Olayemi et al., Journ. Pharm. Sci., March, 2008, Vol. 7 No. 1, P. 131­ 138

Nigerian Journal of Pharmaceutical Sciences Vol. 7, No. 1, March, 2008, ISSN: 0189-823X All Rights Reserved


*Olayemi O. J., Oyi A. R. and Allagh T . S.

Department of Pharmaceutics and Pharmaceutical Microbiology, Ahmadu Bello University, Zaria

*Author for Correspondence:

[email protected], +234 80 33532299

ABSTRACT This investigation aims at comparing locally developed starches from three grains; Maize (Zea mays), Rice (Oryza sativa) and Wheat (Triticum aestivum) grains. These grains are used mainly as foods and they contain high amount of carbohydrate. The presence of starch in these grains varies and thus their use as pharmaceutical excipients will vary to the degree of their starch functionality. The powders obtained were characterised for their particle size, particle size distribution. The organoleptic and physicochemical characterisation such as viscosity, hydration capacity, swelling capacity, moisture sorption capacity, pH, flow rate and porosity, Carr's index and Hausner's ratio were evaluated. The powders passed the identification and solubility tests as required by the BP. Rice starch showed the least Carr's index, Hausner's ratio, porosity, moisture sorption capacity and the greatest flow rate. Rice starch also showed the highest hydration capacity and swelling capacity. The results obtained showed that among the three starches in relation to their flowability, rice starch possesses the best flow property. This knowledge of starch properties will help explain the behaviour of these starches when used as tablet excipients. Key words: Maize, rice, wheat, starch, pharmaceutical excipients.

INTRODUCTION A survey of the literature shows that the usefulness of starches from various botanical sources as pharmaceutical excipients has formed a subject of interesting study for close to four decades. Starches are widely available and have been very useful in tablet production due to their inertness, cheapness and utilization as fillers, binders, disintegrants and glidants and recently a lot of effort has been expended on the development of new starches from local sources as pharmaceutical excipients (Nasipuri, 1979, Esezobo and Ambujam, 1982, Weirik et al, 1996, Alebiowu and Itiola, 2001). Some of the earliest reported works on the use of locally available starches as pharmaceutical raw materials was by Mital and Ocran (1968) who reported that yam and

cassava starches could be used as tablet disintegrant. More recently, starches have been developed for various purposes. This includes a comparative study of modified starches of maize, rice, cassava and cocoyam in direct compression of Chloroquine phosphate tablet as evaluated by Okafor et al (2000). The effect of acid treatment on the consolidation and plasto ­ elasticity of tapioca powder was evaluated by Eichie and Okor (2002). Preliminary investigation into the use of pleurotus tuber-regium powder as tablet disintegrant has been evaluated by Iwuagwu and Onyekweli (2002). The effects of sorghum, plantain and maize starches on mechanical properties of Paracetamol tablet formulations were evaluated by Alebiowu and Itiola (2003). The compression, mechanical and release properties of Chloroquine phosphate tablets containing 131

Olayemi et al., Journ. Pharm. Sci., March, 2008, Vol. 7 No. 1, P. 131­ 138

corn and Trifoliate yam starches as binder have also been evaluated by Itiola et al, (2006). A comparative investigation of the fundamental and derived properties of starches from some species of yam (Dioscorea spp.) was conducted with a view to establishing their suitability as excipients in tablet and capsule formulations by Riley et al, 2006. Influence of cassava, cocoyam starch and maize starch BP on the brittle fracture of paracetamol tablets has been carried out by Uhumwangho et al (2006). The effects of pigeon pea and plantain starches on the compressional, mechanical and disintegration properties of Paracetamol tablets have been investigated by Kunle et al (2006). Ibezim et al (2008) have also investigated the role of ginger starch as binder in acetaminophen tablets. The performance of starch obtained from Dioscorea dumetorium as disintegrant in Sodium Salicylate tablets have been investigated by Ibezim et al (2008). Non-official starches found in abundance in Nigeria have been tested and found to be useful as tablet excipients. These efforts have only established the possibility of using these starches in the pharmaceutical industry. The aim of this study is to investigate the properties of these starches and also study their advantages and disadvantages relative to each other. The objectives therefore are: i) To extract maize, rice and wheat starches from their natural plant sources and process them to pharmaceutical grade starch. ii) To compare the physical properties of these starches in the powdered state relative to each other. MATERIALS AND METHODS Materials The following materials were used as obtained from the manufacturers without further purification. Maize, Rice, Wheat starch powders (prepared in the laboratory). Maize grains (Obatanpa; Samaz-14), Rice grains (Wita-4), Wheat grains (Siete Cerros)

