Relations between chain-length distribution, molecular size, and amylose content of rice starches

Insight to starch retrogradation through fine structure models: A review

The retrogradation of starch is crucial for the texture and nutritional value of starchy foods products. There is mounting evidence highlighting the significant impact of starch's fine structures on starch retrogradation. Because of the complexity of starch fine structure, it is a formidable challenge to study the structure-property relationship of starch retrogradation. Several models have been proposed over the years to facilitate understanding of starch structure. In this review, from the perspective of starch models, the intricate structure-property relationship is sorted into the correlation between different types of structural parameters and starch retrogradation performance. Amylopectin B chains with DP 24-36 and DP ≥36 exhibit a higher tendency to form ordered crystalline structures, which promotes starch retrogradation. The chains with DP 6-12 mainly inhibit starch retrogradation. Based on the building block backbone model, a longer inter-block chain length (IB-CL) enhances the realignment and reordering of starch. The mathematical parameterization model reveals a positive correlation between amylopectin medium chains, amylose short chains, and amylose long chains with starch retrogradation. The review is structured according to starch models; this contributes to a clear and comprehensive elucidation of the structure-property relationship, thereby providing valuable references for the selection and utilization of starch.

Investigating the evolution of the fine structure in cassava starch during growth and its correlation with gelatinization performance

The evolution of the starch fine structure during growth and its impact on the gelatinization behavior of cassava starch (CS) was investigated by isolating starch from South China 6068 (SC6068) cassava harvested from the 4th to 9th growth period. During growth, the short-range ordered structure, crystallinity as well as particle size distribution of starch were increased. Meanwhile, the starch molecular size and amylopectin (AP) proportion increased, while the proportion of amylose (AM) exhibited a decreasing tendency. The chains of short-AM (X ~ 100-1000) were mainly significantly reduced, whereas the short and medium-AP chains (X ~ 6-24) had the most increment in AP. The solubility, thermal stability, shear resistance, and retrogradation resistance of starch were enhanced after gelatinized under the influence of the results mentioned above. This study presented a deeper insight into the variation of starch fine structure during growth and its influence on gelatinization behavior, which would provide a theoretical basis for starch industrial applications.

Impact of starch chain length distributions on physicochemical properties and digestibility of starches

Changing starch structure at different levels is a promising approach to promote desirable metabolic responses. Chain length distribution (CLD) is among the starch structural characteristics having a potential to determine properties of starch-based products. Therefore, the objective of the current review is to summarize recent findings on CLD and its impact on physicochemical properties and digestion. Investigations undertaken to enhance understanding of starch structure have shown clearly that CLD is a significant determining factor in modulating starch digestibility. Enzymatic modifications and processing treatments alter the CLD of starch, which in turn affects the rate of digestion, but the underlying molecular mechanisms have yet to be fully elucidated. Even though advances have been made in manipulating CLD using different methods and to correlate the changes with various functional properties, in general the area needs further investigations to open new awareness for enhancing healthiness of starchy foods.

Isolation and characterization of natural nano starch from amaranth starch

Nano starch exhibits many advantages for application in diverse fields. Amaranth starch consisted of starch particle aggregates, isolated amaranth starch, and few natural nano starch (NNS), while NNS (0.92 ± 0.12 μm) was successfully isolated for the first time. Compared with the isolated amaranth starch, NNS showed smaller particle size but larger molecular weight, suggesting that the molecules arranged densely. NNS had a weak A-type crystal structure because of its more content of short starch chains, but higher amylose content resulted in the increase of its gelatinization temperature. The special NNS, owning several different physicochemical properties from amaranth starch, can open new ways for the production and application of nano biomass materials.

Exploration of unique starch physicochemical properties of novel buckwheat lines created by crossing Golden buckwheat and Tatary buckwheat

Buckwheat is considered as a healthy cereal food, and it is essential to cultivate new buckwheat lines with good starch physicochemical properties for both consumers and food producers. Six novel buckwheat (Duoku, Dk) were generated by crossing of Golden buckwheat and Tatary buckwheat, and their kernel appearance properties and starch physicochemical properties were analyzed together with one domestic line (Cimiqiao) and one wild line (Yeku). The results showed that Dk samples had better appearance properties than two control samples. The Dk samples showed lower amylose content, similar amylopectin molecular structure and chain length distributions, and larger starch granules compared with Cimiqiao. The digestion results showed that two Dk samples: Dk6 & Dk9 had high resistant starch content; while the other two Dk samples: Dk37 & Dk38 had a steady glucose releasing rate. The Dk samples also showed high gelatinization temperature, indicating they were good raw materials for producing glass noodle. This study proved that Dk buckwheat had unique starch physicochemical properties, and could be used as new food materials in the future.

