首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Extrudate expansion of cereal‐based products is largely dependent on the molecular interactions and structural transformations that proteins undergo during extrusion processing. Such changes strongly influence the characteristic rheological properties of the melt. It is possible to modify rheological properties of wheat flour during extrusion processing, in particular shear viscosity, with cysteine. The objective of this work was to further develop an understanding of the molecular interactions and structural transformations of wheat flour from dynamic oscillatory rheological measurements. Temperature and frequency sweeps were conducted in the linear viscoelastic range of the material. Changes in the storage modulus (G′), the loss modulus (G″) and the loss tangent (tan δ) of 25% moisture wheat flour disks as a function of cysteine concentration (0–0.75%) were monitored. Molecular weight between cross‐links (Mc) and the number of cross‐links (Nc) per glutenin molecule were determined from frequency sweep data. Increasing cysteine concentration broke cross‐links by decreasing G′ maximum and increasing tan δ values. Molecular weight between cross‐links increased and the number of cross‐links decreased. G′ values from temperature sweeps showed a similar trend. This information leads to a better understanding of the viscoelastic behavior of wheat flour doughs during extrusion cooking and elucidation of protein‐protein reaction mechanisms and other interactions in extruded cereal‐based snack foods.  相似文献   

2.
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.  相似文献   

3.
Lignans are of increasing interest because of their potential anticarcinogenic, antioxidant, estrogenic, and antiestrogenic activities. In this work, mixed‐cereal pastas manufactured by adding 60% whole‐grain flours of different cereals (wheat, oat, rye, barley, and rice) to durum wheat semolina, a multigrain pasta with different grains (cereals, legumes, and flaxseed), and a traditional industrial durum wheat semolina were analyzed for their lignans content both in the raw and in the cooked state, ready for consumption. For raw mixed‐cereal pastas, total lignans were within the range 94.91–485.62 μg/100 g d.w. After cooking, total lignans losses of about 35.5, 18.31, and 5.46% were observed respectively in oat‐, rye‐, and rice‐added pastas, whereas increases of 5.74 and 13.62% were observed in barley‐added and whole durum wheat pastas. Interesting results were obtained for the multigrain pasta: the raw product exhibited a total lignans content of 9,686.17 ± 287.03 μg/100 g d.w., and the major contribution was given by secoisolariciresinol. This highest total lignans value resulted from its rich and varied composition in seeds of different origin, legumes, and flaxseed in particular. Our findings showed that mixed‐cereal and multigrain pastas can be considered a good source of lignans. The effect of cooking was not the same for each product, and it depended on the different lignans profile of each grain, on the different chemical structure of each lignan, and on the nature of the food matrix.  相似文献   

4.
Many applications have been developed for aqueous dispersions of jet‐cooked starch‐oil composites prepared by excess steam jet cooking. Previous formulations have typically contained 20–50% oil by weight based on the weight of starch. To expand the range of potential applications, new preparation methods were investigated to increase the oil content to as high as four times the weight of starch. High‐amylose corn starch was cooked in an excess‐steam jet cooker in the presence of oleic acid, and soybean oil was added to form the starch‐oil composites. Amylose is removed from solution by forming helical inclusion complexes with the oleic acid and, if the materials are cooled sufficiently quickly, the helical inclusion complexes only form small aggregates and shells around the oil droplets. Depending on the composition and preparation method, a wide range of stable, high‐oil materials from low‐viscosity liquids to smooth pastes can be formed. The flow, textural, and structural properties of these materials are shown. The materials can be used in a wide range of applications, including spray lubricants, lotions, and for fat delivery in cake mixes.  相似文献   

