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Green lemons (Citrus limon (L.) Burm.) were imaged for chlorophyll fluorescence (CF) 30 minutes after immersion of the fruit into 55 °C water for 5 minutes to determine if CF could be used to identify areas of hot water-induced rind injury before the appearance of visible symptoms. Fluorescence was variable in intensity over the surface of the rind with defined areas of enhanced fluorescence being present that corresponded in shape and location with visible injury that later developed during 24 hours of storage. Images showing minimum fluorescence (F₀) and maximal fluorescence (F_m) provided the best image contrast between injured and noninjured areas of the rind. Total F₀ present in the image was closely correlated (r ² = 0.87) with the area of rind injury present following storage. Holding the fruit under conditions of low humidity for 24 h before hot water treatment prevented both the formation of areas of enhanced fluorescence and the corresponding rind injury. Imaging of CF has potential as a means to identify areas of incipient rind injury in citrus to facilitate study of the causal mechanisms of postharvest rind disorders.

`Elegant Lady', `O'Henry' and `September Sun' peaches [(Prunus persica (L.) Batsch (Peach Group)] and `Summer Bright' and `Summer Grand' nectarines [(Prunus persica (L.) Batsch f. nucipersica (Nectarine Group)] heated to a seed surface temperature of 47.2 °C over a period of 4 hours developed mealy flesh sooner and to a much greater extent than nonheated fruit following cold storage at 5 °C for 1 to 3 weeks. Exo- and endopolygalacturonase activities were reduced following 3 to 4 hours of heating and may have been responsible for the increased mealiness. Mealiness often developed in defined regions rather than throughout the entire fruit. Comparison of juicy and mealy regions within individual fruit revealed that mealy regions contained 65% and 86% less exo- and endopolygalacturonase activity, respectively, than juicy regions, whereas pectinmethylesterase activity was unchanged. Extractable protein was reduced by >50% in the mealy regions of the fruit. Intermittent warming periods of 24 hours at 20 °C at weekly intervals during storage at 5 °C were less effective in reducing mealiness in heat-treated than in control fruit. It is important that future work with heat treatments and stone fruit closely monitor potential effects on this disorder to avoid loss of market quality following treatment.

‘Shiranui’ is a mandarin (Citrus reticulata var. austera) that is highly treasured for its unique and delicious flavor, and obtains premium prices in the marketplace. Although flavorful, ‘Shiranui’ tends to develop off-flavor during storage. In this study we examined the use of different storage wax (SW) and pack wax (PW) combinations to determine whether flavor in ‘Shiranui’ can be improved after storage by adjusting wax coating protocols. In the initial test, either SW or no wax was applied after harvest, and each was followed by an application of SW or one of two types of PW after 1 day, 3 weeks, or 7 weeks of storage and then held 1 week at either 7 or 20 °C. Results indicate that the initial wax was not an important factor but the use of SW instead of either type of PW as the final coating led to greater internal oxygen levels in the fruit and less off-flavor formation. The lessening of off-flavor by SW was significant only after 20 °C of storage, when off-flavor was greatest. Greater weight loss accompanied the use of SW as the final coating. In a second test, SW with greater solids concentrations (5%, 10%, and 15%) were evaluated to attempt to reduce weight loss, but this led to greater development of off-flavor and loss in acceptability than observed when using SW with 1% solids in test 1. ‘Shiranui’ is prone to developing off-flavor in storage, but this may be mitigated, at least in part, by using SW as the final wax rather than PW.

