Processing of raspberries to dried fruit foam: impact on major odorants

Abstract

Application of an aroma extract dilution analysis (AEDA) to the volatiles isolated from raspberry fruits by solvent extraction and solvent-assisted flavour evaporation (SAFE) resulted in 40 odour-active compounds with flavour dilution (FD) factors between 1 and 4096. Among the most potent odorants were violet-like smelling β-ionone (FD factor 4096), fruity smelling methyl 3-methylbutanoate (1024), baked-apple-like smelling β-damascenone (1024), raspberry-like smelling raspberry ketone (128), and floral, raspberry-like smelling α-ionone (64). These five odorants were subsequently monitored during processing of raspberry fruits to freeze-dried fruit foam. Major losses occurred during separation of the pulp from the seeds and during the final freeze-drying step. It was shown that the pulp fraction directly adherent to the seeds contained higher odorant concentrations than the outer parts of the pulp, thus losses associated with the removal of the seeds can be minimised by increasing the efficiency of the separation. Losses associated with the freeze-drying process could be reduced using microwave-assisted freeze drying instead of conventional freeze drying. Higher amounts of potato protein and maltodextrin used as foaming agent and foam stabiliser, respectively, reduced the odorant recoveries in the dried foams. Only a small part of the odorants not recovered in the dried fruit foams was found in the condensate.