INTRODUCTION:

Waxes from both animals and plants are esters of high molecular weight monohydroxy alcohols and high molecular weight carboxylic acids. They are chemically different from fats and oils, from hydrocarbons or paraffin waxes, and from synthetic polyether waxes such as carbowax. Rice bran wax is obtained from natural sources (Oryza sativa, Family- Graminae) and is abundantly available¹. Recent work indicated that Rice bran wax is mainly an ester of Lignoceric acid and Myricyl alcohol. It is hard non-tacky wax containing chiefly melissyl cerotate and melts at about 80-85° C. All these factors signify that Rice bran wax will prove to be better substitute of Carnauba wax and may save lot of foreign currency for our country if it replaces^2,3. Therefore, this study is an attempt to probe the utility of rice bran wax in cosmetics products such as moisturizing cream.

MATERIALS:

The RBW was obtained as a gift sample from Space lab, Nasik in flakes form; stearic acid, lanoline, glycerin, sorbitol etc were obtained as a gift sample from Aquatic Remedies Mumbai.

METHODS:

Moisturizing cream formulations were developed from a prototype moisturizing cream formulation based on triethanolamine stearate. The final developed formulations were used for the preparation of all cream formulations developed and tested in these studies.

Formulation development:

In the preliminary stages of these studies, the objective was to manufacture a moisturizing cream formulation extemporaneously that showed no visible signs of physical instability, such as, for example, cracking, creaming, phase inversion and/or bleeding of the cream base from the container. Physical instability was evaluated immediately after manufacture and then twenty-four (24) hours after manufacture and storage at room temperature (25°C). Initial formulation development was undertaken on batches of only 25 g and any formulation that showed signs of physical instability immediately and/or after twenty-four (24) hours of storage at room temperature (25°C) was considered unsuitable and therefore not considered for further investigation. The formulation for the prototype Moisturizing Cream based on Triethanolamine Stearate is as follows:

Table:1 Prototype Moisturizing Cream

No.	Ingredients	Quantity for 100g
	Oil Phase
1.	Stearic Acid	2
2.	Lanolin	2
3.	Cetostearyl Alcohol	0.2
4.	Liquid Paraffin	10
	Water Phase
1.	Triethanolamine	0.5
2.	Glycerin	7.5
3.	Sorbitol	2.5
4.	Propylene Glycol	5
5.	Methyl Paraben	0.18
6.	Propyl Paraben	0.02
7.	Water Q. S.	100g

In order to formulate Rice Bran Wax (RBW) into this cream, stearic acid was completely replaced by RBW and combinations of various emulsifying agents were used in order to prepare a stabilized formulation⁶

Thus, with fixed ratios of RBW, Stearic acid and Triethnolamine, optimized moisturizing creams containing 7.5% (Cream A) and 15% RBW (Cream B) were prepared. These two formulations were further investigated for a comparison in their thermophysical attributes with respect to the proportion of RBW.

Table 2- RBW Moisturizing Cream Formulations

No.	Ingredients	RBW01	RBW02	RBW03	RBW04	RBW05	RBW06
	Oil Phase
1.	Rice Bran Wax	2	2	2	2	2	2
2.	Lanolin	2	2	2	-	-	-
3.	Cetostearyl Alcohol	0.2	0.2	2	3	8	2
4.	Liquid Paraffin	10	10	5	5	5	5
5.	GlycerylMonostearate	-	-	-	-	-	3
	Water Phase
1.	Triethanolamine	0.5	0.5	0.5	3	3	0.4
2.	Glycerin	7.5	7.5	7.5	7.5	7.5	7.5
3.	Sorbitol	2.5	2.5	2.5	2.5	2.5	2.5
4.	Propylene Glycol	5	5	5	5	5	5
5.	Methyl Paraben	0.18	0.18	0.18	0.18	0.18	0.18
6.	Propyl Paraben	0.02	0.02	0.02	0.02	0.02	0.02
7.	Water Q.S.	100g	100g	100g	100g	100g	100g

Table 3- RBW Moisturizing Cream Formulations

No.	Ingredients	RBW07	RBW08	RBW09	RBW10	RBW11	RBW12
	Oil Phase
1.	Rice Bran Wax	1.5	1	1.5	5	7.5	10
2.	Stearic Acid	0.5	1	0.5	1.6	4.5	3.3
3.	Lanolin	-	-	2	2	2	2
4.	Cetostearyl Alcohol	2	2	2	2	2	2
5.	Liquid Paraffin	5	5	5	5	5	5
6.	GlycerylMonostearate	3	3	3	3	3	3
	Water Phase
1.	Triethanolamine	0.4	0.4	0.4	1	1.25	2
2.	Glycerin	7.5	7.5	7.5	7.5	7.5	7.5
3.	Sorbitol	2.5	2.5	2.5	2.5	2.5	2.5
4.	Propylene Glycol	5	5	5	5	5	5
5.	Methyl Paraben	0.18	0.18	0.18	0.18	0.18	0.18
6.	Propyl Paraben	0.02	0.02	0.02	0.02	0.02	0.02
7.	Water Q.S.	100g	100g	100g	100g	100g	100g

