Effect of gelatinisation on slowly digestible starch and resistant starch of heat-moisture treated and chemically modified canna starches

The effects of gelatinisation on slowly digestible (SDS) and resistant starch (RS) of native and modified canna starches were investigated. Starch slurries (10% w/w) were gelatinised at 100 °C for 5, 10, 20 and 40 min using a rapid visco analyzer (RVA). Significant change in the degree of gelatinisation (DG) values of all starch samples was observed during the initial 10 min of gelatinisation; after that the DG values increased gradually with gelatinisation time. The RS contents in all gelatinised starches decreased with increasing gelatinisation time, while the SDS values fluctuated. Chemical modification affected DG values as well as RS/SDS contents. The RS contents in 10% (w/w) acetylated, hydroxypropylated, octenyl succinylated and cross-linked canna starches gelatinised at 100 °C for 40 min were 26.6%, 32.0%, 45.3% and 19.8%, respectively, which were higher than that of the native starch (12.4%). Canna starch modified by crosslinking had the highest SDS content when gelatinised for 20-40 min. Modification of canna starch by heat-moisture treatment resulted in a lower content of RS for all treated samples. However, the Vt-HMT25 (canna starch containing moisture content of 25% during heat treatment) when gelatinised for 5-20 min contained a higher amount of SDS, compared to unmodified starch. The most effective modification method for RS and SDS formation was octenyl succinylation, where the sum of RS and SDS approached that of Novelose260.     

Quantifying Enhancement in Heat Transfer Due to Natural Convection During Canned Food Thermal Sterilization in a Still Retort

Thermal sterilization of canned viscous liquid foods using saturated steam is enabled by natural convective heat transfer. However, the governing equations for two-dimensional convective heat transfer may be only rigorously solved by numerical calculations. On the other hand, if conduction is assumed to be the only mode of heat transfer, the thermal sterilization problem has analytical solutions for simple boundary conditions. However, the conduction model may not be appropriate in describing thermal sterilization of even viscous liquid foods and may cause considerable error in the prediction of the important parameters such as slowest heating zone (SHZ) temperature and lethality. The longer time for sterilization recommended by the conduction model may lead to overprocessing and an unacceptable food product. The objective of this work is to quantify the faster temperature rise in the food can due to natural convection when compared to the temperature rise obtained by only conductive heating. The consequent enhancement in lethalities is also reported. In addition, this work’s objective is to investigate how quickly the natural convective heat transfer effects begin to dominate over the solely conduction heating mode. The volume-averaged temperature as well as the SHZ temperature variations with time was calculated for the convection-augmented mode using computational fluid dynamics (CFD) simulations. Lethality values were then calculated based on volume-averaged temperature as well as the SHZ temperature. Food cans of different aspect ratios and food medium thermal conductivities are considered in this analysis. For the food system investigated, the critical Fourier number at which the transition to convection-augmented mode of heat transfer occurred is identified and explained from scaling considerations. In the conduction-dominated mode, it was possible to use analytical solutions to predict the volume-averaged and SHZ temperatures of the liquid food undergoing thermal sterilization. The Nusselt number correlation developed by Kannan and Gourisankar (2008) was used in the lumped parameter transient heat transfer model to predict the volume-averaged temperatures in the convection-dominated region. The volume-averaged temperatures from this approach were found to be in good agreement with the CFD simulation results. The time predicted for the SHZ to reach the minimum sterilization temperature was significantly lower when convective heating was also considered. The volume-averaged temperature and SHZ temperature enabled an estimation of overall sterility levels attained and minimum sterility levels prevalent inside the can, respectively. Even though the volume-averaged temperature increase due to convection was only about 10 K, the resulting accumulated lethality values were higher by an order of magnitude. The increase in SHZ temperatures was much higher in the convection-augmented mode, and consequently greater integrated lethalities were attained. The simple conduction model that is amenable to analytical solution cannot be used to approximate the heat-transfer-related phenomena even for “quick estimation” purposes when convection effects are significant. This precaution is found necessary even for the reasonably high viscous carboxy methyl cellulose system, whose average viscosity values ranged between 13 and 3 Pa s during the course of the sterilization process.     

