Response to organic cultivation of heirloom Capsicum peppers: Variation in the level of bioactive compounds and effect of ripening

Abstract

Peppers (Capsicum spp.) are one of the most important vegetables and their double use (vegetable or spice) and two commercial stages (unripe and fully ripe) contributed to their use in many recipes and fast diffusion from America. Nowadays, Spain is a center of diversity for C. annuum, with many landraces, offering a great opportunity for adaptation to organic cultivation. Furthermore, Capsicum peppers contain many bioactive compounds, essential to provide high added-value to these cultivars, especially for organic markets, although knowledge about the effect of organic cultivation on Capsicum fruit quality is still scarce. Here, 37 accessions of Spanish landraces and foreign materials from C. annuum and other species were grown under organic and conventional conditions and evaluated for ascorbic acid (AAC), total phenolics (TP) and total red and yellow/orange carotenoids, considering both ripening stages. A large genotypic variation was found within each ripening stage and growing condition for the studied traits. Also, both stages showed high levels, although fully ripe fruits were the richest. Organic conditions enabled higher levels in fully ripe fruits of AAC and TP on average (135 vs 117 mg·100 g-1 and 232 vs 206 mg·100 g-1) and in most accessions, although the genotype×growing conditions interaction also contributed, but at lower extent, to the observed variation. Significant genotype×ripening stage and growing conditions×ripening stage interactions were also found, suggesting that the magnitude of the increase with ripening depends on the accession and growing conditions. By contrast, there were no differences between growing conditions for carotenoids and differences were mainly due to the genotype factor. Finally, the large genotypic variation and favourable organic conditions allowed identifying several materials from different types and uses with very high levels of bioactive compounds for organic cultivation, in both ripening stages but particularly at fully ripe stage (>500 mg·100 g-1).

Fig 1. Comparative study of the content of ascorbic acid (AAC, upper, mg·100 g^-1 fresh weight) and total phenolics (TP, bottom, mg·100 g^-1 fresh weight), in organic (○) and conventional (Δ) growing systems.

The oblique lines included in the graph represent slope 1 (continuous line, ratio fully ripe/unripe = 1, increase 0% with ripening) and slope 2 (discontinuous line, ratio TP fully ripe/TP unripe = 2, increase 100% with ripening).

Fig 2. Comparison among accessions at the unripe stage considering ascorbic acid content (AAC) and total phenolics (TP) under organic (upper) and conventional (bottom) growing systems.

Texture of columns, based on β parameter, indicates better response to organic (Org.), conventional (Con.) or stable behaviour (Sta.). Bars on the top of columns indicates standard error intervals.

Fig 3. Comparison among accessions at the fully ripe stage considering ascorbic acid content (AAC), total phenolics (TP) and total carotenoids (TC_R+TC_Y/O) under organic (upper) and conventional (bottom) growing systems.

Texture of columns, based on β parameter, indicates better response to organic (Org.), conventional (Con.) or stable behaviour (Sta.). Bars on the top of columns indicates standard error intervals.