Thermal characteristics of ohmically heated rice starch and rice flours

ABSTRACT:  Thermal properties of conventionally and ohmically heated rice starch and rice flours at various frequencies and voltages were studied. There was an increase in gelatinization temperature for conventionally heated rice starches since they were pregelatinized and became more rigid due to starch–chain interactions. In addition, there was a decrease in enthalpy (energy needed) for conventionally and ohmically heated starches during gelatinization; thus, the samples required less energy for gelatinization during DSC analysis. Ohmically heated commercial starch showed the greatest decrease in enthalpy probably because of the greatest extent of pregelatinization through ohmic heating. Brown rice flour showed the greatest gelatinization temperature resulting from the delay of starch granule swelling by lipid and protein. Enthalpy of ohmically heated starches at 20 V/cm was the lowest, which was most likely due to the lower voltage resulting in a more complete pregelatinization from a longer heating time required to reach 100 °C. Ohmic treatment at 70 V/cm decreased onset gelatinization temperature of white flour; therefore, it produced rice flour that swelled faster, whereas the conventionally heated sample showed a better thermal resistance.     

The effects of natural fermentation on the physical properties of rice flour and the rheological characteristics of rice noodles

The effects of fermentation of whole polished rice grains on the physical properties of rice flour and the rheological characteristics of rice noodles were investigated. Natural fermentation had little effect on the crystalline structure of rice starch, as measured by X‐ray diffraction, but the ratio of the crystalline to the amorphous regions increased. The thermal properties of rice flours were determined using differential scanning calorimetry and a rapid viscosity analyser (RVA). The gelatinization temperature, T_p, and the RVA peak viscosity of rice flour decreased, while the gelatinization enthalpy, ΔH, increased after fermentation. The FTIR spectra of fermented and control rice flours were similar. Fermented rice starch granules had slight superficial corrosion when examined using scanning electron microscopy. Fermentation may thus change the amorphous region of the starch granule as well as the chemical components and thereby modify both physical properties of rice flour and rheological characteristics of rice noodles.     

Influence of Acid Treatment on Physicochemical Properties of Aged Rice Flour

This study investigated the influence of citric acid and ascorbic acid solutions (0.0–0.9% w/w) on the physicochemical properties of 12 month aged rice flour (aged) using 0.7 month rice flour (fresh) as the reference. The results showed that rice storage did not affect the chemical composition. However, 12 month aged rice flour showed an increase in formation of disulfide bonds and amylose-lipid complexes which could restrict starch granules from swelling during gelatinization. Moreover, 12 month aged rice flour showed an increase in gelatinization temperature and enthalpy. Acid treatment did not break the formed disulfide bond but reduced the protein content in the acid-treated 12 month aged rice flour producing a significant increase in granular swelling and thus increased peak viscosity (p ≤ 0.05) but caused a reduction in retrogradation. The excess concentration (0.9% w/w acid solution) induced granule rupture. Aging of rice also affected the textural properties of freeze-thaw gels, increasing the hardness value but this was reduced by the addition of acids.     

Quality of Gluten-Free Bread Formulations Baked in Different Ovens

The objective of this study was to determine the effects of different tigernut flour/rice flour ratios (0:100, 5:95, 10:90, 15:85, 20:80, and 25:75) on quality of gluten-free bread formulations baked in infrared–microwave combination and conventional ovens. The degrees of the starch gelatinization of breads baked in different ovens were also compared. Conventionally baked breads prepared with tigernut flour/rice flour ratio of 10:90 and the infrared–microwave combination-baked breads prepared with tigernut/rice flour ratio of 20:80 had the most acceptable firmness and specific volume values. These breads had also similar color. Tigernut flour had significantly higher gelatinization temperatures and lower gelatinization enthalpy (ΔH_g) values than rice flour (p?≤?0.05). As rice flour was replaced with tigernut flour, lower ΔH_g values were observed in dough samples. Breads baked in both conventional and combination oven had sufficient starch gelatinization degrees ranging from 91% to 94% and from 84% to 85%, respectively.     

