SME‐Arrhenius Model for WSI of Rice Flour in a Twin‐Screw Extruder

We have modeled a rice extrusion process focusing specifically on the starch gelatinization and water solubility index (WSI) as a function of extrusion system and process parameters. Using a twin‐screw extruder, we examined in detail the effect of screw speed (350–580 rpm), barrel temperature, different screw configurations, and moisture content of rice flour on both extrusion system parameters (product temperature, specific mechanical energy [SME], and residence time distribution [RTD]) and extrudate characteristics (expansion, density, WSI, and water absorption index [WAI]). Changes in WSI were monitored to reveal a relationship between the reaction kinetics during extrusion and WSI. Reaction kinetics models were developed to predict WSI during extrusion. WSI followed a pseudo first‐order reaction kinetics model. It became apparent that the rate constant is a function of both temperature and SME. We have developed an adaptation of the kinetic model based on the Arrhenius equation that shows better correlations with SME and distinguishes data from different screw configurations. This adaptation of the model improved predictability of WSI, thereby linking the extrusion conditions with the extruded product properties.     

Residence Time Distribution and Barrel Fill in Pet Food Twin‐Screw Extrusion Cooking

The residence time distribution and barrel fill of pet food in a twinscrew extruder was determined under conditions of a constant ratio of feed rate to screw speed. Specific feeding load was held constant at 0.16 kg/hr/ rpm while feed rate ranges were 24–56 kg/hr and screw speed ranges were 150–350 rpm. The residence time rapidly decreased as feed rate and screw speed increased. The spread of the residence time distribution (RTD) was smaller at higher feed rates and screw speed, however analysis of the normalized RTD indicated greater mixing. The barrel fill was constant at ≈50% throughout the range of experimental conditions.     

Freeze‐Thaw Stability of Bualoy Thai Dessert Using Waxy Rice Flour

Frozen food products are gaining acceptance in Thai food industry and frozen bualoy dessert is a good opportunity for marketing in domestic and for exports. One important factor affecting quality of frozen starchy foods is retrogradation of starch gels. Thus freeze‐thaw stability of a frozen bualoy made from total waxy rice flour was studied and compared among the samples modified by 20 and 30% cross‐linked tapioca starch (CTS) derivatized with phosphorylation and 0.25% propylene glycol alginate (PGA). The waxy rice flour was pregelatinized by adding boiled water before shaping as a ball, then boiled and mixed with coconut syrup. All samples were subjected to five freeze‐thaw cycles over 60 days in a conventional freezer (–18°C). Texture analysis firmness and stickiness of the nonfrozen gels substituted with 20% CTS (382 ± 43, 20.5 ± 7.1 g·f) and 30% CTS (493 ± 37, 31.1 ± 7.0 g·f) were significantly different as compared with the control (329 ± 22, 14.8 ± 3.1 g·f). Similar results were observed for the samples continuously frozen for 60 days. The effects of freeze‐thaw stability to the frozen gels of the control, CTS, and PGA substituted samples appeared after two cycles and exhibited a large increase in firmness and stickiness at the fourth cycle. The firmness values obtained from the control and the samples substituted with 20% and 30% CTS were 2,397 ± 197, 2,182 ± 203, and 2,104 ± 200 g·f, respectively. This evidence was also observed with the samples containing PGA, but the effect was slightly less. This might account for the recrystallization of amylopectin molecules induced by freeze‐thawings. With DSC, the waxy rice gels showed a significant increase in the melting enthalpy (2.39 ± 0.23 J/g) at the fifth cycle from the nonfrozen gels (0.11 ± 0.02 J/g). The sensory tests of the bualoys were correlated with textural qualities that were acceptable to the panelists when the freeze‐thawing went no further than the second cycle.     

