Impact of mild acid hydrolysis on structure and digestion properties of waxy maize starch

In this study, the molecular structure of acid-treated waxy maize starch residues was investigated, and the in vitro digestibility of the residues with 2.2 N HCl at 35 °C for different time periods, was assessed. The granular appearance of waxy maize starch was destroyed and small fractions formed aggregates. A change in chain-length distribution profiles occurred with the degradation of shortest A chains and long B chains in amylopectin. The rise in the ratio of absorbance height at 1047 cm⁻¹ to the height at 1022 cm⁻¹, the intensities of major peaks, X_c, T_p, T_c, and ΔH were observed during mild acid hydrolysis, but the X-ray diffraction patterns displayed A-type for all starches. The amount of rapidly digestible starch increased, whereas the amounts of slowly digestible and resistant starch decreased. These results demonstrate that the amorphous regions of starch granules, including the shortest A chains and long B chains, are preferentially hydrolysed and affect the slow digestion and resistance properties of waxy maize starch.     

Physicochemical Properties of Carboxy-methylated Sago (Metroxylon sagu) Starch

ABSTRACT: Carboxymethyl starch (CMS) with degree of substitution (DS) ranging from 0.1 to 0.32 was prepared from sago ( Metroxylon sagu ) starch in non-aqueous medium using isopropanol as a solvent. The physico-chemical, rheological, and thermal properties of the starches were investigated. At room temperature (25 °C), CMS hydrated readily, resulting in higher swelling power compared with native (unmodified) starch. Light microscopy revealed that CMS granules imbibed more water than native starch at room temperature and thus caused a larger increase in granule size. Some of the CMS granules lost their integrity. Scanning electron microscopic observation revealed fine fissures on the surface of CMS (DS 0.32) granules compared with a relatively smooth surface of native starch granules. Carboxymethylated sago starch exhibited excellent dispersibility and cold water solubility as judged by the absence of peak viscosity in the pasting profile (determined by Rapid ViscoAnalyzer). Pasting profile of CMS was qualitatively similar to pregelatinized starch. Despite exhibiting greater swelling power, CMS showed significantly lower pasting viscosity compared with the native starch. Intrinsic viscosity was also greatly reduced by carboxymethylation. Studies using differential scanning calorimetry (DSC) showed that transition temperatures and enthalpies decreased with an increase of degree of substitution. CMS at higher substitution levels (DS 0.27 and 0.32) showed significantly lower retrogradation tendency, as indicated by lower setback, absence of DSC endotherm upon storage at 4 °C and lower syneresis upon repeated freeze-thaw cycles. The results suggested that retrogradation might be effectively retarded by the presence of the bulky carboxymethyl group.     

Determination of degree of substitution of carboxymethyl starch by Fourier transform mid-infrared spectroscopy coupled with partial least squares

The degree of substitution (DS) markedly affects the properties of carboxymethyl starch (CMS). The conventional methods for the DS determination are time-consuming and not environment friendly. Fourier transform mid-infrared (FT-MIR) spectroscopy coupled with partial least squares (PLS) regression is applied to determine the DS of CMS in the present study. Calibration models with direct titration as the reference method were optimised by cross validation. A PLS regression model with a coefficient of determination (R²) of 0.9593 and root-mean-square error of cross validation (RMSECV) of 0.0141 was obtained in the spectral range from 500 to 4000 cm⁻¹. The prediction set gave a coefficient of determination (R²) and root-mean-square error of prediction (RMSEP) of 0.9368 and 0.0228, respectively. The results obtained in this study indicate that FT-MIR spectroscopy can be used as an easy, rapid, and novel tool to quantitatively predict the DS of CMS.     

