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A recent study showed that the digestion of glycemic carbohydrates in the distal part of the small intestine has the potential to regulate satiety and food intake levels. In this study, we investigated different processing methods (oil-frying and popping) of rice with citric-acid treatment for the efficient regulation of glucose production in small intestinal mucosal α-glucosidases. Glucose generation from citric-acid-treated rice products was drastically decreased due to the cross-linking of the starch molecules. Interestingly, oil-frying or popping under high-temperature and high-pressure conditions can be used to process rice or other cereals for gelatinizing starch molecules without water. Thus, various rice processing methods combined with citric-acid treatment can be used to develop rice or cereal-based food products, which can attenuate glucose spikes and extend glucose delivery.

In this study, the starch structure and digestibility of glutinous rice cakes were investigated. The rice cakes were steamed or fried at different temperatures; the fried cakes were then separated into three parts—crust, middle, and core. Scanning electron microscopy and X-ray diffraction indicated that the starch structure in both the steamed and fried cakes was completely gelatinised and destroyed. As determined through differential scanning calorimetry, the starch structure became more seriously altered with increasing frying temperatures, with the crust tending to be more severely altered than the middle and core. The fried cakes contained 67.48%–73.64% of rapidly digestible starch, comparable to that in the steamed cakes, but higher than that in raw glutinous rice. Moreover, the fried cakes contained 19.89%–27.95% of slowly digestible starch, comparable to that in the steamed cakes and raw glutinous rice. However, the fried cakes 4.57%–6.57% of resistant starch—significantly lower than that in the steamed cakes and raw glutinous rice. Frying temperatures did not lead to significant changes among the three starch categories. The in vivo test results showed that steamed and fried glutinous rice cakes were both medium-glycaemic index foods.

Parboiling is widely used world-wide, but properties of the final products depend upon processing conditions and rice variety yielding complex results. This study intended to understand the formation of amylose lipid complex (ALC) after parboiling combined with heat moisture treatment (HMT). Differential scanning calorimetry (DSC) and X-ray diffraction were utilized to understand the properties of the parboiled rice. In vitro starch hydrolysis was employed to evaluate the digestibility of the products. The distributions of protein and starch in rice kernels were observed using a light microscope. Data from amylose content measurement using iodine indicated the formation of ALC after parboiling and HMT. The presence of type II ALC was confirmed by DSC and X-ray diffraction. Pressure cooking increased the resistant starch (RS) from 1.95 to 7.95%. Resistant starch (RS) and slowly digestible starch (SDS) were further increased to 10.4% and 45.8%, respectively, by HMT after parboiling. The data indicated that pressure cooking and HMT could increase the contents of RS and SDS of rice, along with other potential health benefits.

Barley flours can be utilized for preparation of chapatti after blending with 7% vital wheat gluten. Mixolab analysis revealed a significant role of non-starchy polysaccharides in increasing dough consistency after mixing (C1) and heating (C3). A significant negative correlation (R = −0.63) of mixolab retrogradation (%) was observed with soluble arabinoxylan contents of flours indicating their positive effects on chapatti quality. Soluble arabinoxylans also exerted beneficial effects by promoting lower rate of shrinkage (R = −0.69) and bake loss (R = −0.77) in chapatti, however β-glucans and insoluble arabinoxylans increased the chapatti shrinkage (p ≤ 0.05). Fresh barley chapatti displayed lower soluble starch contents (1.8–2.6%) as compared to wheat chapatti, which may indicate an inhibitory effect of barley β-glucans on starch swelling, leading to lower retrogradation (R = −0.62). Reduced rapidly digestible starch contents were observed for barley chapatti. Presence of higher levels of total β-glucans in barley flours also promoted the formation of slowly digestible starches in retrograded chapatti (R = 0.61). Upon storage of chapatti for 48 h, both soluble amylose and soluble amylopectin content decreased and starch crystallinity increased. These factors were significantly affected by the presence of β-glucans and arabinoxylans.

