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.     

In vitro digestion rate and resistant starch content of tortillas stored at two different temperatures

In vitro indicators of starch bioavailability were evaluated in freshly prepared maize tortillas and compared to those exhibited by 24, 48 or 72 h-stored samples. Storage took place either at room temperature (approx. 25 °C) or under refrigeration (4 °C). Potentially available starch (AS) content decreased from 670 g kg⁻¹ in the control tortilla to 583 g kg⁻¹ in 72 h-stored preparations. Concomitant increases in total resistant starch (RS) and retrograded resistant starch (RRS) were recorded upon storage. RRS content in 72 h-stored samples (35-39 g kg⁻¹) doubled that of freshly prepared tortillas. Changes in AS, RS and RRS were not affected by storage temperature. Both initial rate and final point of starch hydrolysis by pancreatic amylase were reduced in samples kept for 48 and 72 h, without influence of storage temperature. Storage length is suggested as a major determinant of the bioavailability of starch in tortillas.     

Comparison of the expansion ability of fermented maize flour and cassava starch during baking

The modifications occurring during the fermentation (at 20 or 35 °C) and drying (under the sun or in an oven at 40 °C) of maize flour (ogi) and cassava starch along with their expansion ability during baking were characterised and compared. A high temperature accelerated the fermentation but favoured lactic acid synthesis for maize ogi and butyric acid for cassava starch. The increase in acidity was higher for maize, but dried maize ogi did not evidence any expansion ability whatever the experimental conditions. Cassava starch that had been fermented at 20 °C then sun‐dried presented the highest expansion ability. It was associated with low paste viscosities and high swelling and solubilisation values. When the fermentation was carried out at 35 °C, an annealing of cassava starch occurred that delayed starch gelatinisation and which could be involved in its lower baking expansion ability. © 2000 Society of Chemical Industry     

In vitro digestibility of processed and fermented soya bean,cowpea and maize

Tropical legumes, ie soya bean and cowpea, were pre‐treated and subsequently fermented using pure cultures of Rhizopus spp. Impact of soaking, cooking and fermentation of the legumes on their digestibility was determined using an in vitro digestion method. Processing of white maize included, amongst others, natural lactic acid fermentation, cooking and saccharification using barley malt. An in vitro method was standardised to carry out comparative determinations of the dry matter digestibility of cereal and legume food samples as a function of processing conditions, without attempting to exactly mimic gastrointestinal digestion. Using this method based on upper digestive tract digestion, it was observed that digestibility of the legumes increased during cooking and fermentation. Cooking improved the total digestibility of both soya bean and cowpea from 36.5 to 44.8% and from 15.4 to 40.9% respectively. Subsequent fungal fermentation increased total digestibility only by about 3% for both soya bean and cowpea. Digestibility was also influenced by fungal strain and fermentation time. Cooking and subsequent saccharification using malt almost tripled total digestibility of white maize from 25.5 to 63.6%, whereas lactic fermentation of maize had no effect on in vitro dry matter digestibility. Although total digestibility of cooked legumes was only slightly improved by mould fermentation (3% for both soya bean and cowpea), the level of water‐soluble dry matter of food samples increased during fermentation with Rhizopus oryzae from 7.0 up to 27.3% for soya bean and from 4.3 up to 24.1% for cowpea. These fermented products could therefore play a role as sources of easily available nutrients for individuals suffering from digestive disorders. © 2000 Society of Chemical Industry     

Influence of sorghum flour addition on flat bread in vitro starch digestibility,antioxidant capacity and consumer acceptability

Wheat flour (WF) flat bread was prepared with varying levels of wholegrain “white” sorghum flour (WSF) or “red” sorghum flour (RSF). Farinograph dough rheology indicated reduced water absorption and stability time and increased breakdown with increased sorghum flour addition. The total phenolic content and antioxidant capacity of the 40% RSF flat bread >40% WSF flat bread > control (100% WF) flat bread. The rapidly digestible starch (RDS) level was lower in the 40% WSF and 40% RSF flat breads than the control (100% WF). Hedonic sensory evaluation indicated that sorghum addition did not reduce the sensory preference for the flat breads. Human clinical studies are now required to determine if the lower levels of RDS and higher antioxidants observed in the sorghum containing flat breads translate into beneficial low glycemic index and reduced oxidative stress in vivo.     

