Characterization of Acid Hydrolyzed Taro Boloso-I (Colocasia esculenta Cultivar) Starch as a Diluent in Direct Compression of Tablets

Corn, wheat, rice, potato, and cassava starches have been widely used as pharmaceutical excipients. However, the search for cost-effective local starch alternatives is necessary due to the availability and usage constraints. In Ethiopia, various plant species, including Taro Boloso-I, have been explored as potential sources of pharmaceutical starch. It is a variety of Colocasia esculenta with a high tuber yield and high starch content. However, the native starch requires modifications to enhance its functionality. Therefore, this study aimed to improve the native starch through acid modification and evaluate its performance as a direct compressible tablet excipient. The native starch was treated with a 6% w/v HCl solution for 192 hours, resulting in acid-modified Taro Boloso-I starch, which was then evaluated for suitability for direct compression. XRD patterns of both the native and modified starch showed characteristic A-type crystals, with significantly higher relative crystallinity observed in the latter. Additionally, the acid-modified starch exhibited a lower moisture content and improved flow properties. The compaction study also demonstrated its improved compactibility (tensile strength: 16.82 kg/cm2), surpassing both the native starch (13.17) and Starch 1500® (11.2). The modified starch also showed a lower lubricant sensitivity compared to the native starch and Starch 1500®. Furthermore, paracetamol tablets made with the modified starch exhibited higher mechanical strength and lower friability in all paracetamol concentrations. It incorporated up to 40% paracetamol while maintaining acceptable tablet characteristics, whereas the native starch and Starch 1500® were limited to 30% (w/w). Based on these findings, the modified starch showed promise as an alternative direct compressible excipient in tablet manufacturing.


Introduction
Naturally occurring polymers have been extensively used as pharmaceutical excipients for a signifcant period [1].Among these polymers, starch stands out as a notable example.It is a biodegradable polysaccharide abundantly found in various plant organs [2].Te global production of starch is primarily based on sources such as corn, wheat, rice, potato, and cassava [3].However, the challenge lies in harnessing locally available starches that ofer cost-efective excipients with multifunctional properties [4].In Ethiopia, various plant species such as enset [5], Dioscorea [6], Godare [7], cassava [8], Ethiopian potato [9], and Taro Boloso-I (TBI) [10] have been examined as potential starch sources for pharmaceutical applications.
TBI, an improved variety of Colocasia esculenta, was ofcially released by the Areka Agricultural Research Institute in Ethiopia [11].With its higher cultivation yield and starch content, approximately 84% on a dry weight basis, the tuber of TBI (Figure 1) holds great promise as an alternative source of starch.However, it has limitations as a compressible tablet excipient due to its poor compressibility and fow properties [12].Previous attempts to improve its functional characteristics have involved modifcations such as acetylation and pregelatinization [12,13].However, acetylation proved to be a complex method, whereas pregelatinization did not efectively improve the compressibility.Consequently, a simple yet efective method is needed to enhance the compressibility and fow properties of native TBI starch (NTBIS).
Acid modifcation is one of the modifcations that can be performed with relative ease.It involves the controlled addition of acid to an aqueous suspension of native starch [14].Several studies have explored the potential of acidmodifed starch as a compressible tablet excipient [15][16][17][18][19][20][21].Tese studies have shown that the modifcation improved the fowability, compatibility, and dilution potential of native starches, making them suitable for direct compression (DC).Tese changes were suggested to be due to the change in size, shape, density, packing arrangements, and relative crystallinity of starch granules.Tese, in turn, afect the cohesiveness of their powder particles and the strength of intermolecular force during compression.
DC is a tablet manufacturing process that involves compressing powder mixtures without any prior treatment [22].Tis method improves drug stability and reduces the number of unit operations, resulting in cost benefts.As a result, pharmaceutical manufacturers prefer it [23].Te success of a DC process is highly dependent on the characteristics of the excipients used such as the fowability, compactability, lubricant sensitivity, and dilution potential [16,24].Terefore, this study aims to modify NTBIS through acid modifcation and assess its suitability as a DC excipient in tablet formulations.[10] was followed to extract the starch.Initially, fresh TBI tubers were washed, peeled, and cut into small pieces.Te pieces were crushed with a blender machine (Sinbo, SHB-3088, China) using a 1% NaCl solution (w/v).Te resulting mixture was then washed multiple times with a solution containing 1% NaCl and 0.03 N NaOH and fltered through a muslin cloth to eliminate cell debris.Te sediment obtained was further washed with distilled water until the supernatant was clear and pH neutral.Finally, the starch was dried at 40 °C in a hot air oven (Memmert SM-200, Germany), ground into a fne powder using a mortar and pestle, sieved through a 180 μm mesh (FRESCH, Germany), and stored in a tightly sealed bottle for future use.

