Effect of Roasting on the Proximate Composition, Antioxidant Activity, and Functional Properties of Afrostyrax lepidophyllus (Country Onion) Seeds

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Introduction
Afrostyrax lepidophyllus is a nontimber plant of the Huaceae family, locally known as "bush onion," country onion "Shirum," and "Mruu."It is a very popular spice growing traditionally in central and west African forests.A. lepidophyllus seed is a round shape nut with a strong favor frequently found in the forests or markets in Nigeria, Congo, Cameroon, and the Central Republic of Africa [1]. A. lepidophyllus bark, fruits, leaves, and root have several medicinal uses.A decoction made from bark and root is used as anthelmintic against vomiting, urinary infections, enema, indigestions, and snake bites [2,3].It is also used as an antiseptic for the treatment of gastroenteric illnesses.Te leaves are crushed, infused, and used as bath seat to fght against women hemorrhoids and as mouthwash to treat caries and toothache.Te authors in [4] reported cytotoxic and antimicrobial activities of the essential oils from the A. lepidophyllus seeds.Te polyphenol content of the hydroethanolic bark extract of this plant is greater than 28 mg/g with about 7 mg/g being favonoids [4].In the Central African Republic and in many other African countries, Cameroon included, the seeds are equally one of the most used spices as these possessed a strong garlic-onion favor [5].Tis strong and powerful garlic-onion favor made the seeds to rise among the top spices used in the preparation of several traditional meals such as "nkui," "nak npo," and "Mbongo tchobi" just to name a few in Central and West Africa countries [1,6].
During cooking, the seeds are usually either partially burned in the fre in the village, grilled in a frying pan or the stove, or microwaved in towns, in order to enhance their favors.
Several authors revealed that the pretreatments of food products before cooking may afect negatively or positively the nutritional and functional properties of the fnal product [7][8][9].Audu et al. [10] reported that heat has a positive efect on the nutritional value of white kidney beans by increasing the bioavailability of carbohydrates and proteins while decreasing the levels of antinutrients present.Amandikwa et al. [11], on the other hand, revealed that long heating time reduces the concentration of vitamin C and beta carotene content in some green vegetables.Given that the A. lepidophyllus seeds are mostly heated before being used in food preparation, knowing information about the roasted seed fours may increase their uses in food formulations and improve their consumption as well as the income generation of producers.Terefore, the main objective of this work was to evaluate the efect of the diferent preheating methods such as pot, oven, and microwave roasting on the physicochemical, antioxidant, and functional properties of A. lepidophyllus seed fours.All the chemicals and reagents used were of analytical grade.

Sample Preparation.
A. lepidophyllus seeds were sorted to remove stones, strange particles, and dead seeds.Unafected seeds were then peeled and divided into four batches.One batch served as control when the three others were, respectively, roasted using pot (5, 10, and 15 min at about 250 °C), oven (10 and 20 min at 180 °C), and microwave (200, 300, and 450 W for 10 min).Roasted samples were individually ground and kept in a close polypropylene plastic bag for further analyses.

Proximate Composition.
Te AOAC [12] method was used to determine the moisture, ash, fat, and protein contents of country onion fours.Dilute acid and alkaline were used to hydrolyze 5 g of sample in order to evaluate the crude fber content [13].Te carbohydrate content was computed by diference via equation (1) as described by Mohamed Ahmed et al. [14].% Carbohydrate � 100 − % (Moisture + Fat + Protein + Fiber + Ash). (1)

Total Phenolic Content.
Te total phenolic content (TPC) of the diferent A. lepidophyllus fours was extracted by macerating 20 g of sample in 100 mL methanol for 24 h and fltrated using Whatman No. 1 flter paper.Te extract was concentrated using a rotavapor, and the TPC was evaluated by the colorimetric method using the Folin-Ciocalteu reagent as described by Bekir et al. [15], with slight modifcations.Briefy, in the mixture of 200 μL of the extract plus 800 μL of Folin-Ciocalteu (0.2 N), 2 mL of sodium carbonate (7.5% w/v) was added.Te fnal mixture volume was made up to 7 mL with distilled water, stirred 2000 rpm for 5 min, and incubated at room temperature in darkness for 30 min.Te absorbance was then taken at 765 nm.Gallic acid was used as the standard, and the result was expressed in mg of gallic acid equivalent per gram of dry weight.