Changes in the quality and in vitro digestibility of brown rice noodles with the addition of ultrasound-assisted enzyme-treated red lentil protein

The effects of red lentil protein with ultrasound-assisted enzymatic treatment on the quality of brown rice noodles were investigated. The thermostability and anti-retrogradation ability of brown rice flour decreased significantly (P < 0.05), while the elastic and viscous modulus increased after adding untreated red lentil protein. Meanwhile, the cooking loss rate of brown rice noodles increased from 4.41% to 5.68%. When the red lentil protein was treated with ultrasound and enzyme, the protein–starch interaction was enhanced, and the negative effects of protein on brown rice flour and noodles were weakened. Moreover, the rice noodles with ultrasound-assisted enzyme-treated red lentil protein showed a lower starch digestibility than brown rice noodles, and its protein digestibility was significantly higher than that of rice noodles with ultrasound or enzyme-treated protein. Therefore, the addition of ultrasound-assisted enzyme-treated red lentil protein could effectively decrease predicted glycaemic index value, improve nutritional value and produce high-quality brown rice noodles.     

Effect of seed treatments on the chemical composition and properties of two amaranth species: starch and protein

The seeds of two Amaranth species were studied. The starch contents were 543 and 623 g kg^?1 while crude protein contents were 154 and 169 g kg^?1 for Amaranthus caudatus and Amaranthus cruentus seeds, respectively. The effect of several treatments, including cooking, popping and germination and flour air classification on the protein and starch properties were studied. Air classification decreased the starch content and increased the protein content, while heating increased the protein but did not affect the starch content. Germination decreased both starch and protein contents. Amylose content was increased by air classification and heating, but was not affected by germination. It was found that all treatments increased the starch swelling power and reduced the falling number. The resistant starch content was increased in the high protein flour (HPF) fraction and germinated flour compared with the raw flour, while its content decreased in the heat treated seed flours. These processes also affected the starch gelatinization temperature and peak viscosity. The thermal properties of the starch flour were not affected by air classification while gelatinization energy was decreased significantly (by 52.0 and 90.0% and by 70.0 and 95.0%) in cooked and popped A caudatus and A cruentus seed flours, respectively. The gelatinization energy was highest in germinated seeds dried at 90 °C with values of 2.67 and 3.87 J g^?1. Air classification reduced the level of all protein fractions. Thermal treatment decreased the water‐soluble fraction (albumins + globulins) and alcohol‐soluble fraction (prolamins) in both species. The levels of all fractions except the water‐soluble fraction (albumins + globulins) were reduced significantly in both species by germination, which mainly increased the amount of aspartic acid, serine and alanine, while the amounts of threonine, arginine and tyrosine decreased in both species. The polypeptide bands of the HPF in both species were unchanged compared with the raw seed flours, but more intensive coloured bands were observed. Thermal treatments eliminated major and minor bands above 35.0 KDa in both species. Copyright © 2004 Society of Chemical Industry     

Effect of microwave vacuum drying and hot air drying on the physicochemical properties of durian flour

Unripe durian cv. Monthong was subjected to microwave vacuum drying (MVD) at 1200, 1600 and 2200 W and hot air drying (HAD) at 40, 50 and 60 °C to produce durian flour. Drying rate of MVD and HAD was 0.34–0.58 kg water kg dry solid^?1 min^?1 and 0.02–0.06 kg water kg dry solid^?1 min^?1, respectively. An increase in drying rate by either increasing hot air temperature or increasing microwave power decreased the degree of crystallinity from 21.95% to 2.31% and from 7.72% to 4.05%, respectively. Moreover, the increased drying rate caused a decrease in endothermic enthalpy (ΔH_gel) and pasting properties. Starch content of the durian flour was 41.40–47.03%. The starch granule morphology of durian flour was disrupted which indicated gelatinisation of flour during drying. Due to a short drying process, the MVD flour had less a*‐value (P ≤ 0.05) than the HAD flour.     

Mild steam treatment: Enhancing the rehydration performance of instant rice noodles by changing the physicochemical properties and gel structure of rice starch

The “instant” quality of instant rice noodles is significantly affected by slow rehydration during cooking. This happens as a result of the native rice starch's low ability to gelatinize as well as the high shear and pressure utilized in industries during the widely used extrusion molding process. In order to address this issue, the rice flour was pretreated with mild steam (MS) technology. The results revealed that the rehydration qualities of the rice noodles that were extruded from the steam-treated flour significantly improved. There was a reduction of 25.5% in the rehydration time, from 443 to 330 s. The MS-treated rice starch's peak viscosity increased to 4503 from 4044 mPa/s. Decreases in gelatinization enthalpy (ΔH) and short-range ordering also suggest a reduction in difficulty in accomplishing starch gelatinization. Scanning electron microscopy studies showed particle aggregation increased as the treatment duration lasted longer. In conclusion, our findings indicate that we successfully addressed the issue of slow rehydration in instant rice noodles while presenting a novel approach for their manufacturing in the manufacturing sector.     