Effect of acetylation,oxidation and annealing on physicochemical properties of bean starch

Black and Pinto bean starches were physically and chemically modified to investigate the effect of modification on digestibility and physicochemical properties of bean starch. The impact of acetylation, oxidation (ozonation) and annealing on the chemical composition, syneresis, swelling volume, pasting, thermal properties and digestibility of starches was evaluated. The physicochemical and estimated glycemic index (eGI) of the Black and Pinto bean starches treated with ozone were not significantly (P > 0.05) different than that of their respective control starches. Annealed starches had improved thermal and pasting properties compared to native starches. Acetylated starches presented reduced syneresis, good pasting properties and lower eGI. Also, all modified starches had increased levels of resistant starch (RS). Therefore, the digestibility and physicochemical properties of bean starch were affected by the type of modification but there were no significant (P > 0.05) differences between the Black and Pinto bean starches.     

Preparation and properties of octenyl succinic anhydride modified potato starch

Potato starch was esterified with octenyl succinic anhydride (OSA) in aqueous slurry systems and the major factors affecting the esterification were systematically investigated. The physico-chemical properties of the products were determined by means of Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction and a viscosity analyser (VA). The results indicated that suitable parameters for the preparation of OSA starch from potato in aqueous slurry systems were as follows: concentration of starch slurry, 35% (in proportion to water, w/w), reaction period, 3 h, pH of reaction system, 8.0, reaction temperature, 35 °C, amount of OSA, 3% (in proportion to starch, w/w), OSA dilution-fold, 5. The degree of substitution (DS) was 0.017 and the reaction efficiency (RE) was 72 ± 1.8%. FT-IR spectroscopy showed characteristic absorption of the ester carbonyl groups in the OSA starch at 1724 cm⁻¹. SEM and X-ray diffraction revealed that OSA groups acted by first attacking the surface and some pores formed, but OSA modification caused little change in the crystalline pattern of potato starch (DS 0.045). Apparent pastiness measurement indicated that the starch derivatives gelatinized within a shorter time to achieve higher viscosities over the range of designed concentration of OSA potato starch.     

Physicochemical,thermal and pasting properties of starch separated from γ-irradiated and stored potatoes

The morphological, thermal and pasting properties of starch separated from potatoes of three varieties (Kufri Chandramukhi, Kufri Jyoti and Kufri Chipsona-2), treated either with CIPC (isopropyl N-(3 chlorophenyl) carbamate) or γ-irradiation (Co⁶⁰, 0.1 and 0.5 kGy) and subsequently stored at 8, 12 and 16 °C for 90 days, were studied. Scanning electron microscopy (SEM) showed the presence of oval and irregular shaped starch granules with a diameter range of 15–16 μm. Mean granule size of starch separated from potatoes stored at 12 °C ranged from 18–25 μm and irradiation treatment resulted in an increase in the proportion of small size granules. The irradiation of potatoes with 0.5 kGy resulted in starch with significantly lower peak-, trough- and breakdown-viscosity as compared to starch from potatoes treated with either CIPC or 0.1 kGy irradiation. The irradiation of potatoes with 0.5 kGy caused a significant increase in setback and pasting temperature. Pasting temperature of starch was observed to vary with the storage temperature. Starch separated from potatoes stored at higher temperature showed lower pasting temperature and vice versa. The starch from potatoes stored at 8 °C showed higher peak-, trough- and breakdown-viscosity and lower setback. Peak viscosity increased and swelling volume decreased with increase in storage temperature. FTIR spectra showed that the starch from irradiated potatoes displayed a significant decrease in the intensity of the C–H stretch region between 2800 and 3000 cm⁻¹, which was observed to be irradiation dose-dependent, and higher with 0.5 than 0.1 kGy. However, a slight broadening of O–H stretch (3000–3600 cm⁻¹) in starches from irradiated potatoes was observed. The spectral changes caused by γ-irradiation were apparent in the O–H stretch (3000–3600 cm⁻¹), C–H stretch (2800–3000 cm⁻¹) and bending mode of water (1600–1800 cm⁻¹).     

