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Indian Journal of Nutrition

Research Article


Effects of Malting and Roasting of Millet and Sorghum on Protein Digestibility, Mineral Availability, Soluble Sugar Composition and Consumer Acceptability of Dakuwa

I Nkama1,3*, DI Gbenyi3 and BR Hamaker2

1Department of Food Science & Technology, University of Nigeria, Nsukka, Enugu State, Nigeria


2Department of Food Science, Purdue University, West Lafayette, IN 47907-1160


3Department of Food Science and Technology, University of Maiduguri, P. M. B 1069, Maiduguri, Borno State


Corresponding author: I Nkama, Department of Food Science & Technology, University of Nigeria, Nsukka, Enugu State,Nigeria, Tel No. +234-803-428-1885; E-mail: ironkamas@yahoo.com


Citation: Nkama I, Gbenyi DI, Hamaker BR. Effects of Malting and Roasting of Millet and Sorghum on Protein Digestibility, Mineral Availability, SolubleSugar Composition and Consumer Acceptability of Dakuwa. Indian J Nutri. 2015;2(1): 113.


Copyright © 2015 Nkama I, et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Indian Journal of Nutrition | ISSN: 2395-2326 | Volume: 2, Issue: 2


Submission: 21/09/2015; Accepted: 13/10/2015; Published: 19/10/2015


Abstract


The effects of germination and roasting of pearl millet and sorghum on the hydrochloric acid extractability of minerals, in vitro protein digestibility andacceptability of “dakuwa” (a cereal - groundnut based snack food) was investigated. Results show that there was a significant increase (p < 0.01) in theextractability of calcium, phosphorous and iron from malted millet and sorghum dakuwa. Germination of pearl millet and sorghum increased calcium extractabilityof dakuwa samples from 31.51 to 63.45 %, while iron and phosphorus extractabilities increased from 15.48 to 43.20 % and 39.02 to 62.23 % respectively. Theapparent protein digestibility of the dakuwa samples produced from malted millet and sorghum grains was significantly (p < 0.01) higher than that from theun-germinated grains. The germination of sorghum and millet prior to dakuwa production also significantly (p < 0.01) increased the soluble sugars contents(maltose, sucrose, glucose and fructose) of the final products. Sensory evaluation of the dakuwa samples revealed that malted and un-malted samples wereall acceptable to consumers, although sorghum based dakuwa was rated slightly higher than the millet based ones. No sample was rated as poor.


Keywords: Sorghum; Millet; Malting; Roasting; Protein digestibility; Mineral availability

Introduction


Pearl millet and sorghum are used in a wide variety of snackfoods made in every conceivable manner. In India and some WestAfrican countries pearl millet and sorghum are popped or patched,malted, eaten directly or used to produce various snacks, beveragesand pregelatinized weaning foods [1-4].


“Dakuwa” is one such snack food product produced fromsorghum, pearl millet, maize, tiger nuts and groundnut. It is a commonfood to the people living in Northern part of Nigeria especially theHausas. In the traditional method of its production, the grains are cleaned, roasted and ground together to form a cohesive mass withthe addition of sugar syrup, which is then moulded into small balls forsale [2] by children hawkers. Because it is a high protein energy food,dakuwa can serve as a good source of nutrient supplement to wartorn and famine ravaged areas for growing children, adults, lactatingwomen and the sick. Dakuwa is produced without consideration tothe presence of anti-nutritional factors such as phytates and tannins.


Several studies have shown that germination improves thenutritive value of the sprouts over the ungerminated seeds [5,6].Germination in addition to soaking and roasting has been found todecrease the levels of antinutrients present in the grain and maximize the levels of some utilizable nutrients [8-11]. Nkama & Gbenyi [10]investigated the effects of malting, and roasting on the residualphytate and tannin content of dakuwa. Phytate was reduced by 58% and 57% receptively in malted millet-groundnut, and maltedsorghum - groundnut dakuwa. Tannins were reduced by 91.4% and72.1% respectively in the same products. There are no reports on theeffects of malting and roasting on mineral availability, in vitro proteindigestibility, sugar composition and acceptability of dakuwa. Theobjective of this study was to provide this information.


