Effect of pretreatments and drying techniques on functional and physicochemical properties of aerial yam (Dioscorea Bulbifera) powder

Introduction

Yams are widely cultivated and consumed by different groups of people in the tropics, among them is the Dioscorea bulbifera, which is also known as aerial yam. Dioscorea bulbifera is one of the most valuable tuber species in West Africa. It is often considered as a wild species of yam native to Africa and Asia. (FAO, 1985) [28] . The D.B.S.K.K.V., Dapoli, Dist. Ratnagiri has developed aerial yam variety in 2015, named as Konkan Kalika (KKVDb-1). It has average yield 5.3t/h and it gives high marketable yield, bulbs with pale yellowish flesh color, good taste and cooking quality, resistant to disease and pests and has been released for growing in Konkan region of Maharashtra. It is a major edible medicinal plant employed in the treatment of diverse medical conditions. The use of Dioscorea bulbifera has been well documented in Chinese medicine and West and Central Africa. The plant is used in the treatment of different conditions such as ulcers, dysentery, diabetes, hyperlipidemia, and cancer (Ghosh et [30,34,56] The plant has bioactive compounds like flavonoids, phenols, tannins, saponins, alkaloids and terpenoids. The bioactive compounds in aerial yam showed various pharmacological properties like anti-inflammatory, antioxidant, antimicrobial, antidiabetic, and anticancer properties. The species shows a high degree of adaptability to different environments and has nutritional and medicinal versatility due to its high phytochemical content (Ghosh et al. 2015; Kuete et al. 2012) [30,44] . The phytochemical composition of Dioscorea species, like other plants, may differ depending on factors such as geographical location, environment, and type of plant variety. Phytochemicals are natural bioactive compounds that occur in plants and have potential medicinal properties. Dioscorea species are known to produce secondary metabolites in large quantities and are widely used in the pharmaceutical industry and medicine. (Paul et al. 2022) [70] . Pretreatment techniques are used in a bid to reduce the effects of quality attributes degradation. They can also reduce the total drying time, which is more energy efficient and produce final products of high standards (Kucuk et al. 2014; Xiao et al. 2014) [45,85] . pretreatments prior to the processing of agricultural products as it may destroy the enzymes responsible for degradation reactions, off-flavor, and undesirable changes in color, texture, and nutrients (Xiao et al. 2014) [85] . Dioscorea bulbifera significantly increases the value of this food crop and lowers post-harvest losses, which helps farmers make money. Overall, aerial yam is particularly vulnerable to enzymatic browning, which is brought on by polyphenol oxidases, oxidizing phenolic compounds when oxygen is present. Both enzymatic and non-enzymatic browning in powder are prevented by pretreatments (Igbokwe et al. 2016) [33] . Due to their high moisture content at harvest (Afoakwa and Sefa-Dedeh, 2001) [5] and susceptibility to deterioration, particularly when bruised (Fioreze and Morini, 2000) [29] , yams are challenging to store. However, drying has been suggested as a viable post-harvest management option, particularly in developing nations with inadequately developed low-temperature distribution and handling facilities (Sagar and Kumar, 2010) [75] . It is possible to create a stable form of yam products to meet the demand for health foods because yams are considered health foods rather than staple foods in Oriental countries (Hsu et al. 2003) [32] . Dried yam powder is worth developing because powder can be conveniently used to make formulated foods or capsules for consumption and are easily stored for a long time (Akissoe et al. 2001) [6] . The drying conditions and techniques employed affect the final products flavor, taste, color, and nutrients. Yams may be subject to environmental contamination (Arslan and Özcan, 2010) [12] . Numerous studies have been conducted in recent years to find a substitute for the natural drying procedure, which ought to reduce the drying time, manage pests, and preserve the quality and appearance of yam powders (Jiang et al. 2013) [38] . The present study was undertaken to evaluate the influence of pretreatments and drying methods on the functional and physico-chemical properties of aerial yam powder.

