Distribution, stability and fate of phenolic compounds in white and purple eggplants (Solanum melongena L.)

ZARO, MARÍA JOSÉ; CHAVES, ALICIA R.; VICENTE, ARIEL R; CONCELLÓN, A

POSTHARVEST BIOLOGY AND TECHNOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2014 vol. 92 p. 70 - 78

0925-5214

Eggplants rank among the richest vegetables in antioxidants, but little is known about the allocation, stability and turnover of these metabolites. In this work we determined the distribution, accumulation and degradation of phenolic antioxidants in the inner (I) and outer (O) pulp of two commercially important eggplants types (white and dark purple), at harvest and after 14 and 30 d of refrigerated storage under non-chilling conditions (10 °C and 90% RH). We histolocalized chlorogenic acid (ChA) by fluorescence with 2-aminoethyl-diphenylborinate and determined the activity of phenolic compounds oxidizing enzymes (polyphenoloxidase, PPO and peroxidase, POD) as well as H2O2 concentration in both fruit regions. During storage dark purple fruit were more susceptible to dehydration and showed greater deterioration than white eggplants. Both genotypes accumulated higher sugar contents in the inner pulp as opposed to acids, which were more concentrated in the outer region. At harvest pulp antioxidant capacity was similar in both eggplant types. TEAC and DPPH? assays and in situ localization, showed greater total antioxidants and ChA content in the core than in the O pulp in both white and dark purple fruit. The stability of ChA showed marked differences between genotypes. In white fruit, antioxidants increased during the first two weeks of storage, remaining stable afterwards. In contrast, in dark purple eggplants after an initial stage at which they accumulated, phenolic compounds, declined. PPO and POD in vitro activities, associated mainly with fruit seeds, fibers and vascular bundles did not correlate with pulp browning or loss of phenolic antioxidants. Instead, the reduction of ChA in the core of dark purple fruit was associated with increased production of H2O2. Results indicate that antioxidants are predominantly located in the inner pulp of eggplants regardless of the genotype, but are more stable in white fruit. Rather than being the result of browning reactions, substantial losses of phenolic antioxidants in whole eggplants under the recommended storage conditions likely result from seed coat development and vasculature lignification of the immature fruit.