Review on Microbial Ecology of Fermented Foods and Beverages

Fermented foods and beverages play a significant role in most societies and major contribution in fulfil the protein requirements of large population. There is a relation between microbial diversity of food products and health benefits. Yoghurt is a fermented dairy product, having several health benefits. Yoghurt starter culture consists of a blend of Streptococcus thermophilus and Lactobacillus delbrueckii subsp Bulgaricus. Yoghurt is mainly of two types i.e. set yoghurt and stirred yoghurt. Yoghurt properties can be enhanced by the addition or treatment with various additives. Alternative methods to improve quality of low-fat yoghurt become an area of considerable research interest. Lactic acid can be produced by the yoghurt. Yoghurt is a functional food. The functional food includes probiotics, prebiotics and synbiotics.

Ayib, a traditional Ethiopian cottage cheese, is a popular milk product consumed by the several local groups of the country. It is prepared from sour milk after the butter is removed by churning. Churning of the sour milk is carried out by slowly shaking the contents of the pot until the butter is separated. The defatted milk is heated to about 50°C until a distinct curd forms. It is then allowed to cool slowly, and the curd is filtered through a muslin cloth. Further analysis of ayib micro flora revealed that bacterial and yeast counts did not relate with pH value of ayib samples. The main ingredient in cheese is milk. Cheese is made using cow, goat, sheep, water buffalo or a blend of these milks. The type of coagulant used depends on the type of cheese desired. For acid cheeses, an acid source such as acetic acid (the acid in vinegar) or gluconodelta-lactone (a mild food acid) is used.

Injera is made using teff, a tiny, round grain that flourishes in the highlands of Ethiopia. While teff is very nutritious, it contains very little gluten (which makes it poorly suited for the making of raised bread). However, it still takes advantage of the inherent properties of yeast, as fermentation lends it an airy, bubbly texture. Tef injera, a pancake-like acidic food is prepared from fermented tef (Eragrostis tef), flour. A complex group of microorganisms is involved in the fermentation. Fermentation is initiated by members of the Enterobacteriaceae. Their activities during the first 18 hr of fermentation reduce the pfi of the dough to about 5.8. They are then succeeded by Leuconostoc mesenteroides and Streptococcus faecalis. As the pH is further reduced to about 4.7, Pediococcus cerevisiae, Lactobacillus brevis, Lactobacillus plantarum and Lactobacillus fermentum become the predominating flora and remain so until the fermentation is terminated at 72 hr.

Wakalim is a spiced traditional Ethiopian fermented beef sausage. Early stages (0–12 h) of wakalim fermentation were dominated by lactic acid bacteria and aerobic mesophilic bacteria including staphylococci and members of Enterobacteriaceae. Gram-negative bacteria were below detectable level after day 4 of fermentation. Staphylococci were detected at low levels (around 4 log cfu/g) until the end of fermentation. Lactic acid bacteria grew and dominated the flora at the end of fermentation. Various species of Lactobacillus and Pediococcus initiated the fermentation and the lactic flora was finally dominated by Lb. plantarum1 and Ped. pentosaceus1. First the meat and a few heads of onion are cut into small pieces, and put into a vessel, where they are mixed with several spices - cardamom, coriander. cinnamon, cloves, chamomile, black pepper, cumin-seeds, and hurdinci. These spices, ground into powder and with the addition of a measured quantity of salt and red-pepper, are mixed with the meat so that every piece of meat is well covered with the powder. Next the tube or skin from intestine, called maraci, is prepared. Usually the small intestine of an ox makes the tube. This undergoes a series of washings and cleanings. First the tube is turned inside out and washed with ash in order to remove the dirt and the slippery mucous from its wall. After this it is put into a vessel of pure water and cleaned. Here the first washing ends. The second washing is made with soap and water, and again it is put into a vessel with fresh water. The third and the last washing is with lemon and salty water. By this time the tube has become white membrane; it is turned right side out and tied at one end, blown up with the mouth and the other end tied to make a kind of bladder. This inflation causes the tube to coil automatically. It is twisted around a cane and exposed to the sun to dry for about one hour. After the skin is completely dry it is cut into small pieces of about 9 inches long, which is the length of an average wakalim. Then the spiced meat is forced into the tube with the finger; when the skin is quite full it is bent into a U-shape, and the two ends are twisted together to form a closing. Sometimes while the meat is being inserted, the tube breaks due to old age or to too much drying. To avoid this the tubes are usually damped beforehand by inserting them into the meat. When all the meat has been used up and the wakalim are ready, they are taken to the kitchen and strung on a rope stretched a little way above the hearth so that they receive only the heat and not the direct flame, otherwise the tube will crack. When sufficiently warm the tubes are pricked here and there. After some time moisture oozes from them and falls drop by drop. This process of drying the wakalim does not end in one day. It has to be repeated for three or four days. Usually they are brought to the kitchen when the fire is set for the preparation of lunch or dinner, and taken back after that, or else the kitchen is locked. These precautions are necessary as the young people love wakalim, and would never miss the opportunity to steal one or two, especially during a marriage feast. Now the wakalim which has passed the stage of drying is ready to be eaten.

