Tesi etd-04222024-113536
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Tipo di tesi
Dottorato
Autore
SALAME, ELIGE
URN
etd-04222024-113536
Titolo
Dissecting the effects of dynamic controlled atmosphere (DCA) and postharvest hypoxic stress on ‘Red delicious’ apple fruit physiology.
Settore scientifico disciplinare
AGR/03
Corso di studi
Istituto di Scienze della Vita - PHD IN AGROBIOSCIENZE
Commissione
relatore Prof. TONUTTI, PIETRO
Parole chiave
- Nessuna parola chiave trovata
Data inizio appello
07/10/2024;
Disponibilità
parziale
Riassunto analitico
Dynamic Controlled Atmosphere (DCA) storage is an innovative technology used for the long-term preservation of apples. Unlike traditional Controlled Atmosphere (CA) storages, DCA involves a dynamic adjustment of the atmospheric conditions, according to the real-time monitoring of the physiological status of the fruit, to extend shelf-life while minimizing physiological disorders and decay. Various kind of sensors are employed to measure physiological indicators such as Respiration quotient (DCA-RQ), Ethanol accumulation (DCA-Eth), Chlorophyll fluorescence (DCA-CF), and CO2 production (DCA-CD). DCA techniques allow extreme levels of oxygen to be applied during storage, potentially also causing adverse effects on fruit tissues by inducing excessive anaerobic metabolism and the production of off-flavors. Thus, the importance of understanding the mechanisms involved in the physiological responses and adaptations to extreme hypoxic levels, and the fruit sensitivity to dynamic changes in oxygen levels in relation with time.
‘Red Delicious’ apple (Malus domestica Borkh.) is one of the most widely cultivated and consumed apple varieties globally. However, they are especially prone to accumulate higher amounts of ethanol and develop storage disorders during long-term hypoxic storage compared to other apple varieties. For these reasons, the main objective of the study was to evaluate the effectiveness of DCA protocols for ‘Red delicious’ long-term cold storage. Therefore, along three consecutive seasons (2020-2022) fruits were stored under extreme low oxygen concentrations 0.3% and 0.8% for a period of 6 to 7 months. To simulate the oxygen dynamics under DCA protocols, fruits that were stored under 0.3% and were then transferred to 0.8% (an oxygen concentration considered safer) at different interval of times to study the response of the fruit to re-oxygenation events applied with different timing, simulating the oxygen shifts normally applied in DCA protocols. During the first season, four shifts in oxygen were made, starting after 10, 20, 30 and 110 days in 0.3% oxygen. Fruit pulp and peel were studied separately, and quality parameters (firmness, TSS, color), molecular responses (gene expression and transcriptomics), in addition to metabolomics (VOCs, polyphenols, hormones, amino acids, sugars, and acids content) were investigated with the aim of characterizing ‘Red delicious’ response to the imposed storage conditions in order to identify the most suitable protocol for long-term storage of this variety, preserving the best possible quality and minimizing losses. In the first season our results showed that the earlier shift in oxygen (from 0.3 to 0.8% oxygen) was more effective in maintaining fruit firmness, reducing accumulation of ethanol compared to samples stored under static 0.3% where ethanol content reached the highest levels (around 400 mg/kg FW). However, these samples showed higher accumulation of MDA (reflecting higher oxidative stress) compared to the later shifts of oxygen concentration that accumulated less fermentative by-products but also had lower firmness at the end of the storage. Primary metabolism and ethylene physiology were markedly affected. Ethylene biosynthesis genes showed marked differences in their expression in relation to the static and dynamic protocols applied. Based on our findings, the following season, fruits were monitored under normoxic condition (21% oxygen) to check the normal ripening process under cold storage, as well as under 0.3% with only one intermediate oxygen shift to 0.8%, made after 30 days that compromised the excessive fermentation, oxidative stress, and loss of firmness. To investigate potential post-storage alterations in sensitivity to ethylene, after storage fruits from all the different tested protocols were treated with 10 ppm ethylene for 6 hours and monitored for 13 days during shelf-life at room-temperature. Results showed a higher accumulation of ethanol under 0.3% but also fruits exhibited decay symptoms after 6 months. Oxygen shift significantly lowered ethanol production and also lower levels of MDA have been detected, together with lower content of amino acids from the pyruvate family (e.g., alanine) and higher aromatic amino acids.
