The distribution of acyl lipids in the germ,aleurone, starch and non-starch endosperm of four wheat varieties

The quantitative distribution of 23 classes of acyl lipids was determined in the germ, aleurone, starch and endosperm non-starch fractions of Atou (Soft English), Flinor (Hard English), Waldron (US Hard Red Spring) and Edmore (US Amber Durum) wheats. All four wheats had similar proportions (dry basis) of pericarp (6.8–8.6%), germ (2.5–3.0%), starchy endosperm (78.7–84.5%) and starch (59.3–67.5%), and similar quantities of acyl lipids in the whole kernels (2.8–3.2%), germ (25.7–30.5%), starch (0.8–1.2%) and endosperm non-starch fractions (0.8–1.1%). Flinor, Waldron and Edmore had 7.3–10% aleurone containing 8.7–10.6% lipids, but Atou appeared to have an abnormally low aleurone weight (4.0%) and a correspondingly high lipid content (19.4%). Pericarp acyl lipids were studied only in Atou, where they comprised 1.3% of the dry weight and 3.8% of the total acyl lipids in the whole kernel. Lipids in the germ and aleurone consisted of triglycerides (60.3–79.3%), other nonpolar lipids (5.6–12.0%) and phospholipids (13.6–17.9%). Starch lipids were almost exclusively lysophospholipids (89.4–94.4%). Greater variation was found in the endosperm non-starch lipids which consisted of triglycerides (13.7–34.1%), other nonpolar lipids (33.2–48.5%), glycolipids (18.6–38.3%) and phospholipids (21.9–35.3%). Edmore had the highest levels of triglycerides and non-polar lipids, and the lowest levels of glycolipids (as expected in a tetraploid wheat). Atouresembled Edmore in its low levels of steryl esters and glycolipids, but it also had least phospholipids.     

The stability of wheat starch lipids in untreated and chlorine-treated cake flours

Untreated flour and flour treated with chlorine (2.2 g Cl₂ kg_-1) were stored in air at 25°C for 4 months. Starch samples prepared from the original flours were stored in air at 25°C for 4 months. Starch samples were also prepared from the fresh flours (control starches) and from the stored flours. Some of the starches from the stored flours were subsequently held at 70°C for 1 month. Starch lipids were not affected by flour chlorine treatment, or by storage at 25°C. There was slight hydrolysis of starch lysophospholipids at 70°C, but negligible autoxidation of unsaturated fatty acids in the total starch lipids. There was appreciable hydrolysis of non-starch lipids in the untreated stored flour, but no detectable autoxidation of unsaturated fatty acids. Chlorine treatment of flour caused an immediate loss of approximately half of the oleic, linoleic and linolenic acids in all the non-starch lipids which were examined. There was no further change in the fatty acid composition of the non-starch lipids when the treated flour was stored, but lipid hydrolysis was substantially reduced compared with the untreated stored flour.     

Distribution of soft wheat kernel lipids into flour milling fractions

Samples of whole and manually degermed Atou wheat were milled on a micro-mill to give straight-run flour, coarse offal, fine offal, finished bran and bran finisher flour. The non-starch lipids in these products were compared with non-starch lipids in the aleurone-free starchy endosperm, and with lipids in the germ and aleurone of the original wheat. About half of the triglyceride in flour was derived from the germ; no glycolipids or phospholipids were derived from germ, and no lipids of any kind were derived from the aleurone. Non-starch lipids in the aleurone-free endosperm of a mixed English soft wheat grist were then compared with the non-starch lipids in 11 flour streams from a commercial mill. All flours had much more triglyceride than the endosperm. In flours from the reduction system there were significant correlations between flour colour grade, sterylester, triglyceride, diglyceride, free fatty acid and diacylphospholipids, but none between ash or protein and colour or any class of lipid. Analysis of the principal components of variation in a simplified matrix describing all 11 flours placed triglyceride, diglyceride, free fatty acid, and diacylphospholipids close together in one group, and all glycolipids and N-acylphospholipids in a separate unrelated group. Sterylester and colour were loosely associated with the first group but could also be regarded as part of a third loose group with ash and protein. The results are interpreted in terms of lipid distribution within the wheat kernel, and their significance in milling and baking practice.     