Particle size-starch–protein digestibility relationships in cowpea (Vigna unguiculata)

The kinetics of starch and protein digestion in hammer- and cryo-milled cowpea (70–370 μm) were investigated. The pH during the protein digestion reduced with time, and both the starch and protein digestion exhibited monophasic digestograms, which were suitably (r² > 0.97, p < 0.001) described by a modified first-order kinetic model. The in vitro protein digestibility of the cowpea (>80%) was independent of the milling conditions. The hammer-milled cowpea digested more, but the reciprocal of its rate of protein digestion was independent of the square of the particle size. The rate of protein digestion in the cryo-milled cowpea inversely depended (p < 0.05) on the square of the particle size, with 67 × 10⁻⁷ cm² s⁻¹ as the diffusion coefficient. For the starch digestion, diffusion coefficients (cm² s⁻¹) were 0.6 × 10⁻⁷ (hammer-milled) and 0.3 × 10⁻⁷ (cryo-milled). The protein digestion proceeded at a much faster (100×) rate than the starch digestion.     

Relationship between the structure,physicochemical properties and in vitro digestibility of rice starches with different amylose contents

The in vitro digestibility and molecular and crystalline structures of rice starches (Long-grain, Arborio, Calrose, and Glutinous) differing in amylose content were investigated and the relationship between the structure and in vitro digestibility of starch was studied. Long-grain showed the highest amylose content (27.2%), whereas Glutinous showed the lowest amylose content (4.2%). Long-grain had the highest average amylopectin branch chain length (18.8) and proportion (8.7%) of long branch chains (DP ≥ 37), and the lowest proportion (26.9%) of short branch chains (DP 6–12). Among the non-waxy rice starches (Long-grain, Arborio, and Calrose), Calrose had the lowest average chain length (17.7) and the lowest proportion (7.1%) of long branch chains (DP ≥ 37). The relative crystallinity of rice starch followed the order: Glutinous (33.5%) > Calrose (31.4%) > Arborio (31.0%) > Long-grain (29.9%). Long-grain had the highest gelatinization temperature and the lowest gelatinization temperature range, whereas Glutinous showed the highest gelatinization temperature range and gelatinization enthalpy. Arborio had the highest melting enthalpy for amylose–lipid complex among the tested rice starches. Pasting temperature, setback, and final viscosity increased with increasing amylose content, whereas the peak viscosity and breakdown showed negative correlations with amylose content. The rapidly digestible starch (RDS) content of the tested rice starches followed the order: Glutinous (71.4%) > Calrose (52.2%) > Arborio (48.4%) > Long-grain (39.4%). Contrary to this, the slowly digestible starch (SDS) and resistant starch (RS) contents showed an opposite trend compared to RDS. Digestibility (RDS, SDS, and RS) of the rice starches was significantly correlated (p ≤ 0.05) with amylose content, proportions of DP 6–12 and DP 13–24, relative crystallinity, intensity ratio (of 1047 cm⁻¹ to 1022 cm⁻¹ from Fourier transform infrared spectroscopy), swelling factor, amylose leaching, onset temperature of gelatinization, gelatinization temperature range, gelatinization enthalpy, pasting temperature, peak viscosity, breakdown, setback, and final viscosity.     

The molecular weight,solubility and viscosity of oat beta-glucan affect human glycemic response by modifying starch digestibility

The interaction between oat β-glucan and other food components has the potential to influence starch digestibility and consequently affect its bioactivity in reducing glycemic responses. Blood glucose concentrations were measured before and after ingesting wheat and oat granolas, with 0.6 and 6.2 g of β-glucan, respectively, and two starch doses (40 and 60 g). As the in vitro extract viscosity of β-glucan increased, the in vitro starch digestibility was reduced and the glucose responses were lowered. The peak blood glucose response (PBGR) and the incremental area under the curve (iAUC) were lower in the 40 g than in the 60 g starch formulation. β-Glucan was significantly more active in reducing PBGR and iAUC when the β-glucan/starch ratio was 1.6:10 rather than 1.1:10. This information is valuable for new product development and for quality assessment of bioactive foods containing oat β-glucan.     

