Significance of Dietary Fiber on the Viscometric Pattern of Pasted and Gelled Flour‐Fiber Blends

The aim of this research was to optimize mixtures of fibers from different sources and degree of processing meeting acceptable dough viscometric standards to design low‐calorie wheat bread formulations. Effects of soluble (inuline [FN]), partially soluble (sugar beet [FX]), pea cell wall (SW), and insoluble (pea hull [EX]) dietary fibers on wheat dough pasting and gelling profiles have been investigated. Impact of fibers added singly and in associated mixtures at different levels on the investigated viscometric parameters retrieved from a Rapid Visco Analyser curve has been assessed by response surface methodology, and the thermal parameters derived from the cooking and cooling functional profile were correlated. Flour replacement up to 34% by fibers significantly provided a deleterious effect on pasting and gelling viscosity profiles of the resulting hydrated high fiber‐flour blends. The magnitude of the reduction in dough viscometric characteristics during gelatinization, pasting, and setback closely depended on the nature of the fibers in the blend and on the extent of the flour substitution. A delayed and restricted swelling of starch granules and amylose leaching process preferentially achieved by the pair FN‐FX resulted in higher pasting temperatures and reduced peak viscosities during cooking and a sharp decrease of the setback on cooling. Single addition of FX, FN, and EX, respectively, provided a significant decrease in both breakdown viscosity and viscosity at the end of 95°C. Simultaneous presence of FN and EX that exhibit medium or low hydration properties allowed a partial restoration of initial breakdown viscosity and a simultaneous decrease in holding strength. Caution should be paid to the pairs FN‐FX and EX‐SW because of the adverse extra decline they induced in the viscosities of both hot paste and cold gel.     

Comparison of Starch Pasting Properties at Various Cooking Conditions Using the Micro Visco‐Amylo‐Graph and the Rapid Visco Analyser

Pasting profiles of selected starches were compared by using a Micro Visco‐Amylo‐Graph (MVA) and a Rapid Visco Analyser (RVA). Effects of cooking (heating/cooling) rate and stirring speed on starch pasting properties were examined. The pasting viscosity of a starch suspension (8%, w/w, dsb) was measured at a fast (6°C/min) and slow (1.5°C/min) cooking rate while being stirred at either 75 rpm or 160 rpm. The pasting temperatures (PT) of all starches were higher when measured at the fast cooking rate than those at the slow cooking rate, except for wheat measured by using the RVA. PT was also higher when measured at the slow stirring speed (75 rpm) than at the fast stirring speed (160 rpm) in both RVA and MVA. When stirring speed increased from 75 rpm to 160 rpm, peak viscosity of all starch pastes except potato decreased measured by using the RVA, but increased by using the MVA. In general, amylograms of these starches obtained by using the MVA showed less breakdown, but greater setback viscosity than did that obtained by using the RVA. Differences in starch pasting properties between MVA and RVA, measured at the same cooking and stirring rates, were attributed mainly to the difference in spindle structure.     

Wheat Bran AX Properties and Choice of Xylanase Affect Enzymic Production of Wheat Bran‐Derived Arabinoxylan‐Oligosaccharides