Materials and Methods

Materials

The aerial yam tubers (variety -Kokan Kalika) procured from All India Coordinated Research Project (AICRP) on Tuber Crops, Central Experiment Station (CES), Wakavali, Dr. Balasaheb Sawant Konkan Krishi Vidyapeeth, Dapoli. The experiment carried out in Department of Post-Harvest Management of Medicinal, Aromatic, Plantation, Spices and Forest Crops of the Post Graduate Institute of Post-Harvest Management, Killa-Roha, Dist-Raigad.

Methods

Powder Making

Fresh and mature tubers of aerial yam were washed thoroughly with clean water to remove adhering soil and other undesirable materials. The yam samples were sorted manually to remove damaged tubers, hand-peeled using stainless steel knives and sliced uniformly into 1 mm thickness to ensure uniform drying. The sliced samples were divided into four portions for different pre-treatments. One portion was kept as control without any treatment. The second portion was soaked in cold water (25°C) for 20 minutes. The third portion was soaked in lukewarm water (40 °C) for 20 minutes. The fourth portion was subjected to hot water blanching at 80°C for 2 minutes. After each treatment, excess surface water was drained and the slices were blotted gently to remove adhering moisture. Each pre-treated sample was further divided into three equal portions and subjected to different drying methods. One portion was dried under direct sunlight for 3 days with an average temperature 27.33 ± 0.29°C on clean trays until constant weight was achieved. The second portion was dried in a tray dryer maintained at 40°C until constant weight was obtained. The third portion was dried in a pyramid solar dryer with an average temperature 27.33 ± 0.29°C under solar conditions until a constant weight was reached. Thus, a total of twelve treatments (four pre-treatments × three drying methods) were employed in the study. The dried yam slices were milled using a laboratory pulverizer machine and sieved through a 1 mm mesh sieve to obtain fine aerial yam powder. The powder samples were packed in airtight zip LDPE pouches and stored at room temperature prior to further functional and physicochemical analysis. The flow chart for preparation of aerial yam powder given below.

Flow chart for preparation of aerial yam powder

Methods

Functional properties of aerial yam powder

Bulk density (gm/𝒄𝒎 𝟑 ) Bulk density of aerial yam powder was carried out according to the procedure outlined by Onwuka (2005) [63] . Aerial yam powder sample was poured into a ten mil (10 ml) dried measuring cylinder and the bottom of the measuring cylinder was tapped repeatedly against the lab bench until the level of the sample remained constant at 10 ml. Bulk density was measured as weight per unit volume of the sample.

Bulk density (gm/𝑐𝑚

The oil absorption capacity of the sample was measured according to the methods of (Babu and Parimalavalli, 2014) [16] and (Bikila et al. 2022) [19] , with slight modification. Weigh accurately 1 g of the powdered sample, put in preweighed centrifuge tube and add 6 ml of sunflower oil. Mix well in a vortex mixer for good contact between sample and oil. Then, centrifuged for 15 minutes. The excess oil was removed after centrifugation, and the mass of the centrifuge tube with oil absorbing sample was measured. This weight difference was taken as oil absorbed by the sample. The oil absorption capacity is expressed as grams of oil absorbed by gram of the dry sample with the formula given below:

Oil absorption capacity (g/g) = 𝑊2-𝑊1

𝑊1

Where: W1: The initial weight of the dry sample (g) W2: The weight of the sample after water absorption (g).

