Click here to see Figure 1The technical requirements of the flavors and fragrances industry are dictated by long-term, consumer-driven global trends (see sidebar). Important global trends driving the food industry include the growing interest in "label-friendly" ingredients, health consciousness, and convenience. The key trends driving research in the fragrance industry are international regulatory requirements, environmental concerns, and customer demands for improved performance.
These trends are different for flavors and for fragrances, so we discuss them separately. We also provide examples of how commercial forces are shaping the technical directions of flavor and fragrance research.
Natural methods of processing include physical treatments (e.g., thermolysis and distillation) and biological processes based on enzymology and microbiology. Molecular biology is being investigated to find methods for producing proteins that have desirable flavor properties and enzymes that are useful for the preparation of natural ingredients.
Several methods for the production of natural flavor ingredients are illustrated in Figure 1. Starting from cassia oil, cinnamaldehyde can be isolated by fractional distillation and used directly as a flavor ingredient. Cinnamaldehyde may also be subjected to microbial oxidation to produce cinnamic acid, which in turn can be converted to ethyl cinnamate by heating it with food-grade ethanol. Cinnamaldehyde, on heating with water under slightly alkaline conditions, may be converted to natural benzaldehyde (2).
Click here to see Figure 1One example of the microbiological production of a natural flavor ingredient is shown in Figure 2. Sclareol, isolated from clary sage by solvent extraction, can be efficiently oxidized by the microorganism Cryptococcus albidus to sclareolide (3), which can be used as a flavor enhancer, and then the aroma chemical.
Click here to see Figure 2Microbiological routes to natural flavor ingredients can have the added benefit of producing optically active substances; this can be important, because optical purity often has a marked effect on flavor quality and intensity (4). In addition to de novo bioformation of individual enantiomers, enzymatic transformations are used successfully for the optical resolution of racemates. This is particularly applicable to esters, alcohols, and carboxylic acids (5).
Reduced-fat foods. Reducing the fat content in foods and replacing fat with other substances can drastically alter the flavor of the food, because fat may act as a solvent and protective medium for flavor ingredients. Most flavor ingredients are fat soluble, but they have a wide range of polarities. Thus, fat reduction changes the vapor pressures of flavor components to different degrees so that flavors become unbalanced. In fat-reduced systems, flavor ingredients may partition differently between the hydrophobic and hydrophilic phases present in foods. In addition, ingredients may react with other food components because they are no longer protected in a lipid phase. Examples of such reactions include the oxidation of aldehydes and Schiff base formation.
Graf and deRoos studied the effect of fat reduction in ice cream on the
flavor components of vanilla extract (6). They found that
initial flavor perception depends primarily on the phase partitioning
of the individual components between water and oil. They developed
reformulation factors that can be applied to each ingredient to provide
an initial taste perception equivalent to that of the full-fat product.
The flavor reformulation factors (FRFs) for vanilla flavor components
in ice cream are given here, along with oil-water partition
coefficients (given as log Pow).
Ingredient |
FRF |
logPow |
| Vanillin | 0.75 | 0.40 |
| Phenol | 0.50 | 0.89 |
| p-Cresol | 0.30 | 1.28 |
| 4-Ethylguiacol | 0.13 | 1.74 |
| Eugenol | 0.08 | 1.94 |
| Ethyl benzoate | 0.03 | 2.64 |
| Methyl cinnamate | 0.02 | 2.79 |
| Anethole | 0.01 | 3.33 |
Natural replacements. Food additives used in flavor emulsions that are under increasing consumer and regulatory scrutiny or are in irregular supply include certain weighting agents and gums. Classes of materials having value or potential value as alternative natural ingredients include starches and other carbohydrates, vegetable oils, and proteins. To achieve acceptable flavor emulsion stability in beverages and food products that contain these ingredients, factors such as the density differential between phases, flavor oil particle size distribution, electrostatic interactions and film formation at oil-water interfaces must be evaluated (7).