Effect of fermentation on the starch digestibility, resistant starch and some physicochemical properties of sorghum flour

The effect of natural fermentation of Tabat sorghum cultivar (Sorghum bicolor L. Moench) at 37 degrees C for up to 36 h on pH, titratable acidity, starch digestibility, resistant starch and total starch was studied. The pH of the fermenting dough decreased sharply with a concomitant increase in the titratable acidity. In vitro starch digestibility markedly increased as a result of fermentation, while resistant starch and total starch decreased. Results showed that iodine absorption capacity increased during fermentation. Fermented sorghum had more soluble starch and swelling power at 100 degrees C than at 85 degrees C.     

Physicochemical changes of maize starch during the lime-heat treatment for tortilla making

As measured by the Brabender viscoamylograph, alkali-cooking and soaking of maize in water (nixtamalization) caused large increases in viscosity, as compared with native flour. Marked effects of cooking time on the pasting properties of nixtamal were also observed. As assessed by the blue value method, nixtamalization does not cause extensive gelatinization of the starch. This was supported by differential scanning calorimetric studies, which yielded similar gelatinization endotherms for untreated maize and nixtamal flours. However, no endotherm peak appeared in tortilla samples made from this nixtamal. Furthermore, untreated maize and nixtamal flours contained many unswollen starch granules.     

Changes in flour lipids during the storage of wheat flour

High- and low-grade spring and winter wheat flours of ～13% moisture were stored at 15, 25 and 37 °C and the lipids were then extracted with water-saturated n-butanol. In the original (control) flours there were more neutral lipids and glycolipids in low-grade winter than in high-grade winter and in low-grade spring than in high-grade spring flours, but there were no corresponding differences in the amounts of phospholipids. The total extractable lipid contents of the flours remained constant in the samples stored at 15 °C, but there were slight losses in the samples stored at 25 and 37 °C. Total lipid contents determined by acid hydrolysis remained constant in all cases indicating that no loss of fatty acids had occurred on storage. There was sufficient hydrolysis of all glycerides to account for the increased amounts of free fatty acids in the stored flours. Some complete deacylation of lipids to free fatty acids and water-soluble products was indicated. The fatty acid composition of all lipids remained constant, and there was no evidence of any lipoxygenase or other enzymic degradation of fatty acids. Stereoanalysis of the principal glycerides indicated that phosphatidylcholine (and probably also phosphatidylethanolamine) was specifically hydrolysed at the 2-position, presumably by phospholipase-A₂. Hydrolysis of triglycerides, diglycerides and monoglycerides was attributed to the action of wheat and microbial lipases of unknown specificity. Stereoanalysis of N-acylphosphatidylethanolamine and the galactosyldiglycerides was not attempted, but it was deduced that they were randomly hydrolysed at the 1- and 2-positions. The changes found in the flour lipids differed from those reported to occur in germinating wheat and in stored damp wheat flour which had been damaged by moulds.     

Determination of formulation and processing factors affecting slowly digestible starch,protein digestibility and antioxidant capacity of extruded sorghum–maize composite flour

High‐temperature high‐pressure extrusion of sorghum–maize composite flour, of potential for healthy food manufacture, was investigated by factorial experimental design to determine the effect of level of sorghum in dry mix (15–60%); final barrel zone temperature (120–150 °C); total moisture in barrel (21.4–25.8%); total input rate (2.3–6.8 kg h^?1); and screw speed (250–450 rpm) on extrudate slowly digestible starch (SDS), phenolic content, antioxidant capacity, protein digestibility, density and expansion ratio. Extrudate SDS increased with increasing sorghum level and decreased as the barrel temperature increased. Total phenolic content and antioxidant capacity were positively associated with sorghum level. Protein digestibility was associated negatively with sorghum level and positively with barrel temperature. Extrudate density was associated positively with total moisture and negatively with barrel temperature and input rate. Sorghum in dry mix, final barrel zone temperature and total moisture in barrel were the three most significant independent variables influencing extrudate dependant variables.     

Effect of controlled gelatinization in excess water on digestibility of waxy maize starch

An aqueous dispersion of waxy maize starch (5%, w/w) was controlled gelatinized by heating at various temperatures for 5 min. The treated samples were analysed using in vitro Englyst assay, light microscopy, differential scanning calorimetry, X-ray diffraction, and Fourier-transform infrared spectroscopy. When heated, SDS and RS levels were decreased inversely with RDS. A high SDS content (>40%) was kept prior to the visible morphological and structural changes (before 60 °C). Swelling factor began to increase slightly at 50–60 °C and continued to maximum value at 80 °C. A large decrease in ΔH, crystallinity, and ratio of 1047/1022 cm⁻¹ attributed to partially dissociation of crystalline clusters and double helices occurred at 65–80 °C. These changes showed that controlled gelatinized starch with slow digestion property occurred in the molecular rearrangement process before granule breakdown and SDS mainly consists of amorphous regions and a small portion of less perfect crystallites.     