Thermal and Pasting Properties of Acid‐treated Rice Starches

The physicochemical properties of acid‐treated rice starches were investigated. Rice starches were treated with hydrochloric acid at different acid concentrations and hydrolysis times. The pasting properties were tested using a Rapid Visco Analyser, and gelatinization and retrogradation properties using a differential scanning calorimeter. The results showed that acid concentration had a more pronounced effect on degree of polymerization (DP) and viscosity than hydrolysis time. The onset, peak and conclusion temperatures of gelatinization were increased significantly with hydrolysis time, while the gelatinization enthalpy (ΔH_G) was decreased. In addition, there was an increase in the gelatinization temperature range with longer hydrolysis time. After storing gelatinized starches at 4°C for 7 days, the transition temperature and enthalpy (ΔH_R) to melt retrograded amylopectin did not change significantly. Additionally, the temperature and enthalpy transition for melting amylose‐lipid complex of all gelatinized and retrograded starches were in the same range.     

Nutritional properties of tempeh flour from quality protein maize (Zea mays L.)

The objective of this investigation was to evaluate physico-chemical and nutritional properties of tempeh flour from a quality protein maize (QPM). In comparison to untreated QPM, the QPM tempeh flour showed a higher (P?0.05) gelatinization temperature (81.7 vs 73.9 °C), and resistant starch (4.24 vs 1.9 g/100 g dry flour), and a lower (P?0.05) gelatinization enthalpy (1.94 vs 2.74 J/g) and total starch content (56.9 vs 62.6 g/100 g dry flour). The essential amino acids (EAAs) content of raw QPM flour was improved by the solid-state fermentation process. The contents of His, Ile, and Leu increased (P?0.05) in 0.81, 0.52, and 1.46 g/100 g protein, respectively. The total sulphur and total aromatic EAAs increased (P?0.05) in 0.55 and 3.45 g/100 g protein, respectively. In untreated QPM flour, the first and second limiting EAAs were Lys and Trp, with EAAs score of 0.72. First and second limiting EAAs in QPM tempeh flour were Trp and Lys, with an EAAs score of 0.84. The SSF process increased (P?0.05) nutritional indicators as follows: protein efficiency ratio (PER) from 1.78 to 2.10, calculated PER from 1.43 to 1.74, and protein digestibility corrected amino acid score from 0.55 to 0.83. It is concluded that based mainly on its nutritive value, fermented flour may be considered for the fortification of widely consumed cereal-based food product (tortillas, bread, cookies, atoles).     

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

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

Influence of Gluten-free Flours and their Mixtures on Batter Properties and Bread Quality

Gluten is a major component of some cereals and is responsible for flour technological characteristics to make bakery products. However, gluten must be eliminated from the diet of celiac patients because its ingestion causes serious intestinal damage. The objectives of this study were to assess the effect of different flours and their mixtures on thermal and pasting properties of batters, and to study the quality parameters and staling rate of gluten-free breads. Starch gelatinization temperatures and enthalpies depended on batter composition. Soy flour addition had a higher effect on rice than on corn starch, indicating some differential interaction between starch and proteins. Inactive soy flour incorporation improved all bread quality parameters in both corn- and rice-based breads. Higher batter firmness of formulations with soy addition (extrusion force was doubled in rice/soy and rice/corn/soy batters with regard to rice and rice/corn batters) partially explained higher specific volume (rice breads: 1.98 cm³/g; rice/soy 90:10 2.51 cm³/g, corn/soy 90:10: 2.05 cm³/g, whereas corn/soy 80:20: 2.12 cm³/g), as these batters retained more air during proofing. The staling rate was decreased by soy flour incorporation on rice (staling rate of rice breads with 10% soy diminished 52%, and with 20% of soy addition, 77%, both regarding to 100% rice breads) and corn formulation (the staling rate of corn/soy 80:20 breads was 5.9% lower than corn/soy 90:10) because of the high water-holding capacity of soy proteins and the interactions established with amylopectin that could retard the retrogradation process. Breads made with rice, corn, and soy flours showed the best quality attributes: high volume, good crumb appearance, soft texture, and low staling rate.     