[sourced from Institute of Agriculture, Zaria]. Xylene (Avondale Lab. Supplies Ltd, Banbury, Oxon, England). Methods Extraction of Maize, Rice and Wheat starches The starches were extracted using previously established procedures (Dare et al, 2006). Characterisation of the starches Viscosity of starch mucilage This was done by preparing 5% w/v starch mucilage and using the Brookfield viscometer DV ­ 1 prime, the intrinsic viscosities of the individual starches were gotten at 28oC. Determination of pH One gram (1g) of the individual starches was made into mucilage with 100mls of distilled water and the pH was determined in an electronic pH meter. Moisture Content Determination One gram (1g) of the powder was weighed and then dried in an oven at 1050C for about 1 hour and then weighed again until constant weight was gotten and the percentage loss on drying was calculated;

wf x100...................................................1 wi Where; wf is final weight of powder after drying wi is initial weight of powder before drying. Particle size distribution The particle size distribution and shape of the starch grains were determined by observing 100 particles for each starch under an optical microscope, from which the values of the mean particle diameter were calculated. A photomicrograph of the starches was also taken. Bulk and Tapped densities


Olayemi et al., Journ. Pharm. Sci., March, 2008, Vol. 7 No. 1, P. 131­ 138

Bulk and Tapped densities were determined by using 50g (Wp) of the starch powder. This was gently poured through a short stemmed glass funnel into a 100ml graduated cylinder. The volume occupied by the powder is taken as Vp. The powders were tapped on a wooden surface at height of 7 inches until no further change in volume was observed. This volume (VpT) was taken as the tapped volume. Wp Bd = ...................................................2 Vp Wp Td = ..................................................3 VpT Where Bd = Bulk density and Td = Tapped density Carr's index and Hausner's ratio The Carr's index (CI) and Hausner's ratio (HR) were computed from the determined bulk and tapped densities as Td HR = ......................................................4 Bd

Vv .................................................................7 Vx Hydration capacity This was determined according to the method of Kornblum and Stoopak (1973). One gram (1g) of each of the powders (Y) was placed in a centrifuge tube and covered with 10mls of distilled water. The tube was shaken intermittently for about 2hours and left to stand for 30minutes before centrifuging at 3000 rpm for 10miutes. The supernatant was decanted and the weight of the powder after water uptake and centrifugation (X) was determined. Hydration capacity was calculated as; X .................................................................8 Y Porosity The powder porosity (E) was calculated by the method of Ohwoavworhua and Adelakun (2005) as: Bd E = 1- x100.............................................9 Dt Where Bb is bulk density, Dt is true density of starch. Moisture sorption capacity The method of Ohwoavworhua et al, (2004) was used. Two grams (2g) of the individual starch powders (W) were weighed and put into a tarred Petri dish. The samples were then placed in desiccator containing distilled water at room temperature and the weight gained by the exposed samples at the end of a five-day period (Wg) was recorded and the amount of water absorbed (Wa) was calculated from the weight difference as Wa = Wg - W ...................................................10

Determination of Starch true density The true densities (Dt), of cellulose powders were determined by the liquid displacement method using xylene as the immersion fluid and computed according to the following equation: Dt = Wp / ((a + Wp) - b )xSG..................11

CI =

Td - Bd x100.......................................5 Td

Determination of flow rate Thirty grams (30g) (w) of the starch powder was placed in the Erweka flow apparatus and allowed to flow through the funnel orifice. The time taken for the powder to flow through the orifice (t) was noted and the flow rate was computed as; w ....................................................................6 t Swelling capacity The swelling capacity of the starch powders were determined by the method of Iwuagwu and Okoli (1992). The tapped volume occupied by 5g of the powder Vx was noted. The powder was then dispersed in 85ml of distilled water and the volume made up to 100ml with more water. After 24hours of standing, the volume of the sediment, Vv was estimated and the swelling capacity was computed as;


Olayemi et al., Journ. Pharm. Sci., March, 2008, Vol. 7 No. 1, P. 131­ 138

Where Wp is the weight of powder, SG is specific gravity of solvent, a is weight of bottle + solvent and b is weight of bottle + solvent + powder. Packing fraction


