Postharvest Stress Research Articles

Argovit™ silver nanoparticles transform agro-waste into phenolic biofactories: Postharvest stress for high-value compound production in prickly pear peels

The growing demand for food has resulted in an increased generation of plant waste residues. These waste materials contain various bioactive compounds, but their concentrations are typically low, rendering their extraction economically unviable. In this study, we assessed the impact of abiotic stress induced by silver nanoparticles (AgNPs) on the compounds derived from red and green prickly pear peels. Six different AgNP lots were tested at varying concentrations. The total phenol content was consistently higher than that of the control group across all lots. Notably, the AgNP systems exhibited selectivity in inducing the formation of specific compounds, such as caffeic (10.36%), vanillic (6.71%), p-coumaric (6.63%), malic (4.86%) acids, and catechin (46.15%). Moreover, the betanin content in red prickly pear increased by up to 2.4 times compared to the control group. However, the data analysis indicated a tendency towards increased variability in phenolic acids and flavonoids. This suggests that the AgNP systems might be activating these metabolic pathways. These findings are highly relevant as they demonstrate the potential of AgNP systems to enhance the accumulation of bioactive compounds in agro-industrial waste materials, which can then be utilized in the development of functional ingredients.

Quality improvement of lime fruit (Citrus aurantifolia) between packaged and unpackaged conditions combined with different storage temperatures

Background: The use of limes is increasingly widespread worldwide, both as fresh fruit for consumption and for making juice or other drinks. Lime is also used in making jams and candies. The essential oil obtained from the skin is widely used in the pharmaceutical and cosmetic industries for medicines, perfumes, soaps, body lotions, and detergents. However, during fruit storage, the respiration and metabolic activity in lime fruits is directly related to the increase in ambient temperature, which makes the fruit dry out. Improving the shelf life of lime against post-harvest stress while maintaining the sensory and nutritional qualities of fresh produce can be achieved through low-temperature storage and the use of packaging. This study aims to improve the quality of lime by knowing the difference between the provision of packaging and not-given packaging combined with different storage temperatures. Method: The experimental design used a single-factor completely randomized design with storage type treatment, which includes room temperature without packaging (control), room temperature with packaging, low temperature without packaging, and low temperature with packaging. Observations of non-destructive characteristics include weight loss, respiration rate, and fruit peel color. Observations of destructive characteristics include juice content, fruit peel softness, Soluble Solid Contents (SSC), Total Acidity (TA), SSC/TA ratio, and ascorbic acid content. Finding: Low temperature treatment without packaging provides the best results in delaying weight loss, respiration rate, and SSC/TA ratio. The control treatment provided the best results for peel softness, juice content, and ascorbic acid. Conclusion: Low temperature treatment without packaging is recommended for the storage of lime fruit to extend its shelf life. Novelty/Originality of this Study: This study examines the combined effects of low temperature and newspaper packaging on extending the shelf life of lime fruits, addressing a significant gap in postharvest storage research for non-climacteric fruits such as lime.

Relationship between Damages and other Postharvest Stress Factors Affecting Quality of Fruit and Vegetables

Stress is the main concern hindering the maintenance of postharvest quality of fruit and vegetables. From production to consumption, fruit and vegetables are subjected to various handling activities in which some of these activities result in damaging commodity which make them susceptible to stress through entire post-harvest period. Stresses mostly come from biological and environmental factors such as harvest conditions, temperature, relative humidity, and gas composition of storage environment, as well as metabolic activities and microbial infections which all correlate with damages for one way or another and bring about quality loss and shortening of commodity’s shelf life.

Gene-Based Developments in Improving Quality of Tomato: Focus on Firmness, Shelf Life, and Pre- and Post-Harvest Stress Adaptations

Gene-Based Developments in Improving Quality of Tomato: Focus on Firmness, Shelf Life, and Pre- and Post-Harvest Stress Adaptations

The promoters of two CpMYB106-like paralog genes respond to abiotic stresses and phytohormones and drive differential expression in contrasting cultivars of Cucurbita pepo

