The maturation profile triggers differential expression of sugar metabolism genes in melon fruits

Melons are commercially important crops that requires specific quality attributes for successful commercialization, including accumulation of sugars, particularly sucrose. This trait can be influenced by various factors, such as the type of ripening. Cucumis melo L. is an ideal species for studying sugar metabolism because it has both climacteric and non-climacteric cultivars. Thus, this study aimed to examine the gene expression of sucrose metabolism candidates using RT-qPCR, in conjunction with postharvest physiological analyzes and high-performance liquid chromatography-based sugar quantification, in the melon cultivars 'Gaúcho' (climacteric) and 'Eldorado' (non-climacteric). The results showed that sucrose synthase 1 played a role in the synthesis and accumulation of sucrose in both cultivars, whereas sucrose synthase 2 was more highly expressed in 'Gaúcho', contributing to lower hexose content. Invertase inhibitor 1 was more highly expressed in 'Eldorado' and may be involved in sugar-induced maturation. Neutral α-galactosidase had distinct functions, playing a role in substrate synthesis for the growth of young 'Eldorado' fruits, whereas in mature 'Gaúcho' fruits it participated in the metabolism of raffinose family oligosaccharides for sucrose accumulation. The expression of trehalose-6-phosphate synthase genes indicated a greater involvement of these enzymes in the sugar regulation in 'Gaúcho' melons. These findings shed light on the intraspecific differences related to fruit quality attributes in different types of maturation and contribute to a deeper understanding of the underlying molecular mechanisms involved in the metabolism of sugars in melons, which can inform breeding programs aimed at improving fruit quality attributes in this crop.

Phytochemical Enhancement in Broccoli Florets after Harvest by Controlled Doses of Ozone

The objective of this work was to examine the effect of controlled doses of O₃ (0, 5 µL L⁻¹ of O₃ for 60 min, and 5 µL L⁻¹ of O₃ for 720 min) on the quality and phytochemical content of broccoli florets during postharvest storage. The optimal dose was found at 5 µL L⁻¹ of O₃ for 60 min, from the color retention of broccoli florets exposed to the gas treatment. Overall, the antioxidant capacity of the florets was significantly affected by both doses of O₃ compared to the non-exposed florets. The profile of glucosinolates was determined for up to 14 days in broccoli florets stored at 4 °C by LC-MS. The amount of total glucobrassicins and total hydroxy-cinnamates in florets significantly (p ≤ 0.05) improved by the application of 5 µL L⁻¹ of O₃ for 60 min compared to non-treated florets. The up-regulation of genes of the tryptophan-derived glucosinolate pathway was observed immediately after both treatments. The gene expression of CYP79A2 and CYP79B3 in broccoli was significantly higher in broccoli florets exposed to 5 µL L⁻¹ of O₃ for 720 min compared to non-exposed florets. Although enhancement of secondary metabolites can be achieved by the fumigation of broccoli florets with low doses of ozone, quality parameters, particularly weight loss, can be compromised.

Apple Ripening Is Controlled by a NAC Transcription Factor

Softening is a hallmark of ripening in fleshy fruits, and has both desirable and undesirable implications for texture and postharvest stability. Accordingly, the timing and extent of pre-harvest ripening and associated textural changes following harvest are key targets for improving fruit quality through breeding. Previously, we identified a large effect locus associated with harvest date and firmness in apple (Malus domestica) using genome-wide association studies (GWAS). Here, we present additional evidence that polymorphisms in or around a transcription factor gene, NAC18.1, may cause variation in these traits. First, we confirmed our previous findings with new phenotype and genotype data from ∼800 apple accessions. In this population, we compared a genetic marker within NAC18.1 to markers targeting three other firmness-related genes currently used by breeders (ACS1, ACO1, and PG1), and found that the NAC18.1 marker was the strongest predictor of both firmness at harvest and firmness after 3 months of cold storage. By sequencing NAC18.1 across 18 accessions, we revealed two predominant haplotypes containing the single nucleotide polymorphism (SNP) previously identified using GWAS, as well as dozens of additional SNPs and indels in both the coding and promoter sequences. NAC18.1 encodes a protein that is orthogolous to the NON-RIPENING (NOR) transcription factor, a regulator of ripening in tomato (Solanum lycopersicum). We introduced both NAC18.1 transgene haplotypes into the tomato nor mutant and showed that both haplotypes complement the nor ripening deficiency. Taken together, these results indicate that polymorphisms in NAC18.1 may underlie substantial variation in apple firmness through modulation of a conserved ripening program.

