Dear Label_Name,

Greetings! I hope you are well.

I am writing on behalf of an international publishing house, Science and Education Publishing, USA (http://www.sciepub.com).

Science and Education Publishing (SciEP) is a multidisciplinary open access publisher of Journals covering the fields of Science, Technology and Medicine. All SciEP publications are subject to high-quality peer review, editorial and production processes and are freely available online.

Welcome to the April, 2013 edition of SciEP newsletter, providing monthly summaries of articles on science & education related topics of interest to scientist and professionals. The mission of our journals is to provide an open access forum for publishing new findings on issues pertinent to scientific and academic field. We also invite you to submit original research papers, review articles, short reports, or case studies are considered for publication in our Multidisciplinary Journals.

American Journal of Public Health Research
DOI: 10.12691/ajphr-1-1-3

The Implementation of a Tele-Homecare System with Service Oriented Architecture and HL7 Message Transmission Standard
Ching-Sung Wang

American Journal of Medical and Biological Research
DOI: 10.12691/ajmbr-1-1-2

The Influence of Ethanol on Pyruvate Kinases Activity in Vivo, in Vitro, in Silico
Lelevich Sergey Vladimirovich, Khrustalev Vladislav Victorovich, Barkovsky Eugene Victorovich, Shedogubova Tatyana Aleksandrovna

American Journal of Medical Sciences and Medicine
DOI: 10.12691/ajmsm-1-1-1

Clinical and Histological Features in Wegener Granulomatosis
Li Cavoli Gioacchino, Passantino Rita, Bono Luisa, Tortorici Calogera, Ferrantelli Angelo, Giammarresi Carlo, Rotolo Ugo

American Journal of Infectious Diseases and Microbiology
DOI: 10.12691/ajidm-1-1-2

The Curse of Lymphatic Filariasis: Would the Continual Use of Diethylcarbamazine Eliminate this Scourge in Papua New Guinea?
Anne Lanham, Lillian Mwanri

We have released issues of some journals on February 2013.
American Journal of Public Health Research
American Journal of Medical Sciences and Medicine
American Journal of Medical and Biological Research
American Journal of Pharmacological Sciences
American Journal of Clinical Medicine Research
American Journal of Nursing Research
American Journal of Cancer Prevention
American Journal of Medicine Studies
American Journal of Infectious Diseases and Microbiology
American Journal of Cardiovascular Disease Research
American Journal of Biomedical Research
American Journal of Mechanical Engineering
American Journal of Microbiological Research
Journal of Preventive Medicine
American Journal of Food and Nutrition
American Journal of Hypertension Research
American Journal of Sports Science and Medicine
Journal of Cancer Research and Treatment
American Journal of Zoological Research
Journal of Biomedical Engineering and Technology
American Journal of Microbiological Research
Biomedical Science and Engineering

We are pleased to announce that submissions are now being accepted for peer review for all the journals across all our subject areas in SciEP.

Please submit your manuscript via our online submission system:
http://www.sciepub.com/author/signin

To unsubscribe from our mailing list, please click on the following link: unsubscribe

I am looking forward to hearing from you.

Kind regards,

David Rain
Email:join@sciepub.com
Science and Education Publishing (http://www.sciepub.com)

Effect of Sourdough on Shelf Life, Freshness and Sensory Characteristics of Egyptian Balady Bread

Sobhy. M. Mohsen, Mohamed H. Aly, Afaf A. Attia, Dalia B. Osman*

Bread and Pasta Department, Food Technology Research Institute, Agricultural Research Center, Giza, Egypt

Abstract: The present study was aimed to improve the quality characteristics of Egyptian balady bread by using sourdough containing (2% Saccharomyces cerevisiae+ 1, 2 or 3% Lactobacillus plantarum). Microbial contents i.e. lactic acid bacteria, total bacterial count and yeasts, pH, organic acids and antimicrobial activity were evaluated during sourdough fermentation. Results showed an increase in organic acids, antimicrobial activity and reduction in pH during the preparation of different sourdough samples. These metabolites were increased by increasing lactic acid bacteria ratio in sourdough (3%> 2%> 1% Lb. plantarum). A significant reduction in total bacterial count and a significant increase in LAB and yeast count during fermentation period was recorded. Bread characteristics showed an extension of shelf life for 8 days for bread samples containing sourdough (2 or 3% Lb. plantarum) comparing to 3 days for control bread. Addition of 20% sourdough containing 2 or 3% Lb. plantarum to wheat flour dough also retarded staling rate by 19.98% and 19.30% after 3 days comparing to control sample was (42.84%). Improvements in sensory characteristics and acceptability of balady bread were also recorded. Accordingly, this could reduce the bread losses and consequently reduce the amount of wheat flour used.

