Effect of the germination period on functional properties of finger millet flour and sensorial quality of porridge

Abstract Finger millet is a stable and nutritious cereal crop, mostly grown in the semiarid tropics of the world. Processing is important for improving the nutritional value of finger millets. The aim of the research was to evaluate the effect of the germination period on the functional properties of flours and the sensorial quality of finger millet porridge. Four finger millet varieties were collected, cleaned, and soaked for 24 h, then germinated at room temperature (20–25°C) for 24, 48, and 72 h. The germinated samples were oven‐dried at 60°C for 6 h and milled into flour at the size of 1 mm using a cyclomiller. Unsoaked and ungerminated finger millet grains are also milled into flour and used as control. Porridge was prepared with a flour‐to‐water ratio of 1:12 (weight/volume), and sensory analysis was done by semitrained panelists. Germination enhanced the water absorption capacity, solubility, and oil absorption capacity of flour samples significantly (p < .05). However, it significantly reduced (p < .05) the bulk density and swelling power of flour samples. As the germination period increased from 0 to 72 h, the viscosity of the porridge decreased significantly (p < .05). At 24 h after germination, the sensory analysis revealed no significant difference in color, taste, aroma, mouth feel, or overall acceptability samples when compared to the ungerminated sample. Germination improved the functional properties of finger millet flours as well as the sensory aspects of porridge. Hence, 24‐h germinated finger millet flour is best in all aspects compared to ungerminated, 48‐ and 72‐h germinated flours to prepare porridge. The 24‐h germinated finger millet‐based porridge is recommended for infants, pregnant mothers, and breastfeeding mothers.

beneficial millet grown in the world and is ranked fourth following sorghum (Sorghum bicolor), pearl millet (Pennisetum glaucum), and foxtail millet (Setaria Italica). Finger millet yield constitutes 11% of all millets produced worldwide (Bachar et al., 2013). Mostly, it is produced in the eastern part of African subhumid areas (Opole, 2019).
Finger millet is mainly cultivated in Africa, especially in Uganda, Kenya, Tanzania, Ethiopia, Rwanda, Burundi, Zambia, and Malawi (Opole, 2019). Finger millet (Degussa) contributes about 4% of the total grain yield in Ethiopia and covers an average of 5% of total cereal land (Keneni, 2018).
Finger millet grain has different colors such as brown, light brown and white (Kumar et al., 2016). The white and brown colors are mainly used for the baking industry and porridge, respectively, and also the brown finger millet grain is used in Southern Africa for brewing traditional opaque beer (Ramashia et al., 2019). In Ethiopia, the finger millet grain is used to make bread, injera, porridge, cake, soup, local beer, and distilled spirits, either alone or in combination with wheat, teff, maize, and barley (Asfaw et al., 2011).
Finger millet is an underutilized cereal crop in developing countries but it has a significant role in sub-Saharan Africa and other developing countries in food security system for many poor farmers because of its nutritional value and excellent storage conditions (Amadou et al., 2013). In addition to contributing to food and nutrition security, finger millet is a promising export crop for the country (Gebre, 2019). Although finger millet can be stored for a long time without deterioration or damage, its productivity is low due to a lack of improved finger millet varieties, diseases, improper input application, a negative attitude toward the crop, threshing and milling issues, and a lack of research focus on the crop (Ayalew, 2015). The problem of traditionally made infant porridge is generally rich in water and low in energy. This is due to the structure of native starch which exhibits high ability to absorb water and swell. Conceptually, the porridge must flow enough to help the baby swallow it easily, and it must contain enough dry matter to provide with the energy needed. For this to be achieved, treatments are needed. Germination is used to soften the kernel structure and to increase the nutritional composition and the functional properties of grains (Pushparaj & Urooj, 2011). The breakdown of high-molecular-weight polymers during germination produces bio-functional molecules and enhances the organoleptic properties of certain grains by softening their texture and enhancing their flavor (Banerjee et al., 2020). According to Afify et al. (2015), sorghum flour's capacity to absorb water increased after germination. Nefale and Mashau (2018) explained the effect of germination periods on the pH, viscosity, total titratable acidity, and functional properties of finger millet flour. However, the current research finding focused on the evaluation of the effect of germination duration on functional properties and sensorial quality of finger millet porridge.