Structural characterizations and digestibility of debranched high-amylose maize starch complexed with lauric acid

Structural characterizations and digestibility of debranched high-amylose maize starch complexed with lauric acid (LA) were studied. The cooked starch was debranched by using pullulanase and then complexed. Light microscopy showed that the lipids complexed starches had irregularly-shaped particles with strong birefringence. Gel-permeation chromatograms revealed that amylopectin degraded to smaller molecules during increasing debranching time, and the debranch reaction was completed at 12 h. Debranching pretreatment and prolonged debranching time (from 2 h to 24 h) could improve the formation of starch lipids complex. X-ray diffraction pattern of the amylose–lipid complexes changed from V-type to a mixture of B- and V-type polymorphs and relative crystallinity increased as the debranching time increased from 0 to 24 h. In DSC thermograms, complexes from debranched starch displayed three separated endotherms: the melting of the free lauric acid, starch–lipid complexes and retrograded amylose, respectively. The melting temperature and enthalpy changes of starch–lipid complex were gradually enhanced with the increasing of debranching time. However, no significant enthalpy changes were observed from retrograded amylose during the starch–lipid complex formation. Rapidly digestible starch (RDS) content decreased and resistant starch (RS) content increased with the increasing of debranching time, while the highest slowly digestible starch (SDS) content was founded at less debranching time of 2 h. The crystalline structures with dense aggregation of helices from amylose-LA complex and retrograded amylose could be RS, while SDS mostly consisted of imperfect packing of helices between amylopectin residue and amylose or LA.     

Sponge cake microstructure,starch retrogradation and quality changes during frozen storage

The effect of frozen storage (6 months) on the microstructure (microscopy, flatbed scanning and image analysis), quality (texture, moisture and specific volume) and starch retrogradation of the cake crumb were evaluated. After 2 months of storage, texture (firmness, cohesiveness and resilience) was significantly (P < 0.05) affected and starch retrogradation was observed, while by the fourth month, the crystallinity increased and crumb fractures were noticeable. Additionally, the shrinkage of starch granules was observed as the starch circularity (Sc) values significantly decreased (P < 0.05) by the sixth month of storage. Although structural changes were not detected by image analysis, it was demonstrated that cake microstructure damage is related to physical changes because the Sc was significantly correlated (P < 0.05) with moisture and specific volume and therefore with the cake quality and texture. Moreover, sugar re‐crystallisation occurred during frozen storage, and it was significantly correlated (P < 0.05) with the deterioration in cake quality.     

Functional properties of tortillas with triticale flour as a partial substitute of nixtamalized corn flour

The effect of partial substitution of nixtamalized corn flour for triticale flour in functional properties of dough and tortillas was evaluated. Seven blends of refined triticale and nixtamalized corn flour (NCF) were tested in a traditional process of tortilla production. Triticale flour significantly reduced water absorption of dough, tortillas cooking time and yield. NCF-Triticale flour blends for making tortillas using water to 80 °C improves the consistency and cohesiveness of dough. A mix containing more than 25 g of triticale flour per 100 g of flour develop inadequate adhesiveness of the dough, which is inconvenient when using the manual press. The extensibility of tortilla blends was lower than pure NCF tortillas. The advisable proportion for triticale flour used as a partial substitute of nixtamalized corn flour was 100 g kg⁻¹ (flavor, color, texture and an acceptable adhesiveness).     

变温储藏对大米淀粉回生的影响

利用差示扫描量热仪研究了变温储藏对大米淀粉回生的影响,实验结果表明,变温储藏可以改变支链淀粉的重结晶性状,但对直链淀粉和脂质复合物的结晶没有影响。25℃下放置5d后再置于4℃下储藏可以有效地抑制支链淀粉的重结晶,从而降低大米淀粉的回生速度。     

The optimization of the extrusion process when using maize flour with a modified amino acid profile for making tortillas

