Effect of thermal processing and storage on digestibility of starch in whole wheat grains

Gelatinisation and retrogradation of starch in wheat flour systems and whole wheat grains were studied using DSC and the impact of these events on starch digestibility was investigated. Gelatinisation of starch was possible in wheat flours with more than 60% moisture content (dwb) and gelatinised samples had higher digestibility values. Retrogradation of starch was studied with partially and fully cooked (boiled at 100 °C for 12 min and 32 min, respectively) wheat grains that were subjected to storage at 22 °C for 48 h. Stored samples had lower digestibility values when compared to the freshly cooked counterparts. The effect of moisture on retrogradation was studied with fully cooked wheat grains that were dried to a range of moisture contents (14.6–35.9%, wwb) and stored at 20 °C for 24 h. Retrogradation enthalpy increased with increasing moisture content; however, digestibility values did not reflect the changes in retrogradation enthalpy. The possibility of estimating the degree of retrogradation in fully cooked grains (32 min cooking) was investigated using a wheat flour-water system. The retrogradation enthalpy of fully cooked grains was slightly higher than the wheat flour-water system (at a moisture content of 49%, wwb) during the course of storage at 22 °C.     

Effect of partial gelatinization and retrogradation on the enzymatic digestion of waxy rice starch

The effect of partial gelatinization and retrogradation on in vitro enzymatic digestibility of waxy rice starch was investigated, and the relationship between the residual crystallinity and digestibility measured. An aqueous dispersion of starch (5%, dry weight basis) was partially gelatinized by heating at different temperatures (60, 65, or 70 °C for 5 min). The relative melting enthalpy values of the starch samples, based on the melting enthalpy of native starch, were 69.0, 36.7, and 8.5%, respectively. Retrograded starch samples were also prepared by storing a fully gelatinized starch paste (5% starch) at 4 °C for 2, 4, or 7 d, and the relative melting enthalpy values for the starch samples were 36.7, 67.2, and 79.9%, respectively. The partial gelatinization and retrogradation changed the enzymatic digestion behavior of the waxy rice starch samples, and the changes were significant in the initial stage of digestion. The digestion rate was reduced as the melting enthalpy increased. The amounts of slowly digestible starch (SDS) and resistant starch (RS) correlated positively with the relative melting enthalpy of the partially gelatinized or retrograded starch samples. The glycemic index (GI) estimated using an in vitro digestion test correlated negatively with the relative melting enthalpy. At similar melting enthalpy levels, the partially gelatinized starch samples were more resistant to enzymatic digestion than the retrograded starch samples, indicating that the thermal history and the crystalline morphology affected the enzymatic digestion behavior of starch.     

Effects of added water and retrogradation on starch digestibility of cooked rice flours with different amylose content

Flours derived from rice varieties with different amylose content possess distinct physicochemical and molecular properties. The aim of this study was to determine optimal processing conditions for preparing rice flour-based foods with reduced starch digestibility. To do so, we evaluated the in vitro starch digestibility of rice flours with five varieties. Reducing the amount of water (from 10-fold to 4-fold of rice flour) used for cooking rice flour lowered its starch digestibility, and the magnitude of the decrease was positively correlated with amylose content. When retrogradation of cooked rice flour proceeded for 7 days, the digestibility of high-amylose rice flours declined rapidly in the first 3 days, whereas the digestibility of low-amylose rice flours declined continuously. Our analysis also demonstrated that the chain length distribution of starch molecules and the final and setback viscosity pasting properties were the most important parameters affecting the digestibility of rice flours. Based on our results, it appears possible to reduce rice starch digestibility by establishing optimum processing conditions for different varieties. We suggest a 7-fold addition of water and retrogradation for 1 day for high-amylose rice varieties and a 4-fold addition of water with 3 days of retrogradation for low-amylose rice.     

