MANUFACTURING PROCESS FOR COShIETIC CREAM Table I Cream Composition" Constituent % w/w 639 Stearic acid, double-pressed 12-14 Vegetable oils 5-6 Protein 0.5 Alkylene glycol 1.0 Ammonium hydroxide, strong, U.S.P. 1.0 Perfume 2.0 Lime water, sufficient to make 100.0 "Constituents whose specific compositions are not revealed are company confidential. However, any vegetable oil, such as salad oil, or simple protein or glycol will work. droxide, approximately 0.15%) and ammonium hydroxide are added to partially saponify the double-pressed stearic acid (which is actually 50% palmitic acid, 40% stearic acid, 6% oleic acid, plus smaller amounts of myristic and pentadecanoic acids) (2). The crystallizing ingredient of major importance, double-pressed stearic acid, is mixed with vegetable oils. These oils act as a solvent for the stearic acid and also contribute to the consistency of the cream. In reviewing the manufacturing process, two major requirements were identified for process optimization. One was the need to de- termine the optimum mixing time and technique required to form the emulsion, and the other requirement was to determine the optimum temperature history. Since cream consistency appeared to be the most critical indication of the quality of the product, the procedure adopted in this study was first to develop an understanding of the nature of this consistency. To understand the factors responsible for consistency, and to simplify the investigation, separate examinations of the oil phase, the complete emulsified system, and the critically important ingredients in the emulsification were carried out. Oil Blend The oil blend consists of double-pressed stearic acid plus vegetable oils. To determine the contribution of the oil phase to consistency, test tubes were filled with various proportions of stearic acid to vegetable oil, heated to melting in a constant temperature bath, and cooled at a linear rate of about 16.6øC/hr. The compositions were then observed for freezing point depression, eutectic formation, and/or supercooling by noting the temperature at which the liquid mixtures solidified. The temperatures of the liquids were monitored using calibrated iron

640 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS constantan thermocouples connected to a multipoint recorder. Ratios of double-pressed stearic acid to vegetable oil lower than the 2.54 ratio in the cream formulation were tested because some of the slightly soluble stearic acid can be leached from the oil phase droplets dispersed in the cream emulsion, thus changing the original ratio. Furthermore, reac- tion of double-pressed stearic acid with ammonia may be expected to extract proportionally more stearic acid from small emulsion droplets than from larger droplets, creating a further source of oil/stearic acid ratio alteration. Table II lists the ratios and the comments on the solidification behavior of the oil blend observed in these experiments. Table II Solidification Behavior of Various Mixtures of Stearic Acid and Vegetable Oil Ratio of Acid/Oil Comments on Solidification 2.54 Rapid solidification at 52.6øC, hard crystal formation 2.00 Rapid solidification at 51.7øC, hard crystal formation 1.67 Rapid solidification at 50øC, moderately hard crystal formation 1.00 Rapid solidification at 49 øC, moderately hard crystal formation All mixtures were liquid at 54.4øC and were solid by 49øC. No reluctance to solidify was noted. The characteristic consistency found in the cream during the filling process, which occurs between 40-42øC, is one of a thick, smooth texture. Since the oil blend solidifies at 49øC or above, it must be dispersed in the cream in the form of very fine particles or crystals. However, the presence of many small crystals is thermodynamically unstable and leads to the gradual growth of larger ones. A structure that conceivably takes days to develop fully can be built up in the cream. Whether this mechanism was the one responsible for the characteristic consistency of the cream, however, remained to be proved. Complete Emulsified System Samples of cream taken from a normal production-size batch of product were examined to obtain heat-energy information and to de- termine the reversibility of the characteristic consistency forming mecha- nism.