Antioxidant Activity. Te antioxidant activity of
A. lepidophyllus sample was determined via the free radical 1, 1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity as described by Molyneux [16].A volume of 3 mL diluted extract was mixed in the test tube with 1 mL of DPPH solution (0.1 mM, prepared in methanol).Te mixture was incubated for 30 min at ambient temperature in darkness, and the optical density of the fnal solution was taken at 517 nm against blank (methanol).Tert-hydroquinone was used as the standard, and the antioxidant activity (AOA) was computed using the following equation: where A 0 is the absorbance of the control and A s is the absorbance of the sample.

Functional Properties
(1) Water Absorption Capacity.Te water absorption capacity of the A. lepidophyllus fours was determined by the method described by Sosulski et al. [17].In a centrifuge tube, 5 g of sample was mixed with 25 mL of distilled water and kept at room temperature for 30 min.Te mixture was then centrifuged (4500 g, 25 min), and the sediment was weighed.Te water absorption capacity was expressed as milliliter of water held per gram of the sample.
(2) Oil Holding Capacity.Te oil holding capacity taken as the percentage of oil bound per gram of the A. lepidophyllus four was examined using the method of Sosulski et al. [17].
2 Journal of Food Quality A volume of 10 mL of vegetable oil was mixed with 1 g of sample and kept at room temperature for 30 min.Te mixture was then centrifuged at 4500 g for 25 min.Te oil holding capacity was expressed as milliliter of vegetable oil held per gram of the sample.
(3) Swelling Capacity.Te modifed method of Okaka and Potter [18] was used to evaluate the swelling capacity of the A. lepidophyllus seed fours.A 100 mL graduated cylinder was flled up to 10 mL mark with sample four, and distilled water was added to make a total volume of 50 mL.Te cylinder was tightly covered and thoroughly mixed for 30 min by inverting the cylinder.Te cylinder was kept at room temperature for 30 min, and the volume occupied by the resulting sample was taken.
Swelling Capacity � Mass of wet sediment Mass of dry matter in gel . ( (4) Loose Bulk Density and Packed Bulk Density.Te bulk density was determined according to the method described by Konak et al. [19].Briefy, 50 g of country onion four was measured and put into 100 mL graduated cylinder.Te cylinder was tapped gently 10 to 15 min, until no perceptible change in volume.Te loose bulk density (LBD) and packed bulk densities (PBD) also known as volumetric density were computed as the ratio of the mass of A. lepidophyllus four (g) to the volume (mL) occupied by the four before and after tapping.
(5) Hausner Ratio and Porosity.Te Hausner ratio (HR) and the porosity (P) of A. lepidophyllus four were calculated from the value of packed and loose bulk densities using the following equations, respectively:

Results and Discussion
3.1.Proximate Composition.Te variation of moisture content (MC) of A. lepidophyllus with respect to diferent roasting treatments is presented in Table 1.Generally, the MC of all roasted samples was lower compared to the control (unroasted sample).Te reduction of the MC is important as this prolongs the shelf life and the keeping quality of the seed four.In fact, the reduction of MC is related to the reduction in water activity which governs the microbial proliferation and biochemical reactions, the main parameters responsible for food deterioration.Te decrease in MC obtained in this study is probably due to the evaporation of water during the roasting treatments.A similar fnding was observed by Santos et al. [9], during the roasting of defatted walnut four.Te lowest MC (7.30 g/100 g DW), which was not signifcantly diferent (p < 0.05) from the value recorded with samples roasted in the pot (8.56, 8.76 and 9.80 g/100 g DW, respectively), was found with oven roasting treatment at 180 °C for 20 min.It should be noted that the highest temperature (250 ± 5 °C) during roasting was set for pot roasting, and the slight diference between the MC of the oven and pot roasting treatment could be due to ventilation in the oven that contribute in reducing the MC of the sample.
Concerning the ash content, apart from the sample roasted in the pot for 15 min, there was no signifcant difference (p < 0.05) between the control and the roasted samples.Te slight increase recorded could be attributed to the concentration of other constituents during roasting.In food matrix, ash content represents the mineral present.Te ash content of the roasted A. lepidophyllus seed fours ranged from 1.73 to 2.20 g/100 g DW.Tese values are smaller than 3.9%, as pointed out by Khan and Saini [22], on the roasted faxseed four.
Te protein content varied from 3.68 to 9.46 g/100 g DW.In general, there was a signifcant decrease (p < 0.05) in the protein content of A. lepidophyllus fours irrespective of the roasting method applied.Tis reduction could be due to the participation of proteins in the nonenzymatic browning reaction.Te decrease in protein content could also be attributed to amino acid polymerization and protein denaturation during roasting [7].A similar result was reported by Kumar et al. [23], who found a reduction in the protein content of black chickpea (Cicer arietinum) by 14.8% after roasting.Te decrease in the protein content of defatted walnut four and marble vine (Dioclea refexa) was also reported, respectively, after roasting [7,9].
Te variation of fat content was within the range of 8.80 to 12.90%.Te sample roasted in the oven 180 °C for 10 min, pot for 10 min, and microwave 300 W for 10 min had a signifcantly higher fat content compared to the control.Te increase in fat content could be attributed to the redistribution of nutrients and the disorganization of the food matrix due to high roasting temperature associated with the increase of the fat extraction yield [24]. Te lower fat content (8.80 g/100 g DW) was obtained with microwave roasting 200 W for 10 min treatment, whereas the highest fat content was obtained with the sample roasted in the oven at 180 °C for 10 min.Te presence of fat in a food matrix is important as it has the ability to facilitate the absorption of fat-soluble vitamins in the human track [25].
Te total crude fber content of the roasted A. lepidophyllus fours varied from 0.50 to 1.27 g/100 g DW, while that of the unroasted sample was 0.67 g/100 g DW.

