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- Author or Editor: Charles F. Forney x
Freshly harvested heads of `Cruiser' or `Paragon' broccoli (Brassica oleracea L. Italica group) were heated by immersing in water at 42, 45, 48, 50, or 52C. Immersion times were decreased as treatment temperatures were increased and ranged from 20 to 40 minutes at 42C to 1 to 3 minutes at 52C. Control heads, dipped in 25C water for 0, 10, or 40 minutes, began to turn yellow after ≈3 days storage at 20C and 80% to 90% relative humidity. Immersion in 42C water delayed yellowing by 1 or 2 days; immersion in 45, 48, 50, or 52C prevented yellowing for ≤7 days. Water loss of broccoli during storage at 20C increased by ≤1% per day by some hot-water treatments. Immersion in hot water decreased the incidence of decay during storage at 20C. Immersion in 50 or 52C water for 2 minutes was most effective in controlling decay development. Broccoli immersed in 52C water for 3 minutes had a distinct off-odor. Control and treated broccoli held at 0C for 8 days following hot-water dips were similar in quality. Yellowing of heat-treated broccoli was inhibited when broccoli was warmed to 20C following storage at 0C. Hot-water treatments also delayed senescence at 20C when broccoli was treated following 3 weeks of storage at 0C. Immersion of broccoli in 50C water for 2 minutes was the most effective treatment for reducing yellowing and decay while not inducing off-odors or accelerating weight loss.
Freshly harvested heads of `Cruiser' or `Paragon' broccoli (Brassica oleracea L. Italica group) were heat treated by holding in water for 1 to 40 min at 42, 45, 48, 50, or 52C. Control heads were held in air at 20C or in 25C water for 40 min. Controls turned yellow in about 3 days at 20C. Treatments at 42C delayed yellowing by 1 or 2 days, while treatments of 45, 48, 50, and 52C prevented yellowing up to 7 days at 20C. Hot water treatments had no effect on water loss of broccoli during storage. Incidence of decay was greater in treated broccoli stored wet compared to the dry control. However, when free water was removed by spinning following treatment, no difference in decay was observed. Treatment of broccoli at 52C for 3 or more min sometimes induced a distinct off-odor. When broccoli was held at 0C for 3 weeks following treatment no differences were observed between control and treated broccoli. However, when broccoli was warmed to 20C following storage at 0C, yellowing of treated broccoli was inhibited. Hot water treatments also delayed senescence at 20C when broccoli was treated following 3 weeks of storage at 0C.
Volatile compounds make a significant contribution to the quality and storage life of fresh strawberries, blueberries, and raspberries. Strawberry aroma is composed predominately of esters, although alcohols, ketones, and aldehydes are also present in smaller quantities. The major volatiles contributing to aroma include ethyl butanoate, 2,5-dimethyl-4-hydroxy-3(2H)-furanone, ethyl hexanoate, methyl butanoate, linalool, and methyl hexanoate. In lowbush (wild) blueberries, aroma is predominated by esters and alcohols including ethyl and methyl methylbutanoates, methyl butanoate, 2-ethyl-1-hexanol, and 3-buteneol, while highbush blueberry aroma is dominated by aromatic compounds, esters, terpenes and long chain alcohols. The aroma of raspberries is composed of a mixture of ketones and terpenes, including damascenone, ionone, geraniol, and linalool. The composition and concentration of these aroma compounds are affected by fruit maturity and storage conditions. As fruit ripen, the concentration of aroma volatiles rapidly increases. This increase in volatile synthesis closely follows pigment formation both on and off the plant. In strawberry fruit, volatile concentration increases about 4-fold in the 24-h period required for fruit to ripen from 50% red to fully red on the plant. In storage, volatile composition is affected by storage temperature, duration, and atmosphere. Postharvest holding temperature and concentrations of O2 and CO2 can alter the quantity and composition of aroma volatiles. The effects of postharvest environments on volatile composition will be discussed.
