Hydrothermal Modifications of Tropical Tuber Starches. 1. Effect of Heat‐Moisture Treatment on the Physicochemical,Rheological and Gelatinization Characteristics

Cassava, sweet potato and arrowroot starches have been subjected to heat‐moisture treatment (HMT) under different conditions using a response surface design of the variables. A comparative study was performed on the pasting properties, swelling behaviour and the gelatinization properties of the modified starches and also on the rheological and textural properties of their pastes. X‐ray diffraction studies have shown that cassava starch exhibited a slight decrease in crystallinity, whereas sweet potato and arrowroot starches showed an increase in crystallinity after HMT at 120ºC for 14 h with 20% moisture. The swelling volume was reduced and the solubility was enhanced for all three starches after HMT, but both effects were more pronounced in the case of arrowroot starch. The decrease in paste clarity of the starch after HMT was higher in the case of cassava and sweet potato starches. Viscosity studies showed that the peak viscosity of all three starches decreased after HMT, but the paste stability increased as seen from the reduced breakdown ratio and setback viscosity. Studies on rheological properties have shown that storage and loss moduli were higher for the starches heat‐moisture treated at higher moisture and lower temperature levels than the corresponding native starches. Storage of the gel at ‐20ºC resulted in a significant increase in storage modulus for all the three starches. All the textural parameters of the gels were altered after the treatment which depended on the nature of the starch and also the treatment condition.     

Molecular structure and granule morphology of native and heat‐moisture‐treated pinhão starch

Pinhão seed is an unconventional source of starch and the pines grow up in native forests of southern Latin America. In this study, pinhão starch was adjusted at 15, 20 and 25% moisture content and heated to 100, 110 and 120 °C for 1 h. A decrease in λ max (starch/iodine complex) was observed as a result of increase in temperature and moisture content of HMT. The ratio of crystalline to amorphous phase in pinhão starch was determined via Fourier transform infra red by taking 1045/1022 band ratio. A decrease in crystallinity occurred as a result of HMT. Polarised light microscopy indicated a loss of birefringence of starch granules under 120 °C at 25% moisture content. Granule size distribution was further confirmed via scanning electron microscopy which showed the HMT effects. These results increased the understanding on molecular and structural properties of HMT pinhão starch and broadened its food and nonfood industrial applications.     

Heat‐Moisture Treatment and Enzymatic Digestibility of Peruvian Carrot,Sweet Potato and Ginger Starches

The aim of this work was to study the effects of heat‐moisture treatment (27% moisture, 100°C, 16 h) and of enzymatic digestion (alpha‐amylase and glucoamylase) on the properties of sweet potato (SP), Peruvian carrot (PC) and ginger (G) starches. The structural modification with heat‐moisture treatment (HMT) affected crystallinity, enzyme susceptibility and viscosity profile. The changes in PC starch were the most pronounced, with a strong decrease of relative crystallinity (from 0.31 to 0.21) and a shift of X‐ray pattern from B‐ to A‐type. HMT of SP and G starch did not change the X‐ray pattern (A‐type). The relative crystallinity of these starches changed only slightly, from 0.32 to 0.29 (SP) and from 0.33 to 0.32 (G). The extent of these structural changes (PC > SP > G) altered the susceptibility of the starches to enzymatic attack, but not in same order (PC > G > SP). HMT increased the starches digestion, probably due to rearrangement of disrupted crystallites, increasing accessible areas to attack of enzymes. The viscosity profiles and values changed significantly with HMT, resulting in higher pasting temperatures, decrease of viscosity values and no breakdown, i.e., stability at high temperatures and shear rates. Changes in pasting properties appeared to be more significant for PC and SP starch, whereas the changes for G starch were small. Setback was minimized following HMT in SP and G starches.     

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.     

Heat–Moisture Treatment on Pinhão Starch Impacts the Properties of the Biodegradable Films

Using non-conventional starch can benefit the industry since it can present different properties. It also can lead to new properties upon physical modification, which improves its derivate film properties. Therefore, the aim of this work is to evaluate the heat–moisture treatment (HMT) on pinhão starch and its effectiveness in film properties. After isolation using water as a solvent, the pinhão starch is treated by HMT for 16 h at 110 °C. Native and HMTed starches are used to produce biodegradable films. Pinhão starch and starch films chemical and physical properties are properly characterized. The HMT causes some changes in short-range ordered structures, reduces the relative crystallinity, and shifts the pinhão starch from C-type to A-type. Also, HMT decreases the peak viscosity and the breakdown, and improves thermal stability. These starch changes upon HMT reduces water vapor permeability, increases tensile strength, and elongation at the break of pinhão starch films. Desirable changes in starch and film properties are achieved by physically modifying pinhão starch using HMT, which is a promising alternative to chemical modifications.     

