Effect of curing at different temperatures on biochemical composition of onion (Allium cepa L.) skin from three freshly cured and cold stored UK-grown onion cultivars

Onions are cured in order to form a complete, dry, outer skin which reduces water loss and suppresses incidence of disease, and can promote a darker skin finish. Currently in the UK, standard curing practises for onions involves heating at 28 °C for six weeks (65–75% RH), however, reducing curing temperatures may help to reduce energy usage. There is little empirical data on the effects of curing temperature on flavonol concentration in the skin of brown onions and on flavonol and anthocyanin concentration in the skin of red onions. Therefore, the aim of this study was to elucidate the compounds responsible for the change in onion skin colour when cured at different temperatures.Brown cvs. Sherpa and Wellington, and red onions cv. Red Baron, were cured at 20, 24 or 28 °C for six weeks. Replicated skin samples were analysed immediately after curing and after seven months cold storage at 1 ± 0.5 °C. Measurement of objective colour showed that skin of cvs. Sherpa and Wellington was darker and had a lower hue angle (H°) immediately after being cured at 28 °C compared to 20 °C. In contrast, skin of cv. Red Baron had a higher H° but no change in lightness (L*) when cured at 28 °C compared to 20 °C. Fructose, sucrose and glucose concentrations were analysed as they are thought to play a role in regulating the synthesis of flavonols and anthocyanins, both coloured compounds found in onion skin; however no significant correlations were found between colour data and sugar concentrations. Flavonols were measured in the skin of all cvs. and anthocyanins in the skin of cv. Red Baron. Quercetin glucoside and anthocyanin concentrations in the skin of onions cv. Red Baron immediately after curing were higher in those cured at 20 °C. Total flavonols and total anthocyanins were negatively correlated with H° in the skin of onions cv. Red Baron, but there was no similar correlation between total flavonols and H° for onion cvs. Sherpa and Wellington. This suggests that anthocyanins and flavonols may play a major role in varying skin colour of red onions cv. Red Baron cured at different temperatures; however, the difference between curing temperatures may not have been sufficient to represent a correlation between darkening of cvs. Sherpa and Wellington and flavonol concentration. Further investigation is therefore required to fully elucidate the compounds responsible for colour changes observed in brown onions.     

Extension of fresh-cut “Blanquilla” pear (Pyrus communis L.) shelf-life by 1-MCP treatment after harvest

‘Blanquilla’ pears processed as fresh-cut products are highly sensitive to browning and softening. Common postharvest methods, such as the use of antibrowning compounds and/or modified atmosphere packaging, fail to preserve ‘Blanquilla’ pear slices long enough to be marketable. However, treatment with 1-MCP before cutting and peeling considerably improved their textural properties (9.2 N vs. 1.1 N with and without 1-MCP treatment, respectively) and color (a* values of 1 vs. 5 after 15 d at 4 °C, for slices pear treated with 1-MCP and without treatment, respectively). These positive changes were closely related to a decrease in respiratory activity determined on whole pears after 3 months of storage in air at 0 ± 1 °C and 95% R.H. (0.40 ± 0.05 mmol CO₂ kg⁻¹ h⁻¹ vs. 0.77 ± 0.04 mmol CO₂ kg⁻¹ h⁻¹ with and without 1-MCP treatment, respectively) and ethylene production (1.18 ± 0.36 nmol C₂H₄ kg⁻¹ h⁻¹ vs. 5.751 ± 1.12 nmol C₂H₄ kg⁻¹ h⁻¹ for samples treated with and without 1-MCP, respectively). The use of 1-MCP allows fresh-cut ‘Blanquilla’ pears to be sold up to about 5 d after processing. Treatment with 1-MCP could be a viable alternative to common technologies for extending the shelf-life of ‘Blanquilla’ pears as a fresh-cut product.     

