Measurement of luster in Suri alpaca fiber

Abstract

A study was conducted to evaluate the ability of two instruments for measuring luster in Suri alpaca fiber and to compare the results with subjectively assessed luster scores. In addition, the study was designed to determine the correlations between luster and other value-determining, objectively measured physical properties of Suri alpaca fiber. For this purpose, 205 Suri alpaca fleece samples were submitted by 49 breeders that represented a broad cross-section of Suri alpaca in terms of visually assessed luster, color, and fiber characteristics. Raw staples and “washed-and-aligned” staples were independently and subjectively assessed for luster by 2 alpaca judges certified by the Alpaca Owners and Breeders Association (AOBA). The fiber samples were measured for luster and luminance using a SAMBA Hair System and were scanned using a near-infrared reflectance spectrometer. Standard objective test methods were used to measure mean fiber diameter and variability (at mid-staple and overall), prickle factor, comfort factor, mean fiber curvature and variability, medullation (white, beige, and light fawn samples only), laboratory scoured yield, mean staple length and variability, and mean staple strength and variability. The precision of the luster measurement (MLUS) was estimated using CV based on 3 measurements per subsample and averaged 3.9% across all colors. In contrast, precision of the luminance measurement (MLUM) was higher with an average CV of 2.3%. Agreement between the subjective luster scores of 2 certified alpaca judges was low (r2=0.17 and 0.10 for raw and washed-and-aligned samples, respectively). Despite this, evidence was obtained linking instrument-measured luster and luminance with subjectively assessed luster scores. Two systems were proposed for expressing instrument-measured luster that will permit comparisons between alpacas of different color. Small negative correlations were present between mean fiber diameter and subjectively assessed luster scores. Small positive correlations were present between mean fiber diameter and objectively measured luster values. A strong correlation (r=−0.94) existed between instrument-measured luster and log10luminance. Prediction equations derived from near-infrared reflectance spectra (NIRS) produced precise and accurate estimates of log10luminance. The NIRS estimates of instrument-measured luster were less precise and less accurate, and estimates of subjectively assessed luster were neither accurate nor precise. The SAMBA Hair System is capable of producing estimates of luster that are accurate enough to be useful to Suri alpaca breeders who intend to select for this trait.