Physicochemical and germinative properties of biofortified pearl millet (Pennisetum glaucum) varieties

Introduction

Pearl millet (Pennisetum glaucum (L.) R. Br.) is a nutricereal and is typically grown under hot, dry environments on infertile soils of low water-holding capacity, where other crops usually fail. Pearl millet is grown widely in the arid and semi-arid regions of Africa and Asia with 30 million hectares area under cultivation. In addition, pearl millet alone contributes to about 50% of the total world's millet production and ranks as the world's fourth most tropical food cereal (Kumari et al. 2022 and Sathyavathi et al. 2021) [19] . Physical properties are important in processing and value addition aspects such as thousand kernel weights, length, breadth and bulk density etc. Knowledge of the physical properties of grains and seeds is paramount in designing handling, transporting, storing processing equipment and nutritional security point of view (Mane et al 2022, Badau et al 2002) [21,6] . The germinative properties are useful in selecting grains for malting. In brewing industries, it is necessary to carry out a test on the viability of the grains by making germination counts. If germination falls below 65%, the grain is not viable enough to malt, because diastatic enzymes are activated only during germination (Badau et al 2006) [7] . It is known that pearl millet has a better nutritional profile than sorghum and other major cereals, as reported by other authors such as Mawouma et al., 2022 [23] and Iyabo et al. 2018 [17] . Pearl millet is a rich source of essential nutrients such as fiber and minerals-notably iron, zinc, and calcium, and thus, rightly said as "Nutri-cereal" (Thribhuvan et al., 2023) [39] .

Materials and Methods

Plant materials and preparation

The experiment material used for the study was four biofortified varieties and one nonbiofortified local variety (ABV-04, AHB-1200, RHB 234, Dhan Shakti and Pittaganti) which were collected from ICAR institutes, ICRISAT and State Agricultural Universities. In the laboratory, the samples were carefully cleaned manually to remove broken grains, stones, chaff and dirt and were stored in fresh clean Ziplock bags.

Physical properties Dimensional properties

A total of ten seeds for each replication were randomly selected from each variety. Three different dimensional properties (mm) were determined by measuring the length (L) and width (W) of the grains using a vernier digital calliper at an accuracy of 0.01 mm.

Bulk density

Bulk density (kg/m 3 ) is the ratio of the mass of the sample to its total volume. It was determined by filling a 500 mL cylinder with grains. Bulk density (kg/m3) was calculated as a ratio between the sample weight and the volume of the cylinder using Equation.

Grain 1000 grain weight

The thousand-grain weight was determined by weighing 30 grains in three replications by manual counting. The counted grain samples were weighed using a digital electronic balance with 0.01 g accuracy.

Sprout length

Sprout length was measured by taking the average of length of 10 sprouts (Dahiya 2017) [11] . The rootlets were separated from the germinated pearl millet kernels by rubbing the grains in a nylon bag of coarse mesh size, which allowed the rootlets to escape while retaining the kernels (Morrall et al., 1986).

Germinative energy

One hundred kernels grains were placed on two filter papers (Whatman No. 1; Whatman plc., Maidstone, UK) wetted with 4 ml of distilled water placed at the bottom of a petri dish, taking care to ensure that all the kernels were in good contact with the moist filter papers. The petri dish was then covered and incubated at an average temperature of 30 °C for 48 h. The kernels that sprouted at the end of the incubation were counted and germinative energy (GE) was expressed as suggested by Agbo (1996).

Where N = number of ungerminated grains.

Proximate Composition

The proximate analysis is a quantitative method to determine different macronutrients present in pearl millet grain (Fig. 3.3). It is the partition of seed compounds into various categories such as moisture (g/100 g), crude protein (g/100 g), fat (g/100 g), crude fibre and crude ash (g/100 g), carbohydrate (g/100 g) was estimated as per AOAC method (2006).

Minerals analysis

Raw, soaked and germinated grains were analysed separately for minerals (iron, zinc and calcium) by using ICP (Inductively Coupled Plasma-Optical emission Spectrometry) (Murcia et al., 1999).

