Nutritional, Physicochemical, Functional, and Textural Properties of Red Pepper ( Capsicum annuum L .), Red Onion ( Allium cepa ), Ginger ( Zingiber officinale), and Garlic ( Allium sativum) : Main Ingredients for the Preparation of Spicy Foods in Ethiopia

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Introduction
Ethiopia produces more than 50 types of spices from 109 types of spices in the world listed by the International Organization for Standardization. Te total spice production in the country has increased over the years, while the share of spices production in 2018 was peppers (83%), turmeric (11%), ginger (3%), and others (3%). Te share of chili peppers is very high and has increased over the years in Ethiopia [1]. Ethiopia is one of the largest consumers of spices, and most of the spices produced (96%) are consumed domestically. In food applications, spices are the building components of favors which are used to favor sauces, bread, butter, meat, soups, and vegetables and in the production of medicines and perfumes. Te spices commonly used for the preparation of condiments or spicy foods in Ethiopia are red pepper, garlic, ginger, onion, cardamom, chili, and fenugreek. Tese spices are used as an ingredient for the preparation of condiment such as spicy red pepper paste (Awaze), Ethiopian stew (Shiro wot), hot pepper paste (Datt), Mitmita, Mekelesha, Selejo, Bekolt, and Nitirkibie [2]. Spices stimulate hunger, add favor and texture to food, and give visual appeal to meals during consumption [3]. Spices are also important for their medical properties, including antioxidants and antimicrobials activity. Aspergillus a mold recognized for making afatoxin, a carcinogen, is inhibited by ginger. Cloves are rich source of antioxidants which is crucial to their health benefcial efects, such as free radical scavenging activity [4]. Moreover, the addition of spices as an ingredient in modern and traditional processed foods helps to extend the shelf life of the foods.
Diferent previous studies reported the quality characteristics of spices, but those studies reported only limited quality characteristics and did not compare the quality characteristics of spices. Most of the published works on red pepper, garlic, red onion, and ginger concentrate on the production and production managements [5,6].
Only very few studies have reported the quality parameters of spices such as proximate and mineral contents of red pepper and red onion [7][8][9]. Other important parameters such as macronutrients, micronutrients, physicochemical, functional, and textural properties of red pepper, red onion, garlic, and ginger have remained largely unexplored. Comprehensive studies of the functional, textural, and physicochemical properties of red pepper, red onion, ginger, and garlic are limited. It is, therefore, important that the current study aims to provide comprehensive information about the nutritional, functional, textural, physicochemical, and mineral content of red pepper, red onion, ginger, and garlic which are the commonly used spices in the preparation of diferent types of traditional spicy foods in Ethiopia.

Sample Collection and Preparation.
Dried red pepper (Capsicum annuum L.) sample was collected from Finote Selam, Bure, and Dembecha in January 2022, Amahara region, Ethiopia. Matured red onion (Allium cepa), ginger (Zingiber ofcinale), and garlic (Allium sativum) were collected from vegetable improvement center, Holeta Agricultural Research Center, Ethiopia. Matured red onion, ginger, and garlic were sun-dried for three days, and foreign materials and stalks were manually removed. Te samples were coarsely crushed in a cutter mixer and then processed in a laboratory hammer mill (Perten Instruments, Finland). Ten, the powder was sieved using a 0.5 mm screen before being placed in a polyethylene bag for analysis. Te workfow that was followed is given in Figure 1.

Proximate and Mineral
where MC (wb) is the moisture content, Mw is the mass of water, and M is the sample weight.
where moisture, protein, fat, total ash, and crude fber contents are represented by MC, CP, fat, total ash, and crude fber, respectively.

Energy (Kcal).
Te energy content was calculated using the following formula: Te values were expressed in Kcal.