Studies were conducted over three seasons to determine the relationship of temperature and humidity on the storage life of fresh cranberry (Vaccinium macrocarpon Aiton) fruit. Each year, cranberries harvested from four commercial bogs were stored at temperatures ranging from 0 to 10 °C in combination with relative humidities (RH) ranging from 75% to 98%. Fruit were stored under these conditions for up to 6 months and were evaluated monthly for marketability, decay, physiological breakdown, weight loss, and firmness immediately after removal and after an additional week at 20 °C. The percentage of marketable fruit declined substantially over time in all storage conditions with 41% to 57% becoming unmarketable after 2 months as a result of both decay and physiological breakdown. Relative humidity had a greater effect on fruit storage life than temperature and after 5 months, the amount of marketable fruit stored in high (98%) and medium (88%) RH was 71% and 31% less than that stored in low (75% to 82%) RH. Rates of fresh weight loss increased as RH in storage decreased and was 0.41%, 0.81%, and 0.86% per month in fruit stored in high, medium, and low RH, respectively. Fruit firmness was not significantly affected by RH. The effects of storage temperatures ranging from 0 to 7 °C on marketable fruit after 2 to 5 months of storage were not significant. Only fruit stored at 10 °C consistently had fewer marketable fruit when compared with fruit stored at lower temperatures. Storage temperature had no significant effect on decay incidence. However, physiological breakdown was greatest in fruit stored at 10 °C. Rates of fresh weight loss increased with storage temperature, ranging from 0.35% to 1.17% per month for fruit stored at 0 to 10 °C, respectively. Contrary to previous reports, no evidence of chilling injury was found in cranberry fruit stored at 0 °C. Results suggest that cranberry fruit should be stored at 0 to 7 °C and 75% to 82% RH to retain marketable fruit.
Volatile compounds are responsible for the aroma and contribute to the flavor of fresh strawberries (Fragari×anannassa), red raspberries (Rubus idaeus), and blueberries (Vaccinium sp.). Strawberry aroma is composed predominately of esters, although alcohols, ketones, and aldehydes are also present in smaller quantities. The aroma of raspberries is composed of a mixture of ketones and terpenes. In highbush blueberry (Vaccinium corymbosum), aroma is dominated by aromatic hydrocarbons, esters, terpenes and long chain alcohols, while in lowbush blueberries (Vaccinium angustifolium), aroma is predominated by esters and alcohols. The composition and concentration of these aroma compounds are affected by cultivar, fruit maturity, and storage conditions. Volatile composition varies significantly both quantitatively and qualitatively among different cultivars of small fruit. As fruit ripen, the concentration of aroma volatiles rapidly increases closely following pigment formation. In storage, volatile concentrations continue to increase but composition depends on temperature and atmosphere composition. Many opportunities exist to improve the aroma volatile composition and the resulting flavor of small fruit reaching the consumer.
Polar lipids were extracted from immature through overripe `Honey Dew' muskmelons (Cucumis melo L.) that were exposed to high or low levels of solar radiation. Fatty acid composition of the polar lipids changed and the percentage of unsaturated fatty acids increased as fruit ripened. The percentage of monounsaturated fatty acids palmitoleic and oleic acid as a percent of total fatty acids increased from 8% in melons of minimum maturity to >50% in overripe melons. Also, the ratio of unsaturated to saturated fatty acids increased from 2.2 to 5.0. Total polar lipid fatty acid compostion from middle mesocarp tissue (flesh) did not change as much during ripening as the polar lipid composition from the epidermis (peel). Peel tissue from the top of melons relative to the ground had unsaturation ratios of C18 fatty acids and C16 fatty acids 33% and 62% greater, respectively, than peel from the bottom of the melon. Melons of minimum maturity exposed to solar radiation had significantly more unsaturated C18 fatty acids than shaded melons. Increase in the percentage of unsaturated polar lipid fatty acids in `Honey Dew' melons may relate to increases in chilling tolerance reported to occur with ripening and solar exposure.
High-quality cranberry (Vaccinium macrocarpon) fruit are required to fulfil the growing markets for fresh fruit. Storage losses of fresh cranberries are primarily the result of decay and physiological breakdown. Maximizing quality and storage life of fresh cranberries starts in the field with good cultural practices. Proper fertility, pest management, pruning, and sanitation all contribute to the quality and longevity of the fruit. Mechanical damage in the form of bruising must be minimized during harvesting and postharvest handling, including storage, grading, and packaging. In addition, water-harvested fruit should be removed promptly from the bog water. Following harvest, fruit should be cooled quickly to an optimum storage temperature of between 2 and 5 °C (35.6 and 41.0 °F). The development of improved handling, refined storage conditions, and new postharvest treatments hold promise to extend the storage life of fresh cranberries.
