Terry E. Acree

Molecular Theory of Sweet Taste

THE molecular feature common to the many different sweet tasting compounds has been sought for many years1. For the sugars, it was proposed2–5 that the sweet unit is the glycol group, and that intensity of sweetness varied inversely with the degree to which glycol OH groups appear to be intramolecularly hydrogen bonded. It is now apparent that vicinal OH groups in the glycol unit need to be approximately gauche, or in a staggered conformation. Vicinal OH groups which are in the anti conformation apparently are too far apart to cause sweet taste. Glycol OH groups which are eclipsed probably participate in an intramolecular hydrogen bond which competitively inhibits interaction of glycol with the receptor site. These steric features of sweet and non-sweet sugar glycol units are shown in perspective in Fig. 1. Glycol conformational parameters, and the gross conformation of pyranose and furanose rings, have been used to explain the varying sweetness of the sugars2–5.

A Procedure for the Sensory Analysis of Gas Chromatographic Effluents

Abstract A method is presented for determining those volatile components of foods that have flavour significance. The method leads to quantitative flavour specifications called charm that can be displayed graphically. The procedure is based upon the relative odour detection thresholds of volatile compounds of known gas chromatographic retention indices.

Charm analysis of apple volatiles

Abstract The ‘Charm’ analytical procedure was applied to several apple cultivars and replication gave almost identical charm responses. However, no two cultivars showed close resemblance by the technique. Charm response can be used, together with physical parameters, to describe apple flavour.

Gas Chromatography Olfactometry (GC/O) of Dairy Products

Abstract Analysis of the aroma of dairy products is a complex problem due to the heterogeneous nature of milk. Several analytical methods have been used to study the aroma of dairy products; gas chromatography–mass spectrometry (GC/MS) and gas chromatography– olfactometry (GC/O) are most commonly used. In order to identify the individual odor-active compounds a bioassay that is representative of the pattern of odorants in terms of their smell activity is advantageous. Identification of these compounds is carried out using extraction, distillation, concentration and chromatography. This paper reviews the GC/O work on dairy products to date. Common odor-active compounds were found in various types of dairy products analyzed. Seven common odorants were found in four different types of raw milk: dimethylsulfone, ethyl butanoate, ethyl hexanoate, heptanal, indole, nonanal, and 1-octen-3-ol. The effect of heating cows milk changed the aroma profile of the milk, resulting in the formation of four common odor-potent compounds: hexanal, 2-nonanone, benzothiazole, and δ -decalactone. Five fermented dairy products have been analyzed by GC/O. Fermentation resulted in the formation of common odorants: 1-octen-3-one, methional, 3-methylbutanal, and butyric acid. The flavor chemistry of dairy products has been successfully analyzed using GC/O. However, further work must be conducted to produce a sample that reflects the retronasal composition of the product. This requires the use of a retronasal aroma simulation (RAS) device and/or gas chromatography olfactometry headspace (GCO-H).

Effect of wine type on the detection threshold for diacetyl

Abstract Diacetyl, an important wine flavorant synthesized during alcoholic and malolactic fermentation, has been reported to have a sensory threshold of 2–3 mg/l. A comparative study of threshold for diacetyl in wines was undertaken to determine the effect of wine type on that value. Sensory threshold was determined according to the forced-choice ascending concentration series of limits method described by ASTM (E 679-79), using trained panelists. Panel detection thresholds and standard deviation from the geometric mean were found to be 0.2 mg/l and 0.32 in Chardonnay, 0.9 mg/l and 0.21 in Pinot noir, and 2.8 mg/l and 0.38 in Cabernet Sauvignon. These results demonstrate the important effect of wine type on diacetyl threshold, invalidating the use of a single threshold value for all wines.

Chemical Structure of Compounds and Their Sweet and Bitter Taste

In presenting the material in this chapter, four fundamental propositions are made. These are: (1) Sucrose (sugar) tastes sweet. (2) Quinine tastes bitter. (3) Sodium chloride tastes salty 1. (4) Hydrochloric acid tastes sour.

