Susceptibility of annealed starches to hydrolysis by α-amylase and glucoamylase

The objective of this work was to determine if annealing altered the susceptibility of different starches to enzyme hydrolysis. Five commercial starches, including waxy corn, common corn, Hylon V, Hylon VII, and potato, were annealed by a multiple-step process, and their susceptibility to α-amylase and glucoamylase and the physicochemical properties of the hydrolyzed native and annealed starches were determined. During 36 h of enzyme hydrolysis, significant differences were noted between annealed starch and its native counterpart in the extent of α-amylolysis for Hylon V, Hylon VII, and potato, and in the extent of glucoamylolysis for potato. Waxy and common corn starches were hydrolyzed to a greater degree by both enzymes when compared with the other starches. The apparent amylose content of both native and annealed starches decreased during α-amylolysis for all starches, but increased for Hylon V, VII, and potato starches during glucoamylolysis. Most native and annealed starches exhibited comparable or increased peak gelatinization temperatures and comparable or decreased gelatinization enthalpy on hydrolysis with the exception of annealed potato starch, which showed a significant decrease in peak gelatinization temperature on hydrolysis. Annealed starches displayed significant higher peak gelatinization temperatures than their native counterparts. The intensity of main X-ray diffraction peaks of all starches decreased upon hydrolysis, and the changes were more evident for glucoamylase-hydrolyzed starches. The annealing process allowed for a greater accessibility of both enzymes to the amorphous as well as the crystalline regions to effect significant changes in gelatinization properties during enzyme hydrolysis.     

A new insight into the gelatinization process of native starches

The gelatinization characteristics of seven different food starches (regular corn, high-amylose corn, waxy corn, wheat, rice, potato, and tapioca) were investigated. Each starch sample type was heated to 35, 40, 45, etc. up to 85 °C at 5 °C intervals, and freeze-dried. The treated samples were analyzed using light microscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and high-performance size exclusion chromatography (HPSEC). When heated, granules underwent structural changes prior to the visible morphological changes that took place during gelatinization. The nature of these structural changes depended on starch type. These results indicate that the starch gelatinization process is more complex than a simple granular order-to-disorder transition.     

Chemical and physical properties of ginkgo (Ginkgo biloba) starch

Starch isolated from mature Ginkgo biloba seeds and commercial normal maize starches were subjected to α-amylolysis and acid hydrolysis. Ginkgo starch was more resistant to pancreatic α-amylase hydrolysis than the normal maize starch. The chain length distribution of debranched amylopectin of the starches was analyzed by using high performance anion-exchange chromatography equipped with an amyloglucosidase reactor and a pulsed amperometric detector. The chain length distribution of ginkgo amylopectin showed higher amounts of both short and long chains compared to maize starch. Naegeli dextrins of the starches prepared by extensive acid hydrolysis over 12 days demonstrated that ginkgo starch was more susceptible than normal maize to acid hydrolysis. Ginkgo dextrins also demonstrate a lower concentration of singly branched chains than maize dextrins, and unlike maize dextrin, debranched ginkgo shows no multiple branched chains. The ginkgo starch displayed a C-type X-ray diffraction pattern, compared to an A-type pattern for maize. Ginkgo starch and maize starch contained 24.0 and 17.6% absolute amylose contents, respectively.     

Structural characteristics and physicochemical properties of oxidized corn starches varying in amylose content

