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Relationship of Absorbance to Process Treatments and Flavor during Storage of Ultra-High-Temperature Dairy Products¹

Department of Food Science and Department of Biological and Agricultural Engineering, North Carolina State University, Raleigh 27650

ABSTRACT

Fluid dairy products (fat range .5 to 10.5%) were processed in an ultra-high-temperature steam injection system. Time-temperature relationships of processing included 138, 143, and 149 C for 20.3 s; 143 and 149 C for 6.9 s; and 149 C for 3.4 s. Product from each treatment was stored at 4, 24, and 40 C. Absorbancy readings were at 470 and 720 nm on subsamples at 4-wk intervals for 60 wk. Effects of light scattering were minimized by computing A (A₄₇₀-A₇₂₀). An increase in A corresponded to change in slope of the spectrum between 470 and 720 nm, a change associated with discoloration (browning). All samples demonstrated an initial decrease in A with an eventual increase over the storage period. Samples stored at 4 C decreased the most in A with those at 40 C, the least. The eventual increase of A occurred earlier and at a greater rate as storage temperature increased. With more severe heat treatments, the initial A's were higher.

From taste panel data compiled on the same samples at the same time intervals, an empirical relationship was formulated between A, percent fat, taste panel evaluations, and storage time. A high correlation between taste panel ratings and A readings was possible, suggesting an effective quality assurance test for stored ultra-high-temperature dairy products.

¹ Approved for publication as Paper No. 6237 in the Journal Series of North Carolina State University Agricultural Research Service. The use of trade names in this publication does not imply endorsement by the North Carolina State Agricultural Research Service nor criticism of similar ones not mentioned.