Development and characterization of novel packaging films from composite mixtures of rice-starch, tara gum and pectin

Biodegradable films intend to replace polymers derived from petroleum. The effect of pectin and Tara gum on the properties of films prepared with rice starch and glycerol was studied in this context. FTIR analysis determined the presence of complex interactions between the components. SEM showed regular film surface with minor roughness. The evaluation of mechanical properties of the films proved the importance of pectin, Tara gum and glycerol concentration. When the proportion of pectin to Tara gum was 1:1, the tension at break, the elongation and the solubility reached the highest values while the water vapor permeability dropped to a minimum. Statistical analysis demonstrated non-linear behavior between composition and properties of the films and stated the importance of interactions between the components. Films produced from rice starch and glycerol in combination with pectin and Tara gum present competitive properties in terms of elongation, tensile stress, permeability to water vapor and solubility, displaying a uniform structure suitable for the packaging of food materials.

The textural properties of cooked convenience rice upon repeated freeze-thaw treatments are largely affected by water mobility at grain level

Brown rice (BR) is a promising source for convenience rice that are mostly stored frozen. However, freezing and thawing may cause deterioration in rice texture quality. To investigate how rice texture is influenced by freeze-thaw cycles, BR, the pretreated BR with partially ruptured bran layer (UER) and white rice (WR) were cooked and treated with repeated freeze-thaw cycles, with their textural properties, variations in moisture distribution and starch structure being measured. Results showed that the repeated freeze-thaw treatment induced a progressive reduction in hardness and stickiness of all cooked rice. The reduced hardness of rice could be explained by the enlarged pore size of starch inside rice under scanning electron microscopy. Moisture migration in WR was the fastest responding to multiply freeze-thaw cycles, followed by UER, while water mobility in BR was slowest. Moreover, WR, BR and UER resulted in a similar extent of amylopectin retrogradation and chains length distribution after repeated freeze-thaw cycles. It indicated similar and minor effect of starch variations on determining the texture of different rice samples against freeze-thawing. Water mobility tended to be a main factor leading to the textural difference of fully gelatinized rice samples. This study focused on the relationship between water distribution and starch retrogradation, providing a better understanding on influences of multiple freeze-thawing on textural quality of cooked rice maintaining different extents of surface layer.

Multi-Scale Structures and Functional Properties of Quinoa Starch Extracted by Alkali, Wet-Milling, and Enzymatic Methods

The purpose of this study is to investigate the effects of starch extraction methods (alkali, wet-milling, and enzymatic) on the multi-scale structures and functional properties of quinoa starch. When the enzymatic method was compared with alkali and wet-milling, it showed higher protein content (2.39%), larger size of aggregated granules (44.1 μm), higher relative crystallinity (29.6%), scattering intensity (17.8 α.u.), absorbance ratio of 1047/1022 (0.9), single and double helical content (8.2% and 23.1%), FWHM ratio (2.1), and average molecular weight and radius of gyration (1.58 × 107 g/mol and 106.8 nm), respectively. Similarly, quinoa starch by enzymatic extraction had a higher onset (82.1 °C), peak (83.8 °C), and conclusion (86.3 °C) temperatures, as well as an enthalpy change (6.7 J/g). It further showed maximum hardness (238.8 N), gumminess (105.6 N), chewiness (80.2 N), SDS content (7.5% of raw and 4.8% of cooked), and RS content (15.5% of raw and 13.9% of cooked), whereas it contained minimum RDS content (77.1% of raw and 81.9% of cooked). The results suggest that extraction of starch by the enzymatic method could be a viable approach to retain the native structure of starch and may eventually improve the glycemic response.

Integrated Starches and Physicochemical Characterization of Sorghum Cultivars for an Efficient and Sustainable Intercropping Model

Sorghum has good adaptation to drought tolerance and can be successfully cultivated on marginal lands with low input cost. Starch is used in many foods and nonfood industrial applications and as a renewable energy resource. Sorghum starches with different amylose contents affect the different physicochemical properties. In this study, we isolated starches from six sorghum varieties (i.e., Jinza 34, Liaoza 19, Jinnuo 3, Jiza 127, Jiniang 2, and Jiaxian) and investigated them in terms of their chemical compositions and physicochemical properties. All the starch granules had regular polygonal round shapes and showed the characteristic “Maltese cross”. These six sorghum starches showed an A-type diffraction pattern. The highest amylose content of starch in Jinza 127 was 26.90%. Jiaxian had a higher water solubility at 30, 70, and 90 °C. From the flow cytometry analysis based on six sorghum starch granules, Liaoza 19 had a larger and more complex granules (particle percentage (P1) = 66.5%). The Jinza 34 starch had higher peak (4994.00 mPa∙s) and breakdown viscosity (4013.50 mPa∙s) and lower trough viscosity (973.50 mPa∙s). Jinnuo 3 had higher onset temperature, peak temperature, conclusion temperature, gelatinization enthalpy, and gelatinization range. The principal component analysis and hierarchical cluster analysis based on classification of different sorghum starches showed that Jiniang 2 and Jinnuo 3 had similar physicochemical properties and most divergent starches, respectively. Our result provides useful information not only on the use of sorghum starches in food and non-food industries but for the great potential of sorghum-based intercropping systems in maintaining agricultural sustainability.