Statistical analysis

The data was subjected to analysis of variance (ANOVA) for testing the significance of variation in millet varieties for physicochemical and germinative traits using the statistics software SPSS version 16.

Results and Discussion

Results of the physical and germinative properties of the grains are shown in Table 1.

Physical properties Size

The size of the pearl millet grain was determined in terms of linear dimensions (L, B and T). The range of length, bread and thickness were 2.61-3.30, 1.41-2.25 and 1.18-1.98 mm respectively. There is a significant variation (p<0.001) among all varieties studied for length, breadth and thickness. Prakash et al. 2019 [31] have shown similar results with average values of length, width and thickness varying from 2.997-3.172, 2.433-2.609 and 2.036-2.20 mm respectively. Ramashia et al. (2017) [33] [28] ranged from 7.45 to 13.20 g which is slightly higher than the present study. The pearl millet varieties showed wide variation in thousand-kernel weight with a range of 6.75 g to 12.97 g, 9.114 to 10.123 g and 4.64 to 13.01g according to Kumar et al. 2018 [20] , Prakash et al. 2019 [31] and Pallavi et al. 2020 [25] which were comparable to the present study.

Bulk density

Bulk density ranged from 681 to 800 kg/m 3 . Bulk Density has a significant variation among the varieties studied (p<0.001). The highest bulk density was observed in AHB1200 followed by Dhanshakti (783 kg/m 3 ). The lowest was recorded in the control variety. The mean bulk density in the Pawar et al. 2020 [27] study was 830 kg/m 3 . The mean Bulk Density varied from 827.5-711.9 kg/m 3 and 737.42-765.83 kg/m 3 according to Prakash et al. 2019 [31] and Santakar et al. 2020 respectively concurrent to the present study.

Germinative properties Sprout length

Sprout length was affected by germination time. Sprout length has increased with an increase in the germination period. Sprout length ranged from 0.12-0.80, 0.60-1.36 and 0.57-1.85 cm at 24 hours, 48 hours and 72 hours germination time respectively. Significantly (p<0.001) high sprout length was observed in RHB 234 and lowest in control. There was an increase in sprout length after 48-hour germination. Rootlets and coleoptile or acrospore were also developed after 48 and 72-hour germination. Further germination can lead to the development of the plant itself. Rootlets and coleoptile or acrospire were produced at the expense of material from original seeds which can lead to further loss in the yield of malt as reported by Agarwal et al. 2013. Similarly, Dahiya et al. 2017 [11] reported 0.31 and 1.95 cm of pearl millet sprout length at 24 Hr and 48 Hr germination time at 30 ˚C which is concurrent to the present study.

Germinative energy

Significant (p<0.001) high germinative energy was observed in AHB 1200 (97%) and lowest in control (27%). Dahiya et al. 2017 [11] and Pelembe et al. 2002 [29] reported similar germinative energy of 96.8 and 97.9% respectively. The germinative energy of pearl millet studied by Badau et al. 2006 [7] ranged from 95.0 to 97.0% concurrent to the present study. Germination energy (GE) is the component of seed vigour that corresponds to the speed and uniformity of seedling emergence (Zhang et al. 2020) [41] .

Proximate composition of biofortified pearl millet varieties

Results of proximate composition of the grains was shown in Table 2 Moisture (g) Moisture is an important determinant of food quality and affects the physical and chemical aspects of food which relates to the freshness and stability for storage for a long time, preservation and resistance to deterioration. It is necessary to calculate the content of other food constituents (i.e., total solids) on a uniform basis (i.e., dry weight basis) (Iswarya and Narayanan 2016) [16] . The mean moisture content was 9.26% and ranged between 8.69-10.10% with significantly (p<0.05) high moisture observed in RHB 234 and lowest in Dhanshakti. The moisture content of grains according to Sharma et al. 2023 [38] was ≤10% recommended as a safe limit, for extended preservation of flours. The moisture content of two pearl millet varieties reported were 11.33% in Tohamy millet and 12.67% in Chinese millet from the study of Ali 2023 [4] which was higher than the present study. The moisture content of pearl millet studied by Owheruo et al. 2019 [24] was 4.50% which is lower than the results obtained in the present study. [26] , Pawar et al. 2020 [27] and Iswarya and Narayanan (2016) [16] was 12.8%, 11.5% and 9.78 to 11.80% (Dhanshakti) protein which is higher than the present results. Owheruo et al., 2019 [24] recorded a low protein content in raw pearl millet flour of 7.61%. The www.extensionjournal.com protein content of pearl millet varied due to the varietal difference and the amount of nitrogen available in the soil (Iswarya and Narayanan 2016) [16] .