Mineral Content.
Te mineral content of the samples was analyzed following the AOAC method [10]. 0.5 grams of sample was digested by using a mufe furnace at 550-600°C for 5-6 hours until the residue ash became white. Te ash sample was digested by using concentrated HCl. Te digested sample was diluted up to 100 ml for mineral analysis. Calcium, potassium, sodium, iron, and zinc contents were determined using atomic absorption spectrophotometer (Model: Agilent serious, America): where conc. AASis the reading from atomic absorption spectrophotometer, TV is the Volume marked by 100 ml in the volumetric fask, and df is the dilution factor.

Physicochemical Property
2.4.1. pH Value. It was obtained following the method [11]. Te samples of 5 g were measured and 45 ml of distilled water was added to the sample and homogenized for one minute. Te solution was maintained at room temperature for 1 hour, and the pH of the supernatant was measured using a pH meter (Mettler Toledo, China).

Titratable Acidity.
It was determined titrimetrically according to the method [11]. A 5 gram sample was measured, and 100 ml of deionized water was added and then stirred gently, and the mixture was allowed to stand for one hour. From the mixture, 20 ml solution was taken and added to 0.5 ml phenolphthalein in a 100 ml fask and then it was titrated using 0.1 N NaOH until a pink color appeared for 30 seconds.
where N is the ml of 0.1 N NaOH and wt is the weight of sample.

Total Soluble Solids.
It was determined according to AOAC [10]. A sample of (10 g) was liquefed in 50 mL distilled water with a pH of 7.0. Subsequently, the mixture was fltered. Ten, to determine the TSS, 1.0 mL aliquot was placed in a digital refractometer, and the results were expressed in°Brix.

2.4.4.
Color Value (L * , a * , and b * ). Te L * , a * , and b * color values were observed by Aeros Hunter colorimeter following the method of [12]. Te Aeros Hunter colorimeter was calibrated using the manufacturer's standard white plate. Te powder colors were quantifed in the L * , a * , and b * color space. L * refers to lightness, positive a * refers to red purple color, negative a * values indicate a green color, positive values of b * indicate yellow color, and negative values of b * indicate blue color. Chroma refers the color intensity (saturation), and hue angle indicates the specifc color of the powder.

Determination of Viscosity.
A 3 gram powdered sample was dissolved in 5 ml distilled water, and the viscosity of the solution was determined using a Brookfeld viscometer (model Lv-3, Middleboro, MA 02346, USA) set at 60 rpm and a temperature of 25°C. Te viscosity was recorded in centipoises (cps) [13].

Functional Properties of the Powder.
Te functional properties of red pepper powder, red onion powder, ginger powder, and garlic were evaluated according to the following methods.

Water and Oil Absorption.
It was determined using the centrifugation method [14]. About one gram of the powder was mixed with 10 ml of distilled water or oil in a centrifuge tube and allowed to stand at room temperature of 30°C for 1 hr. Ten, it was centrifuged at 200 rpm for 30 minutes, and the supernatant was measured in a 10 ml measuring cylinder.

Bulk Density.
It was determined by using the method [15]. 50 gram of powdered sample was added in a 100 ml measuring cylinder, and the volume was measured and calculated as follows: bulk density g ml � weight of powder volume of powder .
2.5.3. Tapped Density. It was measured using the same method with bulk density, but manually tapping the cylinder vertically until the height of powder in the cylinder does not change [16].
Tapped density � mass of taping volume of taping .
2.5.4. Porosity. Porosity refects the volume of pores in the bulk material and was measured using the method that was reported in [17], calculated as (ε (%)) as follows:

