Fermentation is derived from the Latin verb fevere, which means to boil. It is an ancient method to preserve food and transform food materials by utilizing the metabolic activity of microorganisms. (1)
Fermented foods may be defined as the foods or beverages produced through the activities of microorganisms that influence the component of food in terms of organoleptic properties (flavor, texture, and color). Fermented food products are produced worldwide as they have health benefits and can be preserved for an extended period.
Advantages of Fermented foods
Traditionally, the foods were fermented to prevent spoilage and preserve for an extended period. Some of the few advantages of fermenting foods are given below.
- It preserves the foods and is economical; for example, cheese prepared from milk can be preserved for longer than the source.
- It also removes the unwanted or harmful properties of raw materials.
- The presence of microorganisms enhances the nutritional content of food.
- In comparison to raw materials, the organoleptic properties of fermented foods are improved due to fermentation.
Traditional Fermented Foods
Fermented foods can be produced from raw materials such as milk, soybean, cabbage, fruits, etc. Other organisms, such as Lactobacillus, ferment these raw materials. Some of the foods produced from these raw materials are mentioned below:
Fermented Milk Products
Milk is used as raw materials for producing foods such as yogurt, curd, kefir, cheese, probiotic drinks, etc.
Yogurt: Yogurt is a popular dairy product fermented by two bacterial species, Streptococcus thermophilus, and Lactobacillus bulgaricus, from milk. In addition, a few other organisms act as starter cultures: Bifidobacterium spp., Lactobacillus delbrueckii, Lactobacillus casei, and Lactococcus lactis, among others. These bacteria ferment milk and produce lactic acid, which drops the milk pH from 7 to 4-5, which coagulates it. Produced lactic acid causes the sour taste of yogurt and inhibits the growth of spoilage bacteria.
Fermented Food from Soybeans
Soybean is a nutritional food rich in protein (42%), oil (18%), and low carbohydrates (17%). The bean consists of phospholipids, nucleic acids, and vitamins such as thiamine, riboflavin, and niacin. (2) Even though it is nutritious, some compounds cannot be digested, which, after fermentation, are reduced to a lower molecular weight and are made digestible. Some fermented soybean products include Soy sauce, Miso, Tempeh, Natto, etc.
Soy sauce is famous in Japan and is known as shoyu, a deep red-brown liquid having a salty taste and distinct aroma. Its primary raw material is soybean, and other ingredients are wheat, salt, and a mixture of molds, bacteria, and yeasts. (3)
Natto originated in Japan more than 1,000 years ago. It is a fermented whole soybean of two types: Hama-natto, fermented by the action of Aspergillus, and Itohiki-natto, fermented by Bacillus natto (3).
Likewise, Tempeh is popular in Indonesia and is eaten as a critical protein source. Several species of Rhizopus are used to ferment soybean, mainly Rhizopus oligosporous Saito. (3)
Miso: Miso is a fermented soybean paste that is popular in Japan. Soybean is mainly used as a substrate for miso production; other legumes such as chickpeas or novel bases like nuts may also be used. Traditionally, it used to be prepared by fermentation soybeans with Koji (produced from Aspergillus oryzae). (4) Organisms such as Bacillus subtilis, Bacillus amyloliquefaciens, Staphylococcus gallinarum, and Staphylococcus kloosii are used as a starter culture for the fermentation of soybeans to produce Miso.(5) For Miso production, two steps of fermentation are carried out. In the first fermentation, barley or rice is used as a raw material, and fermentation is carried out by Aspergillus oryzae forming a product known as Koji. Thus, the Koji is mixed with cooked soybean, salt, pure yeasts, and lactic acid bacteria, and the second fermentation is carried out. After this process, it is aged for years and packaged as Miso.
Fermented Food from Vegetables
Vegetables such as cabbages, olives, cucumber, onions, peppers, green tomatoes, carrots, okra, celery, and cauliflower can be fermented and traditionally have been used as a means to preserve. Some fermented vegetables are kimchi, sauerkraut, olives, pickles, and mustard pickles.
Kimchi: Kimchi is a fermented vegetable dish that originated in Korea. The main ingredients are Chinese cabbage or radishes and flavoring ingredients such as chili, pepper, garlic, onion, ginger, and seasonings such as salt, soybean sauce, sesame seed, and other additional foods such as carrot, apple, pear, and shrimp. All these ingredients are mixed, and the fermentation occurs naturally by microorganisms in the cabbage or other elements. Although fermentation occurs naturally, for the commercial production of kimchi, different bacteria are added as a starter culture, including Leuconostoc, Lactobacillus, Pseudomonas, Pantoea, and Weissella genera. But the concentration of bacteria differs in different stages of fermentation; bacteria belonging to Leuconostoc genera dominate the first three days of fermentation. Since various ingredients are added to kimchi, the composition of microbes may vary accordingly. For example, the concentration of Weissella is high, and Leuconostoc and Lactobacillus are lower after adding red pepper powder. (5)
Sauerkraut originated in the 4th century and is a common form of preserving cabbage. It is popular in Germany and is now common in other European, Asian countries, and the United States. The raw material is cabbage and salt (2.3-3.0) % and is fermented spontaneously. Organisms that contribute to fermentation are Leuconostoc spp., Lactobacillus spp., and Pediococcus spp. (5)
Cucumber (pickling) is eaten raw after fermentation or pickling. Dry salting and brine salting are widely used. During brine salting, salt is added in 5-8% amounts. The unwanted bacteria are removed, allowing lactic and yeast to increase during the primary fermentation, lasting 2 to 3 days. The significant organisms for fermentation include Lactobacillus plantarum and L.brevis, followed by Pediococcus.