Wheat bran‐derived arabinoxylan‐oligosaccharides (AXOS) recently have been shown to potentially exert prebiotic effects. In this study, 15 bran samples obtained by milling different wheat cultivars were treated with xylanases from Hypocrea jecorina (XHJ), Aspergillus aculeatus (XAA), and Pseudoalteromonas haloplanktis (XPH) to assess the effect of bran source and xylanase properties on the AXOS yield and structure. The total arabinoxylan (AX) extraction yield was higher with XHJ (8.2–10.7%) and XAA (8.2–10.8%) than with XPH (6.9–9.5%). Irrespective of the enzyme, a significant negative correlation was observed between extraction yield and arabinose to xylose (A/X) ratio of bran AX (r = –0.7), but not between yield and bran AX level. The A/X ratio of the extracted material was 0.27–0.34 for all bran samples and all enzymes, which combined with yield data and microscopic analysis, indicated primary hydrolysis of aleurone and nucellar epidermis AX. The average degree of polymerization (avDP) of the extracted AX was very low for all enzymes (2–3), owing to the release of high levels of monomeric arabinose and xylose. The release of these monosaccharides could be ascribed to 1) the activity of wheat bran‐associated enzymes (arabinofuranosidases and xylosidases); 2) the hydrolytic properties of the xylanases themselves; and 3) the presence of xylosidases as contaminations in enzyme preparation, in that order of importance. Heat treatment of bran before xylanase treatment significantly decreased the levels of monomeric arabinose and xylose in the extract, without affecting the extraction yield, resulting in a higher avDP of 3–7, thus yielding true AXOS. Overall, for AXOS production, wheat cultivars with a low bran A/X ratio of the AX are preferable as starting materials, and inactivation of bran‐associated enzymes before incubation is desirable. The XHJ xylanase was the best enzyme for wheat bran‐derived AXOS production.     

Effects of Commercial Hydrolytic Enzyme Additives on Japanese‐Style Sponge and Dough Bread Properties and Processing Characteristics

The effects of increasing levels of eight commercial fungal enzymes enriched in four types of activity (α‐amylase, protease, xylanase, or cellulase) on Japanese‐style sponge and dough bread quality and processing characteristics have been studied using a Canadian red spring wheat straight‐grade flour. At optimum levels, the enriched α‐amylases, xylanases, and cellulases increased loaf volume and bread score and reduced crumb firmness, while the proteases only reduced crumb firmness. For α‐amylases, xylanases, and cellulases, optimum levels for crumb firmness were obtained at higher levels of addition than for loaf volume and bread score. At high levels of addition, all four enriched enzyme types reduced loaf volume and bread score and increased crumb firmness relative to optimum levels, with the proteases showing the most dramatic effects. α‐Amylases and cellulases had little impact on dough mixing requirements, while xylanases increased and proteases greatly reduced mixing requirements. All enzymes at optimum levels reduced sheeting work requirements, resulting in softer more pliable dough. Optimum bread properties for α‐amylases, xylanases, and cellulases were attained within a relatively narrow range of dough sheeting work values. This similarity in response suggests a dominant common nonspecific mechanism for their improver action, which is most likely related to water release and the resulting impact on physical dough properties.     

Processing Affects the Physicochemical Properties of Fiber from Wheat and Flax in Ready‐to‐Eat (RTE) Flaked Cereal

Fiber from wheat and flax is mostly insoluble, making addition in high amounts to a food difficult without adversely affecting product attributes. One approach to increasing the level of these fibers in food is to hydrolyze fiber to more soluble forms through processing. This study was designed to evaluate the impact of a steam pressure cooking process on physicochemical properties of ready‐to‐eat (RTE) cereal with 17.7% added unhydrolyzed flax fiber (a combination of arabinoxylans, rhamnogalacturonans, and pectins) or 15.4% added hydrolyzed wheat fiber (a purified arabinoxylan extract). Peak molecular weights of unhydrolyzed and hydrolyzed fibers were ∼2.9 × 10⁶ and ∼800 g/mol, respectively, with a ∼400‐fold higher viscosity for unhydrolyzed fiber. Molecular weight of the unhydrolyzed fiber ingredient was reduced to approximately the molecular weight of the hydrolyzed fiber as a result of the low‐shear steam pressure cooking process used, and consistent with molecular weight results, there was only a twofold difference in viscosity of the cereal remaining. The low‐fiber control RTE cereal had the highest viscosity owing to starch content.     