Improving storability of persimmon cv. Rojo Brillante by combined use of preharvest and postharvest treatments

The combined use of preharvest treatments, gibberellic acid (GA₃) or calcium nitrate, with 1-methylcyclopropene (1-MCP) treatment applied postharvest, was evaluated to improve the storability of ‘Rojo Brillante’ persimmon fruit, at both 1 and 15 °C. Properties linked to commercial quality, such as flesh firmness, external colour, total soluble solids and level of astringency, were evaluated at harvest, periodically during storage, as well as after subsequent shelf-life periods. At both storage temperatures, control fruit and calcium nitrate-treated fruit showed commercial quality for 20 d; the sole application of GA₃ delayed loss of firmness for 30 d while the treatment with 1-MCP by itself allowed storage of the fruit for 40 d. The combined use of calcium nitrate plus 1-MCP did not improve maintenance of quality any more than when 1-MCP was applied alone. The combination of GA₃ and 1-MCP delayed the symptoms of chilling injury, extending the storability at 1 °C for up to nearly 3 months. During storage at 15 °C, the combination of both treatments resulted in high-firmness values for 30 d, but did not prolong the storage period any longer than the 40 d reached by the sole application of 1-MCP. Irrespective of treatment, a loss of efficacy of the deastringency treatment was observed after 30 d of storage at 15 °C.     

White lupine as a beneficial crop in Southern Europe: I. Potential for N mineralization in lupine amended soil and yield and N2 fixation by white lupine

Two experiments were carried out at Pegões (central Portugal) to determine the potential N mineralization in a pulse amended disturbed and undisturbed soil incubated at several temperatures, and to evaluate for 2 years the yield and N₂ fixation capacity of sweet lupine (Lupinus albus L. cv. Estoril) inoculated with a mixture of rhizobia strains or nodulated by indigenous soil bacteria and submitted to conventional tillage or no-till practices. A completely randomized block design for soil mobilization with three replicates was used for the laboratory study, and completely randomized blocks for inoculation and tillage treatments with four replicates were used for the lupine yield and N₂ fixation experiment. Residue N immobilization occurred immediately after mature residue return to the soil independent of temperature, and was greater at 7 °C especially in the disturbed topsoil. Greater immobilization was also observed by doubling the amount of mature residue incorporated in the soil. This was expected since soil microorganisms would be in direct contact with the fresh organic matter and would be provided with more organic carbon under these circumstances. Nitrogen mineralization proceeded after 5 days of amendment. Potential N mineralization was higher at 25 °C than at 18 or 7 °C, for both conventional and no-till practices. At 25 °C, 42% of buried residue-¹⁵N was released over 210 days, at a smaller rate than 18 °C (49%) over 81 days. Lupine yield and N₂ fixation capacity were similar in plots that were not inoculated and those receiving the mixture of three rhizobia strains. White lupine had an efficient symbiosis with indigenous soil rhizobia at pod-filling (>99%, >100 kg N ha⁻¹ year⁻¹) which was not affected by tillage. At this stage, plant residue including visible roots and nodules accounted for a soil N input of +96 kg ha⁻¹ year⁻¹ (91% of crop N), showing the large soil N benefit by the crop at this stage. The lupine residue at pod-filling stage can be used as a green manure under the conditions of organic farming systems. The apparent N “harvest” index of the pulse at pod-filling was only 9% though at maturity phase it should result in a higher value and the legume will show a lower fertilizer N value.     

