Characterisation of starches separated from sorghum cultivars grown in India

Starches from 15 Indian sorghum cultivars were separated and evaluated for physicochemical, morphological, thermal, retrogradation, pasting and textural properties. The morphological characterisation revealed the presence of irregular-polyhedral as well as spherical shaped granules. A wide variation in amylose content ranging from 11.2% to 28.5% was observed. Thermal, retrogradation, pasting and textural characteristics also showed significant differences amongst all the starch cultivars. Principal component analysis was carried out to extract five principal components that could explain 75% of the total variance. The first two principal components PC1 (T_o, T_p, T_c and ΔH_gel) and PC2 (amylose content, range of gelatinisation, PHI and pasting and textural properties) could explain a cumulative variance of 44%, indicating the importance of amylose, thermal and textural properties on the sorghum starch functionality.     

Effects of high pressure and temperature on the structural and rheological properties of sorghum starch

Pressure-induced gelatinisation of sorghum starch was studied and compared to heat-induced gelatinisation. Starch suspensions were treated at increasing pressure (200–600 MPa) or temperature (60–95 °C) for 10 min. The degree of gelatinisation was determined using differential scanning calorimetry, changes in birefringence and damaged starch measurements. Furthermore, the pasting behaviour and structural changes during gelatinisation were investigated using rheology and microscopy. The pressure-induced as well as the temperature-induced gelatinisation curves were sigmoid-shaped. Gelatinisation occurred between 300 MPa and 600 MPa or between 62 °C and 72 °C. No significant differences were found between the rheological properties and the microstructure of the pressure-treated samples and the temperature-treated samples within the gelatinisation intervals. Granules lost their birefringence, but granular structure was maintained; however, when heated beyond the endpoint of gelatinisation, the formation of a “sponge-like” structure was observed. This change in structure at very high temperatures was reflected by a decrease in complex viscosity.

Industrial relevance

In order to apply high pressure as an alternative to temperature in the structural engineering of starch-based systems, a full understanding of the pressure-induced gelatinisation process is necessary. No rheological and ultra-structural differences were observed between pressure- and temperature-induced gelatinisation of sorghum starch. These results indicate that pressure treatment can be utilised as a replacement technology for temperature during processing of complex starch-containing products.     

Effects of annealing on the physicochemical properties and enzymatic susceptibility of rice starches with different amylose contents

This study investigated the effects of annealing (ANN) on the properties of rice starches with high, medium and low-amylose contents. The starches were heated with excess water at 45 °C, 50 °C and 55 °C for 16 h. The swelling power, solubility, pasting properties, enzymatic susceptibility, morphology and X-ray crystallinity of the starches were evaluated. Annealing reduced the swelling power and solubility of the starches. ANN at 55 °C increased the pasting temperature and decreased the peak viscosity of the high-amylose rice starch. However, annealing decreased the peak viscosity of the low-amylose starch. The annealed rice starches presented a lower final viscosity and setback than did the native starches, with the exception of the low-amylose starch, which showed an increase in setback. Annealing increased the starches’ susceptibilities to α-amylase and promoted a reduction in their relative crystallinity.     

Influence of xyloglucan on gelatinization and retrogradation of tapioca starch

Dynamic and steady shear rheometry and differential scanning calorimetry (DSC) were used to investigate effects of xyloglucan (XG) on gelatinization and retrogradation of tapioca starch (TS). The viscosity of TS/XG pastes immediately after gelatinization increased with increasing XG content at the total polysaccharide concentration of 3.5%. Gelatinized TS alone showed pseudoplastic flow at low shear rates and dilatant behavior at higher shear rates (about >1 s⁻¹), while mixtures with XG did not show dilatancy. Mechanical spectra of TS pastes containing XG were more liquid-like than those of TS pastes without XG. XG provides shear stability to the TS during storage. Increases in dynamic moduli during storage at 5 °C were suppressed in the presence of XG. In contrast, the retrogradation ratio determined based on DSC increased more rapidly in the presence of XG. These results suggest that XG forms a continuous liquid phase in a mixture to impart better mechanical stability during storage but to accelerate re-ordering of starch polysaccharides by effectively reducing the amount of water available for starch.     