POTENTIAL USE OF CHEMICAL CUES FOR COLONY-MATE RECOGNITION IN THE BIG BROWN BAT,Eptesicus fuscus

Bats should benefit from recognition of their roost-mates when colonies form stable social units that persist over time. We used Y-maze experiments and gas chromatography–olfactometry (GC-O) to evaluate whether female big brown bats Eptesicus fuscus (Chiroptera: Vespertilionidae) use chemical cues to distinguish among conspecifics. In dual-choice Y-maze experiments, females chose the scent of another female from their own roost over a conspecific female from a different roost in a majority of trials. Analysis of total body odors using GC-O suggests that individuals from a given colony may share a more common odor signature with roost-mates than with non-roost-mate conspecifics. Using four principle components derived from 15 odor variables, discriminant function analysis correctly assigned most individuals to the correct colony.

Comparison of odor-active compounds in grapes and wines from vitis vinifera and non-foxy American grape species.

Native American grape (Vitis) species have many desirable properties for winegrape breeding, but hybrids of these non-vinifera wild grapes with Vitis vinifera often have undesirable aromas. Other than the foxy-smelling compounds in Vitis labrusca and Vitis rotundifolia , the aromas inherent to American Vitis species are not well characterized. In this paper, the key odorants in wine produced from the American grape species Vitis riparia and Vitis cinerea were characterized in comparison to wine produced from European winegrapes (V. vinifera). Volatile compounds were extracted by solid-phase microextraction (SPME) and identified by gas chromatography-olfactometry/mass spectrometry (GC-O/MS). On the basis of flavor dilution values, most grape-derived compounds with fruity and floral aromas were at similar potency, but non-vinifera wines had higher concentrations of odorants with vegetative and earthy aromas: eugenol, cis-3-hexenol, 1,8-cineole, 3-isobutyl-2-methoxypyrazine (IBMP), and 3-isopropyl-2-methoxypyrazine (IPMP). Elevated concentrations of these compounds in non-vinifera wines were confirmed by quantitative GC-MS. Concentrations of IBMP and IPMP were well above sensory threshold in both non-vinifera wines. In a follow-up study, IBMP and IPMP were surveyed in 31 accessions of V. riparia, V. rupestris, and V. cinerea. Some accessions had concentrations of >350 pg/g IBMP or >30 pg/g IPMP, well above concentrations reported in previous studies of harvest-ripe vinifera grapes. Methyl anthranilate and 2-aminoacetophenone, key odorants responsible for the foxiness of V. labrusca grapes, were undetectable in both the V. riparia and V. cinerea wines (<10 μg/L).

Thermodynamics and kinetics of D-galactose tautomers during mutarotation

Abstract The tautomerism of D -galactose in water has been studied by using g.l.c. to separate per- O -trimethylsilyl derivatives of D -galactose tautomers formed during the mutarotation reaction. The initial, rapid stage of the biphasic mutarotation of α- D -galactopyranose is due to the formation of α- D -galactofuranose and β- D -galactofuranose. The slow phase is due to the formation of β- D -galactopyranose. The kinetic data of D -galactose tautomerism have been tabulated. The free-energy difference between pyranose tautomers (anomers) is primarily entropic. The free-energy difference between pyranose and furanose tautomers is distributed between relatively large and opposing enthalpic and entropic energies. It is concluded that the “transition state” for these tautomerization reactions is quite unlike the structure of any of the tautomers, and that, for the activation of a compound for tautomerization reactions, the same entropy and enthalpy exists for the formation both of furanoses and pyranoses.

Sensory impact of free fatty acids on the aroma of a model Cheddar cheese

Abstract The fatty acid profile from the retronasal aroma of Cheddar cheese was determined using the retronasal aroma simulator (RAS). Seven odor potent fatty acids identified in Cheddar cheese were placed in model systems and sampled in the RAS. Volatile acids were trapped by solid phase microextraction and identified by GC/MS. The six released fatty acids were added to a model cheese system and subjected to a descriptive analysis sensory test, using omission testing (N-1). Six cheese models, each omitting one fatty acid, were tested in triplicate against a complete model by a trained panel, under a randomized complete block design. Panelists rated the intensity of six descriptors. In one additional test session, the complete model was tested against a model omitting all fatty acids. Results indicated that the omission of propionic acid from the cheese model led to a significant increase (α=0.10) in the ratings for the ‘cream’ descriptor ( P =0.08). The omission of all fatty acids resulted in a significant decrease in the ratings for the ‘sweaty’ descriptor ( P =0.07). Surprisingly, the ratings for the ‘Cheddar’ descriptor did not change under any circumstances. This suggests that although some compounds contribute heavily to the aroma of a food based on their odor potency, the removal of such compounds does not necessarily alter the sensory perception of the overall food concept.