Means of improving colour expression in pepper fruit.

Abstract

Colour is a characteristic that makes fruit appealing to the consumer, hence, is a prime factor when (s)he chooses to buy certain horticultural commodities. If colour is unappealing, consumers tend to ignore other quality characteristics of the fruit. Although colour expression in Capsicum annuum L. is genetically influenced, it is also affected by environmental factors as well as crop management practices. In an attempt to identify which are the dominant red colour-imparting carotenoids in red pepper and how to influence their occurrence, extracts from crude and saponified mature-green, colour-break and red-ripe fruit were purified on TLC silica gel 60 GF(254) plates. TLC R(f) values of the identified intensive red bands from saponified red-ripe extract were compared to those of authentic capsorubin, capsanthin, 13-Z-capsanthin and 9-Z-capsanthin standards. Two dominant red carotenoids were isolated from red-ripe fruit, by separating either crude or saponified extract by TLC. The two bands were then subjected to reversed-phase HPLC analysis. Both bands were characterized by comparison of their absorption spectra to that of authentic capsanthin and capsorubin standards. Red colour imparting compounds of the red pepper cultivar Capistrano surfaced at colour-break stage and their intensity increased with the ripening process. HPLC results show that there was structural modification of ketocarotenoid, mainly capsorubin. Trials were carried out in a plastic tunnel and in a growth room to investigate the impact of various plant management practices (moisture regimes, macronutrient applications, thinning of reproductive structures, subjecting pepper plants to optimal growing temperature) on pepper fruit pigment concentration. This concentration was determined at the mature-green and red-ripe stage. Subjecting pepper plants to optimal growing temperature (23/18°C) from the vegetative stage onwards, providing them with recommended optimal amount of K fertilizer (25.2 Kg ha-1 ) and supplying Mg at supra-optimal level (455 Kg ha-1 ) as well as subjecting them to drought stress starting from 30 or 50 days after transplanting and water logging conditions from 30 days after first petal fall onwards increased pepper fruit carotenoid concentration significantly. On the other hand, other levels of the above-mentioned factors (subjecting pepper plants to the optimum temperature later than the vegetative stage, supplying 'very low', 'low' or 'high' K or, 'very low', 'low' or 'medium' Mg concentrations as well as thinning of reproductive structures of pepper plants early in the fruit developmental stage and subjecting plants to drought from 30 days after first petal fall onwards or to water-logging from 50 days after transplanting or 30 days after first petal fall onwards) resulted in a significant decrease in the carotenoid concentration. Therefore, management practices can be explored to improve red colour formation in red-ripe Capsicum fruit.