Keywords: sourdough, lactic acid bacteria, antimicrobial activity, organic acids, shelf life, staling and sensory evaluation

Citation: Sobhy. M. Mohsen, Mohamed H. Aly, Afaf A. Attia, Dalia B. Osman, Effect of Sourdough on Shelf Life, Freshness and Sensory Characteristics of Egyptian Balady Bread. Journal of Applied & Environmental Microbiology, 4 (2). 39-45. January 2016. doi:10.12691/jaem-4-2-3

1. Introduction

Bread is generally viewed as a perishable commodity. It is one of the main staple foods consumed by humans. Its shelf life is limited by two main factors, i.e. staling and microbial spoilage (fungi spoilage and ropiness) [1] and [2].

A common trend of sourdough fermentation is the unique symbiosis of certain hetero and homo fermentative lactic acid bacteria with certain yeasts. The interaction of yeasts and lactobacilli is important for the metabolic activity of sourdough. Several yeasts have been found in sourdoughs but Saccharomyces cerevisiae is considered the dominant organism for bread leavening. The most relevant bacteria isolated from sourdough belong to the genus Lactobacillus. The rheology, flavor, nutritional and functional properties of sourdough based baked products greatly rely on the activity of these microorganisms. Lactic acid bacteria usually originate from either the flour, dough ingredients or the environment [3,4,5,6].

The use of the sourdough process as a form of leavening agent is one of the oldest biotechnological processes in food production that used for thousands of years and generally regarded as safe (GRAS). Traditional acidic sourdough is ancient way to improve flavor, texture and microbiological shelf life of bread used in Mediterranean countries [1].

Lactic acid bacteria to yeast ratio in sourdough are generally 100:1 [7]. Sourdough has been classified into three types, i.e. the first type produced with the traditional technique characterized by continuous daily refreshment to keep the microorganisms in an active state, Type II often use dough souring supplements during bread preparation and are characterized by long fermentation periods (from 2 up to 5 days) and fermentation temperature > 30oC to speed up the process. The third type is a dried product that increases the sourdough shelf life [8,9].

Most of the beneficial properties attributed to sourdough were determined to be due to the acidification activity of lactic acid bacteria (LAB) and the produced metabolites i.e. organic acids, exopolysaccharides (EPS) and enzymes. Sourdough LAB fermentation created an optimum pH for the activity of the endogenous enzymes (amylases and proteases)that improve the loaf volume; delaye starch retrogradation and bread firming, inhibit ropiness by spore-forming bacteria and enhance flavor [10-21].

Growth of B. subtilis and Bacillus lichenformis was inhibited by Lb. plantarum VTT in tests with wheat bread. Rope spoilage of wheat bread was inhibited by adding 20- 30 g sourdough/ 100 g of wheat dough containing Lb. plantarum [12].

[22] Stated that, bacteriocin produced by Lb. plantarum has broad spectrum of inhibition against both pathogenic, food spoilage organisms and various lactic acid bacteria.

It has been reported that the antifungal activities of LAB might include reuterin, plantracin, hydroxyl fatty acids, proteinaceous compounds, cyclic peptides, 3-phenyllactic acid, caproic acid, diacetyl and hydrogen peroxide [17,23,24].

[25] Found a gradual increase in all organic acids concentrations during fermentation of sourdough starter (mixed culture of Lb. plantarum and S. cerevisiae). He observed that the rate of development of organic acids production was lower in yeast fermentation compared to other types of doughs containing LAB. The improved microbial shelf life of sourdough was initially attributed to the organic acids produced by LAB. Also, lactic acid bacteria had a fungistatic effect that attributed to acetic acid production [26].

The starter sourdoughs including LAB have greater antimicrobial activity against saprophytic microorganisms: Bacillus subtilis, B. mesentericus, Aspergillus niger, Penicillium sp. and Rhizopus sp., but none of them inhibited the growth of the baker’s yeasts Saccharomyces cerevisiae. It was established that addition of 10% of sourdough could prevent bacterial spoilage during bread making. While for prevention of mold spoilage the necessary amount of starter sourdough was from 15- 20%.The application of the developed starters in wheat bread guaranteed longer shelf life with no adverse alterations in the features of the final bread [27,28].

