In vitro starch bioavailability of corn tortillas with hydrocolloids

Tortillas were prepared using commercial hydrocolloids, stored for 7 and 14 days and their available, resistant and retrograded resistant starches, were evaluated alongside their in vitro starch digestibility. Available starch (AS) decreased with storage time and tortillas with hydrocolloids had lower values than the control sample. Tortillas elaborated with TC-20 gum did not present substantial differences in AS. Control tortilla had resistant starch (RS) content that increased with storage time but, in general, tortillas with hydrocolloids did not show any change in RS values with storage time, except tortillas with TC-1 gum that presented a slight increase after 7 storage days. Approximately 50% of RS is due to the retrogradation phenomenon as it was shown by the amount of retrograded resistant starch (RRS). Tortillas with added hydrocolloids had lower hydrolysis percentage and the hydrolysis was slower than in the control. In general, tortillas prepared with hydrocolloids had a lower tendency for retrogradation than control tortillas; it is important to consider this to obtain tortillas with better texture and lower RS content.     

Effect of endosperm type on texture and in vitro starch digestibility of maize tortillas

Tortilla is the main staple of Mexico and it is made using diverse maize varieties, which have different endosperm types. Three maize varieties with vitreous, intermediate and floury endosperms were used. Texture and starch digestibility were evaluated in freshly prepared and stored tortillas for 24, 48 and 72 h. Tortilla made with maize of vitreous endosperm had the highest force to rupture and the lowest distance of elongation, indicating more rigid texture. Stored tortillas had lower available starch content and higher effect was shown by tortilla of vitreous endosperm, pattern that agrees with the higher increase in the resistant starch content with the storage time. Fresh tortilla of floury endosperm showed the highest hydrolysis rate during the first 15 min followed by tortillas of intermediate and vitreous endosperms. Starch hydrolysis values decreased when storage time increased, in agreement with the resistant starch content in the stored tortillas. At the longest storage time (72 h) tortilla of floury endosperm presented higher hydrolysis rate, followed by tortilla of intermediate and vitreous endosperms. The endosperm type plays an important role in the textural and starch digestibility of fresh and stored tortillas.     

Physicochemical properties and in vitro digestibility of resistant starch from mung bean (Phaseolus radiatus) starch

RS from mung bean starch was prepared by autoclaving, pullulanase debranching, and retrogradation. Physicochemical properties, crystalline structure, and in vitro digestibility of selected RS samples with different RS content were investigated. Compared to native starch, AAM content of RS increased but MW decreased greatly. SEM clearly showed RS samples exhibited irregular shaped fragments with compact structure. XRD pattern indicated that RS samples had typical B‐type pattern with sharp peaks at 17.0°, 22.2°, and 23.9° 2θ. The relative crystallinity, gelatinization temperatures, and enthalpy increased with increasing RS content. The α‐amylase digestibility of RS was lower than that of native starch. The results suggested that the decrease in enzymatic digestion of RS might due to compact and ordered crystalline structures after debranching and recrystallization.     

Effect of storage on resistant starch and amylose content of cereal–pulse based ready-to-eat commercial products

A wide range of ready-to-eat (RTE) foods, with varied shelf life are commercially available to meet the increasing demand for convenience foods, both by the Armed Forces and the public at large. The study evaluated the effect of storage on the resistant starch (RS) and amylose content of selected ready-to-eat (RTE) cereal–pulse based processed foods viz., pongal, khara bhath, dal fry, bisibele bhath, rajmah and kesari bhath, developed by Defence Food Research Laboratory, Mysore. RS was quantified directly in the residues obtained after removing digested starch in simulated physiological conditions. Nutrient composition and carbohydrate profile of the foods were also analyzed. The carbohydrate profile indicated low amounts of sugars, except in case of kesari bhath. The total starch content ranged from 14.5 to 24 g% while amylose ranged from 1.2 to 7.2 g%, respectively. The total and resistant starch in the RTE foods varied depending on the ingredients used and type of processing. Foods containing higher amylose content were found to have maximum increases in RS content after storage. Storage at ambient conditions resulted in significant increases (p < 0.05) in RS and TS content of RTE foods. The findings reveal that the RTE foods studied hitherto contained appreciable quantities of RS, which further increased on storage.     

