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  • Author or Editor: Elizabeth Baldwin x
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The USDA–ARS Citrus and Subtropical Products Laboratory is a food science and postharvest facility for fresh and processed fruits and vegetables of tropical and subtropical origin. The term “tropical” is extended to vegetables grown during the summer of temperate climates like tomato. There are also projects involving strawberry and blueberry since these are important crops for Florida. The majority of the work, however, is on citrus (70%). There are four projects at the facility including quality and by-product research. The two quality projects involve work on juice (mainly citrus juices) and fresh fruit flavor. The other quality project includes work on edible coatings or other surface treatments to reduce decay, water loss and to improve of the appearance of fresh or fresh-cut fruits and vegetables. The two by-product projects aim to develop products from citrus processing waste. One project mines citrus waste for edible fiber, nutraceuticals and compounds in grapefruit that enhance uptake of certain drugs. The other by-product project seeks to develop industrial products from the carbohydrates in citrus peel such as suspension aids and fuel ethanol.

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Exopolygalacturonase (exo-PG) (EC 3.2.1.67) was investigated for ability to induce ethylene production in green cherry tomatoes (Lycopersicon esculentum Mill.). The fruit were vacuum-infiltrated with various levels of exo-PG from green tomato fruit, squash flower, or oak pollen and compared to boiled enzyme or salt controls for ethylene production. In all cases, fruit treated with active enzymes produced significantly higher levels of ethylene than did control fruit. The ethylene response was evident 2 hours after treatment and was transient in nature, returning to basal levels by 22 hours. The amount of ethylene produced did not appear to be influenced by the source of exo-PG.

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Unsaturated fatty acid oxidation results in rancid off-flavors in pecan [Carya illinoinensis(Wangenh.) K. Koch] kernels, which shortens shelf life under ambient conditions. For this reason kernels are stored under costly refrigeration. Edible coatings [hydroxypropyl cellulose (HPC) and carboxymethyl cellulose (CMC), plus various additives] were used to restrict oxygen contact with kernel associated fats by acting as a barrier to gas exchange. Fresh pecans were acquired from orchards, air-dried, shelled, and treated with various coating formulations. The kernels were then drained, dried, and stored several months in open air or perforated zip-lock plastic bags at 20 to 25 °C and periodically evaluated by 18 to 20 sensory panelists using a 9-point hedonic scale for appearance, shine, off-flavor or overall flavor, and texture. Coated kernels generally scored lower for off-flavor, and higher for overall flavor. Preliminary coatings resulted in a less preferred appearance, but modifications to formulations of subsequent coatings resulted in either improved appearance or had no effect on appearance of kernels compared with uncoated control. Coatings with CMC imparted a shine to coated kernels, but did not generally affect texture. Hexanal accumulation, a good indicator of rancidity, of the homogenate of kernels stored at ambient temperatures for 5 and 9 months was lower in kernels coated with CMC than in the uncoated control, with CMC coatings including α-tocopherol being most effective. Thus, CMC-based coatings exhibit potential for extending the shelf life of pecan kernels.

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Fruit of 10 tomato (Lycopersicon esculentum Mill.) cultigens, including five typical fresh market F1's, two rin/ + F1's, two very firm (ultrafirm) inbreds, and an antisense PG F1, were harvested at mature green, breaker, and table ripe stages of development, passed over a grader and taken to a lab (21°C) for analyses of soluble solids, titratable acidity and firmness at the table ripe stage. Shelf life was also measured. Cultigens varied in response to both solids and acids at the three harvest stages, thus there was no clear effect of harvest stage on these variables. The rin /+ F1's and ultrafirm inbreds were significantly firmer than the other cultigens at the table ripe and breaker stages. Shelf life tended to decrease with maturity at harvest. One rin /+ F1 had the greatest shelf life at all harvest stages. Ultrafirm and antisense PG cultigens had greater shelf life than the other six cultigens at the table ripe stage.