The water absorption capacity of the test sample was carried out according to the method outlined in (Babu and Parimalavalli, 2014) [16] and (Bikila et al. 2022) [19] , but with slight modifications. First, 1 g of the ground sample was weighed and added to a pre-weighted centrifuge tube. Ten milliliters of distilled water were poured into the centrifuge tube, followed by thorough mixing of its contents using a vortex mixer. This was done to ensure that the test sample is evenly distributed in the water. Centrifugation was done for 15 minutes. The supernatant was carefully decanted without disturbing the sediment in the tube. The hydrated sample contained in the centrifuge tube was re-weighed. The water absorption capacity was measured based on the increase in the weight of the tube. Water absorption capacity is calculated in grams of water absorbed per gram of the dry test sample using the formula below:

Water absorption capacity (g/g) = = 𝑊2-𝑊1

𝑊1

Where: W1: The initial weight of the dry sample (g) W2: The weight of the sample after water absorption (g)

The moisture content in the sample was determined by using the moisture analyzer. The moisture content of the given sample was determined by using the following formula (Ranganna, 1986) [73] .

𝑊𝑤-𝑊𝑑

𝑊𝑤 × 100

Where, Ww: initial weight of sample (g) Wd: weight of dry sample (g)

Ash is an inorganic residue left behind after the material is burnt to completion at a temperature of 550°C in a muffle furnace. Ash is the sum total of all the non-volatile inorganic compounds. Approximately 5 grams of the finely powdered dry sample was weighted and ash content of the paste sample determined. The tare weight of crucibles was measured and 5g of the sample put in each. The samples were then incinerated on a Bunsen burner and the material ashed at temperatures not exceeding 525 °C for 4-6 hours, in a muffle furnace. The crucibles were cooled and weighed. The difference in the weight was taken as the total ash content and expressed as a percentage (Rangana, 1986) [73] . The formula for calculating total ash (%) is as follows:

The protein content in the sample was estimated using a Micro-Kjeldahl Distillation process. The dried sample, dried at 65°C, was digested through the heating process using concentrated sulfuric acid (H2SO4), along with the digestion mixture, potassium sulphate (K2SO4), and copper sulphate (CuSO4). The resultant mixture was then made alkaline using 40% NaOH solution. Ammonium Sulphate was produced in the process. The ammonia was absorbed in 4% boric acid and titrated back with HCl. The percentage nitrogen content in the sample was estimated using the formula given below. The total protein content was determined by multiplying the nitrogen percentage with an appropriate factor (6.25) (AOAC, 2000) [10] . N% = 1.4× (𝑚𝑙 𝐻𝐶𝐿 -𝑚𝑙 𝑏𝑙𝑎𝑛𝑘 ×𝑐𝑜𝑛𝑐.𝑜𝑓 𝐻𝐶𝐿 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒 (𝑔) % Protein =% N × Factor (6.25)

The amount of crude fat was calculated using the crude ether extract of the dried material. This was done by weighing 5g of the dry material and transferring it into a thimble, which was plugged with cotton and placed in the Soxhlet extractor, where it was extracted with anhydrous ether for 3 hours. Afterwards, the ether was evaporated, and the flask containing the residue was dried in an oven at 80oC to 100oC.

Fat% =

𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑒𝑡ℎ𝑒𝑟 𝑒𝑥𝑡𝑟𝑎𝑐𝑡 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒 𝑡𝑎𝑘𝑒𝑛 × 100

Approximately 2-5 g of fat-free and moisture-free sample was taken into a 500 ml beaker and then 200 ml of 0.25 N boiling sulfuric acid was added and kept boiling for 30 minutes while the volume remained constant by adding water at regular intervals. The mixture was then filtered using a muslin cloth and taken to the same beaker. Then 200 ml of boiling 0.313 N (1.25%) NaOH was added. The mixture was kept boiling for 30 minutes and then filtered using muslin cloth. The residue was washed with hot water until it became free from alkali and then with alcohol and ether. This was placed in the crucible, dried overnight at 80℃ to 100℃ and weighed. The crucible was then heated in the muffle furnace at 525℃ for 2-3 hours. It was cooled and weighed again. The difference in weights showed the weight of crude fiber (Ranganna, 1986) [73] .

Carbohydrate content of a sample dried at 65°C was determined by subtracting the total sum of protein, fiber, ash and fat from the total dry matter (Rangana, 1986) [73] . The carbohydrate was calculated by using following equation.