Fat (g/100 g) Fat content ranged from 4.92-5.88 g/100g with a significant (p<0.01) high value was observed in RHB 234 and lowest in Dhanshakti. Similar results were obtained by Pawase et al. 2021 [28] (4.85 to 5.50%), Satankar et al., (2020) [36] (5%), Pawar et al. 2020 [27] (4.9%), Hassan et al. 2021 [15] (5-7%) and Abdalla et al. 1998 [1] (2.7-7.1%). The fat content in the inbred lines of pearl millet ranged from 2.68 -7.3% as reported by Pallavi et al., 2023 [25] , higher than the present study. The fat content of pearl millet was noted to be 2.2 per cent according to Pandit et al. 2021 [26] which was lower than the present study.

The crude fat content is one of the important components in course cereal grain, which acts as a medium to provide fatsoluble components to human health, however during storage of course cereal flour, the action of lipase enzyme on fat leads to the production of free fatty acids and which leads to rancidity to cereal flour during storage. Hence to study of crude fat content is very important for course cereals flour and course cereal-based food products to increase their storage life.

Carbohydrate

Carbohydrate content ranges from 61.07-66.82 g/100g with the lowest found in ABV 04 and the highest found in AHB 1200 with an average of 64.48 g/100g. There is no significant variation of carbohydrates among the varieties studied. Similar results were obtained by Owheruo et al., 2019 [24] (74.41%) and 71.9 per cent in pearl millet (Pandit et al 2021) [26] . Lower carbohydrate content than the present study was reported by Pawar et al. 2020 [27] (67.0±0.50 %), Satankar et al., (2020) [36] (67.5 g/100 g), Abdalla et al. 1998 [1] (59-70 %.). The carbohydrates in pearl millet grains possess starch, dietary fiber, and soluble sugars. Starch is considered a predominant component of pearl millet endosperm, which comprises glucose in the form of amylase and amylopectin. Various pearl millet grain genotypes vary, in starch composition from 62.8 to 70.5% (Hassan et al. 2021) [15] . The average content of carbohydrates reported in pearl millet grains was 72.2%, which is lower than rice 84.9%, maize 78.1% and higher than wheat 68.8% on dry wt. basis according to Dias-Martins et al. (2018) [12] .

The mean ash content of the five varieties of pearl millet was 1.81 g/100 g with a range of 1.60-1.93 g/100 g. The highest ash was found in Dhanshakti and the lowest in ABV 04. There is no significant variation of ash among the varieties studied. Prajapati et al., (2019) [30] , showed that the ash content of pearl millet was 2%. Martínez-Ballesta (2010) [22] stated that environmental stressors such as high salt levels, low water accessibility, and excessive temperatures, are found to affect the mineral content of food. The ash content in the present study agrees with the findings of Florence et al., (2014) [13] , and Ramashia (2018) [33] where ash content is within the standard range of 1.6-3.6% in whole millet flour.

Crude fiber content

Crude fiber ranged from 1.50-2.37 mg/100 g with the significantly (p<0.01) low content was found in Dhanshakti and the highest in RHB 234. Variations of these levels are possible due to genotype, climatic conditions and soil nutrient content (Dias-Martins et al., 2018) [12] . Similar results were observed by Mawouma et al 2022 [23] , Pandit et al 2021 [26] , Pawase et al. 2021 [28] , Kulthe et al., 2016 [18] and Sade 2009 [35] . Crude fibre in food is a sign of slowly digestible carbohydrates. Crude fiber content of 1.55 g/100 g in pearl millet lessens the assimilation of glucose, fat during metabolism and enhances digestibility (Rajalakshmi et al 2021) [32] .