Salt tolerance at vegetative stage is partially associated with changes in grain quality and starch physicochemical properties of rice exposed to salinity stress at reproductive stage

BACKGROUND

Rice yield and grain quality are highly sensitive to soil salinity. Distinct rice genotypes respond to salinity stress differently. To explore the variation in grain yield and grain trait adaptation to moderate, reproductive-stage salinity stress (4 dS/m electrical conductivity), four rice cultivars differing in degrees of vegetative salt tolerance, including Pokkali (salt-tolerant), RD15 (moderately salt-tolerant), KDML105 (moderately salt-susceptible) and IR29 (salt-susceptible), were examined.

RESULTS

Grain fertility and 100-grain weight of RD15, KDML105 and IR29, as well as grain morphology of KDML105 and IR29, were significantly disturbed. Interestingly, grain starch accumulation in RD15 and KDML105 was enhanced under stress. However, only RD15 showed changes in starch physicochemical properties, including increased granule diameter, decreased gelatinization peak temperature (T_p ) and decreased retrogradation onset temperature (T_o ). Notably, Pokkali maintained productivity, grain quality, and starch properties, while the grain quality of IR29 remained unchanged under salinity stress. Multivariate analysis displayed clear separation of productivity, grain morphology, and starch variables of RD15 in the salt-treated group relative to the control group, suggesting that it was the cultivar most impacted by salt stress despite its moderate salt-tolerance at vegetative stage.

CONCLUSION

Our results demonstrate specific salinity responses among the rice genotypes, and suggest discrepancies between degrees of salt tolerance at vegetative stage versus the ability to maintain both grain quality and starch properties in response to salinity stress imposed at reproductive stage. © 2021 Society of Chemical Industry.

Effects of Processing on Starch Structure, Textural, and Digestive Property of "Horisenbada", a Traditional Mongolian Food

Horisenbada, prepared by the soaking, steaming, and baking of millets, is a traditional Mongolian food and is characterized by its long shelf life, convenience, and nutrition. In this study, the effect of processing on the starch structure, textural, and digestive property of millets was investigated. Compared to the soaking treatment, steaming and baking significantly reduced the molecular size and crystallinity of the millet starch, while baking increased the proportion of long amylose chains, partially destroyed starch granules, and formed a closely packed granular structure. Soaking and steaming significantly reduced the hardness of the millets, while the hardness of baked millets is comparable to that of raw millet grains. By fitting digestive curves with a first-order model and logarithm of the slope (LOS) plot, it showed that the baking treatment significantly reduced the digestibility of millets, the steaming treatment increased the digestibility of millets, while the soaked millets displayed a similar digestive property with raw millets, in terms of both digestion rate and digestion degree. This study could improve the understanding of the effects of processing on the palatability and health benefits of Horisenbada.

Starch molecular fine structure is associated with protein composition in chickpea seed

Chickpea (Cicer arietinum L.) seed is a nutritional food high in starch and protein. This study aims to find the relationships between the molecular fine structure of starch and the composition of storage proteins and metabolic enzymes, using different chickpea varieties. It is found that storage proteins and starch biosynthetic enzymes influence each other. The initial formation of amylopectin molecules is affected by storage proteins, as suggested by the positive correlation (p < 0.01) between the average molecular size of amylopectin and total protein content. In addition, a higher amount of seed globulin could be an indication of higher amylose content and more short - medium amylose chains (degree of polymerization, DP, 118-2000). This study might assist selection of chickpea varieties with desirable qualities, such as low starch digestibility.