In vitro starch digestibility and pasting properties of germinated brown rice after hydrothermal treatments

Germinated brown rice (GBR) recently has received renewed attention due to its enhanced nutritional value. Pasting properties and in vitro starch digestibility of GBR were examined before and after hydrothermal treatments. Steeping in water (30 °C, 24 h) raised the moisture content and germination percentage of brown rice. Pasting viscosity was substantially decreased but gelatinization temperatures and enthalpy were decreased only marginally by germination (30 °C, 48 h). However, annealing (50 °C, 24 h) and heat-moisture treatment (100 °C, 1 h at 30% moisture) after germination resulted in increased pasting viscosity and gelatinization temperatures. The hydrothermal treatments, however, induced browning reactions to darken the flour of GBR. The digestibility of starch in brown rice was increased by germination. The contents of rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS) in the cooked brown rice were 47.3%, 40.8%, and 11.9%, respectively, but changed to 57.7%, 39.1%, and 3.2%, respectively upon germination. The hydrothermal treatments, however, decreased the digestibility of starch in GBR. The heat-moisture treatment decreased the RDS content in GBR near to that of native brown rice. The digestibility and physical properties of brown rice can be controlled by germination and hydrothermal treatments.     

Retrogradation behaviour of milled and brown rice pastes during ageing

Retrogradation of gelatinised starch is the main phenomenon that influences the texture of cooked rice. The rate of retrogradation is affected by several factors including amylose and amylopectin ratio, protein and fibre. The objective of this study was to analyse the pasting properties and the retrogradation behaviour of six traditional and five aromatic Italian rice varieties. The pasted gels, after cooling, were evaluated by dynamic rheological measurements for up to 7 days of storage at 4 °C. The samples were also analysed by a NIR spectrometer. The pasting properties and the retrogradation behaviour of milled rice flours strongly depended on the rice varieties. During gel ageing, a noticeable increase of G′ and G″ was observed only for the milled rice varieties Asia, Gange, Fragrance and Vialone Nano, characterised by a high amylose content. No further hardening was found either for the other milled varieties or for all the brown samples. The methods used in this work (dynamic oscillatory rheometry and FT-NIR spectroscopy) turned out to be very useful in the definition of rice starch gels ageing.     

Effect of jet-cooked wheat gluten/lecithin blends on maize and rice starch retrogradation

Vital wheat gluten and lecithin (GL) (50:50, w/w) were dry blended in a coffee grinder and a 9.5% (w/v) aqueous slurry was jet-cooked (steam pressures of 65 psi/g inlet and 40 psi/g outlet) to disaggregate wheat gluten and facilitate better dispersion of the two components. The jet-cooked material was freeze-dried and stored at 0 °C for future use. The GL blend was added to pure food grade common maize and rice starch at concentrations of 0 (control), 6, 11, 16, and 21%. Starch gelatinization and retrogradation temperature transitions were determined using Differential Scanning Calorimetry (DSC). From the DSC profiles, the change in the ΔH value was used as an indication of starch retrogradation, where a higher ΔH value indicated higher retrogradation. The ΔH values of the blends at 4 °C had higher values than the −20 °C and the ambient (25 °C) storage temperatures. Overall, the 21% GL/starch blends reduced retrogradation by 50%. The lower amylose content of rice starch relative to maize starch was reflected in Rapid Visco Amylograph (RVA) measurements of peak viscosity, and similarly, Texture Analyzer (TA) measurements indicated that maize starch gel is firmer than rice starch gel. Retrogradation was also evaluated by observing G′, the shear storage modulus, as a function of time after running a standard pasting curve. Using this method, it appears that GL has a significant effect on maize starch retrogradation, since low concentrations (<0.4%, w/w) reduced G′ up to 40%. The opposite behavior was seen in rice starch, where G′ increased directly with added GL. It appears that the amylose level in the rice starch is too low to be affected by the GL, and the increase seen in G′ is most likely due to added solids.     

