Comparison of quality of refined and whole wheat tortillas

The use of whole wheat flour instead of refined flour significantly improves the nutritional profile of flour tortillas. However, whole and refined flours differ in properties and in how they process, thus needing process modifications to get the desired product quality. To understand these differences, refined and whole wheat flours, dough and tortillas were evaluated and compared for physical and rheological properties. Overall, whole wheat flour required more water (59% of flour weight) than refined wheat (53%) to make machineable dough. Refined flour doughs were more extensible and softer than whole wheat flour doughs, thus easier to process. Whole wheat flour tortillas were larger, thinner and less opaque than refined flour tortillas. In general, refined wheat tortillas were more shelf-stable than whole wheat tortillas. Smaller particle size and less fiber in the refined wheat flour mainly contributed to the observed differences. Among the whole wheat samples, tortillas from strong flours had excellent shelf-stability, which must be considered when whole wheat tortillas are processed. This will minimize the need to add vital wheat gluten or other dough strengtheners.     

Impact of nitrogen amount and timing on the potential of acrylamide formation in winter wheat (Triticum aestivum L.)

Acrylamide (AA), a potential human carcinogen, is formed in strongly heated carbohydrate-rich food as a part of the Maillard reaction. The amino acid asparagine (Asn) and reducing sugars are considered to be the main precursors for AA formation. In a 2-year field trial the impact of nitrogen (N) amount and timing on the content of AA precursors and the potential of AA formation in different winter wheat cultivars (cv.) were studied in association with respective grain yields and parameters of baking quality. Depending on year, cultivar and nitrogen treatment Asn contents ranged between 4 and 18 mg 100 g⁻¹ flour dry-matter (DM). Nitrogen treatments affecting crude protein contents in flours above 13% caused a considerable increase in free Asn. Nitrogen amounts of 220 kg N ha⁻¹ increased the contents of free Asn by between 130% and 270% depending on year and cultivar compared to the untreated controls. A close linear correlation between the content of free Asn and the potential of AA formation (2004: R² = 0.89, 2005: R² = 0.83) could be observed, whereas no correlation could be found between reducing sugars and the potential of AA formation, pointing to the importance of free Asn as the limiting and thus determining factor for the AA formation potential in wheat flours. To reach high crude protein contents and good sedimentation values demanded for breadstuffs, nitrogen amounts of at least 180 kg N ha⁻¹ were necessary. Nitrogen fertilization measures resulting in high crude protein contents above 13% enhanced the potential of AA formation by increasing the content of free Asn in flours. As long as demands from traders and producers for flour with high crude protein contents are not revised, lowering Asn contents and thus the potential for AA formation by application of N amounts below 180 kg N ha⁻¹ and abandoning the late application of N do not appear to be successful ways to reduce the risk of AA formation in breadstuffs.     

Factors influencing acrylamide formation in rye,wheat and spelt breads

In this study, a simple strategy for acrylamide (AA) reduction in white and dark wheat and spelt and rye breads, including the impact of flour basic composition, flour extraction rate, type of technology and baking time and temperature was addressed. Moreover, the correlation between AA formation in breads and total phenolic compounds (TPC) and antioxidant capacity (AC) of flours and breads was calculated. The studies showed an impact of flours origin on AA formation in breads with the following rank: wheat bread ≤ spelt bread < rye bread. There was no statistically significant effect of flour extraction rates and their chemical components on AA formation in breads baked at 200 °C/35 min. However, a weak effect was noted for wheat and spelt breads baked at higher temperature. In contrast, a positive correlation between AA in wheat, spelt and rye breads baked at both applied conditions (200 °C for 35 min or 240 °C for 30 min) and AC of white and dark flours was noted. The same finding was noted between AA formation and TPC and AC of bread and its crust. The provided data indicated that AA mitigation strategy should be based on the selection of lower baking temperature with longer baking time as the main important factor amongst others.     

Heat induced formation of free radicals in wheat flour

Oxidative Stability of bread is increasingly being recognized as important for long shelf-life. Formation of free radicals in whole wheat flour and white flour during heating was compared using Electron Spin Resonance spectroscopy in order to identify the primary oxidative events. Heating lead to a higher content of free radicals in wholemeal wheat flour than in white flour, since components in the husk seem to make a major contribution. Two different pathways are suggested for the formation of free radicals in wheat flour. The activation energy for the radical formation in the flours was estimated by Arrhenius plot as 34 kJ mol⁻¹ up to 453 K, and above 473 K higher activation energies were observed. The change in activation energies indicates a change in reaction mechanisms for oxidation probably involving species with different mobility, i.e. different molecular weight. The accumulated concentration of free radicals in heated flour increased during one month storage and it is slightly affected by the water activity in the storage container.     