Hausner Ratio (Hr) and Carr's Index (CI).
Hausner ratio (Hr) and Carr's index (CI) indicate the fowability of food powders [18]. Both Hr and CI were calculated by taking the tapped density and bulk density of powders using the method of [19].
2.5.6. Dispersibility. Dispersibility of the powder was determined according to the method in [20]. Dispersibility was measured by placing 10 g of the sample in a 100 mL stoppered measuring cylinder, and distilled water was added to 100 mL, stirring vigorously and allowing it to settle for 3 hr. Te volume of settled particles was subtracted from 100 and the diference was reported as percentage dispersibility as follows: dispersibility(%) � 100 − volume of settled particle.
2.5.7. Foaming Capacity. It was determined according to the method in [21]. 1 gram of the powdered sample was dispersed in 50 mL distilled water. Te resulting solution was vigorously whipped for 30 min in a Kenwood blender and poured into a 100 ml graduated cylinder. Te volume before and after whipping will be recorded, and the foaming capacity was calculated as the percentage volume increase. Te foaming capacity was calculated from the following equation: volume increase(%) � (volume after whipping -volume before whipping) volume before × 100.
2.6. Particle Size and Specifc Surface Area. Particle size distributions of red pepper, red onion, ginger, and garlic powders were determined using a laser difraction particle size analyzer (Master seizer 2000; Malvern Instruments Ltd., Worcestershire, UK) according to the method of [22]. Te powder was dispersed in water (ISO 13320-1). In the particle size distribution curve, D 10 , D 50 , and D 90 representing 10%, 50%, and 90% were used to describe the total percentage particle volume below the given diameter. Te measurement was also used to determine the Sauter mean diameter (D 32 ), volume weighted mean diameter (D 43 ), and specifc surface area (m 2 /g).

Rheological Properties.
Pasting properties of red pepper, red onion, ginger, and garlic powder samples were determined by using a rapid viscoanalyzer (RVA-RECHMASTER, Newport Scientifc Pty. Ltd., Sidney, Australia). Te pasting parameters were measured following the general pasting method. Te sample was equilibrated at 50°C for 1 min, heated to 95°C in 7.5 min, and then held at 95°C for 5 min. Te hot sample was subsequently cooled to 50°C within 7.5 min and maintained at 50°C for 4 min. Paddle speed was 960 rpm for the initial 10 sec. To disperse the sample, the speed of the paddle was set at 160 rpm during the measurement. Pasting parameters included peak viscosity, trough viscosity, fnal viscosity, breakdown value, and set back value, and the viscosity parameters were expressed in centipoises (cPs) units [23].

Texture Profle Analysis (TPA).
Te textural properties of dried red pepper and fresh red onion, ginger, and garlic were measured as puncture forces which were a measure of hardness of the product as measured through Texture Analyzer (model: TA. XT. Stable Micro Systems, UK), based on the method in [24] using a 2 mm cylindrical probe with a speed of 2 mm/s and a penetration distance of 5 mm. Te puncture force to rupture the dried pepper and fresh red pepper, ginger, and garlic was recorded as means for each sample.

Experimental Design and Data Analysis.
Te experiment was designed in a completely randomized design (CRD) for the four powder samples. Analyses were conducted in triplicate, and the results were presented as the mean value of replicates.

Proximate Composition.
Quantitative analysis of proximate composition consisting of moisture content, crude protein, crude fat, crude fber, total ash, carbohydrate content, and energy value (kcal.) for red pepper, red onion, ginger, and garlic is presented in Table 1. Te data in Table 1 illustrate the proximate composition of red pepper, red onion, ginger, and garlic. Red pepper had the highest amount of protein which reached to 14.7% while garlic had the lowest protein content reached to 8.6%. Similarly, red pepper contained the highest crude fat, followed by ginger, while garlic contained the lowest content of crude fat (p < 0.05). Garlic had the lowest fber content (p < 0.05) whereas red paper had the highest. Moreover, the fber content in the red pepper was approximately twelve times higher than that that of garlic. Red pepper contained the highest ash content (6.7%), followed by ginger (6.33%), and red onion had the lowest ash content (3.37%). High ash content is an indication of high inorganic mineral content [25]. Tis indicates that red pepper and ginger are rich in inorganic minerals. Garlic contained the highest carbohydrate content (76.42%) and energy value (346.58 Kcal.), while red pepper had the lowest carbohydrate content (22.13%) and energy value (248.58 Kcal.). Te crude protein, fber, and ash contents of red pepper powder that were obtained in this study appeared to be higher than the reported values for dried red pepper varieties with the values of protein, fber, and ash content in the range of 8.7-11.8, 25.96-28, and 5.2-7.27%, respectively [26]. Another study obtained higher content of crude protein, crude fat, crude fber, and ash content in red onion than the current study, and the values were 12.5, 2.96, 5.90, and 5.58%, respectively [27]. A previous study on ginger reported total fber content, ash content, and fat content of 11.72, 8.25, and 1.85%, respectively [25], which is higher than the current study. Te crude protein, crude fat, crude fber, ash content, and carbohydrate content of garlic in this study appeared to be higher than the fnding of [28] that obtained crude protein, crude fat, crude fber, ash, and carbohydrate content of 7.87, 0.52, 2.3, 2.46, and 22.27%, respectively. Te observed variation in the proximate compositions between the previous and the current study could be growing condition, season, or diference in agronomic practices. Generally, red pepper has relatively higher protein, fber, and total mineral, while ginger, garlic, and red onion have relatively higher carbohydrate content and energy value needed for human nutrition.