Evaluation of shelf-life of fresh-cut pineapple using FT-NIR and FT-IR spectroscopy

The aim of this work was to investigate the loss of freshness of fresh-cut pineapple samples stored at different temperatures using non-destructive spectroscopic methods. Three lots of fresh cut pineapples (Ananas comosus L. cv. Golden Ripe, from Costa Rica), packaged in PVC trays (250 g) were analyzed during storage at three different temperatures (5.3, 8.6 and 15.8 °C). Loss of quality of these fruit was evaluated by chemical and microbiological parameters and using NIR and MIR spectroscopy. The FT-NIR spectra were acquired in reflectance mode directly on the slice of fresh-cut pineapple, over the range 12,500–3900 cm⁻¹, while FT-IR spectra were collected over the range 4000–700 cm⁻¹ using an horizontal ATR cell. Some chemical and microbiological parameters were also measured. Principal component analysis (PCA) was applied to the second derivative of the spectra to uncover molecular modifications occurring over the storage time. A clear discrimination between “fresh” and “old” samples was obtained and a stability time corresponding to the time of the initial loss of freshness was defined at each temperature. The stability times revealed by NIR spectroscopy were in good accordance with those evaluated by MIR. At each temperature the stability times (i.e. the initial loss of freshness times) defined by spectroscopic techniques (4–5 d at 5.3 °C, 3–4 d at 8.6 °C and 1 d at 15.8 °C) were associated with a mesophilic bacteria count ranging between 10⁵ and 10⁶ CFU g⁻¹ and lower than the maximum limit for mesophilic bacteria (<5 × 10⁷ CFU g⁻¹) given by French hygienic regulations at consumption.These results show that NIR and MIR spectroscopy could support conventional techniques (chemical and microbiological analysis) in studying shelf-life of fresh-cut fruit. In particular these techniques define the initial loss of freshness time, indicating a product which rapidly will be no longer acceptable if stored beyond that time. The main advantage of using IR spectroscopic techniques is to rapidly draw a profile of the product related to its change in quality.     

Inheritance of race 1.2 Fusarium wilt resistance in four melon cultivars

The resistance to Fusarium oxysporum f.sp. melonis (Fom) race 1.2 has been studied in melons, such as the Portuguese accession ‘BG-5384’ and in the Japanese ‘Shiro Uri Okayama’, ‘Kogane Nashi Makuwa’, and ‘C-211’, since a good characterization of the resistance is necessary before its introgression into commercial varieties. These four melon accessions showed a high level of resistance to races 0, 1, and 2 of Fom, indicating that the partial resistance to the race 1.2 previously detected may not have been race specific. To determine the mode of inheritance of the resistance to Fom race 1.2, the F₁, F₂, BCP_R, and BCP_S generations from the crosses between the four resistant accessions above and ‘Piel de Sapo’, a Fom race 1.2 susceptible melon, were developed. They were subsequently inoculated with two Fom isolates, one from the pathotype 1.2Y and the other from the pathotype 1.2W. The area under the disease progress curve was determined for each inoculated plant, and the data were analyzed. We show that the resistance seen in these accessions is polygenically inherited with a complex genetic control because many epistatic interactions were detected. The three epistatic effects; additivity × additivity, dominance × dominance, and dominance × additivity are present and significant, with differing magnitudes from one cross to the next. The relatively low heritabilities, and these epistatic effects make difficult the improvement of the resistance, from these sources, through a standard selection procedure.     

Light interception and radiation use efficiency in temperate quinoa (Chenopodium quinoa Willd.) cultivars