Effect of aging at different temperatures on LAOS properties and secondary protein structure of hard wheat flour dough

The effects of aging from t = 0–108 h at two different temperatures (4 and 25 °C) on the non-linear viscoelastic rheological properties and secondary protein structure of hard wheat flour dough (HWD) were investigated using large amplitude oscillatory shear tests (LAOS) coupled with Fourier transform infrared spectroscopy (FTIR) and SDS-PAGE. Storage (G') and loss (G'') moduli rapidly decreased during aging at 25 °C. Subjecting HWD to progressively longer aging times at 25 °C caused dramatic changes in the non-linear viscoelastic properties demonstrated by strain softening (negative values of e₃/e₁) and shear thinning (negative values of v₃/v₁) behavior. Elastic Lissajous curves of the unaged control dough showed clockwise turn and wider elliptical trajectories as dough aging proceeds especially at higher temperatures. Other non-linear LAOS parameters (G'_M-G''_L, η'_M-η'_L, S and T) supported that aging process at higher temperature caused a progressive change in dough structure from strain stiffening to strain softening behavior while dough samples aged at 4 °C showed fairly close behavior with the control dough sample. FTIR spectra indicated that the relative content of β-sheet and β-turn structures decreased while the content of α-helix structure increased for all dough samples as a result of dough aging. SDS-PAGE results supported the breakdown of high molecular weight (HMW) and low molecular weight (LMW) glutenin subfractions. Aging at the higher temperature of 25 °C decreased the HMW/LMW ratio from 0.77 to 0.59, while the ratio was 0.73 for the dough aged at 4 °C which is fairly close to the control sample. Our results show that the degradation rate of gluten/starch network was triggered by aging at higher temperature, longer aging time, and natural fermentation which resulted in increasing acidity and increase in endogenous proteolytic and amylolytic activity, and also increasing gluten solubility and break down of intermolecular disulfide bonds at acid pH.     

Nutritional improvement of lentils,chick pea,rice and wheat by natural fermentation

Effect of natural fermentation process (4 days) on the non-protein nitrogen, crude and true protein, amino acids content and in vitro digestibility of two kinds of legumes (lentils and chick pea) and two kinds of cereals (rice and wheat) was investigated. Non-protein nitrogen increased significantly (p<0.001) in the fermented products. Little increase has occured in the crude protein while no significant change was observed in the fermented true protein samples. It was observed that methionine and cystine which are considered the limiting amino acids in legume seeds were close to those of FAO/WHO patterns. Also, lysine content (the first limiting amino acid in cereals was higher in fermented rice than that of FAO/WHO pattern. Moreover, fermentation process improved significantly, the in vitro digestibility of both legume and cereal products.     

Physical properties of wheat flour composites dry-coated with microparticulated soybean hulls and rice flour and their use for low-fat doughnut preparation

Air-classified wheat flour was dry-coated with microparticulated rice flour (30%, db) and/or microparticulated soybean hulls (up to 10%, db) using a hybridization system, and the physical properties of the dry-coated wheat flour were examined. The composite wheat flours exhibited the higher water-holding capacity but lower swelling power and oil-holding capacity than their counterpart mixtures. In pasting viscosity, the composites of wheat and rice flours had substantially lower values for peak viscosity and breakdown than did pure wheat flour. The incorporation of soybean hulls to the composites of wheat and rice flours further reduced the peak viscosity. The composites with rice flour and soybean hulls showed slightly higher melting (gelatinization) temperatures but lower melting enthalpy compared to the counterpart mixtures. By using the composite flours for the deep-fat fried doughnut preparation, the oil uptake could be substantially reduced by approximately 30%, in comparison to pure wheat flour or the mixture samples. The composite wheat flours with microparticulated rice flour and soybean hulls produced dough matrices with improved compactness and cell structure, which were attributed to the reduced fat uptake during frying.     