Starch gelatinization in the surface layer of rice grains is crucial in reducing the stickiness of parboiled rice

Parboiled rice has high nutritional value but unpleasant palatability. In this study, rice stickiness was significantly reduced by steaming during the parboiling process; however, continuing steaming past certain durations no longer affected rice stickiness. It was also found: (i) the degree of starch gelatinization (DSG) increases and starch crystallinity decreases with increasing steaming time; (ii) the molecular size and chain length distribution (CLD) of leached starch for both white and parboiled rice are significantly different from those of native starch; (iii) the relation between leached amylopectin amount and rice stickiness explains the reduced stickiness by parboiling; and (iv) starch gelatinization in the surface layer of rice grains during parboiling might be critically important in blocking starch leaching, consequently leading to a less sticky texture. This study supplies a way to manage glutinous rice stickiness by parboiling for the production of non-sticky rice foods.

Starch modification through environmentally friendly alternatives: a review

Starch is a versatile and a widely used ingredient, with applications in many industries including adhesive and binding, paper making, corrugating, construction, paints and coatings, chemical, pharmaceutical, textiles, oilfield, food and feed. However, native starches present limited applications, which impairs their industrial use. Consequently, starch is commonly modified to achieve desired properties. Chemical treatments are the most exploited to bring new functionalities to starch. However, those treatments can be harmful to the environment and can also bring risks to the human health, limiting their applications. In this scenario, there is a search for techniques that are both environmentally friendly and efficient, bringing new desired functionalities to starches. Therefore, this review presents an up-to-date overview of the available literature data regarding the use of environmentally friendly treatments for starch modification. Among them, we highlighted an innovative chemical treatment (ozone) and different physical treatments, as the modern pulsed electric field (PEF), the emerging ultrasound (US) technology, and two other treatments based on heating (dry heating treatment - DHT, and heat moisture treatment - HMT). It was observed that these environmentally friendly technologies have potential to be used for starch modification, since they create materials with desirable functionalities with the advantage of being categorized as clean label ingredients.

The increased stickiness of non-glutinous rice by alkali soaking and its molecular causes

Non-glutinous rice is always less sticky than glutinous rice. By soaking two non-glutinous rice (Jingmi and Xianmi) with different concentrations of NaOH solution, the stickiness of cooked non-glutinous rice is significantly increased, which is closely associated with the removal of surface proteins of these treated rice grains. By investigating starch leaching characteristics and the molecular structure of leached starch, we find: (i) total solids and amylopectin amount in the leached materials increase by raising NaOH concentration; (ii) the molecular size and chain-length distributions (CLDs) of leached starch significantly differ between samples with different soaking treatments; (iii) a strong correlation between stickiness of cooked rice and total amount of leached amylopectin is established. (iv) molecular causes for the increased stickiness of alkali-soaked rice are put forward to explain the above observations. This study could broaden the applications of non-glutinous rice by altering its stickiness attribute with alkali soaking.

Physicochemical Properties of Starches in Proso (Non-Waxy and Waxy) and Foxtail Millets (Non-Waxy and Waxy)

Proso and foxtail millets are widely cultivated due to their excellent resistance to biotic and abiotic stresses and high nutritional value. Starch is the most important component of millet kernels. Starches with different amylose contents have different physicochemical properties. In this study, starches in proso (non-waxy and waxy) and foxtail millets (non-waxy and waxy) were isolated and investigated. All the starch granules had regular polygonal round shapes and exhibited typical “Maltese crosses”. These four starches all showed bimodal size distribution. The waxy proso and foxtail millets had higher weight-average molar mass and branching degree and lower average chain length of amylopectin. These four starches all presented A-type crystallinity; however, the relative crystallinity of waxy proso and foxtail millets was higher. The two waxy millets had higher onset temperature, peak temperature, conclusion temperature, and gelatinization enthalpy. However, the two non-waxy millets had higher setback viscosity, peak time, and pasting temperature. The significantly different physicochemical properties of waxy and non-waxy millet starches resulted in their different functional properties.

Molecular causes for the effect of cooking methods on rice stickiness: A mechanism explanation from the view of starch leaching

Microwave, electronic pressure cooking (EPC), and water absorption method are the common but different ways used for cooking rice. To explore mechanisms for effects of cooking methods on rice stickiness, starch leaching behaviour and the fine structure of leached starch are investigated. We find: (i) EPC improves starch leaching, i.e. the highest amount for total solids and leached amylopectin (AP), while microwave restricts starch leaching; (ii) the chain-length distributions (CLDs) of leached AP between rice samples are similar while CLDs of leached amylose (AM) are mainly ranged between degree of polymerization (DP) 100 and 1000; (iii) microwave makes rice leaching more long-AM chains with DP 1000-10,000; (iv) the varied stickiness of differently cooked rice are mainly caused by total amount of leached materials, especially leached AP, rather than the molecular structure of leached starch. This mechanism explanation provides better view towards helping consumers improve cooking and eating quality of cooked rice.