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Identify source of volatile sulfur compounds in milk during thermal processing.

The flavor of milk is a key quality attribute. Unfortunately, the presence of volatile sulfur compound flavors has a negative effect on consumer liking.

These sulfurous off-flavors presumably form by whey protein denaturation. They increase with greater heat load and the rate of heating. Distinct differences exist in the flavor profiles of fluid milk processed by high-temperature short-time (HTST) pasteurization, ultrapasteurization (UP), indirect heat UP (IND-UP) and direct steam injection UP (DSI-UP).

However, scientists have not addressed the source of sulfur flavor compounds or how they form when milk is heat-treated. Scientists at North Carolina State University clarified the source and formation of volatile sulfur compounds in fluid milk. They compared protein sources and how the temperatures from HTST and UP processing impact milk. They found that off-flavor sulfur compounds are primarily sourced from the serum protein fraction of milk proteins.

The researchers obtained raw skim milk and served it as a control. Reformulated skim milks (RSM) were manufactured by blending freshly processed micellar casein concentrate (MCC) 95% serum protein reduced, or serum protein isolate, at the equivalent protein content as skim milk (3.3%) with milk permeate.

Skim milk and reformulated skim milk were pasteurized at 78 C for 15 seconds (HTST pasteurization), or at 140 C for 2.3 seconds using IND-UP or DSI-UP. Then a trained descriptive sensory panel documented sensory properties. The volatile sulfur compounds were evaluated using the solid phase micro-extraction technique. This analysis was followed by gas chromatography-triple quadrupole mass spectrometry combined with sulfur selective flame photometric detection.

Sensory panelists confirmed the existence of increased cooked and sulfur-eggy flavors in skim and reformulated skim milk processed by DSI-UP followed by IND-UP and HTST pasteurization. Reformulated skim milk with serum protein isolate had more sulfur-eggy flavors, compared to skim milk or micellar casein concentrate-reformulated skim milk at any temperature.

Reformulated skim milk with serum protein isolate contained higher concentrations of hydrogen sulfide, carbon disulfide, dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide and methional, compared to micellar casein concentrate-reformulated skim milk or skim milk after DSI or IND-UP.

This research provides baseline information for developing milk-based beverages with fewer undesirable sulfur flavors from high-heat treatment.

Further information. MaryAnne Drake, Department of Food, Bioprocessing, and Nutrition Sciences, 236-E Schaub Hall, Box 7624, North Carolina State University, Raleigh, NC 27695; phone: 919-513-4598; email:

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Publication:Emerging Food R&D Report
Date:Oct 1, 2018
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