Zucchini fruit (Cucurbita pepo L.) is susceptible to chilling injury (CI) during its postharvest life, with this response being cultivar-dependent. A previous transcriptomic analysis comparing cold-tolerant fruit from the cultivar ‘Natura’ with cold-sensitive fruit from the cultivar ‘Sinatra’, revealed the transcription factor (TF) CpMYB106-like as a relevant candidate gene for the acquisition of postharvest low-temperature tolerance. C. pepo has two CpMYB106-like paralogs, which are differentially present in the ‘Natura’ (CpMYB106-likeA) and ‘Sinatra’ (CpMYB106-likeB) cultivars due to gene and promoter deletions. The aim of this study was to investigate the transcriptional regulation of the CpMYB106-like paralogs to unravel their role in the postharvest life of zucchini fruit. For this, gene expression was analyzed and promoter sequences and their activities were studied through reporter β-glucuronidase (GUS) gene analysis in heterologous systems. An expression analysis showed that CpMYB106-like mRNA levels were induced only in the cold-stored fruit of ‘Natura’. The analysis of the promoter sequences showed numerous cis-regulatory elements (CREs), many of which have a differential distribution or frequency between the two paralogs. Promoter basal activity was determined by transient transformation of Nicotiana benthamiana leaves, which showed a higher expression driven by the promoter from the cold-tolerant cultivar ‘Natura’, which could be explained by the presence of three additional copies of the enhancer element EECCRCAH1 in proMYB106A. The tissue-specific expression pattern, and the response to abiotic stresses and phytohormones controlled by CpMYB106-like promoters was analyzed in transgenic Arabidopsis thaliana plants. GUS activity was mainly detected in the vascular system, leaves, and inflorescences, especially in siliques. With respect to abiotic stresses, low temperature decreased GUS expression in Arabidopsis, but increased it in plants carrying the ‘Natura’ promoter after a 24-h acclimation period at 22 °C. Salt treatment induced GUS activity driven by both promoters in Arabidopsis seedlings, but it was higher with the ‘Natura’ promoter. Furthermore, methyl jasmonate (MeJA) also induced a sharp increase of GUS controlled by proMYB106A. These results suggest that the regulation of CpMYB106-like TFs in zucchini is promoter-driven, and reveal the involvement of these genes in the acquisition of cold tolerance in fruit during postharvest stress conditions.

Metabolomic and transcriptomic analyses identify external conditions and key genes underlying high levels of toxic glycoalkaloids in tubers of stress-sensitive potato cultivars.

High levels of toxic steroidal glycoalkaloids (SGAs) in potato tubers constitute a recognized food quality problem. Tuber SGA levels vary between potato cultivars and can increase after post-harvest stresses such as wounding and light exposure. A few cultivars, e.g., 'Magnum Bonum' and 'Lenape,' have been withdrawn from commercial sales due to excessive SGA levels during some cultivation years. However, these sudden SGA increases are diffucult to predict, and their causes are not understood. To identify external and genetic factors that underlie sudden SGA increases in certain potato cultivars, we have here in a 2-year study investigated 'Magnum Bonum' and five additional table potato cultivars for their SGA levels after wounding and light exposure. Results showed that 'Magnum Bonum' has an unusual strong SGA response to light exposure, but not to wounding, whereas 'Bintje' displayed an opposite regulation. Levels of calystegine alkaloids were not significantly altered by treatments, implicating independent metabolic regulation of SGA and calystegine levels also under conditions of high SGA accumulation. Metabolomic and transcriptomic analyses identified a small number of key genes whose expression correlated with SGA differences between cultivars. Overexpression of two key genes in transgenic low-SGA potato cultivars increased their leaf SGA levels significantly. The results show that a strong response to light can underlie the SGA peaks that occasionally occur in certain potato cultivars and indicate that a between-cultivar variation in the expression of single SGA key genes can account for cultivar SGA differerences. We propose that current attempts to mitigate the SGA hazard will benefit from an increased consideration of cultivar-dependent SGA responses to post-harvest conditions, particularly light exposure. The identified key SGA genes can now be used as a molecular tool in this work.