Thermal properties and resistant starch content of green banana flour (Musa cavendishii) produced at different drying conditions

The objective of this research was to verify the effect of drying conditions on thermal properties and resistant starch content of green banana flour (Musa cavendishii). The green banana flour is a complex-carbohydrates source, mainly of resistant starch, and quantifying its gelatinization is important to understand how it affects food processing and the functional properties of the flour. The green banana flour was obtained by drying unripe peeled bananas (first stage of ripening) in a dryer tunnel at 52 °C, 55 °C and 58 °C and air velocity at 0.6 m s⁻¹, 1.0 m s⁻¹ and 1.4 m s⁻¹. The results obtained from differential scanning calorimetry (DSC) curves show a single endothermic transition and a flow of maximum heating at peak temperatures from (67.95 ± 0.31) °C to (68.63 ± 0.28) °C. ANOVA shows that only drying temperature influenced significantly (P < 0.05) the gelatinization peak temperature (Tp). Gelatinization enthalpy (ΔH) varied from 9.04 J g⁻¹ to 11.63 J g⁻¹ and no significant difference was observed for either temperature or air velocity. The resistant starch content of the flour produced varied from (40.9 ± 0.4) g/100 g to (58.5 ± 5.4) g/100 g, on dry basis (d. b.), and was influenced by the combination of drying conditions: flour produced at 55 °C/1.4 m s⁻¹ and 55 °C/1.0 m s⁻¹ presented higher content of resistant starch.     

In vitro fermentation of different types of α-amylase resistant corn starches

α -amylase resistant corn starches were in vitro fermented (72 h) using cecal content of rat as inoculum. Resistant starches were prepared from native (NCS), retrograded (RS_A ), and retrograded and boiled (RS_B ) corn starch by treatment with α-amylase to remove digestible starch. Short-chain fatty acid (SCFA) production, molar ratios (acetate: propionate: butyrate), fermentability with respect to lactulose and dry matter disappearance were measured. SCFA production was significantly correlated with non-fermented residue (P <0.001). The three starches showed a similar fermentability, although the rate of SCFA production and disappearance of substrate were slower for retrograded starches. NCS was fermented early while RS_A and RS_B prolonged their degradation to 72 h. There were slight differences in the molar ratios of acetate, propionate and butyrate. Structural changes in the materials were observed by scanning electron microscopy (SEM). In summary, commonly utilised domestic cooking and technological treatments modified the in vitro fermentative characteristics of resistant corn starches probably due to structural changes. Received: 15 November 1999 / Revised version: 27 January 2000     

Structural studies of resistant starch derived from processed (autoclaved) rice

 Resistant starch (RS), isolated by hydrolysis with Termamyl, protease and amyloglucosidase, of five-cycle autoclaved rice was purified by size exclusion chromatography. Structural characterization by β-amylolysis, ¹³C NMR and methylation followed by GC-MS analysis revealed RS to be a linear (1→4)-α-d-glucan, originating probably from amylose. Its molecular weight was low, 1.20×10⁶ Da, and amounted to 7400 d-glucose residues. X-ray diffraction measurements showed RS to have both B-type and V-type diffraction patterns. Differential scanning calorimetry data revealed the thermal stability characteristics of RS. The undigested material (equivalent to RS) recovered from the ileum of rat intestine exhibited an almost comparable GPC profile, molecular weight and λ_max characteristics with those of in vitro isolated RS. Received: 7 September 1998     

Effects of alkaline treatment on the structure of phosphorylated wheat starch and its digestibility

Phosphorylated wheat starch (PWS) was prepared with sodium trimetaphosphate and sodium tripolyphosphate (99/1, w/w), and the modified starch gave 88.8% total dietary fibre by the Prosky method and 68.7% resistant starch (RS) by the Englyst method. The stability of the phosphate esters in aqueous sodium hydroxide was investigated and related to total dietary fibre and RS contents. The phosphorylated starch was slurried (40%, w/w) at 40 °C for 4 h at pH 9.0, 10.0, 11.0, and 12.0. The phosphorus content of the PWS decreased from 0.37% to 0.29% after treatment at pH 12.0, whereas only a slight decrease in phosphorus content occurred after treatments at pH 9.0–11.0. Despite the 22% decrease in total phosphorus content, total dietary fibre content and RS content of the alkali-treated PWS changed only slightly. ³¹P nuclear magnetic resonance spectroscopy showed that after the alkali treatment at pH 12.0, cyclic monostarch monophosphate and monostarch diphosphate were not detectable and that the level of total monostarch monophosphate decreased from 0.077% to 0.067%. Conversely, distarch monophosphate increased from 0.17% to 0.20%, of ≈18%. The increase in distarch monophosphate (cross-linking) content after alkali treatment at pH 12.0 probably explained the retention of total dietary fibre and RS contents in the alkali-treated PWS.     

