|Abstract:||In order to evaluate pork quality, various instruments are used to measure specific traits, including color and pH. Several instruments, each having several settings, are available for each instrument that impact the values observed, making it difficult for researchers to compare results when the settings are not exactly the same. Even when operational settings are kept the same; it is possible that differences between machines will persist. Additionally, it is not known how instrumental variability changes when using a different aperture type (open or closed) or illuminant (A, C, D65, etc.) when measuring color, or how instrumental variability changes among muscles. Therefore, the overall objectives of this work were to evaluate the variability of instruments used to measure color and ultimate pH, and to see how this variability changes when using different instrumental settings or when measuring different muscles (longissimus dorsi or serratus ventralis).
Instrumental color was measured 3 times on the anterior and 3 times on the posterior end of 250 pork loins with 2 different Minolta CR-400 Chroma meter devices. Each Minolta was programed to use a D65 illuminant, 2º observer with an 8 mm aperture, and calibrated with white tiles specific to each machine. Therefore, a total of 12 instrumental color measurements were collected on each loin. The VARCOMP procedure in SAS was used to estimate the proportion of variation contributed by each factor to CIE lightness (L*), redness (a*), and yellowness (b*), chroma and hue. Based on previous research, the average untrained consumer is able to distinguish approximately 3-L* units, 0.4-a* units, and 0.9-hue angle units. Loins evaluated with machine 1 were 0.71 L* units darker (P < 0.01), 1.09 b* units more yellow (P < 0.01), 0.47 chroma units more saturated (P < 0.01), and had a hue angle 5.12 units greater (P < 0.01) than when evaluated with machine 2 but did not differ (P = 0.24) in redness. The anterior portion of the loin was lighter, less red, more yellow, more saturated and had a greater hue angle than the posterior end (P < 0.01). Loins became darker, less red, and less yellow (P < 0.01) as replication number increased. Inherent color differences among loins contributed the greatest proportion of variability for lightness (58%), redness (57%), yellowness (70%), saturation (70%) and hue angle (49%). Machine contributed 1% variability to lightness 3% to saturation, 23% to yellowness and 31% to hue angle (31%) but did not contribute to variability for redness. Anatomical location contributed 41% to lightness, 43% to redness, 7% to yellowness, 27% to saturation and 31% to hue angle. Replication did not contribute to total variation for any color traits, even though it did differ among measurements.
In a second experiment, three groups of loins and 3 groups of Boston butts were evaluated for instrumental color. In loins, the longissimus dorsi was measured at the approximate location of the 10th rib, and in Boston Butts, the serratus ventralis was measured at the location where the shoulder was separated from the loin. Two Minolta CR-400 chroma meters (Minolta A and Minolta B) were used in this study that were equipped with an 8mm aperture, 2° observer, and calibrated with a white tile specific to that machine. All three groups of loins and Boston butts were measured using Minolta A equipped with a D65 illuminant and closed aperture. Each group of loins and Boston butts were also measured with Minolta B using for a different combination of illuminant (C or D65) and aperture (open or closed). Group 1 used an open aperture and D65 illuminant, group 2 used a closed aperture and C illuminant, and Group 3 used an open aperture and C illuminant. Three additional groups of loins and Boston butts were also evaluated for ultimate pH on three different days. All loins and butts were measured by using two pH meters (Meter 1 and Meter 2). Loins from sets 1 and 3 evaluated with Minolta B had greater variation in lightness (P < 0.01 for both sets) and redness (P < 0.01 for set 1, P = 0.04 for set 3) than loins evaluated with Minolta A, but did not differ in yellowness. Loins from set 2 did not differ in variability for any color traits. Minolta B was able to predict 36 to 54% of variability in Minolta A lightness, 33 to 48% of variability in redness, and 33 to 43% of variability in yellowness. Boston butts from sets 1 and 3 evaluated with Minolta B had greater variation in lightness (P < 0.01 for set 1, P = 0.03 for set 3) than butts evaluated with Minolta A, but did not differ in yellowness. Boston butts from set 2 measured with Minolta A had greater variation in yellowness (P = 0.02) than Boston butts measured with Minolta B, but did not differ in variability of any other color traits. In Boston butts, Minolta B was able to predict 11 to 36% of variability in Minolta A lightness, 15 to 21% of variability in redness, and 21 to 27% of variability in yellowness. Meter B had greater variability than Meter A on all 3 days in loins, and on day 1 in butts; variability between machines did not differ on days 2 or 3 in butts. Meter A was able to predict 17 to 21% of Meter B variation in loins and 79 to 90% of Meter B variation in butts.
Overall, there were differences in instrumental color values between the two machines tested but those differences were likely less than the threshold for detection by a consumer. Even so, inherent color differences between loins were a greater contributor to total variability than the differences between the 2 machines. Therefore, it is more important to define the location of measurements than replication or machine when using a Minolta CR-400 when performing color evaluations, assuming the settings are the same. When using machines with different settings, variation in color traits was increased by using an open aperture but mostly unaffected by illuminant. One machine to measure instrumental color or ultimate pH cannot be used to predict measurements from a second machine when instrumental settings are not the same.