Effect of glutathione on gelatinization and retrogradation of wheat flour and starch

Reduced glutathione (GSH) commonly exists in wheat flour and has remarkable influence on gluten properties. In this study, effect of GSH on the gelatinization and retrogradation of wheat flour and wheat starch were investigated to better understand the GSH-gluten-starch interactions in wheat flour. Compared with wheat starch, wheat flour showed significant decreases in peak and final viscosity, and gelatinization onset temperature with increasing GSH concentration. GSH depolymerized gluten and thereby broke down the protein barrier around starch granules to make the starch easily gelatinized. However, the interaction between GSH and wheat starch restrained starch swelling. GSH addition resulted in weakened structure with higher water mobility in freshly gelatinized wheat flour dispersions but decreased water mobility in wheat starch dispersions. After storage at 4 °C for 7 d, GSH increased elasticity and retrogradation degree in wheat flour dispersions but retarded retrogradation in wheat starch dispersions. The results indicated that GSH promoted retrogradation of wheat flour, which mainly attributed to the depolymerized gluten embedding in the leached starch chains, and inhibiting the re-association of amylose, and subsequently promoted the starch intermolecular associations and starch retrogradation. This study could provide valuable information for the control of the quality of wheat flour-based products.     

Wheat products as acceptable substitutes for rice

The objective of the study was to compare the acceptability to semi-trained US American and Asian palatability panelist, of four wheat products processed to be possible replacers of rice in human diets. Products evaluated using rice as the control standard of excellence were steamed whole wheat, couscous (steamed, extracted wheat flour semolina), rosamarina (rice shaped, extracted wheat flour pasta), and bulgur (steamed, pre-cooked partly debranned, cracked wheat). Using a ten point hedonic rating scale, both groups of panelists gave rosamarina closely followed by couscous, most favorable ratings although these ratings were somewhat lower than that of the positive control, steamed polished rice. Bulgur wheat was given the lowest evaluation and was, in general, found to be an unacceptable replacement for rice by both American and Asian judges because of its dark, greasy color and distinctive flavor. In their personal dietaries, judges included rice from 0.25 to 18 times per week with the Asian judges consuming rice significantly more times per week than did the American judges (10.8±4.71 vs 1.75±1.65,p<0.01). However, rice consumption patterns, nationality, race, or sex of the judges was not demonstrated to affect scoring of the wheat products as rice replacers.Published as University of Nebraska Agricultural Research Division Journal Series No. 9826. Supported by University of Nebraska Agricultural Research Division Project 91-031.     

Sulphur nutrition differentially affects the distribution of asparagine in wheat grain

Asparagine is known to accumulate in wheat grain under conditions of sulphur deficiency, leading to increased levels of acrylamide formation during processing. Analyses of milling fractions and of the outer layers of the grain prepared by hand dissection showed that the highest levels of asparagine were present in the bran fractions and in particular the aleurone layer, when grain were grown with sufficient sulphur supply. However, even mild S deficiency resulted in disproportional increases in the asparagine contents of white flour fractions, implying that optimisation of yield in a conventional milling system is not an appropriate strategy for processing grain from sulphur-deficient crops.     

Mineral binding capacity of dephytinized insoluble fiber from extruded wheat,oat and rice brans

Insoluble fiber fractions from raw and extruded oat, rice and wheat brans were isolated and phytate removed. In vitro mineral binding studies were performed utilizing copper (Cu²⁺), calcium (Ca²⁺) and zinc (Zn²⁺) ions, which were added individually to enzymatically treated (Prosky et al., 1985), acid washed insoluble fiber residues from oat, rice and wheat brans. The enzymatic digestion step with alpha-amylase, protease and amyloglucosidase served to remove protein and starch from the samples. Mineral binding studies were performed on the insoluble fiber residue. Mineral content was determined by flame atomic absorption spectroscopy. Raw brans served as controls. A twin-screw extruder Model DNDG-62/20D, manufactured by Bühlerag (CH-9240, Uzwil, Switzerland) was utilized. The objectives of the study were to determine the total Cu²⁺, Ca²⁺ and Zn²⁺binding capacity of the dephytinized insoluble fiber from each bran; and to determine if extrusion screw speed affected the brans' insoluble fiber mineral binding capacity. Although dephytinized, the brans' insoluble fiber fraction bound Cu²⁺, Ca²⁺ and Zn²⁺ions. Oat bran bound more Cu²⁺, Ca²⁺ and Zn²⁺ than wheat bran, which bound more than rice bran. Extrusion processing did not affect the brans' insoluble fiber binding capacity to bind Cu²⁺. However, it increased the binding capacity of Ca²⁺ and Zn²⁺ of the insoluble fiber fraction from rice and oat brans.     