Comparison of the crystalline properties and structural changes of starches from high-amylose transgenic rice and its wild type during heating

A transgenic rice line (TRS) enriched amylose and resistant starch has been developed by antisense RNA inhibition of starch branching enzymes. In this study, gelatinisation and crystalline properties, swelling power, water solubility, morphological and structural changes of starches from TRS and its wild-type Teqing (TQ) were carefully investigated during heating. Compared to TQ, TRS starch showed higher gelatinisation temperatures, lower gelatinisation enthalpy and swelling power. Morphological and structural changes showed that TQ starch drastically swelled after 70 °C, then gradually disrupted with increasing heating temperature. The surrounding band of TRS starch restrained granule swelling, though the subgranules disrupted to form the cavity. The results of spectroscopic analyses indicated that A-type crystalline of TQ changed to amorphous starch after 75 °C, while C-type crystalline of TRS gradually changed to B-type crystalline after 75 °C, then became amorphous starch at 95 °C. These results add to our understanding of the effect of heating on the high-amylose rice starch.     

Effects of high pressure and temperature on buckwheat starch characteristics

Pressure-induced gelatinisation of buckwheat starch suspensions (25% w/w) was studied and compared to heat-induced gelatinisation. Starch suspensions were treated at increased pressure (200–600 MPa) or temperature (60–95 °C) for 10 min. The degree of gelatinisation and the temperature and pressure ranges of gelatinisation were determined using differential scanning calorimetry, changes in birefringence and pasting behaviour. Furthermore, the structural changes during gelatinisation were investigated using microscopy. The pressure-induced as well as the temperature-induced gelatinisation curves were sigmoid shaped. Gelatinisation occurred between 300 and 500 MPa or between 60 and 70 °C. Scanning electron microscopy images showed retention of the granular structure after treatment with 600 MPa. However, when heated at temperatures above 65 °C, the formation of a “sponge-like” structure was observed. Better preservation of the granular structure for pressure treatment compared to temperature treatment resulted in stronger gels for the former. Pre-treatment with pressure as well as temperature made the buckwheat starch granules more resistant to swelling and disintegration under the influence of additional heat.     

Influence of microwave heating and time on functional,pasting and thermal properties of cassava starch

The effect microwaving power and time on the functional, pasting and thermal properties of cassava starch was investigated. Cassava starch at a moisture content of 30% was microwaved at 600 and 700 W for 0, 5, 15, 30 and 60 s following a preliminary study. Microwaving power and time did not alter the crystalline pattern of the starch, but there were obvious changes in the starch morphology. Starch colour was significantly (P ≤ 0.05) altered by microwave heating, with the total colour difference increasing from 4.85 to 43.01. Microwave treatment increased starch gelatinisation temperatures but decreased the swelling power, water absorption capacity and the relative crystallinity. These changes were influenced by microwave heating power and time. The results further revealed that the peak viscosity (3714.00–1947.00 cP) and setback ratio (1.70–1.49) decreased with increasing microwave heating time. However, breakdown viscosity (322.67–897.63 cP) and pasting temperature (1947.00–3714.00 °C) increased.     

Retrogradation of partially gelatinised potato starch prepared by ball milling

This study was performed to evaluate the effect of partial gelatinisation on the retrogradation of modified potato starch. The partially gelatinised starches with gelatinisation degree at mean levels of 22.47%, 49.18%, 76.80% and 86.19% were prepared by ball milling (0.5, 1.5, 3 and 10 h). The thermal properties and crystal structure of retrograded starch were examined during 21 days of refrigerated storage at 4 °C. Retrograded starch with high initial gelatinisation degree (86.19%) showed higher retrogradation enthalpy of 6.12 ± 0.18 J g^?1 and lower onset temperature of 45.41 ± 0.24 °C than sample with low gelatinisation degree (22.47%) where the results were 1.32 ± 0.18 J g^?1 and 54.05 ± 0.03 °C, respectively. During storage, two peaks in the X‐ray diffractograms for starch with high gelatinisation degree appeared and increased rapidly, while the peaks for starch with low gelatinisation degree increased slowly. These results suggest that a certain amount of remainder crystals presented in partially gelatinised starch impeded the retrogradation.     

