An Investigation Into The Volatile Components Present In Selected Varieties Of Frozen Raspberry (Rubus idaeus L.) Fruit And Juice

Four varieties of raspberry (Glen Clova, Glen Isla, Leo and Glen Prosen), cultivated at the Scottish Crop Research Institute, were selected for examination. Fruit grown in 1983, 1984 and 1985 was harvested for the project. Picking of each crop and transportation to a cool environment in the Department was achieved in a 9 hour period. The fruit was then either slow frozen, rapidly frozen or pressed for its juice. The juice was divided and frozen or pasteurised and frozen. All samples were stored at -19°C in sealed containers, Subsequent to the evaluation of a series of initial experiments, nitrogen entrainment of volatiles followed by adsorption onto Tenax TA and subsequent thermal desorption onto a cryogenic section of geo capillary columns was adopted for the extraction and concentration procedure. Programmed go with non polar and polar bonded phase fused silica columns was applied for the separation of volatiles. Detection was achieved by the use of a FID and by EI mass spectrometry. Identification of separated components was attained through the interpretation of mass spectra and matching Kovats’ indices with published data. Kovats’ indices and mass spectral data for authentic compounds which appeared relevant to the investigation have been determined. Results obtained, whilst being largely in agreement with published data, list a number of clearly identified compounds which have not previously been reported in raspberry volatiles. Comparison of results from different varieties and seasons showed little difference in component content but noticeable variations in apparent quantitative aspects. Pasteurisation resulted in a reduction of total volatiles. No degradation products were identified. Apparent quantitative differences were found in a few volatile components of fruit subjected to differing freezing and thawing regimes.