Üzüm Cibresinin Karanfil Çiçeklerinin Vazo Ömrüne Etkileri

In carnation, vase life is shortened due to ethylene and water stress, resulting in petal curling, browning, and wilting symptoms. Preservative solutions are used to prolong the vase life of cut flowers in the world, and natural substances with antimicrobial properties have been preferred as preservatives in recent years. It is thought that benefiting from the antimicrobial properties of plant wastes will be beneficial for both the cut flower industry and waste management because they are natural. This research was carried out to determine the effect of grape marc extract (GME) on the vase life of cut carnation. D. caryophyllus cv. 'Baltico' was used as a plant material. The plants were placed in vases containing two different concentrations of GME (100 µL L-1, 200 µL L-1). The vase life, relative fresh weight (RFW), daily solution uptake (DSU), lipid peroxidation, proline content, and antioxidant enzyme activities were measured during and at the end of the experiment. In the study, it was determined that GME was effective on the vase life of cut carnation flowers and GME at 200 µL L-1 concentration (22.67 days) extended the vase life by 6.50 days and 40.2% compared to the control (16.17 days), (distilled water). At the same time, GME was found to be effective on the post-harvest stress mechanisms of cut carnation flowers. GME improved vase life by increasing both DSU, and antioxidant enzyme activities, and reducing RFW loss. It also reduced the accumulation of MDA and proline.

Cold shock treatment delays broccoli flower bud yellowing by repressing the gene expression of glycine-rich RNA-binding protein 2, a senescence-associated protein involved in the regulation of stomata opening

Broccoli is a globally appreciated vegetable with high nutritional and market value. The quality of harvested broccoli deteriorates quickly due to senescence induced by postharvest stresses. Glycine-rich RNA-binding proteins (GR-RBPs) are RNA chaperones that mediate physiological processes such as stress responses in plants. However, knowledge about their presence and functions in broccoli is lacking. Here, through proteomic analysis we identified GR-RBP2 along with the other 49 senescence-associated proteins (SAPs) in broccoli florets. We further identified 8 GR-RBP genes, including BoGR-RBP2.1, BoGR-RBP2.2, BoCSP1.1, BoCSP1.2, BoCSP2, BoCSP3, BoCSP4.1, and BoCSP4.2, in broccoli transcriptome. The expression of these genes during 20 and 5 °C storage and in response to cold shock treatment (CST) was investigated. BoGR-RBP2.1, BoGR-RBP2.2, BoCSP1.2, BoCSP2, and BoCSP4.1 were upregulated during 20 °C storage, whereas the induction was diminished at 5 °C. CST suppressed the induction of BoGR-RBP2.1 and BoGR-RBP2.2 during 20 and 5 °C storage, respectively, while alleviating water loss and yellowing of broccoli florets stored under both conditions. In addition, scanning electron microscopy demonstrated that the enhanced stomata opening in broccoli florets coincided with BoGR-RBP2s induction, whereas CST restricted the opening in parallel with the repression of BoGR-RBP2s. BoCSP4.2 appeared to be a cold responsive gene induced by 5 °C storage, while it was less related to broccoli florets senescence. In conclusion, we show here that GR-RBP2 is an SAP involved in the modulation of stomata opening in broccoli florets and elucidate the regulation of GR-RBP genes during ambient temperature storage, refrigeration, and upon CST. These findings shed light on the study of RNA chaperones in postharvest stress.

Variations in oolong tea key characteristic floral aroma compound contents among tea (Camellia sinensis) germplasms exposed to postharvest stress

Tea (Camellia sinensis) germplasm affects the tea aroma quality, especially in oolong tea. However, the mechanism underlying the diversity in aroma formation induced by postharvest stresses among different tea cultivars remains unclear. In this study, correlation analyses between sensory evaluation scores and aroma compound contents of oolong teas made from 12 different cultivars was carried out. The results confirmed the contribution of three characteristic aroma compounds [i.e., indole, jasmine lactone, and (E)-nerolidol] to the oolong tea floral aroma quality. However, only the indole was positively correlated with the jasmonic acid (JA) in the simulated withering (wounding stress due to plucking) and turnover (continuous wounding stress) stages. Furthermore, the expression levels of transcription factor CsMYC2c and structural genes for the three aroma compounds were positively correlated in the simulated withering stage. Transient transcriptional activation analyses in tobacco revealed that CsMYC2c regulated the promoter activity and expression of structural genes. However, yeast one-hybrid assay showed that CsMYC2c did not directly bind to the gene promoters. The information has expanded our understanding of the causes for the variations in aromas among diverse tea cultivars in response to postharvest stress. Furthermore, it may provide the basis for breeding and selection of high-aroma tea cultivars.