| Sample collection and preparation
Axum, Meba, Tadesse, and Tessema improved finger millet cultivars were collected from Melkassa Agricultural Research Center.
For sample preparation and analysis, the obtained samples were transported to Melkassa Food Science and Nutrition Research Laboratory. Finger millet grains were cleaned and sorted to remove stone, dust particles, and broken, undersized, and immature grains.
About 2.4 kg of finger millet grains was taken from each variety and washed three to four times using tap water. Among these, 600 g of sun-dried finger millet grain was milled into flour at 1-mm sieve size using a cyclomiller and used as a control. The remaining cleaned and washed finger millet grains were soaked for 24 h at room temperature (20-25°C) in a seed-to-water (1:3) ratio, as described by Derbew and Moges (2017), with slight modifications. The steeping water and grain were separated using a plastic sieve and the grains placed in muslin cloths. The soaked and washed grains were germinated for 24, 48, and 72 h in plastic bags at room temperature (20-25°C). Then, the germinated finger millet grains were ovendried at 60°C for 6 h, milled using Cyclomiller, and sieved at 1 mm to get germinated finger millet flour. The flour was packed using an airtight polyethylene bag and stored at room temperature until further laboratory analysis.

| Porridge preparation and sensory evaluation
Porridge was developed from germinated finger millet flour as indicated by Onyango and Wanjala (2018). Fifty grams of flour was taken and mixed with 600 ml of water at a ratio of 1:12 (w/v). Then, it was cooked at 92°C for 20 min by adding 7 g of sugar which was used as a flavoring agent. The porridge was prepared at Melkassa Agricultural Research Center (MARC) in Food Science and Nutrition laboratory. The samples were coded with three digits and kept far apart to avoid crowding and for independent judgment.
The porridge samples that were prepared from ungerminated and germinated finger millet were tasted by 15 semitrained panelists using a 9-point hedonic scale from extremely like up to extremely dislike (Wichchukit & O'Mahony, 2015). Most of the panelists were women and selected from Food Science and Nutrition division and other staffs found in Melkassa Agricultural Research Center (MARC), Melkassa, Ethiopia. The panelists were given information about the purpose of the test and how to test the samples.
The panelists were asked to rinse their mouth before and after tasting the porridge samples. According to the given instruction, the panelists rated the color, aroma, taste, mouth feel, and overall acceptability of the porridge samples.

| Determination of bulk density
The bulk density of the flour was determined based on the method used by Baranwal and Sankhla (2019) as cited by Edema et al. (2005).
Fifty grams of sample was put into 100-ml measuring cylinder. The cylinder was tapped on a laboratory bench continuously until a constant volume was obtained. Then, the volume of the sample was recorded. The bulk density was calculated according to the following formula.

| Determination of water absorption capacity
The water absorption capacity of the flour was determined with the method reported by Hellemans (1998). Ten milliliters of distilled water and 1-g flour were added into a weighed centrifuge tube and stirred six times for 1 min at 10-min intervals. The mixtures were centrifuged at 3000 rpm for 25 min and the clear supernatant was decanted and discarded. The adhering drops of water were removed and weighed. Water absorption was expressed as the weight of water bound by 100-g dried flour.

| Determination of dispersibility
Dispersibility of the flour was determined by the method as cited by Edema et al. (2005). Ten grams of flour was measured and added into 100-ml measuring cylinder. Distilled water was added up to 100 ml volume. Then, it was stirred and allowed to settle for 3 h. The volume of settled particles was recorded. The percentage of dispersibility was calculated based on the following formula.

| Determination of oil absorption capacity
Oil absorption capacity was determined using the method reported by Edema et al. (2005). The weight of 1-g flour was taken and 10 ml of corn oil was measured (v1) and added into 25-ml centrifuge tube.
Then, it was stirred for 2 min and centrifuged for 20 min at 4000 rpm.
The separate oil formed as supernatant was measured in 10-ml cylinder (v2). The oil absorption capacity was calculated as follows.
where v1 is the initial volume of oil; v2 is the volume of oil formed as supernatant.

| Swelling power and solubility
Swelling power and solubility were analyzed as described by Adeyeye and Akingbala (2015). One gram of sample (w1) and 10-ml distilled water were added into the weighed centrifuge tube (w2).
The sample was stirred occasionally by heating for 30 min at 90°C.
After stirring, it was cooled and centrifuged at 5000 rpm for 10 min.
The supernatant was decanted into the Petri plate and weighed (w4).
The weight of the Petri plate was taken after drying in oven at 105°C and also the weight of the centrifuge tube (w3) was recorded after removing the supernatant. The swelling power and solubility were calculated as follows.
where w1 is the weight of sample; w2 is the weight of centrifuge tube; w3 is the weight of left/viscous flour.
where w1 is the weight of sample; w2 is the weight of centrifuge tube; w4 is the weight of dried supernatant; VE is the volume of distilled water.

