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Superficial scald is still one of the most important postharvest physiological disorders in apples. Commercial control of this disorder has been accomplished by selecting resistant cultivars, treating fruit with DPA and ethoxyquin, using oil-soaked fruit wraps and storing the fruit under low O2. However, the causal reason for scald development is still a mystery. Research has indicated that the scald-promoting factor or inducing compound may be formed or accumulated in apple cuticle then rediffused back into the hypodermis, thereby causing damage. Hydroperoxides, auto-oxidative product from α-farnesene, have been thought to be the toxic compounds, inducing scald; however, it is not explained how the hydroperoxides move from the cuticle to the hypodermis. The identification and dynamic changes of 6-methyl-5-heptene-2-one as a natural volatile in apple fruit during ripening were made, which accumulated in higher quantitaty in cuticular wax than in headspace. The close relationship between the chloroplast breakdown and amount of α-farnesene changes, the induction of scald-like symptom on the surface of apple fruit by 6-methyl-5-heptene-2-one and the sensitivity of fruit to this ketone damage were investigated. Our results suggest that the accumulation of 6-methyl-5-heptene-2-one in the cuticular wax of apple fruit might be the causal reason for scald development in apples.
Aroma analysis of horticultural produce is an emerging field in which both flavor producing and malodorous compounds are detected from within a complex sample matrix. Qualitative and quantitative information is desired to monitor produce ripeness and provide quality control over processed products such as juices, preserves and canned products. Conventional analysis methods such as purge and trap and gas chromatography–mass spectrometry provide much of this information but are laborious and time consuming. Faster techniques are required when large numbers of samples are being analyzed and when rapid feedback to the produce harvester is required. Solid-phase microextraction (SPME) has recently been shown to significantly reduce the sampling times required by more conventional methods. The use of fast gas chromatographic techniques along with the recently commercialized time-of-flight mass spectrometer has also significantly reduced the separation and analysis times. We have combined SPME with gas chromatography–time-of-flight mass spectrometry as a rapid and quantitative tool for the analysis of flavor volatiles in apples and tomatoes. The sampling and analysis processes provide significant improvements to sample throughput, with analysis times taking only 2–6 minutes. The linear response of this system to butylacetate, ethyl-2-methylbutanoate and hexylacetate ranges from ppb to ppm levels, and the identification of unknown flavor compounds is possible even in the presence of other co-eluting compounds. The SPME technique is able to investigate volatiles changes in apple cuticle and tissues, which open the new possibility for flavor biochemistry research.
Banana [Musa sp.9AAA group0, Cavendish] fruit are climacteric in nature, undergoing a rapid rise in ethylene production and respiration. Ethylene production can peak within 8 h of a detectable rise in production and respiration peaks within 24 h. These rapid changes permit precise timing for events related to or dependent on ethylene presence. Using rapid analytical methodology, we investigated the dynamic changes in volatile biosynthesis and its relation to other ripening parameters. Ungassed, mature-green banana fruit were placed individually at 23°C in flow through glass chambers. Ethylene production, respiration, chlorophyll fluorescence, skin color (hue angle) and volatile production were monitored. The climacteric rise and subsequent fall in ethylene production was found to be complete within 20 h. The respiratory rise peaked 20 h after the initial rise in ethylene production. The onset of the decline in chlorophyll fluorescence, skin color (hue angle) were coincident with the rise of ethylene and respiration, which indicated that the chlorophyll fluorescence may be used to monitor the banana fruit ripening. Volatile production was found to begin ≈60 h after the onset of the ethylene climacteric, peaking 3 to 4 days later. The ester precursors butyric acid and 3-methylbutanol were used in feeding experiments at different developmental stages for pulp and peel. Full ester-forming capacity was found to exist well before the onset of volatile biosynthesis. There were also different biosynthetic capacities for pulp and peel. Low aroma production in pre-climacteric fruit is apparently limited by the supply of precursors, which may be derived from the ethylene-induced enhancement of fruit respiratory metabolism.