Tella is popular Ethiopian traditional beverages, which is made from diverse ingredients. It is, by far, the most commonly consumed alcoholic beverage in Ethiopia. It is assumed that over two million hectoliters of tella to be brewed annually in households and drinking houses in Addis Ababa alone. Some of them consider as local beer. It is traditionally drunk on major religious festivals, saint’s days and weddings. Shamita is another traditional beverage of Ethiopia, which is low in alcohol content, made by overnight fermentation of mainly roasted barley flour and, consumed as meal-replacement. Shamita is a widely consumed beverage in different regions of Ethiopia. It has a thick consistency and most people who cannot afford a reasonable meal consume it as meal replacement. It is produced by fermenting roasted barely overnight. Malt is not commonly used in shamita fermentation, although local shamita brewers in Addis Ababa use it frequently, and starch is the only principal fermentable carbohydrate. The microbes liable for fermentation are mostly from back slopping using small amount of shamita from a previous fermentation as well as from the ingredients and equipment. Ready to consume shamita has a high microbial count made up of mostly LAB and yeast. These microorganisms make the product a good source of microbial protein. However, shamita has poor keeping quality because of these high numbers of live microorganisms and becomes too sour about four hours after being ready for consumption. Borde is a local beer mostly consumed by people in southwestern parts of the country. It is considered as a drink for people in the lower socio-economic status. Borde is prepared by women from fermented maize, sorghum, barley, or a mixture of the three. Borde can be very thick and serve as a substitute for meals during long trips. According to the villagers attitude borde is also used for medical and ritual purposes. The users consider that it enhances lactation and mothers are encouraged to drink substantial amounts of it after giving birth.

The main substrates in awaze are red sweet pepper (C. annum), garlic (Allium ursinum) and ginger (Zingiber officinale) with which some proportions of different spices are added. Awaze is commonly known in the north and central Ethiopia and is often consumed with sliced raw or roasted meat and other traditional pancakes. While the microbiology and biochemical properties of several other traditional Ethiopian fermented foods and beverages have been studied, there are no reports on the fermentation of awaze, indigenous Ethiopian condiment. Datta is among the traditional fermented condiments mainly in the southern parts of Ethiopia and are consumed with other items on the basis of their desirable aromas and flavors. It is results from the microbial fermentations of vegetable-spice mixtures. But the major substrate in the making of datta is the small chili pepper (C. frutescenc) at its green stage. Datta was also prepared following traditional methods. The small green pepper together with its seeds was carefully washed and cut into pieces. Garlic and ginger, in small proportion, were peeled, washed and cut into small pieces. Siljo is one of the traditional fermented condiments of Ethiopia made up of safflower (Carthamus tinctorius) extract and faba bean (Vicia faba) flour. The black mustard powder, which is added after cooking the mixture of the safflower and faba bean, helps as source of starter microorganisms. The fermented product has protein and fat content of 28 and 25%, respectively, with improved protein availability and concentration as a result of fermentation.

Probiotics are live microbes that can be formulated into many different types of product, including foods, drugs, and dietary supplements. Species of Lactobacillus and Bifidobacterium are most commonly used as probiotics, but the yeast Saccharomyces cerevisiae and some E. coli and Bacillus species are also used as probiotics. Lactic acid bacteria, including Lactobacillus species, which have been used for preservation of food by fermentation for thousands of years, can serve a dual function by acting as agents for food fermentation and, in addition, potentially imparting health benefits. Probiotics are live microbial food supplements which beneficially affect the host by improving the intestinal microbial balance. To be used as a probiotic, a bacterial strain is required to have good tolerance to acidity of the stomach and bile salt of the upper small intestine. Prebiotics are dietary substances (mostly consisting of nonstarch polysaccharides and oligosaccharides poorly digested by human enzymes) that nurture a selected group of microorganisms living in the gut. They favor the growth of beneficial bacteria over that of harmful ones. Unlike probiotics, most prebiotics are used as food ingredients—in biscuits, cereals, chocolate, spreads, and dairy products, for example. Commonly known prebiotics are: oligofructose, inulin, galacto-oligosaccharides, lactulose and breast milk oligosaccharides. The term synbiotic is used when a product contains both probiotics and prebiotics. Because the word alludes to synergism, this term should be reserved for products in which the prebiotic compound selectively favors the probiotic compound. In this strict sense, a product containing oligofructose and probiotic bifidobacteria would fulfill the definition, whereas a product containing oligofructose and a probiotic Lactobacillus casei strain would not.

Single-cell protein (SCP) refers to protein derived from cells of microorganisms such as yeast, fungi, algae, and bacteria, which are grown on various carbon sources for synthesis. SCP is a protein source for human food supplements and animal feeds. SCP production may have potential for feeding the ever-increasing world population. Massive quantities of SCP can be produced in a single day. The Hazard analysis and critical control points (HACCP) is a preventive system which seeks to ensure food safety and security. It allows product protection and correction of errors, improves the costs derived from quality defects and reduces the final overcontrol. In this paper, the system is applied to the line of cultivation of mushrooms and other edible cultivated fungi.