Development of oxidised and heat-moisture treated potato starch film

This study investigated the effects of sodium hypochlorite oxidation and a heat-moisture treatment of potato starch on the physicochemical, pasting and textural properties of potato starches in addition to the water vapour permeability (WVP) and mechanical properties of potato starch films produced from these starches. The carbonyl contents, carboxyl contents, swelling power, solubility, pasting properties and gel texture of the native, oxidised and heat-moisture treated (HMT) starches were evaluated. The films made of native, oxidised and HMT starches were characterised by thickness, water solubility, colour, opacity, mechanical properties and WVP. The oxidised and HMT starches had lower viscosity and swelling power compared to the native starch. The films produced from oxidised potato starch had decreased solubility, elongation and WVP values in addition to increased tensile strength compared to the native starch films. The HMT starch increased the tensile strength and WVP of the starch films compared to the native starch.     

Physicochemical, crystallinity, pasting and morphological properties of bean starch oxidised by different concentrations of sodium hypochlorite

The effect of bean starch oxidation at different active chlorine concentrations (0.5%, 1.0% and 1.5%) on the physicochemical, crystallinity, pasting and morphological properties of starch was investigated. The carbonyl content, carboxyl content, starch colour, swelling power, solubility, gel hardness, X-ray crystallinity, pasting properties, gelatinisation characteristics and morphology of the starches were evaluated. The bean starch oxidised with 0.5% active chlorine had the characteristic of a slightly crosslinked starch. As compared to the native and 0.5% active chlorine-oxidised starches, active chlorine at 1.0% and 1.5% increased the carbonyl content, carboxyl content and solubility of the starches. Moreover, these concentrations of active chlorine decreased the swelling power, gel hardness, relative crystallinity, breakdown, peak viscosity and setback, as compared to the native and 0.5% active chlorine-oxidised starches. The starch granules oxidised with 1.5% active chlorine had imperfections in their structure, and its surface appears to be rougher than the other granules.     

Effect of heat-moisture treatment on rice starch of varying amylose content

The effect of heat-moisture treatment (HMT) on the properties of rice starches with high-, medium- and low-amylose content was investigated. The starches were adjusted to 15%, 20% and 25% moisture levels, and heated at 110 °C for 1 h. The swelling power, solubility, pasting properties, morphology, enzymatic susceptibility and X-ray crystallinity of the starches were evaluated. HMT reduced the swelling power and solubility of the starches. The strongest effect of HMT occurred on the high-amylose starch; the pasting temperature was increased and the peak viscosity, breakdown, final viscosity and the setback were reduced. HMT increased the starch’s susceptibility to α-amylase and promoted a reduction in the starch relative crystallinity.     

Functional Properties and Retrogradation of Heat‐Moisture Treated Wheat and Potato Starches in the Presence of Hydroxypropyl β‐cyclodextrin

Some functional and retrogradation properties of native and heat‐moisture treated potato and wheat starches were examined in the presence of hydroxypropyl β‐cyclodextrin (HPβ‐CD). HPβ‐CD increased swelling factor, amylose leaching, and solubility of both native and heat‐moisture treated wheat starches but it had less impact on corresponding potato starches. Gelatinization enthalpy of native wheat starch was decreased in the presence of HPβ‐CD but was increased in potato starch with increasing concentration. Reduction of amylose‐lipid complex endotherm in both native and heat‐moisture treated wheat starch was observed in the presence of HPβ‐CD. Heat‐moisture treatment did not change the transition parameters of amylose‐lipid complex showing its resistance to hydrothermal treatment. HPβ‐CD greatly decreased the pasting temperature of wheat starch. Cold paste viscosity of both native and heat‐moisture treated wheat starch was increased by HPβ‐CD to a greater extent than corresponding potato starch. Amylopectin retrogradation of all the starches was unaffected in the presence of HPβ‐CD but heat‐moisture treatment slightly decreased retrogradation of potato starch. These results suggest that HPβ‐CD can disrupt the amylose‐lipid complex within the starch granule in both native and heat‐moisture treated wheat starch but has no influence on amylopectin retrogradation. However, greatly increased wheat starch setback with HPβ‐CD indicates its greater effect on wheat starch amylose retrogradation.     

