Microstructural and physicochemical properties of heat-moisture treated waxy and normal starches

Starches from normal rice (21.72% amylose), waxy rice (1.64% amylose), normal corn (25.19% amylose), waxy corn (2.06% amylose), normal potato (28.97% amylose) and waxy potato (3.92% amylose) were heat-treated at 100 °C for 16 h at a moisture content of 25%. The effect of heat-moisture treatment (HMT) on morphology, structure, and physicochemical properties of those starches was investigated. The HMT did not change the size, shape, and surface characteristics of corn and potato starch granules, while surface change/partial gelatinization was found on the granules of rice starches. The X-ray diffraction pattern of normal and waxy potato starches was shifted from B- to C-type by HMT. The crystallinity of the starch samples, except waxy potato starch decreased on HMT. The viscosity profiles changed significantly with HMT. The treated starches, except the waxy potato starch, had higher pasting temperature and lower viscosity. The differences in viscosity values before and after HMT were more pronounced in normal starches than in waxy starches, whereas changes in the pasting temperature showed the reverse (waxy > normal). Shifts of the gelatinization temperature to higher values and gelatinization enthalpy to lower values as well as biphasic endotherms were found in treated starches. HMT increased enzyme digestibility of treated starches (except waxy corn starch); i.e., rapidly and slowly digestible starches increased, but resistant starch decreased. Although there was no absolute consistency on the data obtained from the three pairs of waxy and normal starches, in most cases the effects of HMT on normal starches were more pronounced than the corresponding waxy starches.     

Influence of moisture content on the degradation of waxy and normal corn starches acid-treated in methanol

Waxy and normal corn starches with different moisture contents, 5.1-16.9% and 4.8-15.9%, respectively, were prepared and treated in methanol containing 0.36% HCl at 45 °C for 1 h. Recovery of all the treated starches was found to be above 90%. Peak viscosity, gelatinization temperature and enthalpy change of gelatinization of waxy and normal corn starches decreased after treatment and this decrement was found to be more in treated starches having lower initial moisture content. The weight-average degree of polymerization and chain length (CL) of waxy and normal corn starches decreased upon acid-methanol treatment. The decrement ratio of molecular weight of modified starches was found to be negatively correlated with the initial moisture content of the starches. The decrement ratio of normal corn starch was higher than waxy corn starch with similar moisture content of starch. The content and CL of long chain fraction of amylopectin for waxy corn starch slightly decreased after treatment, while no obvious trend was found among starches with different moisture contents. CL of amylose for acid-methanol-treated normal corn starch decreased and this change was found to be higher in starches with lower initial moisture contents. Results demonstrated that the initial moisture content of starch granules strongly influenced the functional properties and degradation of starch treated by acid in methanol.     

Structures and Physicochemical Properties of Acid‐Thinned Corn,Potato and Rice Starches

The structures and physicochemical properties of acid‐thinned corn, potato, and rice starches were investigated. Corn, potato, and rice starches were hydrolyzed with 0.14 N hydrochloric acid at 50 °C until reaching a target pasting peak of 200—300 Brabender Units (BU) at 10% solids in the Brabender Visco Amylograph. After acid modification the amylose content decreased slightly and all starches retained their native crystallinity pattern. Acid primarily attacked the amorphous regions within the starch granule and both amylose and amylopectin were hydrolyzed simultaneously by acid. Acid modification decreased the longer chain fraction and increased the shorter chain fraction of corn and rice starches but increased the longer chain fraction and decreased the shorter chain fraction of potato starch, as measured by high‐performance size‐exclusion chromatography. Acid‐thinned potato starches produced much firmer gels than did acid‐thinned corn and rice starches, possibly due to potato starch's relatively higher percentage of long branch chains (degree of polymerization 13—24) in amylopectin. The short‐term development of gel structure by acid‐thinned starches was dependent on amylose content, whereas the long‐term gel strength appeared dependend on the long branch chains in amylopectin.     

Amylopectin: Structural, gelatinisation and retrogradation studies

Amaranth, waxy corn, and commercial corn amylopectins were enzymically debranched and their fractions separated by gel filtration. In all cases a bimodal distribution of chain lengths was found, containing a high proportion of short chains. Amaranth, waxy corn starches and commercial corn amylopectin displayed an A-type X-ray diffraction pattern, which is characteristic of cereal starches, whereas amaranth amylopectin did not show a well-defined pattern, suggesting that the former samples have granular structure. Gelatinisation and retrogradation data, by differential scanning calorimetry, showed a good agreement between starches and amylopectins of the same source. Amaranth starch and its amylopectin presented a lower tendency to undergo these changes compared to the remaining tested materials. The temperature effiect on retrogradation was more drastic for amaranth and waxy corn amylopectins.     