机械活化对玉米淀粉的直链淀粉含量及老化特性的影响

采用搅拌球磨机对玉米淀粉进行机械活化，研究了机械活化对玉米淀粉的直链淀粉含量及透光率的影响。并以淀粉糊透光率为评价指标，研究了机械活化与储藏时间对玉米淀粉糊老化特性的影响。结果表明：机械活化对玉米淀粉的直链淀粉及透光率有显著影响，均随活化时间的延长而提高。适度的机械活化有利于玉米淀粉分子的重结晶，淀粉糊的透光率迅速下降，老化加速；而过度的机械活化则不利于淀粉分子的重结晶．淀粉糊透光率下降缓慢。     

Physicochemical characterization of sweet potato starches popularly used in Chinese starch industry

Physicochemical properties of starches isolated from 11 sweet potato cultivars popularly used in Chinese starch industry were studied. Moisture, protein, ash, lipid and phosphorus content of the starches varied from 3.86 to 6.52%, 0.28 to 0.75%, 0.10 to 0.47% and 0.00 to 0.02%, respectively. Amylose content varied between 13.33 and 26.83%. The starches differed in their mean granule sizes, particle size distribution, and susceptibility to pancreatin hydrolysis. Swelling power and solubility ranged from 13.46 to 26.13 g/g and 8.56 to 18.77%, respectively. Higher retrogradation tendency was observed in pastes of starches of high amylose content. Gelatinization temperature and enthalpy ranged from 55.54 to 69.11 °C and 6.40 to 11.89 J/g, respectively. Pasting properties including peak viscosity (134–255 BU), breakdown viscosity (91–162 BU), setback viscosity (26–112 BU), peak time (5.97–7.03 min) and pasting temperature (67.20–73.00 °C) varied significantly among the sweet potato starches. Pearson's correlation analysis showed that phosphorus content of the starches had substantial effect on their swelling power (r = 0.70, p ≤ 0.05) showing positive correlations. There was significant positive correlation between swelling power and solubility of the starches (r = 0.64, p ≤ 0.05). Thermal and pasting parameters also showed significant correlations.     

Retrogradation properties of rice starch gelatinized by heat and high hydrostatic pressure (HHP)

Retrogradation process of pressure-gelatinized rice starches was investigated and compared with the heat-gelatinized ones in this study. Our results showed that the retrogradation rate of normal rice starch gelatinized by high hydrostatic pressure (HHP) was slower than that by heat. Nevertheless, there was no difference in retrogradation rate for waxy rice starch gelatinized by the two treatments (P > 0.05). The DSC data were further analyzed using the Avrami equation. The result indicated that the pressure-gelatinized normal rice starch had a lower recrystallization rate (k) and a higher Avrami exponent (n) than the heat-gelatinized one, but the two treatments did not affect the k and n for waxy rice starch. Furthermore, the intact starch granules and lower amylose leaching were observed only in the pressure-gelatinized normal rice starch. These findings suggest that the retardation mechanism of HHP on starch retrogradation is probably attributed to less broken granules and lower leached amylose.     

Influence of sorghum flour addition on flat bread in vitro starch digestibility,antioxidant capacity and consumer acceptability

Wheat flour (WF) flat bread was prepared with varying levels of wholegrain “white” sorghum flour (WSF) or “red” sorghum flour (RSF). Farinograph dough rheology indicated reduced water absorption and stability time and increased breakdown with increased sorghum flour addition. The total phenolic content and antioxidant capacity of the 40% RSF flat bread >40% WSF flat bread > control (100% WF) flat bread. The rapidly digestible starch (RDS) level was lower in the 40% WSF and 40% RSF flat breads than the control (100% WF). Hedonic sensory evaluation indicated that sorghum addition did not reduce the sensory preference for the flat breads. Human clinical studies are now required to determine if the lower levels of RDS and higher antioxidants observed in the sorghum containing flat breads translate into beneficial low glycemic index and reduced oxidative stress in vivo.     

