ReviewPotential use of pearl millet (Pennisetum glaucum (L.) R. Br.) in Brazil: Food security, processing, health benefits and nutritional products
Graphical abstract
Introduction
Cereals have been consumed by humans for thousands of years, and they play an important role in our diet as the main source of energy. World cereal production has been increasing by about 1 billion tonnes over the last 50 years; in 2016, production was 29% greater than 2013 (FAOSTAT, 2017). In this scenario, Brazil is the world's sixth largest cereal producer (about 3% of world production), an average of 85 million tonnes in 2016. In that year, the most produced cereal in Brazil were maize (76%), rice (13%), wheat (8%) and sorghum (1%) (FAOSTAT, 2017).
The agricultural production is one of the most vulnerable sectors to climate change (Alexandratos & Bruinsma, 2012). Also, increase in global temperatures, global water deficit, contamination by mycotoxins associated with increasing world population (estimated in 9 billion by 2050) will be responsible for substantial reduction of crop yields resulting in price increase and major food security concerns (Al-Amin & Ahmed, 2016; Khanal & Mishra, 2017). Thus, questions about which crops should be considered to overcome those negative effects are major challenges facing the agribusiness (Daryanto, Wang, & Jacinthe, 2016).
In this context, pearl millet may be an alternative crop that exhibits great advantageous physiological characteristics when compared to other cereals as it is resistant to drought, low soil fertility, high salinity and high temperature tolerance (Rai, Gowda, Reddy, & Sehgal, 2008). These characteristics are due to its extensive root system, which allows effective water and nutrients extraction from deeper soil layers (Netto & Durães, 2005). In addition for being a non-trangenic crop (Dunwell, 2014), millet has a low incidence of mycotoxin contamination compared to other crops, such as wheat and maize (Bandyopadhyay, Kumar, & Leslie, 2007; Jurjevic, Wilson, Wilson, & Casper, 2007; Kumar, Basu, & Rajendran, 2008; Ware et al., 2017; Wilson et al., 2006).
Millet, which is a generic term that includes various small grain species belonging to the Poaceae family of grasses, has been a food source for humans for more than 10,000 years (Lu et al., 2005; Lu et al., 2009). In 2016, millet stood out as the sixth most produced cereal in the world (28 million tonnes) (FAOSTAT, 2017). However, it is classified as a subsistence crop, and approximately 90% of world production is destined for human consumption in poor regions of Africa and Asia (Council, 1996). One of the major impediment that has restrained the increase of millet production is the scarce economic and technological support provided (Macauley & Ramadjita, 2015). This can be clearly evidenced by observing the world average productivity from the last fifty years, where this crop continues to present the lowest average yield (0.8 t ha−1) when compared to other crops of same botanical family, such as maize (4.0 t ha−1), rice (3.8 t ha−1); wheat (2.6 t ha−1); barley (2.5 t ha−1); rye (2.3 t ha−1); oats (2.1 t ha−1) and sorghum (1.5 t ha−1) (FAOSTAT, 2017b). On the other hand, low productivity is the result of a lack of investment on research genetic programs associated with low use of agronomical techniques, such us fertilizers and mechanization (Macauley & Ramadjita, 2015).
The millet species have different physiological characteristics compared to other cereal crops as they are resistant to drought, low soil fertility, high salinity and high temperatures. These characteristics are due to the extensive root system of these grasses, which allows extraction of water and nutrients from deeper soil layers (Devi, Vijayabharathi, Sathyabama, Malleshi, & Priyadarisini, 2014).
There are several common names of millets: Pearl millet (Pennisetum glaucum (L.) R. Br., Pennisetum typhoides auct. Non (Burm.) Stapf & C.E. Hubbard., Pennisetum americanum (L.) Leeke, Pennisetum spicatum (L.) Körn), Finger Millet (Eleusine coracana (L.) Gaertn), Kodo millet (Paspalum scrobiculatum L.), Little millet (Panicum sumatrense Roth ex Roem. & Schult), Proso Millet (Panicum miliaceum (L.), Foxtail millet (Setaria italica (L.) P. Beauv.), Barnyard millet Japanese, (Echinochloa esculenta (A. Braun) H. Scholz, Echinochloa frumentacea L.; Echinochloa utilis Ohwi & Yab.), Browntop millet (Urochloa ramosa (L.) Nguyen, Brachiaria ramosum (L.) Stapf); Sawa millet (Echinochloa colona (L.) Link), White fonio (Digitaria exilis (Kippist) Stapf) and Black fonio (Digitaria iburua Stapf) (FAO, 1995; USDA,2016a). The Food and Agriculture Organization, FAOSTAT, does not distinguish the production of the different millet species, except pearl millet (Pennisetum glaucum (L.) R. Br.) which is the most produced specie; however, in China, foxtail millet is the most relevant (Taylor, 2016).
Pearl millet grains can be processed and consumed as ingredients in diversified foods. They are called “nutri-cereals” because of their high protein, fiber, mineral, and fatty acids contents, as well as their antioxidant properties. Also they are an alternative food for celiacs and gluten sensitive individuals (Annor, Marcone, Corredig, Bertoft, & Seetharaman, 2015; Chandrasekara, Naczk, & Shahidi, 2012; Rona et al., 2007; Saleh, Zhang, Chen, & Shen, 2013). Furthermore, the chemical composition of millet grains can promote various health benefits such as reduction of oxidative stress among others (Islam, Manna, & Reddy, 2015; Nani et al., 2015).