Cooperation of phosphatidylcholine with endogenous lipids of wheat flour for an increase in dough volume

Phosphatidylcholine (PC) increases the gas-retaining ability of dough, the dough volume on fermentation and the loaf volume of bread. The cooperation of wheat flour endogenous lipids with PC was examined. More than 90% of the total wheat flour lipids were extracted with chloroform, the extracted lipids comprising glycolipids (33 wt%), non-polar lipids (56 wt%), and phospholipids (11 wt%). The increase in the specific volume of dough with delipidated wheat flour by the addition of PC was smaller than the increase in the specific volume of dough with native wheat flour. The addition of the extracted lipids to delipidated wheat flour restored the increase in dough volume by the addition of PC. The glycolipid fraction of the extracted lipids was most effective for enhancing the action of PC. The results suggest that interaction of PC with wheat flour glycolipids may synergistically increase foam stability to enhance the gas-retaining stability of dough.     

Methods for the quantitative analysis of lipids in cereal grains and similar tissues

Methods are described for the extraction and quantification of total lipids in cereal grains and other similar tissues, and for the determination of all the major classes of acyl lipid found in these extracts. Total lipids, obtained by direct solvent extraction or after acid hydrolysis, are quantified as fatty acid methyl esters (FAME) by gas chromatography (g.c.), using heptadecanoate (17:0) as internal standard. Individual lipid classes are separated by thin-layer chromatography; non-polar lipids and glycolipids are measured as FAME by g.c., while phospholipids are determined from phosphorus distribution. Crude lipid extracts are used to avoid losses during purification, and methanolysis of lipid classes is always performed without extracting the lipids from silica gel in order to minimise autoxidation, handling losses and contamination. Corrections are described for minor losses during experimental procedures, and factors are given for conversion of weights of FAME or phosphorus into weights of original lipid. In the authors' laboratory the precision of routine determinations (variations expressed as percentage of mean values) are usually well within the limits: total lipids, 1.5%; major lipid classes, 1.5%; minor lipid classes, 5%.     

Distribution and Composition of the Lipids in Starch Fractions from Wheat Flour

The fine granule starch fraction of a commercially milled, bleached, wheat flour was richer in nitrogen, extractable lipid, and polar lipids (glycolipids and phospholipids) compared with the coarse granule starch, which was richer in triglycerides and its hydrolysis products. The intermediate size starch fraction fell between fine and coarse starch in the level of these components while the “pentosan” fraction was very high in lipid and nitrogen, although it was of similar phosphorus content to the starch fractions. The total fatty acid content of the fine starch was over 50% higher than that of the coarse starch and both results were higher than the extractable lipid contents of the respective fractions. The results are explained in terms of higher protein and phospholipid content of the fine starch, which may be related to its higher specific surface area.     

Changes in flour lipids during the storage of wheat flour

High- and low-grade spring and winter wheat flours of ～13% moisture were stored at 15, 25 and 37 °C and the lipids were then extracted with water-saturated n-butanol. In the original (control) flours there were more neutral lipids and glycolipids in low-grade winter than in high-grade winter and in low-grade spring than in high-grade spring flours, but there were no corresponding differences in the amounts of phospholipids. The total extractable lipid contents of the flours remained constant in the samples stored at 15 °C, but there were slight losses in the samples stored at 25 and 37 °C. Total lipid contents determined by acid hydrolysis remained constant in all cases indicating that no loss of fatty acids had occurred on storage. There was sufficient hydrolysis of all glycerides to account for the increased amounts of free fatty acids in the stored flours. Some complete deacylation of lipids to free fatty acids and water-soluble products was indicated. The fatty acid composition of all lipids remained constant, and there was no evidence of any lipoxygenase or other enzymic degradation of fatty acids. Stereoanalysis of the principal glycerides indicated that phosphatidylcholine (and probably also phosphatidylethanolamine) was specifically hydrolysed at the 2-position, presumably by phospholipase-A₂. Hydrolysis of triglycerides, diglycerides and monoglycerides was attributed to the action of wheat and microbial lipases of unknown specificity. Stereoanalysis of N-acylphosphatidylethanolamine and the galactosyldiglycerides was not attempted, but it was deduced that they were randomly hydrolysed at the 1- and 2-positions. The changes found in the flour lipids differed from those reported to occur in germinating wheat and in stored damp wheat flour which had been damaged by moulds.     