APPLICATION OF OJIP CHLOROPHYLL FLUORESCENCE TRANSIENT ANALYSIS TO STUDY THE POSTHARVEST CHANGES IN PHOTOSINTHETIC APPARATUS IN CUT FOLIAGE SPECIES

Chlorophyll fluorescence (ChlF) is a non-invasive technique that can be potentially used in postharvest research to gain useful information on early responses to postharvest stresses. This study was conducted to validate the application of ChlF transient analysis in determining the postharvest changes in photosynthetic apparatus in three ornamental foliage species, i.e., Cordyline fruticosa ‘Willy’s Gold’ and ‘Rubra’, Dracaena sanderiana ‘White’, and Nephrolepis exaltata. Salicylic acid (100 and 300 mg·L−1), glucose (10 g·L−1), and their combinations were used as holding solutions with control treatment (distilled water) at room temperature (25±2°C). Vase life was evaluated using OJIP analysis. OJIP parameters, i.e., specific energy fluxes per reaction center (ABS/RC, TR/RC, ET/RC, and DI/RC), flux ratios (maximum quantum yield of primary photochemistry-φPo), electron transport efficiency (ψo), and quantum yield of electron transport (φEo), and performance index (PI) were recorded every other day, using a fluorometer (FluorPen 100). Leaf chlorophyll contents of all species and anthocyanin contents of two cordyline cultivars were determined. Data were subjected to ANOVA in a completely randomized design. Mean separation was done by DMRT (p ≤ 0.05). Clear variations in ChlF were observed in every foliage species with the time. OJIP analysis showed species-depended variations. The higher ABS/RC and DI/RC were recorded for D. sanderiana and N. exaltata compared to the PI of those species. At the end of the experiment, the chlorophyll contents were decreased, while anthocyanin contents were increased. Consequently, chlorophyll fluorescence changes in photosynthetic apparatus can be used for the prediction of the postharvest stresses and longevity of cut foliage.

Evaluation of Postharvest Senescence of Broccoli via Hyperspectral Imaging.

Fresh fruit and vegetables are invaluable for human health; however, their quality often deteriorates before reaching consumers due to ongoing biochemical processes and compositional changes. We currently lack any objective indices which indicate the freshness of fruit or vegetables resulting in limited capacity to improve product quality eventually leading to food loss and waste. In this conducted study, we hypothesized that certain proteins and compounds, such as glucosinolates, could be used as one potential indicator to monitor the freshness of broccoli following harvest. To support our study, glucosinolate contents in broccoli based on HPLC measurement and transcript expression of glucosinolate biosynthetic genes in response to postharvest stresses were evaluated. We found that the glucosinolate biosynthetic pathway coincided with the progression of senescence in postharvest broccoli during storage. Additionally, we applied machine learning-based hyperspectral image (HSI) analysis, unmixing, and subpixel target detection approaches to evaluate glucosinolate level to detect postharvest senescence in broccoli. This study provides an accessible approach to precisely estimate freshness in broccoli through machine learning-based hyperspectral image analysis. Such a tool would further allow significant advancement in postharvest logistics and bolster the availability of high-quality, nutritious fresh produce.

SmAvo: Packhouse optimization using smart avocadoes in South Africa

Cultivation of avocadoes serves as a key economic driver for many countries, including South Africa. Nearly all fresh produce produced forms part of a complex, interconnected transportation chain. Packhouses, representing a wide range of capacities and degrees of mechanization, serve to classify, treat and package the fresh produce prior to distribution by road, rail and ocean to its destination. Reducing the damage or postharvest stresses is paramount to ensure consistent quality of the ripened fruit. Packhouse operations represent the phase associated with the greatest degree of mechanical handling. Until now, quantification of packhouse activities exerted on the fruit has not been quantified with sufficient accuracy to identify characteristics of an optimized packhouse. This paper demonstrates the successful application of a novel sensor platform that measures the linear acceleration and rotational velocity of a typical avocado for 24 packhouses spread throughout South Africa. Unique statistics were developed pertaining to the distribution of contact forces, peak accelerations and rotational velocities, freefall events, freefall distance and impact energy experienced by avocadoes. A Damage Index Score (DIS) was developed to classify the relative performance of the sampled packhouses, alongside identification of key areas of concern where the greatest intensity and variation of postharvest stresses are observed. Improvement of avocado quality as a result of improving deficient practices and equipment ultimately reduces waste, prevalence of postharvest diseases and improves the income for farming communities.

