Annals of Applied Biology ISSN 0003-4746 RESEARCH ARTICLE Post-flowering photoperiod has marked effects on fruit chemical composition in red raspberry (Rubus idaeus) S.P. Mazur 1,2 , A. Sønsteby 1 , A.-B. Wold 2 , A. Foito 3 , S. Freitag 3 , S. Verrall 4 , S. Conner 3 , D. Stewart 1,3 & O.M. Heide 5 1 Bioforsk, Norwegian Institute for Agricultural and Environmental Research, Kapp, Norway 2 Department of Plant and Environmental Sciences, Norwegian University of Life Sciences, Ås, Norway 3 Environment and Biochemical Sciences, James Hutton Institute, Dundee, UK 4 Information and Computational Sciences, James Hutton Institute, Dundee, UK 5 Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, Ås, Norway Keywords Anthocyanins; antioxidant capacity; ellagic acid; fruit quality; harvest time; metabolite profile; organic acids; photoperiod; polyphenols; Rubus idaeus; sugars; vitamin C. Correspondence S.P. Mazur, Bioforsk, Norwegian Institute for Agricultural and Environmental Research, NO-2849 Kapp, Norway. Email: sebastian.mazur@bioforsk.no Received: 18 December 2013; revised version accepted: 14 July 2014. doi:10.1111/aab.12153 Abstract 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 signif- icantly increased fruit concentrations of ascorbic acid, total phenolics, organic acids such as malic, quinic and ellagic acids, as well as the ferric reducing activ- ity power, while reducing the concentrations of soluble solids, sucrose and the sugar/acid ratio. The levels of total anthocyanin and oxalic acid were not signif- icantly 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 photoperi- odic mechanism(s) independently of the daily light energy supply. Introduction Fruits, and berries in particular, are rich dietary sources of a range of vitamins, minerals and other phytochemicals of interest for human nutrition and health (Sun et al., 2002, and ref. therein; Rao & Snyder, 2010). Traditionally, L-ascorbic acid (L-AA, vitamin C) has been of predomi- nant interest because of its antiscorbutic properties, but more recently dietary phenolic compounds have received increasing interest due to their potential dietary health benefits (Ness & Powles, 1997; Mullen et al., 2002; Reddy & Katan, 2004; Stanner et al., 2004; López et al., 2010) which were thought to be linked to their direct antiox- idant capacities (AOC). However, due to the reported limited bioavailabilities of such phenolic antioxidants (Manach et al., 2005; Williamson & Manach, 2005), this is now less clear with mechanisms such as induction of endogenous antioxidant systems, cyclooxygenase inhibition and upregulation of endothelial nitric oxide synthase (eNOS) proposed (Smoliga et al., 2011). Public awareness of the potential health benefits of increased intake of fruit and vegetables has increased consumer demands for fresh fruit and associated product, and has intensified research activity on the effects of genetic and environmental factors on fruit chemical composition (Atkinson et al., 2005; and references therein). In the Nordic countries, there has been a long-held notion that the concentration of L-AA and other health-related phytochemicals in plants are increas- ing with the latitude of production (Jaakola & Hohtola, 2010; Remberg et al., 2010), and there is also some sci- entific evidence from both fruit and vegetable research to support this (Hårdh & Hårdh, 1977; Hårdh et al., 1977; Davik et al., 2006; Jaakola & Hohtola, 2010; Remberg et al., 2010). It is believed that the long days (LDs), high total radiation and cool temperatures of the high-latitude summer may increase the synthesis of aromatic com- pounds and vitamins such as L-AA (Jaakola & Hohtola, 2010). Since all these environmental factors, as well as light quality, change with increasing latitude, it is difficult to determine which factor(s) are the causal Ann Appl Biol (2014) 1 © 2014 Association of Applied Biologists