The present study was carried out to evaluate the quality of balady bread as affected by the addition of sourdough containing S. cerevisiae and Lb. plantarum. In addition, identifying the produced metabolites (organic acids and other antimicrobial compounds) and their effect on shelf life, freshness and sensory characteristics of the produced balady bread was also evaluated.

2. Materials and Methods

2.1. Wheat Flour (Triticumaestivum L. Vulgare)

Wheat flour, 82% extraction was obtained from South Cairo Mills Company, Faysal, Giza, Egypt.

2.2. Microorganisms and Media

Pure cultures of Lactobacillus plantarum ATCC 14917., and Saccharomyces cerevisiae ATCC 4126 obtained from Microbiological Resource Center (Cairo – MIRCEN), Faculty of Agriculture , Ain Shams University, Cairo, Egypt were used.

The referenced microorganisms i.e. Aspergillus niger RCMB02317, Penicillium italicum RCMB 03924, Candida albicans RCMB o5031, Geotaricum candidum RCMB 05097 and Fusarium oxysporum RCMB 08213.Three Gram positive bacteria (Staphylococcus aureus RCMB 010028, Bacillus subtilis RCMB 010067 and Enterococcus faecalis RCMB 010068) and three Gram negative bacteria (Pseudomonas aeruginosa RCMB 010043, Escherichia coli RCMB 010052 and Salmonella typhimurium RCMB 010072), obtained from the Regional Center for Microbiology and Biotechnology, Al Azhar University, Cairo, Egypt, were also used. Strains were propagated as follows: S. aureus, E. faecalis, E. coli and S. typhimurium were cultured in a nutrient agar media at 37°C; P. aeruginosa cultured on the same medium at 28°C and B. subtilis were grown in (BHI) broth (Oxoid) at 30°C. All fungi were cultured on YM medium at 25°C.

2.3. The Proximate Chemical Analysis

Moisture, ash, crude fiber, lipids and crude protein (NX 5.71) and carbohydrates content of wheat flour was carried out according to [29].

2.4. Preparation of Sourdough Starters

Yeast strain (Saccharomyces cerevisiae) and (LAB) Lactobacillus plantarum were grown on Yeast Malt (YM) broth and MRS broth (Formula developed by Man. Rogosa and Sharpe to facilitate the growth of lactobacilli in general [30], respectively, at 30ºc for 24 h. The cells were harvested by centrifugation (Sigma 3K12, 5000 xg, 10 min) and washed twice with sterilized distilled water. Under these conditions 1g of either yeast or LAB pellet contained ≈ 10⁶ and 10⁹ cfu respectively, and theses were used for preparation of sourdough starters. Sourdough starter was prepared according to the methods described by [31] as follows:-Wheat flour (400 g) and various amounts of starter culture (w/w based on flour bases as (2% S. cerevisiae (S); 2% S. cerevisiae+ 1%Lb. plantarum (SL1); 2% S. cerevisiae+ 2% Lb. plantarum (SL2) and 2% S. cerevisiae+ 3% Lb. plantarum (SL3))were mixed with 200 ml sterilized tap water, for 5- 10 minutes, and left for 24 h. The prepared sourdough starters were added to bread dough at (20% w/w wheat flour), control bread were made with baker’s yeast as a leavening agent without using sourdough starter.

2.5. Microbiological Analysis

Sourdough samples were analyzed at time points i.e. zero, 6, 12, and 24 h during fermentation period for total bacterial count (TBC), yeast and lactic acid bacteria (LAB) count). Total bacterial and fungal count of balady bread loaves were also determined during storage periodically i.e. zero, 1, 2, 3, 4, 5, 6, 7 and 8 days according to [32].

2.6. Sourdough Acidity and Organic Acids

Sourdough pH was determined by a pin electrode of a PH meter [5]. The organic acid contents of sourdough i.e. lactic, acetic, pyruvic, citric, mallic and formic were determined and quantified by HPLC apparatus (Hewlett Packard, series 1050) according to the method described by [33].

2.7. Determination of Sourdough Antimicrobial Activity

The ability of sourdough starter (Lb. plantarum strain) to produce antimicrobial metabolites was tested by an agar diffusion assay as described by [34] and [22], sourdough centrifugated at 6400 rpm for 15 min, the cells is removed. To eliminate the inhibitory effect of lactic acid and H₂O₂, the cell- free supernatant was neutralized with 1 M NaOH and treated with catalase enzyme (1mg ml ⁻¹), followed by filtration through a cellulose acetate membrane filter with pore size 0.22 μm (ADVANTEC MFS, Inc., Japan). The resulting is referred to as a crude bacteriocin.

