Volatile ester molecules are important contributors to the perception of fruit taste. Biosynthesis of volatile compounds occurs via several biochemical pathways. Ongoing studies have concentrated on alcohol acetyl transferase, the terminal step in the acetate ester synthesis pathway. Our studies on volatile biosynthesis in apples have revealed several interesting phenomena. First, the nature and amount of volatile compounds are cultivarand strain-dependent. Studies with `Delicious' show a relationship between amount of peel coloration and flavor volatile content of tissue. Second, it is possible to manipulate the preharvest growing environment to influence the content of some volatiles in the fruit. Third, generation of volatiles is closely linked to the onset of climacteric ripening. Other experiments show the response of apples to different storage conditions with regard to volatile ester synthesis. In some cultivars softening apparently provides ester precursor molecules, leading us to speculate that there are glycosidically bound intermediates that are liberated by the action of cell-wall degradation.
James Mattheis and John K. Fellman
The commercial use of modified atmosphere packaging (MAP) technology provides a means to slow the processes of ripening and senescence during storage, transport, and marketing of many fresh fruit and vegetables. The benefits of MAP and controlled atmosphere (CA) technologies for extending postharvest life of many fruit and vegetables have been recognized for many years. Although both technologies have been and continue to be extensively researched, more examples of the impacts of CA on produce quality are available in the literature and many of these reports were used in development of this review. Storage using MAP, similar to the use of CA storage, impacts most aspects of produce quality although the extent to which each quality attribute responds to CA or modified atmosphere (MA) conditions varies among commodities. Impacts of MAP and CA on flavor and aroma are dependent on the composition of the storage atmosphere, avoidance of anaerobic conditions, storage duration, and the use of fresh-cut technologies before storage.
Esmaeil Fallahi and John K. Fellman
Effects of three times and five rates of urea application on productivity, tree growth, soil nitrate movement, nutrient partitioning, and postharvest fruit quality of `Redspur Delicious' apple on M.7 rootstock over several years were studied. Time of application did not have significant effects on most fruit quality factors or yield. However, significant differences were observed for quality and yield measurements among different quantities of N. Fruit firmness decreased with every increment in N increase. Trees with N at 0.045 kg/tree had lower yield and higher fruit firmness than those with higher quantities of N. Fruit weight and color decreased with each increment increase in the quantity of N. Trees with N at 0.045 and 0.18 kg/tree had significantly better (more red) color and lower fruit N and leaf N than those with higher quantities of N. Bud tissue nutrients were affected by quantity of N application. Fruit from trees with N at <0.18 kg/tree had lower soluble solids. High N increased fruit ethylene and respiration. Nitrogen application affected 2-methyl butyl acetate of fruit. Monitoring nitrate movement through the soil showed that application of N at >0.45 kg/tree, particularly in fall resulted in excess levels of nitrate, increasing the possibility of underground water contamination. Applying N at ≤0.32 kg/tree did not result in excess soil nitrate at 1.52-m depth.
John K. Fellman and James P. Mattheis
Developments in analytical technology, most notably high resolution fused silica open tubular (FSOT) gas chromatography-mass spectromety (GC-MS), make it possible to investigate physiological roles of volatile molecules occurring at low (ppb-ppm) concentrations. Use of headspace and purge-and-trap sampling coupled with cryofocusing injection techniques minimizes artifacts often created when more traditional methods of volatile molecule extraction are used. A challenging aspect of the work is development of appropriate delivery methods for internal standard quantitation of the molecules of interest. Apparently, biosynthesis of certain volatile substances is O2 dependent and others are manufactured in response to a changing environment. FSOT GC-MS investigation revealed dramatic changes in content and quantity of `Bisbee' apple headspace and purgable flesh volatiles during a 5-week harvest maturity period and 4 months of subsequent refrigerated storage. Other studies with apple mesocarp cultures and other fruits show interesting volatile molecule profiles in response to different treatments.