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Sugars (sucrose, glucose, fructose, or glucose/fructose in combination) were added to coarsely chopped, deodorized tomato puree, increasing the sugar level of the puree by 2% to 3%. Sugars (equal amounts of glucose and fructose) along with citric acid were also added to another puree, at two different levels, to create a range of sugar: acid ratios (4.88–19.07). This second puree was then spiked with two different levels of aroma volatiles, reported to affect tomato flavor, in order to understand the influence of the sugar: acid background on tomato aroma and taste perception. The tomato puree was presented to a trained panel and was rated for intensity of aroma and taste descriptors on a 15-cm unstructured line scale. For the puree spiked with sugars only, panelists detected differences for overall aroma, ripe aroma, overall taste, sweetness and sourness intensities (P< 0.15). Adding sweet sugars, like fructose and sucrose, resulted in decreased ratings for aroma descriptors, apparently detracting from panelists' perception of aroma. The sugar: acid ratio of the second tomato puree was found to correlate with perception of taste descriptors sweet (+), sour (–), bitter (–) (P< 0.05), and citrus (–) (P< 0.15) for most volatiles tested. Correlations were also found for the sugar: acid ratio with overall aftertaste (–) when the puree was spiked with furanol, trans-2-hexenal, geranylacetone, or acetaldehyde; fruity (+) with β-ionone and linalool; and tropical (+) with cis-3-hexenal and geranylacetone (P< 0.15). The study suggests that increasing taste factors, like sweetness, result in decreased perception of tomato aroma in general, and affect how aroma compounds influence sensory descriptors.

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Strawberry fruit were harvested on three different dates from the Strawberry Association plot (cv. Festival), a commercial farm (cv. Camino Real), and at the University of Florida Gulf Coast Research and Education Center (cv. Sweet Charlie), in central Florida in 2005 and 2006. Fruit were transported to the USCSPL in Winter Haven, Fla., sorted, dipped for 10 s in treatment solutions, drained and stored in commercial clam-shells at 15 to 19 °C. Percentage of decay (number of fruit with lesions) was monitored during storage. There were 10 fruit per replicate clamshell, and three to four replicates per treatment for each harvest. Treatments included three size classes of galacturonic acid (GA) oligomers with a degree of polymerization (DP) ranging from 1–13, 8–24, and 22–46 and undigested polygalacturonic acid at 0.2% in 50 mmol LiOAC, LiOAC/NaOAC, with 22% ETOH, or KOAC buffer (all buffers at pH ≈4.4), prepared by enzymatic digestion followed by differential pH and alcohol precipitation. The main pathogens found on these fruit were Rhizopus stolonifer and Botrytis cinera at 1×105 cfu/g fruit in 2005 and 5×107 in 2006. The medium range oligomers (DP 8-24) reduced decay significantly compared to buffer alone or to the lower or higher DP GA oligomers, and elicited ethylene production. Oligomers in this pectin size class have previously been reported to elicit ethylene and plant defense responses in plant tissues.

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Application of edible coatings that can simulate controlled atmosphere storage has become a popular concept. An experimental coating developed at the USDA Winter Haven laboratory, Nature-Seal (patent application #07/679,849), or a commercial composite coating was applied to papaya fruit at the green (immature) stage for comparison to uncoated fruit. Both types of coatings contain a polysaccharide base and therefore have different properties than most commercial “wax” coatings. The fruit were stored continuously at 21C or 3 days at 13C then ripened at 21C with 95 to 98% RH. Sample fruit from each treatment were analyzed for color, weight loss, CO2 ethylene, & % decay and softening. Results showed substantial extension of papaya shelf-life when the fruit were coated with Nature Seal while the commercial coating was less effective. This effect was due to retardation of ripening as evidenced by delayed color development, softening, and effect of coating permeability to CO2 and O2 on climacteric CO2 and ethylene production.

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This study evaluated the effects of huanglongbing (HLB) symptom severity on fruit detachment force (FDF) and fruit mechanical properties in sweet oranges (Citrus sinensis) as indicators of potential HLB-influenced preharvest fruit drop and postharvest damage and breakdown. FDF for fruit from HLB-asymptomatic trees (AS) was substantially greater than for fruits from HLB-symptomatic trees or branches. Fruit hardness, resilience, springiness, and cohesiveness values, measured by texture profile analysis (TPA), represent various aspects of fruit firmness and recovery capacity once compressed, and were lower in HLB-symptomatic fruits in comparison with AS fruits. On the other hand, puncture force, toughness, and deformation values, measured by a puncture test and representing peel toughness, were higher in HLB-symptomatic fruits than in the AS fruits. The results indicate that fruits from severely HLB-symptomatic sweet orange trees are more likely to have problems with preharvest fruit drop, and postharvest pressure damage and breakdown, but may have less puncture damage in harvesting, transportation, packing, and juice processing.

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