Preharvest applications of monopotassium phosphate to improve fruit quality and volatilome composition in cold-stored cherry tomatoes

The experiment addressed the effects of preharvest KH2PO4 foliar spraying (20 mmol · L−1) on fruit quality and composition (including volatile organic compounds, VOCs) of cherry tomatoes (‘Caravaggio’, ‘Sugarland’ and ‘Top Stellina’) after 0 (S0), 7 (S7) and 14 days (S14) of storage at 8.0 °C. On the average of the 3 genotypes, the KH2PO4 treatment improved fruit pressure firmness, total soluble solids (TSS), titratable acidity (TA), total phenols and carotenoids concentrations, along with the fruits' antioxidant capacity (by up to 17% for FRAP assay). Within the S7–S14 period, control fruits showed the highest reductions in TSS, TSS/TA ratio and total carotenoids (−17, −12 and −45, respectively), whereas treated fruits proved the strongest increase in DPPH (+12%). Sixteen out of 32 VOCs were promoted following KH2PO4 application, including the aldehydes hexanal, (E)-2-hexenal and (Z)-3-hexenal and the apocarotenoids (E)-citral, (E)-β-ionone, geranylacetone and 6-methyl-5-hepten-2-one. Proceeding from S0 to S14, several VOCs decreased more strongly in control fruits, as for hexanal (−48%∖) and total aldehydes (−42%∖, whereas at S14 treated fruits had higher concentrations of linalool, geranylacetone and 6-methyl-5-hepten-2-one (1.06, 52.50 and 79.27 μg · kg−1, respectively). ‘Caravaggio’ demonstrated the strongest apocarotenoid reduction at S14, whereas ‘Top Stellina’ was more responsive to KH2PO4 (mainly for β-cyclocitral, geranylacetone and total terpenes/terpenoids), thus highlighting the central role of the genotype in responding to other experimental factors. Nonetheless, these results suggest that proper preharvest KH2PO4 applications can preserve specific commercial, nutritional and quality traits of cold-stored cherry tomatoes.