The influence of milling on the nutritive value of flour from cereal grains. 1. Rye

Rye was milled into flours having extraction rates between 100 and 65%. The nutritive value of the various fractions was studied by chemical analyses and in balance trials with rats. The concentration of essential nutrients decreased when the extraction rate was lowered. The lysine content (g/16 g N) was 4.23 in whole rye, but only 3.76 in the 65% extraction flour, and a corresponding reduction in biological value was found. A reduction of 50% or more was observed for several minerals with zinc and phosphorus being most affected. The apparent zinc absorption and retention expressed in absolute values, were significantly higher from the flours of high extraction than from the more refined flours, in spite of a much higher phytate content in whole rye and lightly milled flours. It could be concluded that milling of rye into highly refined flours not only preclude considerable amounts of nutrients from human consumption, but the remaining flours have a much poorer nutritive value than flour made from whole rye.     

The influence of milling on the nutritive value of flour from cereal grains. 6. Sorghum

Low-tannin sorghum was milled into flour with extraction rates between 100 and 64%. The nutritive value of the flours was studied by chemical analyses and in balance experiments with growing rats. The effects of amino acid supplementation was also examined. In general, the content of essential nutrients decreased when the extraction rate was lowered, but the content of fibre, tannins and phytate was also significantly reduced by milling. The digestibility of energy as well as protein was high, but the protein quality was poor, especially in flours of low extraction. Amino acid supplementation improved protein utilization and weight gain considerably. Femur zinc concentration was significantly depressed in the rats fed the amino acid supplemented diets, and sorghum seems to be a poor source of available zinc, in particular when it is highly refined. The poor zinc availability may be attributed to the high content of phytate.     

The influence of milling on the nutritive value of flour from cereal grains. 5. Maize

Different grades of maize flour were produced by dry milling of yellow maize. The chemical composition of wholemeal, three semi-sifted flours and degermed maize was determined, and the nutritional value of the flours were investigated in balance experiments with growing rats. Distinct differences in nutrient and fibre content were found. Amino acid composition was significantly different in the milled fractions, and the content of minerals and phytate in the flours was determined by the extent to which the germ was retained. Phytate: zinc molar ratios ranged from 43 to 2. Weight gain of rats was closely correlated to the concentration of lysine (r=0.99) and tryptophan (r=0.97). Weight gain of rats fed degermed maize was reduced to half of that of rats fed wholemeal. True protein digestibility was high, but protein quality varied widely between the different flour fractions. Energy density of the flours was quite similar. Rats fed wholemeal had the highest intake of zinc and the highest apparent zinc absorption and retention but the lowest femur zinc concentration. Factors present in whole maize may interfere with zinc utilization. The results might indicate an interaction between phytate and fibre. Supplementation of wholemeal with lysine and tryptophan increased the biological value of the protein and the weight gain considerably, but apparent absorption and retention of zinc as well as femur zinc concentration were similar in unsupplemented and supplemented rats. The percentage of zinc absorbed from degermed maize flour was high, but degermed maize has a very low content of minerals and is highly deficient in lysine and tryptophan.     

The influence of milling on the nutritive value of flour from cereal grains. 2. Wheat

Wheat was milled into flours having extraction rates between 100 and 66%. The nutritive value of the various fractions was studied by chemical analyses and in balance trials with rats. The concentration of essential nutrients decreased when the extraction rate was lowered. The lysine content (g/16 g N) e.g. was 2.52 in whole wheat, but only 2.18 in the 66% extraction flour; however, only a slight reduction in biological value was found. The content of minerals was reduced to 30% of that in whole wheat, and the apparent zinc absorption and retention expressed in absolute values, were significantly higher from the flours of high extraction than from the more refined flours, in spite of a much higher phytate content in whole wheat and lightly milled flours. It could be concluded that milling of wheat into highly refined flours not only preclude considerable amounts of nutrients from human consumption, but the remaining flours have a much poorer nutritive value than flour made from whole wheat.     