Starch (%) 25 g weight of the sample was placed in a beaker. 15 ml of distilled water was added and a stiff paste was made that was left to settle in the beaker. This was taken out, pressed between hands and kneaded under the tap water until all the starch was washed into the collecting beaker through a 100 μm sieve. Supernatant was left to settle down while the excess water was removed. The starch was then dried in a hot air oven (Igbokwe et al. 2016) [33] . Dry starch was weighed and percent calculation is as follows:

Methanolic extract of aerial yam powder was prepared according to the modified method. 0.5 gm of finely powdered sample was weighed accurately into a centrifuge tube and extracted with 20 ml of 80% methanol. The mixture was centrifuged at 6000 rpm for 20 min, and the supernatant was collected. The residue was re-extracted twice with 20 m of 80% methanol under the same conditions. The methanolic extract was used for the estimation of total flavonoid content. Total flavonoid content was determined by the aluminium chloride colorimetric method. An aliquot of 0.6 ml of methanolic extract was transferred into a test tube, followed by the addition of 4.4 ml distilled water and 0.3 ml of 5% sodium nitrite (NaNO₂) solution. The mixture was allowed to stand for 5 min, after which 0.3 ml of 10% aluminium chloride (AlCl₃) solution was added. After 6 min, 2.0 ml of 1 M sodium hydroxide (NaOH) was added and the final volume was made up to 10 ml with distilled water. The contents were mixed thoroughly, and the absorbance was measured at 510 nm using a UV-Visible spectrophotometer against a reagent blank. A calibration curve was prepared using quercetin as the standard, and the results were expressed as% quercetin equivalent of sample (Batuwita et al. 2025) [17] .

Methanolic extract of aerial yam powder was prepared according to the modified Folin-Ciocalteu method. 0.5 gm of finely powdered sample was weighed accurately into a centrifuge tube and 20 ml of 80% methanol was added. The mixture was centrifuged at 6000 rpm for 20 min, and the supernatant was collected. The residue was re-extracted twice with 20 ml of 80% methanol under the same conditions. The extract was used for the estimation of total phenolic content. Total phenolic content was determined by the Folin-Ciocalteu colorimetric method. An aliquot of 0.2 ml of methanolic extract was transferred into a test tube, followed by the addition of 0.5 mL Folin-Ciocalteu phenol reagent. After 3 min, 2.0 ml of 20% sodium carbonate (Na₂CO₃) solution was added and the volume was adjusted to 5.5 ml with distilled water. The reaction mixture was mixed thoroughly and heated in a boiling water bath for 1 min. After cooling to room temperature, the absorbance was measured at 650 nm using a UV-Visible spectrophotometer against a reagent blank. A standard calibration curve was prepared using gallic acid, and the results were expressed as% gallic acid equivalents of sample (Ghosh et al. 2012) [31] .

A water extract of aerial yam powder was prepared following the extraction procedure. About 0.5 g of finely powdered sample was weighed accurately into a 250 ml conical flask. 75 ml of distilled water was added, and the flask was placed in a boiling water bath for 30 min. The extract was then allowed to cool to room temperature and transferred into centrifuge tubes. The suspension was centrifuged at 6000 rpm for 20 min. The supernatant was collected in a 100 ml volumetric flask. The residue was reextracted with 20 ml distilled water, centrifuged again under the same conditions, and the supernatant was combined with the first extract. Finally, the volume was made up to 100 ml with distilled water. This aqueous extract was used for the estimation of total tannin content. Total tannin content was determined using the Folin-Denis colorimetric method. An aliquot of 0.6 ml of the aqueous extract was taken in a test tube, followed by the addition of 7.9 ml distilled water, 0.5 ml Folin-Denis reagent, and 1.0 ml sodium carbonate (Na₂CO₃) solution. The reaction mixture was mixed thoroughly and allowed to stand for 30 min at room temperature for color development. The absorbance was measured at 700 nm using a UV-Visible spectrophotometer against a reagent blank. Total tannin content was calculated from a standard calibration curve prepared using tannic acid and expressed as% tannic acid equivalent of sample (Ojinnaka et al. 2017) [60] .