Effects of time/temperature treatments on potato (Solanum tuberosum) starch: a comparison of isolated starch and starch in situ

Previously, time/temperature treatments of starch have been performed mainly on starch/water systems. In this study the same time/temperature treatments were applied to starch/water systems and to potato starch in situ. Two potato varieties (Solanum tuberosum cultivars Asterix and Bintje) were used. The effect of time/temperature treatments on gelatinisation behaviour was evaluated using differential scanning calorimetry (DSC). A blanching process was simulated by heating samples to 74 °C and then cooling them to 6 °C. A DSC scan showed that starch was completely gelatinised after this treatment. Retrogradation of amylopectin increased during storage at 6 °C from 0 to 24 h after blanching. Annealing of starch, with the aim of altering cooking properties, was performed by heating samples to temperatures below the gelatinisation onset temperature. Treating samples at 50 °C for 24 h caused a shift in gelatinisation onset temperature of 11–12 °C for isolated starch and 7–11 °C for in situ samples. The extent of the annealing effect depended on the difference between onset and annealing temperatures, and prolonged treatment time increased the effect. Starch/water systems and tissue samples behaved similarly when exposed to time/temperature treatments. The most apparent difference was the shift of gelatinisation to higher temperatures in tissue samples. Copyright © 2003 Society of Chemical Industry     

3D numerical simulation of asparagus sterilization in a still can using computational fluid dynamics

The heating and cooling cycles during thermal processing of asparaguses in a still can using Computational Fluid Dynamics (CFD) is the subject of this paper. The CFD code “Fluent®” was used to predict the temperature distribution and the velocity profile in the can. Experiments were run using a metal can containing 1 and 8 asparaguses filled with 4% NaCl brine and immersed in boiling water. Results obtained by CFD for temperature profiles were in good agreement with experimentally determined values. After validation of the model, further simulations were carried out for cans containing 0, 1, 8 and 19 asparaguses and for glass jars containing 19 asparaguses. It was shown that the brine flow depends on the number and spacing of the asparaguses in the can. By increasing the number of asparaguses in the can, the brine velocity increased being higher at the beginning of the heating and cooling phases. The slowest heating zone and the slowest cooling zone are located at a height of about 13.5% of the can height from the bottom and about 13.5% of the can height from the top, respectively, and they are not affected by the number of asparaguses. The final temperature during the heating phase was slightly affected by the number of asparaguses, while the heating rate was affected by the type of the container. Brine velocity did not affect the temperature inside the asparaguses indicating that the main resistance to heat transfer lies inside the asparaguses. The results clearly show that heating of the asparaguses is not uniform but the top of the asparaguses receives higher heat treatment than the bottom since the top of the can is heated faster and is cooled at a slower rate. These results could contribute to the optimization of thermal processing of asparaguses in order to minimize quality losses, such as texture, flavor and nutritional value, while keeping the product safe.     

CFD studies on natural convective heating of canned food in conical and cylindrical containers

Enhancing natural convective heat transfer in canned food sterilization is explored through modifications to container geometry and its orientation. A conical geometry, of equal volume and height as that of the cylinder, pointing either vertically up or down was considered. The non-Newtonian fluid, 0.85% w/w sodium carboxy-methyl cellulose (CMC), was taken as the test food material and its laminar flow behavior was investigated using computational fluid dynamics (CFD). The movement of the slowest heating zone (SHZ) temperature was tracked and compared for the three geometries. The SHZ temperature was observed to attain the final sterilization fluid temperature of 100 °C fastest for an upright conical geometry followed by the cylinder and the downward pointing cone. There is scope for enhancing the thermal sterilization process through geometry modifications but without mechanical agitation or rotation. Further, the geometry modification if non-uniform must be complemented by its suitable orientation.     

