Introduction

Functional foods are defined as the food or dietary components that may provide a health benefit beyond basic nutrition. A food can be made functional by applying any technological or biotechnological means to increase the concentration of, add, remove or modify a particular component as well as to improve its bioavailability, provided that component has been demonstrated to have functional effect (Roberfroid 1999). Again, according to Kalra (2003) when food is being cooked or prepared using “scientific intelligence” with or without the knowledge of how it is being used, the food is referred to as “functional food” (Kalra 2003). In recent years, cereals and its ingredients are accepted as functional food and nutraceuticals because of providing dietary fibre, proteins, energy, minerals, vitamins and antioxidants required for human health. Also, cereals can be used as fermentable substances for the growth of probiotic microorganisms (Charalampopoulos et al. 2002). Wheat, buckwheat, oat, barley, flaxseed, psyllium, brown rice and soy products are notified as the most common cereal based functional food and nutraceuticals (Truswell 2002). Cereals are used world-wide as staple foods. A large proportion of the world cereals production is processed by fermentation prior to consumption. The enhancement of attractive flavour and texture, and the improved shelf-life and digestibility as a result of fermentation are important reasons for this (Nout 2009). Recently, the functional food research has moved progressively towards the development of dietary supplementation, introducing the concept of probiotics and prebiotics, which may affect gut microbial composition and activities (Ziemer and Gibson 1998). In this context, this review aims to summarize the production processes and health benefits of some of the most commonly consumed traditional cereal-based fermented and non-fermented food of the Indian subcontinent.

Cereal- a rich source of nutrients

Cereals offer several challenges from nutrition point of view, especially the swelling of their starch upon cooking, the limited quantity and amino acid profile of their protein fraction, and the limited bioavailability of their mineral content due to relatively low mineral levels and the presence of phytic acid and other antinutritional factors that reduce their bioavailability to 5–15% (Nout 2009).

Cereals are grown in over 73% of the total world harvested area and contribute over 60% of the world food production providing dietary fibre, proteins, energy, minerals, and vitamins required for human health. Possible applications of cereals or cereal constituents in functional food formulations could be use as fermentable substrates for growth of probiotic microorganisms, especially lactobacilli and bifidobacteria or as dietary fibre promoting several beneficial physiological effects. It can also serve as a prebiotic due to their content of specific nondigestible carbohydrates or as encapsulation materials for a probiotic in order to enhance their stability (Charalampopoulos et al. 2002). Increasingly, whole grain is becoming one of the favored choices as a probiotics delivery vehicle. This is mainly because the formulations of probiotics with whole grain products offer consumers both probiotics and whole grain benefits, e.g., non-digestible carbohydrates, soluble fibre, phytochemicals, and other bioactive components (Marquart and Cohen 2005).

Cereals as functional food and nutraceuticals

Strong epidemiological evidence has clearly demonstrated that whole-grain cereals protect the body against age-related diseases such as diabetes, cardiovascular diseases and some cancers (Chatenoud et al. 1998, 1999; Venn and Mann 2004). This may be due to the fibre and micronutrients in the outer layer and germ fractions of the grain acting together to combat oxidative stress, inflammation, hyperglycaemia and carcinogenesis. Whole-grain cereals also contain micronutrients such as vitamin E, folates, phenolic acids, zinc, iron, selenium, copper, manganese, carotenoids, betaine, choline, sulphur amino acids, phytic acid, lignins, lignans, and alkylresorcinols, which all may have potential antioxidant effects (Slavin et al. 1999). Antioxidant micronutrients in whole-grain cereals are given in Table 1. Dietary fibre is one of the major phytochemicals present in cereals, upon water solubility it can be divided into two categories. Water-soluble fraction (soluble fibre) consists mainly of nonstarchy polysaccharides such as beta glucans and pentosans (arabinoxylan). Soluble fibre is known to decrease serum cholesterol, postprandial blood glucose, and insulin levels in humans (Edge et al. 2005). Water-insoluble fraction (insoluble fibre) consists of lignin, cellulose, hemicellulose (water-insoluble arabinoxylan). The Comparison of total dietary fibre content in cereal grains are shown in Table 2.

