Effects of post-silking low temperature on the physicochemical properties of waxy maize starch

Molecular mechanisms underlying low temperature inhibition of grain filling in maize (Zea mays L.): coordination of growth and cold responses

Low temperature (LT) greatly restricts grain filling in maize (Zea mays L.), but the relevant molecular mechanisms are not fully understood. To better understand the effect of LT on grain development, 17 hybrids were subjected to LT stress in field trials over 3 years, and two hybrids of them with contrasting LT responses were exposed to 30/20°C and 20/10°C for 7 days during grain filling in a greenhouse. At LT, thousand-kernel weight declined, especially in LT-sensitive hybrid FM985, while grain-filling rate was on average about 48% higher in LT-tolerant hybrid DK159 than FM985. LT reduced starch synthesis in kernel mainly by suppression of transcript levels and enzyme activities for sucrose synthase and hexokinase. Brassinolide (BR) was abundant in DK159 kernel, and genes involved in BR and cytokinin signals were inducible by stress. LT downregulated the genes in light-harvesting complex and photosystem I/II subunits, accompanied by reduced photosynthetic rate and Fv/Fm in ear leaf. The LT-tolerant hybrid could maintain a high soluble sugar content and fast interconversion between sucrose and hexose in the stem internode and cob, improving assimilate allocation to kernel at LT stress and paving the way for simultaneous growth and LT stress responses.

Physicochemical properties of starches from sweet potato root tubers grown in natural high and low temperature soils

Three sweet potato varieties grew in natural high temperature (HT) and low temperature (LT) field soils. Their starch physicochemical properties were affected similarly by HT and LT soils. Compared with LT soil, HT soil induced the increases of granule size D[4,3] from 18.0-18.7 to 19.9-21.8 μm and amylopectin average branch-chain length from 21.9-23.1 to 24.1-24.7 DP. Starches from root tubers grown in HT and LT soils exhibited CA- and CC-type XRD pattern, respectively. Starches from root tubers grown in HT soil exhibited stronger lamellar peak intensities (366.8-432.0) and higher gelatinization peak temperature (72.0-76.8 °C) than those (176.2-260.5, 56.4-63.4 °C) in LT soil. Native starches from root tubers grown in LT soil were hydrolyzed more easily (hydrolysis rate coefficient 0.227-0.282 h-1) by amylase than those (0.120-0.163 h-1) in HT soil. The principal component analysis exhibited that starches from root tubers grown in HT and LT soils had significantly different physicochemical properties.

Strategies for starch customization: Agricultural modification

Raw starch is commonly modified to enhance its functionality for industrial applications. There is increasing demand for 'green' modified starches from both end-consumers and producers. It is well known that environmental conditions are key factors that determine plant growth and yield. An increasing number of studies suggest growth conditions can expand affect starch structure and functionality. In this review, we summarized how water, heat, high nitrogen, salinity, shading, CO2 stress affect starch biosynthesis and physicochemical properties. We define these treatments as a fifth type of starch modification method - agricultural modification - in addition to chemical, physical, enzymatic and genetic methods. In general, water stress decreases peak viscosity and gelatinization enthalpy of starch, and high temperature stress increases starch gelatinization enthalpy and temperature. High nitrogen increases total starch content and regulates starch viscosity. Salinity stress mainly regulates starch and amylose content, both of which are genotype-dependent. Shading stress and CO2 stress can both increase starch granule size, but these have different effects on amylose content and amylopectin structure. Compared with other modification methods, agricultural modification has the advantage of operating at a large scale and a low cost and can help meet the ever-rising market of clean-label foods and ingredients.

Physicochemical Properties of Granular and Gelatinized Lotus Rhizome Starch with Varied Proximate Compositions and Structural Characteristics

As a traditional and popular dietary supplement, lotus rhizome starch (LRS) has health benefits for its many nutritional components and is especially suitable for teenagers and seniors. In this paper, the approximate composition, apparent amylose content (AAC), and structural characteristics of five LRS samples from different regions were investigated, and their correlations with the physicochemical properties of granular and gelatinized LRS were revealed. LRS exhibited rod-shaped and ellipsoidal starch granules, with AAC ranging from 26.6% to 31.7%. LRS-3, from Fuzhou, Jiangxi Province, exhibited a deeper hydrogel color and contained more ash, with 302.6 mg/kg iron, and it could reach the pasting temperature of 62.6 °C. In comparison, LRS-5, from Baoshan, Yunnan Province, exhibited smoother granule surface, less fragmentation, and higher AAC, resulting in better swelling power and freeze-thaw stability. The resistant starch contents of LRS-3 and LRS-5 were the lowest (15.3%) and highest (69.7%), respectively. The enzymatic digestion performance of LRS was positively correlated with ash content and short- and long-term ordered structures but negatively correlated with AAC. Furthermore, the color and network firmness of gelatinized LRS was negatively correlated with its ash content, and the retrograde trend and freeze-thaw stability were more closely correlated with AAC and structural characteristics. These results revealed the physicochemical properties of LRS from different regions and suggested their advantages in appropriate applications as a hydrogel matrix.

Starch parameters and short-term temperature fluctuations - Important but not yet in focus?

Plants are regularly challenged by unfavorable environmental conditions. As climate change continues, adverse situations such as drought, heat, and cold are expected to increase and become more severe. Most starchy crops are affected by such stresses. In recent years, researchers have made many new discoveries about starch metabolism in general and also on granule structure, including effects on starch following longer-term temperature stresses. However, in this study, we focus on short-term temperature stress on storage starch granule properties. Here our knowledge is less and it is likely that also short-term temperature stresses can affect various starch parameters. Therefore, we see a need for this type of analysis and discuss the matter in more detail and we conclude that a deeper knowledge particularly of starch granule parameters could allow targeted breeding of cultivars that exhibit different starch characteristics as a result of short-term stress. For these reasons, we are convinced that more comprehensive research on the effects of short-term temperature stress on starch granule characteristics is important, necessary, and timely.

Starch structural and functional properties of waxy maize under different temperature regimes at grain formation stage

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Excessive high temperature (>35 °C) enlarges and corrodes the starch granules.

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Heat stress increases the proportion of amylopectin long chains.

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Extremely high temperature induces the lowest pasting viscosity and the highest retrogradation of starch.

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This study provides scientific basis for the deterioration of waxy maize starch under severe high temperature.

Global warming affects crop productivity, but the influence is uncertain under different temperature regimes. The impact of growth temperatures (T0, 28 °C/20 °C; T1, 32 °C/24 °C; T2, 36 °C/28 °C; T3, 40 °C/32 °C) at grain formation stage on the waxy maize starch physicochemical properties of Suyunuo5 (heat-sensitive hybrid) and Yunuo7 (heat-tolerant hybrid) was studied. Compared with T0, T2 and T3 resulted in a higher number of starch granules with more pitted or uneven surface due to the enhanced enzymatic activities of α-amylase and β-amylase. Meanwhile, large starch granule size, long amylopectin chain-length, and high relative crystallinity under T2 and T3 resulted in low pasting viscosities and gelatinization enthalpy and high retrogradation percentage, especially under T3. The low coefficient variation of gelatinization temperatures indicated that the differences were meaninglessness. The influence of T1 on the pasting viscosities were more obvious in Suyunuo5. In conclusion, high temperatures at grain formation stage deteriorated the starch pasting and retrogradation properties.