Moisture diffusivity of rough rice under infrared radiation drying

To design efficient infrared (IR) dryers for rough rice, it is important to understand the drying behavior of rough rice under IR heating. The objective of this study was to determine the moisture diffusivity of rough rice under IR heating followed by cooling. The effects of initial moisture content, rice temperature, drying bed thickness, tempering, and cooling methods on moisture diffusivity and moisture diffusivity coefficient were investigated. Samples of freshly harvested medium grain rice (M202 variety) with initial moisture content (MC) of 25.8, 31.2 and 33.8 g moisture/100 g dry solid were used. They were dried with IR radiation intensity of 5348 W/m², for six exposure times, 15, 30, 40, 60, 90 and 120 s. The tested drying bed thicknesses were single-layer, 5 mm and 10 mm. The unsteady diffusion equation based on Fick’s law and slope methods were used to describe moisture diffusivity. The results indicated that rough rice moisture diffusivities under IR heating and cooling were significantly affected by rice temperature and tempering treatment, respectively. High heating rate and moisture diffusivity were achieved with IR heating. It took only 60, 90 and 120 s to achieve about 60 °C rice temperature with corresponding moisture diffusivities of 4.8 × 10⁻⁹, 3.6 × 10 ⁻⁹ and 3.4 × 10⁻⁹ m²/s during heating for drying bed thicknesses of a single layer, 5 mm and 10 mm, respectively. The moisture diffusivity coefficients during heating and cooling of IR dried rice with tempering were much higher than those of convective drying, which reflected the high drying rate of the IR drying method.     

Effect of Salts and Sugars on Pressure‐induced Gelatinisation of Wheat,Tapioca, and Potato Starches

The impact of a variety of chlorides, sodium salts, potassium salts and low‐molecular sugars on pressure‐induced gelatinisation of wheat, tapioca and potato starches has been investigated. Just as thermal gelatinisation, pressure‐induced gelatinisation is influenced by solutes in the starch suspensions. In general the effects of salts and sugars on starch gelatinisation were comparable for thermal and pressure treatments. For example, the gelatinisation pressure was reduced by sugars whereas the degree of gelatinisation was linearly correlated with the number of equatorial hydroxyl groups. The influence of salts on the gelatinisation pressure varied and the extent of effect on the gelatinisation pressure did not only depend on the solute added but also on the type of starch. At high chloride concentrations (> 2 M) the impact of the salts on starch gelatinisation augmentation followed the order Na⁺<K⁺<Li⁺<Ca²⁺, which corresponds to the order of the lyotropic series. At concentrations above 1 M the effect of potassium salts on starch gelatinisation upon pressurisation also followed the order of the Hofmeister series (Cl⁻<Br⁻<I⁻<SCN⁻).     

Physical,thermal and structural properties of rice starch as affected by the addition of bamboo shoot shell fibres

The effects of different bamboo shoot shell fibre (BSSF) content (1, 2, 5 and 10%, w/w) on the physical, thermal and structural properties of rice starch were investigated. BSSFs significantly affected the properties of rice starch by competitive water absorption and hydrogen bonding. With increased BSSF content, the breakdown value and pasting temperature of rice starch were increased, whereas the peak viscosity, final viscosity and setback value were decreased. Thermodynamic results showed that the gelatinisation temperature and gelatinisation enthalpy of rice starch were significantly increased by the 5% and 10% BSSFs. Furthermore, BSSFs interconnected with amylose through hydrogen bonds to restrain gel-structure formation, thereby resulting in low storage modulus and loss modulus of rice starch paste. A loose structure of rice starch supplemented with 10% BSSFs was clearly visible, exhibiting the minimum values of hardness (32.12 ± 4.47 g) and adhesiveness (64.70 ± 17.32 g). Moreover, BSSFs increased the amount of short-range ordered structures but had no effect on the crystal type of rice starch. These results may contribute to the manufacture and development of fibre-enriched starchy products.     