The influence of milling on the nutritive value of flour from cereal grains. 4. Rice

Brown and milled rices were prepared from rough rice, and the nutritive value of the rices was studied by chemical analyses and in balance experiments with growing rats. The concentration of essential nutrients decreased with the degree of milling, but the energy density of brown and milled rices was similar. In the highly refined white rice the protein content was reduced to 86% and the mineral content to 23% of corresponding levels in brown rice. The zinc concentration was halved. The amino acid composition was rather unaffected by the degree of milling, but the lysine concentration was slightly lower in white rice than in brown rice. Milling was accompanied by an increase in true protein digestibility and a corresponding decrease in biological value. Thus net protein utilization of the different rices was remarkably uniform. A total of 33% of the utilizable protein and 22% of the digestible energy in brown rice was removed during milling. Rats fed rough, brown and lightly milled rices were unable to maintain their femur zinc concentration; deposition of calcium and phosphorus also appeared to be affected. Factors present in the outer part of the rice kernel interfere strongly with zinc utilization. Phytate and/or fibre are not solely responsible for this effect. Unless rice was milled into highly refined white rice, zinc status of rats was adversely affected. The results suggest that zinc might be a limiting factor in rice-based diets.     

Fractionation of cereal flour by sedimentation in non-aqueous systems. II. Rheological characterisation and baking performance of the protein fraction

A previously described method for the non-aqueous fractionation of cereal flours by sedimentation in non-aqueous solvents was carried out using flours of three wheat cultivars differing in baking performance, as well as one rye and one barley flour. The method was based on differences in the densities of starch (higher) and protein (lower). Thus, suspending finely milled flour in an inert solvent mixture with a density in between the densities of starch and protein yielded a sedimented starch fraction and a protein-rich fraction at the surface of the solvent. Further purification of this upper fraction provided a protein fraction, a middle fraction, and a lipid fraction. The protein fractions were examined by means of rheological methods such as micro-extension tests and creep-recovery tests. They also were reconstituted to standard flour with a protein content of 13.5%, which was used for micro-scale baking tests. Compared to aqueous isolated gluten, the hydrated protein fractions from wheat were much more extensible and had a lower resistance to extension. The baking performance of the wheat protein fractions was superior to gluten and comparable to the native wheat flours. The protein fraction from rye gave a wheat-like bread crumb, whereas the barley protein was not suited for bread making.     

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.     

Isolation of wheat endosperm cell walls: Effects of non-endosperm flour components on structural analyses

We report the isolation of a pure form of cell walls from wheat endosperm ‘popped’ out from the whole, enzyme deactivated and soaked grain, and compare them with cell walls isolated from milled flours of extraction rates from 45% to 75%, at physiological (37 °C) and elevated (70 °C) temperatures. Cell walls isolated from flours all contained non-endosperm walls whereas walls from popped endosperm were apparently pure. The monosaccharide composition of ‘popped’ cell walls was different to that of cell walls isolated from flour, particularly glucose and mannose contents (34 and 7% for ‘popped’ cf 29 and 3% for flour respectively) and arabinose to xylose ratios (0.45 for ‘popped’ cf 0.58 for flour). Total phenolic contents of popped endosperm cell walls were three to four times lower than for cell walls from flour. Elevated isolation temperature also had a solubilising effect, altering the cell wall composition. This study provides a novel method of isolating pure wheat endosperm cell walls, and demonstrates how contaminating (thick cell walled) non-endospermic material in milled flours can have a major influence on cell wall compositional analyses.     

Milling,functional and thermo-mechanical properties of wheat,rye, triticale,barley and oat

The milling potential of hulled barley, hulled oat, triticale, rye and wheat was studied using a long tempering process and a laboratory four-roller mill. Regardless of the investigated cereal, the results indicated a significant influence (p < 0.05) of volume per surface area ratio on the milling yield and ash contents of the flour. The lowest milling yield was obtained in case of hulled oat. Solvent retention capacity profiles were determined for all investigated whole cereals and flours for predicting the contribution of different polymers to the functionality of samples. For all solvents higher values were obtained for the whole cereals compared to the corresponding flour. Thermo-mechanical properties of the whole cereals and refined flours were also investigated. If in case of wheat the gluten proteins play an essential role on dough behaviour during kneading at 30 °C, in case of triticale, rye, hulled barley and hulled oat, the fibers play a major role as well. Thermo-mechanical properties of starch registered a large variation between cereals and/or flours. The lowest torque value corresponding to starch gelatinization (C3) was registered in case of the hulled oat flour, 1.92 Nm, while the highest value in case of rye flour, 2.65 Nm.     

