Superficial scald development on apples is related to preharvest environmental conditions, perhaps through effects on endogenous antioxidant concentrations In 1989 we examined effects of maturity, light, and preharvest temperatures (< 10°C) on endogenous antioxidant levels in the fruit at harvest and on scald development after long-term storage in 0°C air. Cortland apple trees were sprayed with 500 ppm ethephon 1 month before normal harvest to create maturity differences. Fruit on other Cortland trees were bagged 1 month prior to harvest to reduce light interception. Samples also were harvested from other Cortland trees after exposures to different numbers of hours < 10°C, Hours < 10°C before harvest were negatively correlated to scald development. Ethephon treatment decreased scald incidence, and bagging increased it, The total lipid-soluble antioxidant activity increased with increasing hours < 10°C and with ethephon treatment, while bagging of fruit slightly decreased this antioxidant activity. To better understand the relationships between preharvest factors and antioxidant levels, individual antioxidants, including ascorbic acid, α tocopherol, anthocyanins and glutathione, are being analyzed.
Cynthia L. Barden and W. J. Bramlage
Shiow Y. Wang, Dean Der-Syh Tzeng, and Gene J. Galletta
Foliar application of a mixture of methionine and riboflavin was effective in reducing the severity of powdery mildew [Sphaerotheca macularia (Wallr. ex Fr.) Jacz. F. sp. Fragariae] infection in 72 strawberry progenies and over 110 clonal genotypes. This biocidal activity was enhanced by supplement of copper, iron, and surfactants [such as sodium dodecyl sulfate (SDS), Triton X-100, or Tween-20]. Compounds free radical scavengers (n-propyl gallate, thiourea), or antioxidants (α-tocopherol, -carotene) reduced its biocidal activity. Plants treated with the MR formulation (26.6 μM riboflavin, 1 mM D,L-methionine, 1 mM copper sulfate pentahydrate and 1 mg·ml–1 SDS) or 29% SP formulation of MR (Technical Division of the American Cyanamid Corporation, Taiwan Subsidiary at Taipei) not only showed decreased powdery mildew infection but also showed increased chlorophyll content and leaf area and improved fruit quality. Results in this study suggest that treatment with mixture of methionine and riboflavin is beneficial to strawberry plants and may serve as an alternative to fungicides for controlling powdery mildew.
Cynthia L. Barden and William J. Bramlage
During the harvest season apples ripen and develop scald resistance. In the Northeast they usually are also exposed to cool temperatures as they mature and ripen. Experiments were conducted to study the effects of cool temperature, light and maturity on the endogenous antioxidants and subsequent scald development in Cortland and Delicious apples. Total lipid-soluble antioxidant activity in apple peel at harvest generally increased as scald incidence after storage decreased. Yet, α tocopherol, ascorbic acid and total water-soluble reducing capacity were not closely related to scald development. The absence of light (bagged fruit) decreased all measured antioxidants and increased scald development. However, ethephon applied in mid-August to induce ripening increased the levels of these antioxidants but had little effect on scald incidence in the absence of cool temperatures (hours <10°C). Cool temperatures, which decreased scald susceptibility, increased lipid-soluble antioxidant activity but had little influence on the other measured antioxidants. These data suggest that the endogenous antioxidants may be only partly responsible for natural scald resistance.
Alexis M. Barbarin, Frank J. Williams, Greg T. Bettmann, Donald P. Hauber, and Harish H. Ratnayaka
'Knowledge of constitutive levels of gas exchange and antioxidant properties under unstressed conditions is critical for elucidating their potential roles in stress tolerance, planning cultural practices, and evaluating nutritional quality of vegetable crops. This greenhouse study reports gas exchange, photosystem II efficiency, and pigment and antioxidant profiles of two spinach cultivars [SpinaciaoleraceaL., cvs. Bloomsdale Long Standing (Bloomsdale) and Hybrid Tyee (Tyee)] with contrasting morphology. `Bloomsdale', the cultivar with more compact stature and larger leaves, had 47% greater photosynthesis (P net) than `Tyee'. Stomatal conductance (g s) and transpiration (E) were 94% and 46% greater in `Bloomsdale' than `Tyee', respectively. However, photosystem II efficiency (F v'/F m') was only 8% greater in `Bloomsdale' than `Tyee'. Instantaneous water use efficiency was similar in both cultivars. `Bloomsdale' had nonsignificantly greater concentrations of chlorophylls a and b, lutein, β-carotene and violaxanthin than `Tyee'. Both cultivars had similar, marginal α-tocopherol concentrations (<0.1 ng·g-1 FW). However, `Tyee' had a greater chlorophyll a:b ratio which, combined with lower g s and E, suggests a possible advantage for `Tyee' over `Bloomsdale' under relatively dry and high light conditions. Further studies must be conducted to compare nutritional quality of the two cultivars, based on constitutive levels of pigments and antioxidants. Greater gas exchange activity in `Bloomsdale' than `Tyee' appears to be due more to CO2 acquisition/metabolism than photosystem II efficiency or concentrations of pigments and antioxidants.