Composition and properties of starches from Virginia‐grown kabuli chickpea (Cicer arietinum L.) cultivars

Composition and properties of seeds and starches from five Virginia‐grown kabuli chickpea cultivars were investigated. The seeds had the average weight of 4.48 g per 10 g and volume of 641.2 mm³, and were rich in carbohydrate with starch as a principal constituent (59.2–70.9%). Resistant starch accounted for 7.7–10.4% of the total starch content. The composition and properties of the starches among the five cultivars were significantly different (P ≤ 0.05). All starches had a C‐type crystalline structure. The degree of crystallinity ranged from 21.1% to 27.4%, gelatinisation temperature from 7.97 to 11.2 °C and gelatinisation enthalpies from 2.18 to 3.76 J g^?1, and water absorption capacities from 90.7% to 117.5%. Different shapes and granule sizes were observed. Molecular weight of amylopectin was in the range of 6.35 × 10⁸–11.6 × 10⁸ Da. Cultivar ‘HB‐14’ was superior to the other cultivars, when combining larger seed size, higher resistant starch level and better properties.     

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

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

Industrial relevance

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

Effect of combined microwave‐hot air drying and superheated steam drying on physical and chemical properties of rice

Jasmine rice (Oryza sativa L.) was subjected to two drying operations: combined microwave‐hot air drying (MHA) at initial power intensity of 3, 4 and 6 W g^?1 and superheated steam drying (SHS) at 300 °C and 400 °C. During drying, kinetic rate constants of SHS were significantly higher than those of MHA. Both drying operations could decrease enthalpy of starch gelatinisation from 9.28 J g^?1 to 1.64–6.17 J g^?1, increase gelatinisation extent to 33.51–82.33%, decrease crystallinity from 28.87% to 18.15–21.33%, improve scavenging ability of 1,1‐diphenyl‐2‐picrylhydrazyl, increase ferric reducing antioxidant power and increase hardness of cooked rice from 5.66 N to 5.83–6.55 N, depending on microwave power and drying medium temperature. However, taste profiles and liking scores were comparable to the regular brown rice. Therefore, MHA and SHS operations could be potentially used for reducing drying process and promoting antioxidant activity.     

Studies on pasting and structural characteristics of thermally treated wheat germ

In order to utilize wheat germ, a nutrient-dense by-product of wheat milling industry, in various food products, different moist and dry heat treatments were used to stabilize and to investigate its influence on protein sub-unit composition, starch pasting characteristics and structural characteristics. The raw germ contained 11% moisture, 31.4% crude protein, 18.4% dietary fibre and 7% fat. Different heat treatments, except for fluidized bed drying, inactivated the lipase activity in germ completely. On the other hand, various heat treatments inactivated lipoxygenase activity to varying extents (78–92%). Extent of gelatinisation, as assessed in electron micrographs was least in steamed and fluidized bed dried samples, while steamed and oven-dried germ and drum dried germ samples exhibited greater extent of gelatinisation. The extent of gelatinisation seemed to be more in drum-dried sample as no intact starch granule was observed. Electrophoretic pattern and sub-unit composition of germ samples remained similar, irrespective of their nature of treatment. Raw germ showed a gelatinisation temperature of 67.9 °C as measured in visco-amylograph and increased to 80.3–88.3 °C for differently treated germ samples, except for drum-dried sample. Differently heated germ samples, depending on their extent of pre-gelatinisation, gave significantly lower peak viscosity (221–268 BU) and break down values (0–9 BU).     