The referenced fungi were cultivated in an incubator at 25°C on yeast malt (YM) media for 3-7 days, whereas referenced bacteria were propagated for 3 days on optimal temperatures. Spores and cells were harvested from slants after growing to prepare inoculums containing ~ 10 ⁵spores/ cells ml⁻¹ of fungi and ~ 10 ⁵ cells ml⁻¹ of bacteria. A 100μl of the indicator strain was poured into Petri dishes and overlaid with soft agar medium cooled to 45oC and mixed. Sourdough supernatant (50μl) was added to each well (6mm in diameter) punched in the cooled agar plates and incubated for 48 h at the optimal growth temperature. The antimicrobial activities were determined by measuring the inhibition zones (mm).

2.8. Balady Bread Making

Balady bread was prepared according to the method described [35].

2.9. Alkaline Water Retention Capacity (AWRC %)

The staling rate of balady bread was determined by alkaline water retention capacity method as described by [36].

2.10. Organoleptic Evaluation of Balady Bread

Fresh samples of balady bread loaves were organoleptically evaluated for i.e. crust color, crust characteristics, crumb color, grain and texture, flavor and taste and chewing as illustrated in Figure 1 according to [37].

Figure 1. The score sheet used by the panelists for sensory evaluation of Egyptian balady bread [37]

2.11. Statistical Analysis

Data were handled by Analysis of Variance using General Liner Model (GLM) procedure according to the procedure reported by [38]. Means were separated using Duncan's test at a degree of significance (P≤ 0.05). Statistical analyses were made using the producer of the SAS soft ware system program [39].

3. Results and Discussions

Chemical composition of wheat flour show that it contained 12.1% moisture, 1.24% ash, 1.13% lipids, 11.59% crude protein, 1.18% crude fiber and 84.69% carbohydrates.

3.1. Sourdough Characteristics

3.1.1. TBC, Yeast and LAB Count

Results in (Table 1) show a highest significant reduction rate of (TBC) in sourdough containing 2% S. cerevisiae+ 3% Lb. plantarum (SL3). Such reduction in TBC could be due to the increase in the produced metabolites, such as organic acids and bacteriocins as well as the decrease in pH (Table 2) that inhibited the growth of the spoilage flora. The above mentioned results are similar with those reported by [40] and [25].

Table 1. Yeast, lactic acid bacteria, total bacterial counts (log ₁₀cfu g ⁻¹) during sourdough starter preparation

The yeast count in sourdough samples were significantly increased by increasing the fermentation period, and the yeast count also increased in the mixed culture of S. cerevisiae with Lb. plantarum. The highest number of yeasts was recorded in sourdough containing 3% Lb. plantarum (SL3). This indicates that the incorporation of Lb. plantarum enhanced the growth of S. cerevisiae during the fermentation of sourdough [40].

Results in (Table 1) also show that sourdough samples prepared by using only S. cerevisiae contained LAB as a normal flora but lower numbers than those for the other treatments. In sample (SL3) LAB counts were significantly increased from9.01 log cfu/ g at the beginning of the preparation to 11.64 log cfu/ g at the end of the preparation period [25,41,42].

3.1.2. Organic Acids and Acidity of Sourdough

Results in Table 2 show the different organic acids formed during the preparation of sourdough. In case of the (S) sample containing only S. cerevisiae, all organic acids i.e. citric, formic, acetic, malic, pyruvic and lactic were almost produced almost at the same concentrations. The highest values of all determined organic acids were found in sourdough samples SL 3 followed by SL 2 and SL 1. Addition of LAB to yeast caused a high increase in the concentration of lactic and acetic acids SL 3, this indicates that the dominant organic acids i.e. lactic and acetic produced during fermentation of sourdough in samples (SL 1, SL 2 and SL 3) were significantly higher than those produced in sample S. Therefore the addition of sourdough containing these metabolites to wheat flour dough would affect dough and final product characteristics (shelf life, freshness and sensory properties). The results are in line with [33,43].

Table 2. Organic acids and pH values during sourdough preparation

In Table 2 it is also shown that the pH values were significantly decreased by increasing fermentation period of sourdough and the highest significant reduction were recorded at (SL3)after 24 h. The reduction in pH would be due to the great production of organic acids during preparation of sourdough by LAB as mentioned before. These results are in agreement with those mentioned by [5,12,14,33,44].

