La conservation des mangues 4ème gamme est limitée par le brunissement enzymatique et la perte de fermeté dus aux différentes opérations de transformation. Cette thèse propose un nouvelle approche pour améliorer la conservation de mangues 4ème gamme : l’application de traitements thermiques par immersion et/ou la conservation sous atmosphère modifiée : passive ou active (5% O2 – 5 % CO2) ou des enrobages (chitosane). Ce travail a permis tout d’abord de déterminer un couple température / temps optimal: 50 °C / 30 min qui permet de maintenir la qualité de plusieurs variétés de mangue (Keitt, Kent, Tommy Atkins). Les effets du traitement thermique sur l’intensité respiratoire, la couleur, la fermeté, les teneurs en antioxydants : vitamine C, caroténoïdes et phénols totaux, et sur l’activité de plusieurs enzymes (pour la fermeté : PME, PG, b-GAL ; et pour la couleur : PPO et PAL) ont été étudiés. Ces travaux ont montré que durant 9 jours à 6 °C, le traitement thermique maintient principalement la couleur par réduction de l’activité de la PPO et réduit la perte en fermeté par réduction de l’activité des enzymes pectolytiques (PME et b-GAL). Par ailleurs, les atmosphères modifiées semblent moins efficaces pour le maintien de la couleur et de la fermeté des mangues 4ème gamme. L’association du traitement 50°C/ 30 min avec une conservation sous atmosphère modifiée apporte peu d’effets additionnels et a même parfois un effet inhibiteur / The storage of fresh-cut mangoes is limited by the enzymatic browning and the loss of firmness due to the various operations of process. This work proposes a new approache to improve the storage of fresh-cut mangoes by: application of heat treatments by dipping with, or not, a storage under modified atmosphere: passive or active (5% O2 - 5% CO2) or using coatings (chitosane). The first step of this work was to determine the traitement 50 °C/30 min as an optimal treatment which maintian the quality of several varieties of mango (Keitt, Kent, Tommy Atkins). Effects of the heat treatment on the respiratory intensity, the color, firmness, the contents antioxydants: vitamin C, carotenoids and phenols total, and on the activity of several enzymes (PME, PG, b-GAL: for firmness; and PPO and PAL for colour changes) were studied. This work showed that during 9 days at 6 °C, the heat treatment maintains mainly the color by reduction of the activity of PPO and reduces the loss in firmness by reduction of the activity of the pectolytic enzymes (PME et b-GAL). In addition, the modified atmospheres seem less effective for the maintenance of the color and the firmness of freshcut mangoes. Combination of heat treatment with a modified atmosphere storage and have less additional effects and has even sometimes an inhibiting effect

Thesis (MSc. Agriculture (Horticulture)) -- University of Limpopo, 2018 / Newly developed mandarin selection ―M37‖ has the potential to become a future export soft citrus cultivar. However, the selection is highly susceptible to chilling injury, which normally reduces post-storage quality and marketability of citrus fruit. Silicon (Si), applied at post-harvest as potassium silicate (K2SiO3), has potential to mitigate against chilling injury. So far, the effect of Si on ―M37‖ mandarin chilling susceptibility is unknown. Therefore, the aim of the study was to investigate the effect of cold storage temperature and postharvest potassium silicate dips on the chilling susceptibility and physico-chemical properties of new mandarin selection ―M37‖ fruit. The experiment was carried out in a factorial, arranged in a completely randomised design (CRD) with three replicates. Treatment factors were: 2 x cold storage temperature (-0.6±1 and 4.5 ±1°C) and 4 x potassium silicate concentration (0, 50, 100 and 150 mL L-1 K2SiO3). Fruit were dipped in different potassium silicate solutions (0, 50, 100 and 150 mL L-1) for 30 minutes, air dried, waxed; and thereafter, stored for 28 days at -0.6 and 4.5°C with 85-90% relative humidity. After withdrawal from cold storage, fruit were held at ambient temperature (±23°C) for 7 days (shelf-life); during shelf-life fruit were evaluated for chilling injury, physical properties (weight loss and firmness loss) and biochemical properties (electrolyte leakage, total soluble acids (TSS), titratable acids (TA) and TSS: TA ratio). The results showed that fruit were highly susceptible to chilling injury after storage at 0.6°C when compared with 4.5°C. However, treating fruit with postharvest potassium silicate dips improved their chilling susceptibility, especially with 50 and 100 mL L-1 K2SiO3 concentrations. Electrolyte leakage was lower for fruit treated with K2SiO3 compared to the control across all the storage temperatures. Although, ―M37‖ fruit stored at 4.5°C showed higher weight loss, firmness loss, TSS and TSS: TA ratio when compared with -0.6°C storage. Fruit firmness increased with the increase in potassium silicate concentrations during storage at -0.6 and 4.5°C; with the highest firmness loss occurring on fruit treated with 150 mL L-1 than control. Similarly, TSS increased concomitant with K2SiO3 concentration. Although, TA decreased with increasing K2SiO3 concentrations for fruit stored at 4.5°C; resulting in higher TSS: TA ratio. In conclusion, postharvest silicon dips effectively improved the storability of ―M37‖ mandarin fruit, preserved quality and extended the cold storage period. xi Keywords: Biochemical properties; Chilling injury; Firmness loss; Potassium silicate dips; Weight loss / Agricultural Research Council (ARC-LNR) and National Research Fund (NRF)