In developing countries like Nigeria, bread consumption has increased since 1970 due to appetite to eat and increase in the population. Nevertheless, people are constantly searching for easy, convenient and rather inexpensive means of taking food in a hygenicaly prepared, ready to eat baked food with high caloric value (Nut, M.J.R 1979) taste panel evaluation of bread culled from proceeding of the launching and first annual conference of Nigeria institute of food science and technology. Modification and improvement in food production including bread making has led to 50% in bread consumption in the entire world population especially in Britain, America and European countries. Murray et al (1970) defined bread as a well known article of food prepared by moistening, kneading and baking meal or flour, generally with the addition of yeast.
Raw materials for production of bread are of two major groups; compulsory and the optimal among the compulsory group are flour, water, yeast and salt while the optimal comprises of milk, sugar, eggs, fats, improvers, preservatives.
Physicochemical change (e.g staling, firming) and microbiological spoilage (e.g ropiness, mold growth) markedly reduce the shelf-life of bread. Attempts have been made to improve the keeping quality of bread either by varying the product formulation (Lude WIG 1989 or Tola et al, 1989) processing (salovaara and valjakka, 1987) or packaging conditions (knorri and tomlins, 1985, ortala et al 1989). The addition to the dough of compounds associated with desired characteristics and good bread keeping quality (Barber et al, 1992, Gobbet, et al, 1995a). The limited knowledge of the physicochemical changes involved in the mechanisms of bread staling and the economic importance of a longer keeping quality make this subject of great interest. Gluten and its ratio with starch were decisive, factors in bread firmness with great influence on elastic changes during bread storage (Benecki, 1982). Variations of water activity and moisture contents In the near-crust area also influence bread stalling and firmness (Czuchajowska and Pomeranz, 1989) spontaneous sourdough with low pH and a high ratio of lactic and acetic acids produce breads with the highest volumes and lowest rates of staling during storage (Barber et al 1992). The level of native lipids in intact flour was enhanced by shortening and was effective in decreasing firmness. (Rogers et al 1988) changes in the ratio of amylose to amylopectin by adding waxy barley starch to a high-product in wheat flour resulted in softer bread one day after baking or after reheating (Ghiasi et al, 1984) low level treatments with a – amylases from different sources increased the water binding capacity and gelatinization temperature of starch as well as the break baking quality (Kuracina et al, 1987) physical methods like crumb firmness and elasticity evaluation (Berglund and Shelton, 1993) and calorimetry analysis of starch changes during staling (Zeleznak and Heseney 1987) have also classically been to study storage changes.
Use of sourdough produces bread or baked goods indicated to have more flavour, and improve rheology and storage characteristics over products obtained using baker’s yeast (Spicher, 1983, Rocken 1996) sourdough lactic acid bacterial (LAB) and yeast have been shown to compete for carbon sources which influence acid production by bacteria (Gobbette et al, 1994) Homo and hetero fermentative LAB have been extensively evaluated for acidification properties, production of volatile compounds and proteolysis have shown great differences among and within species (Gobbetti et al, 1995b, c, 1996a, Domiani et, al, 1996) mixed freeze dried starter formulations have been prepared to overcome some difficulties of sourdough handling (Martinez- Anya et al; 1993 Cossignani et al 1996). Sourdough lactic acid bacteria (LAB) have been shown to inhibit or delay microbial spoilage thus improving bread shelf-life (Spicher, 1983).
Acidification of the dough, proteolysis of gluten and moderate hydrolysis of starch are LAB activities which vary among sourdough strains and which may affect the physiochemical changes throughout bread shelf-life. No studies have been reported on the effect of different sourdough starters on bread staling, our objectives was to study various association of LAB and yeast starters and their influence on the kinetics of sourdough bread firmness and stalling.
The aim of this study was to assess the interactions between saccharomyces cerevisiae and lactic acid bacteria that either form a stable consortium in greek wheat sourdoughs (ie. lactobacillus sanfransiscensis and L. brevis). Lactic acid bacteria increases the nutritional content like the vitamins present and also helps bread to ferment also used as preservatives while saccharomyces helps the bread to rise. On the other hand, the presence of s. cerevisiae favoured mannitol and acetic acid production had a species dependent effect on maximum specific growth rate and had no effect on final cfu/g sourdough and lactic acid production by the lactic acid bacteria and at the same time caused the depletion of glucose, fructose and maltose.
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