Mineral Content.
Te mineral contents (K, Ca, Na, Fe, and Zn) of red pepper, red onion, ginger, and garlic were expressed in mg/100 g on a wet basis and are presented in Figures 2-4.
From the four spices, red pepper contained the highest iron and potassium content, while red onion contained the highest calcium, sodium, and zinc content (Figures 2-4). Te general order of the mineral content for red pepper was K > Ca > Na > Fe > Zn.  [29]. Potassium (K) was the frst most abundant mineral element in the red pepper with a value of 450.7 mg/100 g. Te mineral content of red onion was ranked in the order of K > Na > Ca > Zn > Fe. Te previous study reported relatively lower values of K and Ca for onion with a sodium content of 277.9 mg/100 g and calcium content of 71.09 mg/100 g [30]. Te Fe and Zn content of onion in the current results was higher than the result that was presented by [31], and the study reported Fe and Zn content of onion (3.17 mg/100 g) and (2.64 mg/ 100 g), respectively. Te relative mineral content of ginger in descending order of abundance was found to be as follows: K > Na > Ca > Fe > Zn. Te K, Fe, Na, Ca, and Zn contents of ginger were 330.4, 44.8, 36.18, 36.18, 5.14, and 2.27 mg/100 g, respectively. Tis order was in consistent with the result that was reported by [32] for diferent ginger varieties. Te previous study reported mineral contents of ginger varieties in the range of K (148.7-254.7), Fe (6.74-61.7), Na (36.5-83,73), and Ca (26.05-67.38) mg/100 g, which were higher than the current study. Garlic had considerable amount of K (140.5 mg/100 g), Ca (36.14 mg/100 g), and Na (21.98 mg/100 g), while the quantity of Zn (3.22 mg/100 g) and Fe (1.6 mg/100 g) was the lowest. Te mineral content of garlic that was reported from the previous study was K (54.65 mg/100 g), Ca (19.83 mg/100 g), Na (4.1 mg/100 g), and Zn (0.34 mg/100 g) [28], which was lower than that of the current study.
Collectively, our data highlighted that red pepper can be considered as a good source of iron and potassium while red onion can be considered as a good source of zinc, sodium, and calcium. Consequently, the study confrms that the health beneft of spices may be attributed to the Journal of Food Quality 5 mineral element contents; these elements are useful as metabolism enhancer and antiallergen in the digestion system [33].

Physicochemical Property.
Te physicochemical properties of the powders of red pepper, red onion, garlic, and ginger are presented in Table 2.     Table 2 show the pH and titratable acidity of red pepper that were the highest compared to red onion, ginger, and garlic. Te pH of red pepper (5.23) and red onion (5.16) showed that they have slightly acidic character compared to ginger (5.76) and garlic (6.03). Te acidity for all powders was in the range of 0.7-3.33%. Te acidity for the powder of red pepper was 3.33%, which was the highest acidic content compared to red onion (1.77%), ginger (0.72%), and garlic (1.83%) ( Table 2); this is an indicator of shelf life and quality. Te titratable acidity of onion was 1.77%. Te previous study reported titratable acidity in the range 1.2-2.3% for onion bulbs for diferent storage condition and time [9], which is in agreement with the current study.