Metabolic Profile of Strawberry Fruit Ripened on the Plant Following Treatment With an Ethylene Elicitor or Inhibitor

Strawberry is the most studied nonclimacteric fruit for understanding the role ethylene has in ripening regulation. However, previous studies on the effects of ethylene on strawberry ripening were conducted with detached fruit. Thus, the aim of this work was to determine the effect of ethylene and the ethylene-action inhibitor 1-methylcyclopropene (1-MCP) applied at different developmental stages on important physical-chemical attributes of ripe 'Albion' strawberry. Fruit at four developmental stages that remained attached to the plant were dipped in one of three treatment solutions (Ethephon, 1-methylcyclopropene, and water), plus one absolute control that received no dip. Following treatment, when immature fruit were fully red or 24 h after treatment for red-treated fruit, strawberry fruit were assessed for physicochemical properties (mass, length, diameter, firmness, color, titratable acidity, soluble solids, pH, total phenolics, sugar, organic acid, amino acid, and volatile composition). The days following treatment required for fruit to ripen were also recorded. Treatments did not affect the rate of ripening nor fruit color, titratable acidity, pH, soluble solids, total phenolics, sugars, or organic acids of ripe fruit. Ethephon affected fruit mass, diameter, length, firmness, anthocyanins, amino acids, and volatiles, but these effects were dependent on fruit developmental stage at which the treatment was applied. When green fruit were treated with ethephon, ripe fruit had larger diameter and mass. Ethephon treatment of white fruit resulted in ripe fruit having greater anthocyanin content. Treatment of pink fruit resulted in ripe fruit having smaller diameter, length, and mass and greater firmness. Treatment of red fruit with ethephon altered fruit volatile composition, increasing concentrations of ethyl- and acetate-esters, which were reduced by the 1-MCP treatment. Ethephon treatment increased concentrations of 11 of the 19 free amino acids measured in ripe fruit with treatment of green and white fruit having the greatest effect. A total of 41 volatile compounds had significant correlations with 14 amino acids. While ethylene did not stimulate typical ripening of strawberry fruit, it does appear to alter fruit development and metabolism. The physiological effects of ethylene on strawberry fruit appear to depend on the developmental stage of the fruit.

Genome-wide association studies in apple reveal loci of large effect controlling apple polyphenols

Apples are a nutritious food source with significant amounts of polyphenols that contribute to human health and wellbeing, primarily as dietary antioxidants. Although numerous pre- and post-harvest factors can affect the composition of polyphenols in apples, genetics is presumed to play a major role because polyphenol concentration varies dramatically among apple cultivars. Here we investigated the genetic architecture of apple polyphenols by combining high performance liquid chromatography (HPLC) data with ~100,000 single nucleotide polymorphisms (SNPs) from two diverse apple populations. We found that polyphenols can vary in concentration by up to two orders of magnitude across cultivars, and that this dramatic variation was often predictable using genetic markers and frequently controlled by a small number of large effect genetic loci. Using GWAS, we identified candidate genes for the production of quercitrin, epicatechin, catechin, chlorogenic acid, 4-O-caffeoylquinic acid and procyanidins B1, B2, and C1. Our observation that a relatively simple genetic architecture underlies the dramatic variation of key polyphenols in apples suggests that breeders may be able to improve the nutritional value of apples through marker-assisted breeding or gene editing.

