Effects of variety and particles size on functional properties of Teff (Eragrostis tef (Zucc.) Trotter) flour

Abstract Grain and flour’s, functional and other properties are vital in the food industry. Both variety and flour particle size can influence these characteristics. This study investigated the effect of teff varieties and flour particle size on the functional properties. Three varieties of teff grain (Bora, Jitu, and Filagot) were milled and sieved to obtain the desired particle sizes of three flour fractions (360–250, 250–160, and 160–90 µm) and classified as P1, P2, and P3 respectively. A factorial design was used to carry out nine treatment combinations in triplicate. Functional properties, including water absorption capacity, oil absorption capacity, solubility index, and dispensability, were determined. Water and oil absorption capacity, swelling power, and solubility index of teff flours were significantly (p ≤ 0.05) increased with decreasing particle size. However, there was no significant (p > 0.05) differences in oil absorption capacity and dispersibility due to variety. The finest flour particle size (90–160 µm) demonstrated distinct functional properties compared to flours of larger particle sizes for industrial applications.


PUBLIC INTEREST STATEMENT
Teff is a major food crop native to Ethiopia and Eritrea for the production of a range of traditional foods/beverages such as injera (flatbread), kitta (unleavened bread), and tella (local opaque beer) in a traditional way and has a better nutritional value than other crop cereals.It can be converted into a range of gluten-free products, such as bread, cakes, casseroles, soups, weaning foods, and cookies.But, teff is underutilized globally due to processing parameters at the industrial level.This work investigated the effect of varieties and flour particle size on functional properties which is crucial parameters in the production of pastry products for which teff is very suitable.Based result of the functional properties investigated, the finest flour particle size (90 -160 µm) demonstrated distinct functional properties as compared to flours of larger particle sizes showing that suitable for the production of gluten-free products.
properties, including water absorption capacity, oil absorption capacity, solubility index, and dispensability, were determined.Water and oil absorption capacity, swelling power, and solubility index of teff flours were significantly (p ≤ 0.05) increased with decreasing particle size.However, there was no significant (p > 0.05) differences in oil absorption capacity and dispersibility due to variety.The finest flour particle size (90-160 µm) demonstrated distinct functional properties compared to flours of larger particle sizes for industrial applications.

Introduction
The physical, functional, rheological, and other properties of grains and flour are critical for improving the design and operation of food process equipment used in manufacturing, handling, and storage processes (J.Ahmed, 2018).As a result, determining and recognizing the dataset of diverse agricultural product properties such as physical, functional, rheological, aerodynamic & hydrodynamic, electrical, and optical properties is essential (Kandel et al., 2022).Designing and creating certain machines and their operational activities, such as separating, cleaning, grading, transporting, blending, drying, and baking, depend greatly on these features (Wang et al., 2021).For example, to predict powder flow from hoppers in vending machines on a small scale, or storage silos dispensing material into mixing systems or packaging equipment on a larger scale, the flowability of that material should be classified (Baumann et al., 2021).Knowledge of raw and intermediate material properties such as physical (particle size, angle of repose), functional properties (water absorption capacity), and chemical composition (carbohydrate, mineral) is critical for the realization of many technological processes, as well as for controlling quality and consumer acceptance of final products (Siliveru et al., 2017).
Teff (Eragrostis tef (Zucc.)Trotter is an ancient tropical cereal grain that originated in Ethiopia and Eritrea and has a wide range of varieties (Arendt & Zannini, 2013).It is a small cereal crop worldwide; nonetheless, it is a staple meal in Ethiopia, where it is mostly used to make injera (Jamalluddin et al., 2021).Except for oats and rice, it has all amino acids and is richer in lysine and vitamins than other cereals (Do Nascimento et al., 2018).Teff is also higher in minerals, notably iron, calcium, copper, zinc, and aluminium, than wheat, barley, and sorghum (Yilmaz & Arslan, 2018).It has a better nutritional value than other crop cereals or grains and does not need to be fortified due to its unique nutrient content (Barretto et al., 2021).Several studies have shown that teff can be converted into a range of gluten-free products and beverages such as bread, porridges, pancakes, cakes, casseroles, soups, stews, weaning foods, cookies, extruded products, and malt for brewing fermented beverages with another composite.
Despite having an excellent nutrient profile, teff consumption is mostly limited to Ethiopia (Baye, 2014).Even there are no adequate data from the Food and Agricultural Organization file concerning teff, especially on processing, compared to other cereals grains (Arendt & Zannini, 2013).Furthermore, there are few detailed statistics on teff production, consumption, and processing accessible around the world (Lee, 2018).Teff's global usage for industrial processing and human consumption has been hampered owing to a lack of data on its processing features in adapting teff-based food items for foreign customers (Cheng et al., 2017).
The relevance of bulk flour production, handling, and processing operations involving teff is anticipated to increase due to the rising demand for food manufactured with teff grain flour and teff-based food products because of their health and nutritional advantages.However, there is a knowledge gap about the impact of varieties and flour particle size distribution on the functional characteristics of teff flour.Therefore, the objective of this work was to investigate the effect of variety and particle size distribution on the functional properties of teff flour to provide information and for the production of gluten-free products other than the traditional ones to increase teff utilization for the international community.

