EFFECT OF COOL-STORAGE DELAYS AFTER HARVEST ON THE EXTENT OF RIPENING DURING AND FRUIT QUALITY AFTER COOL-STORAGE

Abstract

Sensation and Tommy Atkins mangoes were placed in cool-storage at 12.SoC for 28 days 12,36,60 or 84 hours after harvest. The fruits were held at 20°C prior to and after cool-storage. On fruit ripening after cool-storage, shelf-life and various fruit quality attributes were assessed. In Sensation, pulp penetration pressure, pulp colouration, and total soluble solids content were assessed on fruit placement in cool-storage and one week after the commencement of cool-storage. Shelf-life decreased markedly with the delay in time of fruit placement in cool-storage. In Sensation, ripening rate during the initial period of cool-storage increased with the delay prior to cool-storage. On fruit ripening, the incidence of lenticel damage in Tommy Atkins and Sensation generally increased with the delay prior to cool-storage. The trend was non-significant in Sensation. In this cultivar, taste appeal tended to decrease slightly with the delay prior to cool-storage. A similar trend was not apparent in Tommy Atkins. In Sensation and Tommy Atkins, differences in ground skin colouration, total soluble solids content, pH, pulp colouration and physiological disorder severity relating to treatment were not apparent. In Sensation, differences relating to treatment in disease, blotch and surface scald were not evident. These disorders did not occur in Tommy Atkins. The present study shows that unduly time delays in placing fruits in cool-storage after harvest can result in fruit being soft on arrival at ports and distributors overseas. Differences in the time taken from harvest until mangoes are placed in cool-storage after packline treatment, sorting and packing were identified by the author as a possible cause for differing outcomes in terms of fruit ripeness and quality after extended cool-storage (sea export of mangoes to Europe). Ripening during transit to the extent of the fruits being soft on arrival is unacceptable, since soft fruits are unsuitable for further distribution due to their reduced tolerance to handling and propensity to rapid deterioration. Degree of ripening during cool-storage and extent of disease manifestation during and after cool-storage were previously shown to be positively correlated (Oosthuyse, 1994). The aim of the present study was to assess the effect of various delays in time from harvest until fruit placement in cool-storage on the rate of ripening during cool-storage, and shelf-life (time taken for fruit to attain the stage of firm ripeness) and fruit quality after cool-storage. Two similar experiments were performed, one using Sensation and the other using Tommy Atkins. Forty 4 kg cartons of mangoes of each cultivar were harvested in the Letsitele Valley during the 1996/97 harvest season. Signs of pulp colouration were evident at the times of harvest. The fruit of each cultivar were treated identically, except that ripening rate during the initial period of cool-storage was not assessed in Tommy Atkins. The following was performed: After washing (1% Bi-Prox soap solution), hot-water treatment (S min. water dip at SO°C), prochloraz treatment (180 ml Omega/lOOl H20 ambient dip), and waxing with TAG, the fruits were repacked into their cartons. The treatments (time delays until placement in cool-storage) were randomly allocated to each carton (allocation according to the randomized complete blocks design). Twelve hours after harvest, 10 of the cartons were placed in cool-storage (12.SoC ±O.S°C). The remaining cartons were placed in a laboratory maintained at 20°C (±1°C). Thirty six, 60 or 84 hours after harvest, a further 10 cartons were placed in cool-storage. All of the fruit were put in the same cool-storage room, and remained in cool-storage for the same period of time (28 days). To assess the extent of ripening of Sensation during the first week of cool-storage, pulp penetration pressure, pulp colouration and total soluble solids content were determined on placement of the fruit in cool-storage and one week after the commencement of cool-storage. Two fruit per carton were removed for evaluation at each of these times. Pulp penetration pressure was measured with a Facchini FT 327 penetrometer to which the 6 mm plunger was attached. Each mango was first cut through twice; 'longitudinally' along the flattened margins of the seed. A measurement was taken from the centre of the exposed pulp of each of the 'cheeks' thus obtained. Total soluble solids content