Acid Modifcation.
NTBIS was subjected to hydrolysis using HCl acid, following the procedure outlined in the study by Atichokudomchai et al. [15].Initially, 400 grams of NTBIS was suspended in 600 ml of HCl solution (6% w/v) at room temperature for 192 hours.Subsequently, the suspension was neutralized with NaOH solution (10% w/v) and washed with distilled water until the pH became neutral (pH 7).Eventually, the acid-modifed TBIS (AMTBIS) slurry was dried in a hot air oven (at 40 °C for 24 hours), powdered, sieved (180 μm sieve), and stored for future use.

Spray Drying.
Spray drying was carried out following the procedure described by Bilancetti et al. [25].A 40% suspension of the sample was prepared and introduced into the drying chamber of the tall-form spray dryer (FT80, Armfeld, USA), with the input and outlet temperatures set at 180 and 75 °C, respectively.Subsequently, the spray-dried samples were sifted through a 180 μm mesh sieve and stored for future use.

Recovery Yield of the Acid Hydrolysis Process.
Recovery yield was calculated as the percentage by comparing the weight of starches by dry weight before and after acid hydrolysis [26].

X-Ray Difraction
Studies.Te samples were analyzed using XRD patterns, following the method outlined by Nwokocha and Williams [27].An X-ray difractometer (XRD-7000, Shimadzu, Japan) was used in 2θ modes.Te position of the peaks was determined using a Cu target tube set at 40 kV (30 mA) power, in the 5-50 °range of 2θ, with a single crystal graphite monochromator.Te degree of crystallinity was then calculated using equation (1), as described by Singh et al. [28],  Te moisture content of the starch samples was determined according to the method described by Olayemi et al. [30].Two grams of sample was weighed on a dry Petri dish and placed in an oven at 130 °C.Ten, 2 hours later, the sample was removed, cooled, and weighed.Te moisture content was then calculated as the percentage of weight loss before and after drying.

Determination of Swelling Power and Solubility.
Te swelling power (SP) and the water solubility index (WSI) were determined as described by Odeku and Picker-Freyer [31].0.5 g starch suspensions in 10 ml of distilled water were prepared in centrifuge tubes and placed in a water bath (HH-S4, 20225101, Germany) at 25, 35, 45, 55, 65, 75, and 85 °C.After 30 min, the test tubes were withdrawn, cooled, and centrifuged at 3000 rpm for 15 min.Te supernatant was then decanted and dried in an oven at 120 °C for 4 hours to a weight (W 1 ).Te weight of the residue (W R ) was also determined, and then, the WSI and SP were calculated using the following equations: 2.2.10.Determination of Moisture Sorption Pattern.Te moisture sorption patterns of the samples were determined as described by Gebre-Mariam et al. [5].First, fve chambers of relative humidity (RH) (100, 75.6, 60, 40, and 20%) were prepared in a Pyrex desiccator at room temperature.Ten, a two-gram sample (predried at 120 °C for 4 h) was placed on dry Petri dishes and kept in the chambers.After seven days, the Petri dishes were removed and the moisture sorbed by the sample was calculated based on the weight diference before and after equilibrium.

Drug-Excipient Compatibility Study.
Te drugexcipient compatibility was investigated using an FTIR spectrophotometer (FTIR-8400S, Shimadzu, Japan).Te FTIR spectra of pure paracetamol and its physical mixture with AMTBIS (1 : 1) were scanned in a wavenumber range between 4000 and 500 cm −1 .A background spectrum was obtained before the samples were run.
2.2.12.Tablet Preparation.Various tablet compacts were prepared using the DC method to investigate compaction, lubricant sensitivity, and dilution potential.Starch compacts with a target weight of 300 mg were formed by applying a compression force that resulted in a crushing strength of 60-80 N for the reference standard (Starch 1500 ® ).All tablets were compressed using a single punch tablet machine (VFD007S21A, Shanghai, China) equipped with a fat-face punch (10 mm in diameter).
(1) Compaction Property of Starch.Te compaction property was evaluated using the method described by Okunlola and Akingbala [32].A powder mixture containing 99.5% starch samples and 0.5% magnesium stearate (MgS) was mixed for fve minutes and directly compressed into tablets.
(3) Dilution Potential.Te dilution potentials of the samples were evaluated as described by Shittu et al. [33].
As shown in Table 1, 50 g batches containing diferent proportions of paracetamol were mixed for ten minutes.Ten, MgS was lubricated for fve minutes and compressed into tablets.