Coencapsulation of Polyphenols and Anthocyanins from Blueberry Pomace by Double Emulsion Stabilized by Whey Proteins: Effect of Homogenization Parameters

Blueberry pomace is a rich source of high-value bioactive polyphenols with presumed health benefits. Their incorporation into functional foods and health-related products benefits from coencapsulation and protection of polyphenol-rich extracts in suitable carriers. This study aimed to create a water-in-oil-in-water (W₁/O/W₂) double emulsion system suitable for the coencapsulation of total phenolics (TP) and anthocyanins (TA) from a polyphenol-rich extract of blueberry pomace (W₁). The effect of critical physical parameters for preparing stable double emulsions, namely homogenization pressure, stirring speed and time, was investigated by measuring the hydrodynamic diameter, size dispersity and zeta potential of the oil droplets, and the encapsulation efficiency of TP and TA. The oil droplets were negatively charged (negative zeta potential values), which was related to the pH and composition of W₂ (whey protein isolate solution) and suggests stabilization by the charged whey proteins. Increasing W₁/O/W₂ microfluidization pressure from 50 to 200 MPa or homogenization speed from 6000 to 12,000 rpm significantly increased droplet diameter and zeta potential and decreased TA and TP encapsulation efficiency. Increasing W₁/O/W₂ homogenization time from 15 to 20 min also increased droplet diameter and zeta potential and lowered TA encapsulation efficiency, while TP encapsulation did not vary significantly. In contrast, increasing W₁/O homogenization time from 5 to 10 min at 10,000 rpm markedly increased TA encapsulation efficiency and reduced droplet diameter and zeta potential. High coencapsulation rates of blueberry polyphenols and anthocyanins around 80% or greater were achieved when the oil droplets were relatively small (mean diameter < 400 nm), with low dispersity (<0.25) and a high negative surface charge (-40 mV or less). These characteristics were obtained by homogenizing for 10 min at 10,000 rpm (W₁/O), then 6000 rpm for 15 min, followed by microfluidization at 50 MPa.

Impact of Listeria Inoculation and Aerated Steam Sanitization on Volatile Emissions of Whole Fresh Cantaloupes

Rapid methods to detect bacterial pathogens on food and strategies to control them are needed to mitigate consumer risk. This study assessed volatile emissions from whole cantaloupe melons (Cucumis melo) as an indicator of Listeria contamination and in response to steam vapor decontamination. Cantaloupe were inoculated with Listeria innocua, a nonpathogenic surrogate for L. monocytogenes, then exposed to 85 °C steam for 240 s (4 min) followed by rapid chilling and storage for 0, 7, 10, or 14 days at 4, 7, or 10 °C. Volatile emissions from whole melons were collected on Carbopack B/Carboxen 1000 headspace collection tubes and analyzed by gas chromatography-mass spectroscopy following thermal desorption. Introduction of L. innocua to cantaloupe rind resulted in a reduction of aromatic compound emission. However, this response was not unique to Listeria contamination in that steam vapor treatment also reduced emission of these compounds. As well, steam vapor treatment diminished the number of viable Listeria and indigenous microflora while causing physiological injury to melon rind. Heat treatment had no significant effects on flesh firmness, color, titratable acidity, or soluble solids, but the production of typical aroma volatiles during postharvest ripening was inhibited. No unique volatile compounds were detected in Listeria contaminated melons. While changes in volatile emissions were associated with Listeria inoculation, they could not be differentiated from heat treatment effects. Results indicate that volatile emissions cannot be used as a diagnostic tool to identify Listeria contamination in whole cantaloupe melons.

PRACTICAL APPLICATION

The detection of pathogen contamination on fresh produce is a continuing challenge. Using a nondestructive screening method, the presence of surrogate Listeria innocua on fresh whole cantaloupes was shown to alter the emissions of aromatic volatiles from whole cantaloupes. However, these altered emissions were not found to be unique to Listeria spp. and therefore cannot be used as a definitive indicator of Listeria contamination.