Energy

The calorific range of varieties studied was 361-390 k.cal/100g of pearl millet with no significant variation. Control has recorded significantly high kilocalories whereas lower kilocalories were observed in ABV 04. Similar results were observed by Choudhary et al. 2023 [10] , Sachan and Shah 2023 [34] and Rajalakshmi et al. 2021 [32] , whereas Sade et al. 2009 [35] recorded a higher energy range of 397-418 K.cal.

Mineral composition of biofortified pearl millet varieties Iron

The iron content of the raw grains ranged from 5.78-8.66 mg/100 g as shown in Table 3. The mean iron content across all varieties is 7.73 mg/100 g. A significant variation (p<0.05) in the iron content among the varieties studied. Significantly high iron content was found in raw grains of the Dhanshakti variety (8.66). Control variety Pittaganti (5.78) has the lowest iron content. Anitha et al 2024 [5] have reviewed that the iron content of pearl millet worldwide can range between 1.4-13.53 mg/100 g. Velu et al. 2008 [40] evaluated variability among 68 improved populations of pearl millet where the iron content of grains ranged from 42-79.9 mg/kg which was slightly less when compared to the present findings. Grain iron content for hybrids ranged from 4.79 to 9.56 mg/kg over environments among all the 30 hybrids evaluated by Thribhuvan et al. 2023 [39] which is in line with the present study.

Zinc

The range of zinc was 2.21-6.12 mg/100 g as shown in Table 3. ABV 04 raw grains (6.12) had the significant (p<0.001) highest zinc content among all the varieties. Significant (p<0.001) low content was observed in control variety grains (2.21). The mean zinc content among the varieties was 4.09 mg/100 g. There is a significant variation (p< 0.001) in the zinc content among the varieties studied.

Results are comparable with the earlier reports of Govindaraj et al. 2022 [14] with 928 entries of pearl millet in replicated trials during the 2012-2013 crop season in India the mean zinc content was 41 mg kg-1 . The mean zinc content of the genotypes studied by Berwal et al. 2017 [19] varied from 27 mg/kg to 51 mg/kg grains. The grain zinc content in the study of Thribhuvan et al., 2023 [39] varied 4.47 and 5.73 mg/100g among Cenchrus americanus (L) lines and from 3.83 to 6.08 mg/100 g among testers (10 restorers). In the earlier study of Ishwarya et al. 2016 where www.extensionjournal.com Dhanshakti has 3.59 mg/100 g of zinc and Sachan and Shah 2023 [34] recorded 1.84 mg/100 g in the available market sample which is lower when compared to the mean value obtained in the present study (4.09 mg/100 g).

Calcium

Calcium was observed to be in the range of 40.66-43.64 mg/100g as shown in Table 3. There is no significant variation in calcium among the varieties studied. Higher calcium content was found in Dhanshakti grains (43.64), whereas ABV 04 grains (40.66) had low calcium content. The mean calcium content was 42.31 mg/100 g. According to Ali, 2023 [4] , the calcium content of two pearl millet varieties studied was 26-27 mg/100 g which is less when compared to the present study. Prajapati et al. 2019 [30] showed that pearl millet's calcium content was 42 mg/100g. A range of 4-40 mg 100 g was recorded in the 14-trial study of Govindaraj et al. 2022 [14] which are in line with the current study. The calcium content ranged from 52.99 to 61.89 mg/ 100 g in the report given by Abdelrahaman et al 2007 [2] .

Conclusion

The study has shown that biofortified pearl millet varieties have superior physicochemical and germinative properties compared to non-biofortified local variety. Among biofortified varieties, Dhanshakti has shown superior quality. As consumer attentiveness is increasing towards the higher quality and nutritive value of the foods biofortified pearl millet can be added to the daily diet to increase the nutritional and inclusiveness to a balanced diet. Biofortified pearl millets are a good source of iron and zinc and can be effectively put to use in the manufacture of nutrient-rich foods to combat micronutrient deficiencies.

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