Experimental materials and site
Bora (DZ-Cr-453), very white, was launched in 2019, Filagot (DZ-Cr-429) red was released in 2017, and Jitu (DZ-01-256) pale white released in 2019 was obtained from the Ethiopian Institute of Agricultural Research Debrezeit Agricultural Research Center (DARC).The national teff improvement program of the Ethiopian Institute of Agricultural Research (EIAR) released these teff varieties.The three teff varieties were selected based on colour and year of release.

Experimental design
Two factors were taken into account when experimenting with a full factorial design (variety and particle size of the flour).This consisted of three varieties (levels) of teff grain (Bora, Filagot, and Jitu) and fractionated flour particle sizes into three parts (levels) (250-360 µm, 160-250 µm, and 90-160 µm) with triplicate analysis.The study was conducted at Central Laboratories in Food Science and Postharvest Technology Laboratory at Haramaya University.

Oil absorption capacity
The approach suggested by Branch and Maria (2017) was employed to determine the oil absorption capacity (OAC).In a pre-weighed centrifuge tube, 1 g of flour and 10 mL of oil were vortexed for 30 minutes.The material was centrifuged for 15 minutes at 3000 rpm after resting for 30 minutes at 25 °C.The centrifuge tubes plus the precipitate were reweighed after the supernatant was decanted following centrifugation.The oil absorption capacity (OAC) was determined using the amount of oil absorbed per gram of sample (Equation 1).
Where: M 3: the mass of the tube plus sediment, M 2: the mass of the tube plus the dry sample, and M 1 : the mass of a dry sample

Water absorption capacity
The water absorption capacity was ascertained by the Branch and Maria (2017) approach.In a preweighed centrifuge tube, 1 g of flour was thoroughly combined with 10 mL of distilled water using a vortex for 30 minutes in the centrifuge tube.Following a 30 minutes hold at room temperature, the material was centrifuged for 15 minutes at 3000 rpm (25 °C).After decanting the supernatant following centrifugation, the precipitate and centrifuge tubes were weighed again.As a final step, the water absorption capacity (WAC) is calculated by weighing the amount of oil absorbed per gram of sample (Equation 2).
Where: W 3: the mass of the tube plus sediment, W 2: the mass of the tube plus the dry sample, and W 1 : the mass of the dry sample

Water solubility index
The method developed by Pranoto and Rakshit (2014) was used to determine water solubility.Vortexes were performed on a pre-weighed centrifuge tube with 1 g of sample material and 10 mL of distilled water.After standing at an ambient temperature of 25 °C for five minutes, 30 minutes were spent submerging the sample in a 95 °C water bath.After that, it was cooled for 10 minutes at 25 °C.Centrifugation at 3000 rpm for 15 minutes separated the particles from the gel and supernatant.After being separated, the supernatant was put in an aluminium dish whose weight had already been determined.The dish was then baked to a fixed weight.The equation described below was used to determine the WSI (Equation 3):

Swelling power
Using the Pavithra et al. (2017) approach, the swelling power of flour was determined.After carefully measuring 3 g of flour sample into a 25 mL centrifuge tube, 10 mL of distilled water was added.The slurry was heated to 80 °C in a water bath for 30 minutes.The cooked slurry will be carefully agitated to prevent the flour from clumping.After 30 minutes of decantation of the supernatant, the paste-containing tube was centrifuged at 3000 rpm for 10 minutes.The weight of the sediment was determined and noted (Equation 4).

Statistical analysis
The Statistical Analysis System for Windows (SAS Institute Inc., Cary, North Carolina, USA) was used to evaluate the statistical data using a factorial test with a two-way Analysis of Variance (ANOVA).The (p ≤ 0.05) was recognized as the threshold for a significant test.Fisher's Least Significance Difference (LSD) analysis was used to compare the means.The results were reported in triplicate as the mean and standard deviation.