A Genome-Wide Association Study of Apple Quality and Scab Resistance

The apple ( × Borkh.) is an economically and culturally important crop grown worldwide. Growers of this long-lived perennial must produce fruit of adequate quality while also combatting abiotic and biotic stress. Traditional apple breeding can take up to 20 yr from initial cross to commercial release, but genomics-assisted breeding can help accelerate this process. To advance genomics-assisted breeding in apple, we performed genome-wide association studies (GWAS) and genomic prediction in a collection of 172 apple accessions by linking over 55,000 single nucleotide polymorphisms (SNPs) with 10 phenotypes collected over 2 yr. Genome-wide association studies revealed several known loci for skin color, harvest date and firmness at harvest. Several significant GWAS associations were detected for resistance to a major fungal pathogen, apple scab ( [Cke.] Wint.), but we demonstrate that these hits likely represent a single ancestral source. Using genomic prediction, we show that most phenotypes are sufficiently predictable using genome-wide SNPs to be candidates for genomic selection. Finally, we detect a signal for firmness retention after storage on chromosome 10 and show that it may not stem from variation in , a gene repeatedly identified in bi-parental mapping studies and widely believed to underlie a major QTL for firmness on chromosome 10. We provide evidence that this major QTL is more likely due to variation in a neighboring ethylene response factor (ERF) gene. The present study showcases the superior mapping resolution of GWAS compared to bi-parental linkage mapping by identifying a novel candidate gene underlying a well-studied, major QTL involved in apple firmness.

Aerated Steam Sanitization of Whole Fresh Cantaloupes Reduces and Controls Rind-Associated Listeria but Enhances Fruit Susceptibility to Secondary Colonization

Recent bacterial illnesses and outbreaks associated with the consumption of fresh and fresh-cut fruit and vegetables emphasize the need to supply produce that is microbiologically safe while retaining its quality and nutrient value. We assessed the capacity of aerated steam to reduce initial levels and control the posttreatment proliferation of a 4-strain mixture of Listeria innocua, a surrogate for L. monocytogenes, and microflora native to the rind of whole cantaloupes. Studies were conducted at the pilot-scale level by passing deliberately contaminated melons through a prototype stainless-steel, continuous-feed heating device. Exposure for 240 s to aerated steam heated to 85 °C achieved a mean reduction in surface-inoculated L. innocua of 3.9 ± 0.6 log₁₀ CFU/cm² (n = 3) and decreased background microorganisms (yeast, moulds, and coliforms) to undetectable levels. No significant outgrowth of surviving L. innocua or yeast and moulds was observed on heat-treated melons during their storage at 4, 7, and 10 °C for 14 days. Treated fruit continued to respire. Although rind quality was altered, edible fleshy portions remained largely unaffected. Cantaloupe inoculated with L. innocua subsequent to its exposure to aerated steam provided a suitable environment for surrogate growth (mean 3.3 log₁₀ increase in rind density over 10 days at 7 °C), whereas its proliferation was restricted on nonheated cantaloupe (mean 0.7 log₁₀ increase). Steam sanitization provides an effective means for the control of pathogen and spoilage organisms, but the proliferation of surrogate organisms on heated cantaloupes raises concern regarding the impact of postprocessing contamination on consumer health risk.

PRACTICAL APPLICATION

Water vapor (steam) at a high temperature can be used to sanitize the surface of fresh, whole cantaloupe melons in a continuous-feed manner. Both Listeria bacteria and spoilage organisms are markedly reduced from initial levels and survivor outgrowth severely restricted during subsequent refrigerated storage. This approach to microorganism control is likely most applicable in situations where rinds and flesh are to be separated immediately via further processing.

QTL analysis of soft scald in two apple populations

The apple (Malus×domestica Borkh.) is one of the world's most widely grown and valuable fruit crops. With demand for apples year round, storability has emerged as an important consideration for apple breeding programs. Soft scald is a cold storage-related disorder that results in sunken, darkened tissue on the fruit surface. Apple breeders are keen to generate new cultivars that do not suffer from soft scald and can thus be marketed year round. Traditional breeding approaches are protracted and labor intensive, and therefore marker-assisted selection (MAS) is a valuable tool for breeders. To advance MAS for storage disorders in apple, we used genotyping-by-sequencing (GBS) to generate high-density genetic maps in two F1 apple populations, which were then used for quantitative trait locus (QTL) mapping of soft scald. In total, 900 million DNA sequence reads were generated, but after several data filtering steps, only 2% of reads were ultimately used to create two genetic maps that included 1918 and 2818 single-nucleotide polymorphisms. Two QTL associated with soft scald were identified in one of the bi-parental populations originating from parent 11W-12-11, an advanced breeding line. This study demonstrates the utility of next-generation DNA sequencing technologies for QTL mapping in F1 populations, and provides a basis for the advancement of MAS to improve storability of apples.