Total Soluble Solid (TSS).
Te highest TSS was observed in garlic with an average value of 26.76°Brix, and the lowest TSS was detected in ginger with an average value of 6.93°Brix. Te TSS for red pepper was 8.5°Brix. Te previous study that was conducted on green paper grown under open feld and green house condition reported a TSS value in the range of 3.2 to 10.0°Brix [34], which agrees well with the current study. A study that was conducted on onion under diferent storage structures and storage time reported a TSS in the range of 10.53 to 13.29°Brix [9], which is in agreement with this study.   [36]; this may be due to the diference in the variety of the red pepper, the maturity, or growing environment.

Viscosity.
Considerable diference in viscosity was found between the spice powders ( Table 2). Te diference in viscosity of spices happened due to the molecular confguration and particle size of the samples [36]. Te viscosity of onion paste reported from the previous study was 496 and 398 cps at diferent temperatures [37], which was higher than the current study. Te previous study on garlic paste viscosity reported a value of 279 cps at 25°C and 100 rpm [38], which was higher than the current study.

Oil Absorption and Water Absorption.
Te water and oil absorption capacities for onion were the highest than those of the others, with the water absorption capacity of 2.51 g/ml and oil absorption of 2.16 g/ml. Te highest value of water absorption for powders attributes to the swelling of the fber and other carbohydrates, and the higher oil absorption capacity of the powder explains the limited amount of nonpolar protein side chains that would bind to the side chains of hydrocarbons of the oil and afects the texture and sensory property of foods [39].

Bulk Density, Tapped Density, Porosity, and
Dispersibility. Te measured values of bulk density, tapped density, porosity, and dispersibility for spice powders are given in Table 3. Te porosity value of red pepper, red onion, ginger, and onion powders was in the range of 14.8-37.4%. Te bulk density and tapped density of garlic and red onion were higher than those of red pepper and ginger. Te porosity of red pepper power was the highest (37.7%), followed by red onion (32.39%), ginger (27.78%), and garlic (14.77%).
Te porosity of red pepper was higher than the result that was reported previously for red pepper (32.3%) [35]. Tese properties are related to packaging, storage, and transportation costs. High bulk density and lower tapped density indicate the development of interparticulate interaction or increased cohesiveness or enhancement of compressibility of the powder. Te action of tapping force brings extra force to overcome the cohesive attraction and causes the particles to fall towards the void spaces that decrease the volume of the powder [40]. Te dispersibility value of red onion, red pepper, and garlic was in the range of 63.3-85.0%. Red onion had the highest dispersibility in water (85%), followed by red pepper (64.3%), garlic (63.3%), and ginger (41.6%). Te dispersibility value of red onion in the current study was in line with the dispersibility (67-99%) of onion that was reported by [41]. Generally, higher bulk density is related to higher dispersibility.  (Table 3). Particles having relatively uniform particle size have better fowability compared to particles with nonuniform particle size. In our current study, the fowability of garlic was the highest which showed that garlic powder had better particle size uniformity compared to the other spice powders. Te fowability of powders is an important parameter in the design of systems for handling, packaging, processing, storage, and transportation of powder food products [42].