Despite its nutritional potential, pearl millet is only used for cereal tillage (vegetable cover for mulch) and feed (grain and forage) in Brazil (Netto & Durães, 2005). The total tillage area in Brazil is around 32 million ha, and pearl millet (Pennisetum glaucum (L.) R. Br.) is one of the main cover crops in the Cerrado and the Southern region, in systems of rotation for important commodities, such as soy, maize and cotton (FEBRAPDP, 2012; FEBRAPDP, 2017; Netto & Durães, 2005). Although, millet is not consumed by man in Brazil, this cereal could be considered as an alternative food for human consumption because of its availability, nutritional aspects and also as a source gluten-free food. Thus, this review aims to emphasize the important nutritional and technological potential of pearl millet grains for human consumption, by awakening food industries and consumers to its benefits specially for celiacs and diabetic individuals due to its low glycemic index.
Section snippets
Pearl millet grain
Pearl millet is an erect grass that has a summer annual cycle of between 75 and 120 days depending on the environmental conditions. Usually, it is of fast growth and reaches an average height of 1.5 to 3 m (Fig. 1). The plant develops compact cylindrical panicles that are 2 to 3 cm wide and 15 to 60 cm long capable of producing between 500 and 2000 seeds per panicle (Durães, Magalhães, & dos Santos, 2003; Taylor, 2016). Its seeds are oval shaped, similar to a pearl, from which it gets its name.
Uses of pearl millet in Brazil
Pearl millet (Pennisetum glaucum (L.) R. Br.) was first introduced to Brazil in 1929 and since then, it has been adapted to the South, Southeast and Center-West regions of the country (Burton, 1972; Kiill, 2005).
Since the 1960s, the research program on P. glaucum in Brazil, has focused on improving the agronomic characterization of cultivars that can be used for different purposes, such as: soil cover for no-tillage systems, forage plant, silage or as grains for animal feed (Campelo, Teixeira
Nutritional quality of pearl millet grains
In recent years, there has been an increase of products based on whole grains because they contain a higher content of dietary fiber, micronutrients and bioactive compounds (Gong et al., 2018). Pearl millet grains can be considered a possible alternative for food diversification because they have the fibers, minerals, proteins and antioxidants with similar or even higher levels than those found in traditional grains such as rice and maize (Saldivar, 2003; Taylor, 2016). The chemical composition
Grain processing and effects
The post-harvest millet process starts with the separation of the grains from the panicle, removal of soils, such as stones and sands followed by debranning. Wholemeal products do not require debranning. Subsequently the grains can be submitted to different secondary processes, such as physical (milling, decortication, cooking, roasting, blanching, extrusion and popping), chemical (acid treatment) and biological processes (fermentation, germination), for elaboration of diversified food
Health promoting properties
Pearl millet grains have several functional properties, due to their high fiber content, fatty acid composition and phytochemical compounds (Annor et al., 2015; Patel, 2015). In addition to its anti-inflammatory, antihypertensive, anticarcinogenic characteristics, and the presence of antioxidant compounds, pearl millet also helps to reduce the risk of heart diseases, inflammatory bowel disease and atherosclerosis (Chandrasekara and Shahidi, 2011a, Chandrasekara and Shahidi, 2011b; Romier,
Foods and beverages products of pearl millet
In Africa and India, pearl millet grains are used to produce a wide variety of traditional local foods, such as porridges, flatbreads, couscous, sweets, alcoholic beverages (opaque beer or Dogon millet beer, chibuku shake, mbeg, merissa) and non-alcoholic drink (pombe, pito, boza, kunun Zaki, bushera, mahewu, oskikundu, marewa) (Adebiyi, Obadina, Adebo, & Kayitesi, 2018). Most of these products are produced in household or in small production units consumed in the main meals. However, few
Conclusions
Based on the information presented, pearl millet grains have great potential as food, due to some relevant nutritional characteristics like: high protein content, dietary fibers and minerals, besides it is considered a low cost crop. In addition, millet has great relevance for guaranteeing food safety, due to the agronomic characteristics of the crop, such as resistance to high temperatures and low rainfall requirements, also the grains have a low incidence of mycotoxins and it is not a
Future perspective and challenges to stimulate the consumption of millet as food in Brazil
Despite the fact that Brazil has the third largest number of international publications on agronomic aspects of pearl millet (search based on Scopus®, 2018 abstract and citation database), studies on the potential use of this cereal as food are still scarce in this country. Based on the present review, it seems clear that pearl millet is a viable cereal alternative for Brazilians consumers and also for export if millet consumption demand increases worldwide. As vast Brazilian agricultural lands
Acknowledgment
The authors would like to give special thanks to Hari Chandana Ponnaluri of blendwithspices (India), Ozoz Sokoh of kitchenbutterfly (Nigeria); Urvi Zanzmera of myfoodmyway (India) and Vinayak Agrawal of hungryhitchhiker (India) for the kindly provided photographs included in this work and, the sholarships received by Amanda M. Dias Martins and Carlos W. P. Carvalho from CAPES and CNPq, respectively.
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