Characteristics of Vegetable‐Based Twin‐Screw Extruded Yellow Perch (Perca flavescens) Diets Containing Fermented High‐Protein Soybean Meal and Graded Levels of Distillers Dried Grains with Solubles

A twin‐screw extrusion study was performed in replicated trials to produce vegetable‐based feeds for juvenile yellow perch. Two isocaloric (3.06 kcal/g) experimental diets were balanced to contain 20 and 40% distillers dried grains with solubles (DDGS) and a constant amount (20%) of fermented high‐protein soybean meal (PepSoyGen) as the fishmeal protein replacers; crude protein content was targeted at 40%. A fishmeal‐based diet was used as a control. Extrusion conditions included conditioner steam (0.11–0.16 kg/min), extruder water (0.11–0.19 kg/min), and screw speed (230–300 rpm). Increasing DDGS from 0 to 40% led to a considerable rise in bulk density, lightness L*), yellowness (b*), and unit density but to decreases in water activity (a_w) and expansion ratio by 12.6, 14.4, 23, 21, 31, and 13%, respectively. The lowest unit density of 791.6 kg/m³ and highest bulk density of 654.5 kg/m³ were achieved with diets containing 20 and 40% DDGS, respectively; changes in DDGS content did not affect extrudate moisture, absorption index, or thermal properties. Raising DDGS from 0 to 40% resulted in an increase in water solubility and redness (a*) by 13.4 and 35%, respectively. All extrudates had high durability (>98%), and low a_w of less than 0.5. Overall, this study yielded viable feeds for yellow perch.     

Twin‐Screw Extrusion Processing of Rainbow Trout (Oncorhynchus mykiss) Feeds Using Various Levels of Corn‐Based Distillers Dried Grains with Solubles (DDGS)

Increasing demand for seafood products and rising demand for fish meal for commercial fish feeds is driving the search for effective alternative protein sources. Twin‐screw extrusion trials were conducted to study the production of nutritionally balanced feeds for rainbow trout fingerlings (Oncorhynchus mykiss). Six isocaloric (≈4.61 kcal/g) ingredient blends with a target protein content of >45% db were formulated with 0, 10, 20, 30, 40, and 50% distillers dried grains with solubles (DDGS) and other feed ingredients. The moisture contents of the diets were initially adjusted to 5–7% db, and then extruded at 250 rpm using dual 1.9 mm dies with varying amounts of steam (7.2–7.7 kg/hr) injected into the conditioner and water (4.3–6.5 kg/hr) into the extruder. Mass flow rates, moisture contents, and temperatures were measured during processing and moisture content, water activity, unit density, bulk density, expansion ratio, compressive strength, compressive modulus, pellet durability index, water stability, and color were analyzed to quantify the effects of varying DDGS content on the extrudate physical properties. Significant differences (P < 0.05) among the blends were observed for color and bulk density for both the raw and extruded materials, respectively, and for the unit density and pellet durability index of the extruded products. There were also significant changes in redness and yellowness, but only minor changes in brightness, among the final products with increasing DDGS content. The compressive strength of the extrudates increased significantly with increasing DDGS. Expansion ratio of all pellets was low. All extruded diets achieved very good water stability.     

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.     

Effect of Alkaline‐Soluble Proteins on Pasting Properties of Nonwaxy Rice Flour

The pasting properties of rice flours and reconstituted rice flours from mixing a common starch with proteins extracted from different rice cultivars at different total protein content levels were studied. Results showed that not only the total protein content but also the protein composition had an effect on the pasting properties of the rice flours. Among the different strands of rice proteins, globulin had the strongest influence on the pasting properties, followed by glutelin, whereas prolamin had the least influence. At the subunit level of the proteins, proteins with a molecular weight of 17,000, most likely from globulin, had the strongest effect on the peak viscosity of the rice flour, followed by those of 33,000. In comparison with that of the rice starch, the influence of proteins in rice was limited. The effect of interactions between the rice proteins and the starch, such as the role of starch‐granule‐associated proteins, was not isolated in this study, and further investigation is required to quantify this effect.     