Table 1 Antioxidant micronutrients in whole-grain cereals
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Table 2 Comparison of total dietary fibre content in cereal grains
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Rice

Protein quality of rice surpasses that of wheat and corn while it is just inferior to oats. Also, rice protein is hypoallergenic and contains good quantity of lysine. Thus it may act as a suitable ingredient for infant food formulations while adding variety to the restricted diets of children with food allergies (Burks & Helm 1994, Gurpreet and Sogi 2007). Amino acid profile of rice protein was better than casein and soy protein isolate in fulfilling the amino acid requirements for 2–5 years old children (Wang et al. 1999). Table 3 presents the composition of different varieties of cereals.

Table 3 Composition of different varieties of cereals expressed as 100 g of edible portion
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Wheat

Whole wheat and wheat bran based cereals are important source of dietary antioxidants. Free and esterified phenolic acids in wheat have the greatest potential to be beneficial to health (Baublis et al. 2000). Wheat antioxidants are mainly concentrated in bran layers and the amount of antioxidants depends largely on the grain variety, with red wheat generally containing higher levels than white wheat (Kim et al. 2006).

Maize

Maize (Zea Mays) is one of the important cereals in Asia. It has the largest kernels. Because of its hardness and size, decortication by abrasion is feasible and fine grinding is essential to obtain smooth texture of cooked products (Nout 2009).

Barley

Barley has a high acceptance in human nutrition, when its new functional and nutritional properties are recognized (Bhatty 1999). Barley grain is used as feed, malt, and food. Our ancestors depended on barley as a staple food more than we do now. Barley played an important role in the origin and development of the Neolithic culture. Barley is used as flour, as semolina, and as whole-dehulled grain. A large variety of dishes, including soups, bread, and couscous are made from barley products (Amri et al. 2005). The major component in barley is β-glucan, which is a major component of soluble fibre implicated in hypercholesterolemia, hypoglycemia, and in reducing incidence of chemically induced colon cancer in experimental animals (Bhatty 1999).

Sorghum

Sorghum is widely grown in the semiarid topics of Asia, and constitutes a major source of carbohydrates and proteins for people living in this region. Although the use of sorghum as human food is widespread, the technology for processing the grains in to consumable product is still far from adequate (Lazaro and Favier 2000).

Millet

Finger millet or Ragi (Eleusine coracana) is an important staple food for the traditional consumers and the people belonging to the lower socio-economic strata in the Indian subcontinent (McDonough et al. 1986). Some of health benefits associated with regular intake of millet foods, such as the hypocholesterolemic, hypoglycemic and antiulcerative characteristics indicate the scope for its utilization by the non-traditional millet consumer also. Since, the anti-nutritional factors of the millet, namely, polyphenols and phytates are mainly concentrated in the seed coat and aleurone layers (McDonough et al. 1986, Ravindran 1991), decortications lowers their contents and as a result improves the bio-availability of the nutrients.

Oat

Oats have recently attracted research and commercial attention mainly due to their high content of β-glucan and of compounds with antioxidant activity (Malkki et al. 2004). The health effects of β-glucan as related to cholesterol reduction, improved gastrointestinal function and glucose metabolism would be achieved at a daily consumption level of 10 g oat β-glucan (Malkki & Virtanen 2001). Soluble fibres of oats, in balance with insoluble fibres, perform important roles in the digestive tract and are essential for maintenance of a healthy colon wall and colonic environment, being available for fermentation by “good bacteria” (pro-biotic microbes), and as such exert pre-biotic effects. Soluble fibre-based pre-biotic are becoming increasingly important as health-promoting functional foods (Macfarlane et al. 2006). Soluble fibres are mainly polysaccharides (e.g. beta glucans, arabinoxylans, plant gums) and oligosaccharides (e.g. fructo-oligosaccharides). These soluble materials are not digested in the human stomach and small intestine and survive mainly intact into the colon, at which point they are available for microbial fermentation (Würsch and Sunyer 1997). Antioxidants function is also helping to maintain the stability of processed oat products, and oat can stabilize oils and fats against rancidity (Truswell 2002).

