Protein–lipid interactions in dough have an important impact on the quality of bakery products. Understanding of protein–lipid interactions in gluten can enhance the development of technological ...solutions to improve the breadmaking quality of flour as well as the functional properties of gluten. In this study, acetic acid at two different concentrations was used for treating and fractionating gluten. The impact of these procedures on the distribution of lipid components was measured. Acetic acid was able to dissociate non-polar lipids from the gluten protein matrix. Upon fractionation monomeric proteins (predominantly gliadins) and phospholipids were high in the 0.01
M acetic acid soluble fraction. The subsequent fractionation step using 0.1
M acetic acid resulted in an increased amount of high-molecular-weight glutenin subunits (HMW-GS) in the soluble fraction, along with more non-polar lipids and glycolipids in both the free and bound lipid extracts. The distribution of lipid classes demonstrates that non-polar lipids are either associated with the glutenin polymeric network through hydrophobic interactions or entrapped within the gluten matrix. The results also indicate that in gluten, glycolipids are likely to be associated with glutenins through both hydrophobic interactions and hydrogen bonds whilst phospholipids preferentially interact with gliadins and lipid binding proteins.
Summary
Analysis of barley shrunken grain mutants has identified lines with a novel high amylose starch phenotype. The causal mutation is located at the sex6 locus on chromosome 7H, suggesting the ...starch synthase IIa (ssIIa) gene as a candidate gene altered by the mutation. Consistent with this hypothesis, no evidence of SSIIa protein expression in either the starch granule or soluble fractions of the endosperm was found. Sequences of the starch synthase IIa gene, ssIIa, from three independent sex6 lines showed the presence of a stop codon preventing translation of the ssIIa transcript in each line. Perfect segregation of the starch phenotype with the presence of stop codons in the ssIIa gene was obtained, providing strong evidence for the lesion in the ssIIa gene being the causal mutation for the sex6 phenotype. The loss of SSIIa activity in barley leads to novel and informative phenotypes. First, a decrease in amylopectin synthesis to less than 20% of the wild‐type levels indicates that SSIIa accounts for the majority of the amylopectin polymer elongation activity in barley. Secondly, in contrast to high amylose starches resulting from branching enzyme downregulation, the sex6 starches have a shortened amylopectin chain length distribution and a reduced gelatinisation temperature. Thirdly, the mutation leads to pleiotropic effects on other enzymes of the starch biosynthesis pathway, abolishing the binding of SSI, branching enzyme IIa and branching enzyme IIb to the starch granules of sex6 mutants, while not significantly altering their expression levels in the soluble fraction.
A salt-washing process to produce gluten with improved rheological properties having reduced lipid content was developed, initially using sodium chloride and subsequently with ammonium chloride. In ...laboratory experiments, the lipid content in gluten was reduced from 6.6% in the gluten control (washed out from flour with water only) to 5.7%, 3.6% and 2.7% in gluten salt-washed with increasing concentrations of NaCl from 0.5%, 1% to 2%, respectively. This was accompanied by the increase in the maximum creep strain of the salt-washed gluten (i.e. better gluten quality) with the increase in NaCl concentration. The new salt-washing process also improved gluten colour with reductions in
b values (yellowness) and increases in
L values (whiteness). Salt-washed gluten using 0.5% NH
4Cl was comparable to gluten washed with 2% NaCl in lipid content and maximum creep strain. Extensograph tests showed increased dough extensibility for salt-washed gluten with 0.5% NH
4Cl compared to water-washed gluten (the control). The improvements in gluten rheological properties and reduced lipid content using the salt-washing process were observed for flours with very different protein content and quality. The advantages of the laboratory-based process were retained when the process was scaled-up to a pilot batch process. The new gluten washing process offers several advantages for the industry including increased gluten yield, ease of gluten washing, superior rheological properties, and improved colour, with no extra capital costs being needed to alter conventional processing equipment. The advantage in using an ammonium salt over a sodium salt is that the volatility of the ammonium salt offers potential for its removal during gluten drying, leading to the virtual absence of salt in the final gluten. Starch quality was also improved by the process.
