Non-destructive determination of pre-symptomatic biochemical markers for Peteca spot and evaluation of edible coatings for reducing the incidence of the disorder on ‘Eureka’ lemons

Abstract

International markets that import citrus fruit from South Africa have imposed regulations that involve cold sterilization at low temperatures, which cause physiological disorders such as peteca spot in lemon. The aim of this study was to, non-destructively determine pre-symptomatic biochemical markers for Peteca spot and the evaluation of edible coatings for reducing the incidence of the disorder on ‘Eureka’ lemons. The first chapter is general background which introduces the key words and clearly outlines the aim and objectives of the study. The second chapter is review of literature, which motivated the three research chapters due to the gaps found. Presymptomatic biochemical markers that are related to peteca spot were evaluated in the third chapter. The Principal Component Analysis (PCA) was able to separate fruit harvested from the inside and outside canopy positions based on their susceptibility to the disorder. Fruit harvested in the inside canopy were more susceptible to peteca spot and these were correlated with physic-chemical properties, which were typically low in the inside canopy. The efficacy of carboxymethyl cellulose (CMC) and chitosan (CH) incorporated with moringa leaf extracts (M) edible coatings on reducing the incidence of peteca spot was also evaluated in the fourth chapter. Fruit harvested from inside and outside canopy positions were assigned to five coating treatments: control, M+CMC, CMC, CH and M+CH. The most effective coating treatment in reducing the susceptibility of ‘Eureka’ lemon to peteca spot was M+CMC followed by CMC and CH. The fifth chapter focused on, non-destructively predicting peteca spot using visible to near infrared spectroscopy (vis/NIRS). Presymptomatic biochemical markers that have been related to peteca spot were successfully predicted. Lastly, general discussions and conclusions were made in chapter six as well as recommendations.