Fiber-optic spectrophotometry of streaking in pork loins injected with sodium chloride and tripolyphosphate

Abstract

Enhanced pork produced by needle injection of sodium chloride and tripolyphosphate loses its visual appeal if it has pale streaks on a dark background. Reflectance (R) spectrophotometry was used to test the hypothesis needle injection causes pale streaks by elution of myoglobin. Pale streaks in commercial pork loins (n = 10) had higher R than dark streaks (P < 0.01 from 350 to 590 nm) but differences between pale and dark streaks were almost a linear function of wavelength (r = -0.92, P < 0.0005) with no evidence of myoglobin elution. Using the same apparatus, myoglobin elution was detected in small disks of pork perfused experimentally for 1 h (n = 31 spectra, 2 min apart), comparing water (control, n = 5 disks) with commercial injection solution (n = 5 disks). Myoglobin elution by water increased R (P < 0.005) from 350 to 650 nm with a maximum effect at 440 nm, close to the Soret absorbance band for myoglobin. Perfusion of disks with commercial injection solution produced a complex result with the myoglobin elution pattern (increased R peaking at 440 nm) superimposed on an overall decrease in R, probably from sodium salts dissolving myofibrillar proteins (P < 0.005 from 350 to 360 nm, from 400 to 420 nm, at 440 nm, and from 460 to 540 nm). Thus, there was no support for the initial working hypothesis pale streaks are caused by myoglobin elution because the myoglobin elution pattern (increased R peaking at 440 nm) was absent in commercial pork loins. If perfusing small disks of pork is a valid experimental model of what happens in needle-injected loins, transient pale streaks might be muscle fasciculi not yet reached by injected solution. Key words: Enhanced pork, streaking, needle injection