Statistical analysis

The experiment was conducted the effect of different pretreatments and drying methods on the quality characteristics of aerial yam powder was studied using a Factorial Completely Randomized Design (FCRD). They were evaluated in a 4 × 3 factorial combination with four replications. The observations recorded for different quality parameters were subjected to analysis of variance (ANOVA). The statistical analysis and interpretation of the experimental data were carried out following the standard procedures described by Panse and Sukhatme (1985) [68] .

Result and Discussion

The bulk density of aerial yam powder varied between 0.545 and 0.755 g/cm³ given in table 1. The bulk density depends on the particle size and density of the powder (Iwe et al. 2016) [36] . Higher bulk density and better flow properties facilitate easy handling, storage, packaging and processing of powders in nutraceutical and pharmaceutical formulations (Jallo et al. 2012) [37] . The maximum bulk density was observed in hot water blanching treatment (0.724 g/cm³) among pretreatments. Bulk density could be attributed to the heat treatment process applied when blanching (AACC, 2000) [1] . Similar findings were reported by Kayode et al. (2017) [40] who studied the bulk densities of blanched aerial yam powder. In a drying methods tray drying showing highest bulk density (0.727 g/𝑐𝑚 3 ). The bulk density of samples dried using heat consistently increased during the tray drying process (Koc et al. 2008) [43] . The same line of work was done by Wahab et al. (2016) [84] who observed variation in bulk density using different drying methods on yam four. Among interaction treatments highest bulk density was recorded in hot water blanching with tray drying (0.755 g/𝑐𝑚 3 ) which was at par with lukewarm water treatment with tray drying (0.734 g/𝑐𝑚 3 ).

The oil absorption capacity ranged from 0.807 g/g to 1.325 g/g shown in table 2. Oil absorption capacity can be defined as the ability to absorb oil (Chandra and Samsher, 2013) [21] .

The oil absorption capacity of the powder also makes it suitable in helping to enhance taste and texture of powder (Chandra and Singh, 2013) [21] . Among all the pretreatments studied, hot water blanching treatment showed the highest effectiveness (1.168 g/g). The impact of various processing techniques raised the value of oil absorption capacity in the powder samples. This was possibly because of the presence of more hydrophobic materials in the powder and by virtue of the heat used in processing (Kaur and Singh, 2006) [39] . Princewill-Ogbonna and Ezembaukwu, (2015) [72] showed the result of the oil absorption capacity on aerial yam flour using different pretreatments. Tray drying method demonstrated superior quality retention (1.196 g/g). Tray drying could have improved the oil binding property of the flour because of water evaporation and structural changes that resulted from heat, making more oil binding sites available (Wahab et al. 2016) [84] . This result was supported by Argaw et al. (2023) [11] on aerial yam flour. Maximum value was found in hot water blanching with tray drying (1.325 g/g) in a combination treatments. [47] . Water absorption capacity is important for food systems due to its ability to help increase yield and consistency as well as body in foods (Osundahunsi et al.

2003) [66] . It was observed that lukewarm water treatment showing good result (2.630%) among pretreatments. The weight and volume percentages and the dimensions of the powder samples increased with time and temperature during soaking (Sfayhi-Terras et al. 2021) [81] . Similarly, Igbokwe et al. (2016) [33] reported the water absorption capacity of pretreated aerial yam flour. Also, Princewill-Ogbonna and Ezembaukwu, (2015) [72] showed the result of the water absorption capacity on aerial yam flour using different pretreatments. Among drying methods, tray drying showed the highest water absorption capacity (2.527 g/g). It exhibited better efficiency than the other drying methods.

