Sanja Fabek

Influence of potassium fertilisation on the levels of phenolic compounds in sweet potato (Ipomoea batatas L.) leaves

Summary The nutritional value of sweet potato leaves (Ipomoea batatas L.) has recently been emphasised as their anti-oxidant and phenolic compounds can improve human health and provide nutritional benefits. This has increased the interest of the food industry and of consumers in using sweet potato greens as a functional food. To increase the level of phenolic compounds in sweet potato leaves, we studied the influence of potassium (K)-fertilisation at different N:K ratios [namely 1:1 (control), 1:2.5, or 1:5] on the phenolics contents and corresponding anti-oxidant activities of two cultivars of sweet potato, ‘Bat1’and ‘Boniato’. In general, enhanced K-fertilisation increased the level of phenolic compounds and the corresponding anti-oxidant activity. However, the two cultivars differed in their response to K-fertilisation. Phenolic acids were increased (by approx. 20%) in ‘Bat1’ only after the application of N:K at a ratio of 1:5, while K-fertilisation at all rates increased the flavonoid contents of both cultivars (by approx. 300%). Our results could be useful for sweet potato producers who wish to make informed decisions on which cultivar and/or mineral fertiliser regime to choose in order to produce sweet potato leaves of the desired nutritional quality.

Yield components and glucosinolate contents of broccoli cultivars in summer-autumn growing cycle

In recent decades, interest for functional food has been increased. Plant derived food is important source of various bioactive compounds. The biologically active components in Brassica vegetables are the breakdown products of glucosinolates which have anticarcinogenic properties. Broccoli is included as a highly nutritious vegetable due to its mineral and vitamin content, fibres and bioactive compounds which depend on genetic, abiotic and agronomic factors. As numerous broccoli hybrid cultivars are available in Croatia, research with aim to select promising hybrid broccoli cultivars with appropriate agronomic and chemical traits was carried out during summer-autumn growing period of 2007. The field trial involving 13 hybrid broccoli cultivars was laid out according to four- replication block design. During harvest period basic morphometric values of top inflorescence were determined. Cultivar Montop had the highest mass, diameter and yield of top inflorescence (506 g, 15.5 cm and 1.5 kg m-2). Green Magic and Lucky belong to the same range with slightly lower values of the mentioned parameters (457 g, 15.4 cm, 1.5 kg m-2 and 447 g, 14.1 cm, 1.5 kg m- 2, respectively). In all analyzed cultivars prevailing glucosinolate were glucoraphanin and glucobrassicin. There are significant differences in glucosinolate concentrations among cultivars. Fiesta had the highest glucoraphanin level, 3.52 μmol g-1 dry weight (dw). This was followed by Agassi and Marathon, which also achieved high glucoraphanin concentrations (2.85 and 2.80 μmol g-1 dw). General obtained the highest glucobrassicin concentration (9.5 μmol g-1 dw), significantly higher than the other cultivars. Marathon reached the highest total glucosinolate concentration (15.45 μmol g-1 dw). Neither cultivar can stand out with the highest values of agronomic parameters and bioactive components at the same time. The results point out Marathon as the cultivar with a considerable content of glucoraphanin, glucobrassicin and total glucosinolates (2.58, 7.32 and 15.45 μmol g-1 dw, respectively), and with satiable marketable top inflorescence yield (1.06 kg m-2).