Materials and Methods


Pearl millet (Peninsetum glaucum) variety Zango was obtainedfrom Lake Chad Research Institute, Maiduguri, Nigeria. Redsorghum (Sorghum bicolor), groundnut (Ex-Dakar), ginger (Zingiberofficinale), hot pepper (Capsicum annum) and salt were purchasedfrom Maiduguri, Monday market, Nigeria.


Sample preparation


All grains, except groundnut were cleaned using a laboratoryaspirator (Vegvari Ferenc Aspirator, type OB125, Hungary) toremove stalks, leaves and other foreign matter. They were thenseparately washed with clean tap water and sun dried. All grainsincluding groundnut were roasted to a light brown colour prior togrinding. The seed coat of the roasted groundnut was removed byfirst rubbing between the palms of the hand and then winnowing[2]. Defective groundnuts such as burnt and immature ones wereremoved by manual picking prior to grinding. The roasted grainswere separately ground using a laboratory attrition grinder (Amuda,India). Grinding was such that 92.6% of the flour passed through a400μm mesh sieve. Ginger, pepper were cleaned and dried in air oven(Chirana type HS 201A, Czechoslovakia) set at 100 °C for 2 hr beforegrinding and sieving to pass 400 μm mesh sieve.


Malt preparation


The millet and sorghum were steeped for 12 hr, germinated for 24hr and then oven dried at 50 °C. The roots and shoots were removedby hand rubbing [12].


Proximate analysis


Moisture, protein, fat, crude fiber and ash were determinedaccording to AOAC [13] methods. Carbohydrate was determined bydifference [14].


Preparation of dakuwa


The process reported by Nkama [2] was adopted with somemodifications (Figure 1). The cereal component was malted andhoney was also added. Millet and sorghum grains were malted asdescribed previously, and then roasted, ground before blending. Allingredients were mixed dry and pounded in a wooden mortar withpestle until very sticky. The honey was added as a binder to facilitatemounding of the dakuwa into the desired shapes.


Figure 1: Modified Laboratory Process for the preparation of dakuwa from malted millet and sorghum grains.


Mineral analysis


Minerals comprising Ca, Cu, Fe, and Mn were determined by theAACC [15] procedure using Atomic Absorption spectrophotometer(model: Perkin -Elmer-2380). The hydrochloric acid (HCI) extractable mineral was determined by the method described by Khetarpaul &Chauhan [16]. 1 g of sample was extracted with 0.03 N HCl solutionfor 3 hr at 37 °C. The filtrate was dried and the residue reported asthe proportion of the total extractable mineral. Total phosphoruswas determined spectrophotometrically by method of Osborne andVoogt [17]. The HCl extractable phosphorus was determined by themethod reported by Khetarpaul & Chauhan [16].


Soluble protein and in vitro protein digestibility


Soluble protein was determined by dissolving 2 g of each samplein 20 ml distilled water at 38 °C and filtering. The filtrate was collected,dried in air oven at 100 °C for 4 hr and soluble protein contentdetermined by Kjeldahl method [18]. In vitro protein digestibilityof samples was determined by the procedure described by Oke andUmoh [19]. 1.0 g of defatted meal was suspended in 1.0 ml 0.01 NNH4Cl and shaken for 48 hr at 35 °C. After centrifugation, the residuewas re-suspended in 10 ml of distilled water and 10ml of 0.1 N sodiumsulphate buffer, pH 8.0 added and then treated with 5 mg of trypsin(Garrad Biological Centre). The mixture was incubated for 16 hr at35 °C and centrifuged at 1000 g. The residue was washed, dried in an air oven and analyzed for nitrogen [17]. Percent digestibility wascalculated as loss of original nitrogen in the sample after enzymaticdigestion.


