A method for predicting the photoprotective performance of a package material for a liquid milk product, the method comprising: (a) providing a sample comprising a homogeneous aqueous solution of riboflavin at about 30 ppm and test materials derived from a series of HDPE packages with differing loadings of titanium dioxide; (b) providing a cell having controlled optical properties to contain the sample at a controlled temperature between -20°C and 100°C; (c) providing a light source that generates a light beam with a controlled spectral signature between 290 and 1000 nm and a controlled intensity between 0.01 and 5 W/cm 2; (d) placing the sample into the cell, rendering a sample cell; (e) placing a first test material between the light source and the sample cell, rendering a shielded sample cell, wherein the light beam impinges upon the first test material and any penetrating light impinges upon the sample cell, and wherein the first test material comprises a known titanium dioxide loading; (f) exposing the shielded sample cell to one or more intensities of said light beam for one or more durations; (g) measuring the changes to the riboflavin contained within the shielded sample cell at one or more durations to generate data points; (h) using the data points to determine a riboflavin degradation rate constant of the first test material; (i) repeating steps (a)-(h) with one or more additional test materials under the same conditions to generate one or more additional riboflavin degradation rate constants; (j) utilizing the two or more riboflavin degradation rate constants to generate a model for the HDPE packages with differing loadings of titanium dioxide that relates the loading of titanium dioxide to the riboflavin degradation rate constant; (k) using the model of step (j), for other HDPE test materials with differing loadings of titanium dioxide, predicting an unknown riboflavin degradation rate constant based upon a known titanium dioxide loading of the material; (l) exposing a liquid milk product in test packages constructed of the test materials described in (a) to retail storage conditions and measuring the riboflavin content of said product for each test package as a function of exposure time; (m) reducing the data from (l) to a riboflavin degradation rate constant for each test package; (n) relating the rate constant values from step (k) to the rate constant values from step (m) to develop a functional correlation; and (o) testing a packaging test material comprised of HDPE and TiO 2 using steps (a) and (b)- (k) and applying the obtained data to the model of step (n) to predict the photoprotective performance under retail storage conditions of a package comprised of the test material and containing the given liquid milk product. (a) providing a sample comprising a homogeneous aqueous solution of riboflavin at about 30 ppm and test materials derived from a series of HDPE packages with differing loadings of titanium dioxide; (b) providing a cell having controlled optical properties to contain the sample at a controlled temperature between -20°C and 100°C; (c) providing a light source that generates a light beam with a controlled spectral signature between 290 and 1000 nm and a controlled intensity between 0.01 and 5 W/cm 2; (d) placing the sample into the cell, rendering a sample cell; (e) placing a first test material between the light source and the sample cell, rendering a shielded sample cell, wherein the light beam impinges upon the first test material and any penetrating light impinges upon the sample cell, and wherein the first test material comprises a known titanium dioxide loading; (f) exposing the shielded sample cell to one or more intensities of said light beam for one or more durations; (g) measuring the changes to the riboflavin contained within the shielded sample cell at one or more durations to generate data points; (h) using the data points to determine a riboflavin degradation rate constant of the first test material; (i) repeating steps (a)-(h) with one or more additional test materials under the same conditions to generate one or more additional riboflavin degradation rate constants; (j) utilizing the two or more riboflavin degradation rate constants to generate a model for the HDPE packages with differing loadings of titanium dioxide that relates the loading of titanium dioxide to the riboflavin degradation rate constant; (k) using the model of step (j), for other HDPE test materials with differing loadings of titanium dioxide, predicting an unknown riboflavin degradation rate constant based upon a known titanium dioxide loading of the material; (l) exposing a liquid milk product in test packages constructed of the test materials described in (a) to retail storage conditions and measuring the riboflavin content of said product for each test package as a function of exposure time; (m) reducing the data from (l) to a riboflavin degradation rate constant for each test package; (n) relating the rate constant values from step (k) to the rate constant values from step (m) to develop a functional correlation; and (o) testing a packaging test material comprised of HDPE and TiO 2 using steps (a) and (b)- (k) and applying the obtained data to the model of step (n) to predict the photoprotective performance under retail storage conditions of a package comprised of the test material and containing the given liquid milk product.