Aroma Composition Changes in Early Season Grapefruit Juice Produced from Thermal Concentration

Differences in aroma components and total volatiles between a single unpasteurized Marsh grapefruit juice and its 65 °Brix concentrate reconstituted to 10 °Brix were examined using GC−olfactometry (GC−O) and GC−FID. Total volatiles (FID) in the reconstituted concentrate were reduced to less than 5% of initial values, but 57% of total aroma (GC−O) remained. Forty-one aroma-active compounds were observed in unpasteurized single strength juice, whereas 27 components were found in the unflavored reconstituted concentrate. Aroma-active compounds were classified into grapefruit/sulfury, sweet/fruity, fresh/citrusy, green/fatty/metallic, and cooked/meaty groups. Five of six components in the sweet/fruity and 14 of 18 green/fatty/metallic components survived thermal concentration. However, only 4-mercapto-4-methyl-2-pentanone in the grapefruit/sulfury group, and linalool and nootkatone from the fresh/citrusy group, were found in the reconstituted concentrate. Methional was the only aroma compound in the cooked/meaty category found in both juice types. β-Damascenone and 1-p-menthen-8-thiol were found only in the reconstituted concentrate. 4-Mercapto-4-methyl-2-pentanol was found for the first time in grapefruit juice. Keywords: GC−O; time−intensity measurement; flavor; aroma-impact compounds; aroma changes; grapefruit-smelling compounds; unsaturated fatty aldehydes; 1,10-dihydronootkatone; 4-mercapto-4-methyl-2-pentanone; β-damascenone; 1-p-menthen-8-thiol