Alcohol-free products. Flavor microemulsions may be used to deliver flavor oils to alcohol-free and low-alcohol products. When proper conditions are achieved, microemulsions form spontaneously. Relatively high flavor loads can be achieved with these systems; the products are thermodynamically stable; and the emulsion is transparent because of the very small droplet size (8).
Masking bad tastes. Encapsulation of bitter or otherwise unpleasant-tasting solids is useful for improving the taste of nutrient-fortified foods and nutriceuticals. Encapsulation can mask the off-tastes of minerals, vitamins, and some pharmaceuticals. Once in the gastrointestinal tract, the coatings are removed by enzymatic action, making the "payload" bioavailable.
Convenience foods. The type and extent of flavor fixation and release requirements are dictated by the nature of the convenience food. For microwave foods, it is necessary to develop methods of flavor release at temperatures suitable for various products. This is important both for palatability of the food and for providing an appetizing odor.
Powdered beverages and soup mixes require the release of flavor on contact with water. Each powdered product has specific time and temperature flavor release requirements, depending on its end use. With some products, such as tea bags, the particle size of the encapsulated flavor may be critical. In all cases, excellent flavor stability must be achieved to ensure long shelf-life. The development of better encapsulation methods has already resulted in improved storage stability (Figure 3).
Click here to see Figure 3
The obvious consequence of these regulations is that the number of new aroma chemicals introduced by the fragrance industry has been greatly reduced. It is estimated that about 3000 materials are currently available to creative perfumers. The new requirements make it quite unlikely that there will be another 3000. New aroma chemicals have to be well chosen and must meet well-defined needs in terms of odor and functional performance.
Waste reduction is also a continuing challenge. Toxic reagents and reactants, as well as the waste that they generate, are being more effectively handled or eliminated altogether. The oxidation of sclareol to sclareolide has been carried out using permanganate or dichromate, both of which give lower yields and generate aqueous waste disposal problems (10, 11). The biotransformation of sclareol to sclareolide or to the diol (Figure 2) is an example of an environmentally friendly process that eliminates the need to use troublesome oxidizing agents (12).
The use of a potentially hazardous chemical intermediate is sometimes difficult to avoid without drastically changing the traditional cost of a material. For example, acrolein is used to manufacture International Flavors & Fragrances' aroma chemical Lyral, which is used in many fragrances (13).
By carrying out the Diels-Alder reaction of myrcenol and acrolein at a manufacturing site where the latter material is produced, transport and use of acrolein in aroma chemical plants can be avoided.
In the United States, processes must satisfy federal and state environmental regulations for use and for the reporting of particularly hazardous materials, and plants must comply with state "Right to Know" laws. Related regulations are in place in other parts of the world. These all affect manufacturing practice.
Category |
Products |
| Personal grooming | Perfumes, colognes |
| Personal care | Soaps, shampoos, cosmetics |
| Laundry care | Powder and liquid detergents, fabric softeners |
| Household care | Bleaches, hard-surface cleaners, toilet cleaners |
As performance requirements for fragrance have increased over many years, a progression has taken place in terms of fragrance creation. Evaluation of fragrances and ingredients on skin was undoubtedly the first example of performance testing. Perfumers moved on to testing materials in products to be perfumed and using those with superior performance in their creations. Performance testing became a part of evaluating new aroma chemicals.
About 20 years ago, performance goals were incorporated into research programs aimed at finding new aroma chemicals. Since then, the range of difficult-to-fragrance products has expanded greatly. These continue to challenge synthetic chemists. More recently, emphasis has been placed on developing controlled-release systems that will improve the performance of a wide range of fragrances, regardless of product content. Such systems may be used to protect fragrances from the product media, reduce fragrance loss, prolong topnotes and, in some cases, increase the stability of the product. A range of new scientific specialties is required to address this formidable area.
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