Increase in Apparent Amylose Content and Change in Starch Pasting Properties at Cool Growth Temperatures in Mutant Wheat

Some mutant wheat lines with low‐amylose content were grown in a field and greenhouse (15 or 20°C) to compare apparent amylose content and starch pasting properties. The apparent amylose content of flour and starch increased and starch pasting parameters as measured by a Rapid Visco Analyser (RVA) changed in the greenhouse (at cool temperatures) during seed maturation. Densitometric analysis of the protein band separated by electrophoresis suggested that the increase in amylose content by cool temperature was related to the amount of Wx‐D1 protein. This data suggests that the Wx‐D1 gene was responsible for these changes. In wheat starch from Tanikei A6099 and Tanikei A6598 at 15°C, the value of final viscosity and total setback was higher than that from the field. In wheat starch from Tanikei A6599‐4 (waxy mutant with stable hot paste viscosity), the peak viscosity temperature was higher and time maintained >80% of the peak was shorter at 15°C than that from the field. Genetic analysis using doubled‐haploid (DH) lines from a combination of Tanikei A6599‐4 and Kanto 118 (low‐amylose line) showed that apparent amylose content increased and the starch pasting curve and properties changed in waxy progenies similar to Tanikei A6599‐4.     

Using an In‐Line Slit‐Die Viscometer to Study the Effects of Extrusion Parameters on Corn Melt Rheology

An in‐line slit‐die viscometer (SDV) was used to measure the viscosity of a melt extrudate independently of the extruder operating conditions. The melt produced by extrusion of the corn grits followed a power law rheological model. The viscosity of the melt and extrusion parameters such as specific mechanical energy (SME), torque, and die pressure decreased with increasing moisture content. The degree of starch gelatinization increased when barrel temperature increased from 90 to 130°C. At temperatures higher than 130°C, most of the starch had gelatinized. The increase in barrel temperature, however, resulted in small changes in the apparent viscosity of the melt, until a maximum of ≈130°C. At a constant feed rate, SME increased and torque decreased when screw speed increased due to the shear thinning behavior of the melt. At a constant screw speed, the torque increased and SME decreased with increasing feed rate. This was due to a decrease in apparent viscosity of the melt at higher feed rates. SME is not an independent extrusion variable and should be used with caution either when predicting the effect of thermomechanical treatment of the product or as the key and only variable for controlling the food extrusion process.     

Thermal and Functional Properties of Hairless Canary Seed (Phalaris canariensis L.) Starch in Comparison with Wheat Starch

Recently, hairless canary seed has received generally recognized as safe (GRAS) status from the U.S. Food and Drug Administration and an approval as a novel food from Health Canada. There is a need to characterize its components for food and nonfood applications. In this study, thermal and functional properties of starch obtained from two hairless canary seed varieties were investigated and compared with commercial wheat starch. Both canary seed starches (CSS) had polygonal granules with a diameter range of 0.5–7.5 μm and average of 2.6 μm. The CSS showed a typical crystal structure (A‐type) of cereal starches but exhibited a strong amylose‐lipid complex peak at 4.4°A. DSC data showed that CSS have higher gelatinization transition temperatures (onset, peak, and conclusion temperatures) and broader gelatinization range compared with wheat starch. The CSS also exhibited higher peak, trough, final, breakdown, and setback viscosity in addition to higher swelling power and water solubility index than wheat starch. The exudate from CSS gels after freeze‐thawing treatment was lower than that of wheat starch gel, but CSS suspensions showed less clarity. The distinct properties of CSS, particularly having uniform and small granules, low amount of damaged starch and amylose, and better gel stability, would make it a promising nonconventional starch source.     

Volatile Compounds in Crumb of Whole‐Meal Wheat Bread Fermented with Different Yeast Levels and Fermentation Temperatures

The influence of fermentation temperatures (8, 16, and 32°C) and yeast levels (2, 4, and 6%) on the formation of volatile compounds in the crumb of whole‐meal wheat bread was investigated. Volatile compounds were extracted by dynamic headspace extraction and analyzed by gas chromatography–mass spectrometry. Results were evaluated with multivariate data analysis and ANOVA. Bread fermented at a high temperature (32°C) had higher peak areas of the Maillard reaction products 2‐furancarboxaldehyde, 2‐acetylfuran, 2‐methylpyrazine, and phenylacetaldehyde compared with bread fermented at lower fermentation temperatures. Bread fermented at low temperatures (8 and 16°C) was characterized by having higher peak areas of the fermentation products 3‐methylbutanal, 2‐methylbutanal, ethyl acetate, ethyl hexanoate, ethyl propanoate, and 3‐methylbutanol. Fermentation of bread with 6% yeast resulted in a higher peak area of the important fermentation product 2‐phenylethanol. It also reduced the peak areas of important lipid oxidation products. The peak area of 2,3‐butanedione was also relatively higher in bread fermented with 6% yeast compared with lower yeast levels; however, an interaction was seen between the high yeast level and all three fermentation temperatures. In contrast, fermentation with a low yeast level (2%) resulted in bread with relatively higher peak areas of 2‐ and 3‐methylbutanal, as well as (E)‐2‐nonenal and (E,E)‐2,4‐decadienal, which are important lipid oxidation compounds in bread.     