Table 3. Mean zone of inhibition in mm in sour dough samples ± standard deviation beyond well diameter (6mm) produced on a range of environmental and clinically pathogenic microorganisms

3.1.3. The antimicrobial Effect of Sourdough

In Table 3 are presented the inhibition zones which are an indication for the antimicrobial effect of the metabolites (crude bacteriocin) produced by Lb. plantarum during sourdough fermentation on the investigated microorganisms (G+, G- and fungi). Results show that the metabolites produced in sourdough containing only (2% S. cerevisiae) or sourdough containing (2% S. cerevisiae+ 1% Lb. plantarum) had no effect on the tested microorganisms. However, increasing Lb. plantarum to 2% and 3% in sourdough resulted in antimicrobial effects on the tested microorganisms after 24 and 6 hrs of fermentation time, respectively. It was also found that E. feacalis was completely inhibited after 12 h of preparation time. This indicates that sourdough containing (S. cerevisiae+ 2 or 3% Lb. plantarum) had an antimicrobial activity that inhibited the tested microorganisms (G+, G- and fungi) compared to the dough containing only S. cerevisiae. The results showed that the produced metabolites (bacteriocins) could inhibit some of the spoilage microorganisms i.e. B. subtilis and A. niger (Previous results in Table 1) in wheat flour dough and might be in bread, which could consequently (this also would)affect the shelf life and other quality characteristics of the produced bread. LABs have been shown by many researches to possess both anti-bacterial and anti-fungal properties. Sourdough addition is an effective procedure to preserve wheat flour dough and bread from spoilage since it complies with the consumer request for additive-free products [4,23,27].

3.2. Balady Bread Characteristics

3.2.1. Shelf Life of Balady Bread

The bacterial and fungal counts in balady bread were determined at intervals i.e. zero, 1, 2, 3, 4, 5, 6, 7 and 8 days (Table 4 and Table 5), the results showed that the shelf life of balady bread was elongated from 3 days for control sample to 8 days for bread samples fermented by either SL 2 (2% Lb. plantarum) or SL 3 (3% Lb. plantarum). The results also showed that the highest values of bacterial and fungal counts were found in the control sample and bread fermented by sourdough starter containing only 2% S. cerevisiae. These counts were reduced as Lb. plantarum increased in sourdough.

Table 4. Log total bacterial count of balady bread

Table 5. Log total fungal count of balady bread

Results also, showed that addition of 20% sourdough containing different combinations of (2 or 3% Lb. plantarum) with 2% S. cerevisiae to wheat flour dough were effective in inhibiting the growth of molds and bacteria in the produced bread. Mold spoilage of the control sample was noticed on the third day, it was delayed until the eighth day of storage without any indication for initiation of attack of mold spoilage in the case of use of sourdough containing either 2% or 3% Lb. plantarum. These concentrations of Lb. plantarum in the sourdough would consequently extend the shelf life of bread. This indicates that the production of organic acids (Table 2) and other metabolites compounds by Lb. plantarum during sourdough fermentation (Table 3) had an antimicrobial effect on the spoiled microorganisms. These results are in agreements with [45] who mentioned that, the bacteriocin associated with organic acids had antimicrobial effect. Also, [10] reported that, lactic acid bacteria produced a mixture of organic acids such as, lactic, acetic formic, caproic, propionic, butyric and n- valleric acting in a synergistic way and responsible for the antimold activity. The results are in line with [46] and [47] who found that using sourdough in bread making preventing mold and bacterial spoilage. [26] Stated that the onset of fungal growth was delayed for 7 days in bread started with S. cerevisiae and Lb. plantarum 21 B. using sourdough led to a positive effect on prolonged shelf-life. [12,48].

3.2.2. Freshness of Balady Bread

Table 6 is shown results of a gradual reduction in bread freshness as measured by AWRC% in all different samples during storage period. The lower reduction in freshness (Alkaline water retention capacity (AWRC)) values was noticed in SL 3 samples (comparing with control and other treatments. The incorporation of LAB with yeast during preparation of sour dough starter decreased the staling rate of balady bread as measured by AWRC ratio. This might be due to the presence of metabolites such as organic acids (Table 2) and antimicrobial compounds (Table 3)that have a positive effect on bread staling. These results are in line with [49] and [15] who reported that, the use of sourdough improved the structure of the gluten network and might alter water migration between starch, protein and bran particles during storage. Epoxypolysaccharides (EPS) acted as bread improvers, while, organic acids affected the protein and starch fractions of flour. Additionally, the drop in pH associated with acid production caused an increase in the enzymes activity of the flour, thus led to a reduction in staling and improved the textural qualities of bread [2,50].

