Impacts of Supercritical Extraction on GC/MS Profiles of Volatiles in Whey Protein Isolate Sampled by Solid Phase Microextraction

Whey protein isolate (WPI) contains at least 90% protein and should ideally possess a bland flavor without typical dairy flavors including sweet aromatic and cooked/milky notes. However, its flavor may be highly variable due to factors including original whey source, processing and storage conditions. Novel technologies removing nonpolar compounds responsible for off-flavors and off-flavor formations are desirable. The major objective of this research was to evaluate impacts of supercritical carbon dioxide (scCO2) extraction, a known green process, on volatile profiles of WPI. A prior sub-objective was to establish an analytical technique for characterization of volatiles. Specifically, adsorption conditions in a well-established head-space solid-phase microextraction (SPME) method were used for quick and reliable assays of volatiles in WPI, using a divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber. The adsorption of volatiles on the SPME fiber was studied at 21, 40 or 50 °C, each with durations of 5, 15 and 20 min, and analyzed by GC/MS. Based on the number of GC/MS peaks and the corresponding peak areas, adsorption conditions of 50 °C for 20 min were selected for subsequent studies. In the second sub-objective, GC/MS profiles of WPI were characterized after scCO2 extraction using a continuous stream of CO2 at 50 g/min, controlled at various combinations of temperature (30-65°C), pressure (7.0-30.0 MPa), and duration (10-90 min). Extractions with a higher temperature and a higher pressure for a longer time were generally more effective in removing volatiles, and most peaks on the chromatogram of the unprocessed WPI sample disappeared or were reduced very significantly after all studied extraction conditions, even at subcritical conditions of 7.0 MPa and 30 °C for 1 hour. Our findings demonstrated that supercritical or subcritical CO2 may provide a green approach to reduce volatiles in whey protein preparations for novel food applications.