Effects of Preparation Temperature on Gelation Properties and Molecular Structure of High‐Amylose Maize Starch

In this study, 3% aqueous high‐amylose maize starch (Hylon VII) dispersions were heated to temperatures of 140–165°C. The onset and rate of gel formation was observed using a small‐strain oscillation rheometer as a function of temperature from 90 to 25°C. The gel formation clearly began earlier in high‐amylose starch paste preheated at lower temperatures, but the rate of gelation was slower and the resulting gel was weaker in comparison with starch pastes preheated at higher temperatures. In addition, the structure of the final gels was studied using large deformation compression measurements. The most rigid gel structure on the basis of small and large deformation tests was obtained for high‐amylose starch gel preheated to 150–152°C, depending on the type of measurement. The rate of gelation was also fastest in that temperature range. High‐amylose gels heated to higher temperatures lost their rigidity. The molecular weight distribution of starch molecules was measured by size‐exclusion chromatography. Heating caused extensive degradation of amylopectin, which had a great effect on amylose gel formation and the final gel properties of high‐amylose maize starch. Micrographs of Hylon VII gels showed that phase separation of starch components visible in light microscopy occurred on heating to higher temperatures.     

Characteristics of Granular Cold‐Water Gelling Starches of Cereal Grains and Legumes Prepared Using Liquid Ammonia and Ethanol

Starches of wheat, corn, smooth and wrinkled peas, and chickpeas were modified to a free‐flowing powder of granular cold‐water gelling (GCWG) starch using liquid ammonia and ethanol at 23°C and atmospheric pressure. Amylose content of starches was 26.3% in wheat, 27.1% in corn, 35.4% in chickpeas, 43.2% in smooth peas, and 79.9% in wrinkled peas. The modified starches remained in granular form with an increased number of grooves and fissures on the surface of the granules compared with native starch, while the crystallinity was mostly lost, as shown by X‐ray diffractograms and DSC endothermic enthalpies. Pasting viscosity of modified starches at 23°C was 171 BU and 305 BU in wheat and corn, respectively, and much higher in legume starches, ranging from 545 BU to 814 BU. Viscosities of modified legume starches at 23°C were at least twice as high as those of native starches determined at 92.5°C. Swelling power of modified starches at 23°C ranged from 8.7 g/g to 15.3 g/g, while swelling power of native starches heated to 92.5°C ranged from 4.8 g/g to 16.0 g/g. GCWG starches exhibited higher dextrose equivalent (DE) values of enzymatic hydrolysis, ranging from 25.2 to 27.0 compared with native starches (1.5–2.9). Modified starches from wheat, corn, smooth peas, and chickpeas formed weak gels without heat treatment and experienced no changes in gel hardness during storage, while native starch gels formed by heat treatment showed an increase in hardness by 1.1–7.5 N during 96 hr of storage at 4°C.     