Targeted quantitative proteomic investigation employing multiple reaction monitoring on quantitative changes in proteins that regulate volatile biosynthesis of strawberry fruit at different ripening stages

A targeted quantitative proteomic investigation employing the multiple reaction monitoring (MRM, SRM) technique was conducted on strawberry fruit at different development stages. We investigated 22 proteins and isoforms from 32 peptides with 111 peptide transitions, which may be involved in the volatile aroma biosynthesis pathway. The normalized protein abundance was significantly changed in coincidence with increased volatile production and advanced fruit maturities. Among them, alcohol acyltransferase (AAT), quinone oxidoreductase (QR), malonyl Co-A decarboxylase, (MLYCD), pyruvate decarboxylase (PDC), acetyl Co-A carboxylase (ACCase), and acyl Co-A synthetase (ACAs) were increased significantly. Several alcohol dehydrogenases (ADHs), and 3-oxoacyl-ACP synthase were significantly decreased. Furthermore, the expression of seven genes related to strawberry volatile production was also investigated using real-time qPCR. Among the tested genes, QR, AAT, ACCase, OMT, PDC and ADH showed increased up-regulation during fruit ripening, while 3-isopropylmalate dehydrogenase (IMD) decreased. Strong correlation between quantitative proteomic data and gene expression suggested that AAT, QR, ACCase, and PDC played critical roles in volatile biosynthesis of strawberry during fruit ripening. Poor correlation between protein abundance and gene expression of ADH was found.

Effect of hot water treatments on quality of highbush blueberries

Highbush blueberries, cv 'Burlington', were treated with 22, 45, 50, or 60 degrees C water for 15 or 30 s along with an untreated control. Fruit were then stored for 0, 1, 2, or 4 wk at 0 degrees C and 2 or 9 d at 20 degrees C prior to evaluation of microbial population and fruit quality. After 4 wk of storage, the hot water treatment at 60 degrees C resulted in 92% marketable berries, followed by 90% at 50 degrees C, 88% at 45 degrees C, and 83% at 22 degrees C compared with 76% in untreated controls. Decay incidence was reduced to 0.6%, 1.2%, 1.4%, or 2.8% with 60, 50, 45, or 22 degrees C water treatments, respectively, compared with 5.1% in controls following 4 wk at 0 degrees C and 2 d at 20 degrees C. After an additional 7 d at 20 degrees C, decay in fruit treated at 60 degrees C for 15 or 30 s remained at 1.8% and 0.4%, respectively, compared to 37.4% in controls. Weight loss of berries treated with hot water was 0.4% against 3.8% in controls, and shriveled and split berries were also reduced compared to controls (P<0.001). Aerobic plate count and yeast and mold count were reduced by 0.45 to 0.7 log at 60 degrees C for 30 s. Botrytis cinerea and Colletotrichum sp. were the dominant fungal pathogens causing decay of Burlington blueberries during storage. Hot water treatments also immediately induced an increase in ethanol and reduced fruit titratable acidity and soluble solids content, but had no significant effect on fruit firmness, pH, or most flavor volatile concentrations.

Effect of hexanal vapor on the growth of postharvest pathogens and fruit decay

The effect of the natural volatile hexanal was studied as an antifungal agent on the major postharvest fungal pathogens Botrytis cinerea, Monilinia fructicola, Sclerotinia sclerotiorum, Alternaria alternata, and Colletotrichum gloeosporioides. The antifungal effect of hexanal vapor was dependent on concentration and treatment duration, but sensitivity of the pathogens varied. All spores of B. cinerea and M. fructicola were killed after exposure to 900 microL/L for 12 h at 20 degrees C, and almost all were killed after a 24-h exposure to 450 microL/L. Only moderate numbers of spores were killed at a concentration of 200 microL/L. Mycelial growth of S. sclerotiorum on agar was completely inhibited after a 12-h exposure to 900 microL/L, but only slight inhibition occurred at 450 microL/L and none at 200 microL/L. Mycelium of A. alternata and C. gloeosporioides appeared more sensitive, with strong inhibition occurring after a 12-h exposure at 450 microL/L. Similar trends in spore viability and mycelial growth were observed at 7 degrees C. The antifungal effect of hexanal vapor was further tested on raspberry fruit naturally infected with B. cinerea and on peach fruit inoculated with spores of M. fructicola. Decay was markedly reduced in raspberry and almost completely controlled in peach after exposure to 900 microL/L hexanal vapor for 24 h. The potential of hexanal for postharvest decay control is discussed.

