Comparison of phenolic acids in organically and conventionally grown pac choi (Brassica rapa L. chinensis)

BACKGROUND: Field and greenhouse studies were performed to investigate whether organic production methods influenced levels of phenolic acid compounds in pac choi (Brassica rapa L. chinensis cv. Mei Qing Choi) compared with conventional cultivation. RESULTS: In the field experiment, organic fertilisation (compost + fish emulsion) resulted in significantly higher phenolic concentrations compared with conventional fertilisation (NPK + CaNO3) under both high tunnel and open field environments. Increased phenolics were accompanied by a significant reduction in plant fresh weight and dry weight, probably due to nitrogen deficiency. However, the elevated level of phenolics in organically grown pac choi could also have been due to confounding effects of nitrogen availability, insect attack and pesticide application. A follow-up greenhouse experiment further demonstrated a significant increase in phenolic compounds and a reduction in yield with organic fertiliser (vermicompost + fish fertiliser) relative to conventional treatment (slow release inorganic fertiliser). Preventive insecticide application did not affect the phenolic levels in pac choi under either organic or conventional fertilisation. CONCLUSION: Given that higher phenolic content in pac choi was associated with low nitrogen availability and considerable yield reduction, research is needed to determine the extent to which phenolic compounds may differ in organic and conventional pac choi when nutrient levels are adjusted to produce comparable yields. Additional study is also warranted to determine the extent to which insect attack might contribute to elevated phenolic content in organic pac choi. (c) 2009 Society of Chemical Industry