Table 4- Optimized RBW Moisturizing Cream Formulations

Ingredients	Cream A	Cream B
Phase A
Rice Bran Wax	7.5	15
Stearic Acid	1.75	3.5
Lanolin	2	2
Liquid Paraffin	5	5
Cetostearyl Alcohol	2	2
GlycerylMonostearate	3	3
Phase B
Triethanolamine	0.8	1.6
Glycerin	7.5	7.5
Sorbitol	2.5	2.5
Propylene Glycol	5	5
Methyl Paraben	0.18	0.18
Propyl Paraben	0.02	0.02
Water	q.s. to 100g	q.s. to 100g

Evaluation of moisturizing cream:

Cream products were characterized by particle size, rheological measurements, pH, spreadability and in vitro occlusivity.

Measurement of Particle Size:

A laser diffraction particle size analyzer (Mastersizer Hydro MU 2000, Malvern Instruments) was employed for measuring the globule size distribution of the emulsion droplets. Briefly, the sample was dispersed in 0.2 micron filtered distilled water to obtain an obscuration of 5 – 15 %.

Rheological Measurements⁴:

BrookefieldSynchro-Lectric Viscometer (Model RVT) with helipath stand was used for rheological studies. The sample (50 g) was placed in a beaker and was allowed to equilibrate for 5min before measuring the dial reading using a T-D spindle at 0.5, 1, 2.5, and 5 rpm. At each speed, the corresponding dial reading on the viscometer was noted. The spindle speed was successively lowered and the corresponding dial reading was noted. The measurements were carried in triplicate at ambient temperature. Direct multiplication of the dial readings with factors given in the Brookfield viscometer catalogue gave the viscosity in centipoises.

In-vitro Occlusivity Test⁵:

Beakers of diameter 3.2 cm and height 4.6 cm were used. The test was performed by placing 10 g of distilled water in each beaker and closing the open end with Whatman Filter Paper (0.45 pore size) on the upper surface of which 200mg of the sample was evenly distributed. These beakers were then placed at 37±2°C/607±5% RH for 48 hours. The samples comprised of 7.5% RBW cream, 15% RBW cream, liquid paraffin, and a negative control where the filter paper was kept uncovered.

The occlusion factor F was calculated as

Where,

A= Water flux through uncovered filter (Percent water loss)

B= Water flux through filter when covered by test preparation (Percent water loss)

PH Measurement: The pH of the 10 % w/v cream suspension was determined at 25°C using a pH meter (pH Tutor, Eutech Instruments), standardized using pH 4.0 and 7.0 standard buffers before use.

Spreadability⁵: The spreadability of test samples was determined using the following technique: 0.5 g test formulation was placed within a circle of 1 cm diameter pre-marked on a glass plate over which a second glass plate was placed. A weight of 500 g was allowed to rest on the upper glass plate for 5 minutes. The increase in the diameter due to spreading of the test formulation was noted.

RESULT AND DISCUSSION:

Measurement of Particle Size:

The study revealed that the formulations exhibited distinct behavior. For creams comprising of lower RBW concentration, there was reduction in globule size after 24 hours of standing. This can be due to the greater proportion of fatty amphiphiles, cetostearyl alcohol and glyceryl monostearate, relative to RBW. The initial measurement comprises mainly of the lipogel phase, resulting in the presence of grainy structures, which are gradually replaced by emulsion droplets over time. Relatively lesser proportion of fatty amphiphiles in 15% RBW favors the formation of emulsion droplets in the continuous phase, over that of liquid crystal phases [46]. The D₉₀ values for initial and final days were found to significantly differ from each other according to a paired t-test⁷.