The starch of wheat (Triticum aestivum L.) flour affects food product quality due to the temperature-dependent interactions of starch with water during gelatinization, pasting, and gelation. The ...objective of this study was to determine the fundamental basis of variation in gelatinization, pasting, and gelation of prime starch derived from seven different wheat cultivars: Kanto 107, which is a partial waxy mutant line, and six near-isogenic lines (NILs) differing in hardness. Complete pasting curves with extended 16-min hold at 93 degrees C were obtained using the Rapid Visco Analyser (RVA). Apparent amylose content ranged from 17.5 to 23.5%; total amylose content ranged from 22.8 to 28.2%. Starches exhibited significant variation in onset of gelatinization. However, none of the parameters measured consistently correlated with onset or other RVA curve parameters that preceded peak paste viscosity. Peak paste viscosity varied from 190 to 323 RVA units (RVU). Higher peak, greater breakdown, lower final viscosity, negative setback, and less total setback were associated with lower apparent and total amylose contents. Each 1% reduction in apparent or total amylose content corresponded to an increase in peak viscosity of about 22 and 25 RVU, respectively, at 12% starch concentration. Of the seven U.S. cultivars, the lower amylose cultivars Penawawa and Klasic were missing the granule-bound starch synthase (GBSS; ADPglucose starch glycosyl transferase, EC 2.4.4.21) protein associated with the Waxy gene locus on chromosome 4A (Wx-Bl locus). Kanto 107 was confirmed as missing both the 7A and 4A waxy proteins (Wx-Al and Wx-Bl loci). The hardness NIL also were shown to be null at the 4A locus Apparent and total amylose contents of prime starch generally corresponded well to the number of GBSS proteins; although the hardness NIL tended to have somewhat higher amylose contents than did the other GBSS 4A nulls. We concluded that reduced quantity of starch amylose due to decreased
ABSTRACT
Three wheat flours, three wheat starches, a regular maize starch and a waxy maize starch were subjected to a number of different RVA profiles. Five different initial temperatures were used, ...40, 50, 55, 60, and 65°C, with different initial holding times (0–3 min), heating times (2fl–10 min), holding times at 95°C (0–6 min), cooling times (2–6 min), and final hold times (0–10 min) being applied. A range of final temperatures of 30–60°C was also utilized. Significant variations in viscosity were observed with these conditions, particularly in wheat starch and flour. The most important parameters causing these variations were the initial temperature, the heating rate, and the final holding time. Short initial holding times also resulted in a wider spread of values for peak viscosity although there was little effect on the mean value and no significant effect on the holding strength or final viscosity. The final temperature was also important in that lower temperatures gave more viscous gels. Provided that the desired cooling rate could be achieved, varying the cooling time had no effect on the peak or trough viscosities and only a very minor effect on the final viscosity. If final temperatures of 40°C or lower are to be used, the cooling conditions and final hold time would need to be adjusted so that maximum viscosity could be achieved. A proposal for a standard Rapid Visco Analyser (RVA) procedure is: at least 1 min at 50°C, heat to 95°C over 4 min, hold at 95°C for 4 min, cool to 50°C in 3 min, and hold at 50°C for 4 min. These conditions should minimize variation within samples and should allow a better comparison between samples.
Differential scanning calorimetry was used to evaluate the effect of storage at 10°C, 20°C and 30°C, and 40% and 65% relative humidity (RH) on adzuki bean starch gelatinisation and protein ...denaturation temperatures. Storage for 6 months at an elevated storage temperature (30°C) caused increases in the starch gelatinisation onset temperature (
T
o) and gelatinisation peak temperature (
T
p) for both Bloodwood and Erimo varieties. Storage at 40% RH resulted in higher
T
o and
T
p values than storage at 65% RH. The
T
o of starch from Bloodwood and Erimo beans stored for up to 1.5 months at 10°C and 65% were similar to those of fresh beans.
The changes in the salt-soluble protein component were less clear cut than those of the starch. Nonetheless, protein extracted from beans stored at 40% RH exhibited significantly lower
T
o and
T
p values compared with those stored at 65% RH. This indicates some destabilisation of the protein at the higher RH.
These results suggest that detrimental changes occur in starch and, to a lesser extent protein, of adzuki beans stored under unfavourable conditions. On the basis of these results, the best storage conditions to maintain the characteristics of fresh beans are low temperatures (e.g. 10°C) and high RH (e.g. 65%).
The old Hungarian wheat variety, Bánkúti 1201 was previously divided into lines on the basis of high molecular weight (HMW) glutenin subunit composition. In this work the starch properties of these ...lines were studied. The amylose contents of the lines ranged from 14.4% to 24.2%, which means a wide variation. The Rapid Visco Analyser (RVA) peak viscosity of the starch ranged from 232 to 372 Rapid Visco Units (RVU) and the enthalpy of gelatinisation (ΔH) measured by Differential Scanning Calorimetry (DSC) varied between 8.3 and 16.3 J/g. To study the relationship between the different lines on the basis of starch properties, Hierarchical Cluster Analysis was carried out based on RVA, DSC and HPLC results. Five groups of Bánkúti lines could be distinguished on the basis of these traits. According to the results, Bánkúti lines heterogeneous with respect to their HMW glutenin composition are also heterogeneous for their starch properties. Nevertheless, there was no correlation between the variability in protein composition and starch properties.
The electrophoretic analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE; reduced and unreduced) of fractions, collected from a size exclusion-high performance liquid ...chromatography (SE-HPLC) separation of gluten proteins using a column with pore size of around 400A, showed clear resolution for the seven elution ranges studied in two Australian bread wheat lines. Polymeric proteins - high molecular weight (HMW) glutenin subunits, low molecular weight (LMW) glutenin subunits, HMW albumins and some modified omega-gliadins - appeared exclusively in the region within the first peak of the chromatogram (fractions 1 to 5), the limit being a region that resolved as a small peak before the large peak of gliadins and where some omega-gliadins eluted. A larger proportion of HMW glutenin subunits and B subunits contributed to polymer formation of higher molecular weight. The polymer size decreased as the proportion of the other protein components increased.
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