Tablet Evaluation
2.3.1.Tablet Hardness.Te crushing strength (F) was measured for ten randomly selected tablets using a tablet hardness tester (PHARMA TEST, PTB 311E, Germany).Te radial tensile strength (TS) was then calculated as described in (4) [29].Te thickness (T) and diameter (D) of each tablet were also measured using the hardness tester.
Advances in Pharmacological and Pharmaceutical Sciences Friability.Ten tablets of known weight were placed on a friability tester (PHARMA TEST, PTF 10E, Germany) and operated at 25 rpm for 4 min.Te tablets were then dedusted and weighed, and their friability was calculated as the percentage of the weight loss of the tablets [29].

Disintegration Test.
Te disintegration test was performed following the method for uncoated tablets [29].Six tablets were placed in a disintegration tester (PHARMA TEST, PTZ S, Germany) flled with distilled water at 37 ± 2 °C.Ten, the time taken for each tablet to fully disintegrate was recorded.

Dissolution Test.
Te in vitro dissolution study was performed using a type II dissolution apparatus (paddle) at a rotation speed of 50 rpm [29].Six randomly selected tablets were placed in dissolution vessels containing 900 ml of phosphate bufer (pH 5.8) maintained at 37 ± 0.5 °C.Ten, 10 ml of sample was withdrawn at a defned time interval, properly fltered, and diluted, and then, UV absorbance readings were taken at λ max of 243 nm using phosphate bufer (pH 5.8) as a blank.Corporation, USA) was used to plot the graphs.Te results were reported as mean and standard deviation (SD).

Results and Discussion
3.1.Acid Recovery Yield.Te acid recovery yield, after 8 days, was 74.16 ± 1.10%.One of the reasons for this weight loss is the hydrolysis of the amorphous regions into shorter watersoluble molecules, which are likely to be removed during the washing process [34].Compared to Dioscorea and Ethiopian potato starch [19,21], a higher recovery yield was achieved in the present study.However, the recovery yield was lower compared to Godare starch [20].[35].Tis suggests that the modifcation process does not alter the type of crystal [36,37].However, the relative crystallinity of the AMTBIS (45.33%) was higher compared to that of the NTBIS (37.87%).Tis might be due to the hydrolysis of the amorphous regions and extensive reordering of the chain segments [26,28].

Powder Flow Properties of Starch.
Bulk and tap densities increased signifcantly by acid modifcation and spray drying individually (p < 0.05).However, when combined, the spray-dried AMTBIS showed a greater increase, surpassing all other starches studied (p < 0.05).Tis might be due to the change in the shape and size of the starch granules, which afects their packing arrangement [38].Tis fnding is in line with previous studies on acid modifcation [17,19].Te fow-related properties of NTBIS, AMTBIS, and Starch 1500 ® are presented in Table 2. AMTBISs exhibited sig- nifcantly lower CI and HR values compared to NTBISs (p < 0.05), indicating improved fow properties.Furthermore, the fow properties of the spray-dried AMTBIS were comparable to those of Starch 1500 ® (p > 0.05).Te spray- dried AMTBIS and Starch 1500 ® demonstrated excellent fowability, with angles of repose measuring 27.10 and 26.53, respectively.However, spray-dried NTBIS had an angle of repose of 36.83,falling within the fair range [29].NTBIS and AMTBIS dried in the oven did not fow through the funnel, making it impossible to determine their angle of repose and fow rate.Tis might be due to the presence of irregular and nonspherical particles in higher quantities [39].

Moisture Content and Moisture Sorption Pattern.
Dry starch powders typically have a moisture content ranging from 6 to 16%.However, for safe storage, it is recommended to keep it below 13% [40].In this study, all starches were found to have a moisture content within the recommended range for safe storage.Te moisture contents of NTBISs, AMTBISs, and Starch 1500 ® are presented in Table 2.
Consequently, AMTBIS exhibited a signifcantly lower moisture content compared to NTBIS (p < 0.05).Tis could be attributed to variations in their relative crystallinity.Te higher crystallinity of AMTBIS makes it less susceptible to moisture penetration compared to NTBIS.
Te moisture sorption profles of NTBIS, AMTBIS, and Starch 1500 ® are depicted in Figure 3.As presented in this fgure, the moisture sorbed by the starches ranged between 4 Advances in Pharmacological and Pharmaceutical Sciences 9.9 and 49.2%.Moisture sorption of all starch samples gradually increased between 20 and 75.6% RH with comparable values (p > 0.05).However, beyond 75.6%RH, the moisture sorption profles of all starch samples showed a signifcant increase and exhibited a higher moisture sorption value at 100% RH (p < 0.05).Tis higher moisture uptake might be related to the subsequent difusion of excess moisture into the bulk powder bed [41].Generally, starch, being a hygroscopic material, requires avoidance of exposure to higher RH values during storage [42].