Soluble sugars


2.5 g of each sample was extracted in 25 ml distilled water at 65 °C,cooled and filtered. The filtrate 2 ml was taken into 10 ml volumetricflask and made up to volume with distilled water. The absorbance wasread using a spectrophotometer (UNICAM UV2 QUARTZ system)at 280 nm for maltose and fructose, 376 nm for sucrose, and 390 nmfor glucose [17].


Sensory evaluation


The hedonic scale was used to assess the degree of acceptability ofthe modified dakuwa samples in relation to the traditional one using15 untrained panelists familiar with dakuwa seated in air conditionedindividual boots in the sensory evaluation laboratory of theDepartment of Food Science and Technology, Federal polytechnic,Mubi, Nigeria. Samples molded into cube forms were served in cleanplastic plates. The panelists were provided with clean portable waterfor oral rinsing between samples. They were asked to rate the colour,texture, taste, flavour and overall acceptability of samples. The bestsample was ranked 6.0 with descriptive term ‘excellent’ while theworst sample was ranked 1.0 with descriptive term ‘very poor’ [20].


Statistical analysis


The statistical analyses were carried out using the analysis ofvariance procedure of the Statistical Analysis System [21]. Meanswere separated using Duncan Multiple Range Test (DMRT) method[22].


Results and Discussion


Proximate composition


The proximate composition of dakuwa samples is given in Table 1. There were significant differences (p ≤ 0.05) in the proximatecomposition of samples with respect to protein, fat, fibre andcarbohydrates. Protein ranged from 15.01 to 16.42% and fat 19.87-24.96%. The traditional dakuwa had the highest amount of fatcompared to the other samples. The moisture content of samples waslow and ranged from 5.93 - 6.36%. Addition of groundnut improvedthe nutrient composition of the product. The protein content ofsamples was within the range recommended for high protein foodproducts.


Table 1: Proximate composition of dakuwa samples 1,2


Mineral composition and HCl extractable minerals


The mineral composition of millet flour, sorghum flour,groundnut and dakuwa from them is given in Table 2. There weresignificant differences (p ≤ 0.01) in the mineral composition ofsamples. Millet flour had more calcium and copper than sorghumand groundnut flour. Groundnut had more iron and manganese thanmillet and sorghum flour. The mineral composition of the dakuwasamples followed that of the raw materials used in their preparation.The iron and calcium content of millet, sorghum and groundnut aresimilar to reported values [23]. Generally mineral composition waslow. It is suggested that if dakuwa is to be produced commercially,mineral fortification would be required especially if it is to be used asa supplementary food for the vulnerable groups.


Table 2: Mineral composition of raw material and dakuwa samples in (mg/100g) 1,2


Table 3 shows the effect of germination on the hydrochloricacid (0.03N HCl) extractability of calcium, phosphorus and iron.There was a significant increase (p ≤ 0.01) in the extractability of both calcium and iron from the germinated millet and sorghumflours. Germination of pearl millet and sorghum increased calciumextractability from 38.59 to 61.99 % and 26.51 to 61.49 % respectively.Iron extractability increased from 22.03 to 36.56% for millet and 14.34to 24.63% for sorghum flours. Similarly, phosphorus extractabilityincreased from 28.51 to 43.0 5 % for millet and from 31.02 to 42.09%for sorghum.


Table 3: Effect of germination and roasting on the percent HCl extractability of divalent cations (minerals) mg/100g 1,2


These results are similar to values reported by Khetarpaul &Chauhan [16]. The HCl extractability of phosphorus, calcium andiron is indication of their bioavailability to humans [16]. The increasesin HCl extractability of calcium, phosphorus and iron may be dueto the breakdown of phytates and polyphenols in these cereals byenzymes during germination [8,10]. Nkama & Gbenyi [10] reportedphytate reduction of 58 % and 57% respectively for malted dakuwafrom sorghum and millet. Also tannin was reduced by 91.4% and 72.1% respectively in malted millet and sorghum dakuwa. The calcium,phosphorus and iron content of dakuwa samples from germinatedmillet and sorghum were also observed to double that of the dakuwafrom ungerminated ones.


