Date of Award:

1973

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Nutrition, Dietetics, and Food Sciences

Advisor/Chair:

D. K. Salunkhe

Abstract

Part 1. Formation and control of chlorophyll, solanine alkaloids, and sprouts of potato (Solanum tuberosum L.) tubers

Incorporation of radioactive carbon from acetic acid-2-14C (sodium salt), β-hydroxy-β-methylglutaric acid (HMG)-3-14C, L-leucine-U-14C, L-alanine-U14C, and D-glucose-U-14C into the predominant glycosidic steroidal alkaloids, &alpha-chaconine of potato sprouts was 4.88, 9.0, 15, 24, and 20 times less than that of mevalonic acid (MVA=2-14C (DBED salt), respectively. The efficiency ratio revealed that β-hydroxy-β-methylglutaric acid (HMG)-3-14 was incorporated via acetate or acetoacetate. The distribution of radioactivity originated from D-glucose-U-14C was nearly nine times higher in the glycoside moiety than that in the aglycone part of the glycoalkaloids. Apparently, Alar( succinic acid 2,2-dimethylhydrazide), Ethrel or Ethephon (2-chloroethylphosphonic acid), and Telone (1 ,3-dichloropropene and related chlorinated hydrocarbons) significantly reduced the rate of incorporation of β-hydroxy-β-methylglutaric acid (HMG)-3-14C into the alkaloids.

A catalytic conversion of solanidine and UDP-glucose-U-14C to β-glucoside by the enzymatic system in a suspension of potato slices and the enzyme preparation from sprouts demonstrated the presence of β-glucosyltransferase in Solanum tuberosum L. Stepwise synthesis of α-solanine and α-chaconine from solanidine in potato tubers or sprouts seems possible.

Formation of solanine alkaloids in peeled potato slices was stimulated when stored at 15 and 24 C in dark or light (200 foot-candles). The slices held under light developed nearly three to four times more alkaloids than those held in the dark. Significantly higher concentrations of solanine alkaloids were formed in the late stage (after 24 hours) than in the early stage of the storage period . Hence, it can be concluded that when potatoes are sliced for chips or French fries, they should be processed immediately, before the glycoalkaloids are synthesized in higher concentrations.

Post-harvest application of chemicals, such as Phosfon (tributyl 2,4-dichlorobenzylphosphonium chloride), Phosfon-S (tributyl 2,4-dichlorobenzylammonium chloride), Amchem 72-A42 [2-(p-chlorophenylthio)- triethylamine], Amchem 70-334 or CPTA [2-(p-chlorophenylthio)-triethylamine hydrochloride], Nemagon (1,2-dibromo-3-chloropropane), and Telone (1,3-dichloropropene and related chlorinated hydrocarbons) at the concentrations of 250, 500, and 100 parts per million (ppm) in water; glycerin (10, 20, and 30 percent weight by volume [w/v] in water); and mineral oil (1.25, 2. 5, 5, 10, 15, 20, and 100 percent [w/v] in ether or petroleum ether) significantly inhibited the formation of chlorophyll and solanine alkaloids in the peripheral (periderm and outer parenchyma) zone of potato tubers exposed to a fluorescent light (200 foot-candles) for 6 or 7 days at 16 C and 60 percent relative humidity. The rates of inhibition increased with concentration of chemicals studied. A 10 percent solution of mineral oil was the minimum required concentration for effective control of chlorophyll and solanine alkaloids. The tubers dipped in 10 percent mineral did not develop chlorophyll on exposure to light (200 foot-candles) for 4 weeks, while the overall rate of inhibition of alkaloids was significantly high. In general, oil treatments were the most effective in controlling the formation of chlorophyll, solanine alkaloids, and sprout growth.

Part II . Formation and control of carbonyl compounds of tomato (Lycopersicon esculentum Mill.) fruits

Incubation of unsaturated fatty acids such as linoleic and linolenic acids with the crude soluble extract from tomato fruits produced carbonyl compounds. The enzyme preparations did not catalyze the conversion of saturated or monounsaturated fatty acids to carbonyls. Inability of potassium cyanide to inactivate the crude soluble extract proved that degradation of these fatty acids was mediated by lipoxidase and nonenzymatic oxidation by heme compounds was eliminated. These findings were supported by the fact that hydrogen peroxide, an inhibitor of lipoxidase enzyme, had inhibitory effects on the degradation of linoleic and linolenic acids by the tomato extract.

Hexanal was found to be one of the products of the enzyme reaction. The identity of hexanal was confirmed by comparing the physical properties such as retention time, infra-red and ultra-violet absorption bands, and Rf value with those of an authentic sample . Biogenesis of hexanal from linoleic or linolenic acid was further substantiated by the use of uniformly labeled 14C isotopes of these fatty acids with the crude soluble extract, filtered homogenate, and tissue slices.

Maximum activities (as evidenced by the production of carbonyls) were observed in the extract prepared with and incubated in a buffer medium of pH 7.5 (0.l M, Tris-HCl). The degradation of linoleic and linolenic acids was maximum at 30 C when incubated for 4 hours with 1 ml of the crude soluble extract. The enzymatic activity was enhanced by metal ions and compounds containing free -SH groups. Increase in the production of carbonyls by addition of citric and L-ascorbic acid may result from their metabolism. In general, ripe fruits contained greater enzymatic activities but smaller amounts of linoleic and linolenic acids than green fruits . The activity of the crude extract was increased by dialysis and the ammonium sulfate fractionation between 30 and 70 percent saturation. The rates of degradation of linoleic and linolenic acids catalyzed by the insoluble fractions of tomato extracts were more than those by the corresponding soluble fractions.

Tomato fruits (green-wrap or large green) stored under hypobaric or sub-atmospheric pressures were analyzed for their volatiles after ripening. The concentrations of selected carbonyls (acetaldehyde, 2-methyl propanal, butanal, 3-methyl butanal, and hexanal) and some other volatiles decreased substantially with decrease in storage pressure.

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