In this study, the effect of immature wheat flour (IWF) on the fermentation activity of lactic acid bacteria (LAB) and on the nutritional quality properties of bread were evaluated. IWF was added in the as the ratio of 10g/100g in sourdough fermentation medium, and the fermentation activity (total LAB, pH, titration acidity (TA), and total reducing sugar (TRS)) of LAB cultures was monitored. Additionally, some physical quality characteristics (specific volume, texture profile and colour value), estimated glycaemic index (eGI), rapidly digestible starch (RDS), slowly digestible starch (SDS), and the total dietary fibre content of sourdough bread were determined. According to the statistical test, it was revealed that the IWF addition stimulated LAB growth and increased their fermentation activity. The pH of the fermentation medium decreased from 6.57 to 3.50, and TA raised from 0.13% to 1.2% in 48 h. The highest TRS content was determined in IWF enriched sourdough samples, and as a result of this, the eGI of sourdough bread increased. Compared to the control sample, the SDS and total dietary fibre content were higher in IWF added sourdough bread, and a positive correlation was noted between these two components. IWF utilisation of sourdough bread formulation increased the hardness value by nearly 50%.

Instant rice has become increasingly popular due to its convenience. Reducing the starch digestibility of instant rice may increase its potential health benefits. The aims of this study were to define the optimum conditions for cooking, retrogradation and drying to reduce the in vitro starch digestibility of instant rice. Three varieties of rice from Taiwan (low-amylose japonica [Taikeng 9], low-amylose indica [Taichung Sen 10] and high-amylose indica [Taichung Sen 17]) were prepared using different cooking conditions and durations of retrogradation. Starch digestibility was determined by analyzing the amount of rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS) in the instant rice. Cooking at 86 °C for 28 min in a 1.0-fold volume of water significantly reduced RDS and increased SDS compared to rice cooked on a traditional electronic cooker. The combination of retrogradation and low-temperature drying significantly reduced the RDS of instant rice after rehydration. A reduction in RDS was accompanied by an increase in SDS and RS in low-amylose japonica rice, increased RS in low-amylose indica rice, and reduced SDS and increased RS in high-amylose rice. Optimizing cooking methods and retrogradation reduced the starch digestibility of instant rice; this may help improve its healthful qualities.

To analyze the effects of the freezing process, frozen storage temperature and frozen storage time on starch digestion characteristics, 3 kinds of foxtail millet-derived products were produced and frozen stored at −18 °C or −40 °C. The in vitro starch digestibility, degree of gelatinization (DG) and estimated glycemic index (eGI) of reheated samples were investigated after frozen for 1, 3, 5, 7, 14, 21 and 28 days respectively. The results showed that the variation trends of DG, eGI and rapidly digestible starch content were basically the same during freezing and frozen storage. Starch digestion characteristics of frozen millet products stored at −40 °C were more stable than those of counterparts stored at −18 °C. The first two weeks, especially the first day of frozen storage, had a greater effect on starch digestibility, as compared to the rest days of frozen storage. Thus fresh prepared foxtail millet-derived products are required for determining the glycemic index of specific food or conducting a short-term dietary intervention while frozen stored products are available for long-term intervention. Moreover, addition of pregelatinized starch into millet pancake may increase its glass transition temperature and thus decrease its degradation rate.

This study investigated the effects of extrusion types (collet and cooking) and parameters (moisture content, screw speed and temperature) on the β-glucan content of barley and the impact of β-glucan content on starch digestibility. The results demonstrated that extrusion significantly reduced the total β-glucan (TBG) content of barley as a raw material, but the differences in TBG from extrudates obtained using different extrusion parameters were not significant. Extrusion at high moisture content, as in cooking extrusion, increased SBG, whereas extrusion at low moisture content, as in collet extrusion, lowered SBG. The regression coefficients revealed that the most significant extrusion parameters affecting SBG and IBG content in barley extrudates were feed moisture content for collet extrusion and screw speed for cooking extrusion. The in vitro digestion analysis demonstrated that collet and cooking extrudates containing high amounts of SBG revealed the highest slowly digestible starch (SDS) content. In conclusion, different extrusion types and parameters exhibited more pronounced effects on the SBG and IBG content than on the TBG content, and higher SBG content implies higher SDS content.