Significance of lipid binding on the functional and nutritional profiles of single and multigrain matrices

Lipid fractions and starch- and protein-lipid binding of single and blended oat, rye, buckwheat and wheat flour, dough and bread matrices were investigated, and results correlated with the functional and nutritional properties of the grain matrices during mixing and baking. Non-starch lipid was the most prominent fraction in terms of absolute content and as a percentage of total lipids. Free lipids, starch lipids and bound lipids were, respectively, the major, intermediate and minor lipid fractions in flours, doughs and breads. Great differences in total lipid content due to sampling result in divergences amongst lipid fraction content and distribution, especially for starch and bound lipid fractions. Lipids bound to proteins during dough mixing are translocated and bound to starch during baking. In blended samples, the higher fibre content seems to provoke a reduction of the lipid–protein and lipid–starch linkages due to interactions between fibres and endogenous biopolymers. Starch lipid showed the most significant correlations with parameters related to dough and bread performance during breadmaking, especially over the mixing step. Valuable fresh bread functional characteristics, such as high specific volume and high sensory score for softness and overall acceptability, correspond to a starch lipid’s increase due to mixing. The higher the free and starch lipids decrease by reason of temperature treatment—baking—the larger the starch hydrolysis and the higher β-glucans and total dietary fibre contents.     

Lipid Composition of Field Pea (Pisum sativum cv Trapper) Seed and Starch

The total lipids in field pea seeds and refined starch were extracted by five aqueous/organic solvent systems and the greatest yield of total. neutral and polar lipids was obtained with hot n-propanol-water (3:1 v/v). Lipids extracted from field pea seeds represented 2.9% of the seed weight and consisted of 43.2% neutral lipids, 3.2% glycolipids and 53.6% phospholipids. The major components of the three fractions were 70% triacylglycerol in neutral lipid, 28% esterified sterol glycoside in glycolipid and 55% phosphatidylcholine in phospholipid. The purified starch fraction contained 0.22% surface lipids and 0.09% internal lipids. The surface lipids were primarily sterol esters and free fatty acids while only free fatty acids were found in the internal lipids. The ability of lysophospholipids and fatty acids to complex with field pea starch was demonstrated by differential scanning calorimetry and X-ray diffraction, respectively.     

Wheat endosperm hardness. Part II. Relationships to content and composition of flour lipids

In Part I we analysed hardness and colour of wheat endosperm and stated that these features are quite well correlated among kernels of individual varieties. In order to enhance knowledge of the biochemical basis of endosperm hardness, this study aimed at determining how the content and the composition of free and starch lipids influence it. Wheat samples (used previously in Part I) were milled in a way that reduced the number of non-endosperm particles in flour. Simple linear correlation coefficients between endosperm hardness and its lipid composition indicated that hardness was positively correlated with the content of free glycolipids (r=0.82) and negatively with the content of surface lipids of starch, especially with their non-polar fraction (r=-0.83). The typical feature of harder wheat varieties was a substantially higher content of oleic acid in lipids of the starch surface.     