月桂酸对小麦淀粉凝胶回生特性的影响

为了解月桂酸对小麦淀粉凝胶回生特性的影响,利用X射线衍射仪和差示扫描量热仪研究了月桂酸对小麦淀粉凝胶晶体结构和热特性的影响。结果表明,月桂酸与小麦淀粉结合形成了月桂酸-淀粉复合物。在短期回生过程中,淀粉含有V-型结晶结构和B-型结晶结构,淀粉凝胶中直链淀粉分子特征衍射峰减弱,月桂酸-淀粉复合物衍射峰增强;短期回生淀粉含有直链淀粉重结晶的熔融峰和淀粉-脂肪酸复合物的熔融峰,月桂酸-淀粉复合物熔融焓显著小于淀粉凝胶熔融焓;月桂酸对淀粉短期回生的抑制作用主要是对直链淀粉重结晶的抑制。长期回生过程中,随贮藏时间延长,支链淀粉分子发生了重结晶,淀粉凝胶的结晶度从15.37%增大至18.75%,而月桂酸-淀粉复合物结晶度从10.36%增大至13.23%;回生淀粉中支链淀粉重结晶的熔融焓增大,复合物重结晶的熔融焓减少。说明月桂酸与淀粉形成复合物能抑制小麦淀粉的短期回生和长期回生。     

Acetylation of intact white rice grains to alter the physicochemical properties

The effect of acetylation of milled rice grains of selected varieties (TDK 8, YRW 4, Reiziq, Amber 33, and SHZ 2) with varying apparent amylose contents (3.8–26.6%) on their physicochemical properties was investigated. Milled rice samples were treated with different acetic anhydride concentrations (0.004–0.04 g per 100 g of milled rice samples in 225 mL of water). Results showed that glutinous (TDK 8), very low amylose (YRW 4) and low amylose containing varieties (Reiziq) were prone to acetylation even with 0.004 g of acetic anhydride. X-ray diffraction patterns showed an increase in the crystallinity in acetylated samples and formation of V-type crystals, suggesting the possible interaction of acetic anhydride with starch. Acetylation of rice grains resulted in reduced peak and final viscosities and gel strength, particularly in glutinous (TDK 8) and very low amylose (YRW 4) rice. Differential calorimetric study showed that acetic anhydride treatment resulted in reduced thermal transition temperatures and enthalpy of all varieties. Although increase in the retrogradation thermal temperatures was observed, the enthalpy of retrogradation was reduced with increasing acetylation, suggesting that the extent of starch retrogradation was lower in all varieties with more prominent reduction in the glutinous type. Furthermore, the texture of cooked acetic anhydride treated rice grains was less hard and showed more adhesiveness. This study demonstrated that the acetylation of rice grains (instead of flour) was successfully achieved, showing the potential of applying acetylation to alter the textural, pasting, thermal and retrogradation properties of rice.     

Effects of altitude above sea level on the cooking time and nutritional value of common beans

The present study was conducted with the objective to determine the effects of altitude above sea level, on the cooking time and nutritional value of common black beans (Phaseolus vulgaris). Three 100 g samples of theOstua variety were cooked at 8 individual locations, ranging in altitude from 0 to 2256 meters, in Guatemala, to establish water uptake and cooking time. The cooked samples were separated into cooked beans and cooking broth for chemical analysis. This included moisture, protein, lysine, tannins, total and enzyme susceptible starch, and fiber fractionation. The cooking liquor was analyzed for total solids, moisture, protein, ash and K. A 1200 g sample was cooked for the cooking time established previously, for biological testing of nutritional value,which included Net Protein Ratio (NPR), Protein Effciency Ratio (PER), and protein digestibility. Altitude influenced cooking time which increased from 78 min at 0 m, to 264 min at 2256 m. Final moisture content in the cooked bean was similar at all altitudes and there was a tendency to yield smaller amounts of solids in the cooking broth at higher altitudes. The increase in cooking time was significant. Bean water uptake at all times was significantly slower and smaller at ambient T, as compared to water uptake at boiling T, at all altitudes. Protein and lysine content were not affected by altitude, however, tannin and catechin were lower in cooked samples, as compared to the raw material. Altitude did not affect the content of these substances. Total starch and total sugars were higher in the raw sample, as compared to the cooked samples, but there was no effect of altitude. Enzyme susceptible starch (ESS) was lower in the raw sample as compared to the cooked samples, which contained similar amounts with respect to altitude. No change was observed in fiber fractions of the cooked beans. Likewise, the composition of the cooking broth was very similar between cooking locations. There was a small tendency to a lower protein quality, with respect to altitude, the effect of which was more obvious in the apparent protein digestibility values. Undercooking or overcooking at one location influenced protein quality values. The extended cooking time of beans at high altitudes, has important economic and environmental implications, since significant amounts of wood have to be used.     

