Study of the micro-organisms associated with the fermented bread (khamir) produced from sorghum in Gizan region, Saudi Arabia

Sourdough production: fermentation strategies, microbial ecology, and use of non-flour ingredients

Sourdough production is an ancient method to ferment flour from cereals for the manufacturing of baked goods. This review deals with the state-of-the-art of current fermentation strategies for sourdough production and the microbial ecology of mature sourdoughs, with a particular focus on the use of non-flour ingredients. Flour fermentation processes for sourdough production are typically carried out by heterogeneous communities of lactic acid bacteria and yeasts. Acetic acid bacteria may also occur, although their presence and role in sourdough production can be criticized. Based on the inoculum used, sourdough productions can be distinguished in fermentation processes using backslopping procedures, originating from a spontaneously fermented flour-water mixture (Type 1), starter culture-initiated fermentation processes (Type 2), and starter culture-initiated fermentation processes that are followed by backslopping (Type 3). In traditional recipes for the initiation and/or propagation of Type 1 sourdough productions, non-flour ingredients are often added to the flour-water mixture. These ingredients may be the source of an additional microbial inoculum and/or serve as (co-)substrates for fermentation. An example of the former is the addition of yoghurt; an example of the latter is the use of fruit juices. The survival of microorganisms transferred from the ingredients to the fermenting flour-water mixture depends on the competitiveness toward particular strains of the microbial species present under the harsh conditions of the sourdough ecosystem. Their survival and growth is also determined by the presence of the appropriate substrates, whether or not carried over by the ingredients added.

Biochemical Changes during Traditional Fermentation of Saudi Sorghum (Sorghum bicolor L.) Cultivars Flour into Khamir (Local Gluten Free Bread)

Effect of traditional fermentation on pH, titratable acidity, proteins, amino acids, and sugars contents of three local sorghum cultivars namely Hamra, Biadah and Shahla used in making khamir local bread were investigated. During 24 fermentations, the pH of fermented dough dropped sharply and this was coincided with increase in total acidity. Fermentation was found to cause no significant change in protein content of the cultivars. Amino acid analysis, revealed slight insignificant improvement in lysine, and leucine content but there was a slight decrease in valine, phenyl alanine and arginine content in fermented dough. Glucose, fructose and maltose content of the three sorghum cultivars increased considerably in the early stages of fermentation, followed by decrease towards the end of fermentation. Low amount of sucrose detected in the three cultivars and it was completely utilized after 8 hrs. of fermentation.

Persistence and Effect of a Multistrain Starter Culture on Antioxidant and Rheological Properties of Novel Wheat Sourdoughs and Bread

Food consumers make decisions primarily on the basis of a product's nutritional, functional, and sensorial aspects. In this context, this study evaluated the persistence in sourdough of a multistrain starter culture from laboratory to bakery plant production and the effect of the starter on antioxidant and rheological properties of sourdoughs and derived bread. Lactobacillus sanfranciscensis B450, Leuconostoc citreum B435, and Candida milleri L999 were used as a multispecies starter culture to produce a sourdough subsequently used to modify two traditional sourdoughs to make novel bread with improved health and rheological properties. Both these novel bakery sourdoughs showed the persistence of L. sanfranciscensis B450 and C. milleri L999, and showed a significantly different lactic acid bacteria (LAB) concentration from the traditional sourdoughs. The novel sourdough PF7 M had a higher phenolic content (170% increase) and DPPH (8% increase) than the traditional bakery sourdough PF7 F. The novel sourdough PF9 M exhibited an improvement in textural parameters. Further research would be useful on the bioavailability of bio-active compounds to obtain bread with improved characteristics.

