William J. Bramlage

Phenolics and lipid-soluble antioxidants in fruit cuticle of apples and their antioxidant activities in model systems

Abstract Phenolics were extracted from fruit cuticles of ‘Delicious’, ‘Golden Delicious’, ‘Empire’ and ‘Cortland’ apples, using either cuticular wax scraped from fruit peel or enzyme-isolated cuticles. The concentrations of free phenolics in fruit cuticle ranged from 8 to 45 μg g −1 and bound phenolics ranged from 50 to 110 μg g −1 in these cultivars. Free cuticular phenolic concentrations in the four cultivars were in the order: ‘Golden Delicious’ > ‘Delicious’ > ‘Empire’ > ‘Cortland’. In a linoleate emulsion (oil-in-water) system, diphenylamine (DPA, lipophilic) displayed higher antioxidant activity than methanol-extracted cuticular phenolics (hydrophilic). Antioxidant activity of quercetin (flavonoids) was higher than that of gallic acids (phenolic acids). Antioxidant activity of free phenolics in fruit cuticle was equivalent to that of quercetin while bound phenolics, when released by chemical methods, displayed activity similar to that of gallic acid. In an α-farnesene-hexane (bulk oil) system, however, antioxidant activities of methanol-extracted cuticular phenolics were higher than that of DPA. Lipid-soluble antioxidants (LSAs) from cuticle displayed higher activity in the linoleate emulsion system than in α-farnesene-hexane system. Only about 10–15% of the total LSA activity in fruit peel was detected in isolated fruit cuticle. Among the four cultivars, LSA activity in epidermal and hypodermal cells was similar in ‘Golden Delicious’, ‘Empire’ and ‘Cortland’ apples, while ‘Delicious’ had lower activity. There was no clear correlation between LSA activity and scald resistance among the four cultivars. However, the total antioxidant activities (activity of free phenolics in cuticle plus activity of LSAs in fruit peel) of the four cultivars were in the order: ‘Golden Delicious’ > ‘Empire’ > ‘Delicious’ > ‘Cortland’, which was similar to their scald resistance potentials.

Relationships of antioxidants in apple peel to changes in α-farnesene and conjugated trienes during storage, and to superficial scald development after storage

Abstract Three experiments were conducted: (1) ‘Cortland’ and ‘Delicious’ apples were harvested at four weekly intervals; (2) ‘Cortland’ apples were induced to ripen prematurely with ethephon sprays; (3) ‘Cortland’ apples were enclosed in brown bags for six weeks before harvest. At harvest and after intervals of storage at 0°C, concentrations of α-farnesene and conjugated trienes, estimates of total lipid-soluble and total water-soluble antioxidant activity, and concentrations of α-tocopherol, carotenes, ascorbic acid, glutathione, anthocyanins and flavonols in fruit peel were measured. The objective was to determine if differences in antioxidants at harvest persisted through storage, and if changes in antioxidants corresponded to accumulations of conjugated trienes and development of scald. Treatments resulted in significant differences in antioxidant and pigment concentrations at harvest. Water-soluble antioxidants and anthocyanins declined during storage, but lipid-soluble antioxidants generally increased. In general, antioxidant concentrations at harvest were inversely related to maximum conjugated triene concentrations at the end of storage, and to scald development. However, no individual antioxidant was associated consistently with conjugated triene accumulation or scald development, and as conjugated triene concentrations increased, total lipid-soluble antioxidant activity also increased. Water-soluble antioxidants generally decreased during storage. Possible involvements of antioxidants with scald development is discussed.

Developmental changes of cuticular constituents and their association with ethylene during fruit ripening in ‘Delicious’ apples