Effects of Solutes on Retrogradation of Stored Starches and Amylopectins: A Calorimetric Study

Starch and amylopectins from different sources were studied to know their calorimetric behavior when mixed with sucrose, glucose and sodium chloride to different concentrations, and stored to different times. It was found that for control samples of amaranth, waxy and normal corn starches slight changes in enthalpy values were observed. The three starches presented retrogradation endotherms, in the presence of sugars, after 2 storage weeks with low enthalpy values; these values tended to be higher by decreasing sugar concentration. The effect of sodium chloride on starch retrogadation was different to that of sugars; waxy corn starch did not show enthalpy values at all experimental conditions. theories on retarding effect of sugars have been proposed but the effect of salt on retrogradation until now is difficult to explain. Amylopectin in the presence of sucrose showed retrogradation endotherms after 3 storage weeks and with glucose after 4 weeks, except potato amylopectin which did not exhibit this trend at any tested condition. With sodium chloride all amylopectins presented retrogradation endotherms after 4 weeks. The different behavior of amylopectins with solutes could be explained by the different chain distribution in such macromolecules.     

Digestibility and Pasting Properties of Rice Starch Heat‐Moisture Treated at the Melting Temperature (Tm )

Non‐waxy and waxy rice starches adjusted to 20% moisture (wet based, w.b.) were heated in a differential scanning calorimeter to determine the optimum parameters for producing slowly digestible starch (SDS). Starches heated to the temperature of melting (T_m) and held for 60 min in the calorimeter showed a slow digestibility compared to unheated samples. Digestibility decreased by 25 and 10%, respectively, for non‐waxy and waxy rice starches relative to non‐treated starches. Heat‐moisture treatment of waxy corn, non‐waxy corn and wheat starches at the T_m determined for non‐waxy rice starch did not result in significant decreases in digestibility. For waxy rice starches heat‐treated in microwave or conventional ovens at the T_m , there were slight but significant increases in digestibility of the treated starches compared to non‐treated starches at all incubation times. Digestibility was higher for starches heated for 30 min than for 60 min. Non‐waxy rice starches did not show any significant changes in digestibility. Heat‐moisture treatment at the T_m and the holding time of sample at that temperature in a differential scanning calorimeter were found to be significant to the formation of slowly digestible heat‐moisture treated starch.     

Slowly digestible starch from heat-moisture treated waxy potato starch: Preparation,structural characteristics,and glucose response in mice

Heat-moisture treatment (HMT) was optimised to increase the formation of slowly digestible starch (SDS) in waxy potato starch, and the structural and physiological properties of this starch were investigated. A maximum SDS content (41.8%) consistent with the expected value (40.1%) was obtained after 5 h 20 min at 120 °C with a 25.7% moisture level. Differential scanning calorimetry of HMT starches showed a broadened gelatinization temperature range and a shift in endothermal transition toward higher temperatures. After HMT, relative crystallinity decreased with increasing moisture level and X-ray diffraction patterns changed from B-type to a combination of B- and A-types. Hollow regions were found in the centres of HMT waxy potato starches. HMT intensity significantly influenced SDS level. This study showed that HMT-induced structural changes in waxy potato starch significantly affected its digestibility and the blood glucose levels of mice who consumed it.     

Resistant starch and thermal,morphological and textural properties of heat‐moisture treated rice starches with high‐, medium‐ and low‐amylose content

This study investigated the effects of heat‐moisture treatment (HMT) on the resistant starch content and thermal, morphological, and textural properties of rice starches with high‐, medium‐ and low‐amylose content. The starches were adjusted to 15, 20 and 25% moisture levels and heated at 110°C for 1 h. The HMT increased the resistant starch content in all of the rice starches. HMT increased the onset temperature and the gelatinisation temperature range (T_finish–T_onset) and decreased the enthalpy of gelatinisation of rice starches with different amylose contents. This reduction increased with the increase in the moisture content of HMT. The morphology of rice starch granules was altered with the HMT; the granules presented more agglomerated surface. The HMT affected the textural parameters of rice starches; the high‐ and low‐amylose rice starches subjected to 15 and 20% HMT possessed higher gel hardness.     