Figure 1 - 3 shows the photomicrograph of the starches at X40 magnification. The ranking order of the particle sizes was wheat > local maize > rice starch as shown in Fig 4. This indicates that rice starch had the least particle size and wheat exhibited the largest particle size. The round shape and smaller particle size of rice and maize starches would be expected to promote closer packing of particles than the ovoid shape and larger particle size of wheat starch. A similar finding has been reported by Itiola and Odeku (2005) with potato, cassava and yam starches. From Table 1, maize starch was the most viscous followed by wheat starch and rice starch was the least viscous. Although, the moisture contents for all the starches were within the official recommendation (BP. 2002), the moisture content for wheat starch was highest and this may be due to its larger average grain size which implies that there are larger pore sizes and this may trap water and result in high moisture contents. The moisture sorption capacity is a measure of moisture sensitivity of a material and it reflects the relative physical stability of the tablets formulated with the material when stored under humid conditions (Ohwoavworhua and Adelakun, 2005). The results show that rice starch absorbed the least moisture followed by wheat starch and maize starch absorbed the most moisture. This could indicate that rice starch when used in tablet formulation would absorb the least moisture and thus eventually give tablets with better physical stability than wheat and much more than maize starch. The common feature of all theories of disintegration is that penetration of water (or liquid medium) must precede disintegration and this can be assessed by the

The packing fraction (Pf) was expressed as the ratio between the bulk density (bt) and the true density (TrD); bt Pf = ......................................12 TrD determination of hydration capacity, swelling capacity and porosity (Caramella, 1991). The hydration capacity of the starches indicates that rice starch is capable of absorbing three times its own weight of water while, maize and wheat starches approximately two times their own weight of water. The swelling capacity which reflects increase in volume of the starches showed rice starch having the highest increase in volume followed by maize and then wheat starches. This suggests that rice starch may be a better disintegrant than the other two starches and if incorporated in tablet formulation as a disintegrant, would probably produce tablet disintegration by two mechanisms: capillary or wicking and swelling. The pH of the starches were similar although, maize starch was observed to have slightly acidic pH while, rice and wheat starches were near neutral. This implies that if rice or wheat starch powders were dispersed in a liquid medium, an alkaline or acidic medium will not result, since this may encourage product instability via effects on the gastro-intestinal tract absorption of the active drug. Similar findings were observed by Iwuagwu and Onyekweli (2002) in the use of Pleurotus tuber-regium powder as tablet disintegrant. Also from the results of bulk, tapped densities, porosity and packing fraction in Table 1, rice starch exhibited the largest maximum volume reduction due to packing while maize starch exhibited the lowest. Thus, it would appear that under the applied tapping pressure, the polygonal shape, fine texture and smaller particle size of rice promoted closer packing of particles than the ovoid shape and larger particle size of wheat starch. The Hausner's ratio and Carr's index has reported to preview the degree of densification that would occur during 134

Olayemi et al., Journ. Pharm. Sci., March, 2008, Vol. 7 No. 1, P. 131­ 138

tabletting. As the values of these indices increase, the flow of the powder decreases (Staniforth, 1996) and gives more likelihood of producing tablets with more weight variation. From the results obtained, the degree of densification was rice > wheat >

maize starch, this indicates that rice starch would give superior flow in comparison with the other two starches. Also, the flow rate supports this as rice starch exhibited the greatest flow rate followed by wheat and then maize starch.

Table 1: Physicochemical Properties of the Starches Maize Parameters Starch Viscosity (mPa.s) 27 Shape Round Moisture content (%) 4 Moisture sorption capacity (%) 4.87 Swelling capacity (%) 16 Hydration capacity 2.54 True density 1.5 Bulk Density (g/ml) 0.37 Tapped Density (g/ml) 0.67 Carr's index (%) 44.8 Hausner's ratio 1.81 Porosity (%) 75 Flow rate (g/sec.) 0.54 Packing fraction 0.25 pH 6.53 Rice Starch 12 polygonal 6 1.86 18.8 3.29 1.51 0.61 0.91 33 1.49 60 0.88 0.4 6.77 Wheat Starch 10.6 Oval 12 2.55 13.9 2.29 1.44 0.49 0.77 36.4 1.57 66 0.71 0.34 6.23

Fig.1: Maize starch X 40 Mag


Olayemi et al., Journ. Pharm. Sci., March, 2008, Vol. 7 No. 1, P. 131­ 138

Fig. 2: Rice starch X 40 Mag

Fig. 3: Wheat starch X 40 Mag

110 100 90 C u m m u la t iv e f r e q u e n c y ( % ) 80 70 60 50 40 30 20 10 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Particle size (µm) maize rice wheat

Fig. 4: Cummulative particle size of the local maize, rice and wheat starches.


Olayemi et al., Journ. Pharm. Sci., March, 2008, Vol. 7 No. 1, P. 131­ 138

CONCLUSION The characterisation of these starches shows rice starch with the lowest cohesiveness would be the starch of choice when good flow ability is desirable. It also shows that rice starch could be a better tablet disintegrant. These findings would be useful in the handling of these starches and in their use as pharmaceutical excipients in the production of powders, tablets and other relevant drug delivery systems. REFERENCES

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