Effect of Mesona Blumes gum on physicochemical and sensory characteristics of rice extrudates

The aim of this study was to evaluate effects of Mesona Blumes gum (MBG) on some physical, chemical, sensory and antioxidant properties of rice extrudates. MBG was added to rice flour at 0%, 5%, 10%, 15% and 20% (w/w). The water solubility index (WSI) increased from 4.19% to 15.32% with MBG addition. Both water absorption index (WAI) and moisture retention (MR) reached maximum at 15% MBG. Bulk density (BD) was the highest at 5% (131.22 g cm^?3) and the lowest at 15% MBG (121.44 g cm^?3). Hardness was maximal at 5% (8.44 N mm^?2) and minimal at 15% MBG (5.98 N mm^?2). Expansion ratio (ER) and lightness (L*) decreased for all extruded products with MBG. MBG at 5% or 10% level could improve sensory characteristics of final products. The extract of extrudates at 15% MBG had the highest antioxidation ability among those extrudates. Thus, it was possible to produce a new palatable rice extrudate with MBG.     

Effects of pulsed electric fields (PEF) treatment on physicochemical properties of potato starch

Potato starch–water suspensions (8.0%, w/w) were subjected to pulsed electric fields (PEF) treatment at 30 kV·cm^− 1, 40 kV·cm^− 1 and 50 kV·cm^− 1, respectively. The physicochemical properties of PEF-treated potato starch samples were investigated using scanning electron microscopy (SEM), laser scattering technique, X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and the Brabender rheological method, with native potato starch as reference. It has been concluded from SEM analysis that dissociation and damage of PEF-treated potato starch granules appeared. Some granules aggregated with each other and showed gel-like structures. It was revealed from particle size analysis that there was an obvious increase of the granule size after PEF treatment. This has been attributed to the aggregation among granules. It was also demonstrated from other analysis that relative crystallinity, gelatinization temperatures, gelatinization enthalpy, peak viscosity as well as breakdown viscosity of modified samples all decreased with increasing electric field strength.

Industrial relevance

In this study, the effect of PEF treatment (up to 50 kV·cm^− 1) on physicochemical properties of potato starch has been investigated. The results from SEM images showed that dissociation, denaturation and damage of potato starch granules had been induced by the PEF treatments. Some of granule fragments showed gel-like structures, and congregated with each other or with other starch granules. Laser scattering measurements of particle size revealed that an obvious increase of granule size under electric field strength of 50 kV·cm^− 1, which was attributed to the aggregation of the starch granules. The X-ray diffraction pattern showed an obvious loss of crystalline structure after the PEF treatment at 50 kV·cm^− 1, which induced a trend of transformation from crystal to non-crystal in potato starch granules. DSC analysis showed a decrease in gelatinization temperatures (T_o and T_p) and gelatinization enthalpy (ΔH_gel) with increasing electric field strength. Brabender rheological method has been used to show that the peak viscosity and breakdown viscosity decrease with increasing electric field strength of PEF treatment. All the results reveal that the PEF treatment can lead to an intragranular molecular rearrangement of potato starch granules, which induces changes of various physicochemical properties of the treated starch thus may endow it some new characteristics and functions. This phenomena may warrant further more detailed study.     

湿热及酶解处理对糯米粉体外消化特性和血糖生成指数的影响

目的 研究酶解处理、湿热处理和湿热复合酶解处理对糯米粉体外消化特性和血糖生成指数(glycemic index, GI)的影响。方法 采用体外消化法测定了不同处理糯米粉的水解度和血糖生成指数值, 并通过X-射线衍射和激光共焦拉曼光谱实验测定了不同处理糯米的淀粉晶体结构。结果 3种处理的水解度和抗性淀粉(resistant starch, RS)相对含量增加, 慢消化淀粉(slowly digestible starch, SDS)相对含量降低; 其中湿热复合酶解处理条件下, RS相对含量最高, 为71.31%; 酶解处理条件下, RS相对含量最低, 为67.66%。酶解处理、湿热处理和湿热复合酶解处理的GI值分别为79.1、76.0和70.6。3种处理后糯米淀粉的晶体结构发生改变, 3种处理均使分子短程有序度与结晶度增加, 其中湿热复合酶解处理条件下, 结晶度最高, 为34.41%。 结论 湿热复合酶解处理后的糯米粉抗消化特性增强且GI值降低, 湿热复合酶解工艺可能通过影响糯米粉的体外消化率来降低GI值。     

