Dale Every

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.

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.

A comparison of bread baking, falling number, α-amylase assay and visual method for the assessment of pre-harvest sprouting in wheat.

A selection of wheat samples from the 1988 New Zealand harvest were analysed for sprout damage by visual assessment of grain, a highly standardized bread baking test, the falling number test and an α-amylase assay. The relationships between these methods were analysed and reasons for anomalous results discussed. The bake test defines six sprout-damage categories (S′1 to S′6) inclusive of sound wheat (S′1). Flour falling number and α-amylase assay clearly distinguished sound samples from S′3 to S′6 samples that would cause problems in a commercial bakery. Meal falling number was less reliable at distinguishing sprout-damage categories. The slightly sprout-damaged S′2 samples were considered to require a bake test and falling number or ′-amylase assay to estimate potential problems to bakeries. The visual method was an unreliable indicator of sprout-damage as assessed by the bake test. There was a good correlation between α-amylase activity and flour falling numbers above 62. Over the whole range of sprout-damage samples, α-amylase activity was about 1·5 times higher in the milling fraction containing aleurone and scutellum tissue than in the corresponding flour fraction. The former milling fraction had increased α-amylase activity when stored for 8 months, whereas the flour fraction had reduced activity when stored.

A simple, four-minute, protein-solubility test for heat damage in wheat

A simple, 4 min test for heat-damaged wheat has been developed primarily for use by mills at wheat intake. The test is based on the loss of solubility of proteins in heatdamaged wheat and uses a Coomassie blue G250 staining reagent to measure protein in saline extracts of wholemeal or white flour. Regression of protein solubility on percent heat-damaged wheat resulted in a high coefficient of determination for a wide range of wheat cultivars from several countries grown at various localities throughout the world. There appears to be a good linear relationship between the bread-baking quality of heat-damaged wheat (measuring by loaf volume) and the protein solubility test values for heat-damaged wheat. Bug-damaged wheat, sprout-damaged wheat, fungus-infected wheat and wheat of high or low protein content had values in the protein solubility test corresponding to sound wheats, that is, they did not give a false prediction of heat damage.

Quantitative measurement of protease activities in slab polyacrylamide gel electrophoretograms

Abstract A simple, rapid, and inexpensive method for the quantitative measurement of protease activity in slab polyacrylamide gel electrophoretograms is described. An electrophoretogram containing separated test samples and dilutions of a standard protease was placed in contact with a thin (0.7-mm) agar gel slab containing gelatin substrate. After 30 min incubation at 37°C, the unhydrolyzed gelatin was precipitated with saturated ammonium sulfate for 10 min. The developed substrate slab proteolytic zymogram was placed between two clear plastic sheets for analysis by densitometry at 525 nm. A standard graph of peak height in the densitometric scan against quantity of standard protease in micrograms or in proteolytic units was plotted. When measurements of a test sample were made in six independent experiments from the initial linear part of the standard curves the mean ± standard deviation was 3.2 ± 0.2 proteolytic units.

General proteinase assay by formation of SDS-protein gels of proteolyzed substrate proteins

A new approach to the assay of proteinases is described. The method relies on water-insoluble protein substrates, such as gluten and fibrin, which form expanded gels in the presence of sodium dodecyl sulfate (SDS) reagent. Powdered substrate is dispersed in buffer and aliquots are pipetted into long, narrow, 400-microliters tubes made of clear polypropylene. After the addition of enzyme and a period of incubation, a SDS reagent is added, the tubes are centrifuged, and the height of the SDS-protein gel is measured. Reduction of gel height gives a direct measure of enzyme activity. Salt concentration, pH, and incubation times must be consistent for both test and control reactions in order to obtain reproducible results. Examples of proteinases measured by this method are trypsin, chymotrypsin, elastase, pronase, papain, pepsin, an insect (Nysius huttoni) salivary proteinase, and wheat proteinase. The assay could detect enzyme in crude extracts or in purified form. In 1-h incubations, 10 ng of pepsin and elastase or 20 ng of purified insect proteinase could be detected. The assay was simple, fast, economical, and sensitive.

A new method of sample application for horizontal slab polyacrylamide gel electrophoresis

Abstract A new method of sample application for horizontal slab polyacrylamide gel electrophoresis has been developed which solves the main problems associated with existing systems. A quick, simple procedure is described for placing a dry powder mixture of Celite and Sephadex into sample wells of any shape cut to the full depth of the gel slab. Samples can then be added to the powder to form a moist firm bed of material in the wells which prevents leakage of sample from the well. The method enables the quantitative electrophoresis of many samples with widely differing concentrations and volumes without the problems of electrodecantation, loss of electrical contact through the wells, or uneven penetration of sample through the full thickness of the gel.

Purification of individual proteinase isozymes from Bacteroides nodosus by use of polyacrylamide gel electrophoresis, a fluorogenic substrate detection system, and a simple electroelution apparatus

Abstract A method is described for the purification from Bacteroides nodosus of five individual proteinase isozymes which could not be purified by column chromatography techniques. The isozymes were separated by horizontal slab polyacrylamide gel electrophoresis. Their exact location within the gel was determined with a fluorescein-casein substrate, and they were extracted from the gel by a simple electroelution apparatus. In a typical purification, microgram quantities of three individual isozymes were recovered free of other isozyme activities. The other two isozymes were each contaminated (