Retrogradation of waxy and normal corn starch gels by temperature cycling

Gelatinized waxy and normal corn starches at various concentrations (20–50%) in water were stored under temperature cycles of 4°C and 30°C (each for 1 day) up to 7 cycles or at a constant temperature of 4°C for 14 days to investigate the effects of temperature cycling on the retrogradation of both starches. Compared to starches stored only at 4°C, both starches stored under the 4/30°C temperature cycles exhibited smaller melting enthalpy for retrogradation (ΔH_r), higher onset temperature (T_o), and lower melting temperature range (T_r) regardless of the starch concentration tested. Fewer crystallites might be formed under the temperature cycles compared to the isothermal storage, but the crystallites formed under temperature cycling appeared more homogeneous than those under the isothermal storage. The effect of starch content on the retrogradation was greater when the starch gels were stored under cycled temperatures. The reduction in ΔH_r and the increase in conclusion temperature (T_c) by retrogradation under 4/30°C temperature cycles became more apparent when the starch concentration was lower (20 or 30%). Degree of retrogradation based on melting enthalpy was greater in normal corn starch than in waxy corn starch when starch content was low.     

Effect of glutathione on gelatinization and retrogradation of wheat flour and starch

Reduced glutathione (GSH) commonly exists in wheat flour and has remarkable influence on gluten properties. In this study, effect of GSH on the gelatinization and retrogradation of wheat flour and wheat starch were investigated to better understand the GSH-gluten-starch interactions in wheat flour. Compared with wheat starch, wheat flour showed significant decreases in peak and final viscosity, and gelatinization onset temperature with increasing GSH concentration. GSH depolymerized gluten and thereby broke down the protein barrier around starch granules to make the starch easily gelatinized. However, the interaction between GSH and wheat starch restrained starch swelling. GSH addition resulted in weakened structure with higher water mobility in freshly gelatinized wheat flour dispersions but decreased water mobility in wheat starch dispersions. After storage at 4 °C for 7 d, GSH increased elasticity and retrogradation degree in wheat flour dispersions but retarded retrogradation in wheat starch dispersions. The results indicated that GSH promoted retrogradation of wheat flour, which mainly attributed to the depolymerized gluten embedding in the leached starch chains, and inhibiting the re-association of amylose, and subsequently promoted the starch intermolecular associations and starch retrogradation. This study could provide valuable information for the control of the quality of wheat flour-based products.     

Water stress during grain development affects starch synthesis,composition and physicochemical properties in triticale

Triticale, a man-made cereal crop developed from a cross between wheat and rye, has excellent agronomic traits to produce starch for bioindustrial applications. The effects of different levels of water stress on expression of starch synthesis genes and starch composition and physicochemical properties were investigated in this study. Three triticale varieties from 5 days post-anthesis were treated with three levels of water stress: low water stress (LWS) at 55–60% of soil moisture, moderate water stress (MWS) at 30–35% soil moisture and severe water stress (SWS) at 10–15% soil moisture. Water stress led to a significant reduction in seed weight at SWS (35–45%). A decrease in starch content was noticeable from MWS onwards and the values were decreased by 42–55% at SWS across all varieties. Such decrease was associated with the reduced expression of starch synthesis genes at 19 days of water stress (DWS). MWS favoured an increase of amylose proportion in triticale starch and it was accompanied by a significant up-regulation of GBSSI expression throughout the grain development. Triticale starch synthesized under water stress showed a reduced population of small granules and an increase of A-type to B-type ratio. SWS caused pitting on starch granules but did not alter the biconcave disc shape of mature granules. An inverse relationship between water stress and a range of starch gelatinization temperature was observed and the MWS environment specifically decreased the peak temperature (Tp) and increased the enthalpy. Our results signify that starch morphology, composition and physicochemical properties in triticale grains could be altered if triticale is grown under drought conditions.     

