Starch Digestion in Pearl Millet (Pennisetum Glaucum (L.) R. Br
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Journal of Applied Botany and Food Quality 90, 126 - 131 (2017), DOI:10.5073/JABFQ.2017.090.015 1Laboratoire d’Etudes et Développement des Techniques d’Epuration et de Traitement des Eaux et Gestion Environnementale, Département de Chimie, Ecole Normale Supérieure de Kouba, Algiers, Algeria 2Département de Biologie, Ecole Normale Supérieure de Kouba, Algiers, Algeria 3Département de Physique, Ecole Normale Supérieure de laghouat, Algeria 4Département des Sciences et Techniques, Faculté de Technologie, Université Amar Télidji - Laghouat, Algeria Starch digestion in pearl millet (Pennisetum glaucum (L.) R. Br.) flour from arid area of Algeria Mohamed Lemgharbi1,2, Rachid Souilah1,3, Badreddine Belhadi1,4, Ladjel Terbag 1,3, Djaffar Djabali 1, Boubekeur Nadjemi 1 (Received August 28, 2016) Summary Grain digestibility also is important. Several works have been con- ducted to study the kinetics of starch digestion of different grains by To assess the nutritive value of minor cereals cultivated in arid ar- alpha-amylase (EZEOGU et al., 2005; FREI et al., 2003; GONI et al., eas of Algeria, nine pearl millet landraces were sampled from two 1997). The glycemic index (GI) is an in vitro measurement based regions: Tidikelt and Hoggar. Some qualitative and quantitative cha- on glycemic response to carbohydrate-containing foods, and allows racters of the panicle and grain were measured, as well as in vitro ranking of food on the basis of the rate of digestion and absorption of starch digestion of the grain flour. Considerable variation was recor- carbohydrates that they contain (ENGLYST et al., 1992; JENKINS et al., ded in seed color, endosperm texture and nutritional value of starch 1981). In vitro methods have also been used to classify foods based and protein content. In vitro starch digestion displayed a first-order on their digestion characteristics similar to the in vivo situation, and kinetic model. For all pearl millet landraces, starch was digested to to identify slow release of carbohydrate in foods (SCHWEIZER et al., a different extent; the hydrolysis index (HI) ranged from 22.29% to 1988; JENKINS et al., 1984). Food materials with GI values more 35.52% and the expected glycemic index (eGI) ranged from 27.41 than 70%, between 56 and 69% and lower than 55% are classified to 38.82. The results show that there is diversity in the physical and as high, medium and low GI foods, respectively (BRAND-MILLER chemical properties of pearl millet accessions from the arid areas of et al., 2003). Algeria: Tidikelt and Hoggar. This study confirms that pearl millet In the Sahara of Algeria, the Tidikelt and Hoggar regions are cha- has an acceptable nutritional value with a low glycemic index suit- racterized by a typical desert climate; they are very hot and very able for human health and nutrition. dry. Moreover, rains have been rare during the last ten years. Aridity of the climate is extreme and the ambient temperature is very high Keywords: Pearl millet, Starch digestion, First-order kinetics, Gly- in Tidikelt (in Salah), which is known to have temperatures ranging cemic index, Nutrition. from 7.8 to 45.2 °C, a very low annual rainfall (16.9 mm), and ir- rigation is done with saline water. The Hoggar region is known to have temperatures ranging from 10 to 38 °C, with daily temperatures Introduction ranging over 23 °C, annual rainfall rate ranging from 7 to 160 mm, Pearl millet [Pennisetum glaucum (L.) R. Br.] is a small-seeded grass and irrigation is done with ground water. Despite these local hard belonging to the Poaceae family and the Panicoideae subfamily. As it climatic conditions, indigenous millet has maintained its original is a drought tolerant crop and has the ability to grow on low fertility morphological diversity for centuries, and it has been able to accumu- soil and moisture (FAO and ICRISAT, 1996), it is mostly cultivated in late significant genetic diversity between populations. However, these arid and semi-arid areas of the Sahel in Africa and in Asia, where it environmental factors have affected the starch properties in different is a major food source. Millet is the 6th largest cereal crop in terms of Sorghum genotypes (BELHAdi et al., 2012; BOUDRIES et al., 2009; world agriculture production. Furthermore, millets have resistance to MASTSUKI et al., 2003). For example, pearl millet; (P. glaucum), is a pests and diseases, a short growing season, and are productive under cereal that also is called mil, mil à chandelle (French), and Dokhen drought conditions, compared to major cereals (DEVI et al., 2014). (Arabic); the local appellation is “bechnna” and “inélé”, originally Millets are unique among the cereals because of their richness in from West Africa, particularly, in the area north-east of the Senegal calcium, dietary fiber, polyphenols and protein. Furthermore, as they