Physicochemical properties of pressure moisture treated (PMT) and heat moisture treated (HMT) starches

Physicochemical properties of pressure moisture treated (PMT, 550 MPa, 10 min) and heat moisture treated (HMT, 100 °C, 10 h) starches were investigated. Effects of PMT and HMT were different depending on starch type. PMT starches showed dramatic changes in moisture sorption isotherm, pasting properties, thermal characteristics, solubility and swelling power (at 90 °C), and in vitro digestibility. The most dramatic difference between PMT and HMT starches was amylopectin melting transition, i.e., broadening in PMT and shift to high temperature in HMT starches. Moreover, B- and C-type starches revealed the more increase in amylopectin melting enthalpy than A-type starch. Both PMT and HMT did not increase the crystallinity but reorganized the amorphous area to compact, resulting in lower rapidly digestible starch and higher slowly digestible starch than those of native starches. Consequently, PMT changed the digestibility and physicochemical properties of starches with different modes of action compared with HMT.     

Influence of Heat‐Moisture Treatment and Acid Modifications on Physicochemical,Rheological, Thermal and Morphological Characteristics of Indian Water Chestnut (Trapa natans) Starch and its Application in Biodegradable Films

Water chestnut starch was subjected to acid modification and heat‐moisture treatment. Hydrochloric acid was used for acid modification at three different concentrations (0.25 M, 0.5 M and 1 M) for 2 h. Modifications did not alter the granule morphology. Heat‐moisture treatment (HMT) resulted in slight reduction in the granular size of the starch granules. Acid modification lowered the amylose content, swelling power, water‐ and oil‐binding capacity but improved the solubility of starch to a considerable level. Light transmittance of acid‐modified (AM) starches improved significantly. A significant reduction in peak, trough, final and setback viscosity was observed by acid‐thinning. In case of heat‐moisture treated starch the final viscosity (F_v) was found to be even higher than the peak viscosity (P_v). Native water chestnut starch exhibited a lower onset temperature (T_o) and peak temperature (T_p) of gelatinization than the corresponding acid‐treated starches. Starch films prepared from native starch exhibited excellent pliability, whereas those prepared from AM and HMT starches showed good tensile strength. Starch films prepared from acid‐treated starches provided better puncture and tensile strength.     

Pasting,Thermal, Hydration,and Functional Properties of Annealed and Heat-Moisture Treated Starch of Sword Bean (Canavalia gladiata)

The effects of annealing (ANN) and heat-moisture treatments (HMT) on the physicochemical and functional properties of Sword bean starches were investigated. The pasting properties differ significantly among the starches, with peak viscosity ranging from 399.17 RVU to 438.33 RVU; however, all the starches exhibited ‘Type C’ class with restricted swelling. The HMT starches had the highest gelatinization temperature, while change in enthalpy of gelatinization, ΔH_gel of the native starch, was higher (13.82 J/g) than that of the modified starches (1.39–6.74 J/g). The solubility and swelling power of all the starches increased as the temperature increased. The oil and water absorption capacity of the starches ranges between 3.24–3.91 g/g and 2.42–3.35 g/g, respectively. HMT (at 25 and 30% moisture level) changes the X-ray diffraction pattern of the starch from Type ‘B’ to Type ‘C’. The Scanning electron micrograph results revealed the starch granules with smooth ellipsoids and indentation in their centre, hydrothermal modification showed little effect on the morphology and size of the granules. Hydrothermal modification improved the physicochemical and functional properties of the starch without destroying the granule of the starch.     

Effect of Heat-Moisture Treatment and Acid Modification on Rheological, Textural, and Differential Scanning Calorimetry Characteristics of Sweetpotato Starch

Sweetpotato starches were characterized to understand the changes upon modification by acid and heat‐moisture treatment (HMT) in the rheological, differential scanning calorimetry (DSC), and textural characteristics of starch isolated from the sweetpotato variety PSP‐21 and to compare these findings with those of commercially available arrowroot starch. The native sweetpotato starch had a Type A pasting profile characterized by a high peak viscosity (PV) (741.5 rapid viscoanalyzer unit [rvu]), with a high breakdown (378.8 rvu) and low cold paste viscosity (CPV) (417.6 rvu). After HMT, there was a marked decrease in the PV (639.1), a very slight breakdown (113.5 rvu) and an increase in CPV (759.5 rvu), more like a Type C pasting profile. However, acid modification did not notably change the pasting profile of native sweetpotato starch. The DSC characteristics were also affected significantly after modifications. The gelatinization temperature parameter to onset (T_o) decreased significantly after HMT and acid modification. The gelatinization enthalpy decreased during HMT from 15.98 to 14.42 J/g. The gel strength of acid‐modified starch was the highest compared with that of HMT and native sweetpotato and arrowroot starches.     