Functional Properties of Submicron‐Scale Rice Flour Produced by Wet Media Grinding

The digestibility and hydration properties of wet‐ground submicron‐scale rice flour were compared with those of dry‐ground coarser microscale flours. The submicron flour (mean size 0.6 µm) was produced in a wet‐media mill with 0.3 mm zirconia beads by continuous 24 h pulverization. The solubility, water absorption index, and swelling power increased as the mean particle size decreased, reaching maximum values in the submicron flour. Starch damage was high in the submicron flour, with the absence of intact starch granules. The digestibility also increased as the particle size decreased, and it was highest in the submicron flour. These results show that wet‐ground submicron rice flour has different functional properties from dry‐ground coarser flour. The digestibility was more strongly influenced by starch damage and the water absorption index than by the mean particle size.     

Near‐Infrared Spectroscopy for Determination of Protein and Amylose in Rice Flour Through Use of Derivatives

The use of the derivative method for near‐infrared (NIR) calibration was investigated to determine protein and amylose content in rice flour. Samples for two years, 1996 and 1999, were combined to give a wide range of the constituents for development of the calibration model. The NIR spectral data were transformed with Savitzky‐Golay derivative with multiplicative scatter correction. To develop the best derivative models, the polynomial fits (quadratic, cubic, and quartic), convolution intervals (3–11 points for protein, 3–17 points for amylose), and derivative orders (1st derivative D1; 2nd derivative D2) were investigated. For the protein analysis, all polynomial fits with 3–11 points were acceptable to develop both the D1 and D2 models. However, the three‐point quadratic and five‐point quartic fits were not acceptable for the D1 model, and the three‐point quadratic fit was not acceptable for D2. For the amylose analysis, the D1 model produced generally better results than D2. Higher convolution intervals were required for the D2 model, whereas the D1 model was not affected by convolution intervals. A quadratic (or cubic) fit with 17‐point convolution interval was acceptable for the amylose D2 model, and the quadratic fit with 5–11 points and cubic (or quartic) fit with 7–17 points were suitable for the D1 model. Based on the standard error of cross‐validation (SECV), the calibration models developed using data for two years resulted in good precision with an SECV of 0.23% for protein using four factors and an SECV of 1.0% for amylose using 10 factors.     

Enhancement of Nutritional and Antioxidant Properties of Brown Rice Flour Through Solid‐State Yeast Fermentation

This study investigated the effect of solid‐state yeast fermentation on the nutritional and antioxidant properties of brown rice flour (BRF). Three brands of commercial baker's yeast (Eagle, Saf‐levure, and Mauripan) were used to ferment BRF at 25°C for 12 h. There were significant increases in protein, ash, insoluble and soluble fiber, phosphorus, zinc, magnesium, calcium, and iron contents after yeast fermentation. Fermented BRF with Eagle yeast possessed the highest contents of protein, ash, zinc, and calcium. Fermentation of BRF with Eagle yeast was more effective in increasing antioxidant activity and total phenolic contents from 1.01 to 1.54 mmol of Trolox equivalents per gram and from 1.09 to 1.21 mg of gallic acid equivalents per gram, respectively. Yeast fermentation reduced phytic acid content of BRF (124.59 ± 0.48 µg/g), and the Eagle yeast‐fermented sample had the lowest value (36.55 µg/g) compared with the other fermented samples. Fermented flour with Eagle yeast also had the highest α‐amylase activity, because it recorded the lowest stirring number. Solid‐state fermentation with commercial yeast, particularly Eagle yeast, was effective in improving the nutritional and antioxidant properties of underutilized BRF as a food ingredient.     

