Walnut husk fly substantially affects sensory attributes and phenolic contents of the kernels in common walnut

Walnut husk fly (WHF) is the main pest of common walnut. Its negative impact on external fruits’ properties is frequently reported, while inner kernel quality loss remains unknown. Brown (Bw), dark brown (Db) and black (Bl) kernels, infested by WHF were compared with non-infested bright kernels (B) in ten walnut cultivars in order to see how much sensory attributes of the kernels and their phenolic contents are affected due to WHF infestation. The changes of phenolic content and intensity ratings of sensory traits significantly depended on the WHF-infestation time and the cultivar. Infested kernels were less aromatic, crispy and oily, having a 1.2-fold (Db) to 5.5-fold (Bl) lower total phenolic content (TPC) than bright kernels. Besides TPC, ten compounds belonging to phenolic acids (PA), flavanols (FL) and hydrolysable tannins (HT) as the predominant group were quantified in the kernels of all colour classes. HT and TPC showed the strongest impact on the kernels’ sensory properties. Correlation between sensory attributes and phenolics increased with kernels’ darkening. In Db kernels, TPC defined bitterness, HT were a key source of aroma, oily taste and overall walnut flavour, whilst PA and FL closely correlated with the perception of crispness. An effictive protection, particularly against early-season WHF infestation, which resulted in dark brown and black kernels, is essential in order to avoid the loss of inner quality of walnut kernels.