Properties of retrograded and acetylated starch preparations Part 2. Dynamics of saccharification with amyloglucosidase and rheological properties of resulting pastes and gels

Various procedures have been used to produce preparations of retrograded starch, by subjecting it to acetylation with methods used in the food industry. The resultant starch preparations were evaluated for their degree of acetylation through titration, swelling power and solubility in water at 80 °C, and saccharification dynamics as affected by amyloglucosidase. Rheological properties of pastes and gels of native starch and modified starch preparations were characterized with the use of a sweep temperature test as a dependency of the storage modulus (G′) and loss modulus (G″) on temperature. In addition, flow curves of pastes were plotted and mechanical spectra of gels of the preparations examined were determined. These modifications had a significant effect on the preparations produced. Retrograded and acetylated starch preparations were characterized by greater solubility in water and greater swelling power, and were less susceptible to amyloglucosidase than the non-acetylated preparations. Rheological properties of the pastes and gels were affected by the methods of their production. Acetylation was found to significantly affect a decrease in the storage modulus value during heating. Pastes of the native starch and modified starch preparations were characterized by the non-Newtonian flow, shear thinning with a tendency to yield stress. In turn, the mechanical spectra demonstrated that - in the concentration applied - both native starch and modified starch preparation were forming weak gels.     

Rheological and baking characteristics of batter and bread prepared from pregelatinised cassava starch and sorghum and modified using microbial transglutaminase

The effect of different concentrations (0, 0.5, 1 and 1.5 U/g) of microbial transglutaminase (MTG) on the creep-recovery properties of gluten-free batter prepared from pregelatinised cassava starch, sorghum and egg white was investigated. The test conducted in the rheometer had an instant loading of 80 Pa for 60 s and recovery of 0 Pa for 140 s. Increasing MTG concentration decreased the batters’ resistance to deformation and compliances but increased zero shear viscosity and elastic recovery. Changes in batter rheological properties were insignificant (P > 0.05) at MTG concentrations beyond 0.5 U/g. Crumb properties of gluten-free bread baked from the batter revealed that increasing MTG concentration increased (P < 0.05) crumb firmness and chewiness, whereas increasing incubation time decreased (P < 0.05) crumb cohesiveness, chewiness and resilience. There were no significant interaction effects (P > 0.05) between enzyme concentration and incubation time.     

An assessment of changes in thermal and physico-chemical parameters of jack bean (<Emphasis Type="Italic">Canavalia ensiformis</Emphasis>) starch following hydrothermal modifications

Starch isolated from jack bean was modified by heat moisture treatment (HMT) and annealing. Scanning electron micrograph indicates oval and round shape for the starch granules, with heterogeneous sizes. The range of the granule size for the starches was between 10 and 20 μm for the width and 14 and 32 μm for the length. The starches exhibited the characteristic “C” pattern for legume starches with increased starch crystallinity after modifications. Swelling power and solubility reduced following annealing and heat moisture treatment. The results also revealed that water absorption capacity increased following the heat moisture treatment but reduced after starch annealing. Both annealing and heat moisture treatment improved gelation capacity of the native starch. Gelatinization temperature increased after modifications. Both annealing and heat moisture treatments reduced starch retrogradation.     

Cassava starch functional properties by etherification – hydroxypropylation

Starches are important food biopolymers with gelling properties that are well explored by the food industry for texture and physical food characteristic control. Brazil contributes to a large part of the starches produced world wide, but the modified starches used are imported and expensive. The objective of this work was to develop a hydroxypropylated starch from cassava starch, at a lower price and in conditions in accordance with Brazilian reality. Dihydroxypropylstarch (DHPS) was produced with a less expensive and less harmful substituting molecule, chloropropylene glycol. DHPS physical chemistry properties, retrogradation and micro structural characteristics were studied and compared with native corn, cassava starches and a commercial hydroxypropylated (HPS) cassava starch, with an extensive use in the food industry. DHPS showed the highest values for swelling power and viscosity, low retrogradation and higher freezing–thawing stability, compared with HPS, cassava and native corn starches. The microstructure of DHPS remained unmodified when compared with commercial HPS. Retrogradation and physical chemistry properties are superior to DHPS, which would indicate its use in industrial food production.     