The effects of amylose content on the extent of oxidation and the distribution of carboxyl groups in hypochlorite-oxidized corn starches were investigated. Corn starches including waxy corn starch (WC), common corn starch (CC), and 50% and 70% high-amylose corn starches (AMC) were oxidized with NaOCl at three concentrations (0.8%, 2%, and 5%). Carboxyl and carbonyl content of oxidized starches increased with increasing NaOCl concentration. High-AMC (70%) had slightly higher carboxyl and carbonyl contents at 0.8% NaOCl, whereas WC had significantly higher carboxyl and carbonyl contents at 2% and 5% NaOCl levels. Carbohydrate profiles by high-performance size-exclusion chromatography indicate that amylose was more susceptible to depolymerization than amylopectin. Degradation of amylopectin long chains (DP >24) was more pronounced in WC and CC than in AMCs. The crystalline lamellae of WC started to degrade at 2% NaOCl, but those of the other corn starches remained intact even at 5% NaOCl level according to X-ray crystallinity. By using anion-exchange chromatography for separation and size-exclusion chromatography for characterization, carboxyl groups were found to be more concentrated on amylopectin than on amylose, particularly in AMCs. Oxidation decreased gelatinization temperature and enthalpy with WC showing the most decrease and 70% AMC showing the least. The gelatinization enthalpy of 50% AMC decreased significantly faster than those of CC and 70% AMC after 0.8% oxidation. Retrogradation of amylopectin slightly increased after oxidation with increasing oxidation level. The peak viscosities of oxidized WC and CC were higher than those of their native counterparts at 0.8% NaOCl, but this increase was not observed in AMCs. The setback viscosities of 2% NaOCl-oxidized 50% and 70% AMCs were much higher than those of the unmodified counterparts. The extent of oxidation and physicochemical properties of oxidized starches varied greatly with the amylase:amylopectin ratio of corn starches. Amylose was suggested to play an important role in controlling the oxidation efficiency.     

Changes in physicochemical properties of waxy corn starches at different stages of harvesting

Starches were isolated from immature waxy corn kernels harvested at 0, 2, 4 and 6 days after optimum stage (DAO) and from mature kernels at 16 DAO. The starch contents showed varied according to genotypes and harvesting stages. The accumulation of starches showed an increasing trend in relation to delayed harvesting time, from the optimum stage until the physiological maturity stage. Among all harvesting stages, medium granules had the highest contribution to the total starch volume (60.8–81.5%), followed by large (5.7–30.1%), and small granules (9.1–15.3%). Average chain length distribution of amylopectin ranged from DP 14.7 to 16.9 for KKU–UB, DP 16.9 to 17.4 for KKU–JD, and DP 5.7 to 30.1 for Violet white. The pasting behaviors of starches were greatly affected by harvesting times. The peak viscosity of starches increased with delayed harvesting until physiological maturity and then decreased until dried kernels at 35 days after pollination.     

Effects of annealing on the polymorphic structure of starches from sweet potatoes (Ayamurasaki and Sunnyred cultivars) grown at various soil temperatures

Starches extracted from the sweet potato cultivars Sunnyred and Ayamurasaki grown at 15 or 33 degrees C (soil temperature) were annealed in excess water (3 mg starch/mL water) for different times (1, 4, 8 or 10h) at the temperatures 2-3 degrees K below the onset melting temperature. The structures of annealed starches, as well as their gelatinisation (melting) properties, were studied using high-sensitivity differential scanning calorimetry (HSDSC). In excess water, the single endothermic peak shifted to higher temperatures, while the melting (gelatinisation) enthalpy changed only very slightly, if any. The elevation of gelatinisation temperature was associated with increasing order/thickness of the crystalline lamellae. The only DSC endotherm identified in 0.6 M KCl for Sunnyred starch grown at 33 degrees C was attributed to A-type polymorphic structure. The multiple endothermic forms observed by DSC performed in 0.6M KCl for annealed starches from both cultivars grown at 15 degrees C provided evidence of a complex C-type (A- plus B-type) polymorphic structure of crystalline lamellae. The A:B-ratio of two polymorphic forms increased upon annealing due to partial transformation of B- to A-polymorph, which was time dependent. Long heating periods facilitated the maximal transformation of B- to A-polymorph associated with limited A:B ratio.     