African Sorghum-Based Fermented Foods: Past, Current and Future Prospects

Sorghum (Sorghum bicolor) is a well-known drought and climate resistant crop with vast food use for the inhabitants of Africa and other developing countries. The importance of this crop is well reflected in its embedded benefits and use as a staple food, with fermentation playing a significant role in transforming this crop into an edible form. Although the majority of these fermented food products evolve from ethnic groups and rural communities, industrialization and the application of improved food processing techniques have led to the commercial success and viability of derived products. While some of these sorghum-based fermented food products still continue to bask in this success, much more still needs to be done to further explore evolving techniques, technologies and processes. The addition of other affordable nutrient sources in sorghum-based fermented foods is equally important, as this will effectively augment the intake of a nutritionally balanced product.

Diversity, Application, and Synthetic Biology of Industrially Important Aspergillus Fungi

The filamentous fungal genus Aspergillus consists of over 340 officially recognized species. A handful of these Aspergillus fungi are predominantly used for food fermentation and large-scale production of enzymes, organic acids, and bioactive compounds. These industrially important Aspergilli primarily belong to the two major Aspergillus sections, Nigri and Flavi. Aspergillus oryzae (section Flavi) is the most commonly used mold for the fermentation of soybeans, rice, grains, and potatoes. Aspergillus niger (section Nigri) is used in the industrial production of various enzymes and organic acids, including 99% (1.4 million tons per year) of citric acid produced worldwide. Better understanding of the genomes and the signaling mechanisms of key Aspergillus species can help identify novel approaches to enhance these commercially significant strains. This review summarizes the diversity, current applications, key products, and synthetic biology of Aspergillus fungi commonly used in industry.

Microbial Ecology and Process Technology of Sourdough Fermentation

From a microbiological perspective, sourdough is to be considered as a specific and stressful ecosystem, harboring yeasts and lactic acid bacteria (LAB), that is used for the production of baked goods. With respect to the metabolic impact of the sourdough microbiota, acidification (LAB), flavor formation (LAB and yeasts), and leavening (yeasts and heterofermentative LAB species) are most noticeable. Three distinct types of sourdough fermentation processes can be discerned based on the inocula applied, namely backslopped ones (type 1), those initiated with starter cultures (type 2), and those initiated with a starter culture followed by backslopping (type 3). A sourdough-characteristic LAB species is Lactobacillus sanfranciscensis. A sourdough-characteristic yeast species is Candida humilis. Although it has been suggested that the microbiota of a specific sourdough may be influenced by its geographical origin, region specificity often seems to be an artefact resulting from interpretation of the research data, as those are dependent on sampling, isolation, and identification procedures. It is however clear that sourdough-adapted microorganisms are able to withstand stress conditions encountered during their growth. Based on the technological setup, type 0 (predoughs), type I (artisan bakery firm sourdoughs), type II (industrial liquid sourdoughs), and type III sourdoughs (industrial dried sourdoughs) can be distinguished. The production of all sourdoughs, independent of their classification, depends on several intrinsic and extrinsic factors. Both the flour (type, quality status, etc.) and the process parameters (fermentation temperature, pH and pH evolution, dough yield, water activity, oxygen tension, backslopping procedure and fermentation duration, etc.) determine the dynamics and outcome of (backslopped) sourdough fermentation processes.

A rapid and simple screening method of Cronobacter spp. in cell suspension and tofu

BACKGROUND

Cronobacter spp. causes illnesses such as neonatal meningitis, sepsis and necrotising enterocolitis that can be fatal in infants and neonates. Thus it is of great concern to the food industry, which requires a simple and miniaturised method for the rapid detection of Cronobacter spp. in food.

RESULTS

A simple and rapid method was developed for the quantitative estimation of Cronobacter spp. Cell suspension cultures and tofu inoculated with Cronobacter spp. as well as a mixed culture (Cronobacter spp. and other micro-organisms) were serially diluted twofold on microtitre plates. Kim and Rhee broth, containing salicin, was added to each well. After 16-18 h of incubation the colour of broth in the wells changed from purple to yellow owing to salicin fermentation by Cronobacter spp. Bacterial counts were predicted by analysing the end points (the last well number in a series of positive wells). The coefficients of determination (r(2)) between the conventional plating method and the current method had high degrees of correlation (0.954-0.963), suggesting that the latter method offers a reasonable quantification of Cronobacter spp.