Journal of Food Quality
As far as pot, microwave, and oven roasting were concerned, there was an increase in fber content with the increase of the roasting time/temperature.Te increases could be attributed to the evaporation of free water and some volatile compounds which caused the concentration of crude fber.Tis fnding is in accordance with that of Lawal et al. [8] and Mohamed Ahmed et al. [14], who found the increase in the fber content of defatted sesame seed fours during toasting and Samh (Mesembryanthemum forsskalei H.) seeds during roasting, respectively.Te best roasting method for the highest crude fber content of the A. lepidophyllus seeds was pot roasting for 10 min.
Concerning the carbohydrate content (CC), the result ranged from 77.59 to 81.5 g/100 g DW.All the roasting methods afected the CC of the A. lepidophyllus seed fours.Tere was a signifcant reduction of the CC with the increase of the roasting time/temperature.Te reduction in carbohydrate content found in these conditions could be due to the utilization of carbohydrate as a substrate in nonenzymatic browning reactions which occurred during roasting processes.A similar observation was reported by Tenyang et al. [26], who noticed a decrease in the carbohydrate content of two sesame varieties during boiling and roasting.Irrespective of the roasting method used, the fnal carbohydrate content was above 77 g/100 g DW which suggests that A. lepidophyllus could bring an added energy value.In fact, it is well known that carbohydrates are the frst important energy source of the human diet [27].

Total Phenolic Content.
Te word polyphenol refers to natural plant substances mostly found in fruits and vegetables [28].Te result of the total phenolic content (TPC) of A. lepidophyllus with respect to the roasting treatment methods is presented in Figure 1.
Generally, the TPC increased with the couple time/ temperature and microwave power.For all treatments, the couple time/temperature was the main factor which infuences the increase in the TPC irrespective of the roasting treatments.Te TPC ranged from 143.77 to 256.31 mg GAE/ g with the lowest and highest values attributed to the sample roasted in the pot for 5 and 15 min, respectively.In plant materials, insoluble polyphenols are covalently bound to lignin.Te thermal hydrolysis of these lignin-polyphenol acid bonds which may have taken place during the roasting treatment of samples could justify the increases of the quantity of the free phenolic compounds.Maillard and Berset [29] reported that, in plant tissues, the quantity of bound phenolic acids after thermal hydrolysis was twice higher than that of free phenolic compounds.Also, the thermal degradation of lignin could release more phenolic acids [28].Several authors previously reported the increase of TPC with the increase in temperature [30,31].Te increase of the TPC could be of great interest as these compounds are mostly correlated to several health benefts such as prevention against cancer and cardiovascular diseases [32,33].Te lowest TPC found in this study is greater than that of Frédéric et al. [5], who reported a maximum value of 51.8 mg GAE/g in A. lepidophyllus seed extracts.Tis difference could be attributed to the variation in geographical zone, soil, climate, or/and the extraction method used.Te important value of TPC found in this work is of great interest as these compounds in most cases are associated with health beneft.