抗性淀粉体外消化模拟的研究

采用体外消化模拟方法,研究了抗性淀粉在人工胃肠液和大肠液中的消化吸收情况,并用原淀粉作为对照组。结果表明,抗性淀粉和原淀粉在生理盐水中均没有被分解,生理盐水对抗性淀粉的消化毫无影响。与对照组原淀粉相比,抗性淀粉在人工胃液(pH3、pH4、pH5)和人工肠液(pH6.8)中变化很小,人工胃液和人工肠液对抗性淀粉不起消化作用。抗性淀粉在大肠液中有明显的失重,说明大肠液对抗性淀粉有影响,抗性淀粉能够被大肠中的微生物发酵或部分发酵。从而说明抗性淀粉不能在胃和小肠中消化吸收。     

Effects of gamma irradiation on starch digestibility of rice with different resistant starch content

Three rice cultivars (RS3M, RS4H and RS5L) differing in resistant starch contents but similar in genetic background were chosen to study the effects of gamma irradiation on starch physicochemical properties and digestibility. Irradiation increases the resistant starch content in all the three cultivars and in a dose‐dependent manner in rice with low‐resistant starch content (RS5L). Irradiation decreases apparent amylose content and gelatinisation temperature and changed the starch granule structure, while increasing V‐type crystallinity. Starch enzymatic hydrolysis rate was reduced following irradiation, and the effect of irradiation on reducing starch digestibility was negatively correlated with resistant starch content. Treatment with gamma irradiation has therefore a potential for increasing resistant starch content and producing low digestibility of starch in common rice.     

抗性淀粉的体外消化及结构变化的研究

以玉米淀粉和增抗玉米淀粉为原料进行体外消化实验,建立了消化动力学模型,利用X-射线衍射、差示扫描量热、傅里叶红外变换等手段,对抗性淀粉不同时间段的消化物进行分析。结果表明:玉米淀粉在2h内几乎完全水解,消化速率常数为2.32h-1,高于抗性淀粉的1.13h-1;抗性淀粉在0～2h内,结晶度增加,焓值增加,表明此时消化过程以水解动力学为主,2h后,结晶度稍有下降,整体呈现一个无规律的变化过程;此时为直链淀粉重新排列的过程,链间通过氢键连接,形成的聚合物能抵抗淀粉酶的水解作用,整个消化过程为水解动力学和老化动力学相互竞争的过程。      

Synthesis and in vitro digestion of resistant starch type III from enzymatically hydrolysed cassava starch

Resistant starch type III (RS III) was synthesised from cassava starch by autoclaving followed by debranching with pullulanase, at varied concentrations (0.4–12 U g^?1) and times (2–8 h), and recrystallisation (?18 to 90 °C for 1–16 h). The highest RS III yield (22 g/100 g) was obtained at an enzyme concentration of 4 U g^?1 after 8 h incubation, followed by recrystallisation at 25 °C for 16 h. Varying the recrystallisation conditions indicated that higher RS III yields (30–35 g/100 g) could be obtained at 90 °C within 2 h. Thinning cassava starch using α‐amylase prior to debranching using pullulanase did not further increase the RS III content. In vitro digestion data showed that whereas 44% RS III was digested after 6 h, the corresponding value for cassava starch was 89%.     