5.
Whole grains contain all parts of the grain: the endosperm, germ, and bran. Whole grains are rich in fermentable carbohydrates that reach the gut: dietary fiber, resistant starch, and oligosaccharides. Most research that supports the importance of grains to gut health was conducted with isolated fiber fractions, rather than whole grains. Whole grains are an important source of dietary fiber and grain fibers such as wheat, oats, barley, and rye increase stool weight, speed intestinal transit, get fermented to short chain fatty acids, and modify the gut microflora. Wheat bran is particularly effective in increasing stool weight; wheat bran increases stool weight by a ratio of 5:1. In contrast, many novel fibers that are easily incorporated into beverages and foods increase stool weight only on a ratio of 1:1. In vitro fermentation studies with whole grains have been published. Carbohydrates of oat bran (rich in β‐glucan) were consumed by bacteria faster than those of rye and wheat brans (rich in arabinoxylan). Grain fibers were fermented more slowly than inulin, causing less gas production. Wheat is particularly high in fructo‐oligosaccharides, while wheat germ is high in raffinose oligosaccharides. Some in vivo studies show the prebiotic potential of whole grains. Whole grain breakfast cereal was more effective than wheat bran breakfast cereal as a prebiotic, increasing fecal bifidobacteria and lactobacilli in human subjects. Wheat bran consumption increased stool frequency. Thus, the gut enhancing effects of cereal fibers are well known. Limited data exist that whole grains alter gut health.  相似文献   

6.
The effects of amylose, protein, and fiber contents on ethanol yields were evaluated using artificially formulated media made from commercial corn starches with different contents of amylose, corn protein, and corn fiber, as well as media made from different cereal sources including corn, sorghum, and wheat with different amylose contents. Second‐order response‐surface regression models were used to study the effects and interactions of amylose, protein, and fiber contents on ethanol yield and conversion efficiency. The results showed that the amylose content of starches had a significant (P < 0.001) effect on ethanol conversion efficiency. No significant effect of protein content on ethanol production was observed. Fiber did not show a significant effect on ethanol fermentation either. Conversion efficiencies increased as the amylose content decreased, especially when the amylose content was >35%. The reduced quadratic model fits the conversion efficiency data better than the full quadratic model does. Fermentation tests on mashes made from corn, sorghum, and wheat samples with different amylose contents confirmed the adverse effect of amylose content on fermentation efficiency. High‐temperature cooking with agitation significantly increased the conversion efficiencies on mashes made from high‐amylose (35–70%) ground corn and starches. A cooking temperature of ≥160°C was needed on high‐amylose corn and starches to obtain a conversion efficiency equal to that of normal corn and starch.  相似文献   

7.
The chemical composition of lipids from bast fibers of flax (Linum usitatissimum), which are commonly used for high-quality paper pulp production, was thoroughly studied by gas chromatography-mass spectrometry. The main compounds identified were waxes, series of long chain n-fatty alcohols, n-aldehydes, n-fatty acids, and n-alkanes. Free and esterified sterols and triterpenols, steroid hydrocarbons, steroid and triterpenoid ketones, as well as sterol glycosides were also found in the flax bast fibers. On the other hand, the fate of these lipophilic compounds in alkaline pulping of flax fibers was investigated by analyzing two pulps obtained under distinct industrial cooking conditions. The results revealed that while waxes could be efficiently hydrolyzed during pulping depending on the alkali charge, most of the other lipophilic compounds present in flax fibers survived cooking and were present in the unbleached pulps.  相似文献   

8.
A high‐performance size‐exclusion chromatography system (HPSEC) was set up with detection based on the specific binding of Calcofluor to β‐glucan for determination of amount and molecular weight of β‐glucan in different cereal extracts. To calibrate the HPSEC system, a purified β‐glucan was fractionated into narrow molecular weight ranges and the average molecular weight was determined before analysis on the HPSEC system. The detector response was similar for β‐glucans from oats and barley and appeared to be independent of molecular weight. Four different methods for extraction of β‐glucan from different cereal products were tested: two alkaline, one with hot water and added α‐amylase, and one with water and added xylanase. Inactivation of endogenous β‐glucanase was crucial for the stability of the extracts, even when extracting at high temperature or pH. Yields varied widely between the different extraction methods but average molecular weight and molecular weight distribution were similar. Extraction with sodium hydroxide generally gave a higher yield and molecular weight of β‐glucan in the extracts.  相似文献   

9.
A phosphorylated cross‐linked type 4 resistant wheat starch (RS4) containing 85.5% total dietary fiber (TDF) replaced 5–20% of the whole corn flour in an extruded ring‐shaped ready‐to‐eat breakfast cereal formulation. TDF content of the dry ingredient blend increased by roughly 3.6% for every 5% of added RS4. TDF loss during extrusion processing increased as RS4 level increased; however, a high percentage (78–89%) of the TDF content was retained in the final product. Product density increased as level of RS4 increased, but no effect on the specific mechanical energy was observed. X‐ray microtomography showed that RS4 addition did not affect internal air‐cell wall thickness, air‐cell size, or porosity. Moreover, addition of 5 or 10% RS4 did not affect expansion, physical appearance, initial crispness, or bowl life of the cereal rings. High levels of RS4 (15 and 20%) decreased cereal ring diameter but increased initial (dry) product crispness and extended bowl life. In general, RS4 addition level did not affect moisture content or moisture uptake of cereal rings during soaking in milk. Furthermore, moisture content and moisture uptake did not appear to influence the crispness of milk‐soaked cereal rings.  相似文献   

