Reveal the relationship between the quality and the cuticle composition of Satsuma mandarin (Citrus unshiu) by postharvest heat treatment

To investigate the influence of heat treatment (HT) on Satsuma mandarin fruit's postharvest quality and cuticle composition, we immersed the fruit for 3 min in hot water at 52°C and subsequently stored them at room temperature (25°C) for 28 days, and fruit quality parameters, such as good fruit rate, weight loss rate, firmness, total soluble solids, total titratable acidity, and ascorbic acid content, were monitored. Additionally, changes in the peel's cuticle composition were analyzed, and wax crystal morphologies on the fruit surface were examined using scanning electron microscopy (SEM). The findings revealed that appropriate HT effectively preserved fruit quality. The main compositions of wax and cutin on the fruit's surface remained consistent between the HT and the CK during storage. The total content of wax and cutin initially increased, peaking on the 14th day of storage, and then decreased, falling below the levels observed on day 0. Notably, the total amount of cutin in the HT group exceeded that of the control group. Specifically, ω-hydroxy fatty acids with mid-chain oxo groups and mid-oh-ω-hydroxy fatty acids constituted approximately 90% of the total cutin content. Moreover, the HT group exhibited higher (p < 0.05) total wax content in relation to the control. Fatty acids and alkanes were the predominant components, accounting for approximately 87.5% of the total wax. SEM analysis demonstrated that HT caused wax crystals to melt and redistribute, effectively filling wax gaps. It suggests that HT holds promising potential as a green, safe, and eco-friendly commercial treatment for preserving the postharvest quality of Satsuma mandarin. PRACTICAL APPLICATION: In this study, Satsuma citrus (Citrus unshiu) underwent heat treatment (HT) and was subsequently preserved at room temperature (25°C) for 28 days. The findings revealed that HT significantly improved fruit quality compared to the control group. These findings provide valuable insights into the advancement of eco-friendly and pollution-free citrus preservation methods, offering essential strategies and process parameters for their practical application.

Controle de doenças fúngicas e de danos por frio em pós-colheita de lima ácida Tahiti

A lima ácida Tahiti apresenta-se muito susceptível ao ataque de doenças pós-colheita e, também, por sua elevada sensibilidade, ao armazenamento em baixas temperaturas. Com a finalidade de reduzir estes danos, este trabalho objetivou verificar a eficiência do tratamento térmico na desinfestação de patógenos e na prevenção de danos por frio na pós-colheita deste cultivar e comparar este tratamento com outros utilizando os fungicidas convencionais. Os tratamentos térmicos estudados foram com água quente variando as temperaturas entre 48 a 56° C. A testemunha consistiu de tratamento com água em temperatura ambiente. Depois de tratados, os frutos foram divididos em dois lotes e mantidos em câmara fria com temperatura de 10° C e UR de 90%, por aproximadamente 45 dias. Para comparação foram feitos três outros tratamentos simultaneamente: um utilizando imazalil, outro com bicarbonato de sódio e o terceiro com carbonato de sódio, sendo as aplicações destes três produtos feitas em banhos com água em temperatura ambiente. Foram avaliados 2 grupos de frutos, um tratado por imersão considerando os patógenos oriundos do campo, e outro por inoculação com esporos dos fungos previamente isolados. Os parâmetros físico-químicos dos frutos avaliados foram a coloração da casca, a textura, a perda de massa, o tamanho, o rendimento de suco, de sólidos solúveis, o °brix, o ratio, a acidez total e a vitamina C. A determinação da sensibilidade dos frutos ao frio foi feita pela exposição deles a temperaturas indutoras de dano por frio. O delineamento experimental utilizado foi blocos ao acaso, com nove tratamentos, analisado pelo pacote estatístico Statgraphics. Verificram-se que os tratamentos térmicos, principalmente a 52° C, mostraram-se mais promissores no controle de fungos patogênicos e de danos por frio, superando os resultados obtidos nos tratamentos com fungicidas convencionais. Não se verificaram-se alterações dos parâmetros intrínsecos e extrínsecos em função da aplicação dos diferentes tratamentos.

Expression of ACO1, ERS1 and ERF1 genes in harvested bananas in relation to heat-induced defense against Colletotrichum musae

The aim of this study was to investigate the connection between heat-induced ethylene signal changes and enhanced disease resistance. Heat enhanced ripening and elevated MaACO1 expression in naturally ripened bananas (NRB), while it delayed ripening and reduced MaACO1expression in the ethephon-treated bananas (ETB). However, in both cases, heat reduced lesion sizes infected by Colletotrichum musae. This indicates that heat-induced disease resistance in bananas was independent of ripening rate. The expression of MaERS1 gene was inhibited by heat treatment in both NRB and ETB, implying that heat as a physical signal could be sensed by banana fruits through the inhibition of ethylene receptor gene expression. The intensity of MaERF1 transcript signals was elevated in heated bananas, suggesting that the enhanced accumulation of MaERF1 transcript following heat treatment could play an important role in activation of the defense system. In ETB, inhibition of JA biosynthesis by application of IBU down-regulated the expression of MaERF and significantly weakened disease resistance, suggesting involvement of endogenous JA in induction of the gene expression, which was reconfirmed by the fact that exposure to exogenous MeJA following the combination of heat plus IBU treatment restored part of the gene expression. On the other hand, in NRB, application of IBU elevated level of MaERF1 expression at 24h and enhanced disease resistance, suggesting that, when banana was not exposed to ethephon, the expression of MaERF1 gene was not JA dependent, which was verified by the fact that MeJA application did not enhance MaERF1 gene expression. In conclusion, heat-induced disease resistance in harvested bananas could involve down-regulation of MaERS1 expression and up-regulation of MaERF1 expression and JA pathway could be involved in heat activation of the defense system in bananas exposed to ethephon.