Interaction of ozone and negative air ions to control micro-organisms

AIMS

The aims of this study were to investigate the effect of ozone and/or negative air ions (NAI) on the viability of bacteria.

METHODS AND RESULTS

Dilute cell suspensions of Pseudomonas fluorescens, Erwinia carotovora pv. carotovora and Escherichia coli were inoculated onto agar and subsequently exposed to ozone and/or NAI. Ozone concentration was maintained at 100 +/- 5 nl l-1 and NAI at 106 ml-1. When exposed to a combination of ozone and NAI, viability among all three bacterial species decreased more rapidly when they were inoculated onto potato dextrose agar (PDA) than onto nutrient agar (NA). A subsequent test examined the effect of ozone and NAI alone or in combination on the bacteria inoculated onto PDA only. Treatment with NAI alone had no killing effect on any of the bacterial species. However, a strong interaction between ozone and NAI was observed. Pseudomonas fluorescens was most susceptible to the combined treatment. Cell viability was reduced to 0.7% after 6 h, while 76% of the cells remained viable when exposed to ozone alone. Viability of Erwinia carotovora pv. carotovora was reduced to 4% after 6 h in the combined treatment compared with 69% when exposed to ozone alone. Escherichia coli was relatively more resistant to the combined treatment; viability was reduced to 40% after 11 h compared with 70% in the ozone alone treatment.

CONCLUSIONS

A strong synergism between ozone and NAI on bacterial cell death was found, but the degree of this effect varied depending on bacterial species.

SIGNIFICANCE AND IMPACT OF THE STUDY

The synergism of ozone with NAI may provide an effective method of reducing food-borne disease and decay of fresh produce.

Using a modified ferrous oxidation-xylenol orange (FOX) assay for detection of lipid hydroperoxides in plant tissue

The ferrous oxidation-xylenol orange (FOX) assay was adapted for quantifying lipid hydroperoxides (LOOHs) in plant extracts. Excised pieces of several fruit and vegetable species were exposed to 83 kJ m(-2) day(-1) of biologically effective ultraviolet B irradiance (UV-B(BE)) for 10-12 days to induce cellular oxidation. The LOOH and thiobarbituric acid reactive substance (TBARS) concentrations of these plant tissues were assessed with the FOX and iodometric assays for the former and a modified TBARS assay for the latter. There was generally good agreement between the FOX and iodometric methods both prior to and following the UV exposure. However, the iodometric assay appeared to have some difficulty in consistently quantifying lower LOOH levels (<11 microM), whereas the FOX assay measured LOOH concentrations as low as 5 microM. All tissues exhibited UV-induced increases in TBARS, indicating a marked degree of cellular oxidation in the exposed tissue segments. Compared with the iodometric assay, the FOX method consistently generated less variable LOOH values. The presence of authentic linoleic acid-OOHs in spiked avocado and spinach samples (11 microM) was identified with liquid chromatography-mass spectrometry techniques, which validated corresponding FOX assay results. The FOX method is inexpensive, is not sensitive to ambient O2 or light levels, and can rapidly generate LOOH measurements. The physiological value of the FOX assay resides in its ability to measure initial rather than more advanced fatty acid oxidation; hence, early membrane-associated stress events in plant tissue can be detected.

A rapid capillary gel electrophoresis method for the quantitative determination of RuBisCo in spinach

A capillary gel electrophoretic (CGE) method for the quantitative analysis of RuBisCo in spinach leaves was developed. RuBisCo was resolved into large and small subunits in the presence of sodium dodecyl sulphate (SDS) by the CGE procedure which enabled the determination of the molecular weight of each unit accurately; the values so determined were in close agreement with those reported using other methods. Advantages of CGE over SDS-polyacrylamide gel electrophoresis and high-pressure gel filtration include decreased sample preparation and analysis time, superior resolution and greater sensitivity permitting reduced sample size and trace analysis. In addition, CGE provided precise quantification of RuBisCo and was demonstrated to be a viable alternative to other available methods of protein analysis.