Elizabeth A. Baldwin and Bruce Wood
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.
Erik H. Ervin, Xunzhong Zhang, and John H. Fike
High ultraviolet-B (UV-B; 290-320nm wavelength) may significantly contribute to kentucky bluegrass (Poa pratensis L.) sod death at harvest and transplanting. As terrestrial UV-B levels continue to increase due to a depletion of the stratospheric ozone layer this problem may worsen. Epidermal attenuation from pigments and detoxification of reactive oxygen species by antioxidant metabolites and enzymes are involved in plant defense against oxidative stress caused by UV-B. Our objective was to determine whether the attenuation and detoxification systems of kentucky bluegrass could be artificially boosted by exogenous applications of ascorbic acid (AA), alpha-tocopherol (AT), or a colorant before exposure to high levels of UV-B. Ascorbic acid, AT, and the colorant Green Lawnger (GL), were applied to plugs of mature kentucky bluegrass alone or in combination, and then subjected to artificial, continuous UV-B exposure (70 μmol·m-2·s-1); three greenhouse experiments were conducted. By 3 to 5 days after UV-B initiation, visual quality and photochemical efficiency, as measured by chlorophyll fluorescence were significantly reduced. However, in Expt. 1, AA alleviated decline of visual quality, delayed loss of photochemical efficiency, and increased recovery relative to the control. In Expt. 3, decreased endogenous AT and antioxidant enzyme activities were measured due to UV-B stress. Application of AA, AA + AT, or GL partially alleviated photochemical efficiency decline from 4 to 12 days after initiation of UV-B. In addition, application of the chemical treatments increased leaf tissue AT concentrations by 32% to 42%, increased SOD activity by 30% to 33% and increased catalase activity by 37% to 59%, relative to the control as measured 10 days after UV-B initiation. Greater AT concentration and SOD and catalase activities were associated with greater visual quality under UV-B stress. The results of these studies indicate that kentucky bluegrass UV-B tolerance may be increased by supplementing its pigment and antioxidant defense systems with foliar applications of AA, AT or GL.
Erik H. Ervin, Xunzhong Zhang, and John H. Fike
High ultraviolet-B (UV-B; 290-320 nm wavelength) radiation may significantly contribute to the quality decline and death of kentucky bluegrass (Poa pratensis L.) sod during summer transplanting. Antioxidants and protective pigments may be involved in plant defense against oxidative stress caused by UV-B. Selected exogenous hormones may alleviate UV-B damage by upregulating plant defense systems. The objectives of this study were to determine if exogenous hormone or hormone-like substances could alleviate UV-B damage to `Georgetown' kentucky bluegrass (Poa pratensis L.) under greenhouse conditions. The hormone salicylic acid at 150 mg·m-2 and the hormone-containing substances, humic acid (HA) at 150 mg·m-2 and seaweed extract (SWE) at 50 mg·m-2, were applied to plugs of kentucky bluegrass and then subjected to UV-B radiation (70 μmol·m-2·s-1). The UV-B irradiation stress reduced turf quality by 51% to 66% and photochemical efficiency by 63% to 68% when measured 10 or 12 days after initiation of UV-B. Endogenous alpha-tocopherol (AT) and antioxidant enzymes (superoxide dismutase (SOD) and catalase) were reduced by UV-B stress. Anthocyanin content was increased from day 1 to 5 and then decreased from day 5 to 10 of continuous UV-B irradiation. Application of SA and HA + SWE enhanced photochemical efficiency by 86% and 82%, respectively, when measured 10 or 12 days after UV-B initiation. In addition, application of the hormonal supplements increased AT concentration, SOD, catalase activity, and anthocyanin content when compared to the control at 10 days after UV-B initiation. Bluegrass with greater AT concentration and SOD and catalase activity exhibited better visual quality under UV-B stress. The results of this study suggest that foliar application of SA and HA + SWE may alleviate decline of photochemical efficiency and turf quality associated with increased UV-B light levels during summer.
