Decrease in rice aroma after application of growth regulators

Abstract

Aromatic rices (Oryza sativa L.) compared to the leading varieties are low-yielding, susceptible to lodging and prone to attack by a number of insect pests and diseases. Under these conditions, various agricultural chemicals such as fertilizers, pesticides and growth regulators have been used for their cultivation. Few investigations, however, have examined the influence of these chemicals on rice aroma and flavor. In this study, changes in rice aroma after treatment with gibberellic acid, paclobutrazol, 3-indole acetic acid, and a regulator mixture consisting of paclobutrazol, proline and zinc chloride were for the first time examined using two aromatic rice cultivars. Applications were carried out after 25% of panicles had emerged. We studied 12 odor-active compounds, extracted and identified using static headspace coupled with gas chromatography. At the concentrations tested, all treatments with growth regulators resulted in reduced aroma content that affected overall flavor. In a smelling evaluation, control samples were significantly higher in intensity than treated samples. The difference between the aromas of control and treated samples was largely related to 2-acetyl-1-pyrroline, the major rice aroma compound, and lipid oxidation volatiles. For instance, in the cultivar Guixiangzhan grown during the late season, gibberellic acid treatment decreased the content of 2-acetyl-1-pyrroline by 19%, 3-indole acetic acid by 9%, paclobutrazol by 22%, and the regulator mixture by 21% compared with the control. Similar trends were observed in the Peizaruanxiang cultivar, with decreases ranging from 10 to 24%. Our findings demonstrate that treatments with growth regulators inhibited the metabolic processes associated with the formation of volatile compounds.