Sweetpotato [Ipomoea batatas (L.) Lam.] roots of two Hawaii-grown clones were treated with 100 to 600 Gy X-ray irradiation and evaluated for quality before and after cooking. Root moisture content, surface color, and glucose and fructose concentrations were not affected by irradiation treatment for either the red-skin, yellow-flesh (RY) or the white-skin, purple-flesh (WP) clones. Firmness decreased at higher doses for RY roots, but not for WP roots. The alcohol insoluble solids and the starch concentrations of raw roots decreased linearly in response to increasing dose for both clones. Maltose decreased at higher doses in cooked RY roots only. Irradiation had the greatest effect on sucrose concentrations, which increased linearly in response to dose as starch concentrations decreased. A sensory panel perceived sweetpotato roots treated with 600 Gy irradiation as sweeter than control roots. Panelists found the overall acceptability to be the same for control and 600 Gy treated roots for both clones.
The fruit quality and ripening response of `Brazilian' bananas (Musa sp., group AAB) were determined following hot water immersion treatments for surface disinfestation. Summer-harvested fruit were exposed to 47, 49, or 51 °C water for 10, 15 and 20 minutes and ripened at 20 °C. The summer experiment established the exposure time and temperature limits for fruit injury. Winter-harvested fruit were immersed in 48, 49, or 50 °C water for 5, 10 and 15 minutes, stored for 12 d at 14 °C, and ripened at 22 °C. The hot water exposure time had a greater effect than the water temperature on banana fruit ripening. Nontreated bananas ripened after 13 to 15 d, and ripening was delayed by 2 to 7 d when fruit were exposed for 15 or 20 minutes to hot water. Hot water treatments did not inhibit pulp softening, but peels tended to be firmer for bananas immersed in 49 to 51 °C water than control fruit. Heat-treated bananas were not different from control fruit in soluble solids content or titratable acidity, however the conversion of starch to sugars was reduced at higher temperatures and exposure times. Bananas exposed for 20 minutes to hot water had delayed respiratory peaks and ethylene production, especially at 51 °C. Mild peel injury was observed on fruit exposed to higher temperatures (49 to 51 °C) for longer durations (15 or 20 minutes).
Fruit quality and ripening of Dwarf Brazilian bananas (Musa sp., group AAB) were determined after x-ray irradiation for disinfestation of quarantine pests. The proximal and distal hands from winter- and summer-harvested bunches were treated with irradiation doses of 0, 200, 400, 600, or 800 Gy, stored for 7 days at 14 °C, and ripened at 20 °C. Irradiation did not extend banana shelf life or affect soluble solids content, but titratable acidity decreased with increasing dose. Starch and total sugar concentrations were similar for control and irradiated fruit at all doses. However, sucrose contents decreased linearly as dose increased, whereas glucose and fructose concentrations increased, indicating an acceleration of sucrose hydrolysis in treated bananas. Irradiation retarded peel softening but not pulp softening for winter-harvested fruit and had a minimal effect on peel and pulp firmness of summer-harvested fruit. For irradiated fruit, the respiratory climacteric rates decreased relative to control fruit, but CO2 and ethylene production increased 1 day after irradiation stress. Proximal fruit (more mature) had higher respiration rates and produced more ethylene than distal fruit (less mature) after irradiation, but differences in physiological maturity between hands did not affect soluble solids, titratable acidity, starch, or total sugar content of ripe fruit. Bananas from distal hands treated with 800 Gy irradiation developed peel injury when harvested in either the winter or summer months. Summer-harvested fruit also were damaged at the 600-Gy dose for distal fruit only. Treatment of fruit from the proximal half of bunches at doses ≤600 Gy would ensure visual quality while providing quarantine security for Dwarf Brazilian bananas.
Sweetpotato [Ipomoea batatas (L.) Lam.] roots of three Hawaii-grown cultivars (`Mokuau', `Okinawan', and `Yoshida') were treated with 0, 200, or 400 Gy x-ray irradiation and stored for 12 weeks at 15 °C. The storage quality of nonirradiated and irradiated roots was compared for weight loss, sprouting, firmness, color, postharvest decay, and carbohydrate concentrations. Nonirradiated roots lost 3 to 4% weight during storage, whereas roots treated with 400 Gy lost 4.7% to 8.6% weight. Sprouting was negligible for all treatments. Storage tended to increase root firmness, while irradiation tended to decrease firmness. When all cultivars were averaged, sweetpotatoes treated with 400 Gy and stored for 12 weeks had the lowest starch concentrations and highest total sugar concentrations. Glucose and fructose concentrations were not affected by irradiation, but these sugars increased during storage. Sucrose concentrations of roots irradiated with 400 Gy were double those of nontreated roots after 12 weeks storage. The purple-fleshed cultivars, `Mokuau' and `Okinawan', retained good quality following irradiation and storage, but firmness decreased somewhat for roots treated with 400 Gy. The `Okinawan' sweetpotato is the primary export cultivar from Hawaii. For the white-fleshed cultivar, `Yoshida', postharvest decay adversely impacted the internal color, firmness, and overall quality of roots treated with 400 Gy and stored for 12 weeks.
The quality of three dragon fruit clones (Hylocereus spp.) was determined after x-ray irradiation for disinfestation of quarantine pests. Fruit were treated with irradiation doses of 0, 200, 400, 600, or 800 Gy and stored for 12 days at 10 °C. Irradiation did not affect soluble solids content, titratable acidity, or fructose concentrations. Glucose, sucrose, and total sugar concentrations decreased linearly as dose increased. Minimal softening occurred in the outer flesh layers for fruit treated with 400 or 600 Gy irradiation. Surface color, peel injury, and bract appearance differed among the three clones with irradiation stress, but in all cases, visible changes were minor. Fruit decay was absent or minimal, and disease ratings were not affected by irradiation. Irradiation treatment of dragon fruit at doses 800 Gy or less would ensure visual and compositional quality while providing quarantine security.
A 2-year field study was conducted to evaluate the effects of maturity and storage on fresh-market onion (Allium cepa L.) quality. Four short-day onion cultivars (`NuMex BR1', `NuMex Sunlite', `NuMex Starlite', and `Buffalo') were seeded in early October each year. Bulbs were harvested at five times; the first and second harvests were when 20% and 80 %, respectively, of the bulbs in a plot had mature necks; the third, fourth, and fifth harvests were at 5,10, and 15 days after the second harvest date, respectively. After curing for 3 days, bulb firmness, weight, and incidence of disease were evaluated for all harvests. Bulbs were re-evaluated after 10 and 20 days storage in a shed under ambient conditions. `Buffalo' and `NuMex Surdite' bulbs had the lowest incidence of disease before storage. For all cultivars, average bulb weight increased and firmness decreased with delayed harvest. Percent diseased bulbs increased for all cultivars as harvest was delayed in 1991 but not in 1992. The optimum harvest time was at 80% maturity. In storage, average bulb weight and firmness decreased, and the incidence of bulb diseases increased.