Glycerol-enhancing heat-moisture treatment of A-type rice and cassava starches and B-type potato and canna starches

Effects of glycerol on the heat-moisture treatment (HMT) of A-type rice and cassava starches and B-type potato and canna starches were investigated. Starch samples were soaked in water or glycerol solution, adjusted to 25% moisture, and then subjected to HMT at 100 °C for 1, 6, and 16 h. Pasting profiles of all four starches plasticised with water clearly showed the B-type potato and canna starches were more susceptible to HMT than the A-type rice and cassava starches. The effect of HMT on the pasting properties of glycerol-plasticised samples was inconclusive; the B-type canna and A-type cassava starches were altered, but not the B-type potato and A-type rice starches, which remained comparable to the water-plasticised samples. Thus, the type of plasticiser as well as the environment surrounding the crystalline region, which is specific to each starch type, also affect the alteration of starch during HMT.     

Starch and Amylopectin - Effects of Solutes on Clarity of Pastes

The effect of sucrose, glucose and sodium chloride at different concentrations on clarity of starch and amylopectin pastes was studied. It was found that clarity of amaranth, waxy corn and normal corn starch pastes tended to increase by increasing carbohydrate concentrations. The percentage of transmittance (%T) values for the same starch sample with sucrose and glucose did not present significantly differences (α=0.05). The starches with sodium chloride did not show a defined pattern. The %T for amaranth and waxy corn amylopectin pastes with all solutes tended to increase by increasing solute concentration. Interestingly, the %T values among all amylopectins at a given solute concentration were significantly different (α=0.05) probably due to different chain length proportion in such amylopectins. The same amylopectin in presence of sucrose and glucose did not show %T significantly different (α=0.05) but with sodium chloride those values were different (α=0.05).     

The Fine Structure of Corn Starches of Various Amylose-Percentage: Waxy,Normal and Amylomaize

The fine structure of high-amylose corn starches has been studied after dispersion of the starch and fractionation into their components amylose and amylopectin. The resulting amylopectin fraction reported in the literature possesses anomalous properties with regard to the waxy and normal amylopectin. However, the experimental results obtained by different authors for determining the structure lead to controversal explanations. Therefore, using an enzymic method, which permits the direct examination of the constitutive chains of the starch, the fine structure of the amylopectin of an amylomaize starch (64% amylose) has been investigated and compared with those of waxy and normal starches. The pullulanase – debranched chains are fractionated by gel permeation and their linearity are checked under the action of β-amylase. The inner chains of the amylopectin fraction are studied after debranching of the β-limit dextrins. The results show the identity between amylopectins from waxy and normal starches. The amylopectin fraction of amylomaize has its own structure with longer inner chains than those of waxy-maize amylopectin.     

Effect of cooking time and ingredients on the performance of different starches in white sauces

The effect of white sauce ingredients and increased cooking time at 90 °C on the degree of gelatinization of corn, waxy corn, rice, potato and modified waxy corn starches was studied. The changes in pasting properties, linear viscoelastic properties, and microstructure were determined. In all the native starches in water, a longer cooking time at 90 °C caused greater starch granule swelling and more leaching of solubilized starch polymers into the intergranular space. These effects were more noticeable in the waxy corn and potato starches. The potato starch was the most affected, with complete disruption of the starch granules after 300 s at 90 °C. The microstructural changes which transformed a system characterized by starch granules dispersed in a continuous phase (amylose/amylopectin matrix) into a system with an increase in the continuous phase and a decrease in starch granules were associated with a decrease in system viscoelasticity. The elastic moduli were higher in the sauce than in the starch in water system. However, with the exception of potato starch, the white sauce showed lower viscoelasticity than the starch in water system. The white sauce ingredients decreased the effect of cooking time on the starch gelatinization process, particularly in potato starch.     

Impact of structural changes due to heat-moisture treatment at different temperatures on the susceptibility of normal and waxy potato starches towards hydrolysis by porcine pancreatic alpha amylase