| Determination of viscosity
The viscosity of porridge was determined by Brookfield viscometer as cited by Derbew and Moges (2017). The porridge was maintained in water bath at 50°C for 10 min. The samples were poured into a viscometer beaker and the viscometer was calibrated at Spindle 4 and 100 rpm. Finally, the viscosity of the porridge was taken after 1 min.

| Statistical analysis
The variation between the mean levels of all treatments was analyzed by two-way ANOVA using SPSS version 23.0 (SPSS Inc.). Sample treatment comparisons were analyzed statistically using Duncan's multiple range post-hoc test with a probability p < .05 significantly different. All measurements were performed in triplicate and the results were recorded as mean ± standard deviation (SD).  The reduction of the bulk density during germination might be due to the breakdown of complex compounds like protein and starch into smaller constituents (Ocheme et al., 2015).
A similar observation has been reported by Obadina et al. (2017) who showed that the bulk density of ex-boron pearl millet variety flour decreased significantly (p < .05) as malting time increased.
The Mungbean malt flour had lower bulk density than unmalted flour as indicated by Onwurafor et al. (2020). Basically oil absorption capacity increased as germination period increased but not significantly. This is due to the hydrolysis of starch during germination because the hydrolyzed starch absorbs more water and oil (Horstmann et al., 2017). Similar results were indicated by Kumar et al. (2021) (Kumar et al., 2021). A similar observation was conducted by Kumar et al. (2021) who reported that water solubility index increased significantly with increasing germination time.

| Effect of germination period on sensory attributes of finger millet porridge
The result of sensory analysis of porridge that prepared from germinated finger millet is indicated in Table 2. The sensory quality such as color, taste, aroma, mouth feel, and overall acceptability of porridge was evaluated by panelist. Mostly, the choice of panelists for attributes of color, taste, aroma, mouth feel, and overall acceptability of the porridge decreased as germination time increased. This might be due to the production of organic acid increased during germination and as result, it affects the color, taste, aroma, appearance, and overall acceptability of the products.

| Color
The color of porridge developed from ungerminated and 24-h ger- According to the finding of the current study, both similar and opposite results were stated by different researchers in sensory attributes of porridge. Ocheme and Chinma (2008) stated that the color of porridge was reduced significantly (p < .05) compared to ungerminated millet flour but no significant difference in aroma, taste, and overall acceptability of the porridge. The color, odor, taste, and texture of malted millet fura decreased significantly (p < .05) at 24 h compared with unmalted millet fura as reported by Auta et al. (2014).
There was a significant difference (p < .05) in the color, aroma, taste, and overall acceptability of finger millet porridge at 72-h germination but there was no significant difference in the mouth feel of the porridge to the rest of porridge samples based on the report of Nefale and Mashau (2018). The other previous report on germinated finger millet indicated that there was a significant difference (p < .05) in the color, aroma, taste, and overall acceptability of finger millet porridge at 72-h germination but there was no significant difference in the mouth feel of the porridge to the rest of porridge samples (Nefale & Mashau, 2018).

| Viscosity
The viscosity of porridge that is prepared from germinated and ungerminated finger millet is presented in  Gardner et al. (2002), porridge with a viscosity of less than 500 m.pa.s is better for infants because it helps them to ingest more food more easily and increases the nutrient density of the porridge.
There was no significant difference between the viscosity of 48and 72-h germinated finger millet porridge. However, the viscosity of porridge that was prepared from 24-, 48-, and 72-h germinated finger millet varieties decreased significantly (p < .05) relative to ungerminated finger millet porridge. The reason for the reduction of viscosity of porridge prepared from germinated finger millet grain flour is that the activity of α-amylase increased during germination (Malleshi et al., 1986). The α-amylase activity may change the structure of the grains (Ocheme & Chinma, 2008) and hydrolyzes amylose and amylopectin into dextrin and maltose, thus reducing the viscosity of porridge (Wanjala et al., 2016).

| CON CLUS ION
Germination is a traditional processing technique that enhances the

ACK N OWLED G M ENTS
The authors would like to thank Addis Ababa University and Ethiopia Institute of Agricultural Research for their financial support and assistance in the research.

CO N FLI C T O F I NTE R E S T S TATE M E NT
The authors have declared no conflict of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
The paper contains all of the necessary information.