Ron G. Buttery

Characterization of some volatile constituents of bell peppers

The steam volatile components of Californian green bell peppers (Capsicum annum aar. grossum, Sendt) have been qualitatively analyzed using conventional and capillary gas-liquid chromatographic separation with characterization by mass, infrared, and in some cases ultraviolet and proton magnetic resonance spectra. Major components identified in oil obtained by vacuum steam-distillation-continuous-extraction included 2-methoxy-3-isobutylpyrazine, trans-p-ocimene, limonene, methyl salicylate, linalool, nona-trans,cis-2,6-dienal, deca-trans,trans2,4-dienal, and hex-cis-3-enol. Additional components detected in small amounts in the vacuum isolated oil but in much larger amounts in oil isolated at atmospheric pressure were non-1 -en-4one, non-trans-2-en-4-one, nona-trans,trans-2,5-dien4-one, 2-pentylfuran, and benzaldehyde. The identities of 24 components were confirmed by direct comparison of their spectral and gas chromatographic retention data with those of authentic samples. Tentative identification was obtained for an additional 19 components from their mass spectral fragmentation patterns. Odor thresholds in water solution were determined for major components. 2-Methoxy-3-isobutylpyrazine was found to possess an extremely potent odor with an odor threshold of 2 parts per 1012 parts of water. Generally about 70 to 80% of untrained sensory panelists (40) indicated that the odor of dilute water solutions of this compound was similar to that of fresh green bell peppers.

Effect of storage and ripening on fresh tomato quality, Part I

Abstract Four varieties of fresh tomato were grown, stored and treated under commercial conditions to assess the effects of storage and ripening conditions on tomato taste and flavor. The qualitative and quantitative changes in values for volatiles, non-volatiles and physical characteristics were determined. The results are reported in two parts. This report discusses the effects of storage temperature and ethylene treatment on changes in the concentrations of 32 tomato volatiles with results expressed in terms of Odor Units (Uo) in order to best approximate human aroma effect. A second report discusses all other parameters along with general statistical analysis. The average Odor Unit value for each of the tracked analytes showed that only half the tracked volatiles were present in concentrations great enough to contribute to over-all aroma. Statistical analysis by Anova showed that the levels of all significant volatiles, except methyl salicylate, can be correlated to changes in storage conditions. The generation of volatiles decreases significantly with storage and ripening temperatures below 10° but the final ripening temperature is the most significant factor in determining levels of volatiles produced. If final ripening temperatures are raised to 20° for tomatoes initially stored at 10° or less, volatiles are produced at a level comparable to tomatoes stored above 10°. When final ripening takes place at temperatures below 10° volatile production is curtailed.

Studies on the aroma of five fresh tomato cultivars and the precursors of cis- and trans-4,5-epoxy-(E)-2-decenals and methional.

Three tasty (BR-139, FA-624, and FA-612) and two less tasty (R-144 and R-175) fresh greenhouse tomato cultivars, which significantly differ in their flavor profiles, were screened for potent odorants using aroma extract dilution analysis (AEDA). On the basis of AEDA results, 19 volatiles were selected for quantification in those 5 cultivars using gas chromatography-mass spectrometry (GC-MS). Compounds such as 1-penten-3-one, ( E, E)- and ( E, Z)-2,4-decadienal, and 4-hydroxy-2,5-dimethyl-3(2 H)-furanone (Furaneol) had higher odor units in the more preferred cultivars, whereas methional, phenylacetaldehyde, 2-phenylethanol, or 2-isobutylthiazole had higher odor units in the less preferred cultivars. Simulation of the odor of the selected tomato cultivars by preparation of aroma models and comparison with the corresponding real samples confirmed that all important fresh tomato odorants were identified, that their concentrations were determined correctly in all five cultivars, and that differences in concentration, especially of the compounds mentioned above, make it possible to distinguish between them and are responsible for the differential preference. To help elucidate formation pathways of key odorants, labeled precursors were added to tomatoes. Biogenesis of cis- and trans-4,5-epoxy-( E)-2-decenals from linoleic acid and methional from methionine was confirmed.

Odor thresholds of various branched esters

A series of branched esters (methyl 2,2-dimethylpropanoate to ethyl 2-ethylhexanoate) were purified by preparative gas chromatography and their odor thresholds were determined using sensory panel methods. The odor thresholds reached a minimum with the butanoate and pentanoate esters. In general, the branched esters have much lower odor thresholds than their straight chain counterparts. Replacing methyl and ethyl branch substituents with mercapto- or hydroxy-groups resulted in higher odor thresholds.