Water absorption capacity
Water absorption capacity (WAC) is a necessary functional feature of flour.Significant differences (p ≤0.05) existed between the teff flour varieties.The Bora had the highest, and Jitu had the lowest, ranging from 1.39 to 2.04 g/g.These values were similar to the WAC results of sorghum flour ranging from 1.08 to 1.43 g/g, obtained from a previous study by Nani and Krishnaswamy (2021).According to Hasmadi et al. (2020), flours with a high WAC contain more polysaccharides and other hydrophilic components.As a result, the difference in water absorption capacity across varieties may be linked to the hydrophilic carbohydrates in the flour.Ojo et al. (2017) hypothesized that starch containing a lot of amorphous substances would likely have more hydration-binding sites, allowing it to take up more water.
The varied particle size distributions have a significant (p < 0.05) variation in water absorption capacity.Water absorption capacity ranged from 1.40 to 2.13 g/g (Table 1), with 90-160 µm (P3) having the highest value.Damaged starch becomes more prevalent as particle size decreases.Starch that has been damaged absorbs more water than starch that has not been damaged.Fine particle water uptake is higher than large particle water uptake, which may be due to the increased surface area (Bressiani et al., 2019).It could have an impact on the texture of foods; using flours with a greater WAC content helps to maintain a soft texture (Di Cairano et al., 2020).This outcome was in line with that of Lapčíková et al. (2021) who stated that the water-absorbing capacity of flour increased as particle size reduced.Another similar result was reported by Pranoto and Rakshit (2014) for jet-milled whole wheat flour.Flour hydration capacity was meaningfully affected by both teff variety and particle size.Flours with a high are likely to be used in the production of some foods, such as bread goods in bakery industry.

Oil absorption capacity
Oil absorption ability is a crucial functional quality to improve mouthfeel and preserve taste and aroma (Awuchi et al., 2019).The OAC of teff varieties is recorded with the value of 0.85 g/g for Jitu, 0.84 g/g for Filagot, and 0.83 g/g for Bora without a significant difference (p > 0.05) displayed in Table 1.
The OAC of teff flour was significantly affected by particle size (p ≤0.05).For 250-360 µm, 250-160 µm, and 90-160 µm, the observed values of the oil absorption capacity of flour were 0.71, 0.80, and 1.01 g/g, respectively.Because there was a more available surface area for the protein to interact with as particle size reduced from 360 to 90 µm, the results were slightly improved.The oil absorption capacity of the fractionated maize flour increased from 1.7 to 2.1 g/g when particle size decreased from 425 m to 75 m, according to similar relationships shown by Bolade et al. (2009).This observation is consistent with those of Bala et al. (2020), who observed increased oil absorption capacity as grass pea flour particle size decreased.The high OAC of flour implies that it might be advantageous in food compositions needing oil-holding capacities, such as bakery products and sausages (A.M. Ahmed et al., 2012;Bala et al., 2020).

Swelling power
For teff varieties, the recorded results ranged from 5.82 to 6.03 g/g showing a significant (p ≤0.05) difference between the maximum and the minimum results.The swelling power was discovered to be comparable to the outcomes of earlier research on teff flour conducted by Alemneh et al. (2022).The swelling power of starch refers to its ability to absorb water and swell.Hydrogen bond breaks occur when a starch granule aqueous solution is heated in water, causing the structures to hydrate and the crystalline structure to become disturbed.Hydrogen interactions between water molecules and the exposed hydroxyl groups of amylose and amylopectin cause granule enlargement (Miller, 2010).Godswill (2019) claims that the availability of water, starch types, other carbs, and proteins all affect how much a structure swells.
Likewise, particle size had a significant (p˂ 0.05) effect on the swelling power of teff flour.The range of swelling power was 4.98 to 7.09 g/g, with samples 250-360 µm as the lowest and samples 90-160 µm as the highest.This is in line with previous findings by Abebe et al. (2015), who found an increase in the swelling power of teff flours with a decrease in flour particle size, resulting in a greater surface area for binding water molecules and increased water absorption.Increased swelling power leads to greater solubility, which explains that the teff with the highest water absorption capacity also had the highest swelling power.Water holding in swollen starch granules is frequently connected with food-eating quality.Swelling power regulates how much a flour sample expands in volume when soaked in water relative to its starting volume (Joy & Ledogo, 2016).

