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Jyh-Bin Sun, Ray F. Severson, and Stanley J. Kays

We describe a relatively simple collection procedure for quantifying volatiles in baked sweetpotato [Ipomoea batatas (L.) Lam.]. Volatiles formed during baking `Jewel' and `Centennial' sweetpotatoes at 204C were purged from a baking vessel with He or a HeO2 mixture, collected in cold methylene chloride, and reduced in volume using a Kuderna-Danish concentrator. Volatile components were quantified by capillary gas chromatography and characterized using gas chromatographic-mass spectrometer analysis. Quantitatively, the major components were identified as 2-furaldehyde; 2-furanmethanol; benzaldehyde; 5-methyl-2-furfural; phenylacetaldehyde; 3-hydroxy-2-methyl-4 H -pyran-4-one; 2,3-dihydro-3,5-dihydroxy-6-methyl-4 H- pyran-4-one; and 5-hydroxy-methyl-2-furancarboxaldehyde. Some quantitatively minor compounds were also identified. The volatile collection system is reproducible for quantitative comparisons among breeding lines.

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Stanley J. Kays, Jyh-Bin Sun, and Ray F. Severson

Changes in the concentration of individual sugars in sweetpotato storage roots with cooking and their relationship to the formation of volatile compounds were studied. During cooking maltose concentration increased from 0.03% fwt at 25.C to a maximum of 4.33% at WC. Microwave pretreatment (2-4 minutes) resulted in a significant decrease in amounts of maltose and volatiles formed. At 80°C, approximately 80% of maltose synthesis was inhibited when pretreated with microwaves. Adding maltose into microwave pretreated samples and then cooking in a convection oven restored most of the volatile profile with the exception of phenylacetaldehyde. Upon heating (200°C), sweetpotato root material that was insoluble in both methanol and methylene chloride produced similar volatile profiles to those from sweetpotatoes baked conventionally. Volatiles derived via thermal degradation of the non-polar methylenc chloride fraction and the polar methanol fraction did not display chromatographic profiles similar to those from conventionally baked sweetpotatoes. Initial reactions in the formation of critical volatiles appear to occur in the methanol and methylene chloride insoluble components. Maltol (3-hydroxy-2-methyl-4-pyrone) was found to be one of the critical components making up the characteristic aroma of baked sweetpotatoes. It was concluded that maltose represents a primary precursor for many of the volatile compounds emanating from baked `Jewel' sweetpotatoes and the formation of these volatiles appears to involve both enzymatic and thermal reactions.

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Jyh-Bin Sun, Ray F. Severson, William S. Schlotzhauer, and Stanley J. Kays

Thermal degradation of fractions from sweetpotato roots (`Jewel') was conducted with gas chromatographymass spectrometry to identify precursors of critical flavor volatiles. Upon heating (200 C), sweetpotato root material that was insoluble in methanol and methylene chloride produced similar volatile profiles to those from sweetpotatoes baked conventionally. Volatiles derived via thermal degradation of the nonpolar methylene chloride fraction and the polar methanol fraction did not display chromatographic profiles similar to those from conventionally baked sweetpotatoes. Initial reactions in the formation of critical volatiles appear to occur in the methanol and methylene chloride insoluble components. Maltol (3-hydroxy-2-methyl-4-pyrone) was found to be one of the critical components making up the characteristic aroma of baked sweetpotatoes. Integration of an analytical technique for the measurement of flavor into sweetpotato breeding programs could potentially facilitate the selection of improved and/or unique flavor types.