Plant Research International has been involved in flavor research for the past ten years. Flavor of plants (fruits, vegetables, herbs) is composed of a blend of volatile and non-volatile compounds. We have a strong track record in metabolic profiling of these compounds in plant parts, as well as in isolating enzymes and genes involved in their biosynthesis. Metabolic profiles are useful tools for optimizing cultivation practices and selecting breeding lines, while flavor genes are applicable in the microbial production of natural plant flavor compounds.

Among our recent achievements in the flavor field are:

1. Extensive profiling of flavor compounds in fruits from tomato, strawberry, cacao, melon, citrus, and apple, and several herbs and vegetables. 
2. Identification of enzymes and genes involved in the biosynthesis of fruit esters, such as hexenyl acetate, isoamyl acetate and octanol-butyrate, from a diverse set of fruit species, including strawberry, banana and tomato.
3. Identification of enzymes and genes involved in the biosynthesis of terpenoids, such as linalool, limonene, nerolidol, myrtenol and pinene, from strawberry, cucumber and citrus.
4. Understanding of the evolution of fruit flavor and genes involved during domestication of strawberry. 

Several of these findings are now being utilized for the microbial production of flavor compounds.

Vision / strategy   
Flavor is a key factor in food appreciation: parents will only be able to feed children with nutritious and vitamin-rich food if it tastes right. Particularly fruit flavor is one of the most important components in food, determining the perception of e.g. ice-creams, beverages, pastry etc., but also of non-food products such as cosmetics (e.g. perfumes, shampoos, toothpastes). Our flavor research is currently aimed at two customer profiles: those interested in breeding for flavor traits, and those interested in producing sustainable aroma compounds.

Flavor for quality
Flavor in plants is a complex bouquet of volatile compounds, to which a multitude of biochemical pathways in the plant contribute. The blend of flavor compounds is very sensitive to breeding, cultivation and storage. Nowadays, consumer traits such as flavor and health are of increasing importance. Metabolic profiling is an indispensable tool to select high-quality lines and best practices.

Flavor for food quality
The demand for flavor compounds as food additives can no longer be met by the supply of plant material.  This is why many food products instead contain ‘aromas’ composed of mixed flavor compounds. Compounds used in these aromas are often synthesized by organic chemistry. However, the food industry is increasingly interested to use ingredients produced by sustainable procedures. In practice, microbial production can be a sustainable alternative for chemical synthesis. Such a microbial production system is based on a GRAS micro-organism (Generally Regarded As Safe). The micro-organism can produce plant flavor molecules by using plant genes that deliver the necessary enzymes.

Flavor Research
Presently our research is aimed at:

• identifying and applying genes involved in the flavor of strawberry and other berry species, with focus on esters, ketones, terpenoids and nor-isoprenoids;
• profiling the flavor compounds (volatiles, acids, sugars) of tomato lines, and correlating these profiles with results from sensory evaluations and genomics data. 

Generally we aim at:

• unravellling biochemical pathways in plants towards flavor compounds, and make these applicable for microbial production of flavor compounds;
• applying comprehensive profiling of flavor compounds for evaluation of breeding lines and cultivation practices. >> Example of flavor research

References (additional references are available upon request)
 
Aharoni et al., (2000) Identification of the SAAT gene involved in strawberry flavor biogenesis by use of DNA microarrays. Plant Cell 12(5): 647-661

Aharoni et al., (2004) Gain and loss of fruit flavor compounds produced by wild and cultivated strawberry species. Plant Cell 16(11)

Beekwilder et al., (2004) Functional characterization of enzymes forming volatile esters from strawberry and banana. Plant Physiol. 135(4): 1865-1878

de-Kraker et al., (2003) Hydroxylation of sesquiterpenes by enzymes from chicory (Cichorium intybus L.) roots. Tetrahedron 59(3): 409-418

El-Tamer et al., (2003) The influence of monoterpene synthase transformation on the odour of tobacco. J. Biotechnology 106(1): 15-21

Lucker et al., (2002) Monoterpene biosynthesis in lemon (Citrus limon) - cDNA isolation and functional analysis of four monoterpene synthases. Eur. J. Biochem. 269(13): 3160-3171

Lucker et al., (2004) Metabolic engineering of monoterpene biosynthesis: two-step production of (+)-trans-isopiperitenol by tobacco. Plant J. 39(1): 135-145