The effect of photoperiod on nutritional quality and chemical composition of
‘Glen Ample’ red raspberry has been studied under controlled environment
conditions. Long day (LD) conditions during fruit growth and maturation significantly
increased fruit concentrations of ascorbic acid, total phenolics, organic
acids such as malic, quinic and ellagic acids, as well as the ferric reducing activity
power, while reducing the concentrations of soluble solids, sucrose and the
sugar/acid ratio. The levels of total anthocyanin and oxalic acid were not significantly
affected by photoperiod whereas semi-quantitative analysis indicated a
significant increase in the levels of some ellagitannins. The same responses were
found whether LD was established by day-length extension with low-intensity
light or by night interruption, thus demonstrating that the observed changes in
nutritional quality of raspberry fruit was mediated through specific photoperiodic
mechanism(s) independently of the daily light energy supply