Undercooling associated with slow freezing and its influence on the microstructure and properties of rice starch gels

It is well accepted that high undercooling or supercooling usually produces numerous small ice crystals. This paper shows that if heat transfer is not rapid enough, high undercooling causes non-homogenous sized ice crystals. Three freezing regimes (i.e. fast, slow and slow with undercooling) were used in this study. Fast freezing produced numerous homogeneously small ice crystals embedded in a thin rice starch gel matrix. This microstructure caused low % syneresis and hardness versus slow freezing’s rather homogenous distribution of fewer large ice crystals embedded in a thicker gel matrix resulting in high % syneresis and hardness. However, slow freezing with undercooling produced non-homogenous clusters involving small and large ice crystals embedded in a very thick gel matrix. Starch retrogradation before ice formation played an important role in this frozen structure. The information gained from this study enhances understanding of the behavior of starch-based food during freezing and storage.     

Effect of storage on resistant starch content and in vitro starch digestibility of some pressure‐cooked cereals and legumes commonly used in India

Resistant starch (RS) is that fraction of starch, which escapes enzymic hydrolysis in the small intestine and passes in the colon. Effect of storage time (12 and 24 h) and temperature (4 °C and 25 °C) was studied on RS content of the pressure‐cooked cereal and legume grains/seeds and their flours. RS content was observed to increase in the stored cereals and legumes, with more enhanced increase in the flour samples stored at refrigeration temperature for longer duration (41.4% in wheat flour and 85.4% in pea flour). Significant positive correlations were observed between RS content (4 °C, 24 h) and amylose (y = 0.388 × –5.948, r = 0.840, P ≤ 0.05, n = 7) as well as between % increase in insoluble dietary fibre content (4 °⁰C, 24 h) and amylose (y = 2.257 × –27.724, r = 0.971, P ≤ 0.05, n = 7). Reduced in vitro starch digestibility of the cooked/stored samples (4 °C, 24 h) was observed when compared to freshly cooked samples.     

Properties of retrograded and acetylated starch preparations: Part 1. Structure, susceptibility to amylase, and pasting characteristics

The aim of the study was to produce a retrograded starch preparation from potato starch using various methods, to modify it by acetylation, and then to estimate the effect of these modifications on its selected properties. The chemical structure of modifiers and the degree of substitution achieved with acetic acid were determined by nuclear magnetic resonance (NMR). The resistance of starch to amyloglucosidase and digestive amylases was determined as well. Also, the thermal characteristics of gelatinization of the starch preparations were studied by differential scanning calorimetry (DSC); the method of starch paste production was investigated by a Brabender viscograph, and morphological and structural differences were visualized using scanning electron microscopy (SEM). Retrograded starch preparations were porous and stratified in structure; with their properties resulting from the method of their production. Their chemical structure did not differ from that of native starch, but they displayed a different course of pasting characteristics and increased susceptibility to acetylation as well as resistance to amylases (by approximately 10 g/100 g). Acetylation contributed to a decrease in the temperature of reaching maximum viscosity, an increase in the maximum viscosity, and a decrease in the amount of heat needed for thermal transition of the produced preparations. Acetylated retrograded starch was characterized by a higher degree of substitution and an increased activity of acetyl groups substituted at carbon atoms 2 and 3 compared to the acetylated native starch, thereby triggering a significant increase in resistance to amylases (approximately 40 g/100 g). Combining the resistance of starch samples RS3 and RS4 may be a new method to obtain resistant starch from potato starch.     