Rice varieties in relation to rice bread quality

BACKGROUND: It is difficult to predict rice bread quality only from the amylose content (AC) or dough characteristics of new lines produced by rice breeding programmes. This study investigated the AC relative to bread baking quality of rice varieties developed in Korea, and identified specific characteristics that contribute to rice bread quality. RESULTS: Manmibyeo, Jinsumi, Seolgaeng and Hanareumbyeo were classified as low AC, YR24088 Acp9, Suweon517, Chenmaai and Goamibyeo as intermediate AC and Milyang261 as high AC. Suweon517, Milyang261 and Manmibyeo had a high water absorption index (WAI), while Goamibyeo, YR24088 Acp9, Jinsumi, Seolgaeng, Hanareumbyeo and Chenmaai had a low WAI. The gelatinisation enthalpy of flour varied from 9.2 J g^?1 in Milyang261 to 14.8 J g^?1 in YR24088 Acp9 . After 7 days of storage the rate of flour retrogradation and crumb firmness were weakly correlated, with the exception of Jinsumi . Bread volumes of Jinsumi, Chenmaai, YR24088 Acp9 and Goamibyeo were comparable to that of wheat flour, but the rest were unsuited to bread making because of their low volume and hard crumb texture. CONCLUSION: Based on volume, texture and crumb firmness ratio, Chenmaai and Goamibyeo were the most appropriate varieties for making bread. An intermediate AC and low WAI were the primary indicators of rice bread flour quality. Copyright © 2011 Society of Chemical Industry     

Effect of Chlorine Treatment on Wheat Flour and Starch: Measurement of Thermal Properties by Differential Scanning Calorimetry

Differential scanning calorimetry (DSC) was used to study the effect of chlorine treatment of wheat flour on the heat of gelatinization of the wheat flour and starch. The DSC thermograms were corrected for heat capacity changes and thermal lag. An endothermic transition occurred in both flours and starches at a temperature commonly associated with starch gelatinization. The enthalpy (ΔH) for the starches was concentration dependent. The chlorine treatment did not affect significantly the transition temperatures nor enthalpies of either the flour or the starch isolated from it. Addition of sucrose delayed the onset of gelatinization and increased the ΔH for both treated and untreated wheat flours and starches.     

Production and Nutritional Evaluation of High-Protein Rice Flour

Optimal processing conditions for the production of high-protein rice flour from two rice varieties were determined. Gelatinized rice flour slurry was treated with 0.25 mg α-amylase per milliliter of slurry at 60°C for 90 min. The hydrolyzed starch was removed by centrifugation. The precipitated paste was then freeze-dried to yield high-protein rice flour which had 38% protein. The amino acid composition of the high-protein rice flour was similar to that of the dehulled rice flour. The protein efficiency ratio of the high-protein rice flour was 2.17. Supplementation with limiting amino acids, lysine and threonine, or with a laboratory-prepared freeze-dried soy isolate increased protein efficiency ratios above that of casein.     

Effect of Different Extrusion Treatments and Particle Size Distribution on the Physicochemical Properties of Rice Flour

Rice flour is an interesting alternative for developing gluten free products, but its features do not always meet the process requirements. The objective of this study was to modify the functional properties of rice flour by combining extrusion and size fractionation. Different extrusion conditions (barrel temperature, feed moisture content and feed rate) were applied to vary the severity of the treatment on the flour constituents. Extrusion and mechanical fractionation of the rice flours modified their behavior affecting hydration, thermal and pasting features, besides their susceptibility to enzymatic hydrolysis. Specifically, onset and peak temperature increased and gelatinization enthalpy decreased when increasing barrel temperature of the extrusion. Fine flours with stronger extrusion (high temperature barrel) showed the highest susceptibility to enzymatic hydrolysis. Overall, the combination of both physical treatments maybe an attractive alternative for obtaining clean label rice flours with modified features.     

Functional,digestibility, and antioxidant properties of brown and polished rice flour from traditional and new‐improved varieties grown in Sri Lanka

Sri Lankan traditional and improved rice varieties were processed into brown and polished rice flours. Samples were analyzed for AM, protein, lipid, total phenolic content, and antioxidant activity. Gelatinization and retrogradation properties were observed in the Rapid Visco Analyzer (RVA) and DSC. The AM content of the samples was high to intermediate (20 to 26%) except for one which was low (17%). Brown rice flour (BRF) samples had lower swelling power, lower RVA viscoamylograph profile, lower gel hardness, lower gelatinization enthalpy but higher gelatinization peak temperature and lower melting enthalpies of its retrograded AP relative to its corresponding polished rice flour (PRF) samples. The BRF showed a lower decrease in peak viscosity in the RVA viscoamylograph as compared to its PRF when treated with α‐amylase indicating inhibition potential. The traditional rice varieties had 68 to 86% higher total phenolic content (TPC) and 86 to 90% antioxidant activity in the BRF samples as compared to the improved varieties. A study on the antioxidant profile of the brown rice of the traditional rice varieties is being undertaken to explore their value as functional foods.