An improved chemical method for measuring intensity of hair pigmentation Public Deposited


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  • Research on mammalian pigmentation has ranged from basic studies on biochemistry of melanin formation to more practical studies involving effects of nutrition, environment and genetics on hair color. In mink such studies have an added significance as fur color is of considerable economic importance; however, research in this area has been hampered by lack of aquantitative measure for pigmentation. Historically, fur color in mink has been evaluated visually; this has the disadvantage of lacking repeatability, sensitivity and objectivity. One existing chemical method for measuring hair color employing spectrophotometric procedures is based on the knowledge that hair pigmentation is derived from microscopic melanin granules within the hair, the corollary being that hair color intensity is a function of melanin granule concentration. The studies reported herein were undertaken to further improve this spectrophotometric method of quantitating the amount of melanin pigmentation in hair. In this regard, trials were conducted in the areas of spectrophotometry, ultrasonic homogenization and sample preparation. Other tests were made to gain further information on application of the method. Spectrophotometry. Determining melanin granule concentrations involves establishment of the turbidity of suspensions of melanin granules. Hence, trials were conducted to determine effects of light source wave length, granule concentration and type of spectrophotometer employed on these turbidimetric measurements. These trials indicate that wave length must be specified, as although the absorption curve is linear, optical density values progressively decrease with longer wave lengths. It was further shown that optical density values of varying concentrations of melanin granules follow Beer's law within the tenfold concentration range studied. This strengthens the fundamental validity of the method since the data indicate optical densities of melanin granule suspensions are directly related to granule concentrations. Results further indicate that the technique can be adapted to any spectrophotometer; however, absorption curves vary as a result of differences in cuvette size and other differences inherent to the equipment giving relative but not absolute results. Establishment of standard curves for particular instruments would render values directly comparable. Ultrasonic Homogenization. Investigations in this area indicate that homogenization of the digested hair by sound waves increases the optical density of melanin granule suspensions by separating groups of pigment granules into individual particles. One and one-half minutes of ultrasonic homogenization, at all four power intensity levels studied, resulted in maximum optical density values indicating complete granule separation. Homogenization of melanin granule suspensions increased the repeatability and consequently the sensitivity of the technique by maximally increasing the surface area of the suspended particles and by uniformly dispersing the particles. Sample Preparation. Studies indicate that grinding the hair sample was not necessary to achieve complete granule liberation when followed by ultrasonic homogenization. This modification resulted in a more useable procedure since grinding of hair required considerable time and effort; however, more difficulty was encountered in obtaining a representative sample of guard hair and underfur, which slightly lowered the repeatability of the procedure. Application of Method. Research indicates that the procedure of hair color analysis, as modified by spectrophotometry and ultrasonic homogenization techniques, is sensitive to small differences in hair pigmentation and can be applied to relatively large numbers of samples, These trials further indicate that hair pigmentation as expressed by "melanin value" is definitely correlated to visually appraised intensities of hair pigmentation. The research also suggests that numerous applications of the technique exist. The studies reported herein indicate that the hair color analysis, as modified, is sensitive and repeatable and can be fairly rapidly applied to relatively large numbers of samples.
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