Physicochemical properties of Pinhão (Araucaria angustifolia, Bert, O. Ktze) starch phosphates

Physicochemical properties of pinhão (seeds of Paraná pine) starch phosphates were evaluated and compared to corn starch phosphates. The phosphorylation process used yielded starch phosphates with three different degrees of substitution (DS): low (0.015), medium (0.07) and high (?0.12). Medium and high DS starch phosphates had higher cold water binding capacity, swelling power, and paste clarity, but lower paste syneresis (at 5 °C and after freeze-thaw cycles) than native starches (P<0.05). Low, medium, and high DS corn starches had higher solubility than native starches (3.8-, 8-, and 6-fold higher; P<0.05), but the solubility of pinhão starch increased only in medium DS starch phosphates (3-fold higher; P<0.05). Low DS starch phosphates had viscosity curves similar to native starches. In contrast, medium and high DS starch pastes had peak viscosity at room temperature, reached the minimum viscosity when heated to 95 °C, and had low setback.     

Techno‐functional properties of wheat flour‐resistant starch mixtures applied to breadmaking

Resistant starch can be used to reduce the availability of carbohydrates in baked products. In this study, the effect of type 4 resistant wheat starch (RS₄) on wheat flour dough and breads was evaluated. Wheat flour was substituted by RS₄ at 10%, 20% and 30% w/w (RS10, RS20 and RS30, respectively). Rheological and thermal behaviours of dough were evaluated. Besides, bread quality, starch digestibility and bread staling were analysed. All substituted dough exhibited viscoelastic behaviour but lower elastic and viscous moduli. Regarding to bread quality, specific volume and crumb texture were negatively affected in samples with RS₄. However, all samples were technologically acceptable. During storage, crumb hardening was observed in breads without and with RS₄ but amylopectin retrogradation was not particularly affected. The in vitro digestibility of bread with RS showed a lower release of reducing sugars and a lower estimated glycaemic index, suggesting a healthier profile for these breads.     

湿热处理对小麦淀粉结构和性质影响

对小麦淀粉进行湿热处理,研究不同初始含水量对小麦淀粉结构和性能影响。实验结果表明,经湿热处理后小麦淀粉颗粒表面出现凹坑,随初始水分含量增加,淀粉颗粒表面凹坑数量增加,同时粘结现象变得严重;湿热处理小麦淀粉糊化温度随初始含水量增加而升高;经湿热处理后小麦淀粉对酸和酶敏感性增加,更易被酸和酶水解。     

Impacts of acid-methanol treatment and annealing on the enzymatic resistance of corn starches

Normal corn, Hylon V and Hylon VII starches were acid-methanol-treated at 25 °C for 1–30 days in methanol containing 0.36% HCl, and then annealing at 50 °C for 72 h in excess water. The rapid digestible starch (RDS), slow digestible starch (SDS) and resistant starch (RS) contents of starch before and after treatments were determined. The molecular structure, thermal properties, double helix content and relative crystallinity of starch were observed for elucidating the impacts of acid-methanol treatment and annealing, as well as the molecular structure, on the enzymatic resistance of starch. Results showed that the weight-average degree of polymerization of acid-methanol-treated corn starches ranged from 884 × 10³ to 404, 778 × 10³ to 299 and 337 × 10³ to 250 anhydrous glucose units for normal corn, Hylon V and Hylon VII starches, respectively. Annealing increased the RS content of starch, and the increment of RS increased with decreasing molecular size of starch. Furthermore, the change in RS content after treatments depended on the content and weight-average chain length of amylose fraction of starch. The RS content of starch after treatments increased from 19.2 to 56.2%, 69.9 to 86.1%, and 73.1 to 89.1% for normal corn, Hylon V and Hylon VII starches, respectively. The gelatinization peak temperature and double helix content of starch increased after acid-methanol treatment or annealing. Results demonstrate that the degradation of starch, causing by acid-methanol treatment, enhances the mobility and realignment of starch chains in molecules during treatments and further increases the enzymatic resistance of starch granules.