10.
Pasting, rheological, and water‐holding properties of buckwheat (Fagopyrum esculentum) flour obtained from whole achenes separated into three particle sizes, and three commercial flours (Fancy, Supreme, and Farinetta) were measured with or without jet‐cooking. Fancy had instantaneous paste viscosity (measured using RVA) after jet‐cooking that was not observed for Supreme or Farinetta, and paste viscosity was lower for the latter two flours. Supreme jet‐cooked flour exhibited higher peak viscosity than flour without jet‐cooking, and paste exhibited high shear‐thinning. Fancy exhibited strongest viscoelastic properties (measured using a rheometer). Jet‐cooking damaged buckwheat flour structure, thereby reducing viscoelasticity. Buckwheat flour pastes experienced shear‐thinning over a wide range of shear rates. Jet‐cooking greatly enhanced water‐holding capacity. Buckwheat flour particle size did not greatly influence paste viscosity. Study showed buckwheat flours have unique pasting and rheological characteristics that have different food applications, which could especially be useful for people with celiac disease as buckwheat is gluten‐free.  相似文献   

11.
Soil degradation is the single most important threat to global food production and security. Wind and water erosion are the main forms of this degradation, and conservation tillage represents an effective method for controlling this problem. The objective of this study was to quantify the effects of three tillage methods [zero (ZT), minimum (MT) and conventional (CT)] and three four-year crop sequences [spring wheat (Triticum aestivum L.)–spring wheat–winter wheat–fallow; spring wheat–spring wheat–flax (Linum usitatissimum L.)–winter wheat; spring wheat–flax–winter wheat–field pea (Pisum sativum L.] on crop establishment, plant height, seed weight, soil water storage, crop water use, crop water use efficiency and grain yield over a 12-year period under Canadian growing conditions. Plant establishment was not adversely affected by tillage systems or crop sequences except for flax, where a small reduction was observed with ZT and MT. Conservation tillage showed a yield benefit over CT of 7%, 12.5% and 7.4% for field pea, flax and spring wheat grown on cereal stubble, respectively over the 12 years of the study. Much of the yield increase was due to an increase in soil water in the 0–30 cm soil layer with ZT and MT. However, tillage systems had no effect on grain yield for spring wheat grown on fallow and field pea stubble due to a lack of differences in spring soil water content. Flax grown in sequence with cereals only yielded higher than when it was grown in the sequence which included field pea, even though flax was seeded on spring wheat stubble in both cases. Winter wheat yielded higher when grown on flax stubble than on spring wheat stubble. The results indicate that a one-year non-cereal break crop was enough to alleviate the negative effects of consecutive cereal crops on winter wheat. Spring wheat grown on field pea stubble always yielded more than when grown on cereal stubble. A 10% increase in water use efficiency was observed with flax grown with ZT and MT management. Crop sequence improved water use efficiency in flax and spring wheat. Growing spring wheat on field pea stubble as opposed to growing it on cereal stubble resulted in a 10% increase in water use efficiency. Overall, rainfall accounted for 73%, 72%, 67% and 65% of total water used by field pea, flax, winter wheat and spring wheat, respectively. This explains the large year effect as a result of variation in growing (May–August) season precipitation. The non-significant tillage system by year interaction implies that the positive benefits of ZT and MT occur over a wide range of growing conditions, while the absence of a tillage system by crop sequence interaction suggests that knowledge developed under CT management also applies to ZT and MT. The results of this study support the large shifts towards in conservation tillage being observed in the Canadian prairies.  相似文献   