Thermal and structural properties of unusual starches from developmental corn lines

Starches from exotic corn lines were screened by using differential scanning calorimetry (DSC) to find thermal properties that were significantly different from those exhibited by starches from normal Corn Belt lines. Two independent gelatinization transitions, one corresponding to the melting of a peak at 66 °C and the other to a peak melting at 69 °C, were found in some starches. The melting characteristics were traced to two separate types of granules within the endosperm. Strong correlations were found between DSC properties and proportion of large granules with equivalent diameter ≥17 μm. Starches with a lower peak onset gelatinization temperature (T_oG), had a lower normalized concentration of chains with a degree of polymerization (dp) of 15–24 and/or a greater normalized concentration of chains with a dp of 6–12. These studies will aid in understanding structure–thermal property relationships of starches, and in identifying corn lines of interest for commercial breeding.     

'Green' crosslinking of native starches with malonic acid and their properties

Starch is a highly hydrophilic biomaterial with weak mechanical properties rendering it useless for commercial applications. A fully 'green' water based process is presented to crosslink corn (cereal) and potato (tuber) starch to enhance mechanical properties as well as lower hydrophilicity. In addition, malonic acid, a green, plant based water soluble and relatively inexpensive polycarboxylic acid, was used as the crosslinker. The reactivity of potato starch toward esterification and crosslinking was found to be higher than that of corn starch owing to the inherent differences in the granule morphology and internal structure of the two starches. It was observed that potato starch granules had a higher degree of substitution (DS) of 0.19 than corn starch granules (DS=0.1) under similar reaction conditions. Chemical, thermal and mechanical test results confirmed the crosslinking as well as reduced moisture sensitivity.     

Internal structure and physicochemical properties of corn starches as revealed by chemical surface gelatinization

The organization of amylose and amylopectin within starch granules is still not well elucidated. This study investigates the radial distribution of amylose and amylopectin in different corn starches varying in amylose content (waxy corn starch (WC), common corn starch (CC), and 50% and 70% amylose corn starches (AMC)). Corn starches were surface gelatinized by 13 M LiCl at room temperature to different extents (approximately 10%, 20%, 30%, and 40%). The gelatinized surface starch and remaining granules were characterized for amylose content, amylopectin chain-length distribution, thermal properties, swelling power (SP), and water solubility index (WSI). Except for the outmost 10% layer, the amylose content in CC increased slightly with increasing surface removal. In contrast, amylose was more concentrated at the periphery than at the core for 50% and 70% AMC. The proportion of amylopectin A chains generally decreased while that of B1 chains generally increased with increasing surface removal for all corn starches. The gelatinization enthalpy usually decreased, except for 70% AMC, whereas the retrogradation enthalpy relatively remained unchanged for CC but increased for WC, 50% and 70% AMC with increasing surface removal. The SP and WSI increased with increasing surface removal for all corn starches, with WC showing a significant increase in SP after the removal of the outmost 10% layer. The results of this study indicated that there were similarities and differences in the distribution of amylose and amylopectin chains along the radial location of corn starch granules with varying amylose contents. More amylose-lipid complex and amylopectin long chains were present at the periphery than at the core for amylose-containing corn starches.     

Formation and isolation of nanocrystal complexes between dextrins and n-butanol

Starch dextrins of different molecular sizes (DP_n 311, 142 and 39) were prepared by hydrolyzing a high amylose maize starch in acidic alcohol solutions. The dextrins were dissolved in an aqueous dimethyl sulfoxide solution (90% DMSO), and then the solution was allowed to migrate down into n-butanol separated by a membrane filter. The complex was gradually formed between the dextrin and butanol, and precipitated in the butanol layer. The dextrin–butanol complex yielded V6-I type crystals with broad reflections (d-spacings 1.123, 0.657 and 0.429 nm) under X-ray diffractograms. Platelets of average length less than 100 nm, interspersed in amorphous matrices, were observed in complexes of DP_n 311 and 142, but that of DP_n 39 showed different morphology, and the formation of complexes was limited. By hydrolyzing the complex of DP_n 311 with α-amylase, amorphous matrices were selectively removed, and crystallites of 23–72 nm showing a V6-I X-ray diffraction pattern were obtained. However, crystallites in complexes of DP_n 142 and 39 were eroded by amylolysis, forming large aggregates.     