Sea level quinoas are grown at low altitudes in Central and Southern Chile. Both sensitivity to photoperiod and response to temperature largely determine quinoa adaptation, but crop biomass production must be quantified to evaluate agronomic performance. The objectives of this work are: (i) to characterize development effects on leaf area evolution for genotypes of sea level quinoa differing in cycle length, (ii) to quantify the extinction coefficient (k) for photosynthetically active radiation (PAR) and radiation use efficiency (RUE) from emergence up to the beginning of grain filling and (iii) to identify which crop attributes related to canopy architecture should be considered to improve biomass production. Four cultivars (NL-6, RU-5, CO-407 and Faro) were cropped in Pergamino (33°56′S, 60°35′W, 65 m a.s.l.), Argentina, at three densities (from 22 to 66 plants m⁻²) in two consecutive years under field conditions with adequate water and nutrient supply. Thermal time to first anthesis and maximum leaf number on the main stem were linearly correlated (r² = 0.87; p < 0.0001). Leaf area continued to increase during the flowering phase, notably in NL-6, the earliest genotype. There were significant differences in maximum plant leaf area between cultivars. Increasing density reduced plant leaf area but effects were comparatively small. Estimated k was 0.59 ± 0.02 across genotypes and was higher (p < 0.05) for 66 plants m⁻². Values for RUE changed as cumulative intercepted PAR (IPAR) increased; at initial stages of development RUE was 1.25 ± 0.09 g MJ IPAR⁻¹, but if cumulative IPAR was higher than 107.5 ± 10.4 MJ IPAR m⁻², RUE was 2.68 ± 0.15 g MJ IPAR⁻¹. That change occurred when leaf area index (LAI) and fraction of PAR intercepted were still low and ranged from 0.61 to 1.38 and from 0.33 to 0.51, respectively. No significant association was found with any developmental stage. Our results agreed to the notion that RUE variation during pre-anthesis phases is largely determined by LAI through its effect on radiation distribution within the canopy. Biomass production could be improved if periods of interception below 50% of incoming PAR were reduced to ensure high RUE. This seems to be possible in temperate areas both by the use of late genotypes with a higher number of leaves on the main stem and by early genotypes provided adequate plant density is chosen. Early increment in LAI and overlapping of the leaf area increase period with the flowering phase are desirable strategies for earliest genotypes to maximize yield.     

Expression of expansin genes during postharvest lignification and softening of ‘Luoyangqing’ and ‘Baisha’ loquat fruit under different storage conditions

Four expansin cDNA fragments, EjEXPA1, EjEXPA2, EjEXPA3 and EjEXPA4, were isolated and characterized from loquat (Eriobotrya japonica Lindl.) fruit. EjEXPA1 mRNA accumulated consistently with the increase in fruit firmness in 0 °C storage of ‘Luoyangqing’ (LYQ) fruit, where chilling injury with increased fruit firmness due to lignification was observed. EjEXPA1 mRNA levels were lower in fruit that underwent low temperature conditioning (LTC, 6 d at 5 °C then 4 d at 0 °C), and in 1-methylcyclopropene (1-MCP) treated fruit, in both cases where chilling injury was alleviated. Fruit of the ‘Baisha’ (BS) cultivar soften after harvest rather than increase in firmness, and high expression levels of EjEXPA1 and EjEXPA4 accompanied the softening of BS fruit stored at 20 °C; such mRNA accumulation was much lower when fruit were stored at 0 °C, where softening was significantly inhibited by the low temperature. Very low expression of EjEXPA2 and EjEXPA3 was observed during storage of both LYQ and BS fruit under the different storage conditions. Our results showed that of the four genes characterized, EjEXPA1 might be associated with chilling-induced lignification while both EjEXPA1 and EjEXPA4 were closely related to softening of loquat fruit during the postharvest period.     

Ethylene synthesis,ripening capacity,and superficial scald inhibition in 1-MCP treated ‘d’Anjou’ pears are affected by storage temperature