Swelling Power and Solubility. SP and WSI ofer in-
formation on the extent of interaction between starch chains within the granules [43,44].As shown in Figure 4(a), the SP of NTBIS and AMTBIS generally increased with temperature, slightly up to 65 °C, and signifcantly beyond that (p < 0.05).Higher temperatures could result in a disruption of the crystalline structure of starch.Tis exposes OH groups to hydrogen bonding with water molecules, leading to increased granule swelling [45].However, acid hydrolysis has been shown to reduce swelling power [16].Tis might be because it breaks down amorphous regions and increases the crystallinity [46].Terefore, in line with that, NTBIS showed signifcantly higher SP than AMTBIS above 65 °C (p < 0.05).As shown in Figure 4(b), the WSI of NTBIS, AMTBIS, and Starch 1500 ® increased with temperature.AMTBISs showed signifcantly higher WSI at all temperatures compared to NTBISs (p < 0.05).Tis might be attributed to the acid modifcation that resulted in the formation of partially degraded and shortened chains.Tis ultimately results in depolymerization and structural weakening of the granules that can enhance the WSI [46][47][48].6

Compaction Property Study.
In Figure 6(a), it can be observed that the spray-dried AMTBIS exhibited greater compactability compared to the spray-dried NTBIS and Starch 1500 ® (p < 0.05).Tis can be attributed to the in- creased relative crystallinity as a result of acid hydrolysis.Te improved crystallinity leads to stronger intermolecular forces during compression, resulting in higher TS [15].Tese fndings are consistent with previous studies conducted on acid-modifed starch [31,51].Te TS of the compacts infuences their friability and disintegration time.As shown in Figure 6(b), the friability of tablets of spray-dried NTBIS is greater than that of spray-dried AMTBIS, which is in line with their TS.However, all compacts exhibited a weight loss of less than 1%.As depicted in Figure 6(c), the spray-dried AMTBIS compacts showed a longer disintegration time compared to the spray-dried NTBIS, possibly due to their higher TS.According to Muzikova and Eimerova [52], the extended disintegration time of Starch 1500 ® tablets, with weaker TS, can be attributed to the development of a gel-like layer on the surface of the tablet.

Lubricant Sensitivity Study.
Te formation of MgS layer around the powder particles reduces the cohesive interactions among them [53].Tis can be observed in Figure 7(a), where the TS of the tablets generally decreased with MgS concentration.However, the TS of the tablets made from spray-dried AMTBIS was signifcantly higher compared to those made from spray-dried NTBIS and Starch 1500 ® at all MgS concentrations (p < 0.05).Tis indicates that spray-dried AMTBIS has a lower lubricant sensitivity compared to spray-dried NTBIS and Starch 1500 ® .
Tablets in the study of lubricant sensitivity showed an increase in friability with higher concentrations of MgS, as shown in Figure 7(b).Tablets made from spray-dried AMTBIS had friability below 1% concentrations, making them less friable compared to spray-dried NTBIS and Starch 1500 ® at all levels of MgS used in the study (p < 0.05).
Similarly, acetylated TBISs showed lower lubricant sensitivity with acceptable friability of at least 2% MgS level [13], while pregelatinized TBIS [54] was limited to 0.5%.However, this comparison will hold if the diferent parameters such as compression force were assumed to be similar.On the other hand, the formation of hydrophobic lubricant flms around the particles prevents water penetration, wetting, and disintegration of the tablets [55].Hence, all tablets took longer to disintegrate as the concentration of MgS increased, as shown in Figure 7(c).