DPPH Radical Scavenging Activity.
Te result of the antioxidant activity of the A. lepidophyllus seed fours evaluated in terms of free radical scavenging activity is shown in Figure 2. All the studied samples exhibited antioxidant activity (AOA) with diferent intensities.Tis corroborated the result of Frédéric et al. [5], who found that the methanol extract of the A. lepidophyllus seeds possessed AOA.Generally, for the same roasting method, the AOA increased with the concentration of the sample used irrespective of the roasting treatment applied.With the exception of the oven roasting methods, where the decrease in AOA was observed with the maintaining of the thermal exposition of the sample, there was a general increase in AOA with the increase of the temperature.Tis increase could be explained by the releases of the free phenolic acids with high AOA potentiality.Te fnding could be confrmed with the trend of the result recorded with the evaluation of the TPC presented in paragraph 3.2.Moukette et al. [4] previously studied the TPC of A. lepidophyllus and discovered that they were mainly made up of favonoids which are powerful antioxidant compounds.Te best method which exhibited the highest AOA was found to be pot roasting for 15 min.Journal of Food Quality 3.4.Functional Properties.Te functional properties of food fours are parameters that determine its taste, favor, processing method, transportation, and storage time [34].Diferent functional properties of A. lepidophyllus four were evaluated, and the results are presented in Table 2.
3.4.1.Water and Oil Holding Capacities.Te result of water holding capacity (WHC) of the roasted A. lepidophyllus revealed that irrespective of the applied roasting methods, the value increased signifcantly as compared to the control (unroasted sample).Microwave roasting resulted in the highest increase in WHC (20.1%), followed by pot roasting (19.5%), while the oven roasting had the lowest (16.3%) increase in WHC.For the same roasting method, there was a proportional increase in WHC with time and temperature.Te increase in WHC could be accredited to the formation of the porous structures within the four matrix during the roasting process due to heat, which may therefore increase the capacity of the sample to absorb water.Additionally, the gelatinization of the starch content of the sample which is proportional to the processing temperature could increase the WHC.In fact, the WHC of the starch granules increases with the process of gelatinization [35,36].Jogihalli et al. [37] reported an increase in WHC of the chickpeas roasted in the microwave due to starch gelatinization.Te value of WHC found in this study is lower than 132 to 176% reported by Chandra et al. [38], in composite biscuit fours and 199.60 to 336.58% obtained by Ohizua et al. [39], in unripe cooking banana, pigeon pea, and sweet potato four blends.Tese diferences can be attributed to the diference in starch content between A. lepidophyllus fours and those food fours.Te result of oil holding capacity (OHC) (Table 1) revealed a signifcant increase after roasting processes.Te OHC of the roasted sample ranged from 8.05 to 8.50% with the highest value found with the sample roasted in the microwave 450 W for 10 min.Tis variation could be attributed to the solubilization of the subunits of proteins resulting from the thermal dissociation during the roasting process.In fact, previous research found that, during thermal treatment, proteins dissociate and become more soluble, modifying their polarity which contribute to the increase in the OHC [40].Tis increase in OHC could also be explained by the augmentation of the sample porosity due to the evaporation of some constituent during processes.Tis result suggests that A. lepidophyllus roasted fours can be used for food formulation as their important OHC will increase the palatability and the ability of retaining favors.However, the roasting conditions should be well defned and controlled in order to take beneft of these properties.

Swelling Capacity.
Te swelling capacity (SC) is one of the important technological parameters in food processing.Te higher the SC, the lower is the bonding energy between molecules that constitute a food system [39].Te efect of diferent roasting methods on the SC of A. lepidophyllus was evaluated, and the result is presented in Table 2. Tere was a signifcant increase (p < 0.05) in SC compared to the control.Te diferent roasting methods improved the SC of A. lepidophyllus four.Tis result is in line with that of Djikeng et al. [20], who found that thermal processing positively afects the SC of the Archachatina maginata powder meat.Tis increase can be attributed to the reorganization of the proteins during heating.In fact, according to Li et al. [40], heat treatment destabilized the aggregation of protein molecules which favor the establishment of the cross-linking network between peptide bonds and side chains.Te formation of this network contributes signifcantly to water retention and therefore increases the SC.Te value of the SC found in this study is higher compared to 9.91 to 12.71% as obtained by Ocheme et al. [41], on wheat and groundnut protein concentrate four blends.