A continuing challenge for commercializing 1-methylcyclopropene (1-MCP) to extend the storage life and control superficial scald of ‘d’Anjou’ pear (Pyrus communis L.) is how to initiate ripening in 1-MCP treated fruit. ‘D’Anjou’ pears harvested at commercial and late maturity were treated with 1-MCP at 0.15 μL L⁻¹ and stored either at the commercial storage temperature −1.1 °C (1-MCP@−1.1 °C), or at 1.1 °C (1-MCP@1.1 °C) or 2.2 °C (1-MCP@2.2 °C) for 8 months. Control fruit stored at −1.1 °C ripened and developed significant scald within 7 d at 20 °C following 3–5 months of storage. While 1-MCP@−1.1 °C fruit did not develop ripening capacity due to extremely low internal ethylene concentration (IEC) and ethylene production rate for 8 months, 1-MCP@1.1 °C fruit produced significant amounts of IEC during storage and developed ripening capacity with relatively low levels of scald within 7 d at 20 °C following 6–8 months of storage. 1-MCP@2.2 °C fruit lost quality quickly during storage. Compared to the control, the expression of ethylene synthesis (PcACS1, PcACO1) and signal (PcETR1, PcETR2) genes was stable at extremely low levels in 1-MCP@−1.1 °C fruit. In contrast, they increased expression after 4 or 5 months of storage in 1-MCP@1.1 °C fruit. Other genes (PcCTR1, PcACS2, PcACS4 and PcACS5) remained at very low expression regardless of fruit capacity to ripen. A storage temperature of 1.1 °C can facilitate initiation of ripening capacity in 1-MCP treated ‘d’Anjou’ pears with relatively low scald incidence following 6–8 months storage through recovering the expression of certain ethylene synthesis and signal genes.     

Identification of quantitative trait loci for bruchid (<Emphasis Type="Italic">Callosobruchus maculatus</Emphasis>) resistance in black gram [<Emphasis Type="Italic">Vigna mungo</Emphasis> (L.) Hepper]

An inter-subspecific mapping population was generated by crossing V. mungo var. mungo (cv. TU 94-2, bruchid susceptible) and V. mungo var. silvestris (bruchid resistant). About 37.8% of the bruchid completed their lifecycle on seeds of V. mungo var. silvestris compared with 100% on the susceptible variety TU 94-2. The total developmental period of C. maculatus on Vigna mungo var. silvestris was considerably extended (88 days as compared with 34 days on TU 94-2). A genetic linkage map constructed using recombinant inbred lines (RILs) in F₉ generation with 428 markers [86 random amplified polymorphic DNA (RAPD), 47 simple sequence repeat (SSR), 41 inter-SSR (ISSR), 254 amplified fragment length polymorphism (AFLP)] was used for QTL detection. One hundred four individuals were used for detection of QTLs associated with bruchid resistance. The RILs exhibited a high level of variation in percentage adult emergence (0–100%) and developmental period (0–105 days). Two QTLs, Cmrae1.1 and Cmrae1.2, were identified for percentage adult emergence, on linkage group (LG) 3 and 4, respectively. For developmental period, six QTLs were identified, with two QTLs (Cmrdp1.1 and Cmrdp1.2) on LG 1, three QTLs (Cmrdp1.3, Cmrdp1.4, and Cmrdp1.5) on LG 2, and one QTL (Cmrdp1.6) on LG 10.     

Effect of antifungal hydroxypropyl methylcellulose (HPMC)–lipid edible composite coatings on postharvest decay development and quality attributes of cold-stored ‘Valencia’ oranges

Edible composite coatings based on hydroxypropyl methylcellulose (HPMC), hydrophobic components (beeswax and shellac), and food preservatives with antifungal properties were evaluated on ‘Valencia’ oranges during long-term cold storage. Selected food preservatives included potassium sorbate (PS), sodium benzoate (SB), sodium propionate (SP), and their mixtures. Intact oranges or oranges artificially inoculated with Penicillium digitatum or Penicillium italicum were coated and stored up to 60 d at 5 °C followed by 7 d of shelf-life at 20 °C. Some antifungal HPMC–lipid coatings significantly reduced incidence and severity of both green (GM) and blue (BM) molds on inoculated and cold-stored oranges, and PS + SP-based coating was the most effective. In general, the coatings controlled GM better than BM. After 30 and 60 d at 5 °C plus 7 d at 20 °C, fruit weight loss, rind firmness, internal gas concentrations, ethanol and acetaldehyde contents of the juice, sensory flavor, off-flavor, and fruit appearance were not adversely affected by application of the antifungal coatings, which showed promise as potential substitutes for citrus commercial waxes. However, further studies should follow to improve some coating physical characteristics in order to provide better water loss control and higher gloss on coated oranges.     