The objectives of this study were to determine the impact of structural changes within the amorphous and crystalline domains of normal potato (NP) and waxy potato (WP) starches subjected to heat-moisture treatment (HMT) at 80, 100, 120 and 130 °C for 16 h at a moisture content of 27% and to determine the impact of structural changes at each of the above temperatures on the susceptibility on hydrolysis by porcine pancreatic α-amylase (PPA). The results showed that structural changes due to HMT were influenced by differences in starch chain mobility at the different temperatures of HMT. Starch chain mobility in turn was influenced by the interplay between the extent to which B-type crystallites were transformed into A + B-type crystallites, kinetic energy imparted to starch chains and amylose content. The main type of structural changes influencing physicochemical properties at the different temperatures of HMT was starch chain interactions (at 80 and 100 °C), disruption of hydrogen bonds between amylose (AM)–amylopectin (AMP) and AMP–AMP chains (at 120 and 130 °C), disorganization of AMP chains near the vicinity of the hilum (at 100, 120 and 130 °C) and formation of interrupted helices (at 130 °C). The susceptibility of NP and WP starches towards α-amylase decreased at 80 °C, but increased in the range of 100 to 130 °C. This suggested that α-amylase hydrolysis of HMT starches was influenced by the interplay of: 1) amount of A-type crystallites, 2) starch chain interactions and 3) changes to double helical conformation. Differences in granule morphology in PPA hydrolyzed NP and WP starches were largely influenced by the higher granular swelling in the latter. NP and WP starches exhibited heterogeneity in degradation (NP > WP) in both their native and HMT states.     

Effect of Retrograded Waxy Corn Starch on Bread Staling

Waxy corn starch pastes (10%) were stored at 5 °C for up to 35 days, and the powder specimens of retrograded starches thus obtained were added to wheat flour for bread baking at a level of 5%. The effect of retrograded starch on the staling of bread was determined. The loaf which contained retrograded waxy corn starch, which was prepared by storing the 10% paste at 5 °C for 7 days, showed an increase in specific volume and the results of the sensory evaluation showed that it was very acceptable. During the storage of bread, the increase in firmness and decrease in degree of gelatinization were suppressed by adding retrograded waxy corn starch. The moisture content of bread crumbs did not relate to firmness. Added retrograded waxy corn starch decreased the final viscosity of flour. The crystalline region of retrograded waxy corn starch used for bread baking included longer chains from amylopectin which in raw starch occurred in the amorphous region.     

Retrogradation of Starch Mixtures Containing Rice Starch

ABSTRACT: Different starches often coexist in food systems. Starch retrogradation is the primary reason for quality deterioration of a food system during storage. This article addresses the retrogradation behaviors of several starch mixtures containing normal rice starch (NRS). Potato starch, tapioca starch, waxy corn starch, hydroxypropylated potato starch, hydroxypropylated tapioca starch, and acetylated tapioca starch were mixed with NRS. Starch suspensions were gelatinized and the relative solid content, (S′) measured by pulsed nuclear magnetic resonance, was used to characterize the retrogradation behavior of starch systems. The retrogradation behaviors of starch mixtures can be divided into two categories according to the additive or non‐additive nature of S′, for which the concept “regional moisture content” was introduced.     

酸解对不同链/支比含量玉米淀粉特性的影响

以4种不同链/支比含量的玉米淀粉为原料,酸解处理不同时间,以酸解玉米淀粉的形貌特性、冻融稳定性、膨胀度、溶解度、晶体性质为指标衡量不同酸解时间对玉米淀粉结构性质的影响。结果表明:4种玉米淀粉酸水解程度的顺序为:蜡质玉米普通玉米淀粉G50G80。酸解后,同品种的4种玉米淀粉的析水率随着酸解天数的增加而增加;溶解度增加,膨胀度降低。酸解并未改变淀粉的晶型,随着酸解时间的延长,蜡质玉米淀粉和普通玉米的相对结晶度先增大后保持不变,G50和G80的相对结晶度随着酸解时间的增加而增大。表明酸解对低直链淀粉(蜡质玉米淀粉和普通玉米淀粉)的结构、性能影响最大。     

Pasting properties of hydroxypropylated starches before or after proteinase treatment

To examine the effect of starch protein on hydroxypropylation, corn (normal and waxy) and potato starches were hydroxypropylated with propylene oxide at two levels (8.3 and 12.3% based on dry basis of starch weight) before or after proteinase (thermolysin) treatment, and then pasting properties of the starches were measured. For normal corn starch, protein appeared to be involved in hydroxypropylation, especially at the higher concentration of reagent (12.3%); the starch hydroxypropylated after proteinase treatment (Enz‐HP) showed less reaction efficiency than that only hydroxypropylated (HP) or proteinase treated starch after hydroxypropylation (HP‐Enz). This suggests a possible reaction between some of the reagent and the starch proteins that exist in the channel and surface of the starch granules. However, not much difference was found with the waxy corn starch, as it contains much lower amounts of amylose and protein than normal corn starch. The potato starch, which has no channels, showed complicated protein effects. For potato starch, a different access of the enzyme and chemical reagents to the granule matrix could be possible.     

