Browsing by Subject "Controlled atmosphere"

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Optimizing pome fruits storage
(2024) Balkees, Basem Mahmoud; Zörb, Christian
Horticultural perishables are prone to fast deterioration and high losses. As the volume of production increases, further challenges are imposed to preserve these valuable foods in terms of quantity and quality. Accelerated development in science and applied technologies has helped to radically prolong the useful post-harvest life of horticultural produce. Notable success has been achieved with apples and pears as a result of their comparatively higher storability. Effective procedures and techniques have been developed to handle these fruits, including pre- and post-harvest physical and chemical treatments, in conjunction with the cutting-edge storage systems. However, certain procedures cannot be universally applicable. Considerations such as genotypic differences, climatic variations, and production factors necessitate adaptation of post-harvest practices to accommodate changing variables. This thesis describes the findings of experiments conducted as a contribution to advance preservation practices for apples and pears. Furthermore, we sought to investigate the biological actions underlying changes in fruit quality during storage and how these were influenced by various treatments. The first experiment was conducted to preserve the quality of late-harvested ‘Galaxy’ apples during extended storage. The effects of 1-methylcyclopropene (1 MCP) treatment and storage conditions on postharvest quality were analysed. Alongside quality measures, indicators like ethylene production, respiration rate, 1 aminocyclopropane-1-carboxylic acid oxidase (ACO) activity, and membrane permeability were assessed. After 7 months storage and 7 days shelf-life, apples subjected to 1-MCP and controlled atmosphere (CA) exhibited reduced ethylene production, respiration rate, and ACO activity compared to untreated or regular atmosphere counterparts. The combination of controlled atmosphere and pre-storage 1 MCP was the most effective in lowering ACO activity. Irrespective of conditions, 1 MCP curtailed ethylene production, respiration rate, and ACO activity during shelf-life, maintaining fruit firmness and slowing acidity loss. Only controlled atmosphere preserved quality and minimized disorders for optimally harvested apples, not late-harvested ones. None of the treatments maintained late-harvested apples quality after long-term storage plus shelf-life. The second experiment evaluated the effects of two ethanol vapor doses (250 or 500 ppm) or 1 MCP (650 ppb) with or without ethylene application (150 ppm) on the metabolism and quality of the apple cultivars ‘Elstar’ and ‘Nicoter’, over 14 d of holding at room temperature (20 ± 2 °C). For both cultivars studied, ethanol vapor treatments, especially 500 ppm, slowed the ripening of apples and inhibited the effect of applied ethylene on the ethylene production and respiration, but not as much as the 1 MCP treatment in ‘Nicoter’ apples. Ethanol application also resulted in higher succinate, malate and total organic acids concentrations. Ethanol application significantly reduced the sucrose conversion to glucose and fructose, while the ethanol + ethylene treatment resulted in high total sugars, fructose and sorbitol concentration after 14 d at 20 °C. The ethanol application (500 ppm) also affected conversion of succinate to fumarate, suggesting the succinate dehydrogenase activity as one possible action point of ethanol on the apple fruit metabolism. The combination of ethanol + ethylene treatments had a different response as compared to their isolated application, affecting sugars and organic acids metabolism differently. Fruit treated with ethanol vapor maintained lower electrolyte leakage, higher flesh firmness, greener color and had more sound fruit. However, its application increased the pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) activity and also enhanced acetaldehyde and ethyl acetate accumulation, but in concentrations below the odor threshold reported in the literature. The 1-MCP treatment increased decay incidence compared to the other treatments, reducing the amount of sound fruit in ‘Nicoter’ apples, but allowed higher acidity maintenance after 14 d holding at room temperature. There was no incidence of external and internal physiological disorders in either of the cultivars. In a third experiment, we explored the effects of the interaction between controlled atmosphere and 1-MCP treatment on ‘Alexander Lucas’ pears in storage, aiming to minimize internal storage disorders. Following treatment with 1-MCP at 300 ppb, the fruit were stored either at -0.5 or 1.0 °C in regular air or in CA (2.0 kPa O2 plus <0.7 kPa CO2). After six months of storage, superficial scald did not develop in fruit. The highest occurrence of flesh browning (72.2 %) was observed in air-stored fruit at -0.5 °C without 1-MCP treatment. Storage in regular air at 1.0 °C combined with 1-MCP resulted in 88.8 % sound fruit. Conversely, 1-MCP increased the incidence of flesh and core browning under CA conditions. Both 1-MCP and CA maintained greener skin color and higher titratable acidity. No significant differences were found for fruit firmness, total soluble solids and ascorbic acid content between the treatments. In conclusion, the quality of ‘Alexander Lucas’ pear was best maintained during six months storage under regular air at 1.0 °C combined with 300 ppb 1-MCP treatment.