Effect of temperature on stability of anthocyanins, ascorbic acid and color in strawberry and raspberry jams

Strawberry (cv. Senga Sengana) and raspberry (cv. Veten) were processed into jams at 60, 85 or 93 degrees C and stored at 4 or 23 degrees C for 8 and 16 weeks. High processing temperature reduced ascorbic acid, total monomeric anthocyanins (TMA) and total phenolics (TP) in strawberries (p < 0.05), but not in raspberries. Processing temperature had minor effect on bioactive compounds in the jams during storage (< 10% explained variance), but influenced color (L*, degrees Hue, Chroma), especially L* of the strawberry jams (73.3%). Storage period explained most of the variance in ascorbic acid (> 90%), TMA (> 42%) and TP (> 69%). Storage temperature affected stability of anthocyanins, but had minor effect on ascorbic acid, which declined rapidly independent of storage temperature. Storage temperature also explained most of the variance (> 40%) in Chroma of the jams and L* of raspberry jams (53%). Bioactive compounds and color were more stable in raspberry jams than in strawberry jams.