Figure: 1 Globule size distribution for Creams A and B over 24 hours

Rheological Measurements:

Figure: 2Plot of Shear stress vs. Shear rate for Cream A

Figure:3 Plot of Shear stress vs. Shear rate for Cream A

Table 5.Comparative evaluation of rheological parameters of RBW creams

Parameters	Cream A (before)	Cream A (after)	Cream B (before)	Cream B (after)
Viscosity at 5 rpm (mPa s)	2.4 x 10⁶	8.0 x 10⁶	10.8 x 10⁶	11.6 x 10⁶
Consistency Index	8589061	23300841	37169534	38725157
Flow Index	0.232	0.342	0.261	0.250

A major model for emulsion rheology is that the viscosity of oil-in-water emulsion decreases with shear until a minimum value is reached. In our experimental model all cream formulations show the same rheology pattern, i.e. there is a decrease in viscosity with an increase in shear rate. All creams follow non-Newtonian (pseudo plastic flow) and the rheograms of all the formulated creams are of the hysteresis-loop type with the down curves to the left of the up curves showing thixotropy. The increase in the hysteresis loop reflects the structural development of the cream, where the cream containing 15% RBW develops a creamy consistency faster over a period of 24 hours as compared to the 7.5% RBW cream. It has also been reported that the apparent intrinsic viscosity of a semi-solid formulation isinfluenced by the size of the droplets of the dispersed phase and it follows that droplets of smallsizes will produce creams of higher viscosity than those of dispersed phases with large dropletsizes⁸.

In-vitro Occlusivity Test:

Figure 4.comparative in vitro occlusivity in terms of percent water loss of various formulations

The weight loss of water (water flux) depends on the occlusivity of membrane offered by the formulations tested. The results of occlusivity are shown in the Fig. 4. When values were compared to that of uncovered filter, both the RBW creams showed significantly lower percentage of water loss than that of the uncovered filter. The better occlusivity of RBW creams could be attributed to the lipid nature of the developed formulations, preventing water evaporation to a greater extent.

pH Measurement and Spreadability:

Table 6: Comparative evaluation of rheological parameters of RBW creams

Parameters	Cream A	Cream B
pH	8.20±0.195	8.31±0.244
Spreadability (cm)	6.4±0.08	6.1±0.08

The pH of the creams were determined to be 8.20±0.195 and 8.31±0.244 for 7.5% and 15% rice bran wax content respectively. Although alkaline, this pH is typical of creams containing triethanolamine and acceptable by the ISI standards. The two creams showed excellent spreadability and skin feel.

CONCLUSION:

The above studies show that moisturing creams containing a high proportion of Rice bran wax, despite its content of unsaponifiable matter, can be formulated with the aid of triethanolamine stearate and non-ionic emulsifiers. The thermo physical behavior of the creams was found to be dependent on the proportion of Rice bran wax relative to the emulsifiers. The creams showed good in-vitro occlusivity and spreadability and thus could be effective formulations to incorporate Rice Bran Wax in high amounts, to avail of its cosmetic benefits.

REFERENCES:

1. Houston, D.F., Eds., In; Rice Chemistry and Technology, 2^nd Edn., A.A.C.C., Inc., St. Paul, MN, 1972, 294.

2. Goenka O.P. Rice bran oil-The golden heart oil, 12^th national seminar on rice bran oil and doctors meet; 2009 Aug. 2^nd ; Vijaywada: SEAI; 2009, pp 3.

3. Radha T. Health for all through rice bran oil, 8^th National seminar on rice bran oil; 2005 july 29^th ; New Delhi: SEAI; 2005, pp 68.

4. M. Korhonen. Rheological properties of pharmaceutical creams containing sorbitanfatty acid ester surfactant. University of Helsink Helsinki, 2004, 1-58.http://ethesis.helsinki. fi/julkaisut/mat/farma/vk/korhonen/. Retrieved 26/02/2012.

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6. R. C. Rowe, P J. Sheskey, P. J. Weller. Handbook of Pharmaceutical Excipients. London: Pharmaceutical Press, 2003.

7. G.M. Eccleston. Functions of mixed emulsifiers and emulsifying waxes indermatological lotions and creams.Colloids and Surfaces A: Physicochemical and Engineering Aspects 1997; 123-124:169-182.

8. M. Korhonen. Rheological properties of pharmaceutical creams containing sorbitanfatty acid ester surfactant. University of Helsink Helsinki, 2004, 1-58.http://ethesis.helsinki.fi/ julkaisut/mat/farma/vk/korhonen/. Retrieved 26/02/2012.

9. P. Taylor. Ostwald ripening in emulsions.Advances in Colloid and Interface Science1998; 75(2):107-163.

10. S. D.Mandawgade, V. B. Patravale. Development of SLNs from natural lipids: application to topical delivery of tretinoin. Int. J. Pharm. 2008; 363(1-2): 132-138.

Received on 15.12.2012 Accepted on 19.12.2012

Res. J. Topical and Cosmetic Sci. 3(1): July-Dec. 2012 page 40-44