Effects of added water and retrogradation on starch digestibility of cooked rice flours with different amylose content

Flours derived from rice varieties with different amylose content possess distinct physicochemical and molecular properties. The aim of this study was to determine optimal processing conditions for preparing rice flour-based foods with reduced starch digestibility. To do so, we evaluated the in vitro starch digestibility of rice flours with five varieties. Reducing the amount of water (from 10-fold to 4-fold of rice flour) used for cooking rice flour lowered its starch digestibility, and the magnitude of the decrease was positively correlated with amylose content. When retrogradation of cooked rice flour proceeded for 7 days, the digestibility of high-amylose rice flours declined rapidly in the first 3 days, whereas the digestibility of low-amylose rice flours declined continuously. Our analysis also demonstrated that the chain length distribution of starch molecules and the final and setback viscosity pasting properties were the most important parameters affecting the digestibility of rice flours. Based on our results, it appears possible to reduce rice starch digestibility by establishing optimum processing conditions for different varieties. We suggest a 7-fold addition of water and retrogradation for 1 day for high-amylose rice varieties and a 4-fold addition of water with 3 days of retrogradation for low-amylose rice.     

Rheological properties and baking quality of wheat varieties from various geographical regions

Eight wheat varieties, originating from various geographical regions were examined for their rheological properties during large uniaxial and biaxial extensions and for their baking quality. Extensibility during uniaxial extension as well as biaxial extensional viscosity proved to be significant properties in predicting loaf volume. Multiple regression analysis indicated uniaxial extensibility and biaxial extensional viscosity as best predictors for loaf volume. The varieties with the highest strain hardening index were those of high loaf volume and also fine and soft crumb, whereas varieties of low strain hardening index were of poor baking quality. However, baking behaviour was not completely explained by considering only the strain hardening index. Crumb fineness was also investigated and it was taken into consideration when evaluating the varieties for their baking quality. 3D scatter plots of loaf volume, cell volume, and number of cells in the slice, divided the wheat samples in groups depending on their baking quality and common rheological characteristics were observed for these groups. The samples were also examined for their proofing capacity. Maximum dough height from the rheofermentometer correlated with loaf volume and was affected by rheological properties of the samples.     

高水分蒸煮挤压小麦混合粉的研究

食品蒸煮挤压技术是多学科交叉所产生的一门高新技术,蒸煮挤压作为一种高温短时的加工方法,能够将输送、压缩、混合、蒸煮、杀菌、成型等多种操作单元同时完成。本实验优化了双螺杆机的加工工艺参数,DS56-Ⅲ型双螺杆挤压膨化机挤压腔内限流区的温度在125℃．含水率为40％、螺杆转速为215rpm,该条件下得到的最好产品膨化度为2．51,经过蒸煮挤压后的食品含水率为35％～37％。     

A comparative study of physicochemical tests for quality prediction of Argentine wheat flours used as corrector flours and for cookie production

Several physicochemical tests are employed in quality evaluation of wheat. Most of the exported Argentinean wheat flour is used as corrector flour in breadmaking. A small percentage is actually used in cookie production. No study has determined which predictive tests are most suitable for the quality prediction of bread (using flour as corrector) and cookies made from Argentinean wheat. The objectives of this study were to compare the suitability of predictive tests in the assessment of wheat flour attributes in the production of bread and cookies and to establish the relationship between the tests and flour components. Several expected associations were found between the SRC test and the composition parameters. Moreover, various flour components influencing the SDS sedimentation index (SDS-SI), the Zeleny index and the alkaline water retention capacity (AWRC) were established. The cookie factor (CF) was negatively correlated with sucrose, carbonate and water SRC and with AWRC. In addition, the bread loaf specific volume (LV) was correlated with the SDS-SI, the Zeleny index and the lactic acid SRC. In conclusion, several components of Argentine wheat affecting predictive tests were found. The SRC test allowed straight assessment of the bread and cookie quality of Argentinean wheat.     