River. Millet was probably introduced during the eighth century into do not contain gluten, they can be recommended for use by celiac North Africa; its culture was intended to produce seed and fodder patients (DEVI et al., 2014). In addition to their nutritive value, several (TOSTAIN, 1998). Actually, pearl millet production in these margina- potential health benefits have been reported such as lowering the risk lized areas depends on traditional harvesting and processing. Most of of cancer and cardiovascular disease, lowering blood pressure and the harvest is used as animal feed and rarely for human consumption. risk of heart disease, lowering cholesterol and rate of fat absorption, In the past, a wide range of traditional food products has been made and delaying gastric emptying by supplying gastrointestinal bulk from millet including kisra, porridge, and beverage. (SALEH et al., 2013). One of the objectives of our laboratory research is to study the nutri- There are several plant characteristics that define grain quality, such tional and quality traits of Sorghum and pearl millet grains as well as their structural and biochemical characteristics, digestibility, and as the isolation of starch and protein fractions and their beneficial bioavailability of nutrients. The structure of the grain kernels varies characteristics for food and non-food uses (SOUILAH et al., 2014; significantly because of environmental and genetic factors. Shape, BELHAdi et al., 2012; HAdbAOUI et al., 2010; MOKRANE et al., 2010; size, proportion and nature of the endosperm, germ, and pericarp, the BOUDRIES et al., 2009; MOKRANE et al., 2009). In a previous work, presence and absence of a subcoat, and color of the pericarp are all the protein nutritional quality of seven Sorghum cultivars cultivated genetically determined (ROONEY and MURTY, 1982). in the Sahara of Algeria was assessed (MOKRANE et al., 2010). High percentages of protein, up to 16% db, were found in these cultivars * Corresponding author with a favorable amino acid composition. The measure of in vitro Starch digestion in pearl millet flours 127 pepsin digestibility shows that some cultivars exhibit high digestibi- In vitro starch digestion lity, whereas, other cultivars are characterized by their low digesti- In vitro starch digestion was determined according to the modified bility (MOKRANE et al., 2010). The measurement of in vitro starch method of GONI et al. (1997). Around 600 mg of pearl millet flour digestibility shows that the nine local Sorghum cultivars exhibit high was prepared in large tubes containing 25 ml of phosphate buffer digestibility of up to 90% (SOUILAH et al., 2014). (pH 6.9). To start starch hydrolysis, 5 ml of α-amylase (2×10-4 mg/ The aim of the present study is to evaluate the digestibility of starch ml), type VI.B from porcine pancreas (A3172, Sigma-Aldrich) was in Algerian arid area pearl millet grain cultivars by investigating added. The prepared mixture was incubated at 37 °C for 2 h with starch in vitro digestion in pearl millet grain flour, assessing the in constant shaking. Aliquots of 0.2 ml were withdrawn at 5, 10, 15, vitro digestion kinetic data, and evaluating the effect of landrace dif- 20, 30, 60, 90 and 120 min. α-Amylase was inactivated immediately ferences on kinetic parameters. by placing the tubes in a boiling water bath for 5 min. Then, 0.6 ml of a 0.4 M sodium-acetate buffer solution (pH 4.75), and 0.2 ml of an enzyme solution containing 0.833 μl of amyloglucosidase from Materials and methods Aspergillus niger (300 U/ml, Sigma, A-7095) were added. In order Materials to hydrolyze digested starch into glucose, the sample was incubated Nine pearl millet [Pennisetum glaucum (L.) R. Br.] grains from local at 60 °C for 45 min. Finally, the volume was adjusted to 1-5 ml with landraces were sampled from the arid Sahara areas of south Alge- distilled water and glucose concentration in the digesta was mea- ria: i.e., within Tidikelt and Hoggar. Landraces labeled as MLT.P, sured within the range (0.1-0.5 g/l) using an oxidase-peroxidase Kit MLT.P.P, MLT.Saf, MDT.Smix, MLT.Ham, MDT.Sepl, MLH.Z, (Biomaghreb, Tunisia). MLH.epc and MDH.Saf.T were harvested from different localities A concentration of free glucose (0.459 g/l) was used to correct the within Tidikelt and Hoggar; Djafou, Foggaret Ezzoua, El Malah, In starch digestion values. Starch digestion was expressed as percentage Amghel, Tamanrasset and Abalessa. The samples were characterized on the amount of starch present at the start of the reaction. by their kind of use (eg., cultivated millet, and domestic) and by dif- ferent harvest years (2008, 2010 and 2011). Tab. 1 lists pearl millet Modelling of starch digestograms landraces from arid areas of Algeria. First-order exponential kinetics were used to estimate starch hydro- Millet grains were ground to flour in IKA Labotechik using an A10 lysis and glycemic indices in the food and feed studies (EZOGU et al., sample mill.