Physiochemical properties and kinetics of glucoamylase produced from deoxy-d-glucose resistant mutant of Aspergillus niger for soluble starch hydrolysis

Glucoamylases (GAs) from a wild and a deoxy-d-glucose-resistant mutant of a locally isolated Aspergillus niger were purified to apparent homogeneity. The subunit molecular mass estimated by SDS–PAGE was 93 kDa for both strains, while the molecular masses determined by MALDI-TOF for wild and mutant GAs were 72.876 and 72.063 kDa, respectively. The monomeric nature of the enzymes was confirmed through activity staining. Significant improvement was observed in the kinetic properties of the mutant GA relative to the wild type enzyme. Kinetic constants of starch hydrolysis for A. niger parent and mutant GAs calculated on the basis of molecular masses determined through MALDI-TOF were as follows: k_cat = 343 and 727 s⁻¹, K_m = 0.25 and 0.16 mg mL⁻¹, k_cat/K_m (specificity constant) = 1374 and 4510 mg mL⁻¹ s⁻¹, respectively. Thermodynamic parameters for soluble starch hydrolysis also suggested that mutant GA was more efficient compared to the parent enzyme.     

Modelling starch digestion in sweetpotato with biphasic digestograms

The kinetics of starch digestion in 20 sweetpotato samples obtained from Papua New Guinea were investigated using an in vitro procedure based on glucometry. Irrespective of the cultivars (3-mun, Carot kaukau, Wahgi besta, Nillgai, Baiyer kaukau, and 1-mun), provinces, farmers and locations, the samples exhibited biphasic digestograms, possibly due to initial impediments to amylolysis and/or transport of digestion products by non-starch components (e.g. plant cell walls). The biphasic digestograms were segmented into two monophasic digestograms using a second-order polynomial (average r² = 0.723; p < 0.001), and a modified first-order kinetic model adequately described the digestograms (average r² = 0.984, p < 0.001; mean relative deviation modulus, MRDM, =8). Generally, the digestion rate constants (initial, K_i = 3.2-5.2 × 10⁻³ min⁻¹; final, K_f = 3.8-18.4 × 10⁻³ min⁻¹) indicated faster digestion during the final segment after the initial impediments to digestion had possibly been overcome. K_i was significantly (p < 0.05) different among the samples, which did not significantly (p < 0.05) differ in K_f. A logistic model, which treated each digestogram as a single process, also adequately described the biphasic behaviours (average r² = 0.994, p < 0.001; mean relative deviation modulus, MRDM, =15). The digestion parameters from the segment and logistic approaches significantly (p < 0.05) differed among the sweetpotato samples. The rate of digestion from the logistic model was significantly (p < 0.05) related to the initial and final rates of digestion from the segment approach (K = 3.99 K_i + 0.65 K_f; r² = 0.456; p < 0.001). Irrespective of the approach, maximum starch digestion was less than 100% in some samples to indicate the presence of resistant starch type 1, 2 or both. The present study is the first to model biphasic starch digestograms.     

Effects of spontaneous heating on estimates of total digestible nutrients for alfalfa-orchardgrass hays packaged in large round bales