Study on the granular characteristics of starches separated from Chinese rice cultivars

Granule size distribution, the relative crystallinity, morphology and thermal degradation of starches from 10 different non-waxy rice cultivars were measured in present study. The relationships between granular structure and thermogravimetric parameters of tested starches were evaluated using Pearson correlation analysis. The range of median size for rice starches was 6.23-7.81 μm. The relative crystallinity of 10 non-waxy rice starches ranged from 20.4% to 33.4%. The range of activation energy from different rice starches was between 155.6 and 201.5 kJ/mol. The Pearson correlation results showed that the relative crystallinity was positively correlated (r = 0.6750, p < 0.05) with the percentage of branch chains with DP12-23. Furthermore, the activation energy of the rice starches showed a positive correlation (r = 0.7903, p < 0.01) with relative crystallinity.     

Influence of growth temperature on the structure and thermodynamic parameters of barley starches

Barley starches grown at different temperatures were investigated using high sensitivity differential scanning microcalorimetry and X-ray diffraction. By applying physico-chemical approaches, thickness of crystalline lamellae, thermodynamic and structural characteristics (such as gelatinisation) of cooperative units and parameters characterising thermodynamic properties of crystal surfaces were determined. It was established that a difference of growth temperature experienced by plants during development does not lead to changes in the thickness of amylopectin crystalline lamellae and hence constituent double helix length. The role of defects in structural organisation of native barley starches is discussed. It is suggested that not all fatty acids necessarily form crystalline inclusion complexes.     

Effects of structure and modification on sustained release properties of starches

Starches of different sources and compositions were investigated to determine the effect of structure and chemical modification on the sustained release properties of the resultant modified starches. Starches were cross-linked with epichlorohydrin and substituted with carboxymethyl or aminoethyl groups at different levels. Substitution efficiency was overall higher for waxy corn and potato starches than for Hylon VII, and was higher for starches at low cross-linking levels than those at high cross-linking ones. Waxy corn starch displayed better sustained release properties when cross-linked to a lower level, whereas Hylon VII showed better performances when cross-linked to a higher level. Matrices substituted with carboxymethyl and aminoethyl groups at the high level showed better sustained release properties than those substituted at the low level. The proportion and structure of amylose and amylopectin in starches from different botanical sources strongly influenced the level of modification required to produce a satisfactory sustained release matrix.     

Physicochemical properties of endosperm and pericarp starches during maize development

Endosperm starch and pericarp starch were isolated from maize (B73) kernels at different developmental stages. Starch granules, with small size (2–4 μm diameter), were first observed in the endosperm on 5 days after pollination (DAP). The size of endosperm-starch granules remained similar until 12DAP, but the number increased extensively. A substantial increase in granule size was observed from 14DAP (diameter 4–7 μm) to 30DAP (diameter10–23 μm). The size of starch granules on 30DAP is similar to that of the mature and dried endosperm-starch granules harvested on 45DAP. The starch content of the endosperm was little before 12DAP (less than 2%) and increased rapidly from 10.7% on 14DAP to 88.9% on 30DAP. The amylose content of the endosperm starch increased from 9.2% on 14DAP to 24.2% on 30DAP and 24.4% on 45DAP (mature and dried). The average amylopectin branch chain-length of the endosperm amylopectin increased from DP23.6 on 10DAP to DP26.9 on14DAP and then decreased to DP25.4 on 30DAP and DP24.9 on 45DAP. The onset gelatinization temperature of the endosperm starch increased from 61.3 °C on 8DAP to 69.0 °C on 14DAP and then decreased to 62.8 °C on 45DAP. The results indicated that the structure of endosperm starch was not synthesized consistently through the maturation of kernel. The pericarp starch, however, showed similar granule size, starch content, amylose content, amylopectin structure and thermal properties at different developmental stages of the kernel.     

Comparison of potato amylopectin starches and potato starches — influence of year and variety

Starches from three potato varieties and their respective transformants producing amylopectin starch were studied over a period of 3 years. The gelatinisation, swelling and dispersion properties were studied using differential scanning calorimetry (DSC), X-ray diffraction, swelling capacity measurements and a Brabender Viscograph.