Loretta J. Mikitzel, Max E Patterson and John K. Fellman
Walla Walla Sweet onions (Allium cepa L.) have a short storage and marketing season. Studies to determine viable shelf life and to extend post-harvest life with controlled atmosphere (CA) storage were conducted. Onions were exposed to various CA gas mixtures in combination with heat curing (35°C) and/or chlorine dioxide (ClO2) fumigation, to control disease. Preliminary results indicated Botrytis was the primary cause of post-harvest losses. A 1% O2, 5% CO2 atmosphere appeared to maintain onion quality better than other gas mixtures tested during 15 weeks of CA storage (0°C). Carbon dioxide series above 5% show promise in reducing the 35% storage loss that occurred with the 5% CO2 treatment. Curing for at least 72 hours followed by a 1-hour ClO2 fumigation resulted in the least bulb decay and after 15 weeks of storage (1% O2, 5% CO2), 75% of the bulbs were in marketable condition. Onions stored 15 weeks in air (0°C, 70% RH) were unmarketable. Shelf life of freshly harvested onions was 18 days, after which the onions rapidly decayed. After CA storage, shelf life was reduced to 10-14 days due to rapid sprouting. To enjoy a 30-day market window, disease control is necessary for freshly harvested onions and sprouting must be controlled in post-storage onions.
Xuetong Fan, James P. Mattheis and John K. Fellman
The effect of exogenous methyl jasmonate (MJ) and jasmonic acid (JA) compared with the effect of ethephon on surface color and quality of `Golden Delicious' and `Fuji' apples (Malus ×domestica Borkh.) was studied. Treatments were applied by dipping fruit in water solutions of JA, MJ, or ethephon or by exposing fruit to MJ vapors. Response to MJ vapor treatment depended on fruit developmental stage, with the maximum effect occurring as fruit began to produce ethylene. MJ promoted color changes more effectively than JA. The promotive effect of JA increased with JA concentration. A minimum concentration of 0.1 mmol·L-1 JA was needed to promote significant color change within 15 d at 20 °C. JA at 1 or 10 mmol·L-1 promoted color change more effectively than 0.35 or 3.5 mmol·L-1 ethephon. The magnitude of JA-promoted responses decreased at lower temperatures. Treatments with 10 mmol·L-1 JA or 3.5 mmol·L-1 ethephon were phytotoxic. Treatments using JA at 1 or 10 mmol·L-1 in water promoted loss of fruit titratable acidity compared to controls. Firmness and soluble solids content were relatively unresponsive to JA treatments. Based on these results, using JA and MJ to promote degreening of apple fruit with minimal loss of other quality attributes appears feasible.
Randy R. Lee, John K. Fellman and Esmaeil Fallahi
The influence of flower bud position on bloom, fruit quality, and fruit maturity was investigated on `Rome Beauty' apple (Malus domestica Borkh.). Limbs on trees containing spur terminal flower buds and lateral flower buds were tagged and the number of blossoms counted every three days until bloom ended. At harvest, fruit from each bud type were selected and seed number, fresh weight, fruit quality characteristics, and onset of ethylene production were measured. Spur terminal flower buds began blooming earlier, blossomed for a longer period of time, and produced more blossoms than lateral flower buds. Fruit from spur terminal flower buds had more seeds, were heavier, and contained more starch than lateral bud fruit. Lateral bud fruit had higher pressure values, due to smaller size, and higher soluble solids, due to consumption of starch reserves. Fruit color and titratable acidity were not significantly different regardless of bud position. Spur terminal fruit started producing ethylene eight days later than lateral bud fruit, indicating they were maturing less quickly. Cultivars such as `Fuji', `Gala', and `Braeburn' display similar growth and fruiting habits.
David R. Rudell, John K. Fellman and James P. Mattheis
Repeated preharvest applications of methyl jasmonate (MJ) to 'Fuji' apple [Malus sylvestris var. domestica (Borkh.) Mansf.] fruit were evaluated for impacts on peel color, size, fruit finish, and maturation. MJ treatments at 2 week intervals began 48 days after full bloom (DAFB) (early season) or 119 DAFB (late season) and fruit were harvested 172 DAFB. MJ treatment stimulated significant increases in peel red color following the initial application and thereafter. Early season MJ treatment reduced fruit diameter and length to diameter ratio but slowed softening and starch hydrolysis. Fruit receiving late season MJ treatments had increased incidence of bitter pit and splitting, shorter green life, and slower softening. Results suggest preharvest application of MJ impacts apple color development and other aspects of fruit quality. Chemical name used: methyl 3-oxo-2-(2-pentenyl)cyclopentane-1-acetate (methyl jasmonate).