Phytic Acid Level in Wheat Flours

The phytic acid content of refined (hand-made and factory-made) and whole (factory-made) wheat flours, much consumed in the Canary Islands, have been determined in this study. A total of 200 samples of flours from different types (100 refined and 100 whole) were analysed. The method proposed by Garcı́a-Villanova et al. (1982) was used for determination of phytic acid content in wheat flours. Most of the phytic acid concentrations are within the range 2–4 mg/g for the refined flours and 6–10 mg/g for the whole ones. The arithmetic mean obtained from all the samples studied is 3·77 mg/g for hand-made, refined flours, 2·96 mg/g for factory-made refined flours and 8·50 mg/g for the whole ones. On analysing the phytic acid content in all the flour samples, significant differences were observed for the different types of flour. Refined flours had a content lower than whole ones.     

Effect of barley and oat flour types and sourdoughs on dough rheology and bread quality of composite wheat bread

The potential of sourdough to improve bread quality of barley and oat enriched wheat breads may depend on the characteristics of the added flour (cereal type, variety, extraction rate). We compared the effect of different barley flours and oat bran (substitution level 40%), unfermented and as sourdoughs (20% of total flour), on composite wheat dough and bread characteristics by combining empirical rheological analyses (DoughLab, SMS/Kieffer Dough and Gluten Extensibility Rig) with small-scale baking of hearth loaves. Whole grain barley flour sourdough increased resistance to extension (Rmax) of the dough and improved the form ratio of hearth loaves compared to unfermented whole grain barley flour. However, sourdough showed little effect on the breads prepared with sifted barley flour or oat bran. The breads made with oat bran showed highest bread volume, lowest crumb firmness and highest β-glucan calcofluor weight average molecular weight (MW). The heat treatment of oat bran inactivated endogenous enzymes resulting in less β-glucan degradation. High MW β-glucans will increase the viscosity of the doughs water phase, which in turn may stabilise gas cells and may therefore be the reason for the higher bread volume of the oat bran breads observed in our study.     

Wheat Bread Quality as Influenced by the Substitution of Waxy and Regular Barley Flours in Their Native and Cooked Forms

The substitution of wheat flour with barley flours altered the bread loaf volume, colour and bread crumb firmness. These changes were found to be dependent on the barley cultivar, substitution level and flour treatment. In native form, Phoenix barley flour at 15% substitution produced breads with bigger loaf volume and softer crumb than Candle barley flour. However, when the barley flours were heat-treated (pan-cooked in excess water and then dried) before substitution, Candle barley flour produced better quality breads in terms of loaf volume, crumb firmness and crust colour than the Phoenix counterparts. The baking functionality of Candle flour was markedly improved when added after heat treatment.     

Effects of Soybean Fortification on Protein Quality of Tortilla-Based Diets Produced from Regular and Quality Protein Maize

The physiological development of laboratory rats fed with a typical indigenous tortilla diet was studied for two generations. The experiment compared casein control diet and five different types of diets: (1) a diet of tortillas obtained from fresh masa (FM); (2) regular tortillas produced from enriched dry masa flour containing vitamins B₁, B₂, niacin, folic acid, and the microminerals iron and zinc (REDMF); (3) tortillas produced from enriched dry masa flour fortified with 6% defatted soybean meal (FEDMF); (4) tortillas produced from enriched quality protein maize flour (EQPM); and (5) and, tortillas produced from enriched quality protein maize flour fortified with 3% defatted soybean meal (FEQPM). The growth of rats fed FEDMF and FEQPM diets was significantly higher (P<0.05) in both generations than their counterparts fed EQPM, REDMF, or FM diet. Animals fed quality protein maize (QPM) tortilla had the highest protein digestibility, but the FEQPM and FEDMF diets had the highest biological value (BV), net protein utilization (NPU), and protein-digestibility-corrected EAA scores (PDCEAAS). The difference among treatments was more evident in the second-generation rats. The pregnancy rate, number of newborns/litter, litter weight, and newborn survival rate was also higher for rats fed FEDMF, EQPM, and FEQPM diets than their counterparts fed REDMF and FM.     