Isolation and Characterization of Starch from Seeds of Araucaria brasiliensis: A Novel Starch for Application in Food Industry

The pinhão seeds (Araucaria angustifolia), are composed of 34% of starch and very low fractions of protein, lipids and phenolic compounds. This composition is favorable to obtain a stable, white in color and odorless starch, useful in the food industry. The isolated starch is constituted predominantly of small‐sized round granules (10–25 μm), rather than oval ones. Compared to corn starch, pinhão starch has a lower temperature and enthalpy of gelatinization. Retrogradation occurs to a lower extent in pinhão starch, due to its lower amylose content (∼25%). The pasting profile of pinhão starch showed a higher consistency than that of corn starch, with lower temperature in the peak of maximum viscosity. The higher swelling and solubility values of pinhão starch, in conjunction with the higher storage modulus (G') suggest new different applications of this novel starch. The low protein content of the starch granule favors applications like production of glucose and fructose syrups. The simple method of extraction and the high yield of starch from pinhão seed might be attractive not only for pilot‐plant but also for commercial‐scale production.     

Structural Transformation of Sago Starch by Heat‐Moisture and Osmotic‐Pressure Treatment

Sago starch was modified by osmotic‐pressure treatment (OPT) and heat‐moisture treatment (HMT) and physicochemical characteristics were compared. In OPT, sago starch was suspended in saturated sodium sulfate solution and heated for 1 h at 100, 110 and 120°C, corresponding to a calculated osmotic pressure of 32,728, 33,640 and 34,552 kPa (assuming sodium sulfate dissociates completely), respectively, and in HMT, sago starch with 20% moisture content was used. Change of X‐ray diffraction pattern from C‐type to A‐type was obtained for OPT and HMT starch at 110°C and 120 °C, respectively. RVA viscograms of both OPT and HMT starch exhibited a decrease of peak and breakdown viscosity but increase of final viscosity and pasting temperature. Onset (T_o), peak (T_p), and conclusion temperature (T_c) of gelatinization of both OPT and HMT starch increased significantly with increase of treatment temperature. Biphasic broadening of T_p was observed for HMT starch indicating an inhomogeneous heat transfer during HMT. The observed narrow peaks of DSC curves indicated better homogeneity of OPT. These properties suggest that OPT starch is more suitable for large‐scale production.     

Microencapsulation of β‐carotene using native pinhão starch,modified pinhão starch and gelatin by freeze‐drying

Beta‐carotene was microencapsulated by freeze‐drying using native pinhão starch, hydrolysed pinhão starch 6 dextrose equivalent (DE), hydrolysed pinhão starch 12 DE and the mixture of these materials with gelatin as coating material. The purpose of this research was to produce and characterize these microcapsules. The capsules’ efficiency, surface content, moisture, morphology, solubility, particle size and glass transition temperature were analysed. The hydrolysed pinhão starch 12 DE showed the highest total β‐carotene content and the lowest surface β‐carotene content, unlike the native starch. Using scanning electron microscopy, it was observed that all microcapsules presented undefined shapes. The samples with gelatin had wider particle size distribution, higher diameters, lower solubility and higher glass transition temperature when compared with other the samples. Results obtained suggest that the modified pinhão starch can be considered as potential wall material for encapsulation of β‐carotene.     

Physicochemical Properties of Non‐thermally Cross‐linked Corn Starch with Phosphorus Oxychloride using Ultra High Pressure (UHP)

Corn starch (20%, w/w) was non‐thermally and conventionally cross‐linked with phosphorus oxychloride (POCl₃; 0.01, 0.05, or 0.1%, based on dry weight of starch) at 400 MPa for 5, 15 and 30 min and at 45°C for 2 h, respectively. Swelling power and solubility of both non‐thermally and conventionally cross‐linked corn starches were relatively lower than those of native corn starch. The pressure holding time did not affect the solubility and swelling power of non‐thermally cross‐linked corn starches. X‐ray diffraction patterns and relative crystallinity were not significantly altered by both conventional and non‐thermal cross‐linking. DSC thermal characteristics of both non‐thermally and conventionally cross‐linked corn starches were not significantly changed indicating that the double helical structure of amylopectin was not influenced by both conventional and non‐thermal cross‐linking reactions. Both non‐thermal and conventional cross‐linking greatly affected the Rapid Visco Analyser (RVA) pasting properties, such as increase in pasting temperature and decrease in peak viscosity compared to native starch. This result suggests that in case of cross‐linking using POCl₃, both non‐thermal and conventional methods result in similar physicochemical properties and non‐thermal cross‐linking with POCl₃ can reduce the reaction time from 2 h to 15 min. This work shows the potential and possibility of non‐thermal starch modification and provides the basic and scientific information on the physicochemical properties of non‐thermally cross‐linked corn starches with phosphorus oxychloride using UHP.     