Burkwheat

Buckwheat (Fagopyrum esculentum Moench) is known as a valuable source of protein, and its amino acid composition is nutritionally superior to that of cereal grains (Pomeranz & Robbins 1972). For many years, the cultivation of buckwheat was in decline, yet recently it has been observed to increase because of the health-promoting properties of its grains. Buckwheat grains and other tissues contain numerous nutraceutical compounds (Li & Zhang 2001). The amino acid composition of buckwheat proteins is well balanced and of a high biological value (Kato et al. 2001, Christa and Soral-Śmietana 2008). Buckwheat grains are an important source of microelements, such as: Zn, Cu, Mn, Se (Stibilj et al. 2004) and macro elements: K, Na, Ca, Mg (Wei et al. 2003) with 80% unsaturated fatty acids more than 40% are constituted by polyunsaturated fatty acid (PUFA) (Krkošková & Mrázová 2005). The significant contents of rutin, catechins and other polyphenols as well as their potential antioxidant activity are also of significance to the dietary value (Oomah & Mazza 1996, Wanatabe 1998). Moreover, buckwheat grains are a rich source of TDF (total dietary fibre), soluble dietary fibre (SDF), and are applied in the prevention of obesity and diabetes (Brennan 2005).

Cereal based fermented functional food

Fermentation is one of the oldest technologies used for food preservation. Research has reviled that by the process of fermentation flavor enhancing compounds, useful enzymes and essential amino acids are produced. Some fermentation microorganisms have been found to produce antimicrobial products that lead to safe and long storing of foods. Probiotics are live microorganisms associated with fermentation that, upon ingestion, beneficially affect their host by improving the balance of the intestinal microflora (Kalui et al. 2010). A specific type of mechanism by which probiotics may prevent and treat gastrointestinal disorders is represented in Figure 1. These health enhancing microorganisms bring about fermentation resulting in production of lactic acid and hence commonly referred to as Lactic acid bacteria (LAB) (Holzapfel and Schillinger 2002, Shah 2007). Most of them are generally regarded as safe (GRAS). Common microorganisms used in probiotic preparations are predominantly Lactobacillus species, such as Lactobacillus acidophilus, L. casei, L. reuteri, L. rhamnosus, L. johnsonii, and L. plantarum and Bifidobacterium species, such as Bifidobacterium longum, B. breve, B. lactis (Shortt, 1999).

Fig. 1
figure 1

Mechanisms by which probiotics may prevent and treat gastrointestinal disorders (adapted from Santosa et al. 2006)

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  1. a)

    Rice based products:

    A global interest in rice and its fermented product is increasing due to their calorie value, unique quality characteristics and high acceptability (Steinkraus 1994). In most of the countries, rice is fermented either by using mixed culture(s) into alcoholic beverages, or by natural fermentation into leavened batter formed dough breads which are usually baked or steamed (Yokotsuka 1991).

    1. 1.

      Idli:

      Cereal/legume-based foods are a major source of economical dietary energy and nutrients world-wide. Among the fermented food of India, idli, a fermented steamed product with a soft and spongy texture is a highly popular and widely consumed snack food in India. Traditionally, the product is made from naturally fermented batter prepared from a mixture of milled rice (Oryza sativa) and dehulled Blackgram dhal (Phaseolus mungo), the proportion of which varies (Desikachar et al. 1960, Radhakrishnamurthy et al. 1961). The lactic acid bacteria Leuconostoc mesenteroides, Streptococcus faecalis, Lactobacillus delbrueckii, Lactobacillus fermenti, Lactobacillus lactis and Pediococcus cerevisiae have been found to be responsible for the fermentation process, although L. mesenteroides and S.faecalis are considered to be the microorganism essential for leavening of the batter and for acid production in idli (Purushothaman et al. 1993, Ramakrishnan 1993).

    2. 2.

      Dosa:

      Dosa batter is similar to idli batter but the batter is thinner (Steinkraus 1996). After fermentation, the leavened dosa batter is baked on hot pan as a thin, crisp pancake and eaten with chutney and sambar (Purushothaman et al. 1977). A dosa suspension is prepared by grinding wet rice and black gram separately with water. The two suspensions are then mixed and allowed to undergo natural fermentation, usually for 8–20 h. To make a dosa, the fermented suspension is spread in a thin layer (of 1–5 mm thickness) on a flat heated plate, which is smeared with a little oil or fat. A sol to gel transformation occurs during the heating and within a few minutes, a circular, semi-soft to crisp product resembling a pancake, ready for consumption is obtained (Battacharya & Bhat 1997).