Table 6. Alkaline water retention capacity (AWRC %) of sour balady bread during storage at room temperature (≈ 25ºC)

Table 7. Sensory evaluation of balady bread made from sour dough

3.2.3. Sensory Characteristics of Balady Bread

Sensory characteristics of fresh balady bread samples fermented with 20% sour dough starter showed no significant differences (p> 0.05) in crust color, crust characteristics and crumb color between control sample and other samples. The addition of sourdough starter to wheat flour dough improved the grain and texture characteristics. A slight improvement in bread flavor and taste was noticed between control sample and those made from sour dough. Furthermore, sourdough samples scored higher sensory characteristics when compared to those without sourdough [19,40,48,51].

4. Conclusion

From the above results it might be concluded that the fermentation of wheat flour dough by using sourdough containing 2% S. cerevisiae and 1, 2 or 3% Lb. plantarum result in the formation of organic acids, that together with other compounds formed (bacteriocins) have antimicrobial activities also the pH decreases. It is probable that these effects are cause by the extra activities when S. cerevisiae and LAB are brought together in the fermented dough. The combination cause an increase in the effect of the total active metabolites than that present in the added sourdough starter. The metabolites added and formed in the dough were shown to greatly improve the final bread. The results also strengthen the reason to use of Lb. plantarum in food processing as a bio-preservative due to the broad inhibition spectrum found especially in bread making and bakery products.

References

[1]   | Katina, K. (2005). Sourdough: A tool for the improved flavor, texture and shelf life of wheat bread. Vtt Technical Research Center of Finland, Vtt Publications.
[2]   | Arendt, E.K.; L.A.M. Ryan and F.D. Bello (2007). Impact of sourdough on the texture of bread. Food microbial., 24: 165-174.
[3]   | De Vuyst, L. and P. Neysens (2005). Biodiversity and identification of sourdough lactic acid bacteria. Food Microbiol., 24(2): 120-127.
[4]   | Gobbetti, M., M. Angelis, A. Corsetti and R. Di Cagno (2005). Biochemistry and physiology of sourdough lactic acid bacteria. Trends Food Sci. Technol., 16 (1-3): 57-69.
[5]   | Paramithiotis, S.; S. Gioulatos; E. Tasakalidou and G. Kalantzopoulos (2006). Interactions between Saccharomyces cervisiae and Lactic acid bacteria in sourdough. Process Biochem., 41: 2429-2433.
[6]   | Corsetti, A. and L. Sattani (2007). Lactobacilli in sourdough fermentation. Food Res. Int., 40: 539-558.
[7]   | Corsetti, A., L. Settanni, S. Valmorri, M. Mastrangelo and G. Suzzi (2007). Identification of subdominant sourdough lactic acid bacteria and their evolution during laboratory scale fermentation. Food Microbiol., 24(6): 592-600.
[8]   | Stolze, P. and G. Böcker (1996). Technology, properties and applications of sourdough products. Advances in Food Sci., 18: 234-236.
[9]   | Hammes, W.P. and M.G. Gänzle (1998). Sourdough breads and related products. In: Microbiology of fermented foods. PP. 199-216. Edited by B.J.B. Wood, ed. Blackie Academic and Professional: London.
[10]   | Corsetti, A.; M. Gobbetti; J. Rossi and P. Damiani (1998). Antimould activity of sourdough lactic acid bacteria: identification of mixture of organic acids produced by lactobacillus sanfrancisco CB1. Appl. Microbiol. Biotechnol. 50: 253-256.
[11]   | Corsetti, A., M. Gobetti, B. De Marco, F. Balestrieri, F. Paoletti, L. Russi and J. Russi (2000). Combined effect of sourdough lactic acid bacteria and additives on bread firmness and staling. J. Agric. Food Chem., 48: 3044-3051.
[12]   | Katina, K.; M. Sauri; H.L. Alakomi and T. Mattila-Sandholm (2002). Potential of lactic acid bacteria to inhibit rope spoilage in wheat sourdough bread. LWT, 35: 38-45.
[13]   | Thiele, C.; M.G. Gänzle and R.F. Vogel (2002). Contribution of sourdough lactobacilli, yeast, and cereal enzymes to the generation of amino acids in dough relevant for bread flavor. Cereal Chem., 79: 45-51.
[14]   | Clarke, C.; T. Schober; P. Dockery; K. Ơsullican and E. Arendt (2004). Wheat sourdough fermentation: effects of time and acidification on fundamental rheological properties. Cereal Chem., 81 (3): 409-417.
[15]   | Katina, K.; M. Samenkallio-Marttilla; R. Partanen; P. Forssell and K. Autio (2006). Effects of sour dough and enzymes on staling of high fibre wheat bread LWT – Food Sci. and Technol., 39 (5): 479-491.
[16]   | Ur- Rehman, S.; H. Nawaz; S. Hussain; M. M. Ahmad; M. A. Murtaza and M. S. Ahmad (2006). Effects of sourdough bacteria on the quality and shelf life of bread. Pakistan J. Nutr. 6(6): 562-565.

