Bread moisture content

Stale bread tastes and feels dry, even though the moisture content is actually the same as in fresh bread. The recrystallization of the starch in bread is what makes it go stale. To combat this, fats and oils are added to bread to form a complex with the starch in its gelled form, slowing down the recrystallization process and keeping the starch in its flexible gel form. 

It should be appreciated that a high level of starch damage is not essential in bread. French bread is made from soft wheat flour with a low starch damage. Starch damage is generally undesirable in biscuits. In biscuits the product is cooked to a very low moisture content so binding in water is undesirable. 

The bread making properties of ordinary white bread flour improve for some time after manufacture, which is the origin of oxidative flour treatments. The shelf life of such a flour is around a year. If the moisture content can be kept low, either by selecting low moisture wheat or by drying wheat, the shelf life can be increased to three years. This sort of flour is supplied for ship s stores and similar purposes. This is the modern alternative to ship s biscuits. 

Typically, sorption isotherms are constructed for a single food ingredient or food system. An alternative approach is to plot the moisture content versus water activity (or relative vapor pressure) values for a variety of as is food ingredients and food systems. The result is a composite food isotherm (Figure 17). The composite isotherm fits the typical shape observed for a sorption isotherm for an individual food system, with a few products falling above or below the isotherm curve (chewing gum, honey, raisins, bread, and colby and cheddar cheeses). Slade and Levine (1991) were the first to construct such a plot using moisture content and aw values from van den... 

The moisture content of bread is very vanable and increases with the volume of the loaf, in bread well made and well baked and of the usual size and shape it should not exceed 30-35%... 

Thermo-mechanical analysis (TMA)26 and DMTA292 have been used to study the viscoelastic properties of bread, a composite two-phase system. The moisture dependence of Tg was similar to that of pure amorphous starch and gluten.242,282 293-295 At the moisture content of bread, water exerts its full plasticization effect on the composite polymer matrix, reducing the effective Tg to about -10° to - 12°C,26,292 well below normal shelf life storage temperatures of this product. 

Figure 8.16 Effect of moisture content on retrogradation kinetics of starch in starch gels or bread 1 wheat starch gels stored at 4°C for 14 days 175 2, 3 and 4 correspond to wheat starch gels, bread and bread with 0.5% monoglyceride, respectively, stored at 25°C for seven days.178...

Another laboratory invoked the role of water in bread staling involving a zipper mechanism that results in the formation of interchain crosslinks 492 Moisture redistribution from crumb to crust played a significant role in crumb firming and amylopectin recrystallization for breads stored for more than seven days 493 According to Piazza and Masi494 to inhibit staling it is more important to slow the dehydration phenomena than it is to increase the initial moisture content in the bread. 

The caloric behavior of water has been studied by Riedel (1959), who found that water in bread did not freeze at all when moisture content was below 18 percent (Figure 1-16). With this method it was possible to determine the nonffeezable water. For bread, the value was 0.30 g per g dry matter,... 

A mould inhibitor in the form of sodium propionate was incorporated into films of cellulose acetate, the films were sandwiched between slices of bread and the sliced bread packed in LDPE bags and stored for 15 days at about 25C. The effect of the mould inhibitor on mould growth on the surface of the bread slices was investigated by means of microbiological analysis and water activity, moisture content and pH analyses. The presence of sodium propionate in the cellulose acetate films was found to have an inhibitoiy effect on microbial growth on the bread. 12 refs. 

Type of agent High fat content (butter, fats, cheese, meat, bacon, and shell eggs, etc.) Low fat, high moisture content (fruit, vegetables, sugar, salt, etc.) Low fat, low moisture content (cereal, tea, coffee, flour, bread, rice, etc.)... 

Maleki, M., Hoseney, R.C., and Mattem, P.J. 1980. Effects of loaf volume, moisture content and protein quality on the softness and staling rate of bread. Cereal Chem. 57, 138-140. 

Several applications can be found in literature regarding the use of NIR for the paediction of the main physical and rheological parameters of pasta and bread. De Temmerman et al. in 2007 proposed near-infrared (NIR) reflectance spectroscopy for in-line determination of moisture concentrations in semolina pasta immediately after the extrusion process. Several pasta samples with different moisture concentrations were extruded while the reflectance spectra between 308 and 1704 ran were measured. An adequate prediction model was developed based on the Partial Least Squares (PLS) method using leave-one-out cross-validation. Good results were obtained with R2 = 0,956 and very low level of RMSECV. This creates opportunities for measuring the moisture content with a low-cost sensor. 

Typical equilibrium moisture contents of some food materials at approximately 298 K (2j C) (/) macaroni, (2) flow, (J) bread, (4) crackers, (5) egg albundn. [Curoe (5) from ref (El). Curves (/) to (4) from National Research Council, International Critical Tables, Vol. ll. New York McGraw-Hill Book Company, 1929. Reproduced with permission of the N ational Academy of Sciences. ... 

A word about reporting data for nutritional purposes. When materials with high moisture content, such as fresh fruits and vegetables, meat, fish, or cooked items, such as canned peas, or even breads, are to be used in formulation of diets or feeds, the composition may have to be reported on an as-is basis with respect to moisture content. For example, the protein content of peas is well known to be about 27 to 30% on a moisture-free basis. But nothing or no one eats dry peas — they are much too hard, and they are cooked before eating. The moisture content of cooked peas is about 67%, so the protein content of the peas as they are actually eaten is reduced to about 9 to 10%. This is the contribution that the peas make to the diet, where the diet or animal feed is to be prepared to contribute a certain amount of protein, etc. per day. 

Combined mechanical (DMA) and DSC studies on moist bread [156] showed that the tan 8 and E curves spanned a temperature range of 50°C in the ice-melting region. DSC results showed that freezable water was present at > 33% moisture content. At lower moisture contents the transitions began to move to higher temperatures and broaden. 

DMA has been used by Hallberg and Chinachoti [143] to determine the glass transitions responsible for the mechanical firmness of bread, namely the effective network 7 g, at various moisture content and storage time in a shelf-stable bread for 3 years (see Figure 26). 

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