Effects of Ammonium to Nitrate Ratio and Salinity on Yield and Fruit Quality of Large and Small Tomato Fruit Hybrids

Abstract Tomato cultivars respond differently to nitrogen (N) sources and to saline conditions, in terms of both yield and fruit quality. Interactions between salinity and ratios with tomato genotypes were studied. The effect of four ammonium levels (0, 1, 2, 4 mM of total 8 mM N) and two salinity levels (0 and 45 mM NaCl) on cv. “R-144”, and the effect of two salinity levels (0 and 45 mM NaCl) on four tomato hybrids (“R-144”, “R-175”, “FA612”, and “FA624”) were studied in two greenhouse experiments. The effects of two levels, (0 and 2 mM out of total N at 8 mM), and two salinity levels (0 and 20 mM NaCl) on large-fruit (“R-144”) and small-fruit (“FA612”) tomato hybrids were also studied in a net-house. The NaCl at 45 mM resulted in a smaller leaf area index (LAI), lower plant dry matter and lower fruit yield than controls. Addition of 1 mM to the nutrient solution contributed to improved growth. Genotypes bearing large fruits were more prone to suffer yield losses under saline conditions than those with small fruits. In the second experiment, salinity treatment resulted in improved fruit TSS, EC and titratable acidity in all of the hybrids except of “FA612”. Fruit TSS was inversely correlated with yield. However, the ratio in TSS decline versus yield varied among the hybrids. At mild salinity (20 mM NaCl), fruit TSS and titratable acidity were significantly increased in “R-144” while yield was slightly decreased. Transpiration rate decreased with the presence of ammonium in the nutrient solution in both hybrids. The highest and lowest values were obtained for “FA612” and “R-144”, respectively. The detrimental effect of salinity is mainly attributed to the decrease in LAI and the subsequent reduction in water uptake, resulting in low fruit weight. Addition of 1 mM ammonium to 7 mM nitrate in the nutrient solution had an ameliorating effect on tomato fruit yield under salinity.

Flavor Chemistry and Odor Thresholds

Determination of odor thresholds of components in water solution was an early method adopted by many researchers for evaluating the relative contribution of food aroma/flavor components. Some more recent methods determine odor thresholds in air added to GC effluent from flavor volatile separation. Relatively simple methods are available for calculating thresholds in air from thresholds determined in water. Similar methods can be used for calculating oil and oil-water mixture thresholds from water threshold data. The ratio of a component’s concentration in the food to its water odor threshold value has been useful in determining relative aroma/flavor importance for mostly aqueous foods. Small variations in chemical nature and structure can lead to large changes in threshold values. Water threshold values are compared for various acetyl nitrogen heterocyclic compounds, alkylhydroxyfuranones and 4-alkoxyfuranone derivatives. Even the most careful studies can lead to errors in threshold measurements. Some examples are given where threshold determination errors were caused by minor amounts of very low threshold impurities.

Cooked carrot volatiles. AEDA and odor activity comparisons. Identification of linden ether as an important aroma component.

MS with GC-RI evidence was found for the presence of linden ether in cooked carrot (Daucus carota). Evaluation of the GC effluent from cooked carrot volatiles using aroma extract dilution analysis (AEDA) found linden ether with the highest flavor dilution (FD) factor. Others with 10-fold lower FD factors were β-ionone, eugenol, the previously unidentified β-damascenone, (E)-2-nonenal, octanal (+ myrcene), and heptanal. All other previously identified volatiles showed lower FD factors. Odor thresholds, concentrations, and odor activity values of previously identified compounds are reviewed. This indicated that at least 20 compounds occur in cooked carrots above their odor thresholds (in water). Compounds showing the highest odor activity values included β-damascenone, (E)-2-nonenal, (E,E)-2,4-decadienal, β-ionone, octanal, (E)-2-decenal, eugenol, and p-vinylguaiacol.

DIRECT VAPOR ANALYSES WITH GAS CHROMATOGRAPHY.

The need for an easy, quick, quantitative and objective measure of aroma quality is apparent to all involved with food research. Although the final judging must be with human senses, a permanent record of a simple instrumental analysis is desirable. The obvious approach is the application of gas-liquid chromatography (GLC), especially since the advent of the very sensitive ionization detectors. The problem is as difficult as the need is easy to define; for, although the human olfactory senses are not as acute as those possessed by some animals, the thresholds of detection for 5ome compounds are far beyond any present GLC instrument. Also, very few of the constituents responsible for certain aromas of food have been identified with much certainty. Therefore, detection and recording volatile constituents are only part of the problem. Identification and correlation to organoleptic characteristics constitute the other part, and an arduous part, indeed. In this paper, we wish to discuss some of the problems encountered in detecting and recording food volatiles, the parameters which must be considered in order to utilize the sensitivity possible with the ionization detectors, and some examples of direct vapor sampling analyses.

Odor Thresholds of Cyclic Esters

We have previously determined the odor thresholds of various cyclic and branched esters and found them to be surprisingly low [1]. In this chapter we examine the effect of substitution of different heteroatoms in the ring system on odor thresholds. In addition, we determine the odor thresholds of various polycyclic esters.