The effects of heat–moisture treatment of rice grains before parboiling on viscosity profile and physicochemical properties

The effects of heat–moisture treatment (HMT) (120 °C for 10, 30 and 60 min) on paddy rice grains before parboiling, on head rice yield (HRY), pasting and thermal properties, and colour and cooking characteristics of parboiled rice were studied. The results indicated that the HMT performed intensifies the changes in grains after parboiling, impacting pasting and thermal properties, which results in rice kernels with yellowish colouration and greater cooking time. HMT increased the temperatures of gelatinisation, with increasing HMT time from 10 to 60 min and reduced the gelatinisation enthalpy. HMT also affected the pasting properties of rice flours, reducing setback and viscosity and increased their stability to heat and mechanical agitation. The HMT performed in rice grains before the parboiling process with 60 min of the treatment decreased the HRY and increased the level of metabolic defects only in the treatment with 60 min.     

Modification and properties of African yam bean (Sphenostylis stenocarpa Hochst. Ex A. Rich.) Harms starch I: Heat moisture treatments and annealing

African yam bean (Sphenostylis stenocarpa) starch was subjected to heat moisture treatments at 18% (HMT-18), 21% (HMT-21), 24% (HMT-24), 27% (HMT-27) and excess (Annealing) moisture levels. Proximate chemical composition of the starch samples revealed that the moisture content of the starches ranged between 6.7% and 12.5%. Following modification of the native starch, there was a reduction in the moisture level of the heat moisture treated starches from HMT-18 to HMT-27. However, the annealed starch (HMT-ANN) retained higher moisture content compared to native starch (AYB-Native). The carbohydrate, protein, ash, amylose and fat content reduced with all the forms of heat treatments. At the temperature range studied (60–90 °C), increasing level of heat moisture treatments reduced the solubility and swelling capacity. pH also exert a profound effect both on the solubility and the swelling of the starch. Increasing degree of alkalinity increased both solubility and swelling capacity. In the native and modified starch samples, replacement of the wheat flour by the starch resulted in increased alkaline water retention of the blends. Water absorption capacity of the starch increased with the severity of moisture treatments, while the oil absorption capacity decreased. Apart from HMT-18, there was improved gel forming capacity of all the other heat-modified starches.Pasting temperature increased after hydrothermal modifications, whereas peak viscosity (P_v), Hot Paste Viscosity (H_v), setback and breakdown values all reduced after heat moisture treatments. All the starches were of type-B viscosity.Differential scanning calorimetry studies revealed that heat moisture treatment shifted the onset temperature (T_o), peak temperature(T_p) and conclusion temperature (T_c) to higher values. The gelatinisation temperature of the annealed starch was comparable to native starch. In addition, gelatinisation band of the native starch increased progressively from HMT-18 to HMT-27. Heat moisture treatment reduced the gelatinsation enthalpy (ΔH), while the enthalpy of retrogradation(ΔH_r) increased with the storage time of the gelatinised starch. Retrogradation enthalpy of the heat moisture conditioned starches were lower than the value obtained for the native starch.X-ray diffraction studies of the starch indicated that all the starch samples showed the type-C diffraction pattern. Differences were however observed in their degree of crystallinity. Native starch exhibited the lowest crystallinity (20%) while annealed starch had the highest crystallinity (27%)Microscopy studies revealed surface indentation, formation of groves in the central region, folding of starch granules and formation of doughnut-like appearance in some of the starch samples.     

Physico‐chemical properties of starches from Indian kidney bean (Phaseolus vulgaris) cultivars

Starches isolated from four Kidney bean cultivars (French Yellow, Contender, Master Bean, Local Red) grown in temperate climate were studied for their physico‐chemical, morphological, thermal, pasting, textural and retrogradation properties. Physico‐chemical properties such as composition, amylose content, water absorption capacity, swelling power, syneresis, freeze–thaw stability and light transmittance showed significant differences among starches. Amylose content (36.4–41.7%) showed strong correlations with peak, trough, breakdown, final and setback viscosity, gel hardness, gumminess and chewiness. The starch granule morphology of these starches showed considerable variation when studied by scanning electron microscopy. Starch granules were observed to be round, irregular or elliptical with smooth surfaces. Master Bean starch granules were larger than those of other kidney bean starches. Pasting and textural properties of French Yellow starches were found to be higher than other kidney bean starches. Local Red starches showed the highest gelatinisation transition temperatures, whereas Master Bean starches showed the lowest transition temperatures.