Effect of packaging conditions on quality and shelf-life of fresh-cut pineapple (Ananas comosus)

Influence of packaging conditions on fresh-cut ‘Gold’ pineapple shelf-life were studied during 20 d of storage at 5 °C. Fresh-cut fruit pieces were packed in polypropylene trays (PP) and wrapped with 64 μm polypropylene film under active (high 40% or low oxygen, 11.4%) or passive modified atmospheres (air or cut fruit coated with 1%, w/v alginate). Changes in headspace composition, titratable acidity, pH, soluble solids content, juice leakage, color, texture, and microbial growth were evaluated over time. For all packaging conditions, oxygen concentration continuously decreased below its initial concentration over 20 d storage, but never reached levels below 2% O₂. Meanwhile, CO₂ concentration inside all packages continuously increased over time up to 10.6–11.7% from the initial conditions. Ethylene concentrations were always less than 0.4 μl L⁻¹ while ethanol was detected only after 13 d of storage. Color parameters L^* and b^* significantly decreased over time in all packaging conditions and were directly attributed to the translucency phenomenon in the fruit flesh. When alginate coating was used, juice leakage was significantly reduced in contrast with the substantial juice accumulation observed in the rest of the packaging conditions. Texture profile analysis (TPA) parameters, did not significantly change over time, suggesting that structural characteristics of fresh-cut pineapple pieces were preserved throughout storage. From the microbial point of view, the shelf-life of ‘Gold’ fresh-cut pineapple was limited to 14 d by mesophilic bacterial growth. Further studies are needed to evaluate the sensory aspects, as well as to characterize the flesh translucency phenomenon and reduce juice leakage of fresh-cut pineapple.     

Suitability of aqueous chlorine dioxide versus sodium hypochlorite as an effective sanitizer for preserving quality of fresh-cut lettuce while avoiding by-product formation

Aqueous chlorine dioxide (ClO₂) has been postulated as an alternative to sodium hypochlorite (NaClO) for fresh-cut produce sanitization with the advantage of avoiding the risks associated with chlorination by-products. However, little is known about its influence on preserving quality and the potential formation of trihalomethanes (THMs) under typical processing conditions. The suitability of aqueous chlorine dioxide (3 mg L⁻¹) as an effective sanitizer of fresh-cut iceberg lettuce stored under active modified atmosphere packaging (MAP) at refrigerated conditions was determined and compared with sodium hypochlorite (100 mg L⁻¹). Fresh-cut lettuce washed with tap water was used as a control. The epiphytic microbiota were characterized by the evaluation of the major relevant microbial groups such as mesophiles, psychrophiles, Pseudomonas spp., Enterobacteriaceae, lactic acid bacteria, yeasts and moulds. Additionally, gas composition, sensory quality, vitamin C and individual and total phenolics were monitored after washing and during storage for 3 d at 4 °C followed by 7 d at 8 °C. In general, the natural microbiota of fresh-cut lettuce after washing and storage was equally affected by the different washing solutions, with the exception of yeasts which showed the highest growth after 10 d storage in samples washed with chlorine dioxide. None of the tested washings negatively affected sensory quality, which was acceptable after 10 d storage. Additionally, the content of bioactive compounds was not significantly affected either by washing solution or by storage time. The potential formation of THMs was evaluated by the analysis of lettuce washed in water with a chemical oxygen demand (COD) of 700 mg L⁻¹ treated for 30 min with sodium hypochlorite (100 mg L⁻¹) or chlorine dioxide (3.7 mg L⁻¹). Trihalomethane formation was only detected in the process water in which sodium hypochlorite was applied (217 ± 38 μg L⁻¹). However, THMs formation in fresh-cut lettuce was negligible despite the sanitation procedure. The formation of THMs was only detected in fresh-cut lettuce when sodium hypochlorite was used under very extreme conditions where lettuce was washed in water with a high level of organic matter (COD = 1800 mg L⁻¹), high sodium hypochlorite concentration (700 mg L⁻¹) and long contact time (60 min). Our data suggest that aqueous chlorine dioxide is as suitable as sodium hypochlorite for fresh-cut lettuce sanitation with the advantage of preventing the formation of THMs.     