The molecular structures of starch in cooked wheat were measured and related to its in vitro digestibility. The structures were characterized by size-exclusion chromatography (SEC) and fluorophore-assisted carbohydrate electrophoresis (FACE) to measure the chain-length distribution (CLD) of amylose and amylopectin chains and the whole-molecule weight distribution. The CLDs were fitted to two biosynthetic models, one for amylopectin and another for amylose, which reduced the data to a small number of biologically significant parameters expressing enzyme activities. The digestibility of starch was greatly influenced by medium amylose chains, and the percentage of total starch digested at a long time ( C ∞ ) was negatively correlated with the amount of medium amylose chains (hAm,ii) and positively correlated with the length of medium amylose chains (βAm,ii). These results suggested that the medium amylose chains reduced the total digestible starch fraction. This study may help in making informed decisions about wheat starches to aid the formulation of wheat-based diets for conditions such as diabetes.

Physicochemical and digestive properties between wheat starch (WS) and wheat flour (WF) which had been modified by using heat-moisture treatment (HMT) were investigated. Reduced peak viscosity and increased pasting temperature were found in both WS and WF after HMT. Samples treated with a higher moisture treatment (25% and 35%) exhibited biphasic endotherms. HMT significantly changed crystal structure of WS and WF, and patterns transferred from A to A + V with moisture content increase indicating a formation of starch–lipid complex. Besides, HMT caused the clumping of starch granules and the aggregation of denatured protein, observed using confocal laser scanning microscopy (CLSM) and light microscopy. The higher moisture contents produced HMT samples with higher resistant starch content. In addition, HMT wheat flour showed a higher resistant and slowly digestible starch content when compared to the other counterpart of WS.

Starch is the main constituent of cereal grains, but less attention has been paid for its contribution to the health benefits of whole-grain foods. In the current investigation, the slow digestion property of corn starch in a whole-grain-like structural form (WGLSF), which mimicked the whole grain microstructure, was studied to better understand the nutritional property of whole grain starch. The WGLSF-starch prepared through Ca2+-induced alginate gelation in the presence of starch and β-glucan showed a reduced content of rapidly digestible starch (RDS) (∼40.4–23.6%) and increased content of resistant starch (RS) (∼20.7–30.9%) and slowly digestible starch (SDS) (∼38.9–47.8%) along the alginate concentrations (0.1–0.4%, w/v). Consistently, the postprandial glycaemic response of the cooked WGLSF-starch (0.3% alginate) exhibited a significant reduction (35.5%) of glucose peak compared to their physical mixture. Scanning electron microscope (SEM) observation demonstrated that the starch granules were embedded in the β-glucan-alginate co-formed gel matrix with a cell wall-like structure, which might cause a decrease of enzyme accessibility to the substrate, and ultimately a slow digestion profile of starch and reduced glycaemic response. Thus, maximization of the slow digestion property of starch in whole-grain food processing might be essential to further improve the nutritional property of whole-grain foods.

Whole grain oat flour was extruded under different moisture contents (15%, 18%, 21%), barrel temperatures (100 °C, 130 °C), and screw speeds (160 rpm, 300 rpm, 450 rpm), and selected physicochemical properties, in vitro starch digestibility, and β-glucan extractability of the extrudates were analyzed. An increase in screw speed resulted in an increase in radial expansion index, water absorption index, and water solubility index. Screw speed significantly affected slowly and rapidly digestible starch. Moderate screw speed (300 rpm) led to higher slowly digestible starch with an accompanying decrease in rapidly digestible starch. Low moisture conditions (15%) resulted in the highest resistant starch and water-extractable β-glucan. Under the conditions used in this study, extrusion did not result in changes in water-extractable β-glucan molecular weight. Thus, extrusion might be beneficial in improving functionality and consumer acceptability by affecting physicochemical properties, in vitro starch digestibility, and β-glucan extractability of oat extrudates.

