Production of low-potassium tomato fruit for dialysis patients by NFT or by rockwool culture

Humans tend to ingest excessive amounts of fat and salt but fewer vegetables, exercise less and maintain more sedentary, inordinate-hours lifestyles. These lifestyles are causal factors in diseases called “lifestyle-related diseases”. Especially, chronic kidney failure is becoming a global problem in recent years. In this study, a method of producing low-potassium (K) tomato fruit was investigated. Two medium-sized tomato (Solanum lycopersicum L.) cultivars 'Frutica' and 'Aichan' were used, and the K supply was restricted using hydroponic (NFT and rockwool culture) technique. Fruit weight was not affected by K restriction in both cultivars. As for K content in the fruit, 'Frutica' seemed to be more sensitive to K-deficient treatment than 'Aichan'. Under rockwool culture condition, fruit K content decreased to 62% by K restriction compared to control in 'Frutica', and to 72% in 'Aichan'. Soluble solid content of the fruit showed around 6% under both cultivars and both production systems except the fruits of 3^rd truss in K-deficient treatment plot. Acid content of the fruit tended to decrease by K-deficient treatment, especially in 'Aichan' under rockwool culture. The difference between two cultivation systems may due to the difference of water status around the roots. In conclusion, control of K supply by hydroponics was effective to reduce the K content of tomato fruit. The most important problem is the decrease of acid content, and this might lead to the change of fruit taste. In addition, the effect of the treatment was not stable depending on the cultivation system. More precise technique to control K supply should be necessary to stabilize the yield and quality of low-K tomato fruit production.