Comparison of the antioxidant enzymes of broccoli after cold or heat shock treatment at different storage temperatures

An experiment was conducted to study the association between cold shock treatment (CST) (0 °C, 1 h) and heat shock treatment (HST) (55 °C, 30 s) on antioxidant enzymes of broccoli at different storage temperatures (20, 10, or 5 °C). There was no difference in antioxidant enzyme activities between CST and HST under storage at 20 °C; superoxide dismutase (SOD) and catalase (CAT) activities were increased in comparison with the controls. However, activities of antioxidant enzymes, except for ascorbate peroxidase (APX), with CST were higher than those with HST during storage at 10 °C, while there were opposite results except for CAT activity at 5 °C. These results suggest that CST and HST have the same effect on the antioxidant enzymes of broccoli during 20 °C storage, but have different effects at below 10 °C, which become more pronounced as the temperature is lowered.     

Shiraz vines maintain yield in response to a 2–4 °C increase in maximum temperature using an open-top heating system at key phenostages

We measured the effects of increased daytime temperature during 2- (2007/08) or 3-week periods (2008/09) on the yield and yield components of irrigated Shiraz vines in the Barossa Valley of Australia. A simple and inexpensive open system was used to elevate temperature during a single phenological window, either bracketing budburst (E-L stage 4), shortly after flowering (E-L stage 23), bracketing pea size (E-L stage 31), around veraison (E-L stage 35) or shortly before harvest (E-L stage 38). Two important features of the heating systems were tracking of diurnal temperature dynamics, and maintaining relative humidity, hence avoiding the interaction between temperature and vapour pressure deficit. Minimum temperature was unchanged.Compared to controls, maximum ambient temperature was increased between 1.8 and 4.1 °C in treated plots but canopy temperature of treated vines only increased by 0.9–1.1 °C. Elevation of bunch temperature was 2.3–3.2 °C. Increasing temperature around budburst transiently accelerated development in comparison to controls; no phenological changes were detected for other timings of treatment. Yield averaged 4.3 kg vine⁻¹ in 2007–08 and 6.1 kg vine⁻¹ in 2008–09. In both seasons and for all timings of treatment, increasing temperature did not affect yield or its components; lack of yield response did not result, therefore, from compensatory mechanisms, e.g. heavier berries compensating for fewer fruit. The dynamics of berry growth and total soluble solids were largely unaffected by temperature. Under our experimental conditions, the capacity of irrigated Shiraz canopies to partially buffer a 2–4 °C increase in maximum ambient temperature may have been important for the maintenance of yield, and berry growth and sugar accumulation.     

Influence of the stage of ripeness on phenolic metabolism and antioxidant activity in table grapes exposed to different CO2 treatments

We have analyzed the influence of the stage of ripeness on L-phenylalanine ammonia-lyase (PAL) gene expression, accumulation of anthocyanins and total phenolics, and on antioxidant activity in the skin of table grapes treated with 20% CO₂ + 20% O₂ + 60 % N₂ for 3 or 6 d at low temperature (0 °C). The residual effect of high CO₂ treatment after transfer to air was also studied. In early harvested grapes, neither the anthocyanin content nor the accumulation of VcPAL mRNA was affected by any of the CO₂ treatments applied. However, in late harvested grapes, the duration of high CO₂ treatment determined its effect and a 6 d treatment with CO₂ sustained higher levels of total phenolics and anthocyanin accumulation, and VcPAL expression than observed in untreated late harvested grapes. The increased antioxidant capacity was correlated with the total amount of phenolics and anthocyanins. Conversely, in grapes treated for 3 d with CO₂ the phenylpropanoid pathway did not appear to be induced and a relationship between antioxidant activity and anthocyanins was not observed. Thus, further studies are needed to identify the most important antioxidants in these treated fruit.     