The impact of wheat (WT) flour replacement up to 45% (weight basis) by incorporation of ternary blends of teff (T), green pea (GP) and buckwheat (BW) flours on the viscometric pasting and gelling profiles of quaternary blended dough matrices was investigated by applying cooking and cooling cycles to rapid viscoanalyser (RVA) canisters with highly hydrated samples (3.5:25, w:w). Viscometric cooking and cooling parameter trends related to suitable patterns for lower and slower starch hydrolysis, and lower and/or slower firming and starch retrogradation kinetics in blended breads mainly include higher viscosity values for peak viscosity, breakdown on cooking and viscosity of hot (95 °C) paste, but lower viscosity values after gelling (50 °C). These visco-metric requirements for achieving suitable textural and thermal features in blended breads, were met by adding T/GP/BW to replace 22.5% of WT flour in blended dough formulations. Larger WT flour replacement by 37.5% of the ternary mixture T/GP/BW (7.5/15/15) provided hydrated blends with higher values for viscosity of hot (95 °C) paste, and lower viscosity values after gelling (50 °C), in good accordance with poorer formation of rapidly digestible starch and total digestible starch, and more prominent formation of resistant starch and slowly digestible starch in breads, respectively., Financial support of the Spanish institutions Consejo Superior de Investigaciones Científicas (CSIC) and Ministerio de Economía y Competitividad (Projects AGL2011 22669 and AGL2015-63849-C2-1-R).

High amylose maize flour (HAMF), normal maize flour (NMF), extruded normal maize flour (ENMF) and extruded high amylose maize flour (EHAMF) were employed to analyze the effects of the extrusion process on their physicochemical properties and in vitro digestion. The disruption degree of NMF and HAMF under extrusion followed the degree of gelatinization order. HAMF and EHAMF had higher onset temperature, peak temperature and conclusion temperature but lower melting enthalpies in comparison with NMF and ENMF. Extrusion treatment decreased viscosity and transformed A-type and B-type starch in NMF and HAMF into B + V-type. The solubility of all samples and swelling power of NMF and HAMF showed an increase, while swelling power of extruded maize flour decreased with increasing temperature. HAMF and EHAMF had a higher content of resistant starch but a lower content of slowly digestible starch and rapidly digestible starch than NMF and ENMF.

There is a growing interest for an environment-friendly nixtamalization process. Nixtamalization with calcium salts generates a minimum level of polluting residues. The effect of a nixtamalization process with calcium carbonate (NCC) on the indigestible carbohydrate content and starch digestibility of tortillas was evaluated. Traditional and NCC tortillas showed lower moisture content than commercial tortillas. Similar protein, ash, and carbohydrate content were found for the three tortillas, but NCC tortillas showed the highest lipid content. The NCC tortilla had the highest dietary fiber content, with the highest insoluble dietary fiber level. Fresh and stored (96 h) NCC and traditional tortillas showed similar resistant starch content. Fresh traditional tortilla showed the highest slowly digestible starch (SDS), but upon storage the rapidly digestible starch (RDS) content of NCC tortilla decreased. Fresh traditional and NCC tortillas had lower predicted glycemic index (pGI) than commercial tortillas, and upon storage, the three tortillas presented lower pGI values than their fresh counterparts. Consumption of tortillas produced with the NCC can produce positive effects in the human health.

Bioactive phytochemicals play an important role in the health benefits of whole grain foods, but the exact mechanism is still poorly understood. In the current investigation, the slow digestion property of whole grain starch was investigated using an ethanol extract from Tartary buckwheat that is a unique pseudocereal with a high content of phytochemicals. Liquid chromatography analysis of Tartary buckwheat extract (TBE) showed that rutin, kaempferol-3-O-rutinoside, and quercetin as well as trace amount of phenolic acids are the main phytochemicals. An in vitro digestion of Tartary buckwheat whole grain flour showed a typical digestion pattern of slowly digestible starch (SDS), and a significantly reduced postprandial glycemic response was also observed in a mouse study when compared to the cooked pure starch (a typical rapidly digestible starch (RDS)). Furthermore, the addition of TBE (2%) to a high fat diet attenuated the oxidative stress with a significant increase of antioxidant enzymes of SOD and GSH-Px in both the liver and small intestine of the high fat diet-induced obese mice. Considering the impacts of TBE on starch digestion and induced physiological responses, the modification of the nutritional property of whole grain starch is likely an important mechanism of phytochemicals’ contribution to the health benefits of whole grain foods.

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.