Yellow- and white-fleshed peach [Prunus persica (L.) Batsch] and nectarine [Prunus persica (L.) Batsch var. nectarina (Ait) Maxim.] cultivars of mid- and late-season maturity classes were subjected to combined controlled atmosphere–temperature treatment system (CATTS) using heating rates of either 12 °C/hour (slow rate) or 24 °C/hour (fast rate) with a final chamber temperature of 46 °C, while maintaining a controlled atmosphere (CA) of 1 kPa oxygen and 15 kPa carbon dioxide. Fruit seed surface temperatures generally reached 45 °C within 160 minutes and 135 minutes for the slow and fast heating rate, respectively. The total duration of the slow heating rate treatment was 3 hours, while 2.5 h was required for the fast heating rate treatment. Following treatment the fruit were stored at 1 °C for either 1, 2, or 3 weeks followed by a ripening period of 2 to 4 d at 23 °C and subsequent evaluation of fruit quality. Fruit quality was similar for both heating rate treatments. Compared with the untreated controls, CATTS fruit displayed higher amounts of surface injury, although increased injury was only an important factor to marketability in cultivars that had high amounts of surface injury before treatment. The percentage of free juice in the flesh was slightly less in CATTS fruit early in storage but was often greater in treated fruit toward the end of the storage period. Slower rates of softening during fruit ripening were apparent in CATTS fruit. Soluble solids, acidity, weight loss and color all were either not affected or changed to a very small degree as a result of CATTS. Members of a trained sensory panel preferred the taste of untreated fruit over fruit that had been CATTS but the ratings of treated and nontreated fruit were generally similar and it is unclear whether an average consumer could detect the difference. Although further work needs to be done regarding the influence of CATTS on taste, it otherwise appears that CATTS does not adversely affect the marketability of good quality fruit and therefore shows promise as a nonchemical quarantine treatment for peaches and nectarines.

Maturity standards that determine when navel oranges can be harvested in California are currently based upon the ratio of soluble solids content (SSC) to titratable acidity (TA) and the rind color of the fruit. These standards may be inadequate to describe the quality of the fruit, which is important given the increased competition from other commodities in the marketplace and declining consumption of fresh citrus. To reevaluate the basis of the maturity standard, navel oranges were harvested at intervals throughout the season and evaluated for SSC, TA, juice ethanol concentration, percent juice, peel coloration, and sensory characteristics. Three varieties of navel oranges, representing early-, mid- and late-season maturities, were used. SSC: TA ratios averaged 6.3 at the beginning of the season and steadily increased to 23.4 at the end of the season. Changes in the hedonic rating, or likeability of the fruit taste as rated by the sensory panelists, were closely related to the SSC: TA ratio and ratings of sweetness and tartness. These relationships showed a similar pattern for all of the navel varieties. A hedonic rating of 6 (like slightly) was not reached until the SSC: TA ratio exceeded the current legal minimum of 8:1, suggesting that the standard should be raised. Juice ethanol levels and percent juice did not have any apparent influence on the sensory ratings. Fruit that were run over a packing line and waxed developed higher amounts of ethanol during storage than control fruit but did not differ substantially from them in hedonic rating.

Navel oranges were subjected to high-temperature forced-air (HTFA) treatment to evaluate the effect on quality and sensory attributes as well as flavor volatiles of a treatment protocol designed to disinfest citrus of Anastrepha spp. fruit flies. The treatment consisted of heating the fruit to a core temperature of 44 °C and then holding it there for 100 min, after which the fruit were placed into storage for 4 weeks. The fruit were removed from storage and evaluated for surface injury, soluble solids concentration (SSC), titratable acidity (TA), and then judged for sensory characteristics by a semiexpert panel. In a separate experiment, fruit were removed at 30-min intervals from the treatment chamber and sensory quality as well as flavor volatiles determined to obtain an estimate of when the flavor changes occurred. It was found that the HTFA treatment caused a significant loss in flavor quality that was most closely linked to a loss in the fresh flavor of the fruit. The HTFA-treated fruit were also determined by panelists to be less sweet, although the SSC/TA ratio was increased by treatment. Neither storage nor waxing after treatment appeared to alter the HTFA effect, although waxing before treatment greatly enhanced the negative effect on flavor. Flavor began to be significantly affected during the final 30 min of treatment. The flavor changes occurred at the same time as large increases in the amount of four esters, two of which were present in concentrations exceeding aroma thresholds and are likely involved in the loss in flavor quality induced by HTFA treatment.