Free and glycosylated green leaf volatiles, lipoxygenase and alcohol dehydrogenase in defoliated Nebbiolo grapes during postharvest dehydration

Background and Aims Nebbiolo grapes are used to produce Sfursat wine, following partial dehydration. This research aimed to clarify the influence of fruit exposure to light and postharvest water loss on the concentration of green leaf volatiles (GLVs) and lipoxygenase (LOX) and alcohol dehydrogenase (ADH) activity of grapes. Methods and Results Nebbiolo grapes from Control vines (no defoliation) (ND) and from vines defoliated at fruitset (DFS) or defoliated post-veraison (DPV) were harvested at about 23°Brix and dehydrated at 10 and 20°C, 60% RH and air flow of 1.5 m/s. Berries were sampled at 10 and 20% mass loss (ML). Significant differences in crop yield, bunch mass and berry mass were observed. As expected, the higher the dehydration temperature, the faster the dehydration process: 20% ML at 20°C occurred between 18 and 25 days, the shortest time corresponding to ND and the longest to DFS; at 10°C, the dehydration lasted between 27 and 32 days. At 10°C, the ADH activity was almost double that at 20°C, and in DFS was much higher than in other samples. At harvest, LOX did not show any difference among the samples, while at 10°C and 10% ML, the enzyme activity increased significantly and then declined at 20% ML, especially in defoliated samples. At harvest, the total free GLVs associated with the metabolism of lipid oxidation were 9434, 7212 and 11 656 μg/kg dry weight (DW) in ND, DFS and DPV samples, respectively; the total bound GLVs lipid-derived were 7599, 18 486 and 15 409 μg/kg DW in ND, DFS and DPV samples, respectively. During dehydration at 10°C, the ML induced ADH + LOX activity, especially in defoliated samples, but the bound GLVs, produced by defoliation, greatly decreased. Conclusions Defoliation affected the response of Nebbiolo grapes to dehydration temperature: postharvest cold stress (10°C) and ML induced glycosylation of GLVs, alcohol formation (via ADH) and membrane oxidation (via LOX); a further stress effect was observed with leaf removal, regardless of the time of application. Significance of the Study The timing of defoliation and postharvest dehydration temperature are significant factors to mitigate the postharvest stress response of Nebbiolo grapes.

Effects of Wounding Stress and Storage Temperature on the Accumulation of Chlorogenic Acid Isomers in Potatoes (Solanum tuberosum)

Wounding stress is an effective strategy to increase the content of bioactive compounds in horticultural crops. Potato tubers subjected to wounding stress accumulate chlorogenic acid (CGA) and CGA isomers (neo-CGA and crypto-CGA), which are phenolics that prevent and treat different chronic and degenerative diseases. In this study, the effects of wounding stress and storage temperature (10 °C and 20 °C for 168 h) on the accumulation of CGA isomers in potatoes were evaluated. Results indicated that CGA accumulation was favored when wounded potatoes were stored at 20 °C for 120 h, obtaining a 1923.1% higher concentration when compared with samples before storage. Furthermore, wounded potatoes stored at 10 °C for 120 h showed the highest neo-CGA increase in concentration (712.2%). Likewise, the highest crypto-CGA concentration (84.9% higher than control samples) was quantified in wounded potatoes stored at 20 °C for 144 h. Based on the results from both the present study and previous reports, a strategy that summarizes effective postharvest stress conditions that induce the accumulation of specific CGA isomers in potatoes is presented. The tissue with an increased content of bioactive compounds could be used as raw material to produce functional foods or could be subjected to downstream processing to produce dietary supplements.