Effects of polymerization changes in maize proteins during nixtamalization on the thermal and viscoelastic properties of masa in model systems

Although nixtamalization is widely used in the food industry, a comprehensive understanding of the influence of proteins on the viscoelastic behavior and thermal properties in masa is still lacking. In this work, the effect of protein changes and its influence on the masa viscoelastic behavior were studied using model systems. Mixtures of lime-starch, zein-starch and lime-zein-starch were cooked at 90 °C from 20 to 150 min. Zein changes during cooking were analyzed by SDS-PAGE. Thermal transition temperatures and enthalpies were determined using differential scanning calorimetry (DSC). Dynamic oscillatory tests were undertaken on model system samples with 50% (w/v) moisture content, using a strain-controlled rheometer. SDS-PAGE showed that zein polymerizes during cooking. In the zein-starch model system, no visible protein bands were found after 30 min cooking; however, when lime was present, five bands were observed in all samples. Thermal transitions were observed around 55–62 °C for all model systems, probably corresponding to starch retrogradation. Rheological studies showed that protein exhibited higher influence in the gel strength by increasing the elastic character of the system. It was hypothesized that the combined effects of lime on starch, zein polymerization and the formation of calcium-zein bonds during cooking, yield a stronger and more elastic gel structure.     

Water stress during grain development affects starch synthesis,composition and physicochemical properties in triticale

Triticale, a man-made cereal crop developed from a cross between wheat and rye, has excellent agronomic traits to produce starch for bioindustrial applications. The effects of different levels of water stress on expression of starch synthesis genes and starch composition and physicochemical properties were investigated in this study. Three triticale varieties from 5 days post-anthesis were treated with three levels of water stress: low water stress (LWS) at 55–60% of soil moisture, moderate water stress (MWS) at 30–35% soil moisture and severe water stress (SWS) at 10–15% soil moisture. Water stress led to a significant reduction in seed weight at SWS (35–45%). A decrease in starch content was noticeable from MWS onwards and the values were decreased by 42–55% at SWS across all varieties. Such decrease was associated with the reduced expression of starch synthesis genes at 19 days of water stress (DWS). MWS favoured an increase of amylose proportion in triticale starch and it was accompanied by a significant up-regulation of GBSSI expression throughout the grain development. Triticale starch synthesized under water stress showed a reduced population of small granules and an increase of A-type to B-type ratio. SWS caused pitting on starch granules but did not alter the biconcave disc shape of mature granules. An inverse relationship between water stress and a range of starch gelatinization temperature was observed and the MWS environment specifically decreased the peak temperature (Tp) and increased the enthalpy. Our results signify that starch morphology, composition and physicochemical properties in triticale grains could be altered if triticale is grown under drought conditions.     

Comparative Protein Digestibility in Growing Rats of Cooked Rice and Protein Properties of Indica and Japonica Milled Rices

College,Laguna, Philippines.Received 1 ABSTRACT Eight indica and japonica milled rices with low amylose content and low starch gelatinisation temperature were analysed for cooked rice energy and N balance in growing rats and for protein properties. Digestible energy values were similar. Japonica rices Koshihikari and Sasanishiki had higher true digestibility (TD) and net protein utilisation in rats than indica rices IR24 and PR23383-15. Similar results were obtained from in vitro proteolysis. High TD of cooked rices was not significantly correlated with low prolamin content in raw rice and with low waxy gene product (protein bound to starch granule) but was significantly correlated with low cysteine content in protein and with low denatured prolamin content in cooked rice. In two pairs of cooked waxy milled rices, which are devoid of waxy gene product, japonica rice still tended to show higher rat TD and in vitro protein digestibility than indica rice, consistent with lower cysteine content in japonica protein.     