CONCLUSION

The simple method developed in this study could be used for the efficient and rapid screening of Cronobacter spp. in the food industry.

Cronobacter spp. in powdered infant formula

Cronobacter species are opportunistic pathogens, and a mortality rate of 40 to 80% is associated with infections. This pathogen can cause a range of serious diseases such as meningitis, septicemia, necrotizing enterocolitis, and brain abscesses and has been responsible for a variety of sequelae such as quadriplegia. Although Cronobacter can cause disease in both adults and infants, infant infections associated with powdered formula are the focus of this review. Since the first reported Cronobacter infection outbreak in 1958, powdered infant formula has been identified as a major source of these outbreaks, resulting in many recalls of powdered infant formula worldwide. This contamination has created an immense problem for the powdered infant formula industry. In this review, we discuss the taxonomy of Cronobacter species, the natural habitat of Cronobacter and its presence in foods, the physiology, pathogenicity, and virulence of Cronobacter species, and available detection methods. We also discuss reported cases of Cronobacter infection linked to powdered infant formula consumption and then focus specifically on the official World Health Organization guidelines for preparation of powdered infant formula.

Food fermentations: microorganisms with technological beneficial use

Microbial food cultures have directly or indirectly come under various regulatory frameworks in the course of the last decades. Several of those regulatory frameworks put emphasis on "the history of use", "traditional food", or "general recognition of safety". Authoritative lists of microorganisms with a documented use in food have therefore come into high demand. One such list was published in 2002 as a result of a joint project between the International Dairy Federation (IDF) and the European Food and Feed Cultures Association (EFFCA). The "2002 IDF inventory" has become a de facto reference for food cultures in practical use. However, as the focus mainly was on commercially available dairy cultures, there was an unmet need for a list with a wider scope. We present an updated inventory of microorganisms used in food fermentations covering a wide range of food matrices (dairy, meat, fish, vegetables, legumes, cereals, beverages, and vinegar). We have also reviewed and updated the taxonomy of the microorganisms used in food fermentations in order to bring the taxonomy in agreement with the current standing in nomenclature.

Microbiological and chemical characterisation of ting, a sorghum-based sourdough product from Botswana

Ting is a fermented sorghum product of Botswana which is used to prepare porridges of different consistencies. This study aimed to characterise ting with respect to fermentation microbiota and metabolite composition, and to develop starter cultures for ting fermentation. The pH values of 10 ting samples from Botswana ranged between 3.5 and 4.0 and cell counts ranged between 1.2×10(8) and 1.2×10(10)cfu/g lactic acid bacteria. Yeast cell counts were below 10(5)cfu/g in all samples and Enterobacteriaceae were less than 10 cfu/g. The microbiota of samples consisted of 2-4 dominant strains and strains were identified based on the sequence of their 16S rRNA genes as Lactobacillus reuteri, Lactobacillus fermentum, Lactobacillus harbinensis, Lactobacillus plantarum, Lactobacillus parabuchneri, Lactobacillus casei and Lactobacillus coryniformis. Binary strain combinations were employed as starter cultures to produce ting. Major fermentation products were lactate, acetate and ethanol, additionally, 1,2 propanediol and 1,3 propanediol were produced by some strains. All strains were capable of producing ting, which was accompanied by a decrease in pH from 6.3 to 4 within 8h. Traditionally processed ting requires 2 to 3 days to attain a pH below 4; the starter cultures thus reduced the fermentation time to 8h.

Sourdough in gluten-free bread-making: an ancient technology to solve a novel issue?

