Abstract
Solanum melongena L., also known as eggplant, is a widely consumed vegetable and it is well-known for its beneficial antioxidant properties, due to phenolic compounds. In this work, the influence of different cooking procedures on the content of chlorogenic acid was evaluated on eggplant samples of different geographic origin by high-performance liquid chromatography (HPLC). An easy and quick extraction procedure with 50% methanol as the extraction solvent was optimized for the first time by means of a design-of-experiment and applied to heat treated samples of eggplant. The antioxidant capacity of eggplant extracts was also evaluated by using the ABTS assay and it was correlated with the data obtained by the HPLC method. The content of chlorogenic acid was different in each heat-treated eggplant sample and it depended on the temperature applied during the cooking procedure. In particular, an increase of chlorogenic acid content with rising temperature was observed. Conversely, a very high temperature (250 °C) caused a decrease of chlorogenic acid amount. The influence of storage on the content of chlorogenic acid was also monitored. While the level of chlorogenic acid in fresh samples decreased during four weeks of storage, an increase in its content in heat treated eggplant was observed within the same period. Multivariate data analysis was used to classify eggplant samples into different groups, according to the country of origin and heat treatment procedure. This study provides new insights to preserve the antioxidant properties of eggplant phenolics during different thermal and storage treatments in order to highlight their health promoting effects.
Highlights
Solanum melongena L., known as eggplant, is a native plant from Southeast Asia that was domesticated more than 4000 years ago
The content of samples was chlorogenic acid (Figure 2), in agreement with the results previously described in the chlorogenic acid in fresh samples was in the range
The influence of different cooking procedures on chlorogenic acid content in eggplant samples different geographic origin was evaluated by using a quick and easy extraction method, which was of different geographic origin was evaluated by using a quick and easy extraction method, which optimized here for the first time, followed by high-performance liquid chromatography (HPLC) analysis
Summary
Solanum melongena L., known as eggplant, is a native plant from Southeast Asia that was domesticated more than 4000 years ago. The world production of eggplant in 2017 was around 52.3 million tons, with China being the main producer, followed by India, Egypt, Turkey and Iran. The production of eggplant in Europe in the same year was around 0.93 million tons, Italy being the main producer, followed by Spain, Romania, Ukraine and Greece [2]. Eggplant is known for the antioxidant activity related to its phenolic compounds [3], with chlorogenic acid (5-O-caffeoylquinic acid) being the most abundant one [4,5]. Isomers of chlorogenic acid, such as cryptochlorogenic acid (4-O-caffeoylquinic acid) and neochlorogenic acid (3-O-caffenoylquinic acid), are minor eggplant phenolics [6,7]. A high amount of chlorogenic acid derivatives has been found in vegetables related to eggplant, such as cardoon, with a content around 5 mg/g [8]. A very low amount of this compound has been determined in cucumber [10]
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