Hydrothermal modification of wheat starch. Part 2. Thermal characteristics of pasting and rheological properties of pastes

Water suspensions of starch (with the concentration of 8 g/100 g) were prepared in a measuring vessel of a Brabender viscograph and heated to temperatures of 74, 76.5, 79, 81.5, 84, 86.5, 89, 91.5 or 94 °C under continuous stirring. The resultant solution was cooled and frozen, and then defrosted. Thermal characteristics of re-pasting, rheological properties of produced pastes, starch solubility in water and swelling power were determined.The heating and freezing of the wheat starch suspension induced changes in its properties, with tendency and extent of these changes depending on temperature of pre-heating. The thermal characteristics of the analyzed starches revealed three peaks that corresponded to transitions proceeding during solubilization of retrograded amylopectin and retrograded amylose and solubilization of amylose–lipid complexes. Retrogradation of amylose induced by starch pre-heating followed by its freezing affected also the consistency coefficient and yield stress of the pastes formed by the analyzed starches. Values of these rheological parameters were higher at higher temperatures of pre-heating, compared to the pastes prepared from native starch, and were changing accordingly to the determined second order polynomial function. Amylose retrogradation occurring during the production of starch preparations diminished their solubility in water and increased their swelling power compared to native starch.     

Impact of amylose content on starch retrogradation and texture of cooked milled rice during storage

Milled rice from 11 varieties, with amylose levels from 1.2 to 35.6% dry base, were collected to study the impacts of amylose content on starch retrogradation and textural properties of cooked rice during storage. The relationship between amylose content and different properties was determined using Pearson correlation. Starch retrogradation enthalpy (ΔH_r) of cooked rice was determined by differential scanning calorimetry. ΔH_r values were found to be positively correlated with amylose content (0.603 ≤ r ≤ 0.822, P < 0.01) during storage. Textural properties were determined by a Texture Analyser. The hardness of cooked rice showed a positive correlation with amylose content (0.706 ≤ r ≤ 0.866, P < 0.01) and a positive correlation with ΔH_r of cooked rice (r = 0.650, P < 0.01) during storage. The adhesiveness showed a negative correlation with amylose content (−0.929 ≤ r ≤ −0.678, P < 0.01) and a negative correlation with ΔH_r of cooked rice (r = −0.833, P < 0.01) during storage. Hardness showed a negative correlation with adhesiveness (r = −0.820, P < 0.01). These results indicated that amylose content has significant effects on starch retrogradation and textural properties of cooked rice. The cooked rice with high amylose content is easy to retrograde, the cooked rice with low amylose content retrograded slowly. Sarch retrogradation contributes to the changes of textural properties of cooked rice during storage.     

Properties of Thai cooked rice and noodles differing in glycemic index in noninsulin-dependent diabetics

Glycemic index responses of two cooked rices and six types of cooked noodles consumed by eight noninsulin-dependent diabetics correlated positively within vitro starch digestibility of food slurry and negatively with amylose content of the food. Glutinous (waxy) rice had the highest values, and mung bean noodles the lowest.     

Soaking time of rice in semidry flour milling was shortened by increasing the grains cracks

To shorten the soaking time of rice grains in the process of semidry-milling, the changes in moisture absorption, damaged starch, and magnetic resonance images during soaking, as well as effect of increasing grains cracks on moisture absorption were investigated. As the results, the soaking time to reach the maximum moisture of Glutinous and Indica rice grains was 40 min and 20 min, respectively, but was 3 h and 30 min to reach the minimum damaged starch contents in rice flour. The moisture penetrated quickly from the embryo attachment site, ventral side, and cracks into the inside, and then diffused through the cracks. The result showed that homogeneous distribution of moisture in the rice grains was necessary to reduce damaged starch. Moreover, owing to the increase of grains cracks, the soaking time of Glutinous and Indica rice grains was shortened from 3 h to 1 h, and from 30 min to 10 min, respectively, by increasing drying temperature to 60 °C.