Navel oranges (Citrus sinensis) were sorted into four groups under ultraviolet illumination in commercial packinghouse black light rooms based upon the amount of fluorescence visible on each fruit to determine if fluorescence was predictive of peel quality. The groups corresponded to fruit with 1) little or no fluorescence (group 0), 2) low fluorescence (group 1), 3) moderate fluorescence (group 2), and 4) large fluorescent areas (group 3) that were indicative of developing decay lesions. Identification and elimination of group 3 fruit in black light rooms is a common practice now, but the other groups pass through these rooms. Six tests were conducted over a 2-year period during different times in the mid to late navel orange season. Fruit were visually evaluated for peel quality within 24 hours of their initial segregation into fluorescence groups and again following 3 weeks of storage at 15 °C. Peel quality assessment was based upon commercial grading practices, and the fruit were placed into fancy, choice, juice, or decay classes. Fruit with low to no peel fluorescence (groups 0 and 1) had numerous fancy-grade fruit and few juice- and decay-grade fruit in comparison with the other two groups. In contrast, fruit with moderate fluorescence (group 2) were of poor peel quality. In the initial evaluation, this group had 28% fewer fancy fruit and 19% more juice fruit than did group 0. During storage, group 2 fruit declined markedly in quality and numerous fruit of group 2 in the choice and juice classes decayed; the percentage of decayed fruit increased from 1% initially to 29% after 3 weeks of storage. Navel oranges in group 3, with numerous and obvious fluorescent decay lesions, mainly consisted of either juice grade or decayed fruit; 70% of group 3 decayed after 3 weeks. In addition to removing fluorescing fruit that have obvious indications of decay (group 3), it would be advantageous to remove or otherwise recognize that fruit with moderate levels of fluorescence (group 2) are also of lower quality and that they should not be selected for long storage or distant transport. Their identification may be most practical with an automated system using machine vision and ultraviolet illumination.

The use of ultraviolet fluorescence to identify freeze-damaged navel oranges (Citrus sinensis) was evaluated using fruit harvested following a natural freeze that occurred in California in Jan. 2007. Navel oranges were harvested after the freeze from 14 sites that were previously determined to have a slight to moderate amount of freeze damage. The fruit were evaluated for the presence of small yellow spots characteristic of freeze damage that fluoresce when viewed under a ultraviolet-A (365 nm) source and were then cut and rated using a method currently used by the California Department of Food and Agriculture (CDFA) to determine the presence of internal freeze damage. The percentage of freeze-damaged fruit in each lot as determined by the CDFA method ranged from 0% to 89%. The accuracy of classifying fruit as freeze damaged in each lot by peel fluorescence averaged 44%, with the fruit lots containing the greatest amount of freeze damage having the highest classification percentages. False-positives occurred at a lower rate than false-negatives among the lots. Although some fading was evident, the fluorescence persisted and was readily visible for at least 9 weeks after the freeze event. Removal of fruit with ultraviolet peel fluorescence was ineffective in reducing the percentage of damaged fruit within the examined lots. In the second part of the test, eighteen lots of potentially freeze-damaged fruit were obtained from a packing house, immediately evaluated for freeze damage using ultraviolet light, and then after 4 weeks of storage, were evaluated again using the CDFA method. Fruit that had a slight to moderate degree of freeze damage were tasted and evaluated for sensory characteristics. Both methods of freeze damage detection were poorly related to the sensory characteristics.

It is commonly believed within the citrus industry that handling, waxing, and storage of navel oranges may have undesirable effects on flavor. However, the effect of each potential influencing factor under commercial conditions is not completely understood. The purpose of this study was to systematically investigate these potential influences on navel orange flavor. Navel oranges were harvested on two separate dates, using three grower lots per harvest date, and the fruit run on a commercial packing line. Fruit were sampled at four different stages of the packing process: in the field bin; after the washer; after the waxer; and after packing into standard cartons. Fruit quality, flavor, and juice ethanol concentration were evaluated immediately after sampling and following 3 and 6 weeks of storage at 5 °C. The overall hedonic score, a measure of flavor, significantly declined from 6.5 to 5.7, as a result of 6 weeks storage. Fruit selected from field bins, from after the washer, and after the waxer were all judged by the taste panel to be equivalent in flavor. The packed fruit were judged to be slightly inferior in flavor. Titratable acidity declined while soluble solids increased as a result of storage; the stage of the packing process influenced neither. Waxing and storage both were associated with higher ethanol levels in the fruit.