Large round or large square hay packages are more likely to heat spontaneously during storage than hay packaged in conventional (45 kg) bales, and the effects of this phenomenon on the associated energy estimates for these hays can be severe. Our objectives for this project were to assess the relationship between estimates of total digestible nutrients (TDN) and spontaneous heating and to describe any important differences in energy estimates that may result specifically from 2 methods of estimating truly digestible fiber (TD-Fiber). Using the summative approach to estimate TDN, TD-Fiber can be estimated from inputs of protein-corrected neutral detergent fiber (NDFn) and acid detergent lignin (TD-FiberLIG) or from NDFn and 48-h neutral detergent fiber digestibility (TD-FiberNDFD). Throughout 2006 and 2007, mixed alfalfa (Medicago sativa L.)-orchardgrass (Dactylis glomerata L.) hays from 3 individual harvests were obtained from the same 8.2-ha research site near Stratford, Wisconsin. Both options for estimating TD-Fiber (TD-FiberLIG or TD-FiberNDFD) were then used independently via the summative approach to estimate the total TDN concentrations (TDN-LIG or TDN-NDFD, respectively) within these hays. Estimates of both TDN-LIG and TDN-NDFD then were related to heating degree days >30°C accumulated during storage by various regression techniques. Changes (poststorage - prestorage) in TDN-LIG that occurred during storage (ΔTDN-LIG) were best fitted with a nonlinear decay model in which the independent variable was squared [Y = (11.7 × e^{−0.0000033×x×x}) − 11.6; R² = 0.928]. For changes in TDN-NDFD (ΔTDN-NDFD), a quadratic regression model provided the best fit (Y = 0.0000027x² − 0.010x + 0.4; R² = 0.861). Generally, ΔTDN-LIG estimates were 2.0 to 4.0 percentage units lower than ΔTDN-NDFD estimates when heating exceeded 500 HDD. For regressions on maximum internal bale temperature, both ΔTDN-LIG (Y = −0.38x + 16.3; R² = 0.954) and ΔTDN-NDFD (Y = −0.25x + 10.2; R² = 0.848) were best fitted by linear models with heterogeneous (P < 0.001) slopes and intercepts. In both cases, coefficients of determination were high, suggesting that simple measures of spontaneous heating are excellent predictors of energy losses in heated forages. Regardless of method, reductions in TDN were associated primarily with losses of nonfiber carbohydrate, which is known to occur via oxidation of sugars during spontaneous heating. For heated forages, some discrepancy between TDN-LIG and TDN-NDFD existed because the relationship between NDFD and spontaneous heating was shown previously to be very poor, resulting in minimal changes for estimates of TD-FiberNDFD as a consequence of heating. In contrast, TD-FiberLIG declined in close association with heating, largely because TD-FiberLIG was sensitive to changes in concentrations of both NDFn and acid detergent lignin. Discrepancies between TDN-LIG and TDN-NDFD were exacerbated further when neutral detergent fiber rather than NDFn was used to estimate TD-FiberNDFD. Estimates of TDN declined by as much as 13.0 percentage units within severely heated hays, and this is a serious consequence of spontaneous heating.     

Mild hydrolysis of resistant starch from maize

To investigate structural changes of resistant starch (RS) caused by mild-acid treatment, native maize starch, retrograded (RS3), and cross-linked (RS4) resistant starches, prepared from maize starch, were hydrolyzed with 0.1 M HCl at 35 °C for 30 days. The hydrolysis rate of RS3 was shown to be the highest, at 44.1% after 30 days of the hydrolysis. The hydrolysis rapidly progressed upto 10 days but gradually changed after that. Native starch and RS4 showed less than 5% of hydrolysis during the period of hydrolysis. As for the RS level of the residue after the hydrolysis, RS4 did not show any significant change, but RS3 exhibited an increase of up to 25.9% after 30 days, which led to 88% increase in comparison with 13.8% at the initial stage. As a result of examining the molecular weight (MW) of RS3 by the SEC-MALLS-RI system, the non-hydrolyzed RS3 exhibited three peaks, having MW 53.4 × 10⁶, 7.4 × 10⁶, and 0.8 × 10⁶, respectively, but the MW of the molecules decreased to 4.9 × 10⁶ and 0.6 × 10⁶ after 7 days of hydrolysis. It was difficult to verify the MW of RS4 because this was not dispersed in 1 M NaOH. The crystallinity of native starches, RS3 and RS4, by X-ray diffractometry of the residue hydrolyzed with 0.1 M HCl was equal to that of the non-hydrolyzed starch. The peak intensity at 2θ = 17° of RS3 increased sharply after hydrolysis.     