Effects of Microencapsulated High‐Fat Powders on the Empirical and Fundamental Rheological Properties of Wheat Flour Doughs

Microencapsulated high‐fat powders are a healthy and convenient alternative to fats normally used in cereal‐based products. In powder form they are easier to use than block fat. Microencapsulation involves dispersion of the fat using homogenization. The globules are then fixed by spray‐drying. Empirical and fundamental rheological tests were conducted on doughs containing commercial vegetable fat and four microencapsulated high‐fat powders. The doughs were compared with a standard dough containing no fat. The powders contained 70% vegetable fat or milk fat. The encapsulating agent used was either sodium caseinate or whey protein concentrate (5–10%). Sucrose or lactose were also present in the powders (20–25%). The powders were manufactured at low‐ or high‐pressure homogenization. Farinograph and extensigraph tests were performed on all doughs. Dynamic oscillation tests were conducted in the linear visco‐elastic region of the dough. Addition of fat and microencapsulated high‐fat powders produced using low‐pressure homogenization reduced the complex modulus of the doughs. The results showed an increase in phase angle with incorporation of commercial fat and the microencapsulated high‐fat powders. Scanning electron microscopy was conducted to examine the effects of the additives on dough structure. This study demonstrated that microencapsulated high‐fat powders, especially powders produced using low‐pressure homogenization, had some beneficial effects on dough rheology when compared with doughs produced with commercial fat.     

Effect of Single‐Screw Extruder Die Temperature,Amount of Distillers' Dried Grains With Solubles (DDGS), and Initial Moisture Content on Extrudates

Corn distillers' dried grains with solubles (DDGS) was extruded with corn meal in a pilot plant single‐screw extruder at different extruder die temperatures (100, 120, and 150°C), levels of DDGS (0, 10, 20, and 30%) and initial moisture contents (11, 15, and 20% wb). In general, there was a decrease in water absorption index (WAI), water solubility index (WSI), radial expansion, and L* value with an increase in DDGS level, whereas a* value and bulk density increased. Increase in extruder die temperature resulted in an increase in WSI and WAI but a decrease in L* and bulk density. Peak load was highest at 30% DDGS as compared with 0, 10, and 20% DDGS extrudates. Die temperature of 120°C and initial moisture content of 20% resulted in least peak load. The a* value remained unaffected by changes in extruder die temperature. Radial expansion was highest at extruder die temperature of 120°C. Maximum WAI, WSI, radial expansion, and L* value were obtained at 15% initial moisture content. An increase in initial moisture content, in general, decreased L* value and bulk density but increased a* value of extrudates.     

Optimization of Near‐Infrared Reflectance Model in Measuring Gelatinization Characteristics of Rice Flour with a Rapid Viscosity Analyzer (RVA) and Differential Scanning Calorimeter (DSC)

This study compared the calibration models generated by combinations of different mathematical and preprocessing treatments as well as regression algorithms to optimize the analysis of gelatinization properties of rice flour by using near‐infrared spectroscopy, in comparison with conventional techniques of differential scanning calorimetry (DSC) and rapid viscosity analysis (RVA). A total of 220 milled rice flours were used for model construction. A model generated by the modified partial least squares regression (MPLS) with mathematical treatment “2, 8, 8, 2” (second‐order derivative computed based on eight data points, and eight and two data points in the second smoothing, respectively) and detrend preprocessing was identified as the best for simultaneously measuring onset temperature (T_o), peak temperature (T_p), and conclusion temperature (T_c) of DSC. MPLS/“2, 8, 8, 2”/weighted multiplicative scattering correction preprocessing was identified as the best for RVA properties. The results indicated that near‐infrared reflectance spectroscopy could be used to rapidly predict gelatinization properties of rice flour for the purposes of quality evaluation of germplasm and selection of intermediate lines in breeding programs.     