Protein solubility and in vitro protein digestibility


Table 4 shows the results of protein solubility and in vitroprotein digestibility of raw grain samples, roasted flour and dakuwa Table 4 shows the results of protein solubility and in vitroprotein digestibility of raw grain samples, roasted flour and dakuwa


Table 4: Apparent protein digestibility of cereal flours and dakuwa samples (units/g) 1,2


Table 4 also shows the apparent protein digestibility (in vitro)of samples. There were significant differences in apparent proteindigestibility (p ≤ 0.01). Raw sorghum grain flour had the lowestdigestibility (38.29%). Hamaker et al. [25] made similar observations.The reason for this low protein digestibility is not very clear. Itmay however be due to the presence of kiffirins, which are the lastproteins to be digested in sorghum flour [25,26] or probably due tothe presence of polyphenols, which bind proteins and make themunavailable for digestion [27]. Malted millet dakuwa had the highestapparent protein digestibility (71.47%), while unmalted sorghumdakuwa had the lowest apparent protein digestibility after 16 hrenzyme digestion. Generally, malted cereal based dakuwa sampleshad higher apparent digestibility values compared to dakuwa fromunmalted cereal dakuwa samples. This may be due to the hydrolysis ofthe anti-nutrients such as phytate and polyphenol during germination [25,27]. Nkama and Gbenyi (10) reported a significant degradationof phytates (57-58%) and polyphenol (72-91%) in dakuwa producedfrom malted millet and malted sorghum.


Soluble sugars


There was significant increase (p ≤ 0.01) in the concentrationof all sugars in the germinated sorghum and millet and the dakuwaproduced from them (Table 5). These increases may be due to diastaticactivity caused by germination of the grains. Subramanian et al. [28]and Khetarpaul and Chauhan [25] also reported significant increasesin diastatic activity and in vitro starch digestibility when sorghum andmillet grains were respectively germinated. Maltose increased by 71%in malted millet based dakuwa and 64 % in the malted sorghum basedone. Also fructose increased by 52% in malted millet based dakuwaand 68% in malted sorghum based dakuwa [28,29].


Table 5: sugar content of various flours and dakuwa samples (mg/ 100g)1,2


Sensory properties


The results of the sensory properties of the malted and traditionaldakuwa samples are given in Table 6. There were no significantdifferences among samples in terms of texture and flavor. There werehowever significantly differences (p ≤ 0.01) in overall acceptability andcolour. Unmalted sorghum dakuwa had the highest rating, followedby the traditional dakuwa, and then malted sorghum dakuwa. Themalted millet dakuwa was rated lowest in overall acceptability. Nosample was rated as ‘poor’ or “very poor”. The reason for the lowoverall acceptability of millet based dakuwa may be due to the factthat the sensory evaluation was conducted in a location (AdamawaState) in Nigeria where sorghum is the most popular cereal and thered sorghum is the most preferred for the production of dakuwa.


Table 6: Sensory evaluation results for dakuwa samples1,2


Conclusion


The study has revealed that an acceptable dakuwa with increasedprotein digestibility, soluble sugars and mineral availability can beproduced from malted pearl millet and sorghum. Efforts should bedirected along this line in attempt to commercialize the product. Thestorage and packaging studies of dakuwa should be investigated aseffort is geared to popularize it in the country. Since one of the majoringredients groundnut is associated with mycotoxins effort should bemade to screen groundnuts used for dakuwa production.


Acknowledgement


This study was supported in part by grants from the SWISSCorporation to West and Central African Millet Research Network(ROCAFREMI-WCAMRN) through Lake Chad Research Instituteand from INTSORMIL Management Entity, University of Nebraskato University of Maiduguri.


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