Relationships between dry matter content,ensiling, ammonia-nitrogen,and ruminal in vitro starch digestibility in high-moisture corn samples

The objectives of the study were (1) to determine relationships between high-moisture corn (HMC) dry matter (DM), ammonia-N [% of crude protein (CP)], and soluble CP concentrations, and pH, with 7-h ruminal in vitro starch digestibility (ivStarchD), and (2) to evaluate the effect of ensiling on pH, ammonia-N, soluble CP, and ivStarchD measurements in HMC. A data set comprising 6,131 HMC samples (55 to 80% DM) obtained from a commercial feed analysis laboratory was used for this study. Month of sample submittal was assumed to be associated with length of the ensiling period. Data for month of sample submittal were analyzed using Proc Mixed in SAS (SAS Institute Inc., Cary, NC) with month as a fixed effect. Regressions to determine linear and quadratic relationships between ivStarchD and ammonia-N, soluble CP, pH, and DM content were performed using Proc Mixed. The ivStarchD increased by 9 percentage units from October to August of the following year. Similar results were observed for ammonia-N and soluble CP with increases from 1.8 to 4.6% of CP and 31.3 to 46.4% of CP, respectively, from October to August of the following year. Ammonia-N was positively related to ivStarchD (R² = 0.61). The DM content of HMC at silo removal was negatively related (R² = 0.47) to ivStarchD with a decrease of 1.6 percentage units in ivStarchD per 1-percentage-unit increase in DM content. The pH of HMC was negatively related to ammonia-N (R² = 0.53), soluble CP (R² = 0.57), and ivStarchD (R² = 0.51). Combined, ammonia-N, DM, soluble CP, and pH provided a good prediction of ivStarchD (adjusted R² = 0.70). Increasing pH, ammonia-N, soluble CP, and ivStarchD values indicate that HMC may need up to 10 mo of ensiling to reach maximum starch digestibility. Ammonia-N, DM content, soluble CP concentration, and pH are good indicators of ruminal in vitro starch digestibility for high-moisture corn.     

Migration of α-tocopherol and resveratrol from poly(L-lactic acid)/starch blends films into ethanol

Poly(L-lactic acid) (PLLA)/starch blends with various concentrations of two natural antioxidants, α-tocopherol (α-TOC) and resveratrol, were fabricated by a melt blending and compression molding processes. The effects of the two antioxidants on the optical (color), thermal and mechanical properties of PLLA/starch blends with antioxidants were assessed. PLLA/starch blend films with α-TOC and resveratrol showed a yellowish color influenced by the combined effect of white starch and the brown color of the antioxidants. The glass transition and melting temperatures were significantly reduced with the addition of antioxidants while enhanced thermal stability was observed, which could be a benefit and important for processing and production. The enhanced mechanical properties could be attributed to not only a compatibilization effect based on the chemical linkage between PLLA and starch chains, but also restriction of the chain mobility by antioxidants. The release of resveratrol from PLLA and PLLA/starch blend films into ethanol followed Fickian behavior. The D values of α-TOC were in the range of 0.47–3.95 × 10⁻¹¹ cm² s⁻¹ for PLLA films and 0.70–6.83 × 10⁻¹¹ cm² s⁻¹ for PLLA/starch blend films at 13 °C, 5.67–13.0 × 10⁻¹¹ cm² s⁻¹ for PLLA films and 4.10–24.2 × 10⁻¹¹ cm² s⁻¹ for PLLA/starch blend films at 23 °C, and 89.0–118.0 × 10⁻¹¹ cm² s⁻¹ for PLLA films and 123–282 × 10⁻¹¹ cm² s⁻¹ for PLLA/starch blend films at 43 °C. The D values of resveratrol were in the range of 0.073–0.54 × 10⁻¹⁰ cm² s⁻¹ for PLLA films and 1.42–6.93 × 10⁻¹⁰ cm² s⁻¹ for PLLA/starch blend films at 13 °C, 0.90–3.44 × 10⁻¹⁰ cm² s⁻¹ for PLLA films and 4.16–22.3 × 10⁻¹⁰ cm² s⁻¹ for PLLA/starch blend films at 23 °C, and 24.8–74.1 × 10⁻¹⁰ cm² s⁻¹ for PLLA films and 40.1–309 × 10⁻¹⁰ cm² s⁻¹ for PLLA/starch blend films at 43 °C.     