Effect of Flour‐Blasting Brown Rice on Reduction of Cooking Time and Resulting Texture

Long‐grain nonparboiled, long‐grain parboiled, and American basmati‐type brown rice were bombarded with parboiled rice flour particles to create microperforations on the water‐resistant outer layer of the kernels. These microperforations in the treated rice significantly increased the rate of hydration. Optimum conditions to produce microperforations without removal of the bran included air pressure maintained at 413 kPa and a parboiled rice flour average particle size of 124 μm. The optimum blasting time was 40–60 sec, depending on the type of rice. The relative hardness of the fully cooked flour‐blasted rice was the same at half the cooking time of the untreated brown rice but % water absorption of the untreated flour‐blasted brown rice was higher because it required longer time to cook. Overall, untreated brown rice was ≈4.7% higher in % water absorption due to longer cooking time in comparison with the treated counterpart. The blasting treatment resulted in shorter cooking time and firmer and less gummy cooked rice as compared to freshly cooked untreated brown rice.     

Effects of Allelic Variations in Wx‐1, Glu‐D1, Glu‐B3, and Pinb‐D1 Loci on Flour Characteristics and White Salted Noodle‐Making Quality of Wheat Flour

Doubled haploid wheat lines developed from a cross between a hard white winter wheat variety of normal starch endosperm and a waxy wheat variety were used to determine the effects of allelic variation in Wx‐1, Glu‐D1, Glu‐B3, and Pinb‐D1 loci on physiochemical properties of flour, noodle dough properties, and textural quality of cooked noodles. Milling yield, damaged starch content, protein content, and SDS sedimentation volume of flour were influenced the most by allelic composition of Pinb‐D1 loci, less by Wx‐1 loci, and least by Glu‐B3. Wheat lines carrying Pinb‐D1b or Glu‐B3h alleles exhibited higher milling yield and damaged starch content of flour than those with Pinb‐D1a and Glu‐B3d alleles. Wheat lines carrying the Pinb‐D1b allele were higher in protein content and SDS sedimentation volume than those carrying Pinb‐D1a. Mixograph water absorption was largely influenced by allelic composition of Wx‐1 loci, whereas mixograph mixing time and mixing tolerance were predominantly determined by allelic composition of Glu‐D1 loci. Amylose content and pasting properties of starch were mainly determined by allelic composition of Wx‐1 loci with little influence by allelic compositions of Glu‐D1, Glu‐B3, and Pinb‐D1 loci. Allelic composition of Wx‐1 loci contributed 53.4% of the variation in optimum water absorption of noodle dough and 26.7% of the variation in thickness of the noodle dough sheet. The variation of 7.8% in optimum water absorption of noodle dough was contributed by the allelic composition of Pinb‐D1 loci. Allelic composition of Wx‐1 loci was responsible for 73.2, 74.4, and 59.6% in the variation of hardness, springiness, and cohesiveness of cooked noodles, respectively. Cohesiveness of cooked noodles was also influenced by the allelic compositions of Glu‐B3 and Pinb‐D1 loci to a smaller extent.     

Quality Characteristics of Yellow Alkaline Noodles Enriched with Hull‐less Barley Flour

Roller milled flours from eight genotypes of hull‐less barley (HB) with normal, waxy, zero amylose waxy (ZAW), and high amylose (HA) starch were incorporated at 20 and 40% (w/w) with a 60% extraction Canada Prairie Spring White (CPSW, cv. AC Vista) wheat flour to evaluate their suitability as a blend for yellow alkaline noodles (YAN). The barley flour supplemented noodles were prepared using conventional equipment. Noodles containing 40% HB flour required less work input than the corresponding 20% blend noodles due to a higher water absorption at the elevated level of HB flour addition, which probably caused them to soften. The addition of any HB flour at either level to the CPSW flour resulted in significantly decreased brightness (L*) and yellowness (b*), elevated redness (a*), concomitant with a significantly greater number of specks per unit area of noodle sheet compared with the control flour. The addition of 40% HB flour to YAN decreased cook time and cooking losses. Noodle firmness, as determined by maximum cutting stress (MCS), was significantly increased by the addition of 40% HB flour. Noodle chewiness, as determined by the texture profile analysis (TPA), was affected by the type of starch in the barley samples; the addition of waxy and ZAW HB flour decreased chewiness, whereas normal and HA HB flour increased chewiness of composite noodles.     