Particle Size Distribution and Specifc Surface Area.
Te particle size distribution (D 10 , D 50 , and D 90 ), specifc surface area, Sauter mean diameter (D 32 ), and volume weighted mean diameter (D 43 ) of the powders are shown in (Table 4). Te particle size distribution of the powder that was generated using a similar crusher/mill and screen setting is shown in (Figure 6). From the particle size distribution, it was obvious that ginger powder was the fnest of all which indicates more ability for mixing with other spices or ingredients. Te highest particle size value was measured for garlic with the D 90 value of 561 µm. It is known that particle size, specifc surface area, and volume weighted mean diameter infuence the characteristics of food, such as fuidity, water holding capacity, water solubility index, protein solubility, moisture content, extractable matter, color, and antioxidant activity of the food. Te particle size (D 10 , D 50 , and D 90 ) and volume weighted mean diameter of garlic were the highest compared to those of red pepper, red onion, and ginger which is an indication for its potential for antimicrobial and antioxidant activity. Previous report on the specifc surface area of garlic was in the range of 53.31 to 136.4 m 2 /g [43], which is in agreement with the current result for garlic (77.41 m 2 /g). Ginger powder had the highest specifc surface area value (126.17 m 2 /g). Te highest specifc surface area of ginger indicates the infuence of food characteristics, such as moisture content, extractable matter, color, and antioxidant activity [44]. Te particle size of ginger infuenced the extraction efciency of antioxidants [45]. Te highest volume weighted mean diameter and Sauter mean diameter values were measured for red pepper (238 µm and 52.1 µm), respectively. It was reported that the particle size of red pepper afected the microbial activity of Escherichia coli ATCC25922 in red pepper powder [46].

Rheological Properties.
Rheological properties of the powders are given in Table 5 and Figure 7.
3.6.1. Pasting Property. Table 5 presents the pasting property of the samples. Ginger exhibited the highest fnal viscosity (311.50 cps) and fnal pasting temperature (91.12°C) while onion showed the lowest viscosity (42.50 cps) and pasting temperature (50.72°C) (Figure 7). Tus, ginger requires more cooking energy than onion, and it can be used in processing of food products under high temperature and acidic condition that requires high viscosity. A similar study on ginger starch reported a fnal viscosity of 2066.5 cps and pasting temperature of 89.42°C [47], which is higher than the current study; this may be due to the use of pure starch from ginger rather than the whole ginger powder.
3.6.2. Texture. Ginger (1516.66 g) produced the highest puncture force (hardness), followed by garlic (860.033 g), red onion (675.83 g), and red pepper (572.3 g) ( Table 5). Tis showed that red pepper and red onion need lower force to process and easy in product formulation compared to ginger and garlic. Te puncture forces (hardness) for the fresh red onion, ginger, and garlic were the highest compared to the dried red pepper puncture force (hardness) that showed that the samples in the dried form required low-puncture force than the fresh samples. A study on fresh red onion samples and freeze-dried red onion samples reported that freeze-drying substantially reduces the hardness of onions, and there was a decrease from the fresh (1529.55 gram) to the dried state (305.91 gram) [48], which is higher than the current study result from the fresh onion. Values with the same letter in the same row are not signifcantly diferent at P < 0.05.  Values with the same letter in the same row are not signifcantly diferent at P < 0.05.

Conclusion
A comprehensive study of the functional, textural, and physicochemical properties of red pepper, red onion, ginger, and garlic was conducted. Given their chemical composition, red pepper, red onion, garlic, and ginger are good sources of protein, fber, carbohydrate, and minerals. Potassium, calcium, sodium, and iron were the most abundant minerals present in the spices. It can also be stated that garlic had the highest fowability and particle size which are important properties in the design of systems for food processing and indication for its potential for antimicrobial and antioxidant activity. Moreover, the results indicated that ginger had a relatively good pasting property with the highest fnal viscosity compared to red pepper, red onion, and garlic. It is, therefore, important that spices are mixed with the appropriate proportions to get the required functional, textural, and physicochemical properties of formulated foods. Further studies on the formulation, optimization, and packaging of the traditional Ethiopian spicy foods would be valuable using red pepper, red onion, ginger, and garlic as main ingredients.

Data Availability
Te data used to support the fndings of this study are available from the corresponding author upon request.

Conflicts of Interest
Te authors declare that there are no conficts of interest. Journal of Food Quality 11