Leavened bread

Sauermachen, n. acidification, sauermachend, p.a. acidifying, s uem, v.t. acidify, acidulate sour leaven (bread). — v.i. sour. 

Both lipases and lipoxygenases are present in the bran and the germ. Phytases are nutritionally important as they liberate the phosphorus, of which approximately 70% is in the kernel bound to phytin. Phytin blocks the intestinal absorption of both iron and calcium. Phytase is also present in yeast, which is why leavened bread is nutritionally superior to unleavened bread. There have been concerns about the incidence of rickets among those of South Asian origin who eat chapattis, live in the UK, and have a tendency to keep their skin covered up from the sun. 

Presumably, at some point in history a batch of unleavened bread dough became contaminated with wild yeast and the first leavened bread was made. The only way in which such a system can be kept going is to keep back a portion of the old dough and add more flour and water to keep the fermentation going. In such a system various side-reactions occur and fatty acids start to be produced, hence the name. The acids give the dough some protection from contamination with undesirable moulds, which would be an advantage in a primitive society. 

Soda bread is a chemically leavened bread made in Ireland. Instead of yeast the bread is raised chemically using sodium bicarbonate. The traditional source of acid is buttermilk, which contains lactic acid. The use of cream of tartar is now more common. This prevents the bread becoming too alkaline. 

Yeast used to leaven bread and make beer and wine Moldy soybean curds used to treat boils (first antibiotic) Crops and livestock domesticated Powdered chrysanthemums used as first insecticide Microscope invented... 

Bioprocesses and Biotechnology Humans have used biologically based processes (bioprocesses) since they first made cheese, leavened bread, and brewed spirits. Bioprocesses are increasingly used to produce chemical products, and there is a whole world of potential biocatalysts to be discovered. 

It is unstable to heat, neutral or alkaline pH, and can be easily leached out of foods. Thiamin is destroyed by sulfur dioxide (often used as a food preservative), potassium bromate (oxidizing agent used in bread) and by sodium bicarbonate (in chemically leavened breads). 

Crust volatiles were isolated immediately after baking by extraction with dichloromethane and sublimation in vacuo ( ). Application of aroma extract dilution analysis 6) to the acid-free crust extract led to the detection of 31 odorants. After separation and enrichment, these compounds were identified by comparison of the MS/EI, MS/Cl and retention data on two columns of different polarity to reference compounds. Aroma quality was also assessed. The results of the identification experiments (Table I) revealed that 2(E)-none-nal (No. 1), followed by 2(E),4(E)-decadienal (No. 2) and 3-methyl-butanal (No. 3) showed the highest FD-factors in the crust of the chemically leavened bread. Additionally l-octen-3-one, 2(Z)-nonenal, 2(E),4(E)-nonadienal and an unknown compound with a metallic odor contributed high FD-factors to the overall flavor (For a discussion of FD-factors, see Chapter by Schieberle and Grosch, this book). 

The flavor compounds of the crust from the chemically leavened model bread were then compared to those recently identified (6) in the crust of a standard wheat bread which was leavened by addition of yeast (Table I). One striking difference was that Acp (No. 16), which showed the highest FD-factor in the yeast-leavened bread showed a very low FD-factor in the chemically leavened bread. This indicated, that the flour contained only minor amounts of the precursor (s) for the formation of Acp. On the other hand, 2(E),4(E)-decadienal, 2(E),4(E)-nonadienal, l-octen-3-one and 2(Z)-nonenal, which are undoubtedly formed by a heat-induced oxidative degradation of the flour lipids, became predominant odorants in the chemically leavened compared to the yeast-leavened bread. 

To reveal the contribution of yeast in the formation of the Acp the amount of Acp in a bread crust from yeast-fermented dough was compared to the amount present in the crust of a chemically leavened bread. The production of Acp was reduced from 34 jig/kg to 9.6 jug/kg flour when the yeast was replaced by a commercial leavening agent. 

The earliest tests of the phytate zinc molar ratio concept in humans was provided by data supplied by Reinhold (51, 52). He analyzed a large number of samples of Middle Eastern bread for phytate and zinc. These breads were of two types "Bazarl and Sangak" which are leavened breads sold in the urban areas and "Tanok" which is an unleavened bread consumed in the villages of the Middle East (Table III). For many of the villagers, "Tanok",... 

Zinc deficiency has been found among peasant populations in rural areas of the Middle East. Unleavened whole wheat bread can account for 75% of the energy intake in these areas, that is, Iran, Egypt, and Turkey. This diet, which does not contain meat, does contain zinc, but it also contains phytic acid at a level of about 3 g/day. The phytic acid inhibits zinc absorption. The yeast used to leaven bread produces phosphatases that hydrolyze the phosphate groups from phytic acid. 

The utilization of sugars by yeasts has long been turned to account in making leavened bread, wine, and beer. An early industrial exploitation of microbial biochemistry was the manufacture of glycerol during the First World War by the addition of sulfite to a fermenting mixture of yeast and sugar 7 9 for a review, see Ref. 10. Since then, a... 

Baked yeast-leavened bread Ferric ammonium citrate Ferrum redactum... 

Additional aroma components common to yeast-leavened bread are lower alcohols, acetaldehyde, propanal, pentanal, and furfural, and ethyl esters, such as ethyl acetate(19). 

Manufacturing processes can result in a substantial loss of the vitamin for example, during the milling of whole wheat to white flour, 75% of the folate is lost (B8). Bread was found to contain more folate than the flour fixim which it was made and this was due to the effect of the added yeast. Folate deficiency has been found to be relatively uncommon in Iran and this prompted Russell (R8) to measure the folate content of various Iranian breads since bread is the staple food in that country. They found village wholemeal bread to have a free folate concentration of 340 M.g/kg and leavened breads made... 

Compared with other subjects, chemistry is commonly believed to be more difficult, at least at the introductory level. There is some justification for this perception for one thing, chemistry has a very specialized vocabulary. However, even if this is your first course in chemistry, you already have more familiarity with the subject than you may realize. In everyday conversations we hear words that have a chemical connection, although they may not be used in the scientifically correct sense. Examples are electronic, quantum leap, equilibrium, catalyst, chain reaction, and critical mass. Moreover, if you cook, then you are a practicing chemist From experience gained in the kitchen, you know that oil and water do not mix and that boiling water left on the stove will evaporate. You apply chemical and physical principles when you use baking soda to leaven bread, choose a pressure cooker to shorten the time it takes to prepare soup, add meat tenderizer to a pot roast, squeeze lemon juice over sliced... 

The loaf of bread as we have it to-day represents the accumulated improvements of all ages and all peoples. The most important of all these improvements in bread-making no doubt was the introduction of the use of the leaven. We first hear of the art of leavening bread with yeast in Biblical times in Israel. 

A great variety of products are made from cereals. However, to keep the topic focused, we will concentrate on only one type of product aerated or leavened breads. Bread from wheat has been studied more extensively than other wheat products or the processing of other cereals. Much of the basic science developed in this area can, however, serve as a basis for other areas of cereal processing. 

Table IV shows the annual production of beikery foods in the United States. Yeast-leavened, bread-type products (bread, rolls, and sweet-goods) dominate the market, accounting for v- 70% of the total poundage. White pan bread is the single most important bakery food (Table V), and each one-pound loaf contains up to 1.4g added surfactant, or a total potential market in breadmaking of 90,000 lb day l (4.1 MT/day). Use of dough...

Other common applications of colloidal gases include solid foams, such as those occurring in the areas of food (leavened breads), geology (pumice stone, zeolites), manufacturing (polystyrene foam, polyurethane foam), and personal care... 

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