Biomedical subjects

D D Rowan

Publications and source records attributed to D D Rowan.

3 recordsLinked to original sources

PubMed2001

Conjugated triene oxidation products of alpha-farnesene induce symptoms of superficial scald on stored apples.

The sesquiterpene alpha-farnesene (1) and its conjugated triene oxidation products accumulate in the skin of apples after harvest and are implicated as the causal agents of superficial scald. Conjugated triene oxidation products and analogues were synthesized and applied to the surface of Granny Smith apples either as vapors or in squalane. Farnesyl hydroperoxide (2a), trienol (2b), endoperoxide (3a), dehydronerolidol (5), and cumyl hydroperoxide (4) all produced the symptoms of superficial scald when applied at nanomolar doses. Scald-inducing activity was dependent on the mode of application. Farnesyl hydroperoxide (2a) was the most active conjugated triene when applied directly to the apple skin. Trienol (2b) also induced scald symptoms and partially reversed the inhibition of scald caused by diphenylamine.

Food Handling↗

PubMed1999

Biosynthesis of straight-chain ester volatiles in red delicious and granny smith apples using deuterium-labeled precursors.

Biosynthesis of straight-chain ester volatiles by Granny Smith and Red Delicious apples was investigated using deuterium-labeled fatty acids, C-6 aldehydes, and alcohols. Perdeuterated saturated and monounsaturated fatty acids were metabolized to hexyl-d(11), hexanoate-d(11), heptanoate-d(13), and octanoate-d(15) esters, whereas perdeuterated linoleic acid produced only hexyl-d(11) and hexanoate-d(11) esters. Exposure of fruit to vapors of deuterated 3Z-hexenal, 2E-hexenal, and hexanal identified the following biosynthetic processes: (1) isomerization between 3E, 3Z, and 2E-hexenals; (2) reduction to 3E, 3Z, and 2E-hexenyl esters; (3) reduction to hexanol and hexyl esters; (4) oxidation to hexanoic acid and formation of hexanoate esters; (5) beta-oxidation of hexanoic acid leading to butyl and butanoate esters; and (6) alpha-oxidation of hexanoic acid leading to pentyl and pentanoate esters. Unsaturated straight-chain ester volatiles appear to arise only by the lipoxygenase pathway and may be useful indicators of lipoxygenase activity in fruit.

Chromatography, Gas↗

PubMed1996

Solid phase microextraction for quantitative headspace sampling of apple volatiles.

Solid phase microextraction (SPME) was evaluated for use in the quantification of aroma volatile production by Granny Smith apples during cool storage. Particular attention was paid to quantifying alpha-farnesene (3,7,11-trimethyldodeca-1,3(E),6(E),10-tetraene) due to its involvement in superficial scald, a disorder of cool stored apples. Comparison between SPME and solid phase extraction (SPE) showed that the SPME fiber had greater adsorption of high molecular weight (MW) volatiles such as alpha-farnesene. When sampling by SPME, these higher MW volatiles did not equilibrate between apples, headspace, and fiber within sampling times as long as 90 min, while lower MW volatiles equilibrated within 5 min. This behavior was also shown by a simple model system consisting of five selected volatiles dissolved in an involatile, lipophilic liquid (squalane). The less volatile high MW aroma compounds evaporated slowly from the surface of the apples and were depleted from the headspace because of very rapid adsorption by the SPME fiber. The amount of alpha-farnesene adsorbed by the fiber increased with air movement through the system. In a static headspace system, the amount of alpha-farnesene adsorbed by the fiber decreased nonlinearly with increasing distance from the apples, due to adsorption onto the glass walls. While SPME is ideal for rapid, qualitative determination of apple headspace volatiles, the slower equilibration of higher MW volatiles limits its use for quantification in more complex systems.

Chromatography, Gas↗