Contributions to breadmaking of inherent variations in lipid content and composition of wheat cultivars. II. Fractionation and reconstitution studies

doi:10.1016/S0733-5210(09)80005-2

Journal of Cereal Science

Volume 13, Issue 3, May 1991, Pages 263-274

https://doi.org/10.1016/S0733-5210(09)80005-2 Get rights and content

The effects on test-bake loaf volume of variations in flour lipid content and composition of the order found in the survey (accompanying paper: McCormack et al. Part I. J. Cereal Sci.13 (1991) 255–261) have been directly measured using fractionation and reconstitution methods. Loaf volume decreased linearly for flours from several cultivars when the percentage of lipid that was non-polar was varied from 0 to 100, keeping the total non-starch lipid level constant at its natural value by corresponding adjustment with the polar lipid fraction (i.e. the percentage of polar lipid varied from 100 to 0). This allowed an estimation of the contribution to differences in loaf volume for cultivars having their proportions of non-polar lipid at the low and high ends of the range. This contribution was small relative to differences measured between cultivars of high and low loaf volume potential and this was confirmed by interchange experiments. Differences in the amount of non-starch lipid were also shown to contribute to loaf volume differences but were more important for poorer quality cultivars. A high correlation was found between loaf volumes of defatted and untreated flours from 15 cultivars, again confirming that the lipid contribution to loaf volume, although measureable, was minor compared to that from protein. The magnitude of the lipid contribution to the variation in loaf volume between cultivars, deduced from reconstitution studies, is consistent with that estimated from statistical analysis of the survey data.