Zhiguo Ju and Eric A. Curry
`Granny Smith' apples (Malus × domestica Borkh) and `d'Anjou' pears (Pyrus communis L.) were dipped in a 2.5%, 5%, or 10% stripped corn oil (α-tocopherol <3 mg·kg-1) emulsions, 2000 mg·L-1 diphenylamine (DPA), respectively, at harvest and stored in air at 0 °C for 8 months. Untreated fruit served as controls. In oil-treated apples and pears, ethylene and α-farnesene production rates were lower in early storage and higher in late storage than in control. Control fruit developed 34% scald in `Granny Smith' apples and 23% scald in `d'Anjou' pears after 6 months storage, whereas fruit treated with oil at 5% or 10%, or with DPA at 2000 mg·L-1 were free from scald. After 8 months storage, oil at 10% was as effective as DPA in controlling scald in pears, whereas in apples, fruit treated with 10% oil developed 18% scald and DPA-treated fruit were scald-free. DPA-treated apples developed 32% senescent scald, while 5% or 10% oil-treated fruit had none. Oil-treated fruit were greener, firmer, and contained more titratable acidity after 8 months of storage than control or DPA-treated apples and pears. In `Granny Smith', 100% of the controls and 79% of the DPA-treated fruit developed coreflush after 8 months of storage, but both 5% and 10% oil-treated fruit were free from coreflush. In `d'Anjou', 34% of the controls and 27% of the DPA-treated fruit showed decay after 8 months of storage, compared with 5% decay in 5% oiltreated fruit, and no decay in 10% oil-treated fruit.
C.R. Brown, D. Culley, C.-P. Yang, R. Durst, and R. Wrolstad
A breeding effort designed to increase the antioxidant level of potato (Solanum tuberosum L.) by means of high concentrations of anthocyanins and/or carotenoids provided selected materials for analysis. Extraction methods suitable for isolating both hydrophilic and lipophilic compounds were used and measurements of total anthocyanin and total carotenoid were made. Two methods of measurement of oxygen radical absorbance capacity (ORAC) adapted to hydrophilic and lipophilic compounds were applied. Total anthocyanin values varied between 9.5 and 38 mg per 100 g fresh weight (FW). The hydrophilic fraction ORAC measurements among anthocyanin-rich clones varied between 250 and 1420 μmol Trolox equivalents per 100 g FW. These two variables were significantly correlated, r = 0.73, and with significant positive slope in linear regression. Measurement of total carotenoids revealed differing degrees of yellowness covered a range of total carotenoid extending from 35 to 795 μg per 100 g FW. Dark yellow cultivars had roughly 10 times more total carotenoid than white-flesh cultivars. The lipophilic fraction ORAC values ranged from 4.6 to 15.3 nmoles α-tocopherol equivalents per 100 g FW. Total carotenoid was correlated with the lipophilic ORAC values, r = 0.77, and also had a statistically significant positive regression coefficient. Clones with red and yellow pigments visible in the flesh had anthocyanins and carotenoids in elevated levels and ORAC contributions from both fractions. The introgression of high levels of carotenoid from germplasm directly extracted from the Papa Amarilla (yellow potato) category of cultivars of South America into long-day adapted North American materials is presented here. Although anthocyanins and carotenoids are major contributors to antioxidant activity, other constituents of potato flesh likely play significant roles in total antioxidant values.
Rafael Socias i Company and A.J. Felipe
, that of higher quality for fat stability and nutritive value in the lipid fraction, is especially high in ‘Belona’, over 75% ( Table 4 ). This cultivar also shows a very high content of tocopherols (both of α-tocopherol and total tocopherol), although