Differences in content and composition of free lipids and carotenoids in flour of spring and winter wheat cultivated in Poland

The work presents the content and composition of free lipids and carotenoids in spring and winter classes of wheat flour. It discusses genetical and physiological aspects of their synthesis and accumulation in wheat kernels and also indicates how methodological differences explain differences in results presented in the literature. It has been reported that spring wheat flours are richer in free lipids, especially in the non-polar fraction. The content of glycolipids ranged from 134 to 215 mg/100 g flour and was more stable within the winter wheat class. The percentages of the two main fractions, namely DGDG and MGDG, were similar in both wheat classes and reached ca. 77%. Phospholipids constituted the smallest fraction of the flour free lipids in both wheat classes; however, spring wheat flours were richer in these compounds, which is likely associated with a greater content of spherosomes in the endosperm of this wheat class. The free lipids of spring wheat flour contained more oleic and slightly less linoleic and linolenic acids. Spring wheat flour was also richer in carotenoids, although there were varieties in both classes that deviated from this. The main carotenoid was lutein, whose total percentage in the form of different isomers ranged from 71.3% to 83.3% and was slightly lower for spring wheat flour. Lutein, in the form of a trans-isomer, constituted about 62% and 70% of all carotenoids in spring and winter wheat flours, respectively.     

The distribution of acyl lipids and tocopherols in flours millstreams

Kernels from a mixed hard wheat grist were dissected into germ, bran (pericarp, testa and aleurone), and starchy endosperm for direct analysis of tocopherols in lipid extracts by high-performance liquid chromatography. α- and β-tocopherols were almost exclusively in the germ, α-tocotrienol was mostly in the bran, and β-tocotrienol was equally distributed between the bran and the starchy endosperm. Acyl lipids and tocopherols were quantified in 23 millstreams obtained from this grist. Components related to germ and bran (triglyceride, diacylphospholipids, ã- and β-tocopherols) and testa (flour colour) showed the highest coefficients of variation whereas endosperm components (glycolipids, N-acylphospholipids and β-T-3) showed exceptionally low variation. The quantities of marker tocopherols in the streams were used to calculate the composition of the lipid transferred to the flour from germ and aleurone, and to predict the composition of the basic endosperm, free of aleurone and germ lipids. Low proportions of diacylphospholipids in the lipid transferred to high-grade millstreams indicated the transfer of spherosome lipid. The low-grade streams exhibited high proportions of phospholipids suggesting additional transfer of germ tissue and aleurone tissue containing membrane lipids. Protein and ash contents of the transferred fraction confirmed that a substantial proportion of the transferred lipid was probably accompanied by protein bodies or by tissue fragments. It is estimated that aleurone contributed less than one-quarter of the transferred lipid in any stream. Hexane-extractable free lipids in four representative streams consisted of almost all the non-polar lipids, 40–67% of the glycolipids, 47–54% of the diacylphospholipids and 30–60% of the lysophospholipids.     

Characteristics of lipids in buckwheat grain and isolated starch and their changes after hydrothermal processing

Studies were carried out on bond and free lipids of buckwheat grain and isolated starch. As regards free and bond lipids, fraction composition (percentages of neutral and polar fraction) and fatty acids were determined. It was found that the content of free lipids in buckwheat grain was twice higher than of bond lipids. On the other hand, in case of starch percentage of free lipids was twice lower than of bond lipids. As regards free and bond lipids of buckwheat grain and starch, main fraction was represented by the neutral one. Percentages of glycolipids and phospholipids amounted to only from 5 to 7%. Fatty acids were predominated by unsaturated acids C_18:2 and C_18:1. Fire and steam hydrothermal processing resulted in several quantitative changes, the most important ones being an increase of free lipid content in the grain and of bond lipid content in the starch, changes in the percentage of glycolipids and phospholipids, an increase of saturation of free lipid fatty acids in the grain, and of saturation of bond lipid fatty acids in the starch.     

