Biochemical Bases for Controlled-atmosphere Effects on Reducing Chilling Injury of `Hass' Avocado Fruit

California-grown `Hass' avocado fruit were stored at 5C, in air or a controlled atmosphere (CA) of 2% oxygen and 5% carbon dioxide. Fruit were evaluated at 0, 2, 4, 6, 8, 10, and 12 weeks, both immediately upon removal from storage and after ripening at 20C. Severe chilling injury (flesh browning) developed in the airstored fruit after 6 weeks, while only moderate symptoms were observed in CA-stored avocado fruit after 12 weeks. Lipid peroxidation breakdown products increased during storage and ripening in both air and CA treatments. Sterols, steryl esters, steryl glycosides, glycolipids, and phospholipids were analyzed. Quantity of acylated steryl glycoside in ripe fruit changed from 34 nmoles initially, to 51 or 27 nmoles after 6 weeks at 5C in air or CA, respectively. Glycolipid fatty acid unsaturation in air-stored fruit decreased with the development of chilling injury. Fatty acid unsaturation in phospholipids (phosphatidylinositol, phosphatidylcholine, phosphatidylglycerol, and phosphatidylethanolamine) of air-stored avocados decreased with the development of chilling injury. CA storage delayed the development of chilling injury and the loss of fatty acid unsaturation.

138 LIPID CHANGES IN TOMATO FRUIT MICROSOMAL MEMBRANES DURING RIPENING

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.

Growth Conditions and Ripening Influence Plastid and Microsomal Membrane Lipid Composition in Bell Pepper Fruit

Plastids and microsomal membranes were isolated from pericarp tissue of mature-green and red-ripe bell pepper (Capsicum annuum L.) fruit harvested from greenhouse- and field-grown plants. The lipid composition of these membrane fractions changed much 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 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 to chromoplast transformation were similar in field- and greenhouse-grown fruit, including an increase in the galactolipid: PL ratio.

EFFECTS OF GROWTH CONDITIONS AND RIPENING ON PLASTID AND MICROSOMAL MEMBRANE LIPID COMPOSITION IN BELL PEPPER FRUIT

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.

A steryl glycoside fraction from Momordica charantia seeds with an inhibitory action on lipid metabolism in vitro

A saponin fraction was isolated from Momordica charantia seeds by delipidation, saline extraction, ammonium sulfate precipitation, and extraction of the resulting supernatant with n-butanol. Thin-layer chromatography, in the upper phase of the n-butanol – ethyl acetate – water (4:1:5, by volume) system on plastic sheets coated with silica gel 60 F254, revealed the presence of a single spot after spraying with 10% sulfuric acid. The lack of contamination of the saponin preparation with proteins was judged by the absence of protein bands in sodium dodecyl sulfate – polyacrylamide gel electrophoresis, agarose electrophoresis, and agarose diffusion, and by the absence of an absorption maximum around 278 nm. The saponin acted as a noncompetitive inhibitor of corticotropin, glucagon, and epinephrine in lipolysis in isolated rat adipocytes, and it also antagonized dibutyryl cAMP induced lipolysis. The antilipolytic activity was resistant to heat, trypsin, chymotrypsin, pronase, and glutathione, in keeping with the chemical nature of saponin. Incorporation of [3-3H]glucose into lipid was inhibited. Adipocyte viability and ATP content were not affected by the saponin, suggesting that its inhibitory effects on lipolysis and lipogenesis were not due to an adverse effect on cell viability.

The free sterol, steryl ester, and steryl glycoside content of tomato cultivars resistant and susceptible to Phytophthora infestans

Leaf sterols were extracted from three late blight resistant ('Nova,' 'New Yorker,' and 'West Virginia 63') and three late blight susceptible ('Beefsteak,' 'Jubilee,' and 'San Marzano') cultivars of tomato (Lycopersicon esculentum Mill.). There were no significant differences (P < 0.05), either quantitatively or qualitatively, between the sterol contents of the resistant and the susceptible cultivars. Of the six cultivars only the steryl glycoside class of 'San Marzano' was significantly higher than that of the other cultivars. The total sterol content was 2.95–3.84 mg/g dry weight and was composed of 23–32% free sterol, 4–6% steryl ester, and 63–71% steryl glycoside. The relative susceptibility of tomato to late blight is not related to the free sterol or conjugated forms of sterols in the plant.