The effect of γ-irradiation on the physicochemical properties of cross-linked waxy maize resistant starches was examined. The cross-linked waxy maize starches contained resistant starch (RS) of 56.1 and 63.5%, respectively for 5 and 10% sodium trimetaphosphate (STMP)/sodium tripolyphosphate (STPP) cross-linking, and the RS contents slightly decreased as the irradiation dose increased whereas the RS content in unmodified waxy maize starch increased with an increase in irradiation dose. For both native and cross-linked starches, the rapidly digestible starch (RDS) content increased and the slowly digestible starch (SDS) content decreased by the irradiation. The solubility of the native and cross-linked starches increased as the irradiation dose increased. The cross-linked starches did not swell in boiling water without showing pasting viscosity. However, the starches became swellable, forming pastes by irradiation, and the pasting viscosity gradually increased with an increase in irradiation dose. The crystallinity as determined by an X-ray diffraction analysis remained unchanged upon cross-linking and γ-irradiation. However, the gelatinization enthalpy of the cross-linked starches decreased in proportion with irradiation dose. The melting temperatures of cross-linked starches gradually decreased and the temperature range for melting increased with an increase in irradiation dose.

High amylose rice starch was modified by dry heat treatment for different heating times (0, 1, 2, and 4 h) after mixing with various hydrocolloid type (carboxymethyl cellulose (CMC), guar gum, and xanthan gum) to improve its processability and nutritional properties. The hydration/pasting properties, gel texture, and in vitro starch digestibility of dry heat treated hydrocolloid-starches were investigated and analyzed by principle component analysis (PCA). Dry heat treatment increased the pasting properties of rice starch, although a longer heating time led to lower pasting and hydration properties as well as gel strength. Highest peak viscosity and gel strength were observed for dry heat treated xanthan-starch, followed by CMC- and guar-starch. In the results of in vitro starch digestibility, dry heat treatment significantly decreased the rapidly digestible starch contents and predicted glycemic index (pGI) compared to native starch, while dry heat treated xanthan starch most effectively retarded starch digestibility. PCA indicated that hydrocolloid type affected the hydration properties, and that heating time was correlated with pasting properties and pGI. These results demonstrated that high amylose rice starch dry heat treated with xanthan for 2 h could be effective in changing the hydration, pasting and gel characteristics as well as in vitro starch digestibility.

Blending cereals can maximise their food values, and understanding material-processing-property relationships guides this. A sorghum-barley (60:40) blend was extruded at different conditions to investigate the effects on extruder responses and extrudate properties. Starch digestion in the extrudates was more than in the non-extrudates, but extrusion feed rate did not significantly (P > 0.05) affect the digestibility. Specific mechanical energy reduced with the feed rate, which suggested suppressed molecular and/or structural transformations in a full extruder. Extrudate properties essentially exhibited a significant (P 0.05) effects on starch digestibility, but with more supplied heat as the temperature increased, water binding properties and transverse expansion increased. The increased frictional heat with the screw speed enhanced the transverse expansion also, and the browning, rate of starch digestion and rapidly digestible starch of the extrudates. There were significant Pearson correlations between the extrudate properties and with the extruder responses, which can assist in selecting conditions for desirable extrudate properties.

Native and moistened wheat flours (moisture contents were 13.5 and 27.0%, respectively) were treated with superheated steam (SS) at different temperatures (140 and 170 °C) and times (1, 2 and 4 min). Their physicochemical and digestive properties were analyzed. For native flour, SS treatment altered the starch molecular structure and behavior slightly. While for moistened flour, crystalline degree, gelatinization enthalpy, amylose leaching (AML) and falling number significantly decreased, but thermal transition temperatures increased with the rise of treating severity. Clumping of starch granules, aggregation of proteins and formation of amylose-lipid complexes occurred in both native and moistened flours. Broader pasting temperature ranges and higher viscosities were found on SS-modified flours. Additionally, SS treatment on moistened flours increased resistant and slowly digestible starch contents. In general, SS treatment induced changes in starch molecular structure and reactions among flour components leading to more stable structures, thus affecting their pasting behavior, thermal properties and in vitro digestion.

The development of low calorie foods to aid obesity control is a growing area of research. Among these, resistant starch (RS) in cereals has beneficial effects on reducing colon cancer rate and better fatty acid composition as well as lowering calories. Rice contains digestible starch and indigestible RS, the proportions of which are affected by starch biosynthetic enzymes. Rice lines that carry mutations in starch biosynthesis genes may have high levels of RS. In this study, percentage RS and non-digested component values were determined in steamed rice from several rice lines. These include several high-amylose indica rice cultivars, and lines carrying mutations in the starch synthase (SS) IIIa and/or branching enzyme (BE) IIb genes. High RS rice lines contained high levels of non-digested component. RS values ≤ 4% correlated with apparent amylose content. RS values of BEIIb-deficient mutant lines were particularly high (15 ≤ RS ≤ 35%), and were correlated with the amount of amylopectin long chains. Among rice lines used in this study, be2b mutant lines having large portions of amylopectin long chains were the best candidates for high RS rice foods.