Based on this study, continuous heat application and high temperatures in tray drying can enhance the water absorption capacity of the powder more than the use of solar and sun drying (Leonel et al. 2009; Osundahunsi et al.

2003) [47,66] . These findings are in agreement with reports by Obadina et al. (2014) [58] in Dioscorea species. In a combination treatments highest water absorption capacity was recorded in lukewarm water treatment with tray drying (2.887 g/g). [71] . The low levels of moisture are linked to increased shelf stability of powder as the moisture required for microorganism growth is greatly reduced (Tenyang et al. 2025) [82] . Among pretreatments lowest moisture content was found in hot water blanching treatment (9.233%). The process of hot water blanching treatment inhibits the browning reaction through the inactivation of polyphenol oxidases, which usually cause enzymatic browning helps in moisture removal as compared to cold water treatment and lukewarm water treatment (Li et al. 2019) [48] . Similar observations were reported by Falade et al. (2007) [27] on Dioscorea alata and Dioscorea rotundata slices. Also, Kayode et al. (2017) [40] reported the moisture content of blanched aerial yam flour. Among drying methods tray drying showing lowest moisture content (9.088%). In a tray dryer with thin-layer drying, the sample is dried in one layer, hence facilitating moisture removal (Kumar et al. 2012) [46] . Similar line of work was done by Nwadike et al. (2023) [57] who reported the moisture content of dried aerial yam flour. The combined effect of treatments further highlighted variation, with hot water blanching with tray drying showing minimum moisture content (8.400%) which was at par with untreated sample with tray drying (8.525%).

The results revealed that ash content ranging from 2.575% to 3.563% showing significant differences among pretreatments and drying methods in Table 5. The amount of ash content is used as an index for assessing mineral content in Dioscorea. (Tortoe et al. 2017) [83] . The ash content is an indication of how much minerals are packed into the cultivars of yams (Akonor et al. 2017) [7] . Among pretreatments control (untreated) sample showing highest mean ash content (3.392%). Pretreatments like soaking and blanching will lower ash because of the leaching of water-soluble minerals (Obadina et al. 2014) [58] .

This result was supported by Ayo et al. (2018) [14] in aerial yam flour.

In drying methods tray drying showed good result (3.188%)

The highest ash content in tray drying is attributable to the low moisture content of the tray dried sample and the influence of heat and air flow during drying (Mondal et al. 2019) [53] . Similar findings were reported by Kayode et al.

(2023) [41] on aerial yam flour using different drying methods. Ojinnaka et al. (2017) [60] reported the similar range of ash content in dried aerial yam flour. The untreated sample with tray drying is most effective for achieving higher ash content (3.563%) in a combination treatments.

The protein content of aerial yam powder for different pretreatments and drying methods ranging from 5.978% to 6.487% is summarized in table 6. Proteins are one of the major macronutrients that play vital roles in cell formation and physiology. They are also very important components of the human diet (Padhan and Panda, 2020) [67] . The highest protein value was observed in control (untreated) sample (6.423%). Pretreatments like soaking and blanching lower the protein content as a result of leaching of the soluble nitrogen compounds. Heating during blanching could denature the proteins, making them insoluble and thus easier to remove (Obadina et al. 2014) [58] . Similar findings were reported by Obadina et al. (2014) [58] in yam flour. Also, Induar et al. (2023) observed reduction in protein content of aerial yam flour after pretreatment. Among drying methods, tray drying showed the highest protein content (6.458%). Uniform circulation of air is responsible during tray drying to facilitate higher soluble protein content in the powder. There was better retention of nutrient like protein and nutritional characteristics in a tray drying (Mondal et al. 2019) [53] . Similar work was done by Kayode et al. (2017) [40] who evaluated the protein content of dried aerial yam flour using different drying methods. When both factors pretreatment and drying method were considered together, the highest protein content was achieved with untreated sample with tray drying (6.592%).