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When the extractions of lipids from different flours were carried out with chloroform, negative correlations were observed between LV and the proportion of nonpolar to total lipids and nonpolar to polar lipids (McCormack et al., 1991a). Furthermore, it was observed that chloroform removes a greater amount of lipids than other solvents, without affecting the properties of the flour (MacRitchie and Gras, 1973; McCormack et al., 1991b; Sroan and MacRitchie, 2009). In particular, more galactolipids and phospholipids are extracted than with the nonpolar solvents like hexane, but lower levels of galactolipids are extracted than those obtained with more polar solvents such as WSB (Bahrami et al., 2014).
During the storage of wheat grains and flours, a natural deterioration occurs due to aging over time, which is accelerated by adverse conditions of temperature and humidity that cause the growth of fungi. The local climates and infrastructure available for storage affect the preservation and duration of the safe storage time. Wheat lipids are a minor component, whose level and composition are decisive in the quality properties of wheat final products. Lipids are easily degraded, which is the main cause of quality loss. The enzymatic degradation of lipids is carried out by the activation of endogenous and/or fungal enzymatic activities, which produces hydrolytic and oxidative rancidity. Fusarium, Aspergillus, Penicillium and Alternaria are the most frequent genera found in infected grains. Wheat infection by Fusarium spp. is associated with considerable economic losses in crops throughout the world. The volatile compounds produced by oxidative rancidity are the main indicators of deterioration. Lipid rancidity must be monitored periodically using a combination of different analytical methods, ranging from traditional to modern alternative techniques of varied scope. Sensitivity to lipid deterioration varies with the wheat cultivar genotype, thus the selection of cultivars with better stability allows to obtain better quality products. In addition, a large proportion of the harvested wheat is usually stored for a long time until use, so achieving suitable environmental conditions and applying control measures prevent quality loss. This review updates the knowledge about wheat lipids, the importance of preserving their integrity during storage, presenting different monitoring alternatives to detect their rancidity, which would allow better decision-making.
Seventy years of research into breadmaking quality
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This meant that the loaf volume decreased from 225 cc to 160 cc when the lipid composition was lowered from one hundred per cent polar lipid to zero per cent polar lipid. As mentioned above, results of an extensive survey showed that no more than 11% of the variation in loaf volume could be accounted for by differences in the polar/non-polar lipid ratio (McCormack et al., 1991b). It can therefore be concluded that the lipid composition of current varieties of bread wheat flours must be substantially constant in terms of their relative proportions of polar and non-polar lipids.
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Feature of air classification product in wheat milling: Physicochemical, rheological properties of filter flour
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At the same time, fatty acids, particularly unsaturated fatty acids, could strengthen the gluten by way of oxidation of SH' groups through enzyme-coupled reactions (Addo and Pomeranz, 1992; Prabhasankar et al., 2000). Lipids also have been reported to markedly influence the baking quality of flours and loaf volume of bread (Bekes et al., 1986; McCorrnack et al., 1991). The extensograph properties of dough samples of filter flours are given in Table 4.
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Defatted flours of wheat varieties Karl and Jagger, after removing lipids by chloroform, were used to investigate the contribution of lipid to physicochemical properties and Mantou-making quality by comparing microstructure and thermal properties. The results indicated that defatted flours tend to have more single starch granules, higher gelatinization enthalpy, more water absorption, longer pasting peak time, higher peak and hold viscosity, lower setback and breakdown than those of the control. Meanwhile, the defatted flours had improved cooking stability and better ability to withstand mechanical shear stress. The Mantou-making test showed that the volume of Mantou made from defatted flour did not change significantly. C-Cell analyses on the internal crumb grains of Mantou revealed a deterioration in crumb grain characteristics upon removal of lipids from the flours. The grain cells of Mantou became bigger with thicker cell walls upon removal of lipids.
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Mechanism of gas cell stabilization in bread making. I. The primary gluten-starch matrix
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For Soft, minimum volume is reached at a relatively lower percentage of natural flour lipids (∼30%) in comparison to Jagger (∼50%) (Fig. 2). The results of loaf volume variations in response to natural flour lipid level variations agreed qualitatively with those of MacRitchie and co-workers (MacRitchie, 1976a; MacRitchie and Gras, 1973; McCormack et al., 1991). Loaf volume seems to be governed by expansion capacity of the gas cells.
Expansion of dough and hence bread making performance is postulated to depend on a dual mechanism for stabilization of inflating gas bubbles. Two flours were used in this study, one from the wheat variety Jagger (Jagger) and the other from a composite of soft wheat varieties (Soft). Thin liquid lamellae (films), stabilized by adsorbed surface active compounds, act as an auxiliary to the primary gluten–starch matrix in stabilizing expanding gas cells and this mechanism operates when discontinuities begin to appear in the gluten–starch matrix during later proving and early baking stages. Contributions of the liquid lamellae stability to dough expansion were assessed using flours varying in their lipid content. Incremental addition of natural lipids back into defatted flour caused bread volume to decrease, and, after reaching a minimum, to increase. Strain hardening is a key rheological property responsible for stabilizing the primary gluten–starch matrix. Jagger gave higher test-bake loaf volume than Soft and higher strain hardening index for dough. The different lipid treatments were found to have negligible effects on strain hardening index. Image analysis of crumb grain revealed that differences in number of gas cells and average cell elongation with different lipid treatments were insignificant. The evidence agrees with a dual mechanism to stabilize the gas cells in bread dough. To understand dough rheology at a molecular level, rheological properties of doughs were varied by addition of flour protein fractions prepared by pH fractionation. Fractions were characterized by SE-HPLC and MALLS. The molecular weight distribution (MWD) of fractions progressively shifted to higher values as the pH of fractionation decreased. Mixograph dough development time paralleled the MWD. However, the strain hardening index and the test-bake loaf volume increased with increasing MWD up to a point (optimum), after which they declined. At a given strain rate, the behavior at the optimum is thought to result from slippage of the maximum number of statistical segments between entanglements, without disrupting the entangled network of polymeric proteins. Shift of MWD to molecular weight higher than the optimum results in a stronger network with reduced slippage through entanglement nodes, whereas a shift to lower molecular weights will decrease the strength of the network due to a lesser number of entanglements per chain.

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Contributions to breadmaking of inherent variations in lipid content and composition of wheat cultivars. II. Fractionation and reconstitution studies

J. Cereal Sci.

Cereal Chem.

J. Food Technol.

Cereal Chem.

Food Technol.