Peel Of Grapefruit Research Articles

Effect of Gamma Radiation on the Synthesis of Scopoletin and Scopolin in Grapefruit Peel in Relation to Radiation Damage

RIov, J., GOREN, R., MONSELISE, S. P., AND KAHAN, R. S. Effect of Gamma Radiation on the Synthesis of Scopoletin and Scopolin in Grapefruit Peel in Relation to Radiation Damage. Radiat. Res. 45, 326-334 (1971). Two unknown compounds, featuring blue fluorescence under ultraviolet light on thin-layer chromatography plates, were found to accumulate in the peel of gamma-irradiated grapefruit. The two compounds were isolated and identified as scopoletin (6-methoxy-7-hydroxycoumarin) and scopolin (7-glucoside of scopoletin). Both the content of the two compounds and radiation damage (peel pitting) were positively correlated with radiation doses up to 300 krads. Irradiation with 300 krads also increased the incorporation of phenylalanine-14C into the scopoletin molecule. Rate of incorporation and content of free and hydrolyzed scopoletin increased with time following the irradiation. It is suggested that phenolic compounds which accumulate in the peel after irradiation contribute to the formation of radiation damage in citrus fruits.

Effects of gamma radiation and ethylene on protein synthesis in peel of mature grapefruit

Effects of gamma irradiation on protein synthesis in grapefruit peel were studied by incorporating 14C-leucine into newly synthesized protein. A linear relationship was found between the increase in irradiation doses and the inhibition of protein synthesis. Four hundred krads inhibited almost completely protein synthesis. No recovery of protein synthesis was detected for 5 days after irradiation. Irradiation had little or no effect on total uptake of 14C-leucine. Senescence of non-irradiated fruits was characterized by a decrease in protein synthesis, while total uptake remained unchanged. Inhibition of protein synthesis by irradiation was not affected by fruit senescence. Ten ppm ethylene did not affect protein synthesis, while 100 ppm inhibited it by 50 per cent. The relationship between protein synthesis, ethylene and irradiation-induced PAL activity is discussed.

Gamma Radiation Effects on the Pectic Substances in Citrus Fruits

SUMMARY— Exposure of citrus fruits to gamma radiation at doses of 150 and 300 krad increased the water‐ and oxalate‐soluble pectins and decreased the protopectin in component parts of Valencia oranges and Duncan grapefruit. The quantities of water‐soluble pectin and protopectin in the peel and membrane were affected the most by irradiation. Degradation of the pectins as measured by jelly grade increased in all components of the irradiated fruits. The greatest decrease in jelly grade occurred in the March samples when the Brix/acid ratio was least. Methoxyl contents of the pectins from the peel of oranges and grapefruit decreased, while this characteristic decreased only slightly in pectins from the membrane of irradiated fruits. Pectinesterase activity in the peel of both oranges and grapefruit decreased with increased dosages, while the activity in the membrane of both fruits increased.

The Carbohydrates in the Peel of Oranges and Grapefruita

SUMMARYThe carbohydrates of the citrus peel were divided according to their solubility in 80% ethanol. The alcohol‐soluble solids were composed of about 80% total sugars. Free xylose was found in trace amounts. Glucose, fructose, and sucrose were the main sugars present. Sucrose content of the peel was in general lower than the total reducing sugars. The alcohol‐insoluble solids were separated into “pectic substance,”“hemicellulose,” and “cellulose” fractions by extracting with different solvents. The “pectic substance” fraction upon hydrolysis yielded arabinose, galactose, and galacturonic acid. “Hemicellulose” fraction contained xylose, arabinose, galactose, glucose, and some uronic acids in its hydrolysate. In the “cellulose” fraction, glucose was dominant with some xylose and arabinose being also present. Traces of galactose and some uronic acids and in some cases mannose were found. On the average only between 53 and 70 per cent of the alcohol‐insoluble solids were recovered as carbohydrates in the peel of various citrus varieties.

Carbohydrate Fractions of Grapefruit Peel

1. Whole peel of grapefruit was extracted with 80% ethyl alcohol and separated into two distinct fractions, the alcohol-soluble and alcohol-insoluble solids. The carbohydrate constituents of these two fractions were investigated, and certain of their physical and chemical properties were determined. All analyses were made on fruit samples obtained from trees that had been fumigated with hydrocyanic acid or sprayed with oil for pest control during the growing season. 2. The alcohol-soluble fraction of the peel contained substances which liberated a small amount of carbon dioxide on hydrolysis with 12% hydrochloric acid. The total solids of this fraction composed 66.31% and 67.35% of the dry matter of the peel of fumigated and oil-sprayed fruit, respectively. 3. The soluble sugars in the peel averaged 40.29% and 41.28% of the dry weight of the fumigated and oil-sprayed fruit, respectively. These amounts of soluble sugars accounted for 60.76% and 61.28% (mean values) of the total alcoholic extractives. Approximately 40% of the dry weight of the alcohol-soluble fraction was composed of substances other than sugars, namely, essential oil, waxes, organic acids, naringin, and various concentrations of undetermined constituents. 4. The alcohol-insoluble fraction of the peel contains the cell-wall constituents-cellulose, hemicellulose, and pectin. This fraction comprised 33.69% and 32.65% of the dry weight of the peel. Lignin and starch were not present in sufficient quantities to be determined by the prevailing chemical methods. 5. Since the alcohol-insoluble fraction contains the pectin, most of the carbon dioxide which can be liberated by hydrolysis with 12% HCl and all the methoxyl groups occur in this fraction. The ratio of methoxyl to carbon dioxide was much lower in grapefruit peel than in lemon peel. 6. The carbon dioxide equivalent to the sum of the esterified and non-esterified carboxyl groups was equal to the total carbon dioxide of the alcohol-insoluble fraction obtained on hydrolysis with 12% hydrochloric acid. 7. The sum of the water-soluble and acid-soluble pectin (as calcium pectate) of the alcohol-insoluble fraction of the peel of the fumigated and oil-sprayed fruit amounted to 43.79% and 43.95%, respectively. These values are much lower than those for the total pectin calculated from the carbon dioxide and the methoxyl values. 8. To establish criteria of purity, the calcium pectate values are accompanied by corresponding values for carbon dioxide, calcium, and furfural. The percentages of calcium in the calcium pectates are somewhat higher than the 7.50% usually reported for pure calcium pectate. The percentages of carbon dioxide are slightly higher than the 17.40% reported for pure calcium pectate. The furfural values are in accord with those reported by other investigators. 9. The residue that remains after extracting the pectin from the alcohol-insoluble solids of the peel is composed of cellulose and hemicellulose and a comparatively small amount of firmly bound pectin that is difficult to extract and determine quantitatively. 10. The sum of the carbon dioxide in the aqueous extract, acid extract, and residue amounted to 94.26% and 95.19% of the total carbon dioxide of the alcoholinsoluble solids in the peel of fumigated and oil-sprayed fruit, respectively. In the aqueous and acid extracts, calcium pectate accounted for more than 90% of the carbon dioxide dissolved by the extractants.