Influence of Potassium Fertilisation on the Induction of Phenolic Markers of Resistance to Internal Browning in Pineapple (Ananas comosus L. Merr.)

Abstract

The post-harvest quality of pineapple is often compromised by physiological disorders, including internal browning, which affects not only the appearance of the fruit but also its nutritional quality and consumer acceptability. Internal browning is a major limiting factor in the post-harvest quality of pineapple, negatively impacting its marketability. This study aims to evaluate the effect of potassium fertilisation on the induction of phenolic compounds associated with resistance to browning. The experimental field was established on sandy and low-fertility land at the Nangui Abrogoua University experimental farm (5º23'21''N; 4º11'09''W), Abidjan-Côte d'Ivoire. Four levels of potassium supply (20, 28, 34 and 40 g K₂O/plant) were tested on MD2 and smooth Cayenne varieties. After harvest, fruits were stored at a low temperature of 10°C for 14 days, then at 22°C for 5 days before browning symptoms were assessed. Phenolic metabolites were then characterised using ultra-high performance liquid chromatography (U-HPLC). After preservation, samples of the pulp from each fruit were taken in “dice” form and placed in a freeze-dryer (Alpha Christ 1-2 plus) for 2 days. Samples were analysed on two coupled U-HPLC chains. The results showed that an increasing amount of potassium fertiliser in pineapple cultivation significantly reduced the severity of fruit browning. Symptoms disappear from 34 g K₂O/plant. Analysis of phenolic profiles reveals increased biosynthesis of flavonoids such as rutin, myricetin, genistin, gallic acid, protocatechic acid, genistein, quercetin, kaempferol, taxifolin, epicatechin and quercitrin.  These are identified as markers linked to resistance to internal rusting in pineapple. Furthermore, the MD2 variety proved more tolerant to browning than the smooth Cayenne, probably due to an initially richer phenolic composition. These results indicate that optimising potassium intake could be an effective strategy for limiting post-harvest losses and improving the quality of fruit intended for export. A better understanding of the interactions between mineral nutrition and phenol metabolism could lead to the development of optimised cultivation strategies for the pineapple industry. Further studies on the enzymatic mechanisms involved in internal browning will allow refining these recommendations and optimising post-harvest fruit management.