Gregory M. Peck, Preston K. Andrews, John P. Reganold and John K. Fellman
Located on a 20-ha commercial apple (Malus domestica Borkh.) orchard in the Yakima Valley, Washington, a 1.7-ha study area was planted with apple trees in 1994 in a randomized complete block design with four replications of three treatments: organic (ORG), conventional (CON), and integrated (INT). Soil classification, rootstock, cultivar, plant age, and all other conditions except management were the same on all plots. In years 9 (2002) and 10 (2003) of this study, we compared the orchard productivity and fruit quality of `Galaxy Gala' apples. Measurements of crop yield, yield efficiency, crop load, average fruit weight, tree growth, color grades, and weight distributions of marketable fruit, percentages of unmarketable fruit, classifications of unmarketable fruit, as well as leaf, fruit, and soil mineral concentrations, were used to evaluate orchard productivity. Apple fruit quality was assessed at harvest and after refrigerated (0 to 1 °C) storage for three months in regular atmosphere (ambient oxygen levels) and for three and six months in controlled atmosphere (1.5% to 2% oxygen). Fruit internal ethylene concentrations and evolution, fruit respiration, flesh firmness, soluble solids concentration (SSC), titratable acidity (TA), purgeable volatile production, sensory panels, and total antioxidant activity (TAA) were used to evaluate fruit quality. ORG crop yields were two-thirds of the CON and about half of the INT yields in 2002, but about one-third greater than either system in 2003. High ORG yields in 2003 resulted in smaller ORG fruit. Inconsistent ORG yields were probably the result of several factors, including unsatisfactory crop load management, higher pest and weed pressures, lower leaf and fruit tissue nitrogen, and deficient leaf tissue zinc concentrations. Despite production difficulties, ORG apples had 6 to 10 N higher flesh firmness than CON, and 4 to 7 N higher than INT apples, for similar-sized fruit. Consumer panels tended to rate ORG and INT apples to have equal or better overall acceptability, firmness, and texture than CON apples. Neither laboratory measurements nor sensory evaluations detected differences in SSC, TA, or the SSC to TA ratio. Consumers were unable to discern the higher concentrations of flavor volatiles found in CON apples. For a 200 g fruit, ORG apples contained 10% to 15% more TAA than CON apples and 8% to 25% more TAA than INT apples. Across most parameters measured in this study, the CON and INT farm management systems were more similar to each other than either was to the ORG system. The production challenges associated with low-input organic apple farming systems are discussed. Despite limited technologies and products for organic apple production, the ORG apples in our study showed improvements in some fruit quality attributes that could aid their marketability.
Harold N. Fonda, John K. Fellman, X. Fan and J.P. Mattheis
In order to investigate biochemical events occurring at the surface of apple skin, UV light exposure was used to generate a skin-browning reaction in apples. `Fuji' apple fruit that had been kept for 2 months in regular atmosphere storage at 0°C were exposed to short-wave UV light for 24 or 48 hr at 0°C or 23°C. After treatment, skin browning was monitored on fruit returned to 0°C storage or kept at room temperature under laboratory conditions. Fruit exposed to short-wave UV light at 0°C developed skin browning after 2 to 3 days at room temperature, whereas fruit held at 0°C did not show signs of skin browning until 7 days later. Short-wave UV exposure for 24 or 48 hr at 23°C resulted in skin browning that continued to develop on fruit kept at both room temperature and 0°C. When fruit were exposed to short-wave UV light for 72 hr at 0°C, a small amount of skin browning was already apparent. Long-wave UV light exposure for 48 hr had no observable effect on fruit treated at 0°C and then placed at room temperature. Our observations suggest that events that lead to browning are related to dispersion of energy absorbed by the hydrophobic molecules in the skin, a temperature dependent phenomenon.