Hormonal endogenous changes in response to the exogenous 6-benzylaminopurine application in pre- and post-harvesting lilium flower stalks

Abstract Phyto-hormones play a key role in regulating plant responses to stress. Cytokines are a type of phyto-hormones involved in the regulation of many important biological processes related to growth, development, and response to environmental variables. The exogenous application of cytokines increases the possibility of delaying senescence; however, this is a physiological process, and, under certain conditions, degradation processes may be triggered. The effect of 6-bencilaminopurine application and the endogenous hormonal changes involved in lilies floral stalks after their cutting were studied. In order to improve vase life and quality of Lilium longiflorum ‘Brindisi’ flower stalks, they were sprayed with 6-BAP, at a concentration of 300 ppm at pre-harvest, post-harvest, and pre- and post-harvest stages. After that, they were compared to non-sprayed control stalks. The application of 6-BAP caused endogenous hormonal changes in abscisic acid and cytokinin levels, and the most effective treatment was pre-harvest spraying. This treatment proved to be an appropriate method to improve the stalk tolerance to post-harvest stress as it delayed the appearance of senescence symptoms and reduced the speed of chlorophyll degradation with differences of up to 10% with respect to untreated stalks. In addition, the opening of flowers was delayed by up to 2 days, although there were no significant differences in total vase life.

Involvement of DNA methylation in regulating the accumulation of the aroma compound indole in tea (Camellia sinensis) leaves during postharvest processing

The manufacturing process of tea (Camellia sinensis), especially oolong tea, involves multiple postharvest stresses. These stresses can induce the formation and accumulation of many important aroma compounds, such as indole—a key floral aroma contributor of oolong tea. However, little is known about the regulation mechanisms of aroma compound formation, especially epigenetic regulation. DNA methylation is an important epigenetic modification. Changes in the DNA methylation levels of promoter sequences can regulate gene expression under stress conditions. In this study, the differences in DNA methylation levels and histone 3 lysine 9 dimethylation levels of indole key biosynthetic gene (tryptophan synthase β-subunit 2, CsTSB2) were detected between untreated and continuous wounding treatment tea leaves. The results show that the DNA methylation levels affect the ability of the basic helix–loop–helix family transcription factor CsMYC2a to bind to the promoter of CsTSB2. Analyses of the transcript levels of DNA methyltransferases during oolong tea processing screened out candidate genes involved in the regulation of secondary metabolite product biosynthesis/accumulation. The results suggest that the domains rearranged methyltransferase 3, a DNA methyltransferase, is involved in the DNA methylation regulation of indole formation during the oolong tea manufacturing process. This is the first report on the involvement of DNA methylation in the regulation of aroma compound formation in tea leaves exposed to postharvest stresses.

Biochemical Pathway of Benzyl Nitrile Derived from l-Phenylalanine in Tea (Camellia sinensis) and Its Formation in Response to Postharvest Stresses.

Volatiles affect tea (Camellia sinensis) aroma quality and have roles in tea plant defense against stresses. Some volatiles defend against stresses through their toxicity, which might affect tea safety. Benzyl nitrile is a defense-related toxic volatile compound that accumulates in tea under stresses, but its formation mechanism in tea remains unknown. In this study, l-[2H8]phenylalanine feeding experiments and enzyme reactions showed that benzyl nitrile was generated from l-phenylalanine via phenylacetaldoxime in tea. CsCYP79D73 showed activity for converting l-phenylalanine into phenylacetaldoxime, while CsCYP71AT96s showed activity for converting phenylacetaldoxime into benzyl nitrile. Continuous wounding in the oolong tea process significantly enhanced the CsCYP79D73 expression level and phenylacetaldoxime and benzyl nitrile contents. Benzyl nitrile accumulation under continuous wounding stress was attributed to an increase in jasmonic acid, which activated CsCYP79D73 expression. This represents the first elucidation of the formation mechanism of benzyl nitrile in tea.

Short-Term Post-Harvest Stress that Affects Profiles of Volatile Organic Compounds and Gene Expression in Rocket Salad During Early Post-Harvest Senescence.

