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Bruce D. Whitaker

Lipid composition and pigment content were determined in pericarp of `Pik Red' tomatoes (Lycopersicon esculentum Mill.) that were harvested when mature-green (MG) then ripened for 1 or 14 days at 20C, chilled for 11 or 21 days at 2C, or chilled for 21 days and transferred to 20C for 4 days (rewarmed). During ripening, chlorophyll fell below a detectable level, carotenes increased 100-fold, phospholipids (PLs) dropped ≈20%, and galactolipids (GLs) dropped ≈35%. Fatty-acid unsaturation decreased slightly. Steryl esters (SEs), more than free sterols (FSs) and steryl glycosides (SGs), increased at the expense of acylated steryl glycosides (ASGs), and in all four steryl lipids, the stigmasterol: sitosterol ratio rose dramatically, whereas the level of isofucosterol fell sharply. During chilling, chlorophyll declined ≈40% and carotenes ≈60%. PL content did not change, whereas GL fell ≈15%. Fatty-acid unsaturation increased slightly. FS, much more than SG and SE, increased at the expense of ASG. The stigmasterol: sitosterol ratio changed little in ASG, SG, and SE but declined in FS. Isofucosterol increased in FS and SE. Rewarming had little effect on the levels of chlorophyll, carotenes, or PL levels, but caused GL to fall another ≈15%. Fatty-acid unsaturation decreased slightly in GL and ASG. The distribution of total sterol in ASG, SG, FS, and SE changed dramatically, yielding proportions close to those in unchilled MG fruit. Also, 4 days after rewarming, the stigmasterol: sitosterol ratio had increased sharply, particularly in FS and SE, and there was a further rise in isofucosterol in all four steryl lipids. These results indicate that chloroplast damage occurs during chilling, but PL-rich cell membranes are not degraded, even upon rewarming. Changes in sterol composition and conjugation during chilling and after rewarming could result in membrane dysfunction.

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Bruce D. Whitaker

, phosphatidylethanolamine; PG, phosphatidylglycerol; PI, phosphatidylinositol; PL, phospholipid; SG, steryl glycoside; TSL, total steryl lipids (FS + ASG + SG). Use of a company or product name by the U.S. Dept. of Agriculture (USDA) does not imply approval or

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Bruce D. Whitaker

Plastids and microsomal membranes were isolated from pericarp tissue of mature green and red-ripe tell pepper fruit harvested from greenhouse and field grown plants. The lipid composition of these membrane fractions changed far more with ripening of field grown than greenhouse grown fruit. Also, the phospholipid (PL), free sterol (FS), steryl glycoside (SG) and acylated steryl glycoside (ASG) content of microsomes and plastids from both green and red fruit were very different under the two growing conditions. Total steryl lipids (TSL = FS + SG + ASG), and the TSL/PL ratio, increased in microsomes and decreased in plastids with ripening. These changes were much greater in field grown fruit. The ASG/SG ratio decreased with ripening in both membrane fractions, under both growing conditions. Ripening and growth conditions affected the phospholipid and sterol composition in plastids much more than in microsomes. Lipid changes associated with the chloroplast – chromoplast transformation were similar in field and greenhouse grown fruit, including an increase in the galactolipid/PL ratio. Future studies will assess how differences in membrane lipid composition affect postharvest storage life of the fruit.

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Bruce D. Whitaker

Altered metabolism of membrane lipids has been proposed as a mechanism for the beneficial effects of postharvest calcium treatment on apple quality. A previous study showed that after transfer of apples stored 6 months at 0C to 20C, calcium-treated fruit exhibited slower loss of galactolipid and altered levels of sterol conjugates. The present study of lipids in “control” fruit was conducted as a prelude to further in-depth analyses of the effects of postharvest calcium and heat treatments on lipid metabolism in apples during and after cold storage. Neutral lipid, glycolipid (GL), and phospholipid (PL) fractions were obtained by column chromatography followed by TLC separation of GL and PL classes. The major GL were steryl glycosides (SG), acylated steryl glycosides (ASG), cerebrosides (CB), and mono- and digalactosyl diacylglycerols. Phosphatidylcholine (PC) > P-ethanolamine (PE) > P-irositol (PI) were the major PL. The fatty acids of PC and PE were quite similar, whereas those of PI were more saturated. CB included only 2-hydroxy fatty acids. Among the steryl lipids, free sterols > SG > ASG, with beta-sitosterol >90% of the total sterol in each.