Overall, our data showed that after the exposure to extreme low oxygen levels (0.3%), the shift to higher (safer) levels results in lower accumulation of ethanol and fermentative precursors and by-products, in addition to a better maintenance of firmness and a reduced decay incidence with an unambiguous, holistic, and specific regulation of the metabolism starting from transcriptomics to secondary metabolism.
‘Red Delicious’ apple (Malus domestica Borkh.) is one of the most widely cultivated and consumed apple varieties globally. However, they are especially prone to accumulate higher amounts of ethanol and develop storage disorders during long-term hypoxic storage compared to other apple varieties. For these reasons, the main objective of the study was to evaluate the effectiveness of DCA protocols for ‘Red delicious’ long-term cold storage. Therefore, along three consecutive seasons (2020-2022) fruits were stored under extreme low oxygen concentrations 0.3% and 0.8% for a period of 6 to 7 months. To simulate the oxygen dynamics under DCA protocols, fruits that were stored under 0.3% and were then transferred to 0.8% (an oxygen concentration considered safer) at different interval of times to study the response of the fruit to re-oxygenation events applied with different timing, simulating the oxygen shifts normally applied in DCA protocols. During the first season, four shifts in oxygen were made, starting after 10, 20, 30 and 110 days in 0.3% oxygen. Fruit pulp and peel were studied separately, and quality parameters (firmness, TSS, color), molecular responses (gene expression and transcriptomics), in addition to metabolomics (VOCs, polyphenols, hormones, amino acids, sugars, and acids content) were investigated with the aim of characterizing ‘Red delicious’ response to the imposed storage conditions in order to identify the most suitable protocol for long-term storage of this variety, preserving the best possible quality and minimizing losses. In the first season our results showed that the earlier shift in oxygen (from 0.3 to 0.8% oxygen) was more effective in maintaining fruit firmness, reducing accumulation of ethanol compared to samples stored under static 0.3% where ethanol content reached the highest levels (around 400 mg/kg FW). However, these samples showed higher accumulation of MDA (reflecting higher oxidative stress) compared to the later shifts of oxygen concentration that accumulated less fermentative by-products but also had lower firmness at the end of the storage. Primary metabolism and ethylene physiology were markedly affected. Ethylene biosynthesis genes showed marked differences in their expression in relation to the static and dynamic protocols applied. Based on our findings, the following season, fruits were monitored under normoxic condition (21% oxygen) to check the normal ripening process under cold storage, as well as under 0.3% with only one intermediate oxygen shift to 0.8%, made after 30 days that compromised the excessive fermentation, oxidative stress, and loss of firmness. To investigate potential post-storage alterations in sensitivity to ethylene, after storage fruits from all the different tested protocols were treated with 10 ppm ethylene for 6 hours and monitored for 13 days during shelf-life at room-temperature. Results showed a higher accumulation of ethanol under 0.3% but also fruits exhibited decay symptoms after 6 months. Oxygen shift significantly lowered ethanol production and also lower levels of MDA have been detected, together with lower content of amino acids from the pyruvate family (e.g., alanine) and higher aromatic amino acids.
Overall, our data showed that after the exposure to extreme low oxygen levels (0.3%), the shift to higher (safer) levels results in lower accumulation of ethanol and fermentative precursors and by-products, in addition to a better maintenance of firmness and a reduced decay incidence with an unambiguous, holistic, and specific regulation of the metabolism starting from transcriptomics to secondary metabolism.
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