Once harvested, leaves undergo a process of senescence which shares some features with developmental senescence. These include changes in gene expression, metabolites, and loss of photosynthetic capacity. Of particular interest in fresh produce are changes in nutrient content and the aroma, which is dependent on the profile of volatile organic compounds (VOCs). Leafy salads are subjected to multiple stresses during and shortly after harvest, including mechanical damage, storage or transport under different temperature regimes, and low light. These are thought to impact on later shelf life performance by altering the progress of post-harvest senescence. Short term stresses in the first 24 h after harvest were simulated in wild rocket (Diplotaxis tenuifolia). These included dark (ambient temperature), dark and wounding (ambient temperature), and storage at 4 °C in darkness. The effects of stresses were monitored immediately afterwards and after one week of storage at 10 °C. Expression changes in two NAC transcription factors (orthologues of ANAC059 and ANAC019), and a gene involved in isothiocyanate production (thiocyanate methyltransferase, TMT) were evident immediately after stress treatments with some expression changes persisting following storage. Vitamin C loss and microbial growth on leaves were also affected by stress treatments. VOC profiles were differentially affected by stress treatments and the storage period. Overall, short term post-harvest stresses affected multiple aspects of rocket leaf senescence during chilled storage even after a week. However, different stress combinations elicited different responses.

Influence of Chloroplast Defects on Formation of Jasmonic Acid and Characteristic Aroma Compounds in Tea (Camellia sinensis) Leaves Exposed to Postharvest Stresses.

Characteristic aroma formation in tea (Camellia sinensis) leaves during the oolong tea manufacturing process might result from the defense responses of tea leaves against these various stresses, which involves upregulation of the upstream signal phytohormones related to leaf chloroplasts, such as jasmonic acid (JA). Whether chloroplast changes affect the formation of JA and characteristic aroma compounds in tea leaves exposed to stresses is unknown. In tea germplasms, albino-induced yellow tea leaves have defects in chloroplast ultrastructure and composition. Herein, we have compared the differential responses of phytohormone and characteristic aroma compound formation in normal green and albino-induced yellow tea leaves exposed to continuous wounding stress, which is the main stress in oolong tea manufacture. In contrast to single wounding stress (from picking, as a control), continuous wounding stress can upregulate the expression of CsMYC2, a key transcription factor of JA signaling, and activate the synthesis of JA and characteristic aroma compounds in both normal tea leaves (normal chloroplasts) and albino tea leaves (chloroplast defects). Chloroplast defects had no significant effect on the expression levels of CsMYC2 and JA synthesis-related genes in response to continuous wounding stress, but reduced the increase in JA content in response to continuous wounding stress. Furthermore, chloroplast defects reduced the increase in volatile fatty acid derivatives, including jasmine lactone and green leaf volatile contents, in response to continuous wounding stress. Overall, the formation of metabolites derived from fatty acids, such as JA, jasmine lactone, and green leaf volatiles in tea leaves, in response to continuous wounding stress, was affected by chloroplast defects. This information will improve understanding of the relationship of the stress responses of JA and aroma compound formation with chloroplast changes in tea.

Emersion survival manipulation in Greenshell™ mussels (Perna canaliculus): Implications for the extension of live mussels' shelf-life

Farmed adult Greenshell™ mussels were exposed to a range of conditions immediately after harvest to evaluate the effects on emersion survival and the implications for live transport. Two experiments were performed, coinciding with the mussel harvest season during summer and winter 2017. In the summer experiment, a wide range of conditions were tested to identify alternatives to be evaluated in more detail during the winter experiment. The postharvest experimental conditions selected included transient re-immersion at different temperatures, cold and heat-shock, tidal simulation, and packing with ice. These treatments aimed to either reduce postharvest stress and/or give the mussels a potentially beneficial physiological and behavioural advantage to help them cope with emersion. The mussels' responses in terms of gaping and survival differed between summer and winter, and among and within treatments. Sub-ambient temperature seawater exposure after harvest tended to improve the survival time of the mussels in both seasons, the effect being dependent on both temperature and duration of the exposure. Some of the differences observed could be explained by the conditions (in the wild and in the laboratory) to which the mussels were exposed before emersion and the different capability that each mussel has to cope with stress. However, the exact mechanisms driving these changes are not fully understood and require further investigation. This study, nevertheless, indicates that emersion survival (i.e. live mussel shelf-life) could be extended by re-immersion after harvest combined with a sub-lethal cold-shock followed by immersed recovery before transportation. If the commercial shelf-life of live product can be significantly extended, the implications for food quality and safety will also need to be evaluated. A similar approach could be applied in other shellfish such as other species of mussels as well as oysters or clams to improve shelf-life, considering their physiological capabilities and behaviour and how those are affected by environmental conditions in different seasons or regions.