Molecular Level Protein Composition of Flour Mill Streams from a Pilot‐Scale Flour Mill and Its Relationship to Product Quality

Flour mill streams prepared from two Australian and two New Zealand wheat cultivars using a pilot‐scale roller mill were analyzed for rheological and baking quality characteristics and for protein composition using size‐exclusion HPLC. Differences in mill stream protein composition, on an industrially relevant scale, and the relationships between the distribution of proteins (and their degree of thiol exposure) and the technological quality of the flour mill streams were examined. Consistent, significant differences were observed in the physicochemical and processing characteristics of the flour streams. Between mill streams, changes in the quantities of the storage protein groups were more marked than for nonstorage protein groups. Changes in protein composition differed between the break and reduction stream flours. In contrast, the degree of exposure of thiol groups on the various protein groups followed different patterns between mill streams. Numerous significant relationships were observed between dough mixing and product baking tests and the composition and thiol exposure state of the various protein classes. These relationships are discussed in context of manipulating the processing quality of flour‐based products using mill streaming. A possible role for exposed thiol groups on storage proteins in the phenomenon of flour “aging” is suggested.     

Formation of Enzyme‐Resistant Starch in Bread as Affected by High‐Amylose Wheat Flour Substitutions

High‐amylose wheat flour was used to substitute for normal wheat flour in breadmaking and formation of resistant starch (RS) in bread during storage was determined. Substitution with high‐amylose wheat flour (HAF) decreased peak and final viscosities, breakdown, and setback. Doughs with HAF substitutions were weaker and less elastic, and absorbed more water than those of the normal wheat flour. After baking, RS contents in breads with 10, 30, and 50% HAF substitutions were 1.6, 2.6, and 3.0% (db), respectively, higher than that of the control (0.9%, db). The levels of RS increased gradually during storage for one, three, and five days. With substitutions of 30 and 50% HAF, the total levels of dietary fiber (DF) and RS in bread after five days of storage were 15.5 and 16.8% (db), respectively, as compared to 13.0% (db) in bread from the normal wheat flour. The loaf volumes and appearances of bread crumbs made from HAF substitutions of 10 and 30% were not significantly different from those of the control, whereas the substitution with 50% HAF decreased loaf volume and resulted in inferior appearance of breadcrumbs. The firmness of breadcrumbs increased along with increase in the level of HAF substitutions after baking. During storage, the firmness of breadcrumb with 10% HAF substitutions was higher than that of the control, whereas breads with 30 and 50% HAF substitutions had similar firmness to the control. As a result, HAF might be used to substitute for up to 50% normal wheat flour to make bread with acceptable bread quality and significantly high amount of RS.     

Distribution of Total,Water‐Unextractable,and Water‐Extractable Arabinoxylans in Wheat Flour Mill Streams

Arabinoxylans are a minor but important constituent in wheat that affects bread quality, foam stability, batter viscosity, and sugar snap cookie diameter. Therefore, it is important to determine the distribution of arabinoxylans in flour mill streams to better formulate flour blends. Thirty‐one genetically pure grain lots representing six wheat classifications common to the western U.S. were milled on a Miag Multomat pilot mill, and 10 flour mill streams were collected from each. A two‐way ANOVA indicated that mill streams were a greater source of variation compared to grain lots for total arabinoxylans (TAX), water‐unextractable arabinoxylans (WUAX), and water‐extractable arabinoxylans (WEAX). TAX and WUAX were highly correlated with ash at r = 0.94 and r = 0.94, respectively; while the correlation for WEAX and ash decreased in magnitude at r = 0.60. However, the 5th middlings mill streams exhibited disparity between TAX and ash content as well as between WUAX and ash content. This may indicate that TAX and WUAX in mill streams are not always the result of bran contamination. Cumulative extraction curves for TAX, WUAX and WEAX revealed increasing gradients of arabinoxylans parallel to extraction rate. Therefore, arabinoxylans may be an indicator of flour refinement.