氮锌肥配施对小麦籽粒不同类型混合粉锌营养品质的影响

为明确氮、锌肥配施对小麦籽粒不同类型混合粉锌营养品质的影响规律,采用田间试验,研究了氮、锌肥配施对小麦籽粒产量、不同类型混合粉中氮、锌含量及其累积量的影响及混合粉中植酸含量、植酸与锌的摩尔比（PA/Zn）和锌日吸收量的变化规律。结果表明,锌肥处理对小麦籽粒产量、各类型混合粉中的氮含量及其累积量无显著影响;与不施氮对照比较,施氮处理小麦籽粒产量提高93.7%,各类型混合粉中氮含量及其累积量显著提高,以施氮量240 kg·hm^-2处理最高。喷锌处理下,各类型混合粉中锌含量显著增加,精制粉、标准粉、通粉和全粉中锌累积量较对照依次提高了63.3%、58.0%、48.6%和50.9%;施氮后,各类型混合粉的锌含量及其累积量显著增加,以喷施锌肥处理更为明显。全粉和通粉中的植酸含量显著高于精制粉和标准粉,但PA/Zn低于精制粉和标准粉。喷锌后,精制粉、标准粉和全粉中植酸含量增加13.0%~ 15.4%,但PA/Zn下降23.8%~34.7%;施氮降低了精制粉、通粉和全粉中的植酸含量和PA/Zn。全粉中锌日吸收量为0.98 mg·d^-1,显著高于其他各混合粉;喷施锌肥后,各类型混合粉的锌日吸收量提高了 35.9%~61.0%;施氮显著提高了各类型混合粉的锌日吸收量。     

Wheat Bread Quality as Influenced by the Substitution of Waxy and Regular Barley Flours in Their Native and Extruded Forms

The substitution of wheat flour with barley flour (i.e. native or pretreated/extruded) reduced the loaf volume. Depending on the barley variety and flour pretreatments, the colour and firmness/texture of the bread loaves were altered. Amongst the barley breads prepared from native flours (at 15% barley flour substitution level), Phoenix had higher loaf volume and lower crumb firmness than Candle. However, amongst the barley breads prepared from extruded flours, CDC-Candle had higher loaf volume and lower crumb firmness than Phoenix. The lower loaf volume and firmer crumb texture of barley breads as compared with wheat bread may be attributed to gluten dilution. Also, the physicochemical properties of barley flour components, especially that of β-glucan, can affect bread volume and texture. β-glucan in barley flour, when added to wheat flour during bread making, could tightly bind to appreciable amounts of water in the dough, suppressing the availability of water for the development of the gluten network. An underdeveloped gluten network can lead to reduced loaf volume and increased bread firmness. Furthermore, in yeast leavened bread systems, in addition to CO₂, steam is an important leavening agent. Due to its high affinity for water, β-glucan could suppress the amount of steam generated, resulting in reduced loaf volume and greater firmness. In the present study, breads made with 15% HTHM CDC-Candle flour had highly acceptable properties (loaf volume, firmness and colour) and it indicated that the use of extruded barley flours would be an effective way to increase the dietary fibre content of barley breads.     

Additional wet milling step for fractionation of barley flour after hull separation

Fuel ethanol production from barley is increasing and there is a need to develop more efficient production processes. In the conventional ethanol production process, the hulls (fiber) in barley do not get fermented. The objective of this study is to evaluate a wet fractionation method, similar to the one used in corn wet milling in the endosperm fiber separation step, on the flour remaining after hull separation from barley in order to increase the starch content of barley flour. Hulls were separated from hammer milled barley flour using a combination of sieving and air classification. The remaining flour was soaked in water and the slurry was ground using an attrition mill. The cell wall material was screened out from the fine slurry. The fermentation material produced by hull separation followed by wet fractionation comprised 80.9% by weight of the original flour and contained 10.1% higher starch and 7.9% lower fiber (neutral detergent fiber; NDF) contents than the original flour. The cell wall coproduct has potential as a functional food ingredient because it has high fiber (NDF of 42.7%), high beta-glucan (4.5%) and high protein (20.2%) contents. The increase in starch content may be beneficial in fuel ethanol production.     