Peel discs (0.2 mm in diameter) of refrigerated, air-stored apple that were immersed in a medium isotonic with that of fruit sap were allowed to photosynthesize either in a closed or flow-through system. The photosynthetic net evolution of O2 in the light or consumption in the dark was used to predict the duration of the experiment that would be within the critical limits of aerobiosis. Using GC-MS system, volatile emissions from these tissues were determined, in the head space and liquid medium. The volatile profile generated from head space analysis was essentially similar to that of whole fruit. Light, compared to the dark treatment, stimulated the synthesis of nearly all volatiles, especially α-farnesene. The synthesis of 6-methyl-5-hepten-2-one, an oxidative product of α-farnesene that causes scald like symptoms in whole fruit, was observed only under lighted conditions. While O2 content in the medium seemed to have no effect on the volatile build-up in the head space, a C15 sesquiterpene with a mass spectrum similar to hydroperoxide breakdown products of α-farnesene was synthesized only in presence of O2 in the reaction medium. Inhibition of light reactions of photosynthesis with DCMU, suppressed the synthesis of various volatiles in the head space suggesting the role of chloroplast activity in aroma development. We suggest that peel discs work well as a model system to study flavor chemistry in apple.
Hexanal vapor inhibited hyphae growth of P. expansum Link. and B. cinerea Pers. on PDA media and on apple slices. After 48 hours exposure to 100 μl·liter–1 hexanal, the hyphae growth of both fungi was ≈ 50% that of nontreated controls. At a concentration of 250 μl·liter–1, neither fungi grew during the treatment period, however, some growth of both fungi occurred 120 hours after treatment. At concentrations of hexanal vapor of ≥450 μl·liter–1, the growth of both fungi ceased, and the organisms were apparently killed, neither showing regrowth when moved to air. When fungi were allowed to germinate and grow for 48 hours in hexanal-free air, a subsequent 48-hour exposure to 250 μl·liter–1 hexanal slowed colony growth relative to controls for several days and a 48-hour exposure to 450 μl·liter–1 stopped growth completely. Concentrations of hexanal that inhibited fungal growth on PDA also retarded decay lesion development on `Golden Delicious' and on `Jonagold' apple slices. Hexanal treatment stimulated aroma volatile production in `Jonagold' and `Golden Delicious' apple slices with hexanol and hexylacetate production strongly enhanced after 20 to 30 hours of treatment. A small amount of butylhexanoate and hexylhexanoate production also was noted. Since hexanal was converted to aroma-related volatiles by the fruit, the possibility of developing a system for nonresiduel antifungal agent is promising. This possibility was examined in modified-atmosphere packages.
Chloroplast fluorescence as a nondestructive tool for assessing `Red Delicious', `Golden Delicious' and `Law Rome' apple fruit quality was examined after approximately 4.5 months storage. Fluorometry parameters of minimal fluorescence (Fo), maximal fluorescence (Fm) and quantum yield (Fm-Fo)/Fm (otherwise denoted as Fv/Fm) were determined. All fluorescence parameters declined with time as apple fruit were maintained at 22°C in air. Fv/Fm was found to correlate well with firmness for `Red Delicious' fruit. A decline in Fo with time correlated very well with the development of yellow coloration of `Golden Delicious' fruit. The Fv/Fm value was consistently higher for controlled-atmosphere (CA) stored fruit than for regular-air (RA) stored fruit. When CA and RA stored `Law Rome' fruit were combined and a Fv/Fm value of 0.685 was used to resegregate fruit from the two storage regimes. Resegregation was achieved with 75% accuracy, with only 5% RA-stored fruit incorrectly identified as CA-stored. The accuracy, speed of assessment and light-based nature of fluorometry suggest it may have some practical use as a tool for sorting apple and other chlorophyll-containing fruit on commercial packinglines.