Trends of climatic potential and on-farm yields of rice and wheat in the Indo-Gangetic Plains

Rice and wheat are the two most important cereals in the Indo-Gangetic Plains (IGP) and are responsible for the food security of the region. To understand the productivity trends in the transects of the IGP: (1) the climatic potential yields of rice and wheat were simulated using a crop simulation modeling approach and (2) the long-term trends of potential and on-farm yields were compared. The potential yields of rice and wheat in the IGP ranged from 7.7 to 10.7 and 5.2 to 7.9 Mg ha⁻¹, respectively. The upper transects of the IGP are more productive and yield decreases by 27% for rice and by 32% for wheat from transect 2 to transect 5. The rate of change in the potential yield trend of rice from 1985 to 2000 ranged from −0.12 to 0.05 Mg ha⁻¹ per year. Negative yield trends were observed at six of the nine sites, four of which were statistically significant (P<0.05). The decrease in radiation and increase in minimum temperature were the reasons for the yield decline. The potential yield trend of wheat, however, appeared to be stable. On-farm yields of rice also showed a negative trend but for wheat the trend was mostly positive. The adverse changes in the weather parameters and declining trends of potential and on-farm yields of rice should be taken as an indication of a future problem. Regular on-farm monitoring of crops and climatic factors is urgently needed for predicting problems and allowing measures to be taken to improve productivity.     

Impact of re-grinding on hydration properties and surface composition of wheat flour

The combination of two analytical methodologies (water vapor sorption isotherm by using the DVS and chemical surface composition by using the XPS) has been used to enhance the understanding of the impact of re-grinding on the wheat flour hydration mechanism. A controlled atmosphere microbalance was used to construct water sorption isotherms at 25 °C of different samples of wheat flours obtained by successive re-grinding of native wheat flour.     

Physicochemical properties of dry- and semi-wet-milled rice flours after fermentation by Lactobacillus amylovorus

Rice milling is one of the important factors that determines the physicochemical properties of rice flour. Dry milling is a simple and quick process, though it produces high levels of damaged starch that is not desirable in some application. Since fermentation can change the structure of starch as well as its physicochemical properties, the effect of fermentation on dry-milled rice flour was evaluated with the aim of improving flour quality for use as food ingredient in food industry. After fermentation at 37 °C for 24 h by Lactobacillus amylovorus, the dry-milled rice flour showed similar proximate compositions, physicochemical properties, and surface structures as semi-wet-milled rice products. Thus, the results suggest that it can be applied to produce desirable food materials for preparation of rice-based products.     

A novel method for ash analysis in wheat milling fractions by using laser-induced breakdown spectroscopy

Ash content is an important quality control parameter in milling industry. Measurement of ash content is routinely performed using standard ash analysis method in which the sample is burned at 500–600 °C for 5–6 h. However, this method is not convenient for industrial applications, and thus, rapid and reliable methods are needed to be developed. The aim of this study was to develop a new method for ash analysis to be used in wheat milling fractions by using laser induced breakdown spectroscopy (LIBS). LIBS is an optic based multi-elemental, spectroscopic method which can analyze high number of samples in a considerably short time. In the study, wheat flour, whole wheat meal and semolina samples with different ash contents were analyzed using LIBS, and the spectra were evaluated with partial least squares (PLS) method. The results were correlated with the ones taken from standard ash analysis method. Calibration graph showed good linearity with the ash content between 0.48 and 2.44%, and 0.997 coefficient of determination (R²). Limit of detection for ash analysis was calculated as 0.11%. The results indicated that LIBS is a promising and reliable method with high sensitivity for routine ash analysis in milling industry.     

Predicting hot-press wheat tortilla quality using flour,dough and gluten properties

A cost-effective, faster and efficient way of screening wheat samples suitable for tortilla production is needed. This research aimed to develop prediction models for tortilla quality (diameter, specific volume, color and texture parameters) using grain, flour and dough properties of 16 wheat flours. Another set of 18 samples was used to validate the models. The prediction models were developed using stepwise multiple regression. Dough rheological tests had higher correlations with tortilla quality than grain and flour chemical tests. Mixograph mixing time and dough resistance to extension (from extensibility test using a texture analyzer) were correlated best with tortilla quality, particularly tortilla diameter (r = −0.87 and −0.86 respectively, P < 0.01). Insoluble polymeric proteins (IPP) and gluten index were significantly correlated with tortilla diameter (r = −0.70 and −0.67 respectively, P < 0.01) and specific volume (r = −0.73, P < 0.01). Tortilla diameter was the quality parameter best explained (R² = 0.86) by the prediction models using mixing time and dough resistance to extension. Rheological parameters such as rupture distance and maximum force were also successfully predicted. These prediction models, developed from linear equations, will be an easy and fast tool for breeders to advance or eliminate wheat lines specifically bred for tortilla production.