The effect of extractable lipid on the viscosity characteristics of corn and wheat starches

The defatting of both corn and wheat starch with 85% methanol yields starches which start to gelatinise at lower temperatures and have increased overall viscosities compared with untreated starches. The lipids extracted from wheat and corn starch with 85 % methanol were similar in total amount but showed very large differences in the proportions of neutral and phospholipids. The extracted corn lipids contained eight times as much neutral lipids (mainly free fatty acids) as phospholipids whereas the proportions of neutral and phospholipids in wheat starch were approximately equal. Addition of extracted lipids to defatted starches significantly modified the swelling and viscosity characteristics. Addition of wheat and corn lipids to potato starch (which contains almost no lipids) indicated that the higher percentage of phospholipids in wheat starch probably contributed towards the lower viscosity characteristics of wheat starch compared with corn starch.     

Changes of chemical composition and dough rheology in two fractions of sieve-classified Polish spring wheat flour

The study of chemical composition and dough rheology changes in sieve-classified two fractions (up to 60 and 60-240 microm particles) of wheat flour was the subject of this study. The straight grade flours were obtained by the milling of three Polish varieties of spring wheat, differing in particle size index (PSI) values. The flours were separated with the use of an SZ-1 laboratory sifter. The yield of fine fraction was in the range 50.0-55.7%. The obtained fractions were assayed for the content and composition of free lipids, gluten proteins, damaged starch, ash, water absorption and amylograph viscosity. Dough rheology (extrusion in OTMS cell, alveograph and farinograph tests) and baking trials were also performed. The content of free lipids, including the non-polar and phospholipids was lower and the content of glycolipids was higher in fine flours. Those fractions were more rich in linoleic acid but the lower content of oleic and linolenic acids resulted in a higher oxidizability index of free lipids. Fine flours contained less ash and significantly more damaged starch. At the same time, they were characterized by a higher content of wet gluten, water absorption, amylograph viscosity and better dough parameters. This was reflected in the bread volume, which was higher by 6.3-10.7%. The influence of the changes in composition and the content of free lipids upon the rheology of the dough after the 90 days flour storage has not been defined unambiguously and requires further research.     

The composition of a gel formed when wheat flour is suspended in phenol-acetic acid-water (1:1:1, w/v/v)

A gel which formed when wheat flour was suspended in phenol-acetic acid-water (1:1:1, w/v/v/) was fractionated into a protein-rich soluble fraction and a carbohydrate-rich insoluble fraction. Gel electrophoresis showed that the soluble fraction contained several proteins and had an amino acid composition with a high content of proline and glutamyl residues and a low content of lysine. The soluble fraction also contained lipids which were mainly phospholipids, phospholipid derivatives and glycolipids and other compounds, which yielded galactose and glucose after acid hydrolysis. The insoluble fraction contained a polysaccharide with similar properties to starch, and lipids which were mainly neutral fats, sterols and sterol esters. Both fractions contained arabinoxylans and mannans. The gel did not contain any nucleic acids. The protein-rich soluble fractions of gels prepared from other wheat flours and air-classified flour fractions, from wheat gluten and from rye and barley flours, showed marked differences in amino acid composition. It is concluded that a heterogeneous class of proteins, rather than specific proteins in fixed proportions, is involved in gel formation.     

The lipids of young cassava (Manihot esculenta,Crantz) leaves

Lipids were extracted quantitatively from young cassava (Manihot esculenta Crantz) leaves with a chloroform-methanol mixture. Total lipids were purified by the Folch procedure and separated into non-polar lipid, glycolipid and phospholipid fractions by column chromatography. Lipids of each fraction were further subjected to thin layer chromatography and gas-liquid chromatography. Young cassava leaves were found to have low content of lipids (3.02%) of which 22.4, 25.1 and 48.2 were non-polar lipids, glycolipids and phospholipids, respectively. Pigments (11.5%), wax and hydrocarbons (1.2%), steryl esters (2.9%), methyl esters of fatty acids (2.0%), trigly-cerides (1.5%), fatty acids (2.1%), diglycerides (1.1%) and sterols (0.1%) constituted the leaf non-polar lipids. The leaf glycolipids were made up of esterified steryl glycosides (2.1%), monogalactosyl diglycerides (12.5%), steryl glycosides (1.1%), cerebrosides (4.2%) and digalactosyl diglycerides (5.2%). The leaf phospholipids were found to include cardiolipin (3.6%), phosphatidylglycerol (21.5%), phosphatidylethanolamine (16.4%), phosphatidylserine (0.7%), phosphatidylinositol (4.0%) and other unidentified phospholipids (2.5%). Phosphatidylcholine was present only in trace quantity. Analysis of the fatty acid composition of each of the leaf lipids revealed that, with the exception of steryl esters, all leaf lipids have high content of polyunsaturated fatty acids.     