Gelatinization and Retrogradation Kinetics of High‐Fiber Wheat Flour Blends: A Calorimetric Approach

The impact of dietary fiber (DF) mixtures on dough thermal properties needs to be investigated when designing high‐fiber wheat bread. Effects of flour replacement at different levels (6–34%) by soluble (inuline [FN]), partially soluble (sugar beet [FX], pea cell wall [SW]), and insoluble (pea hull [EX]) DF on wheat dough thermal profiles have been investigated by simulating baking, cooling, and storage in differential scanning calorimetry (DSC) pans. In general, DF incorporation into water‐flour systems delayed endothermic transition temperatures for both gelatinization and retrogradation phenomena except for the peak temperature (T_p) of retrogradation. With some exception, the pattern of the enthalpy of amylopectin retrogradation was lower and slower (lower constant of proportion, k) over 10 days of storage in gelatinized hydrated flour‐fiber blends when compared with control without DF. FX, a partially soluble fiber, provided major effects on gelatinization (T_p decrease and ΔH increase) and retrogradation kinetics (the Avrami exponent, n, increase). Single presence of EX allowed a significant reduction in the Avrami exponent n leading to slower kinetics for amylopectin retrogradation when included in the blends.     

Supra‐optimal growth temperature exacerbates adverse effects of low Zn supply in wheat

Rising temperatures are a major threat to global wheat production, particularly when accompanied by other abiotic stressors such as mineral nutrient deficiencies. This study aimed to quantify the effects of supra‐optimal temperature on growth, photosynthetic performance, and antioxidative responses in bread wheat cultivars grown under varied zinc (Zn) supply. Two bread wheat cultivars (Triticum aestivum L., cvs. Lasani‐2008 and Faisalabad‐2008) with varied responsiveness to Zn supply and drought tolerance were cultured in nutrient solution with low (0.1 µM) or adequate (1.0 µM) Zn under optimal (25/20°C day/night) or supra‐optimal (36/28°C day/night) temperature regimes. Supra‐optimal temperature severely reduced root but not shoot biomass, whereas low Zn reduced shoot as well as root biomass. Shoot‐to‐root biomass ratio was reduced under low Zn but increased under supra‐optimal temperature. Supra‐optimal temperature inhibited root elongation and volume particularly in plants supplied with low Zn. In both cultivars, Zn efficiency index was reduced by supra‐optimal temperature, whereas heat tolerance index was reduced by low Zn supply. Supra‐optimal temperature decreased photosynthesis, quantum yield, and chlorophyll density in low‐Zn but not in adequate‐Zn plants. In comparison, low Zn decreased specific activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) and increased glutathione reductase (GR), where supra‐optimal temperature increased SOD, decreased GR and did not change APX activity in leaves and roots. Moreover, supra‐optimal temperature severely reduced shoot Zn concentration and Zn uptake per plant specifically under adequate Zn supply. Overall, supra‐optimal temperature exacerbated adverse effects of low Zn supply, resulting in severe reductions in growth traits viz. shoot and root biomass, root length and volume, and consequently impeded Zn uptake, enhanced oxidative stress and impaired photosynthetic performance. Adequate Zn nutrition is crucial to prevent yield loss in wheat cultivated under supra‐optimal temperatures.     

Modeling of the fine‐scale temperature response of arylsulfatase activity in soil

Fine‐scale (1.0–2.2 °C) temperature dependence of soil arylsulfatase activity (arylsulfate sulfohydrolase, EC 3.1.6.1) was measured at 0 to 75 °C in a Danish sandy, arable soil. Assays were done with field‐moist soil samples in the absence of toluene as plasmolytic agent – a procedure that primarily measures the extracellular enzymes. The aim was to evaluate the use of temperature models to describe the temperature response of soil arylsulfatase activity. In addition, we searched for increases in activity at high temperatures (e.g., 50–60 °C), which might be associated with unmasking (exposure) of intracellular enzymes. Arylsulfatase activities ranged from 1.1 to 60.3 μg p‐nitrophenol (g dry weight soil)^–1 h^–1, with an optimum temperature at 58.1 °C. The temperature response below 58.1 °C could be described by the Arrhenius equation (r² = 0.978, n = 83) and the simple Ratkowsky equation (r² = 0.977, n = 83). The expanded Ratkowsky equation, which covered the entire temperature range (0–75 °C), was less satisfactory (r² = 0.958, n = 90) because the model underestimated the reaction rates near the optimum temperature. The activation energy (E_a) calculated from the Arrhenius equation was 42.2 kJ mol^–1. This was higher than previously found for other soils (16.5–34.7 kJ mol^–1), possibly due to the use of toluene in these studies. Further analysis of the temperature response showed that no increase in activity occurred due to potential unmasking of intracellular enzymes by disintegration of bacterial cell membranes at high temperatures. Thus, the use of high incubation temperatures did not facilitate the differentiation between intra‐ and extracellular enzyme activity.     