Hausner Ratio and Porosity.
Te Hausner ratio which indirectly measured the property of a bulk density of material to reduce its volume in case of mechanical infuence was calculated by taking the ratio of loose bulk density to the apparent density after tamping [42].Te HR value ranged from 1.12 to 1.37 (Table 2), indicating that the A. lepidophyllus fours have low interparticle friction; therefore, it will exhibit a high degree of fowability.In fact, according to Chinwan and Castell-Perez [43], fours with HR > 1.45 have poor fowing behavior.Tis lower HR could be due to the poor moisture content of the diferent samples [41].In fact, during drying, the formation of pores which controls the variation of the HR is proportional to the quantity of evaporated water.Te highest HR obtained in this study is smaller compared to the least value (1.40), as reported by Amankwah et al. [44], in a composite four made of wheatrain tree.
Te porosity of a food four is related to the particle size, shape, and density of the four.It guides the type of the packaging material required as well as the storage condition [11].Te porosity of A. lepidophyllus ranged from 12.84 to 34.54%.Te diferent roasting methods signifcantly afected the porosity except for the sample roasted in the pot for 5 min.Te porosity increased with the heating time, irrespective of the treatment method.Tis could be attributed to evaporation of the free water which allowed the material to settle well and increased the porosity.Te highest porosity was recorded with the sample roasted in a microwave at 450 W for 10 min, which contributes in justifying the highest water holding activity obtained with the same sample.High porosity is technologically important as porous samples are lighter and suitable for packaging and transport [45].

3.4.4.
Loose and Packed Bulk Density.Te loose and packed densities are two important parameters that determine the packaging system and the packaging material of a food four [46].Te bulk densities of A. lepidophyllus varied from 0.75 to 0.85 g/mL (loose bulk density) and from 0.95 to 1.07 g/mL (packed bulk density) (Figure 3).Te bulk densities obtained in this study follow the same trend of the moisture content.Tis corroborated the fnding of Chandra et al. [38], who reported the dependency of the bulk density on the initial moisture content of the food four.According to David et al. [47], food four with a high value of bulk density can be conveniently used for food preparation.Te higher bulk densities found in this study suggest that A. lepidophyllus fours could be used as a thickening agent in food formulation.Low bulk density fours, on the other hand, are more suitable for formulation of complementary foods as it may promote easy digestibility and promote nutrients availability [41].Te value of bulk density obtained was higher than 0.40 to 0.52 g/mL and 0.57 to 0.77 g/mL, as pointed out by Awuchi et al. [48], respectively, in Mole ranchero, Piquin chilli, Guajillo chilli, and Arbol chilli.

Conclusion
In this study, A. lepidophyllus fours were produced after diferent roasting methods.Results revealed that these methods infuenced the nutrient, functional, and antioxidant  properties of these fours.Te total phenolic content as well as the antioxidant activity of the produced fours showed a signifcant increase after roasting treatments.Tese fours have slightly low moisture and protein contents compared to the unroasted sample.Pot roasting (15 min at 250 ± 5 °C) treatment was found to be better maintained or increased antioxidant activity, moisture, ash and total phenolic contents, water holding and swelling capacities, and Hausner ratio.
Te A. lepidophyllus four has good health potential and could be used to develop nutraceutical foods.However, further studies need to be conducted on toxicity, overall acceptability, and levels of insertion for new product development.

Figure 1 :Figure 2 :
Figure 1: Variation of the TPC of the A. lepidophyllus seed four during roasting methods.

Figure 3 :
Figure3: Variation of the loose and packed bulk densities of A. lepidophyllus with respect to diferent roasting methods.Te histogram of the loose and packed bulk densities, respectively, carrying the same superscript letters, is not signifcantly diferent.

Table 1 :
Proximate composition (g/100 g DW) of A. lepidophyllus seed four after diferent roasting treatments.Mean values in the same column carrying the same superscript letters are not signifcantly diferent (p > 0.05).

Table 2 :
Functional and physical properties of A. lepidophyllus fours with respect to diferent roasting treatments.Mean values in the same column carrying the same superscript letters are not signifcantly diferent (p > 0.05).WHC (water holding capacity), OHC (oil holding capacity), and SC (swelling capacity).