Abstract Developmental changes in total cuticle and cuticular constituents and their responses to ethylene during fruit ripening were studied using ‘Delicious’ apples. Total chloroform extractable wax and total cutin (including carbohydrate polymers) were 3.1 and 5.4 g m −2 , respectively, in young fruit. They increased during fruit development and reached 14.1 and 24.7 g m −2 of fruit peel, respectively, at harvest. During postharvest fruit ripening at 20°C, total cutin did not change but total wax increased to 21.5 g m −2 at 6 weeks. The increase of cuticular wax paralleled the increase of internal ethylene in fruit. Wax was separated by column chromatography into four portions — hydrocarbons and wax esters, free alcohols, free fatty acids, and diols. More than half of the diol fraction was ursolic acid. During fruit development, more hydrocarbons and diols than free fatty acids and alcohols accumulated in cuticle. During fruit ripening, all four portions increased, coinciding with the climacteric rise in ethylene, but rates of increase of free fatty acids and alcohols were higher than those of other portions. Preharvest treatment with 220 mg l −1 aminoethoxyvinylglycine (AVG) inhibited internal ethylene to −1 during 6 weeks at 20°C and no wax accumulation was detected in AVG-treated fruit. Preharvest treatment with 200 mg l −1 ethephon increased internal ethylene and accelerated wax accumulation compared with controls. Ethephon accelerated and AVG inhibited α-farnesene accumulation.

Changes in calcium level in apple cortex tissue shortly before harvest and during postharvest storage

Abstract During 3 consecutive years, occurrences of storage disorders of McIntosh apples (Malus domestica, Borkh.) increased with decreasing Ca concn in the outer cortical flesh at harvest. Time‐course studies showed that during maturation and storage of apples, Ca concn in the core region declined by about 50%. In the outer flesh, Ca concn declined during maturation, reached a minimum at or shortly following harvest, and then rose significantly during subsequent storage. Preharvest treatments increased Ca concentration in the outer flesh at harvest, and did not influence the rise in Ca following harvest.

Calcium accumulation in delicious apple fruit

Abstract Seasonal patterns of fruit growth and calcium (Ca) accumulation in ‘Delicious’ apple fruit were observed over four years and four growing regions. Although temperature and precipitation varied greatly, fruit consistently accumulated Ca in a quadratic fashion, with maximum uptake occurring early in the season. Little Ca accumulated in fruit during the three weeks prior to harvest. Under some conditions, fruit appeared to lose Ca during this time. Loss of fruit Ca was not closely associated with precipitation. Calcium uptake was greatest during periods of high evaporative demand.

Cultivar and growing region influence efficacy of warming treatments for amelioration of superficial scald development on apples after storage

Abstract Single warmings of ‘Cortland’, ‘Delicious’, ‘Granny Smith’ and ‘Pacific Rose’ apples to 20°C for 0–9 days after cold storage of 0–27 days were tested as a potential non-chemical method to control superficial scald development. Only in ‘Granny Smith’ was scald development reduced to commercially acceptable levels by warming, and even for this cultivar the response varied among growing regions. Warming treatments greatly advanced ripening, as indicated by softening of ‘Cortland’, and to a lesser extent ‘Delicious’, but had only small ripening effects on ‘Granny Smith’ and ‘Pacific Rose’. The extent of any warming effects on fruit ripening was greater with longer storage time before warming and with longer warming periods. Warming ‘Cortland’ apples twice reduced scald to the level of DPA treatment but increased the amount of ripening induced. There was no evidence that warming could delay rather than prevent scald development.

Endogenous levels of abscisic acid in aging carnation flower parts

Aging carnation flower parts were used to determine whether or not any correlation existed between the concentration of abscisic acid (ABA) and a predisposition of the tissue for ethylene synthesis. Levels of ABA were measured using an enzyme-linked immunosorbent assay (ELISA) following purification steps including prepacked silica gel columns. Increased ABA levels paralleled the increase of ethylene and the onset of irreversible wilting in the carnation petals. Neither the green tissue nor the receptacle showed any sign of wilting with the remainder of the flower parts, but increased ABA was detected in both tissues subsequent to, or coincident with, the ethylene climacteric peak in the senescing petals. An increase of ABA in both the styles and the ovary was detected in the preclimacteric flower, and did not appear to be triggered by the production of ethylene. Increased ABA in the gynoecium also did not result in the onset of ethylene production in the preclimacteric flower.

Effects of foliar calcium on McIntosh apple storage disorders

Abstract Seven foliar applications supplying 13.4 kg/ha CaCl2 biweekly increased surface flesh Ca by 44 ppm Oct 10. Scenescent breakdown of fruit after 100 days regular storage was reduced from 13 to 1%; scald (24 hrs, 23°C) was reduced from 32 to 4%. Similar reductions in storage disorders were effected by foliar CaCl2 on fruit that had been stored 180 days in CA.