Measurements of soil water content near the soil surface often are required for efficient turfgrass water management. Experiments were conducted in a greenhouse to determine if the dual-probe heat-pulse (DPHP) technique can be used to monitor changes in soil volumetric water content (θv) and turfgrass water use. `Kentucky 31' Tall fescue (Festuca arundinacea Schreb.) was planted in 20-cm-diameter containers packed with Haynie sandy loam (coarse-silty, mixed, calcareous, mesic Typic Udifluvents). Water content was measured with the DPHP sensors that were placed horizontally at different depths between 1.5 and 14.4 cm from the surface in the soil column. Water content also was monitored gravimetrically from changes in container mass. Measurements started when the soil surface was covered completely by tall fescue. Hence, changes in θv could be attributed entirely to water being taken up by roots of tall fescue. Daily measurements were taken over multiple 6- or 7-day drying cycles. Each drying cycle was preceded by an irrigation, and free drainage had ceased before measurements were initiated. Soil water content dropped from ≈0.35 to 0.10 m3·m-3 during each drying cycle. Correlation was excellent between θv and changes in water content determined by the DPHP and gravimetric methods. Comparisons with the gravimetric method showed that the DPHP sensors could measure average container θv within 0.03 m3·m-3 and changes in soil water content within 0.01 m3·m-3.
Potatoes with hollow heart or brown center are considered to be of poor quality for both fresh and processing markets. A reliable nondestructive method, which can distinguish affected and normal potatoes, is described here. A Varian 4.7 Tesla, 33-cm horizontal-bore spectroscopy/imaging system was used to obtain nuclear magnetic resonance (NMR) images of potatoes. A two-dimensional multi-slice spin-echo imaging technique was used to acquire the cross-sectional images along the longitudinal direction. The echo time was 35 msec and the repetition time was 1.2 sec. A total of 13 slice images were taken for each potato. A one-dimensional projection technique was also performed to evaluate the possibility of using fast-scan method. The brown center showed high intensity in long echo scans due to its longer TL relaxation time. A suberin-like layer resembling the periderm developed on the cavity wall of hollow heart causing a tan or dark brown coloration. This cavity wall also appeared in high intensity on the image. The affected potatoes can easily be sorted out using this nondestructive NMR imaging technique.
Aroma production by apple fruit is an important quality criterion and has been found to be a fruit-ripening-related process. 1-Methylcyclopropene (1-MCP), an effective ethylene action inhibitor, was used to study the relationship between volatile biosynthesis, ethylene action, and fruit ripening in `Golden Delicious' apple fruit. Pre-climacteric fruit were treated with 1-MCP vapors at a concentration of 500 parts per billion (v/v) at 23°C. 1-MCP prevented the climacteric rise of ethylene production, respiration, and volatile production, while untreated fruits developed typical climacteric changes in ethylene production, respiration and volatile production. Applying ethylene at 15–20 parts per million for 24 hr 11 days after 1-MCP treatment could not overcome the effect of 1-MCP, suggesting that 1-MCP inhibited ethylene action irreversibly. Interestingly, when 1-MCP-treated tissue were fed butanol and butyric acid, they converted these compounds to their corresponding esters butylacetate and butylbutanoate. Thus precursor supply is apparently limiting and appears to be ethylene-dependent.
‘Hansen 536’ (Prunus dulcis × Prunus persica) is an important commercial rootstock for peach and almond. However, susceptibility to wet soil and bacterial canker has limited its use primarily to areas with less annual rainfall. Genetic engineering techniques offer an attractive approach to improve effectively the current problems with this cultivar. To develop an efficient shoot regeneration system from leaf explants, 10 culture media containing Murashige and Skoog (MS) or woody plant medium (WPM) supplemented with different plant growth regulators were evaluated, and adventitious shoot regeneration occurred at frequencies ranging from 0% to 36.1%. Optimal regeneration with a frequency of 32.3% to 36.1% occurred with WPM medium containing 8.88 µm 6-benzylamino-purine (BAP) and 0.98 to 3.94 µm indole-3-butyric acid (IBA). The regenerated shoots had a high rooting ability, and 80% of the in vitro shoots tested rooted and survived after being transplanted to substrate directly. Transient transformation showed an efficient delivery of the β-glucuronidase (GUS) reporter gene (gusA) using all three Agrobacterium tumefaciens strains tested with a concentration of OD600 0.5 to 1.0 for 4 days of cocultivation. The protocols described provide a foundation for further studies to improve shoot regeneration and stable transformation of the important peach and almond rootstock ‘Hansen 536’.