The increasing demand for high quality gluten-free (GF) bread, clean labels and natural products is raising the need for new approaches in GF bread-making. Sourdough is the foremost fermentation used for baking purposes and it has been proven to be ideal for improving the texture, palatability, aroma, shelf life and nutritional value of wheat and rye breads. These characteristic features derive from the complex metabolic activities of the sourdough-resident lactic acid bacteria and yeasts, e.g. acidification, production of exopolysaccharides, proteolytic- amylolytic- and phytase activity, and production of antimicrobial substances. These effects have been extensively studied and well described for traditional baking, whereas little is known about the role of sourdough in GF baking. Yet, the microbiological and qualitative characterisation of local GF fermented products indicate an overlap with the microbiota of wheat/rye fermentation and suggest that the positive metabolic activities of the sourdough microbiota are still retained during fermentation of GF crops. Thus, the use of sourdough in GF baking may be the new frontier for improving the quality, safety and acceptability of GF bread.

Enterobacter sakazakii in food and beverages (other than infant formula and milk powder)

The ubiqitous microorganism Enterobacter sakazakii is a rare contaminant of infant formula and may cause severe systemic infection in neonates. So far, other food is not known to cause E. sakazakii-infections. The scarce information about the ecology of E. sakazakii and the uncertainty concerning the source of infection in children and adults warrant a summary of the current knowledge about the presence of this opportunistic microorganism in food other than infant formula. This review systematizes publications on the presence of E. sakazakii in food and beverages until June 2006. Food other than infant formula has been rarely investigated for the presence of E. sakazakii. Nevertheless, this microorganism could be isolated from a wide spectrum of food and food ingredients. E. sakazakii was isolated from plant food and food ingredients like cereal, fruit and vegetables, legume products, herbs and spices as well as from animal food sources like milk, meat and fish and products made from these foods. The spectrum of E. sakazakii-contaminated food covers both raw and processed food. The kind of processing of E. sakazakii-contaminated food was not restricted to dry products. Fresh, frozen, ready-to-eat, fermented and cooked food products as well as beverages and water suitable for the preparation of food, were found to be contaminated by E. sakazakii. Although E. sakazakii-contaminated food do not have general public health significance, measures for prevention should consider the presence of E. sakazakii in food, food ingredients, their processing and preparation as possible source of contamination, colonization or infection.

Enterobacter sakazakii: a coliform of increased concern to infant health

The first cases of neonatal meningitis believed to have been caused by Enterobacter sakazakii were reported in 1961. Prompted by several subsequent outbreaks of E. sakazakii infections in neonates and an increasing number of neonates in intensive care units being fed rehydrated powdered infant formula, considered to be a source of the pathogen, public health authorities and researchers are exploring ways to eliminate the bacterium or control its growth in dry infant formula, processing environments and formula preparation areas in hospitals. Reviewed here are advances in taxonomy and classification of E. sakazakii, methods of detecting, isolating and typing the bacterium, antibiotic resistance, clinical etiology and pathogenicity. Outbreaks of E. sakazakii infections in neonates and adults are summarized. Reports on the presence of E. sakazakii in clinical settings, the environment and foods and food processing facilities are reviewed. Tolerance of the pathogen to environmental stresses, its behavior in powdered and rehydrated infant formulae and hazard analysis and risk management are discussed. Research needs are presented.

Potential osmoprotectants for the lactic acid bacteria Pediococcus pentosaceus and Tetragenococcus halophila

The physiological responses of the lactic acid bacteria Pediococcus pentosaceus and Tetragenococcus halophila (formely known as P. halophila), subjected to osmotic stress in the presence of molecules known to act as osmoprotectants for other bacteria were studied. In a defined medium, glycine betaine, dimethylsulfonioacetate, choline, proline and L-carnitine were able to relieve inhibition of growth at 0.8 M NaCl. The five compounds were shown to efficiently compete with glycine betaine transport, suggesting the existence of common transporter(s) for these molecules. T. halophila, the most tolerant strain, exhibited a larger spectrum of compatible solutes including dimethylsulfonioacetate, dimethylsulfoniopropionate and ectoine. Preliminary data suggest that restoration of growth by ectoine under osmotic constraint seems specific to the genus Tetragenococcus.