Browsing by Subject "Fruit storage"

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Effects of a two-factorial dynamic storage system on apple fruit metabolism, quality attributes, disorder incidences and biochemical properties
(2024) Büchele, Felix; Vögele, Ralf; Kittemann, Dominikus
Dynamic Controlled Atmosphere (DCA) technologies are designed to monitor the metabolism of fruit as a function of time and the oxygen partial pressure (pO2) in the storage atmosphere. By identifying signals sent by the fruit in response to low oxygen stress, this concept allows defining the lowest oxygen level tolerated by the fruit material and the specific and transient pO2, which is proposed to slow down the aerobic respiration of the fruit to a minimum and accordingly the ripening-related loss of fruit quality. This work examines a novel storage technology for pome fruit referred to as DCA-CD+, which can be considered the first generation of a two-factorial dynamic storage system. DCA-CD+ aims to define both a transient optimum pO2 and storage temperature in real-time, based on monitoring the carbon dioxide (CO2) production rate of the stored product. The CO2-release rate is proposed as a dependable indicator of low oxygen stress and an accurate depiction of the metabolic intensity of the fruit in response to temperature variations. The idea behind dynamic temperature adjustments is based on the assumption, that increased storage temperatures can reduce the energy usage of the refrigeration systems during long-term storage substantially, while also mitigating oxidative stress in the fruit, thus contributing to reducing the occurrence of storage disorders. The extremely low pO2 levels established in the storage atmosphere are suggested to counteract the ripening-inducing effects of this dynamic temperature approach. The assessment of DCA-CD+ in this work is based on a comparison to other postharvest conditions such as cold storage (RA) or static controlled atmosphere (CA). Furthermore, the interactions between storage atmosphere, temperature, and applications of the ethylene-inhibitor product 1-methylcyclopropene (1-MCP) are investigated. The conducted biochemical analyses highlight that apples stored under DCA-CD+ undergo repeated periods of hypoxia. Fruit adapt to the energy crisis induced by low oxygen stress by increasing their glycolytic flux, which is coupled to the activation of the fermentative pathway. Importantly, none of the examined apple cultivars in any of the experimental seasons exceeded critical thresholds for volatile fermentative products acetaldehyde (AA) and ethanol (EtOH), which could potentially be associated with the development of off-flavors or internal disorder symptoms. Consequently, the atmospheric conditions implemented did not result in any fruit damage associated with low oxygen stress in any of the tested scenarios. These findings suggest that DCA-CD+, specifically the use of carbon dioxide as an input value, is effective in identifying low oxygen stress in stored fruit and defining the pO2 for optimum quality conservation. pO2 setpoint calculation by the DCA-CD+ algorithm showed an interaction effect with the respective storage temperatures. Furthermore, the sensitivity of the stored fruit to temperature variation was found to be cultivar-dependent and transient during the storage period. Depending on the stored apple cultivar and season, DCA-CD+ calculated temperature setpoints reaching up to 3°C to 4°C, from the baseline temperature of 1°C. Temperature peaks were generally followed by a significant decrease in the calculated temperature setpoints, as an increased CO2 production rate signaled an intensifying fruit metabolism due to elevated storage temperature. The analysis of quality-defining parameters and disorder symptoms support the conclusion that DCA-CD+ allows for dynamic temperature adjustments without accelerating fruit ripening and the associated loss of quality. Preliminary findings indicate that this approach can reduce the energy usage of the cooling system in commercial storage rooms, without requiring cost-intensive additional installation of technology or renovations of room structural components. Lower pO2 setpoints were calculated at higher temperatures, suggesting that increasing the storage temperature can contribute to alleviating low oxygen stress in apples. Improved conservation of fruit quality attributes and a reduction in storage disorder incidences of DCA-CD+ in comparison to CA could be demonstrated in some instances, contingent on experimental season and apple cultivar. These benefits presumably become more pronounced with extended storage durations exceeding eight months. Ultimately, it can be argued that the complementary and interactive effects of dynamic temperature and oxygen in DCA-CD+ with 1-MCP application provide the highest potential for fruit quality conservation, limiting storage disorder, and reducing cooling-related energy usage. DCA-CD+ was demonstrated to potentially counteract detrimental effects of 1-MCP applications, e.g. an increased risk of carbon dioxide injuries. This work aimed to contribute to understanding the mechanisms behind the interference of the established temperature and atmospheric conditions in the DCA-CD+ system with the volatile aroma profile of apples. It was demonstrated that the synthesis capacity of volatile organic compounds (VOC) is primarily suppressed on a principal substrate level, and less in the later conversion of aldehydes to alcohols and esters. The pathways for the synthesis of linear volatiles originating from fatty acids were determined more responsive to low oxygen environments, in comparison to the pathways of branched volatiles derived from amino acids. Further insights were gained into the physiological mechanisms underlying the activation of the fermentative pathway, suggesting it functions as an adaptation mechanism not exclusively linked to low oxygen stress. Moreover, efforts were made to establish a connection between ripening and disorder-related modifications in cell structural components and associated alterations in the volatile profile, primarily highlighting the role of the lipoxygenase pathway. Statistical classification demonstrated that the repeated induction of low oxygen stress in DCA-CD+ storage resulted in a distinct volatile profile and a higher association with aroma defining compounds compared to CA storage. The observed increased EtOH accumulation is discussed to mitigate the ripening-inducing effects of the hormone ethylene, while also providing additional substrate for the synthesis of ethyl esters. Preliminary findings of this work indicate that storage temperatures can play a role in the aroma development of stored apples, even when low pO2 conditions are established. In summary, this study created a comprehensive documentation of the commercial viability of two-factorial dynamic storage systems for pome fruit and provided insights into the metabolomic responses of apples to extremely low oxygen levels, particularly in interaction with dynamic storage temperature adjustments.
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.