Small‐Scale Extrusion of Corn Masa By‐Products

Corn masa by‐product streams are high in fiber and are amenable for utilization in livestock feed rations. This approach is a potentially viable alternative to landfilling, the traditional disposal method for these processing residues. Suspended solids were separated from a masa processing waste stream, blended with soybean meal at four levels (0, 10, 20, and 30% wb), and extruded in a laboratory‐scale extruder at speeds of 50 rpm (5.24 rad/sec) and 100 rpm (10.47 rad/sec) with temperature profiles of 80‐90‐100°C and 100‐110‐120°C. Processing conditions, including dough and die temperatures, drive torque, specific mechanical energy consumption, product and feed material throughput rates, dough apparent viscosity, and dough density, were monitored during extrusion. The resulting products were subjected to physical and nutritional characterization to determine the effects of processing conditions for these blends. Extrudate analysis included moisture content, water activity, crude protein, in vitro protein digestibility, crude fat, ash, product diameter, expansion ratios, unit and true density, color, water absorption and solubility, and durability. All blends were suitable for extrusion at the processing conditions used. Blend ratio had little effect on either processing parameters or extrudate properties; extrusion temperature and screw speed, on the other hand, significantly affected both processing and product properties.     

Seedball‐induced changes of root growth and physico‐chemical properties—a case study with pearl millet

Seedball is a cheap “seed‐pelleting‐technique” that combines local materials, seeds and optionally additives such as mineral fertilizer to enhance pearl millet (Pennisetum glaucum (L.) R. Brown) early growth under poor soil conditions. The major objective here was to study the mechanisms behind positive seedball effects. Chemical effects in the rhizosphere and early root development of seedball‐derived pearl millet seedlings were monitored using micro‐suction‐cups to extract soil solutions and X‐ray tomography to visualize early root growth. Pearl millet (single seedling) was grown in soil columns in a sandy soil substrate. Root and shoot biomass were sampled. X‐ray tomography imaging revealed intense development of fine roots within the nutrient‐amended seedball. Seedball and seedball+NPK treatments, respectively, were 65% and 165% higher in shoot fresh weight, and 108% and 227% higher in shoot dry matter than the control treatment. Seedball+NPK seedlings showed promoted root growth in the upper compartment and 105% and 30% increments in root fresh and dry weights. Soil solution concentrations indicate that fine root growth ass stimulated by release of nutrients from the seedballs to their direct proximity. Under real field conditions, the higher root length density and finer roots could improve seedlings survival under early drought conditions due to better ability to extract water and nutrients from a greater soil volume.     

Impact of Rice Flour Cold‐Water‐Soluble Fraction Removal on Gelatinization and Pasting Properties

The influence of the cold‐water‐soluble fraction on gelatinization and pasting properties of rice flour was investigated. The cold‐water‐soluble fraction was removed by water extraction under room temperature. The gelatinization properties of untreated and treated flour were analyzed with a differential scanning calorimeter, and pasting profiles were measured with a rapid viscosity analyzer. The removal of the cold‐water‐soluble fraction resulted in the formation of a loosened starch granule structure, a morphological alteration of protein bodies, a markedly lower gelatinization temperature, and a significantly higher pasting enthalpy. The impact on paste viscosity followed different trends. In some cultivars that had lower endogenous amylase activity, the paste viscosity was greatly reduced by the removal of the cold‐water‐soluble fraction. In others, the higher level of endogenous amylase activity led to more soluble saccharides being released through starch hydrolysis. Removing the soluble fraction caused a remarkable increase in peak viscosity. The overall effect on paste viscosity of removing the cold‐water‐soluble fraction was attributed to multiple factors, involving loosening of the starch granule structure, alteration of morphology of protein bodies, and the release of saccharides by endogenous amylase activity.     