[17]  
Dalbello, F., C.I. Clarke, L.A.M. Ryan, H. Ulmer, T.J. Shober, K. Ström, J. Sjögren, D. Van Sinderen, J. Schnürer and E.K. Arendt (2007). Improvement of the quality and shelf life of wheat bread by fermentation with the antifungal strain Lactobacillus Plantarum FST 1.7. J. Cereal Sci., 45(3): 309-318.

[18]   | De Vuyst, L. and Vancanneyt, M. (2007). Biodiversity and identification of sourdough lactic acid bacteria. Food Microbiol. 24: 120-127.
[19]   | Mentes, Ö.; R. Ercan and M. Akcelik (2007). Inhibitor activities of two lactobacillus strains, isolated from sourdough, against rope- forming Bacillus strains. Food Microbiol., 18: 359-363. (c.f. Ahmed, M.A.A. (2009). M.R.G. M. Sc., Thesis, Fac. of Agric. Ain Shams Univ).
[20]   | Sadeghi, A. F. Shahidi, S.A. Mortazavi, A. Koocheki and M. Mohebbi (2007). Evaluation of sourdough effect on Iranian Barbari bread staling. World Applied Sci. J., 2(5): 490-498.
[21]   | Sadeghi, A. (2008). The secrets of sourdough: a review of microflora potential of sourdough in bread shelf life. Biotechnol., 7(3): 413-417.
[22]   | Ogunbanwo, S.T.; A.I. Sanni and A.A. Onilude (2003). Characterization of bacteriocin produced by Lactobacillus plantarum F1 and Lactobacillus brevis OGI. African J. Biotechnol., 2 (8): 219-227.
[23]   | Messens, W. and L. De Vuyst (2003). Inhibitory substances produced by Lactobacilli isolated from sourdoughs: A review. Int. J. Food Microbiol., 72(1-2): 31-43.
[24]   | Clarke and Arendt, (2005). A Review of the Application of Sourdough Technology to Wheat Breads. Advances in Food and Nutrition Research 49: 137-161.
[25]   | Yousif, M.R.G. (2011). Studies on production of some functional bakery products. Ph.D. Thesis. Fac. of Agric. Ain Shams Univ.
[26]   | Lavermicocca, P.; F. Valerio; A. Evidente; S. Lazzaroni; A. Corsetti and M. Gobbetti (2000). Purification and characterization of novel antifungal compounds from the sourdough Lactobacillus plantarum strain 21B. Appl. and Environ. Microbiol., 66(4): 4084-4090.
[27]   | Cizeikiene, D.; G. Juodeikiene; A. Paskevicius and E. Bartkiene (2013). Antimicrobial activity of lactic acid bacteria against pathogenic and spoilage microorganism isolated from food and their control in wheat bread. Food Control, 31: 539-545.
[28]   | Denkova, S.; I. Z. Denkova, G. Ljubk; M. Yordanovaa; D. Nikolova and Y. Evstatieva (2014). Production of wheat bread without preservatives using sourdough starters. Biotechnology & Biotechnological Equipment. 28 (5): 889-898.
[29]   | A.O.A.C. (2000). Official Methods of Analysis, 17th Ed., Association of Official Analytical Chemists International. Gaithersburg, Maryland, USA.
[30]   | Oxoid Manual (1990). The Oxoid Manual of Culture, Media and Other Laboratory Services. Sixth Edition.
[31]   | Plesssas, S.; A. Bekatorou; J. Gallangh; P. Nigam; A.A. Koutinas and C. Psarianos (2008). Evolution of aroma volatiles during storage of sourdough breads made by mixed cultures of Kluveromycesmarxianus and lactobacillus delbrukii ssp. Bulgaricus or lactobacillus helveticus. Food Chem., 107: 883-889.
[32]   | GÜl, H.; S. Özcelik; O. SăGdic and M. Certel (2005). Sourdough bread production with Lactobacilli and S. cerevisiae isolated from sourdoughs. Process Biochem., 40: 691-687.
[33]   | Robert, H.; V. Gabriel; D. Lefebvre; P. Rabier; Y. Vayssier and C. ontagné- Faucher (2006). Study of the behavior of Lactobacillus Plantarum and Leuconostoc starters during a complete wheat sour dough breadmaking process. LWT 39: 256-265.
