Flavour quality of early and late harvested tomatoes from different organic growing systems

Summary

Flavour and firmness are important quality criteria for tomatoes [1]. Tomato flavour is mainly attributed to the content of sugar and acid and volatile compounds. Many factors determine tomato flavour e.g. cultivar, growing system, maturity, harvest time and post-harvest treatments [1, 2]. In Denmark, organic tomatoes are grown directly in the soil. It is difficult, however, to provide enough organic manure, to prevent leaching out of nutrients and to control soil-born diseases in a soil system. Recently, Sørensen and Thorup-Kristensen [3] reported results on two alternative systems in which plants were grown in compost and nutrients and water was re-circulated. The aim of the present study was to determine the effect of growing system (open, confined and combined systems) on selected flavour compounds and sensory quality of tomatoes harvested in the spring and autumn.
Tomatoes (Lycopersicon esculentum Mill. cv. ‘Aromata’ drafted on ‘Beaufort’) were grown organically in a greenhouse in soil in an open system (control), on compost beds in a confined system and on compost beds with holes for root penetration in a combined system. Tomatoes were harvested in spring (May) and autumn (October) at comparable maturity and analysed for flavour compounds and sensory quality. A total of 31 volatile compounds were collected from blended tomatoes by dynamic headspace technique and identified and quantified by GC and GC-MS. The aroma profile of organically grown tomatoes was in agreement with published data on conventional tomatoes. The content of volatiles, soluble solids, citric acid and dry matter was almost the same regardless of growing system. Sensory analysis revealed that tomatoes harvested in the spring from the confined system scored higher in tomato flavour and sourness than those from the combined system. In the autumn there was no effect of growing system on sweetness, sourness, and tomato flavour but on the content of hexanal, (Z)-3-hexenal and (Z)-3-hexen-1-ol. Principal component analysis (PCA) revealed that system accounted for 15 % and harvest time for 67 % of the variation in the volatile data indicating that growing system had only a minor effect on the chemical composition and sensory quality of tomatoes harvested at comparable maturity. It therefore seems that growers of organic tomatoes can switch to a confined or combined growing system without affecting quality.