Effect of Heat‐Moisture Treatment on Structural and Thermal Properties of Rice Starches Differing in Amylose Content

Starches from glutinous rice (1.4% amylose), Jasmine rice (15.0% amylose) and Chiang rice (20.2% amylose) were exposed to heat‐moisture treatment (HMT) at 100 °C for 16 h and at different moisture levels (18, 21, 24 and 27%). The effect of heat‐moisture treatment on structural and thermal properties of these three rice starches was investigated. The HMT did not change the size, shape and surface characteristics of rice starch granules. The A‐type crystalline pattern of rice starches remained unchanged after HMT. The relative crystallinity (RC) and the ratio of short‐range molecular order to amorphous (RSA) of heat‐moisture treated glutinous and Jasmine rice starches decreased with increasing moisture level of the treatments. In contrast, the RC of the treated Chiang rice starch remained practically unchanged. A peak of crystalline V‐amylose‐lipid complexes was clearly presented in all treated Chiang rice starches. The peak became progressively stronger with increasing moisture level of the treatment. Differential scanning calorimetry (DSC) of all treated rice starches showed a shift of the gelatinization temperature to higher values. Increasing moisture level of the treatments increased the onset gelatinization temperature (T_o) but decreased the gelatinization enthalpy (ΔH) of rice starches. A broad gelatinization temperature range (T_c‐T_o) with a biphasic endotherm was found for all treated Chiang rice starches and Jasmine rice starch after HMT₂₇ (HMT at 27% moisture level). Additionally the (T_c‐T_o) of treated Chiang rice starches increased linearly with increasing moisture level of the treatments.     

Development and Physicochemical Characterization of New Resistant Citrate Starch from Different Corn Starches

Resistant starch has drawn broad interest for both potential health benefits and functional properties. In this study, a technology was developed to increase resistant starch content of corn starch using esterification with citric acid at elevated temperature. Waxy corn, normal corn and high‐amylose corn starches were used as model starches. Citric acid (40% of starch dry weight) was reacted with corn starch at different temperatures (120–150°C) for different reaction times (3–9 h). The effect of reaction conditions on resistant starch content in the citrate corn starch was investigated. When conducting the reaction at 140°C for 7 h, the highest resistant starch content was found in waxy corn citrate starch (87.5%) with the highest degree of substitution (DS, 0.16) of all starches. High‐amylose corn starch had 86.4% resistant starch content and 0.14 DS, and normal corn starch had 78.8% resistant starch and 0.12 DS. The physicochemical properties of these citrate starches were characterized using various analytical techniques. In the presence of excess water upon heating, citrate starch made from waxy corn starch had no peak in the DSC thermogram, and small peaks were found for normal corn starch (0.4 J/g) and Hylon VII starch (3.0 J/g) in the thermograms. This indicates that citrate substitution changes granule properties. There are no retrogradation peaks in the thermograms when starch was reheated after 2 weeks storage at 5°C. All the citrate starches showed no peaks in RVA pasting curves, indicating citrate substitution changes the pasting properties of corn starch as well. Moreover, citrate starch from waxy corn is more thermally stable than the other citrate starches.     

Characterization of Different Starches Oxidized by Hypochlorite

The effects of starch origin (potato, corn, and rice starches) and hypochlorite level (NaOCl, 0.8% and 2% w/w) on the structures and physicochemical properties of oxidized starches were investigated. Carboxyl and carbonyl group contents of oxidized starches increased with increasing NaOCl level, with potato starch having the highest and corn starch having the lowest carboxyl groups content at both NaOCl levels. Oxidation generally reduced the pasting temperature and viscosity of native starches as demonstrated by using a Rapid Visco Analyser. The peak viscosities of oxidized rice and corn starches were higher than those of their native counterparts at 0.8% NaOCl. The morphology of starches was not altered and X‐ray diffraction patterns of all the starches remained unchanged after oxidation. Oxidized starch batters exhibited greater adhesions than did native starch batters, with rice starch batter exhibiting the greatest adhesion. Carbohydrate profiles by high‐performance size‐exclusion chromatography indicated that both amylopectin and amylose were degraded during oxidation. The level of oxidation was largely dependent on the degree of crystallinity of starch and the degree of polymerization of amylose, whereas the adhesion property of oxidized starch was mainly attributed to its granular size and shape.