12.
The effects of transglutaminase (TG) on the properties of semolina dough and pasta cooking properties in durum‐only and fiber‐enriched pasta were investigated. TG was blended at levels 0, 0.05, 0.1, 0.25, 0.5, and 1% of semolina weight with semolina and semolina‐pollard (60% w/w) and semolina‐guar gum (15%) mixtures. The addition of TG increased dough maximal resistance, making the dough inextensible at >1%. Optimum effects on dough strength were obtained at 0.5% TG; this dough gave the firmest and least sticky pasta. A more extensive and thicker protein matrix was observed in the TG pasta by confocal scanning laser microscopy, indicating more cross‐links were formed, a finding supported by measuring percentage of unextracted polymeric protein. TG was unable to overcome the negative effect of 60% pollard on cooking loss or 15% guar gum on stickiness. Gluten was generally more effective than TG in restoring the properties of pastas with added fiber.  相似文献   

13.
The beneficial role of soluble dietary fiber in human nutrition is well documented and has lead to a growing demand for the incorporation of β‐glucan, particularly from oats and barley, into foods. β‐Glucan with high solubility and high molecular weight distribution results in increased viscosity in the human intestine, which is desirable for increased physiological activity. Molecular weight, level, and solubility of β‐glucan are affected by genotype, environment, agronomic input, and the interactions of these factors and food processing methods. Available literature reveals that the level of β‐glucan in a finished product (e.g. bread, cake, muffins) depends upon several factors in the production chain, whereas food processing operations are major factors affecting molecular weight and solubility of β‐glucans. Therefore, to avail themselves of the natural bioactive compounds, food manufacturers must pay attention not only to ensure sufficient concentration of β‐glucan in the raw material but also to the processing methods and functional properties of β‐glucan, minimizing enzymatic or mechanical breakdown of the β‐glucans in end‐product and optimizing processing conditions. This review discusses the different sources of β‐glucan for use in human functional foods and factors affecting the levels and the molecular weight of β‐glucan at various pre‐ and postharvest operations.  相似文献   

14.
This report highlights the structure and myriad properties of wheat starch in various food systems. Granule shape, size, and color, plus the proportion of A‐ and B‐granules, amylose content, and molecular structure largely determine its functionality in food. The role of wheat starch is portrayed in three categories of flour‐based foods that differ in water content. Wheat starch influences the appearance, cooking characteristics, eating quality, and texture of pasta and noodles, and its role is more than a filler in yeast‐leavened bread products. Recent developments in the properties and applications of commercially important wheat pyrodextrins and RS4‐type resistant wheat starches are reported, along with their use to produce fiber‐fortified foods. Gluten‐free foods are also discussed.  相似文献   

15.
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.  相似文献   

16.
This study focused on the application of native strains of arbuscular mycorrhizal fungi (AMF) and Sinorhizobium in effective crop production during reclamation of coal‐mine spoil banks. Two greenhouse experiments were conducted in spoil‐bank clay with a low dose of organic amendment to determine whether the microbial inoculation improves growth and utility qualities of two cultivars of Linum usitatissimum L. (oil and fiber flax). Inoculation with two native AMF isolates (Glomus mosseae, G. intraradices, and their mixture) significantly increased growth and shoot phosphorus (P) concentration of both flax cultivars. Inoculated fiber flax plants produced fivefold more fibers than the uninoculated ones. In oil flax, mycorrhizal inoculation significantly but quantitatively to a minor degree decreased the concentration of nonsaturated fatty acids in the seed oil. A mixture of five native Sinorhizobium sp. strains supported growth and P uptake of oil flax only in the absence of AMF. However, these beneficial effects of the bacteria were significantly lower as compared to AMF. No synergic action of Sinorhizobium strains and AMF was observed, and their interactions were often even antagonistic. Inoculation with AMF significantly decreased population density of Sinorhizobium in the soil. These results suggest that a careful selection of suitable bacterial strains is necessary to provide effective AMF combinations and maximize flax‐growth support.  相似文献   

17.
As part of a general study aiming to clarify the role of arabinoxylans (AX) in pasta processing and quality, AX were modified by the addition of endoxylanases during pasta processing. The influence on processing parameters and quality were determined. Pasta (800 g) was produced from two commercial semolinas (semA and semB) using dosages of Bacillus subtilis (XBS) and Aspergillus niger (XAN) endoxylanases of 0–0.225 Somogyi units/g of semolina. Increased dosages resulted in a drop of extrusion pressure. The endoxylanase treatments had no great effect on the resulting pasta quality (color of dry products and surface condition, viscoelastic index, and resistance to longitudinal deformations of cooked products). High dosages of XAN and XBS resulted in high levels of solubilized AX (as an extra source of soluble dietary fiber) of low molecular weight which were expected to easily leach out during the cooking process of pasta. Surprisingly, only low levels of AX were found in the cooking water, even with extremely high dosages of endoxylanases used and cooking beyond optimum time. A method is provided to obtain high‐quality pasta with increased levels of soluble fiber.  相似文献   