Immersion of lemons into imazalil mixtures heated at 50 degrees C alters the cuticle and promotes permeation of imazalil into rind wounds

The influence of the immersion of lemon fruit in aqueous imazalil (IMZ) mixtures at 25 or 50 degrees C on the deposition and persistence of IMZ within the fruit rind and its effectiveness in controlling postharvest green mold, caused by Penicillium digitatum, was investigated. Concentrations of IMZ in the albedo tissue surrounding deep wounds in the rind were higher than the mean EC50 values for IMZ-resistant strains (1.0 microg *mL(-1)) after immersion of fruit into IMZ mixtures containing 25, 50, or 75 mg* L(-1) heated to 50 degrees C, but not those at 25 degrees C, where fungicide deposition was insufficient. IMZ residue, one day after treatment with 25, 50, or 75 mg* L(-1), was 3, 5, or 7 times higher after treatment at 50 degrees C compared to treatment at 25 degrees C. IMZ residues within the albedo of unwounded fruit treated with 25, 50, or 75 mg* L(-1) at 50 degrees C were 0.8, 1.3, or 2.0 microg * g(-1), respectively, while those similarly treated at 25 degrees C had negligible residues. Residues following treatment at 50 degrees C in the albedo did not decline during storage at 10 degrees C after 60 days. IMZ residues in the flavedo were higher than those in the albedo: after treatment with 25, 50, or 75 mg* L(-1) IMZ, they averaged 1.0, 1.2, or 2.7 microg * g(-1), respectively, after treatment at 25 degrees C, and 5.5, 7.9, or 16.2 microg * g(-1), respectively, after treatment at 50 degrees C. IMZ effectiveness as an eradicant to control green mold improved when it was heated. Green mold was reduced by 22 or 95% after treatment of lemons inoculated 1 h before immersion of lemons in IMZ at 50 mg* L(-1) at 25 or 50 degrees C, respectively. Green mold was reduced by 18 or 61% after treatment of lemons inoculated 1 day after immersion of lemons in IMZ at 50 mg* L(-1) at 25 or 50 degrees C, respectively. Scanning electron microscopy of the rind surface indicated that treatment at 50 degrees C for 2 min also caused ruptures in the cuticle.

Improved Control of Green Mold of Citrus with Imazalil in Warm Water Compared with Its Use in Wax

The effectiveness of imazalil for the control of citrus green mold (caused by Penicillium digitatum) improved significantly when fruit were treated with heated aqueous solutions of the fungicide as compared with the current commercial practice of spraying wax containing imazalil on fruit. When applied at less than 500 μg·ml^-1 in solutions heated to 37.8°C, control of postharvest green mold of citrus was significantly superior to applications of 4,200 μg·ml^-1 imazalil in wax sprayed on fruit at ambient temperatures. The improvement in imazalil efficacy was obtained with a decrease in fungicide residues on the fruit. Residues of about 3.5 μg·g^-1 imazalil deposited by the application of imazalil in wax reduced the incidence of green mold on lemons from 94.4% among untreated controls to 15.1%, whereas an equal residue deposited by passing fruit through heated aqueous imazalil reduced green mold incidence to 1.3%. Similar differences were found in tests with oranges. Residues of 2 and 3.5 μg·g^-1 imazalil were needed to control the sporulation of P. digitatum on oranges and lemons, respectively. The mode of application of imazalil did not influence control of sporulation. The influence of immersion time, imazalil concentration, and solution temperature on imazalil residues on oranges and lemons was determined in tests using commercial packing equipment, and a model that describes residue deposition was developed. Residues after a 30- or 60-s treatment in heated aqueous imazalil were sufficient to control sporulation, but residues after 15-s treatments were too low and required an additional application of 1,070 μg·ml^-1 imazalil in wax to deposit an amount of imazalil sufficient to control sporulation. An imazalil-resistant isolate of P. digitatum was significantly controlled by heated aqueous imazalil. The incidence of green mold of navel oranges was reduced from 98.8 to 17.4% by treatment in 410 μg·ml^-1 imazalil at 40.6°C for 90 s. However, control of the resistant isolate required imazalil residues on the fruit of 7.9 μg·g^-1, which is within the U.S. tolerance of 10 μg·g^-1 but above the 5 μg·g^-1 tolerance of some countries that import citrus fruit from the United States.