    3. 3.

      Dhokla:

      Dhokla is also similar to idli, but black gram is replaced by Bengal gram in the preparation (Battacharya & Bhat 1997). A mixture of rice and chickpea flour is also used as the substrate for the fermentation. As in idli preparation, the fermented batter is poured into a greased pie tin and steamed in an open steamer (Purushothaman et al. 1993, Ramakrishnan 1993). A significant improvement in the biological value and net protein utilisation of dhokla due to fermentation has been reported (Aliya & Geervani 1981, Sands & Hankin 1974).

    4. 4.

      Selroti:

      Selroti is a popular fermented rice-based ring shaped, spongy, pretzel like, deep fried food item commonly consumed in Sikkim and Darjeeling hills in India, Nepal and Bhutan.For the preparation of selroti, local variety of rice (Oryza sativa L.) attey is sorted, washed, and soaked in cold water for overnight or 4 to 8 h at ambient temperature. Water is then decanted from the rice by using bamboo made sieve called chalni and spread over a woven tray made up of bamboo, locally called naanglo and dried for 1 h. Soaked rice is pounded into coarse powder in a wooden mortar and pestle known as okhali and mushli, respectively. Larger particles of pounded rice flour are separated from the rest by winnowing in a bamboo tray. Then the rice flour is mixed with nearly 25% refined wheat (Triticum aestivum L.) flour, 25% sugar, 10% butter or fresh cream and 2.5% spices/condiments containing large cardamom (Amomum subulatum Roxb.), cloves (Syzygium aromaticum Merr.), coconut (Cocos nucifera L.), fennel (Foeniculum vulgare Mill.), nutmeg (Myristica fragrans Houtt.), cinnamon (Cinnamomum zeylanicum Bl.), and small cardamom (Elletaria cardamomum Maton.), are added to the rice flour and mixed thoroughly. Milk (boiled/unsoiled) or water is added, kneaded into a soft dough and finally into batter with easy flow. Batter is left to ferment naturally at ambient temperature (20–28οC) for 2 to 4 h during summer and at 10–18 °C for 6–8 h during winter. The oil is heated in a cast iron frying pan locally called tawa. The fermented batter is squeezed by hand or metallic serving spoon, deposited as continuous ring onto hot edible oil and fried until golden brown and is drained out from hot oil by poker locally called jheer or suiro or also by a spatula locally called jharna. Deep fried Selroti is served as confectionary (Yonzan Hannah & Tamang Jyoti Prakash 2009).

    5. 5.

      Khaman:

      Khaman is similar to dhokla, but it is made entirely of Bengal gram dhal. Idli, dhokla and khaman are steamed as soon as the batter is leavened and acidified. They are consumed the same day. The acid content retards the growth of food poisoning and food spoilage organisms (Sekar & Mariappan 2007).

    6. 6.

      Ambeli:

      Ambali is a fermented product from ragi [Eleusine coracana (L.) Gaertn] Leuconostoc mesenteroides (1.6 × 109/gm), Lactobacillus fermentum (1.6 × 109/gm) and Streptococcus faecalis (8 × 108/gm) have been isolated from fermented ragi. The pH usually decreases from 6.4 to 4.0 and volume increases by about 20%, indicating CO2 production (Ramakrishnan 1979).

    7. 7.

      Sez:

      The traditional semi-fermented food used by the Bhotiyas in Uttaranchal of India is called sez. It is made from rice, and is mostly used as snacks. Earlier, it was a delicacy and was prepared only during certain festivals. In most cases, sez is extracted while preparation of rice jann (local beer) (Roy et al. 2004).

    8. 8.

      Adai and Vada:

      Adai and vada both are cereal legume based breakfast or snack food in India. Pediococcus, Streptococcus, Leuconostoc are predominant microorganism required for the fermentation of both the products (Adams 1998, Chavan & Kadam 1989, Harlander 1992, Sankaran 1998, Soni & Sandhu 1990, Blandinob et al. 2003).

    9. 9.