[34]   | Schillinger, V. and F. K. Lücke (1989). Antimicrobial activity of Lactobacillus sake isolated from meat. Appl. Environ. Microbiol. 55: 1901-1906.
[35]   | Faridi, H.A. and Rubenthalar (1984). Effect of baking time and temperature on bread quality, starch gelatinization and staling of balady bread. Cereal Chem., 61: 151-154.
[36]   | Kitterman, S. and G.L. Rubanthaler (1971). Assessing the quality of orally generation wheat selection with the micro AWRC test. Cereal Sci., Today, 16: 313.
[37]   | Mousa, E.I.; R.H. Ibrahim; W.C. Shuey and R.D. Maneval (1979). Influence of wheat classes, flour extractions, and baking methods on Egyptian Balady Bread. Cereal Chem., 56 (6): 563-566.
[38]   | Sendecor, G.W. and Cochran, W.G. (1997).Statistical Methods; 7th Ed. Oxford and J; B.H.Publishing Co. pp. 504.
[39]   | SAS (1997). Statistical Analysis System. User's Guide: Statistics, SAS Institute Inc, Gary, Nc., USA.
[40]   | Ahmed, M.A.A. (2009). Role of mixed microbial cultures in improvement of bread quality. M.Sc. Thesis. Fac. of Agric. Ain Shams Univ.
[41]   | Gobbetti, M.; M.S. Simonetti; A. Corsetti; F. Santinelli; J. Rossi and P. Damiani (1995). Volatile compound and organic acid productions by mixed wheat sour dough starters: influence of fermentation parameters and dynamics during baking. Food Microbiol., 12: 497-507.
[42]   | Corsetti, A.; P. Lavermococca; M. Morea; F. Baruzzi; N. Tosti and M. Gobbetti (2001). Phenotypic and molecular identification and clustering of lactic acid bacteria and yeasts from wheat sourdoughs of southern Italy. Int. J. of Food Microbiol., 64: 95-104.
[43]   | Yousif, M.R.G1 and S. M. Faid (2014). Effect of Using Different Types of Yeasts on the Quality of Egyptian Balady Bread. Journal of American Science 10 (2):100-109.
[44]   | Wehrle, K. and E.K. Arendt (1998). Rheological changes in wheat sourdough during controlled and spontaneous fermentation. Cereal Chem., 75 (6): 882-886.
[45]   | Oscroft, C.A.; J.G. Banks; and S. Mephee (1990). Inhibition of thermally-stressed bacillus spores by combinations of nisin, pH and organic acids. Lebensm. Wiss. Technol., 23 (6): 538-544. (c.f. Yousif, M.R.G. (2011). Ph.D Thesis, Fac. of Agric. Ain Shams Univ).
[46]   | Ur- Rehman, S.; H. Nawaz; S. Hussain; M.M. Ahmad; M.A. Murtaza and M.S.Ahmad (2007). Effect of Sourdough Bacteria on the Quality and Shelf Life of Bread. Pakistan J. of Nutrition 6 (6): 562-565.
[47]   | Rumeus, I and M. Turtoi (2013). Influence of sourdough use on rope spoilage of wheat bread. J. Agroalimentary Processes and Technol. 19(1), 94-98.
[48]   | Hansen, A. and P. Schieberle (2005). Generation of aroma compounds during sourdough fermentation: Applied and fundamental aspects. Trends in Food Sci. and Technol., 16: 85-94.
[49]   | Korakali, M.; M. Pavlovic; M.G. Ganzle and R.F. Vogel (2003). Exopolysaccharides and kestose production by lactobacillus sanfranciscensis LTH2590. Appl. and Environ. Microbiol. 69(4): 2073-2079.
[50]   | Sadeghi, A.; F. Shahidi, A. Mortazavi and M.A. Mahallati (2008). Evaluation of lactobacillus sanfrancisco (ATCC 14917) and Lactobacillus plantarum (ATCC 43332) effects on Iranian Barbari bread shelf life. 7(18): 3346-3351.
[51]   | Petrulákova, Z.; H. MikuŠová, L. Gereková; M. Kockova and E. Šturdik (2009). The effect of lactobacilli starter culture on quality of bread. Acta Chimica Slovaca. 2(2): 120-128.