In separate treatments, fruit of Litchi chinensis Sonn. were subjected to 15 days at 1.1 °C or to gamma irradiation from a 60Co source at dosages of 100, 200, or 300 Gy. Cold-treated `Mauritius' fruit lost some color intensity externally and internally, and the pale flesh had a greener hue. The pericarp of `Brewster' fruit was injured to a greater extent by cold treatment than that of `Mauritius', and the pulp of treated fruit had lower concentrations of acids and soluble solids. Cold treatment increased decay susceptibility of both cultivars. `Mauritius' fruit were also more susceptible to decay following irradiation at 300 Gy and 6 days of storage at 5 °C. Both cultivars lost firmness after this treatment. The pericarp of irradiated `Mauritius' fruit became more orange, whereas the flesh of both cultivars became greener. Irradiated `Brewster' fruit were less acidic and contained less soluble solids, but sensory evaluations could not differentiate between irradiated and nontreated fruit regardless of cultivar. Loss of quality was minimal with either cold or irradiation treatment, and both should be acceptable for lychees requiring quarantine treatment for eradication of exotic pests.
Raymond G. McGuire
Raymond G. McGuire
The market quality and condition of grapefruit (Citrus paradisi Macf.) were compared after three heat treatments for quarantine control of Caribbean fruit flies [Anastrepha suspensa (Loew)]. Treatment by forced air at 48C for 3 hours was compared with immersions in water at either a constant 48C for 2 hours or with a gradual increase to 48C lasting 3 hours. The immersion at a constant 48C significantly increased weight loss and promoted injury and decay while reducing firmness and color intensity after 4 weeks of storage. By more slowly heating fruit in the gradient water immersion, weight, firmness, and natural color were retained, and injury was substantially reduced, but the incidence of decay remained high. No loss in quality resulted from treatment by forced hot air. These heat treatments had little effect on juice characteristics, although acidity was slightly reduced by each method of application. In taste tests, juice from fruit treated in water that was gradually raised to 48C was preferred over that of fruit treated at a constant 48C.
Raymond G. McGuire
Immersion of guavas (Psidium guajava L.) for 35 min in water at 46.1 ± 0.2 °C slowed softening, sweetening, and color development of fruit and delayed ripening by 2 days. Heat treatment also increased susceptibility to chilling injury, decay, and weight loss in storage, but overall loss of quality was minimal. Waxing fruit within 90 min of heat treatment exacerbated chilling injury, further delayed ripening with a concomitant increase in the percentage of fruit not ripening, and caused fruit to remain greener. Waxed fruit had a lower acidity and soluble solids concentration and did not appear to ripen normally. Although heating did not appreciably affect the percentage of fruit that failed to ripen, the combination of heating and nearly immediate waxing increased the proportion not ripening to 45%. Heat and wax treatments, alone or in combination, caused CO2 levels to increase significantly before the initiation of ripening, but waxing also reduced the O2 content of fruit at this time. Before ripening, O2 levels were inversely correlated (r ≤ – 0.950) with injury, firmness, date and percentage of fruit ripening, and pH and directly correlated (r ≥ 0.950) with peel color and the concentration of acids and sugars in the pulp. Delaying the waxing of heat-treated guavas or reconditioning them for 24 h at 20 °C before cold storage promoted normal ripening and helped to maintain the quality of heat-treated fruit.
Raymond G. McGuire
In separate treatments, leaves of the curry leaf tree [Murraya koenigii (L.) Sprengel] were subjected to 15 days at 1 °C, to gamma irradiation from a 60Co source at dosages from 100 to 1000 Gy, or to fumigation with methyl bromide from 16 to 64 g·m–3. Cold-treated leaves retained their fresh appearance with minimal weight loss when stored in sealed plastic bags; although color intensity of the underside of leaves was measurably reduced, the change was not visually perceptible. Similarly, irradiation was associated with a darkening of leaves and a loss of color intensity, but these changes were not visibly apparent even at the highest dosage. Methyl bromide fumigation, however, greatly increased susceptibility of leaves to postharvest decay. Cold or gamma irradiation treatments should be tolerated by this commodity when treated for pests such as the Asian citrus psyllid (Diaphorina citri Kuwayama) prior to export.
Raymond G. McGuire and Guy J. Hallman
Harvested, mature-green guava (Psidium guajava L.) fruit were coated with cellulose- or carnauba-based emulsions to compare the effect on fruit ripening and quality of ripened fruit. Coatings containing 2% or 4% hydroxypropylcellulose significantly slowed softening an average of 35% or 45%, respectively, compared to uncoated fruit (a delay of 1 to 2 days in September and 4 to 5 days by January). A 5% carnauba formulation slowed softening by 10% to 30% and was most effective at reducing weight loss. Neither of the cellulose- nor the carnauba-based coatings affected the decay susceptibility of softened fruit, but coated fruit did not develop as much color, had a lower soluble solids concentration, and were more prone to surface blackening in storage than uncoated fruit.
Raymond G. McGuire and Jennifer L. Sharp
Roots of sweetpotatoes [Ipomoea batatas (L.) Lam.] were treated with 200 to 1000 Gy of ionizing radiation from a 60Co source. Within this range, radiation dosage had no effect on surface injury and decay when roots were evaluated after 1 month of storage at 13C and 90% relative humidity. During storage, weight loss by irradiated roots was 0.5% to 3.3% over that of nontreated roots, which, in some instances, affected root firmness. Changes in peel color were visually imperceptible, but raw medullar tissue of the staple-type, white-fleshed cultivar Picadito had a more intense yellow hue with increasing irradiation. The greatest differences were evident after roots had been baked. The hue of the cooked medullar tissue of the sweet, orange-fleshed cultivar Jewel was not changed by increasing irradiation, although roots were darker and had a lower color intensity. With baking, the medullar tissue of irradiated roots of `Picadito' lost some of its yellow tinge, but it also became darker with increased irradiation. Taste panelists reported that irradiated roots were sweeter, but these were not preferred to nonirradiated roots, due, in part, to the darkened appearance of treated samples.
Raymond G. McGuire and William F. Reeder
Early, mid-, and late-season grapefruit (Citrus paradisi Macf.) were treated with hot air at 46, 48, and 50C for 3, 5, or 7 hours to determine the effects of time and temperature on market quality. Early and late-season fruit were more easily' damaged by the higher temperatures than midseason fruit. Increased times at the lower temperatures had less of a deleterious effect on weight loss, loss of firmness and color, and susceptibility to scalding injury and fungal decay than did shorter times at the higher temperatures. Nevertheless, regression equations predicted that 3 hours at 48C or 2 hours at 49C would not adversely affec: market quality of early and midseason fruit. The suitability of these equations was verified through taste tests of Juice. It may not be possible, however, to raise the treatment temperature for late-season fruit above 47.5C without damaging the quality of juice from these fruit.