      Bhattejaanr and Anarshe:

      Bhattejaanr and Anarshe both are rice based breakfast in India. Anarshe is sweetened snack food fermented by lactic acid bacteria whereas bhattejaanr is sweet and sour alcoholic paste fermented by Hansenula anomala and Mucor rouxianus (Adams 1998, Chavan & Kadam 1989, Harlander 1992, Sankaran 1998, Soni & Sandhu 1990, Blandinob et al. 2003).

  2. b)

    Wheat based fermented food:

    1. 1.

      Balam:

      The beverage jann is prepared using starter material called as balam in Kumaon and balma in Garhwal region of Uttaranchal. It is made up of wheat flour, clove (Cinnamomum zeylanicum Nees), elaichi (Amomum subulatum Roxb.), kalimirch (Piper longum L.) and leaves of wild chillies and seeds of pipal (Ficus religiosa L.). In addition, old balam is also mixed. The mixture is prepared with required amount of water and made into a thick paste. This mixture is pressed between palms to make balam balls of the required size. These are dried in shade and stored for future use (Roy et al. 2004).

    2. 2.

      Jalebi:

      It is a sweetened fermented product made from maida (refined wheat flour), dahi and water. The fermented batter is deep fat fried in oil in spiral shapes and immersed in sugar syrup for few minutes. This traditional food is prepared during marriage ceremonies and festivals of South India. Lactobacillus fermentum (6 × 108/gm),L. buchneri (3.2 × 108/gm, Streptococcus lactis (6 × 108/gm), S. faecalis (6 × 108/gm) and Saccharomyces cerevisiae are found in the fermented batter. The pH decreases from 4.4 to 3.3 and there is a 9% volume increase in the batter. Both amino nitrogen and free sugar decrease during fermentation (Steinkraus 1996).

    3. 3.

      Kulcha, Nan and Bhatura:

      Various types of traditional wheat based fermented snack foods like Bhatura (white wheat flour product), kulcha (white wheat flour product), Nan (wheat flour product), are prepared indigenously in India. For the fermentation of those products, mainly Saccharomyces cerevisiae, LAB are used (Sanjeev & Sandhu 1990).

    4. 4.

      Kurdi and Taotjo:

      Kurdi is a type of wheat based solid fried chips, whereas taotjo is a kind of condiment made from fermentation of roasted wheat meal by Aspergillus oryzae,it is mainly popular in eastern India (Adams 1998, Chavan & Kadam 1989, Harlander 1992, Sankaran 1998, Soni & Sandhu 1990, Blandinob et al. 2003).

    5. 5.

      Soy sauce:

      Soy sauce is a dark brown liquid, made from a blend of soybeans and wheat, that is mainly used as an all purpose seasoning in Japan, China and the Far East countries (Yokotsuka 1993). Soy sauces have a salty taste, but are lower in sodium than traditional table salt. The characteristic aroma and flavour of soy sauce is due to the enzymatic activities of yeasts and some LAB. As soybeans contain high levels of proteins and oligosaccharides, but no significant level of simple sugars, fermentation by lactic acid bacteria and yeasts requires the exogenous saccharifying enzymes supplied by the koji. In general, the pH of the sauce is between 4.6 and 4.8, and the typical salt concentration is 17–19%. Concentration of salt less than 16% can result in the development of putrefactive species during fermentation and ageing. On the contrary, levels greater than 19% interfere with the growth of halophilic bacteria such as Pediococcus halophilus and osmotic yeasts such as Z. rouxii (Beuchat 1983).

Conclusion

In the developed countries, due to large obesity problem and also for maintaining normal and sound health, different formulations and activities are coming up, specially delivering soluble fibres to the consumers via different foods like cereals and cereal products containing antioxidants. Cereals like wheat, maize, rice, oats etc. are now employed in preparation of food that are similar in appearance to conventional food and used in normal diet but have an added advantage of aiding physiological functions along with providing nutrition. Eating habits can drastically reduce healthcare expenditures if individuals were to modify their diets based on an existing knowledge of nutrition. In today’s world the development and utilization of different cereal based functional foods is a challenging task. Invention of newer technologies for processing of cereals to improve their nutritional value vis-à-vis their acceptability by the end users will be the focus area in the near future.