Dry heat parboiling is a unique paddy processing technique that has been scarcely exploited. Dry heat parboiling at high temperature for short time and low temperature for long time on physical and physicochemical properties of three rice varieties differing in amylose content were studied. Hardness of the kernels increased from 66.4 N, 68.8 N and 59.8 N in raw samples to 89.1 N, 86.9 N and 59.8 N in parboiled high amylose, low amylose and waxy rice samples respectively. Rapid migration and evaporation of water from severely heated kernels caused cavity formation at the centre. Irreversible damage of amylopectin structures to leachable fractions caused continuous rise of the pasting curve. Crystallinity was thereby reduced. Parboiled high amylose samples gave X-ray diffraction patterns with peaks characteristic of A, B and V-type starch crystallinity. Crystalline starch-lipid complexes were observed in low amylose and waxy rices. The significant increase in the amount of rapidly digestible starch from 56.7%, 61.7% and 66.6% in raw samples to 92.1%, 90.8% and 94.8% respectively in severely processed rice samples and subsequent reduction in resistant starch from 24.5%, 21.2% and 18.4% to 0.4%, 1.9% and 0.1% indicated possibilities for targeted food use of the dry heat parboiled samples.

Micronization refers to high temperature short time processing of grains using near infrared rays. The present study is focused on optimization of process conditions for micronization of maize flour with an emphasis on enhancing rapidly digestible starch (RDS) content for enhancing starch digestibility and inactivation of peroxidase enzyme for probable extension of shelf-life. The study employed a central composite design (CCD) with three variables namely, time (60–180 s), temperature (130–170 °C) and moisture content (20–40%) with RDS and peroxidase contents as responses. The optimized micronization conditions (173 s, 159 °C, 40% mc; 164 s, 166 °C and 40% mc) resulted in 7.1–7.7% increase in RDS content and 92.5–96.2% inactivation of peroxidase enzyme, respectively, without significantly affecting protein, carbohydrate and fat content of flour. Validation studies showed that experimental values matched well with that of predicted, suggesting suitability of the model used. At the optimized conditions, micronization was also able to inactivate lipase activity by 66.9–68.2%.

Starch is the main glycemic dietary carbohydrate, and its nutritional quality is associated with the amount of slowly digestible starch (SDS) that is beneficial to glycemic control. In the current study, a microencapsulation of normal corn starch by zein protein and its slow digestion property were investigated. A significant increase of SDS and RS was shown for starch capsules (weight ratio of zein to starch: 1:6) containing plasticizers of glycerol and oleic acid after high temperature (≥70 °C) treatment. Further studies showed a substantially decreased viscosity and the formation of an amylose–lipid complex after starch gelatinization. Thus, the hydrophobic physical barrier of the zein matrix and the amylose–lipid complex might together limit the water accessibility and starch swelling leading to a dense packing of starch materials with a high amount of SDS. The acceptable sensory property makes it an ideal ingredient for specialty food preparation and glycemic control.

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.

The development of an in vitro enzymic batch method for pretreatment of cereal samples prior to in vitro fermentation is presented. A statistical experimental design is described and the importance of bile and pepsin for the digestibility of starch was investigated. Day-to-day variation was studied by measuring glucose released and total starch in the digestion residue of rye flour. Four samples, wholemeal rye flour and bread, wholemeal and white wheat breads, were tested to evaluate the performance of the digestion procedure. Pepsin and bile enhanced the hydrolysis of slowly digestible starch. The extent of starch hydrolysis in rye and wheat breads (93–95%) was reproducible and about the same as using thermostable alpha -amylase. More soluble fibres were released from the wholemeal rye bread than from the wholemeal wheat bread. The procedure is an efficient method for the removal of starch and protein under physiological conditions prior to in vitro fermentation. The method can also be used as a tool for studying the solubility of dietary fibre (DF).