Maize with a modified amino acid profile, i.e. greater amounts of lysine and tryptophan than normal, is known as ‘quality protein maize’ (QPM). The objective of this work was to find the best combination of extrusion process variables to produce QPM flour for making tortillas. QPM grits were mixed with lime and water and had a moisture content of 28%. The single screw extruder operation conditions were selected from factorial combination of three process variables: extrusion temperature (ET, 70–100 °C), lime concentration (LC, 0.1–0.3% of the maize weight) and screw velocity (SV, 80–250 rpm). Response surface methodology was used as an optimization technique. In vitro protein digestibility (PD); total colour difference (ΔE) of the flours, and tortilla puffing (TP) were chosen as response variables. A graphical method was used to obtain maximum PD, TP and minimum ΔE. The optimum combination of process variables was: ET = 85 °C/LC = 0.21%(w/w)/SV = 240 rpm. Tortillas from QPM flour had similar chemical composition, physicochemical and sensory properties to tortillas from commercial nixtamalized maize flour; however, the former had the highest (P ≤ 0.05) available lysine content and were therefore better nutritionally.     

Effect of sourdough on quality and acceptability of wheat flour tortillas

As an alternative on the search for functional food products, this study evaluated the use of sourdough in the preparation of wheat flour tortillas. The sourdough was elaborated with Lactobacillus sanfranciscensis and the wheat flour tortillas were prepared with different concentrations of mother sponge (5%, 15%, and 25%) and fermentation times (1 and 3 h) at room temperature (25 ± 2 °C). Quality (diameter, height, color, pH, stretchability scores, and Kramer shear cell results) of wheat tortillas was evaluated after 24 h of preparation. The mother sponge concentration and fermentation time affected some quality parameters and acceptability properties (taste, aroma, color, opacity, and rollability). In addition, the sourdough tortillas had higher stretchability values than control tortillas. Since most of the prepared sourdough tortillas had acceptability values similar to those of tortilla controls, the introduction of sourdough is a viable means to incorporate additional nutritional and nutraceutical value into wheat tortillas.     

Structural changes induced by high speed jet on in vitro digestibility and hydroxypropylation of rice starch

Influences of high speed jet (HSJ) at different pressures (0, 80, 160, 250 MPa) on digestibility and hydroxypropylation of rice starch were evaluated. HSJ treatment increased the content of rapidly digestible starch and slowly digestible starch and decreased the content of resistant starch with increasing of the treatment pressure in native starch. The degree and the reaction efficiency of hydroxypropylation of rice starch increased with an increase in treatment pressure. Scanning electron microscopy and X‐ray diffraction analysis showed that both the crystalline structure and the overall granular structure were partially destroyed. Meanwhile, HSJ treatment led to degradation of starch molecules. The results suggested that the changes of starch structure resulted in decreasing gelatinisation enthalpy of rice starch and might be response for the changes of reactivity and its digestibility to some extent.     

Effect of storage on resistant starch content and in vitro starch digestibility of some pressure‐cooked cereals and legumes commonly used in India

Resistant starch (RS) is that fraction of starch, which escapes enzymic hydrolysis in the small intestine and passes in the colon. Effect of storage time (12 and 24 h) and temperature (4 °C and 25 °C) was studied on RS content of the pressure‐cooked cereal and legume grains/seeds and their flours. RS content was observed to increase in the stored cereals and legumes, with more enhanced increase in the flour samples stored at refrigeration temperature for longer duration (41.4% in wheat flour and 85.4% in pea flour). Significant positive correlations were observed between RS content (4 °C, 24 h) and amylose (y = 0.388 × –5.948, r = 0.840, P ≤ 0.05, n = 7) as well as between % increase in insoluble dietary fibre content (4 °⁰C, 24 h) and amylose (y = 2.257 × –27.724, r = 0.971, P ≤ 0.05, n = 7). Reduced in vitro starch digestibility of the cooked/stored samples (4 °C, 24 h) was observed when compared to freshly cooked samples.     

Effect of maize type and extrusion‐cooking conditions on starch digestibility profiles

This study aimed at evaluating the influence of screw speed (250–600 rpm), barrel temperature (100–160 °C) and water content (16.4–22.5%) on rapidly digestible (RDS), slowly digestible (SDS) and resistant (RS) starch levels of waxy, normal and high‐amylose maize starches. In native starches, an increase in amylose content was correlated with lower SDS content. After extrusion, this trend was reversed. Both waxy and normal maize starches became rapidly digested. However, for normal maize starch, some SDS fraction remained. In contrast, the high‐amylose maize starch showed a significant increase in digestibility and an increase in SDS content from 20.4% in the native starch up to 27.5% after extrusion. This high level of SDS may be attributed to the presence of some remaining granular structures and formation of crystalline orders, which have slow digestion properties.