Starch hydrogels from discarded chestnuts produced under different temperature-time gelatinisation conditions

It is essential to know the temperature-time dependence on the chestnut starch gelatinisation process. With this aim, physicochemical and thermomechanical properties of native chestnut starch and with different gelatinisation degrees, isolated from discarded chestnut fruits under environmental friendly aqueous procedures, were studied. Isolated starch (144.96 ± 1.74 μm) presented high total starch (91.83 ± 0.24%), low damage starch (0.10 ± 0.04%), apparent amylose content of 20.31 ± 1.48% and relative crystallinity of 15.7 ± 0.4% with a C-type pattern. Chestnut starch dispersions were formulated at 40% (w/w). Rheological measures indicated that temperatures below 60 °C were not able to form a hydrogel. The hydrogels formed between 62.5 and 65 °C (peak and final gelatinisation temperature, respectively) developed a stable and strong network with short maturation times and full thermoreversibility. Finally, hydrogels prepared above 65 °C were weaker and no completely thermoreversible. A linear relationship was identified between elastic features determined by rheology (G′_gel,1 Hz) and texture (springiness, D₁/D₂).     

Prediction of the degree of starch gelatinization in wheat flour dough during microwave heating

In order to produce quick-boiling noodles, we made partially pre-gelatinized wheat flour dough by the microwave heating method. A cylindrical-shaped piece of wheat flour dough containing 3% NaCl was heated by 117 W microwave oven operating at 2450 MHz. The sample dough was intermittently heated to allow sufficient gelatinization of the starch granules of the dough. The resultant changes in the internal temperature profiles of the sample dough were measured and compared with numerical prediction, which is the two-dimensional heat conductive equation with a term for internal heat generation based on Lambert’s law. In order to calculate the internal heat generation during microwave heating, we measured the dielectric properties of wheat flour dough at 2450 MHz from 10 to 70 °C by the open-ended coaxial probe method. The calculated temperature history could describe the feature of the experimental one during intermittently microwave heating. Furthermore, the progress of starch gelatinization according to the heat transfer in the sample dough was predicted by the Runge–Kutta gel method. A tendency that the total gelatinization degree increased slowly during the microwave intermittent heating was obtained in the calculated result.     

Evaluation of starch analysis methods for feed samples

The objectives of this work were to evaluate the efficacies of commercial starch analyses and of starch analysis extraction and gelatinisation procedures. In Study 1, accuracy and specificity of commercially available starch analyses were evaluated with six co‐operating laboratories (five commercial, one university). Results from 11 test samples showed three laboratories with recoveries of purified starch of 92 g kg⁻¹ or less. Three and four laboratories had inflated values when samples contained glucose or sucrose, respectively. Analyses appeared to have good specificity for glucose. Incompleteness of starch detection and interference by non‐starch carbohydrates can affect commercially available analyses. In Study 2, extraction with 80:20 ethanol/water (v/v; 80EtOH) or 90:10 ethanol/water (v/v; 90EtOH) to remove low‐molecular‐weight carbohydrates, and gelatinisation with heat, alkali (KOH), 6 M urea or 8 M urea were evaluated. Extraction with 80EtOH or 90EtOH reduced interference from non‐starch carbohydrates. Gelatinisation with heat was adequate for good recoveries of starch glucose for both control (non‐extracted) and 80EtOH‐extracted samples; gelatinisation with alkali was required for 90EtOH‐extracted samples. Recoveries of pure starch samples were greatest with no extraction and heat gelatinisation. 80EtOH extraction with heat gelatinisation appears to be an adequate preparation method when removal of low‐molecular‐weight carbohydrates is desired. © 2000 Society of Chemical Industry     

Gelatinisation of starch and wheat flour starch—A review

Gelatinisation of wheat starch is reviewed, making comparisons with other starches.Starch in wheat kernel endosperm is briefly described. Various aspects of gelatinisation of starch in water are considered, including swelling and interaction with water before the onset of gelatinisation, increase in consistency during gelatinisation, gelatinisation temperature, types of gelatinised system and gel and paste formation upon cooling. In addition, the traditional rationale of gelatinisation and gelatinisation from the viewpoint of water mobility are discussed.Experimental methods used to study gelatinisation are also reviewed, as are the effects of starch concentration, protein, pentosans, surface active agents, fats, salt and sugars on gelatinisation and shear rate on consistency.