Characterization of Internal and Surface Lipids of Oat Starches from Two Isolation Processes

Oat starches representing two different isolation methods were studied for lipid contents and compositions. One of the starch isolation methods utilized water and the other slightly alkaline solution. The internal lipids were practically identical in both starches. However, starch from the alkaline method contained 21% less non-starch lipids as total fatty acids, 63% less Kjeldahl nitrogen, and the content of non-starch free fatty acids was low. Instead, starch from the water method contained almost three fold higher amounts of free fatty acids which contributed up to 49% of non-starch lipids. Therefore, it was concluded that isolation of starch under alkaline conditions both reduces the content of non-starch lipids and maintains a better composition in the residual starch lipids.     

Changes in wheat lipids during mixing and resting of flour-water doughs

Lipids extracted with water-saturated n-butanol from flour and flour-water doughs were examined to determine the extent of oxidations and other changes which occurred in mixing and resting dough. Extracted lipids were converted to fatty acid methyl esters (FAME) and quantified by gas-liquid chromatography (g.l.c.) using heptadecanoic acid (17 : 0) as internal standard. The original flour or dough and the corresponding solvent-extracted residues were acid hydrolysed, and the hydrolysate lipids converted to FAME for g.l.c. determination of the total lipid and residual unextracted lipid contents. The total flour or dough lipids equalled the extracted lipids + unextracted lipids, except where there were unavoidable autoxidative losses of linoleate (18 : 2) and linolenate (18 : 3). The unextracted flour lipids (13% of total lipids) were not oxidised during dough mixing. There were no changes in any of the extracted lipid classes other than free fatty acids (FFA) and monoglycerides (MG) which showed losses of 18 : 2 and 18 : 3 after aerobic dough mixing. Losses of FFA and MG are attributed to lipoxygenase activity during dough mixing and the period immediately after. The small amount of 18 : 2 in the “free” petroleum ether-extracted FFA appeared to be unaffected by lipoxygenase. Recoveries of FFA other than 18 : 2 or 18 : 3 were constant, indicating no lipolysis of glycerolipids and no general oxidation or degradation of FFA. Experiments with [U-¹⁴C]palmitic acid confirmed that there was no oxidation, degradation or re-esterification of FFA. Much of the non-polar lipids (steryl ester, triglyceride, diglyceride, FFA, MG) and almost all of the polar lipids were bound on dough mixing. Binding was non-selective with regard to fatty acid composition. Triglyceride was the only lipid class bound to a greater extent in anaerobic dough than in aerobic dough. Some selectivity of binding between lipid classes was indicated.     

Isolation and Partial Characterization of Black Gram (Phaseolus mungo L) Starch

Black gram (Phaseolus mungo L.) starch was isolated. The starch yield was 45% on flour weight basis. Starch granule size ranged from 7.5–28.5 μm (length) to 7.5–27.0 μm (width). Hylum length ranged from 25–100% of the starch granule length. Amylose content of starch was 26.65% (starch basis). Gelatinization temperature range for the starch was 71.5–74.0°C. Unlike several legume starches, black gram starch had a peak viscosity as indicated by Brabender Viscoamylograph. The starch viscosity was dependent on pH and ionic strength. The raw as well as cooked starch was resistant to hog pancreatic α-amylase hydrolysis in vitro.