Bioavailability of Calcium,Iron and Zinc Fortified Whole Wheat Flour Chapatti

The bioavailability and interactive effects of calcium, iron and zinc fortified whole wheat flour chapattis on female Sprague–Dawley albino rats were determined. The whole wheat flour was fortified with CaCO₃, FeSO₄ and ZnSO₄ at 1000, 40 and 20 mg/kg, respectively and fed to 64 female Sprague–Dawley rats for 4 weeks. Retention of Ca, Fe and Zn was determined in plasma, femur and liver tissues. Ca levels in plasma and liver did not alter significantly while the Ca retention in femur changed significantly with the change in fortificants. The calcium retention was higher in the femur of rats fed on the diet supplemented with Ca + Zn (221 ± 13.61 mg/g) than the rats fed on the diet supplemented with Ca + Fe (219 ± 18.92 mg/g). The iron in plasma, liver and femur ranged from 2.19 ± 0.11 to 2.77 ± 0.10 μg/ml, 203.5 ± 13.24 to 251.5 ± 17.19 μg/g and 43.5 ± 1.05 to 52 ± 2.07 μg/g while zinc content ranged from 1.31 ± 0.089 to 1.55 ± 0.114 μg/ml, 89.5 ± 3.41 to 132 ± 6.10 μg/g and 175 ± 8.29 to 191 ± 10.85 μg/g, respectively. The minerals interacted with each other resulting in decrease of bioavailability among each other. The absorption was higher in the rats fed on fortified diet than those fed on unfortified chapatti diet. Hence, it is concluded that fortification of whole wheat flour is feasible to overcome the Ca, Fe and Zn malnutrition in the vulnerable groups.     

Milling and extrusion of six barley varieties,effects on dietary fibre and starch content and composition

Barley is a rich source of dietary fibre that can promote beneficial physiological effects. The carbohydrate composition in different barley varieties differs considerably and choice of variety is thus important. This study examined whether differences in carbohydrate composition observed in barley kernels of different varieties persisted in the sifted flour and in an extruded product. Six barley varieties were milled and extruded and dietary fibre and starch in the kernels, flour and extruded product were analysed. The starch content was found to be higher in flour and extruded product than in kernels. The content of arabinoxylan was higher in sifted flour than in kernels, but was decreased by extrusion. The extractability of arabinoxylan was increased by extrusion, while its average molecular weight was decreased. Extrusion also decreased the content of mixed-linkage (1 → 3),(1 → 4)-β-D-glucan in all varieties, but increased its extractability. The six barley varieties were affected in much the same way by milling and extrusion, but clear differences could still be observed. For example, the arabinoxylan in variety SW 28708 was less affected and variety KVL 301 had much lower extractability (76% vs 91–98%) of mixed-linkage (1 → 3),(1 → 4)-β-D-glucan after extrusion than the other varieties.     

Low moisture milling of wheat for quality testing of wholegrain flour

The objective of this study was to produce wholegrain wheat flour on a laboratory-scale with particle size distributions similar to commercially-milled samples without re-milling the bran. The moisture contents of four hard winter wheat cultivars were adjusted to 7.29–7.98% (by drying), 9.00–10.6% (“as is”), and 15.6% (by tempering) prior to milling into wholegrain flour. The moisture treatments appeared to affect the partitioning of wholegrain flour particles into each of three categories: fine (<600 μm), medium (600–849 μm) and coarse (≥850 μm). When the distributions of particles were grouped into these categories, wholegrain flours made from dried and “as is” wheat fell within the values for commercial wholegrain flours, while that from tempered wheat contained more coarse particles than even the coarsest commercial wholegrain flour. Loaf volumes and crumb firmness were not significantly different between bread made from wholegrain flour that had been produced from dried or “as is” wheat, but loaf volume was significantly lower and bread crumb firmness was significantly higher when wholegrain flour from tempered wheat was used. These results show that wheat may be milled without tempering to produce wholegrain flour with particle size similar to some commercially-milled flours without needing to re-grind the bran.     

Comparison of Polyphenol Oxidase Activities in Wheats and Flours from Australian and U.S. Cultivars

Polyphenol oxidase (PPO) activities of wheats from various classes and cultivars (grown both in the U.S.A. and in Australia), of some U.S. and Australian wheats, of wheat flours at various extraction rates and of kernels separated by size from various cultivars were measured by the oxygen electrode method. PPO activity of wheats was affected by both cultivar and growing location. Wheat flour contained on the average 3% of the PPO of the wheat grain. PPO activities of the flours increased as the flour extraction rates increased. Contrary to expectation, for a single cultivar, small kernels contained less PPO (on a weight basis and especially on a kernel basis) than did large kernels. Differences among kernels of various sizes for a single cultivar were smaller than differences in PPO among kernels of comparable sizes among various cultivars.