initiation. One of core events for starch synthesis initiation is short maltooligosaccharide (MOS) mobilization consisting of long MOS primer production and excess MOS breakdown. By mutant analyses and biochemical investigations, we present here functional identifications of plastidial α-glucan phosphorylase (Pho1) and disproportionating enzyme (DPE1) during starch synthesis initiation in rice (Oryza sativa) endosperm. Pho1 deficiency impaired MOS mobilization, triggering short MOS accumulation and starch synthesis reduction during early seed development. The mutant seeds differed significantly in MOS level and starch content at 15 days after flowering and exhibited diverse endosperm phenotypes during mid-late seed development: ranging from pseudonormal to shrunken (Shr), severely or excessively Shr. The level of DPE1 was almost normal in the PN seeds but significantly reduced in the Shr seeds. Overexpression of DPE1 in pho1 resulted in plump seeds only. DPE1 deficiency had no obvious effects on MOS mobilization. Knockout of DPE1 in pho1 completely blocked MOS mobilization, resulting in severely and excessively Shr seeds only. These findings show that Pho1 cooperates with DPE1 to control short MOS mobilization during starch synthesis initiation in rice endosperm.

Effect of climate warming on the grain quality of early rice in a double-cropped rice field: A 3-year measurement

Introduction

The threat of climate warming to global rice production has been widely addressed, but little is known about its influence on the quality of rice grains.

Methods

A free-air temperature increase (FATI) facility with two widely-planted high-quality cultivars was used to explore the impact of warming on the grain quality of early rice in subtropical China over 3 consecutive years.

Results

Compared with the control, FATI increased diurnal canopy temperature by 1.5°, and thus, rice growth duration was shortened by 4.0 d under warming. We found that warming significantly reduced both the milled rice and head rice rates relative to the control, thereby leading to a decrease in the milled rice and head rice yield by 3.9 and 8.3%, respectively. The chalky grain rate and chalkiness were increased by 19.1 and 22.2% under warming compared with the control, respectively. The content of protein, essential amino acids, and non-essential amino acids were increased by 4.1, 5.4, and 4.9% under warming, respectively. Warming reduced the amylose content and setback by 2.0 and 47.5% but increasing peak viscosity, trough viscosity, breakdown, and final viscosity by 9.5, 13.6, 5.7, and 6.0%, respectively.

Conclusion

Our results suggest that the deteriorated milling and appearance quality induced by warming may be an upcoming challenge for high-quality early rice production in the future.

Low temperature and light combined stress after heading on starch fine structure and physicochemical properties of late-season indica rice with different grain quality in southern China

Late-season indica rice frequently encounters low temperature (LT) along with low light (LL) after heading in southern China, which deteriorates the grain quality by altering starch quality. However, the detailed effects on starch properties of these stressors remain unclear. Herein, two indica rice cultivars with good and poor grain quality were grown under control (CK), LT, and LT + LL conditions after heading and the structural and physicochemical properties of their starch were evaluated. Compared with CK, LT and LT + LL worsened thermal and pasting properties of starch in the two cultivars, mainly because they increased branch chain branching and A chain (DP ≤12), and decreased average branch chain length and crystallinity. Compared with LT, LT + LL deteriorated the pasting properties of the poor-quality cultivar, such as reducing breakdown (BD), final and peak viscosity, which mainly owing to decreasing the starch branching and crystallinity degrees, and increasing the small starch granules (d < 10 μm). Gelatinization enthalpy and BD both had significant and positive correlations with amylose content, the ratio of amylose and amylopectin, B3 chain and crystallinity. Taken together, these results suggest that LT and LT + LL during grain filling can deteriorate the physicochemical properties of starch in late-season indica rice cultivars by disrupting starch multilevel structure, especially upon LT + LL. In particular, while poor-quality cultivar had poorer physicochemical properties, the good-quality cultivar had poorer thermal properties under LT + LL.

The relationship between ecological factors and commercial quality of high-quality foxtail millet "Jingu 21"

The commercial quality of foxtail millet grain (Setaria italica L.) includes appearance quality, functional quality, and cooking and eating quality, which directly determine whether consumers will purchase the product. We studied the relationship between ecological factors and commercial quality attributes of foxtail millet "Jingu 21" from twelve production areas. The results showed that altitude, latitude, and diurnal temperature range were negatively correlated with b*, total flavones content (TFC), setback (SB), consistence (CS) and pasting temperature (PTM), but positively correlated with L/B and breakdown (BD). In contrast, average temperature, average precipitation, average humidity, available nitrogen, phosphorus, and potassium had positive effects on 1,000-grain weight (KGW), b*, TFC, CS, and PTM and had a negative impact on L/B and BD. Climate factors had a greater effect on the commercial quality of foxtail millet than soil factors, and the influence of climatic factors was particularly obvious in the early and middle growth periods. The multivariate equation between ecological factors and the comprehensive score of foxtail millet commercial quality is Y = 1,159.745-4.496X₁ (altitude) + 19.529X₅ (≥10℃ effective accumulated temperature) - 166.327X₁₀ (organic matters). In conclusion, high temperature and precipitation are conducive to high quality appearance and the accumulation of functional substances, while a high diurnal temperature range and high soil nutrients are conducive to the formation of cooking and eating quality. The impact of ecological factors on foxtail millet quality is complicated and it is essential to select a cultivation site that is matched to the intended use of the foxtail millet being produced.

Differences in starch multi-layer structure, pasting, and rice eating quality between fresh rice and 7 years stored rice

With the continuous improvement of rice production capacity and the accumulation of reserves year by year, rice sometimes has to be stored for a long time. However, long-term storage of rice has poor sensory properties, which may be related to the structural changes of starch. Different from the previous studies on short-term storage of rice (often 3–12 months), the focus of this study was to understand the differences in starch multi-layer structure, pasting, and rice eating quality between 7 years stored rice and fresh rice. Our research indicated that 7 years stored rice showed higher hardness and lower stickiness compared to fresh rice, which ultimately led to poorer eating quality. These bad changes were related to differences in starch multi-layer structure. The 7 years stored rice had lower amylose content, a lower thickness of crystalline lamellae and short-range ordered structure of starch, and more large starch granules. In particular, the volume mean diameter of 7 years starch was more than 4 times that of fresh starch. 7 years stored rice had more large granular starch and unstable crystal structure, which led to the increase of pasting temperature and the decrease of gelatinization enthalpy during starch gelatinization, and ultimately reduced the eating quality of the rice.

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7 years stored rice had higher hardness and poorer eating quality.

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Volume mean diameter of 7 years stored starch was 4 times larger than fresh starch.

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7 years stored rice had lower short-range order structure of starch.

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The pasting temperature of 7 years stored starch was higher than fresh starch.

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Higher pasting temperature and lower gelatinization enthalpy reduced the eating quality.