The effects of the application of foliar fertilisation and pesticide on nutritional quality of mandarin orange juices were evaluated using (1)H NMR metabolomics. Significant differences between the use of fertiliser and pesticides during fruit formation were observed, and included changes in sugar, amino acid and organic acid composition. To determine whether the difference in sugar concentration was enough for the consumer to detect, a sensory experiment was performed in which two orange juice samples were prepared to resemble the sweet/sour taste balance of juice from mandarin oranges in which foliar fertilisation was either applied or not. In a test using non-trained individuals, 68% could correctly identify which juice had a sourer, or less sweet, taste. The implications of this study could impact citrus growers, and ultimately aid in development of fruit with superior sensory quality.