Rapidly declining levels of ascorbate (vitamin C) have been associated with advancing senescence and postharvest quality loss in spinach (Spinacia oleracea L.). To further explore the association between ascorbate metabolism and senescence, two cultivars of spinach previously shown to differ in their postharvest senescence rates were grown under controlled conditions (18 °C, 14 light: 10 dark photocycle) and harvested 6 weeks after planting. Detached leaves of `Spokane F1' (relatively fast senescence rate) and `BJ412 Sponsor'(relatively slow senescence rate) were bagged and placed in the dark at 10 °C. Samples were removed on days 0, 7, 14, 21, and 28, and analyzed for activities of L-galactono-γ-lactone dehydrogenase (GLDH), ascorbate peroxidase (ASPX), ascorbate oxidase (AAO), dehydroascorbate reductase (DHAR), and monodehydroascorbate reductase (MDHAR), and levels of ascorbate [reduced (AsA) and oxidized (DHA)] and malondialdehyde (MDA) (estimator of lipid peroxidation). Oxidative stress, as estimated by MDA levels, steadily increased in both spinach cultivars during storage, but increased more in `Spokane'than in `Sponsor'. GLDH activities peaked on day 14 for both cultivars and leveled off thereafter, while activities of ASPX, DHAR, and MDHAR declined during storage. ASPX activities were lower in `Spokane'than in `Sponsor'after day 21. No difference in AAO activities was noted between `Sponsor'and `Spokane'during storage. Total ascorbate concentrations declined in both cultivars on day 14 after which no further decreases were noted, while DHA/AsA ratios increased during storage. Early in the storage regime (days 0 and 7), ascorbate levels were lower in `Spokane'than in `Sponsor. GLDH activities may have increased as part of a strategy to maintain the ascorbate pool during escalating oxidative stress. However, decreased levels of ascorbate suggests that, even though ascorbate biosynthesis was increased, ascorbate was being degraded, possibly through hydrolysis of DHA to 2,3-diketogulonate. Initially lower levels of ascorbate (days 0 and 7) and lower activities of ASPX (day 28) in `Spokane' may have resulted in comparatively greater susceptibility of this cultivar to oxidative stress than `Sponsor'.
Abstract
Concentrations of starch and sugars were measured in the cap leaf (leaf no. 1) and in every fifth leaf (5, 10, 15, 20) in heads of crisphead lettuce (Lactuca sativa L.) harvested at 0700 hr (AM) or 1400 hr (PM) PDT. Starch content increased in the cap leaf from the AM to the PM harvest, but remained unchanged in other leaves. Sucrose concentration was <5 mg·g−1 dry weight in AM-harvested lettuce, but the cap leaf, leaf 20, and stem tissue contained 43, 24, and 61 mg·g−1 dry weight, respectively, in lettuce from the PM harvest. AM harvested lettuce contained 70% to 260% more glucose and 20% to 120% more fructose than PM-harvested lettuce. Glucose and fructose concentrations were greatest in leaf 10 (110 and 120 mg·g−1 dry weight, respectively) and decreased 20% to 50% in inner and outer leaves. Exposure of lettuce to 7.5% or 10% CO2 for 12 days at 2.5°C followed by air for 3 days at 10° caused more severe injury on AM- than on PM-harvested lettuce. Injury occurred primarily on leaves 7 through 17, with those between leaves 10 and 15 being most severely affected. High reducing sugar content at harvest did not appear to decrease the sensitivity of lettuce to high CO2 during storage.
Abstract
Sucrose was not detected in developing fruit of ‘Brighton’ strawberry (Fragaria × ananassa Duch.) until 10 days after anthesis. Thereafter, its concentration increased rapidly but then declined as fruit became red ripe. The concentration of glucose and fructose were similar and higher than that of sucrose during early fruit growth and in ripe fruit. Uptake of 14C-sugars was followed in excised disks of cortical tissue from fruit 15–17 days old. The addition of CaCl2 was necessary to maintain tissue respiration. Sucrose uptake into tissue disks was nearly constant over 4 hr and had a pH optimum of 5.0. Kinetic analysis of sucrose uptake revealed both linear and saturable components. The kinetic characteristics of fructose uptake was similar to those for sucrose. Glucose, however, was taken up much more rapidly than either sucrose or fructose and only demonstrated saturation kinetics. The metabolic inhibitors NaCN (5 mM), dinitrophenol (DNP, 3 Mm) and carbonyl cyanide m-chlorophenyl hydrazone (CCCP, 100 μM) stimulated sucrose uptake 34%, 94%, and 54%, respectively. DNP eliminated the saturable component. Uptake of sucrose was inhibited by 36% with 10 μm DNP, 16% with 5 mM glucose, and 16% in a 100% N2 atmosphere. After incubation in 14C-sugars for 2 hr, about 90% of the label recovered from disks was in a neutral fraction. Half or more of this was in either glucose or fructose, depending upon the sugar fed. The distribution of 14C between glucose and fructose moieties of sucrose isolated from tissue fed (14C-fructosyl) sucrose indicated that a portion of the sucrose recovered underwent hydrolysis and randomization. Similar results were found with sucrose isolated from attached, whole fruit 8 hr after abraded leaves were fed labeled sugars. Results suggest that sucrose may be hydrolized prior to uptake into fruit tissue.