Fermented beverages are in either alcoholic form or stimulant form. Beer and wines are alcoholic drinks, while tea, coffee, and cocoa are stimulant beverages.
Alcoholic beverages: Alcoholic beverages are famous worldwide and are being produced in different societies. It is mainly based on the conversion of sugar to alcohol by yeasts. The primary organism involved in the fermentation of alcohol is yeasts, and the raw material used in most distilled liquors are honey, sugarcane, palm sap, beetroot, maize, or corn. The yeasts used in mainly brewing belong to Saccharomyces cerevisiae, with each strain having its characteristics, while some yeasts belong to Saccharomyces ellipsoids.
In the case of wine, historically, the fermentation of grape species called Vitis vinifera produces wine. When a grape is ripe, its moderate acidity is favorable to make wine. Its natural sugar content acts as a raw ferment material and can produce wine with 10% or higher alcohol. It contains tannins that provide flavor and protect wines from spoilage bacteria. Other fruits such as guava, mangoes, pineapple, tangerine, cashew fruit, and many more contain 10-20 % fermentable sugar, which can be used to produce wine. Still, the names of fruits included papaya wine, guava wine, and so on.
Beer, a beverage, is obtained by the fermentation of malted cereals. Malted cereal is extracted with water and other carbohydrates. This extract is boiled with hops and later cooled and fermented with yeast. Fermentation of cereal extracts by Saccharomyces is a crucial step involved during brewing. Even though all Saccharomyces strains produce ethanol, the type of strain used determines the production of beers and is classified as lager or ale beers. (6) Lager beer: It is a bottom-fermented beer, where barley is fermented by Saccharomyces carlsbergensis (also called bottom-fermenting yeast). Ale beer: It is a top-fermented beer produced by Saccharomyces cerevisiae (Top-fermenting yeast).
In addition, there are distilled beverages such as whiskey, rum, brandy, etc. Whiskey, rum, and Brandy are obtained by distillation of aqueous extract of infusion of malted barley or other cereals, the fermented juice of cane syrup or sugarcane derivates, and fermented grape, apple, pear, wine, and so on, respectively.
Stimulant beverages: Stimulant beverages such as tea, coffee, and cocoa are mainly produced in the rainforest zones of the Indian sub-continent, South America, and West Africa, respectively. A few stimulant beverages are discussed below.
In the case of coffee fermentation, it originated in Ethiopia. The microorganisms used in fermentation include spore-forming and non-spore-forming bacteria. In addition, other lactic acid bacteria (Leuconostoc spp and Lactobacillys spp) and yeasts (Saccharomyces spp and Schizosaccharomyces spp.) are also used. Processing of coffee involves two methods: the wet method and the dry method.
While using the wet method, fruits are passed through a pulping machine to remove the pulp, and pectinolytic enzymes produced by microorganisms remove the mucilage. On the other hand, while using the dry method, fruits are dehulled to remove dry outer portions. The coffee may also be dried by exposing it to the sunlight.
The tea was originated in South-East China and is now popular worldwide. Young tea leaves are handpicked and withered. Leaves are squeezed to extract juices by rolling, which is further spread on the surface of the leaves. Juice consists of polyphenols exposed to oxidation, changing the green color to brown. This is followed by chemical reaction fermentation. The tea is then subjected to hot air between 80 – 90⁰C, sorted, and graded. (3)
Cocoa is native to South America but is now produced in Ghana, Ivory Coast, Cameroon, Malaysia, and Nigeria. The tree grows a pod consisting of 40-60 seeds. The mucilaginous outer covers of sources are broken. They are allowed to ferment by microbial action changing the seed color from pinkish to black, and the aroma is due to the lactic acid bacteria.
Health Benefits of Fermented Foods
Fermented foods have a long history of safe use and are accepted widely by the public owing to their favorable health effects. The positive impacts of fermented foods have attracted consumers in large numbers.
- Fermented food consumption is associated with mood, brain activity, and gut microbes. Yogurt consumption reduces the risk of cardiovascular disease, type-2 diabetes, and mortality. Intake of kimchi is linked to anti-diabetic and anti-obesity effects. (7)
- Fermentation transforms the raw materials allowing the food to be tolerated by consumers. This process improves the digestibility of starch and polypeptides by breaking them down into oligosaccharides and amino acids. For instance, the casein micelle of milk is destabilized by the fermentation of bacteria present in the milk, enhancing the digestibility of milk protein. In addition, the fermentation process causes the catabolism of protein, lipid, and carbohydrate-producing bioactive compounds, which lowers blood pressure and cholesterol, has anti-cancer effects and improves metabolic syndromes and overall immune functions. The dairy products fermented by Lactobacillaceae also produce Vitamins B7, B11, and B12 beneficial for health.
- Microorganisms such as Zymomonas, Leuconostoc, Pediococcus, and Streptococcus species and other members of the Lactobacillaceae family produce exopolysaccharides. These organisms have high molecular weight exopolysaccharides from simple sugars found in raw materials. EPS-producing LAB helps in immunomodulation which depending on factors, may be suppressive or stimulatory.
- Fermented food modulates the gut microbiome. For example, wine is rich in polyphenols, alters gut microbiota, and lowers total cholesterol and blood pressure. It also inhibits pathogenic bacteria and benefits the beneficial bacteria. (7)
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