The potato amylopectin starches (PAP) exhibited higher endothermic temperatures as well as higher enthalpies than the normal potato starches (NPS). PAP samples gave rise to an exceptionally sharp viscosity peak during gelatinisation and a relatively low increase in viscosity on cooling. Swelling capacity measurements showed that PAP granules swelled more rapidly, and that the dispersion of the swollen granules occurred at a lower temperature (85°C). Analysis of variance (ANOVA) also revealed that the year influenced the DSC results, and that both year and variety affect some of the Brabender parameters. Furthermore, the PAP and NPS samples were subjected to heat–moisture treatment at three different moisture levels, and the Brabender viscosity properties were studied.     

Locations of hypochlorite oxidation in corn starches varying in amylose content

The general oxidation mechanism by hypochlorite on starch has been well studied, but the information on the distribution of the oxidation sites within starch granules is limited. This study investigated the locations where the oxidation occurred within corn starch granules varying in amylose content, including waxy corn starch (WC), common corn starch (CC), and 50% and 70% high-amylose corn starch (AMC). Oxidized corn starches were surface gelatinized by 13 M LiCl at room temperature to different extents (approximately 10%, 20%, 30%, and 40%). The surface-gelatinized remaining granules were separated and studied for structural characteristics including carboxyl content, amylose content, amylopectin chain-length distribution, thermal properties, and swelling properties. Oxidation occurred mostly at the amorphous lamellae. More carboxyl groups were found at the periphery than at the core of starch granules, which was more pronounced in oxidized 70% AMC. More amylose depolymerization from oxidation occurred at the periphery of CC. For WC and CC, amylopectin long chains (>DP 36) were more prone to depolymerization by oxidation. The gelatinization properties as measured by differential scanning calorimetry also supported the changes in amylopectin fine structure from oxidation. Oxidized starches swelled to a greater extent than their unmodified counterparts at all levels of surface removal. This study demonstrates that the locations of oxidation and physicochemical properties of oxidized starches are affected by the molecular arrangement within starch granules.     

Determination of the maximum water solubility of eight native starches and the solubility of their acidic-methanol and -ethanol modified analogues

The maximum water solubilities of eight native starches from potato, shoti, tapioca, maize, waxy maize, amylomaize-7, wheat, and rice and their acid-methanol and acid-ethanol modified analogues have been determined. Maximum solubilities of 18.7 and 17.4 mg/mL were obtained for waxy maize and tapioca and 12.4 mg/mL for potato and maize starches by autoclaving 220 mg/10 mL at 121 degrees C; 8.7 mg/mL was obtained for shoti starch by stirring in 85:15 (v/v) Me(2)SO-H(2)O at 20 degrees C; and 7.0 and 5.2mg/mL for rice and amylomaize-7 starches by stirring in 1M NaOH at 20 degrees C. The acid-alcohol treated starches were 4-9 times more soluble than their native starches. The compositions of the solubilized starches had, in general, much higher ratios of amylose to amylopectin than the ratios in their native granules. A major exception to this was the acid-methanol treated potato, shoti, and rice starches that had much lower ratios of amylose to amylopectin than the ratios in their granules.     

Structural and thermodynamic properties of starches extracted from GBSS and GWD suppressed potato lines

A combined DSC–SAXS approach was employed to study the effects of amylose and phosphate esters on the assembly structures of amylopectin in B-type polymorphic potato tuber starches. Amylose and phosphate levels in the starches were specifically engineered by antisense suppression of the granule bound starch synthase (GBSS) and the glucan water dikinase (GWD), respectively. Joint analysis of the SAXS and DSC data for the engineered starches revealed that the sizes of amylopectin clusters, thickness of crystalline lamellae and the polymorphous structure type remained unchanged. However, differences were found in the structural organization of amylopectin clusters reflected in localization of amylose within these supramolecular structures. Additionally, data for annealed starches shows that investigated potato starches possess different types of amylopectin defects. The relationship between structure of investigated potato starches and their thermodynamic properties was recognized.