Dilution Potential Study. Te dilution potential (DP)
refers to the amount of API that can be efectively compressed into tablets using a specifc DC excipient [56].To meet the necessary characteristics of the tablet, such as hardness (>50 N) and friability (<1%), the DC excipient should have sufcient DP [57,58].
3.9.1.Tablet Hardness.Te TS of the tablets used for the DP study decreased with the paracetamol content, as depicted in Figure 8(a).Tis is due to the poor compactability and the higher elastic recovery of paracetamol [59].However, tablets from AMTBIS exhibited signifcantly higher TS compared to NTBIS and Starch 1500 ® at all paracetamol content.Tis can be attributed to the higher DP of AMTBIS associated with its superior compactability that overcomes disruptive elastic recovery.Furthermore, tablets made from AMTBIS maintained acceptable hardness (53.5 N) up to 50% paracetamol content, compared to the NTBIS (38.5) and Starch 1500 ® (37.8 N).
3.9.2.Friability. Figure 8(b) shows that thefriability of the tablets increased signifcantly with the paracetamol content (p < 0.05), corresponding to the decrease in TS.However, the tablets prepared from AMTBIS exhibited lower friability in all paracetamol content and maintained acceptable friability up to 40% paracetamol content.On the other hand, the NTBIS and Starch 1500 ® were limited to 30%.Te dilution potential of AMTBIS is higher compared to a pregelatinized TBIS [54] which was limited to 30% and lower than acetylated TBIS [13], which were acceptable at least 50% paracetamol content.However, these comparisons would provide conclusive information if the diferent parameters, mainly compression force, were kept similar.
3.9.3.Disintegration Time. Figure 8(c) illustrates that the disintegration time of tablets decreased signifcantly with the paracetamol content (p < 0.05).Tis can be attributed to the poor compactability of paracetamol, which weakens the tablets and allows water to penetrate the tablet core more easily.However, tablets made from spray-dried AMTBIS exhibited longer disintegration times compared to both spray-dried NTBIS and Starch 1500 ® at all paracetamol contents.Tis could be attributed to the higher TS of AMTBIS tablets.Overall, all tablets disintegrated within the acceptable timeframe (<15 minutes) following the pharmacopeial specifcations [29].

Study of the Dissolution of Paracetamol Tablets.
Tablets that passed the evaluations for hardness, friability, and disintegration were selected for the dissolution study.Terefore, tablets containing 20 and 30% paracetamol were Advances in Pharmacological and Pharmaceutical Sciences selected for each excipient evaluated.As depicted in Figures 9(a) and 9(b), the percentage of drugs released at 30 minutes followed the results of the disintegration time of the tablets.Furthermore, the amount of drug released at 30 minutes generally increased with increasing paracetamol content.Tis might be attributed to the tablet's weakness with increasing paracetamol content, which facilitated the disintegration of the tablets and hence the dissolution rate.Generally, all paracetamol tablets released more than 80% of their content in 30 minutes, which satisfes the USP specifcations for the dissolution of conventional tablets [29].Advances in Pharmacological and Pharmaceutical Sciences

Conclusions
Te fow properties of NTBIS were signifcantly improved by acid modifcation and spray drying.Furthermore, the compactability study showed that AMTBIS had better compactability compared to both NTBIS and Starch 1500 ® , as indicated by the TS of their compacts.Tis allowed AMTBIS to successfully incorporate up to 40% of the poorly compressible paracetamol while maintaining acceptable tableting performance.Furthermore, AMTBIS showed a lower lubricant sensitivity compared to the other excipients, even when containing up to 2% MgS, while still maintaining acceptable tableting performance.Overall, based on the results of this study, it can be concluded that spray-dried AMTBIS, specifcally the spray-dried version, has the potential to serve as an alternative DC excipient.

4. 1 .
Limitations of the Study.Te compaction characteristics of the AMTBIS were not studied at diferent levels of compression forces due to the limitation of the compression machine, which does not read compression forces.

Figure 9 :
Figure 9: Dissolution profle of tablets prepared from spray-dried NTBIS, spray-dried AMTBIS, and Starch 1500 ® at 20 (a) and 30% (b) Titan Biotech Ltd., India) were donated by Addis Pharmaceutical Factory P.L.C. Starch 1500 ® (Col- orcon, France) was kindly donated by the Department of Pharmaceutics and Social Pharmacy, School of Pharmacy, Addis Ababa University.
Tis is demonstrated by strong peaks at approximately 15.1, 17.0, 17.9, and 23.2 °2θ Starch.Figures 2(a) and 2(b) illustrate the XRD patterns of NTBIS and AMTBIS, respectively.Both samples display similar difraction pattern characteristics of A-type crystals.

Table 1 :
Paracetamol tablet formulations used for the study of dilution potential.