The effects of ethylene, depressed oxygen and elevated carbon dioxide on antioxidant profiles of senescing spinach leaves

It has been suggested that antioxidants play a role in regulating or modulating senescence dynamics of plant tissues. Ethylene has been shown to promote early plant senescence while controlled atmospheres (CA; reduced O2 levels and elevated CO2 levels) can delay its onset and/or severity. In order to examine the possible importance of various antioxidants in the regulation of senescence, detached spinach (Spinacia oleracea L.) leaves were stored for 35 d at 10 degrees C in one of three different atmospheres: (1) ambient air (0.3% CO2, 21.5% O2, 78.5% N2), (2) ambient air + 10 ppm ethylene to promote senescence, or (3) CA (10% CO2, 0.8% O2 and 89.2% N2) to delay senescence. At weekly intervals, material was assessed for activities of the antioxidant enzymes ascorbate peroxidase (ASPX; EC 1.11.1.11), catalase (CAT; EC 1.11.1.6), dehydroascorbate reductase (DHAR; EC 1.8.5.4), glutathione reductase (GR; EC 1.6.4.2), monodehydroascorbate reductase (MDHAR; EC 1.6.5.4), and superoxide dismutase (SOD; EC 1.15.1.1), and concentrations of the water-soluble antioxidant compounds ascorbate and glutathione. Indicators of the rate and severity of senescence (lipid peroxidation, chlorophyll, and soluble protein levels) were also determined. Results indicated that the rate and severity of senescence was similar between the leaves stored in ambient air or CA until day 35, at which point the ambient air-stored leaves exhibited a sharp increase in lipid peroxidation. Tissues under both storage regimes demonstrated significant declines only in levels of ASPX, CAT, and ascorbate. Glutathione content in the CA-stored tissue also significantly dropped, but only on day 35. In contrast, spinach leaves stored in ambient air + ethylene experienced a rapid decrease in levels of all the antioxidants assessed except SOD. Declines in levels of ASPX, CAT, and ascorbate over the 35 d storage period regardless of the composition of the storage atmosphere suggests that regulation of H2O2 levels plays an important role in both the dynamics and severity of post-harvest senescence of spinach.

Antioxidant capacity, vitamin C, phenolics, and anthocyanins after fresh storage of small fruits

Fresh strawberries (Fragaria x ananassa Duch.), raspberries (Rubus idaeus Michx.), highbush blueberries (Vaccinium corymbosum L.), and lowbush blueberries (Vaccinium angustifolium Aiton) were stored at 0, 10, 20, and 30 degrees C for up to 8 days to determine the effects of storage temperature on whole fruit antioxidant capacity (as measured by the oxygen radical absorbing capacity assay, Cao et al., Clin. Chem. 1995, 41, 1738-1744) and total phenolic, anthocyanin, and ascorbate content. The four fruit varied markedly in their total antioxidant capacity, and antioxidant capacity was strongly correlated with the content of total phenolics (0.83) and anthocyanins (0.90). The antioxidant capacity of the two blueberry species was about 3-fold higher than either strawberries or raspberries. However, there was an increase in the antioxidant capacity of strawberries and raspberries during storage at temperatures >0 degrees C, which was accompanied by increases in anthocyanins in strawberries and increases in anthocyanins and total phenolics in raspberries. Ascorbate content differed more than 5-fold among the four fruit species; on average, strawberries and raspberries had almost 4-times more ascorbate than highbush and lowbush blueberries. There were no ascorbate losses in strawberries or highbush blueberries during 8 days of storage at the various temperatures, but there were losses in the other two fruit species. Ascorbate made only a small contribution (0.4-9.4%) to the total antioxidant capacity of the fruit. The increase observed in antioxidant capacity through postharvest phenolic synthesis and metabolism suggested that commercially feasible technologies may be developed to enhance the health functionality of small fruit crops.