Characteristics and application of enzyme-modified carboxymethyl starch in sausages

Enzyme-modified carboxymethyl starch (ECMS) was prepared by etherification of starch and enzymatic hydrolysis. The characteristics of ECMS and its application as fat replacers in 10 g/100g and 20 g/100 g target fat sausages were evaluated. FT-IR spectroscopy indicated that the absorption peaks of carboxyl in ECMS were characterized at 1635 and 1426 cm⁻¹. ECMS had better paste clarity and freeze–thaw stability than enzyme-modified starch (ES) or native starch. The addition of ECMS in sausages increased (P < 0.05) water holding capacity and emulsion stability of the products. Sensory analysis showed that the 10 g/100 g fat sausage with added ECMS was similar (P > 0.05) to the 20 g/100 g fat sausage control for juiciness, oiliness, texture, flavour and overall acceptability at storage days of 0, 7, 14 and 21. The results indicated that the new multiplex modified starch-ECMS could be used as a suitable fat replacer since it offset some of the changes led by fat reduction.     

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.     

Effect of cross-linking on the resistance to enzymatic hydrolysis of waxy maize starch and low-methoxy pectin

Gelatinised waxy maize starch and low-methoxy pectin mixtures were solubilised/dispersed in water and cross-linked with sodium trimetaphosphate (STMP). The polysaccharides were subjected to α-amylase, β-amylase or amyloglucosidase (AMG) hydrolysis for different times, and at two starch to pectin combination ratios (3:2 and 2:3). The extent of hydrolysis by porcine pancreatic α-amylase of the cross-linked (gelatinised) starch was 54.8–58.9% in comparison with gelatinised starch (for different incubation times), corresponding to 52.3–58.9% and 51.3–55.3% of the starch in the uncross-linked (UL) 3:2 and 2:3 starch to pectin ratios (for the same hydrolysis times). Blends of individually cross-linked starch to pectin ratios (3:2 and 2:3) were hydrolysed to 66.2–67.0% and 65.4–71.8%, respectively, compared with the corresponding UL counterparts. When the gelatinised starch was incubated for 0.5–36 h with β-amylase, hydrolysis ranged from 9.2% to 26.2%, and from 5.4% to 12.2% when the starch was cross-linked (corresponding to 40.0–58.7% of the gelatinised starch). For starch to pectin ratios of 3:2 or 2:3 blended after cross-linking, or by simultaneous cross-linking, hydrolysis represented 2.3–3.4% and 0.3–0.6% for the 3:2 ratio but only 1.2–2.0% and 0–0.3% for the 2:3 ratio. Hydrolysis with AMG using a 0.1 mg ml⁻¹ enzyme concentration caused 51.8% hydrolysis of gelatinised starch, which was lowered to 35.2% (i.e. by 68%) after cross-linking. At a higher enzyme concentration (1 mg ml⁻¹), the comparable figures were 91.7% and 71.9% (a reduction of 78.4%). For the UL 3:2 starch to pectin ratio and 0.1 and 1 mg ml⁻¹ enzyme concentrations, there was 27.8% and 56.5% hydrolysis of the polysaccharide which translated to 24.3% (87.4%) and 45.8% (81.1%), respectively, after cross-linking. Comparable figures for the 2:3 ratio (for the 0.1 and 1 mg ml⁻¹ enzyme concentrations) were 20.2% and 36.5% hydrolysis of the UL samples and 18.2% (90.1%) and 32.5% (89.0%) hydrolysis, respectively, after cross-linking.