The fat content of aerial yam powder as influenced by different pre-treatments and drying methods is presented in table 7 ranged from 0.467% to 0.683%. Fat is generally preferred in smaller amounts when it comes to tuber powders because it will help to increase their storage capability (Serna-Saldivar and García-Lara, 2016) [79] . Among all the pretreatments studied, blanching showed the lowest fat content (0.506%). Fat content reduction can be associated with heat disruption of cellular components through blanching, which facilitates lipid loss from the membrane during further processing (Melese and Keyata, 2022) [52] . Due to the low amount of fat in the blanched samples, there was a high likelihood of a prolonged shelf life in relation to rancidity (Oluwalana and Oluwamukomi, 2011) [62] . Similar findings were reported by Orhevba and Ajiboye, (2020) [64] in yam (Dioscorea rotundata) flour, where blanching time and slice thickness significantly affected the fat content.

Tray drying method demonstrated superior result (0.533%) compared to the remaining drying methods. The reason behind the low fat value of tray dried samples lies in its low moisture content and high yield (Mondal et al. 2019) [53] . Argaw et al. (2023) [11] observed variation in fat content in aerial yam flour due to the effect of drying methods. Abara, (2011) [2] found similar findings in proximate of the of Dioscorea bulbifera tuber. The lowest fat content was recorded in hot water blanching with tray drying (0.467%) which was at par with hot water blanching with pyramid solar drying (0.483%) in a combination treatments. [24,77] . According to study fiber consumption decreases the risk of obesity, cardiovascular diseases, diabetes and causes soft stools (Anderson et al. 2009) [8] . Among all the pretreatments studied, lukewarm water treatment showed highest fiber content (2.383%). This may have been caused by the extraction of the anti-nutrient components (Adebayo, 2014) [3] . Ayo et al. (2018) [14] also reported a relatively high fiber content in soaked-dried aerial yam flour. In drying methods tray drying showing highest fiber content (2.196%). Variations in values could be due to differences in the methods used for drying and the extent of homogenization. Dhore et al. (2023) [25] similarly reported higher crude fiber content in cabinet tray-dried aerial yam flour than in sun-dried powder. Maximum value was in lukewarm water treatment with tray drying (2.583%) in a combination treatments. [15] . Hot water blanching treatment showed highest carbohydrate content (80.858%). This implies that the content of carbohydrate will be increased through blanching (Egbuonu and Nzewi, 2016) [26] . Similar findings were reported by Igbokwe et al. (2016) [33] , who observed that blanching significantly increased the carbohydrate content of Dioscorea bulbifera flour.

In drying methods highest carbohydrate content found in tray drying (80.743%). This could be due to the removal of water in aerial yam which makes it concentrated in a smaller volume leading to an increase in the carbohydrate content (Ojeniran et al. 2025) [59] . Similar line of work was done by Nwadike et al. (2023) [57] who reported the carbohydrate content of dried aerial yam flour. In a interaction treatments highest value was observed in hot water blanching with tray drying (81.468%). [76] . Among the pretreatments, lukewarm water treatment recorded the highest starch content (28.733%). During lukewarm water soaking, there is leaching of other nutrients, resulting in changes to the structure thereby improving the accessibility of the starch and increasing starch content of powder (Marconi et al. 2000) [50] . Similar variation in starch content due to different pretreatment methods was reported by Olatunde et al. (2016) [61] , who observed a significant effect of pretreatment on the starch content of sweet potato flour. Among the drying methods, tray drying recorded the highest starch content (27.884%). Tray drying affected the starch structure by lowering its digestibility and creating resistant starch (Björck et al. 1984) [20] . Starch content was found low in sun dried and pyramid dried samples because starch crystallinity was decreasing with an increase in the drying temperature (Aviara et al. 2010) [13] . Similar effects of processing conditions on starch content of underutilized tuber flours were also reported by Orji, (2023) [65] . Olatunde et al. (2016) [61] also reported significant variation in starch content of sweet potato flour due to drying methods, indicating that drying conditions can influence starch retention in flour. The combined effect of treatments further highlighted variation, with lukewarm water treatment with tray drying showing maximum starch content (29.471%). [18] . Control (untreated) sample showed superior performance with the highest flavonoid content (4.403%QE). Loss of nutrients in the process of other treatments can be attributed to the leaching effect (Mukherjee and Chattopadhyay, 2007) [55] . Similar findings were reported by Indaur et al. (2023), who observed variation in flavonoid content between raw and boiled Dioscorea bulbifera flour. Drying method tray drying contributed to higher flavonoid content (3.549%QE).