Changes in unreacted starch content in corn during storage

In the dry grind process, corn is ground, mixed with process water and cooked; starch is enzymatically hydrolyzed to sugars, and subsequently fermented to ethanol by yeast. The conversion of starch into ethanol, however, is not complete as distillers dried grains with solubles (DDGS) often contain more than 5% starch. The amount of unreacted starch represents inefficiencies in the process and reducing this amount is important to improving profitability of the ethanol industry. Additionally, dry grind facilities have reported seasonal variation in ethanol yields. In order to minimize variation in ethanol yields and the amount of unreacted starch in DDGS, it is important to understand the effects that storage temperature and time have on the digestibility of the corn starch. While starch quality is largely controlled by genetics and growing conditions, postharvest practices (handling, storage, and processing conditions) also affect starch composition and structure. In this study, changes in unreacted starch content of corn during storage were monitored to provide an explanation for the seasonal variation in ethanol yields observed by dry grind facilities. Yellow dent corn was harvested in 2011 and 2012 and stored indoors, outdoors, and under refrigeration for 5–12 mo. Results with the 2011 harvest corn showed unreacted starch content ranging from 2.17 to 14.1% over a 48 wk period. Unreacted starch was more influenced by storage time, initially decreasing at a rate of 0.31% per wk during the first 10 wk and steadily increased at an average rate of 0.16% per wk for the duration of storage. Results with the 2012 harvest corn, however, showed a higher average unreacted starch content of 13.0% during 20 wk of storage and no appreciable change in unreacted starch content regardless of storage temperature.     

Improvement of resistant starch content and baking quality of cross-linked soft rice flour

Food Science and Biotechnology - To increase resistant starch (RS) content of rice flour, soft and normal rice flours were cross-linked with different flour concentrations (40, 50%). RS contents,...     

Preparation of resistant starch from starch–guar gum extrudates and their properties

Mixtures of starch, guar gum and citric acid were extruded at a temperature of 150 °C and screw speed of 180 rpm. Properties of the extrudates such as bulk density, expansion ratio, apparent viscosity and resistant starch content were measured with different concentrations of guar gum. Extrusion with citric acid influenced the physical properties and resistant starch content of the extrudate. Expansion ratios were lower for samples extruded with citric acid, and decreased as starch–gum concentration increased. The apparent viscosity of the extrudate increased with increasing guar gum concentration; however, citric acid at 2.0% concentration was found to lower the viscosity of the extrudate. Resistant starch content increased from 6.23% for extruded starch only to 14.21% for starch–gum extrudate, and further enhanced to 16.19% with the addition of 2.0% citric acid to the starch–gum extrudate. Resistant starch increased with increase of gum concentration and decreased with increase of starch–gum concentration from 7.5% to 12.5%.     

抗性淀粉直链淀粉含量测定及消化性研究

以蜡质玉米淀粉为原料,经过糊化后使用普鲁兰酶脱支,产生更多的短直链淀粉重新结晶来制备抗性淀粉。通过碘吸光度法测定,直链淀粉含量高的样品的抗性淀粉含量不一定高,但直链淀粉含量低的样品不容易产生高含量抗性淀粉。在In-Vitro消化模型中,和原淀粉相比,所有的抗性淀粉样品消化产物的量、还原糖释放率和平均消化速率都减少或降低,并且抗性淀粉含量越高,减少或降低得越多。     

Physicochemical Changes of Starch in Maize Tortillas During Storage at Room and Refrigeration Temperatures

Physicochemical changes of starch and loss of texture were determined in maize tortillas during 72 h storage at room and refrigeration temperatures. Properties analyzed included apparent amylose content, content of enzyme resistant starch (RS) type III, and thermal properties determined with differential scanning calorimetry (DSC) and X‐rays diffraction. In addition, tortilla firmness was assessed using an uniaxial compression test with a texture analyzer. Storage temperature did not significantly affect firming rate or starch properties, except from thermal properties. Firmness was developed mainly during the first 24 h storage, remained nearly the same during 24—48 h and slightly increased after 72 h storage. Resistant starch (RS) formation followed the same trend as development of firmness. A first order endothermic transition that can be attributed to amylopectin retrogradation was observed after 2 h storage at both temperatures. This transition shifted to higher temperatures during storage, the effect was specially evident for refrigerated tortillas. X ray diffraction patterns of stored tortillas suggested that crystallinity slightly increased during storage. Most of the loss of tortilla texture, determined as firmness, occurred during the first 24 h storage at room and refrigeration storage conditions. This loss of texture was likely due to starch retrogradation and the latter possibly increased content of resistant starch.