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Bruce D. Whitaker

A previous study of lipids from pericarp tissue of tomato fruit ranging from mature-green to red-ripe showed a large increase in total sterols accompanied by dramatic changes in sterol composition and conjugation with ripening. This study was conducted to determine whether similar changes occur in microsomal membranes derived from tomato fruit pericarp. Acylated steryl glycoside (ASG), the predominant steryl lipid, declined during ripening, with increases in steryl glycoside (SG) and free sterol (FS). Only minor changes in fatty acid composition were associated with the drop in ASG. The stigmasterol:sitosterol ratio increased throughout ripening, but much more in Fs than in SG or ASG. The ratio of FS to phospholipid (PL) increased with ripening. However, FS was never greater than 10 percent of the total membrane sterol (TMS), and TMS:PL actually declined over the middle stages of ripening. It is not known why tomato tissues maintain such high levels of ASG and SG, but sterol conjugation is thought to regulate the physical properties of cell membranes.

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Bruce D. Whitaker

MG tomato fruit were stored for four or 12 days at chilling (2C) or nonchilling (15C) temperature. Fruits stored 12 days at 15C ripened to the turning stage, whereas fruits at 2C did not ripen. Lipids of microsomes and plastids from pericarp tissue were analyzed at harvest and after four or 12 days of storage. After 12 days at either 15C or 2C, the ratio of phospholipid (PL) to protein in microsomes declined, with a concomitant increase in the ratio of total membrane sterols (TMS) to PL. The TMS/PL ratio also increased in crude plastids. In both microsomes and plastids, free sterols (FS) increased more at 2C than at 15C, and thus accounted for a larger percentage of the TMS. The ratio of stigmasterol to sitosterol in steryl lipids, particularly in FS, increased more at 15C than at 2C. The unsaturation index of fatty acids in PL and galactolipids generally increased slightly during storage at both 15C and 2C. The ratio of phosphatidylethanolamine to P-choline increased in both membrane fractions at both temperatures. In plastids, the ratio of mono- to digalactosyldiacylglycerol declined substantially at 2C but not at 15C.

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R.E. McDonald, W.R. Miller, and T.G. McCollum

Irradiation is being evaluated as a quarantine treatment of grapefruit (Citrus paradisi Macf. `Marsh'), but it can cause damage to the fruit. Research was conducted to determine if preirradiation heat treatments would improve fruit tolerance to irradiation as they improve tolerance to low temperature injury and to determine if canopy position influenced fruit tolerance to irradiation. Initially, grapefruit were irradiated at 0 or 2.0 kGy at a dose rate of 0.14 kGy·min-1 and selected biochemical changes were monitored over time. There was a marked increase in phenylalanine ammonia-lyase (PAL) activity following irradiation. Maximum activity (≈18-fold increase) was attained 24 hours after irradiation. Subsequently, grapefruit were harvested from interior and exterior canopy positions and irradiated at 0 or 1.0 kGy at a dose rate of 0.15 kGy·min-1 before storage for 4 weeks at 10 °C. Following storage, pitting of flavedo was the most evident condition defect noted as a result of irradiation. Pitting was observed on 27% and 15% of irradiated exterior and interior canopy fruit, respectively, whereas there was no pitting on nonirradiated fruit. Heat treatment before irradiation decreased susceptibility of fruit to damage. Pitting was 26%, 19%, and 17% when fruit were held 2 hours at 20 (ambient), 38 or 42 °C, respectively. Irradiation-induced PAL activity was reduced by temperature conditioning at 38 or 42 °C. Exterior canopy fruit flavedo contained higher levels of total phenols, including flavanols and coumarins compared with interior canopy fruit. Deposition of lignin was not related to canopy position. Neither irradiation nor heat treatment had an effect on total phenols or lignin deposition. Generally, cholesterol, campesterol, stigmasterol, β-sitosterol, and isofucosterol were found to be higher in four steryl lipid fractions in exterior canopy fruit compared with interior canopy fruit. Irradiation increased campesterol in the free sterol and steryl glycoside fractions and decreased isofucosterol in the free sterol fraction. Heat treatments had no effect on individual sterol levels. It seems that irradiation causes a stress condition in the fruit, which leads to pitting of peel tissue. Heat treatment before irradiation reduced damaging effects of irradiation.

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Shirin Shahkoomahally and Asghar Ramezanian

inhibit the development of maleness Acta Hort. 682 1171 1178 Picchioni, G. Watada, A. Conway, W. Whitaker, B. Sams, C. 1995 Phospholipid, galactolipid, and steryl lipid composition of apple fruit cortical tissue following postharvest CaCl 2 infiltration

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David R. Rudell, Sara Serra, Nathanael Sullivan, James P. Mattheis, and Stefano Musacchi

. 51 2 123 130 Picchioni, G.A. Watada, A.E. Conway, W.S. Whitaker, B.D. Sams, C.E. 1995 Phospholipid, galactolipid, and steryl lipid composition of apple fruit cortical tissue following postharvest CaCl2 infiltration Phytochemistry 39 763 769 Pluskal, T