Hot‐Water Solubilities and Water Sorptions of Resistant Starches at 25°C

Resistant starches (RS) were prepared from wheat starch and lintnerized wheat starch by autoclaving and cooling and by cross‐linking. Heat‐moisture treatment also was used on one sample to increase RS. The experimental resistant starches made from wheat starch contained 10–73% RS measured as Prosky dietary fiber, whereas two commercial resistant starches, Novelose 240 and 330, produced from high‐amylose maize starch, contained 58 and 40%, respectively. At 25°C in excess water, the experimental RS starches, except for the cross‐linked wheat starch, gained 3–6 times more water than the commercial RS starches, and at 95°C gained 2–4 times more. Cross‐linked RS4 wheat starch and Novelose 240 showed 95°C swelling powers and solubilities of 2 g/g and 1%, and 3 g/g and 2%, respectively. All starches showed similar water vapor sorption and desorption isotherms at 25°C and water activities (a_w) < 0.8. At a_w 0.84–0.97, the resistant starches made from wheat starch, except the cross‐linked wheat starch, showed ≈10% higher water sorption than the commercial resistant starches.     

Partial Characterization of Buckwheat (Fagopyrum esculentum) Starch

Laboratory-isolated buckwheat (Fagopyrum esculentum) starch was compared to commercial corn and wheat starches. Buckwheat starch granules (2.9–9.3 μm) were round and polygonal with some holes and pits on the surface. Buckwheat starch had higher amylose content, waterbinding capacity, and peak viscosity, and it had lower intrinsic viscosity when compared with corn and wheat starches. Buckwheat starch also showed restricted swelling power at 85–95°C and lower solubility in water at 55–95°C and was more susceptible to acid and enzymatic attack. Gelatinization temperatures, determined by differential scanning calorimetry, were 61.1–80.1°C for buckwheat starch compared to 64.7–79.2°C and 57.1–73.5°C for corn and wheat starches, respectively. A second endotherm observed at 84.5°C was an amylose-lipid complex attributed to the internal lipids in buckwheat starch, as evidenced by selective extraction. The retrogradation of buckwheat, corn, and wheat starch gels was examined after storage at 25, 4, and -12°C for 1–15 days. In general, buckwheat starch retrogradation was slower than that of corn and wheat starch, but it increased as storage time increased, as did that of the other starch pastes. When the values of the three storage temperatures were averaged for each storage period analyzed, buckwheat starch gels showed a lower percentage of retrogradation than did corn and wheat starch gels. Buckwheat starch also had a lower percentage of water syneresis when stored at 4°C for 3–10 days and had better stability to syneresis after three freeze-thaw cycles at -12 and 25°C.     

Preparation of High‐Quality Protein‐Based Extruded Pellets Expanded by Microwave Oven

The aim of this work was to study the effects of extrusion barrel temperature (75–140°C) and feed moisture (16–30%) on the production of third‐generation snacks expanded by microwave heating. A blend of potato starch (50%), quality protein maize (QPM) (35%), and soybean meal (SM) (15%) was used in the preparation of the snacks. A laboratory single extruder with a 1.5 × 20.0 × 100 mm die‐nozzle and a central composite routable experimental design were used. Expansion index (EI) and bulk density (BD) were measured in expanded pellets, viscosity at 83°C (V₈₃), thermal properties, and relative crystallinity were measured in extruded pellets. EI increased and BD decreased when the barrel temperature was increased, while the feed moisture effect was not significant. V₈₃ increased when feed moisture increased. Extrusion modified the crystalline structures of the pellets and the X‐ray data suggests the formation of new structures, probably due to the development of amylose‐lipid complexes. The maximum expansion of pellets was found at barrel temperatures of 123–140°C, and feed moisture of 24.5–30%. It is possible to obtain a functional third‐generation snack with good expansion characteristics using a microwave oven, and this snack has health benefits due to the addition of QPM and SM.