Bread enzymes

FIGURE 15.13 Type 1 and type 2 MetAPs ( pita-bread enzymes), (a) E. coli MetAP-1 (b) P. furiosis MetAP-2 (c) human MetAP-2. In contrast to the type 1 enzymes, type 2 MetAPs contain an a-helical subdomain (orange) inserted within the catalytic domain (cyan and green a-helices and p-strands, respectively). (From Lowther Matthews, 2002. Reprinted with permission of the American Chemical Society.)... 

Consumers enjoy soft bread. To ensure high-quality bread, enzymes are often used to modify the starch that in turn keeps the bread softer for a longer period of time. 

When you eat starchy foods, they are broken down into glucose by enzymes. The process starts in your mouth with the enzyme amylase found in saliva. This explains why, if you chew a piece of bread long enough, it starts to taste sweet The breakdown of starch molecules continues in other parts of the digestive system. Within 1 to 4 hours after eating, all the starch in food is converted into glucose. 

Sodium propionate is also often used as an antifungal agent. Calcium is often preferable to sodium, both to reduce sodium levels in the diet and because calcium ions are necessary for the enzyme a-amylase to act on the starches in bread, making them available for the yeast, and improving the texture of the bread. Stale bread is caused by the starch amylose recrystallizing. The enzyme a-amylase converts some of this starch to sugars, which helps prevent recrystallization. 

Calcium propionate is often preferred as an antifungal agent, to reduce sodium levels in the diet, but also because calcium ions are necessary for the enzyme a-amylase to act on the starches in bread,... 

Levels of the enzyme a-amylase in wheat grains also affect breadmaking quality. Flour for bread-making requires low levels of a-amylase and this is favoured by a dry ripe dormant grain. The Falling Number (Hagberg) Test is used to determine a-amylase levels. A... 

Caballero PA, Gomez M and Rosell CM. 2007. Improvement of dough rheology, bread quality and bread shelf-life by enzymes combination. J Food Eng 81 42—53. 

There are a few areas in the subjects covered by this book where unfortunately the same words or are used to describe different things. They are gluten and flour improver. In food law a flour improver would cover a substance added to flour to improve its performance, usually in bread. Such a substance is ascorbic acid. In a bakery, the expression flour improver covers a mixture that is added to the dough. In this context a flour improver will contain not only substances like ascorbic acid but also, for example, enzyme active soya flour, emulsifiers and possibly fat. 

The enzymes in wheat, and hence in flour, that often cause problems in the bakery are present in the seed to make nutrient available to the seed. Similarly, this is why sprouted wheat causes problems if it is allowed to get into flour. Thus, the a-amylase is low in mature wheat grains but rises rapidly on germination. In bread, a low, but not too low, level of a-amylase is desirable since it produces sugars to feed the yeast and opens up the structure. Deliberate additions of malt flour were once common, but are now rarely made, to increase the amylase level. 

An overdose of malt flour will introduce too much enzyme activity in the dough, potentially reducing the product to a sticky syrup. Fungal a-amylase is now much more commonly used than malt flour. However, some malt flour is still used, particularly in wholemeal bread. 

Soy beans are another crop that will not grow in Europe. The soy bean is used as a source of both protein and vegetable oil. Enzyme active soy flour has been used in bread since the 1930s. The flour contains a lipoxygenase system that assists with the development of the dough and slightly bleaches the bread. Soy flour is classed as an ingredient rather than an additive. 

Yeast Fermenting in Dough. When yeast is in a bread dough the traces of sugars present can be fermented directly. As yeast contains the enzyme invertase, any sucrose present can be inverted into dextrose and fructose which can then be fermented. If any dextrose from a high DE glucose syrup is present then it can be directly fermented. If there is any lactose present it can not be fermented at all. Similarly, any polyols such as sorbitol can not be fermented. 

Barley and Oats. While barley and oats do not have any bread making properties they can be added to bread. Obviously introducing amyl tic activity with the barley is to be avoided. Similarly, oats can introduce undesirable enzymic activity. Originally, oats and barley found their way into bread because of shortages now oats are likely to be incorporated into bread because they are believed to be healthy. 

In view of the above it is very difficult to predict the future however, here is an attempt. It is reasonable to suppose that the development of biotechnology will lead to still more enzymes being used in baked products. This could lead to a rapid biochemical system that would replace the Chorleywood bread process with a rapid enzyme-based dough development system. 

Suppose we start with a starch-rich meal, say one containing a lot of pasta or bread. The digestion of starches begins in the mouth. Saliva contains an enzyme, salivary amylase (aka ptyalin), which catalyzes the conversion of starch to simple sugars such as glucose. This process is completed in the small intestine under the influence of other enzymes in the amylase class. This completes the first phase of carbohydrate catabolism the conversion of complex, polymeric carbohydrates (e.g., starches) to their simple monomeric units, the sugars. 

Chemical reactions enhanced by catalysts or enzymes are an integral part of the manufacturing processes for the majority of chemical products. The total market for catalysts and enzymes amounts to 11.5 billion (2005), of which catalysts account for about 80%. It consists of four main applications environment (e.g., automotive catalysts), 31% polymers (e.g., polyethylene and polypropylene), 24% petroleum processing (e.g., cracking and reforming), 23% and chemicals, 22%. Within the latter, particularly the catalysts and enzymes for chiral synthesis are noteworthy. Within catalysts, BINAPs [i.e., derivatives of 2,2 -bis(diphenylphosphino) -1, l -bis-l,l -binaphthyl) have made a great foray into chiral synthesis. Within enzymes, apart from bread-and-butter products, like lipases, nitrilases, acylases, lactamases, and esterases, there are products tailored for specific processes. These specialty enzymes improve the volumetric productivity 100-fold and more. Fine-chemical companies, which have an important captive use of enzymes, are offering them to third parties. Two examples are described here ... 

ROOZEN ET AL. Use of Enzyme-Active Soya Flour in White Bread... 

In many countries additives are forbidden in bread, except aromas in, for instance, fruit-flavored bread. Natural additives like enzyme active soya flour get only little attention for application in bread improvers because ... 

As discussed, addition of enzyme active soya flour changes the composition of volatile compounds of white bread. In its practical application as a bread improver component, the soya lipoxygenase isoenzymes are sufficient stable for 5 months to meet the bleaching requirements. 

Bitterness mechanism, 28 receptor model, 29,31/,34,35/ receptor structure, 161,162/ similarity to sweetness perception, 31/ Bread, white, use of enzyme-active soya flour, 192-198... 

Flour, soya, enzyme-active, use in making white bread, 192-198 Food(s)... 

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