Tray drying owing to its effectiveness because of their moderate temperature in preventing the breakdown of flavonoids (Ling et al. 2015) [49] . The processes of sun drying depend on weather conditions and duration of daylight cause dehydration. The low level of flavonoids could be due to the long drying period (Ling et al. 2015) [49] . Kayode et al. (2017) [40] studied different drying methods for Dioscorea bulbifera flour and reported presence of flavonoid content. The interaction between factors was significant, suggesting that the combination of lukewarm water treatment with tray drying (4.657%QE) is most effective for achieving higher flavonoid content which was at par with untreated sample with tray drying (4.508%). [51] . Control (untreated) sample showed the highest phenol content (3.433%GAE). The decrease in phenol concentrations is due to their leaching from the samples into the water used in the pretreatment process (Chipurura et al. 2010) [23] . Setyawan et al. (2021) [80] reported that processing techniques influenced the total phenolic content of Dioscorea bulbifera flour. Similarly, Ratnaningsih et al.

(2018) [74] reported that soaking treatments affected the phenolic content of Dioscorea alata flour.

Drying method tray drying contributed to higher phenol content (2.923%GAE). Tray drying generally involves convective heat transfer, in which hot air is circulated over the sample to facilitate heat transfer (Patil and Shukla, 1998). Extreme heat can cause the destruction of phytochemicals that are susceptible to high temperatures (Kerr, 2013) [42] . Adebowale et al. (2018) [4] reported that drying method significantly affected the phenolic content of yam flour. When both factors were considered together, they were showing significant difference. The highest phenol content was achieved with untreated sample with tray drying (3.749% GAE) which was at par with lukewarm water treatment with tray drying (3.667%).

The tannin content of aerial yam powder as influenced by different pre-treatments and drying methods is presented in table 13 ranged from 0.428%TAE to 1.576%TAE. Tannins have some neat therapeutic uses because of their antiinflammatory, anti-fungal, antioxidant, and healing properties (Zuanazzi and Montanha, 2004; Santos and Mello, 2004) [86,78] . The highest tannin content was recorded in control (untreated) sample (1.529%TAE). The reason for the low concentration of tannin in other treatments because they were leached out. (Mongwaketse et al. 2022) [54] . Similar findings were reported by Egbuonu and Nzewi. (2014) [26] who observed a significant and time-dependent reduction in tannin content of bitter yam flour The highest tannin content was observed in tray drying (1.328% TAE). The type of heat transfer in tray drying is important in determining the amount of phytochemicals that remain (Patil and Shukla, 1998). Adebowale et al. (2018) [4] reported that drying method influenced the tannin content of yam flour. Among interaction treatments highest tannin content was recorded in lukewarm water treatment with tray drying (1.576% TAE) which was at par with untreated sample with tray drying (1.152% TAE). values of water absorption capacity, fiber content and starch content whereas the control (untreated) recorded the highest values of ash content, protein content, total flavonoid content, total phenol content and total tannin content. Among the different drying methods, tray drying was found to be the best drying method for preparation of aerial yam powder based on its overall quality characteristics. Based on the comparative evaluation of different pre-treatments and drying methods, the powder prepared from aerial yam using lukewarm water treatment with tray drying was found to be the most suitable treatment.

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