18.
Food products that are high in fiber and low in glycemic impact are healthier. Amylose is a form of resistant starch that mimics dietary fiber when consumed. A durum wheat (Triticum durum) line was created that lacks starch synthase IIa (SSIIa) activity, a key enzyme in amylopectin biosynthesis, by identifying a null mutation in ssIIa‐B following mutagenesis of a line that has a naturally occurring ssIIa‐A null mutation. Our objective here was to compare seed, milling, pasta, and nutritional characteristics of the SSIIa null line with a wild‐type control line. The SSIIa null line had increased amylose and grain protein with lower individual seed weight and semolina yield. Refined pasta prepared from the SSIIa null semolina absorbed less water, had increased cooking loss, had a shorter cook time, and was considerably firmer even after overcooking compared with the wild‐type line. Color of the SSIIa null cooked and uncooked pasta was diminished in brightness compared with the wild type. Nutritionally, the SSIIa null pasta had increased calories, fiber, fat, resistant starch, ash, and protein compared with the control line, along with reduced total and available carbohydrates. Pasta made from high‐amylose durum wheat provides a significant nutritional benefit along with enhanced end‐product quality via firmer pasta that resists overcooking.  相似文献   

19.
Barley and oat β‐glucans of low viscosity form reversible gels when prepared in sufficiently high concentrations. Solutions of three barley β‐glucan gums differing in molecular weight and thus in viscosity were prepared at 1.0, 2.5, or 5.0% (w/w) concentration levels. Medium‐ and high‐viscosity gums were prepared in a pilot plant (PP) and laboratory (LAB), respectively. Low‐viscosity (LV) gum was extracted in the laboratory at pH 7, which allowed for native enzymatic activity and decreased molecular weight. Network formation was monitored overnight through changes in storage (G′) and loss (G″) moduli. The strength of the formed network was determined from oscillatory rheological measurements by increasing the strain from 2 to 100%. Findings demonstrate that gelation of β‐glucan is molecular weight dependent and practically an instantaneous process for low‐viscosity gum solutions at concentrations of ≤5% gum (or ≤4% β‐glucan), levels lower than previously anticipated. The purity of β‐glucan also seems to affect gelation rate. Better understanding of the β‐glucan gelation behavior is important for its functionality in both food product applications and physiological mechanisms of its health benefits.  相似文献   

20.
Whole‐grain wheat flour is used in baking to increase fiber content and to provide vitamins from the bran layers of the kernel. We surveyed whole‐grain soft flour samples from North America to determine the nutritional profile using recently revised fiber quantification protocols, Codex 2009.1. Standard compositional and vitamin analyses were also included in the survey. Three separate studies were included in the survey: sampling of commercial whole‐grain soft wheat flour, a controlled study of two cultivars across three years and two locations, and a regional study of soft white and soft red grain from commercial grain production. The Codex method for fiber measurement estimated total fiber concentration in the commercial sampling at 15.1 g/100 g, dry weight basis (dwb). In the controlled research trial, the largest source of variation in total fiber concentration was attributed to year effects, followed by genotype effects. For the two locations used in this study, location effects on fiber concentration were significant but an order of magnitude less important than the year and genotype effects. The third study of regional variation within North America found limited variation for total fiber, with the resistant oligosaccharide fraction having the greatest variation in concentration. When all three studies were combined into a meta‐analysis, the average total fiber concentration was 14.8 g/100 g dwb. In the meta‐analysis, concentrations of folate, thiamin, riboflavin, niacin, and pyridoxine were lower than in previous summary reports. Vitamin E and pantothenic acid were the exceptions, with concentrations that were nearly identical to previous standard reports. Several other recent studies also point to current cultivars and production systems as producing lower concentrations of the essential vitamins than previously reported. The results suggest that vitamin concentrations in diets of populations using grain‐based diets from modern cereal‐production systems may require review to determine if previous assumptions of vitamin consumption are accurate.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号