Water solubility index
Teff flours from three varieties had a significant (p ≤0.05) difference value of the water solubility index, with the highest value of 5.29% for Bora and the lowest of 4.83% for Filagot (Table 1).These results were found to be similar to 5.32%, which was reported by DiCairano et al. ( 2020) for sorghum flour.The water solubility index is the leachability of water-soluble components from flour, and solubility is the capability of food materials to dissolve in a given solvent.The values of the water solubility index were positively correlated with those of water absorption capacity because high WAC can improve the solubility of flour by facilitating the starch hydration rate; both depend on starch content (Jukić et al., 2019).The water solubility index relates to dispersible or soluble component molecules, including albumins, amylose, sugars, and oligosaccharides.The presence of amylase complexes, notable lipids in flour starch, which prevent it from dissolving in water, may justify flour's poor water solubility index.Another factor could be the structure's high stability, which prevents heating-induced degradation of the amylopectin and starch in flour (Alashbayeva et al., 2021).
Table 1 shows the measured water solubility index for the different teff flour particle sizes.The results were in the range of 4.18 and 5.84 for 250-360 µm, 250-160 µm, and 90-160 µm respectively.A statistically significant difference (p ≤0.05) existed between the particles.As a result of damaged granules' rapid hydration and susceptibility to amylolytic hydrolysis, the water solubility index has a negative relationship with particle size and a positive relationship with damaged starch.Similarly, mean particle size might impact the hydration capabilities of teff flours by increasing the surface area exposed for water binding.The findings were consistent with Shi et al. (2016) discovery, in which the solubility index of maize flour increased as the flour's particle size dropped.The increased particle surface area, which exposes soluble molecules, and waterbinding sites, leads to increased solubility due to the smaller flour particle size (Gu et al., 2022).The high solubility of food can imply great digestion, which may indicate an appropriate application for infant formula and meals.

Dispersibility
Dispersibility of teff flours ranged from 65.00 to 69.66%, with samples with large particles as the lowest and those with small particles as the highest.The current study discovered significant changes (p ≤0.05) in flour samples' dispersibility because of particle size variations.Dispersibility of teff flour shows a linear increase with decreasing particle size.This concurs with the finding made by J. Ahmed et al. (2014) on the dispersibility of pumpkin flour.The ability of flour to reconstitute its starch or other constituents in water is known as dispersibility.The dispersibility feature of flour reflects its hydrophilic activity and affects its propensity to move toward water molecules.When combined, the better the flour reconstitutes and produces fine, homogenous dough, the higher the dispersibility.

Interaction effects of varieties and particle size distribution on functional properties of teff flour
Table 2 indicates the impacts of flour variety and particle size on the functional properties of teff flours.Significant (p ≤0.05) differences in WAC were identified.The highest water absorption capacity of 2.19 g/g was obtained for the Bora variety with the interaction of 90-160 µm particle (BP3) and the lowest 0.89 g/g was reported for the Filagot variety with 250-360 µm particle size (FP1).
A statistical study revealed that the interactions between teff variety and particle size affected the oil absorption capacity of teff flour and that the differences were statistically significant (p < 0.05).Its readings showed the highest value for the Jitu variety of 90-160 µm, and the lowest value for the variety Bora of 250-360 µm was 1.02 g/g and 0.70 g/g, respectively.
The interaction of variety and particle size had significant effects (p ≤ 0.05) on the swelling power of teff flour.The highest values of 7.13 and 7.10 g/g were recorded for the Jitu and Bora varieties, respectively, of 90-160 µm particle size.On the other hand, the lowest readings were 4.94 and 4.97 g/g of varieties Flagot and Jitu, respectively, for size ranges of 250-360 µm teff flour.Similarly, flour's interaction of variety and particle size had significant effects (p ≤ 0.05) on the water solubility index and dispersibility of teff flour.From the results, it can be concluded that the interaction effect on the functional properties of teff flour is dominated by flour particle size.The results suggest that the interaction effect on the functional properties of teff flour is mostly influenced by the flour particle size.

Conclusion
The variety and particle size distribution of teff flour significantly impacted the functional properties of the flour.Functional properties were tested, and the majority of these parameters differed considerably as a function of variety and particle size.These variations can be linked to environmental factors, soil types, and flour particle size due to milling, which is connected to surface area and hence affects the structure of flour components.The ability of the teff flour to absorb water, its water solubility index, and its swelling power increased as the flour's particle size dropped.Based on the functional properties investigated, it can be concluded that the finest flour particle size (90- 160 µm) demonstrated distinct functional properties as compared to flours of larger particle sizes.
The bakery and milling industries may use these data to control functional properties in the production of gluten-free products like cookies, cakes, breads, or biscuits.According to the panelists, Bora variety was among the types ideal for making cookies.

Table 1 . Main effects of varieties and particle size on functional properties of teff flour
Notes: All values are means of triplicates ± standard deviation.Values with different superscripts within the same column are significantly (p < 0.05) different WAC: Water Absorption Capacity; OAC: Oil Absorption Capacity; SP: Swelling Power; WSI: Water Solubility Index; Disp: Dispersibility.