Marcela Ross

Staling in starch bread: The effect of gluten additions on specific loaf volume and firming rate

Hypotheses on the role of gluten in bread staling range from gluten having an anti-firming effect, or no effect on firming, to gluten-starch interactions being essential for bread firming. To test these hypotheses, the firming rate of starch bread made from protein-free synthetic flour was compared with that of starch-gluten breads made from synthetic flours containing 1-15% gluten (Fig. I ). Only loaves of similar specific loaf volume and crumb moisture content were compared to eliminate these parameters as variables that might influence firming rate. The starch breads clearly increased in firmness up to six days, indicating that gluten was not essential to the firming process, starch alone causing bread to firm with time. The starch-10% gluten breads and starch-15 % gluten breads had very similar specific loaf volumes, moisture contents and firming rates to that of the starch breads. This indicates that protein possibly has some role in firming, because if only starch has a role in firming then adding gluten would effectively dilute the starch and reduce the rate of firming. We propose that increasing bread firmness results from glucan chains of partially leached amylose and amylopectin attached to swollen starch granules forming hydrogen bonds with other starch granules and, to a smaller extent, with gluten fibrils.

Distribution of Redox Enzymes in Millstreams and Relationships to Chemical and Baking Properties of Flour

ABSTRACT Millstream flours, bran, pollard, and germ fractions were prepared from two Australian and two New Zealand wheat cultivars using a pilot-scale roller mill. The distribution of six redox enzymes in milling fractions and the relationship of the enzymes to baking parameters were investigated. Lipoxygenase (LOX), dehydroascorbate reductase (DAR), and protein disulfide isomerase (PDI) tended to be higher in the tail-end fractions of break and reduction flour streams, but the highest levels were in the bran, pollard, and germ fractions. These enzymes had moderate to strong correlations with ash content of flour. These results indicated that a considerable amount of these enzymes in the tail-end flour streams were likely to be derived from contamination with bran, aleurone, or germ components of grain. Peroxidase (POX) tended to be higher in the break flours, but polyphenol oxidase (PPO) and ascorbate oxidase (AOX) tended to be evenly distributed in the millstream flours. These three enzymes generally h...

Amylase, falling number, polysaccharide, protein and ash relationships in wheat millstreams

Wheat of two strong high-protein and two weak low-protein cultivars from New Zealand and Australia were milled to commercial specifications. All millstreams were tested for α-amylase, β-amylase, falling number, protein, starch, damaged starch, amylose, amylopectin, pentosan and ash. The distribution of β-amylase in millstream flours was more variable among cultivars than α-amylase. Generally, both enzymes had lowest activity in sizing and early reduction flours. α-Amylase was very high in the bran, pollard and germ fractions, in which ash content was very high, whereas β-amylase was low in these fractions. These observations, together with the moderate correlation of α-amylase and poor correlation of β-amylase to ash content, suggest that most α-amylasein flour derives from contamination with bran, pollard and germ, whereas most β-amylase derives from the endosperm. Falling numbers varied between the cultivars, but variation amongst millstreams for each cultivar was low, except for cv. Frame, which had particularly high falling number values (834 and 1197) in second and third break flours. These two flours had some of the highest α-amylase levels and lowest starch levels. However, they also had very high protein content (22 and 26%) and very low starch damage (3.2 and 4.5%), which may contribute to the high falling numbers. When endogenous α-amylase in the flour with the highest falling number was supplemented with high levels of barleyα-amylase, the flour withstood the detrimental effects of α-amylasein baking (sticky crumb, poor crumb texture and loaf volume) better than flours of lower falling number, but did not withstand the effects ofα-amylase on falling number.

Distribution of glutathione in millstreams and relationships to chemical and baking properties of flour

ABSTRACT Fourteen millstream flours, a straight-run flour, bran, pollard, and germ were prepared separately from two Australian and two New Zealand wheat cultivars using a 650 kg/hr pilot roller mill. Glutathione (GSH) and oxidized glutathione (GSSG) were measured in all samples. The Australian cultivars had higher levels of GSH and GSSG than the New Zealand cultivars, and in all cultivars the levels in pollard and germ were considerably higher than in flour samples. Generally, the early break flours and early reduction flours had lower GSSH/GSSG levels than the tail-end break and reduction flours. There was a strong correlation between GSH/GSSG and ash content in millstream flours, which indicated that much of the GSH/GSSG in the flour was likely to have derived from contamination by bran, aleurone (pollard), and germ. There were also moderate to strong correlations between GSH/GSSG and the cysteine content of all proteins in flour. GSH/GSSG correlated strongly with the albumin and globulin content of fl...

Bran in bread: effects of particle size and level of wheat and oat bran on mixing, proving and baking

The effects of adding wheat and oat bran, at different levels and milled to varying particle size ranges, to dough formulations were investigated, with respect to aeration and dough development during mixing, expansion during proving and final baked loaf characteristics. Addition of bran reduced the density of the dough at the end of mixing, largely because of the increased water absorption, with bran particle size having little effect on dough density. Wheat bran substituted for flour at 7.5% increased the capacity of the doughs to expand during proving, but despite this the baked loaf volumes were lower, and even lower at 15%. Grinding the wheat bran had little effect on optimum work input, water absorption and expansion during proving, but gave slightly lower loaf volumes and a finer crumb texture. The low correlation between proving expansion and baked loaf volume suggested that the effects of the wheat bran in bread formulations occurred during baking. By contrast, adding oat bran reduced both the maximum expansion capacity of the dough during proving and the baked loaf volume, suggesting that the oat bran exerted its effects largely during proving. Grinding the oat bran gave lower optimum work inputs and higher water absorptions, and reduced both proving expansion and baked loaf volumes.

The Effect of Non‐Gluten Proteins on the Staling of Bread

As part of our studies on the mechanisms of bread staling, starch bread was used as a research tool that enables us to gain insights into the individual contributions that starch and gluten have on staling. Reconstitution experiments have demonstrated that bread of equivalent specific loaf volume stales at the same rate irrespective of protein concentration, or type of protein. However, other properties of bread, such as specific loaf volume, may be altered by specifically changing the protein component in the flour.

Expansion capacity of bran-enriched doughs in different scales of laboratory mixers

The dynamic dough density system, which simulates growth during proving of bread dough, was refined to enhance the accuracy and reproducibility of the technique. The system was then used to quantify the expansion capacity of doughs, as indicated by the minimum density achieved by a proving dough piece, in three different scales of geometrically similar laboratory dough mixers. The effects of bran level on dough expansion and baked loaf characteristics were investigated. Dynamic dough density measurements showed no difference in expansion capacity during proving from doughs mixed in the three scales of mixer. Bran at 7.5% flour substitution had no significant effect on the minimum density, but decreased loaf volumes compared with no bran. Addition of bran at 15% substitution decreased loaf volume further and also decreased the maximum expansion during proving, indicating that at this level bran exerts at least part of its effect in reducing loaf volumes during the proving stage of the breadmaking process. Baking scores were comparable for loaves baked from doughs mixed in the two larger scales of mixer, while specific loaf volume decreased as mixer scale decreased.