Colour and in vitro quality attributes of walnuts from different growing conditions correlate with key precursors of primary and secondary metabolism

Walnuts (Juglans regia L.) are well known for their flavour, nutritional and health properties. The light colour of walnuts is a quality attribute that leads to consumer preference. The aim of this study was to correlate attributes such as colour and antioxidant capacity with the precursors of primary and secondary metabolism. Two growing areas and four different colours of walnuts cv. Chandler from the central region of Chile were evaluated. Walnuts grown in the zone with Andes Mountains influence showed higher (p < 0.05) sugar and unsaturated fatty acid contents, which could be attributed to lower minimum temperatures during seed filling. Extra light walnuts had higher (p < 0.05) total phenolic compounds, antioxidant capacity and arbutin levels than amber walnuts. To the best of our knowledge, this is the first time that arbutin has been reported in walnuts and could provide the first insight into how enzymatic browning is prevented in the Chandler cultivar.