The effect of temperature and other factors on chlorophyll a fluorescence and the lower oxygen limit in apples (Malus domestica)

The effects of temperature, scan interval and rate of oxygen (O₂) decline on pulse frequency modulation (PFM)-based minimum fluorescence (F_α) and the F_α-based lower oxygen limit (LOL) were investigated using ‘Honeycrisp’ apples (Malus × domestica Borkh). The effects of temperature and hypoxic stress on pulse amplitude modulation (PAM) fluorescence parameters were also investigated. The PFM scan interval had no effect on the F_α baseline, but increases in the scan interval decreased the low-O₂-induced fluorescence spike intensity (ΔF_α). Temperature negatively correlated with the F_α baseline while ΔF_α °C⁻¹ was greater at lower than at higher temperatures. When using a PAM fluorometer, the minimum fluorescence (F_o), and to a lesser extent the maximum fluorescence (F_m), were similarly affected by temperature as was F_α. Temperature altered the LOL in fruit. Apples stored at 20, 10, 3.5 and 0 °C spiked at 0.72, 0.33, 0.22 and 0.08 kPa O₂, respectively, under a rapid O₂ decline (i.e., 20.9 to <1 kPa O₂ in ≈5–6 h). Although the low-O₂ F_α spike apex values did not change with temperature, the spike intensity increased with temperature due to a reduced fluorescence baseline. A slower O₂ decline rate produced slightly higher LOL and lower spike intensity values. In conclusion, temperature and rate of O₂ decline affected the low-O₂-induced PFM fluorescence spike intensity as well as the LOL, while the PFM scan interval affected the spike intensity.     

Effects of minimal temperatures on low-linolenic rapeseed oil fatty-acid composition

Rapeseed oil is rich in alpha-linolenic acid (C18:3) and has a low content in saturated fatty acids. It is therefore considered as a very healthy edible oil. However, its high polyunsaturated fatty acid content makes it sensitive to temperature oxidation and therefore not suitable for deep-frying. Low-linolenic varieties with C18:3 content lower than 3.5% have been bred, but a large variability of alpha-linolenic acid content has been often observed in agricultural production of these new lines. Identifying factors affecting the fatty acid profile of oilseed rape should make it possible to produce rapeseed with alpha-linolenic acid content lower than 2.5% and therefore more suitable for frying and other uses in the food industry.Fatty acid composition is affected by environmental conditions, temperature being the main factor. Previous works showed that for conventional double-low rapeseed varieties, low minimal temperatures during the 60 days following the onset of flowering were related to higher alpha-linolenic acid contents.Monitoring the fatty acid profile in low-linolenic varieties from the beginning of seed filling to full maturity showed that alpha-linolenic acid synthesis occurred mainly between 550 and 850 degree-days (base 0 °C) after the onset of flowering, that is during the 20 first days of seed filling in Swiss conditions, i.e. 41–60 days after the onset of flowering. During this period, the determination coefficient of a second order regression between final alpha-linolenic acid (C18:3) content and minimal daily temperature was even better, with R² = 0.87. A significant positive relation was also found for the regression between minimal temperature and oleic acid (C18:1) content for the cultivar Splendor (R² = 0.77) but no correlation could evidence a relation between temperature and linoleic acid (C18:2) content.An easier way to show the relationship between linolenic acid content and minimal temperatures is based on the assumption that fatty acid desaturases regulated by temperature are active at low temperatures only. It consists in counting how many times during this period daily minimal temperature reaches a minimal threshold temperature of 13 °C. The relationship between final alpha-linolenic acid content and the number of days with minimal temperature below 13 °C is as good as the one presented before, i.e. with a determination coefficient, R² = 0.85. This simple model could be used to determine the growing areas with low linolenic acid content.