Handbook of Vanilla Science and Technology

PPO and peroxidase-catalyzed oxidation of aromatic compounds is obviously important in pod browning. However, oxidative processes may also entail an oxidative degradation of other cellular compounds, lipid peroxidation for example (Figure 6.9). Arana (1944) emphasized the role of oxidative reactions, particularly quinone polymerization, in the formation of flavor notes during the prolonged conditioning phase. We suggest that the oxidation of lipids, which gives rise to volatile compounds including ketones, aldehydes, alcohols, or hydrocarbons (Niki 2008,2009), might also give rise to flavor constituents found in cured vanilla beans (Adedeji et al. 1993), a view supported by recent studies (Dunphy and Bala 2009). This view underscores the need for further studies to understand the role and contribution of oxidant-induced reactions in the formation of aroma and flavor constituents during the curing process of a vanilla pod.

6.7 VANILLA PRODUCTS

Cured vanilla beans are used for the extraction and the preparation of vanilla products. The four basic types of vanilla products are vanilla extract, by far the most used vanilla product, as well as vanilla oleoresin, vanilla absolute, and vanilla powder/sugar. Each form has its typical organoleptic, physical, and functional attributes tailored by the choice of beans used for the process and the processing conditions. In addition, the products in each category must meet the government regulations of the country where the products are manufactured or sold. Vanilla products are used in the food, dairy, confectionary, beverage, pharmaceutical, and fragrance industries.

6.8 SUMMARY AND CONCLUSIONS

The curing of green vanilla beans is intended to create the prized vanilla flavor and, in addition, lend shelf-life to cured beans. The process is predicated on the disruption of cellular organization and the consequent unleashing of the activity of hydrolytic and oxidative enzymes and, apparently, non-enzymatic processes that drive the formation of aroma and flavor constituents in cured vanilla bean. However, the curing process used in commerce, employing harsh temperature conditions to stimulate aroma and flavor formation, is a balancing act. Appropriate curing protocols, entailing controlled killing and a short sweating period around 50°C, may be favorable to enzyme-catalyzed production of vanillin or other flavor constituents, but severe temperature conditions may arrest development of a full flavor complement, due to enzyme denaturation. Additional interference might stem from proteolytic activity or enzyme denaturation by de-compartmentalized phenolic compounds or other metabolites, which might lead to decay in activity of beneficial enzymes. Prolonged drying and conditioning may be yet another source of loss in formed flavor compounds.

The curing process is founded on the view that destruction of biological order in green vanilla beans unleashes enzymatic reactions by bringing the enzymes in contact with their respective substrates, which drives the formation of vanilla aroma and flavor. However, it is not entirely clear where these enzymes are localized in the cells or in the pod and, moreover, the conditions that allow their interaction with appropriate substrates. It is also desirable to understand whether sufficient activity of flavor-forming enzymes is spared from proteolytic degradation. Other issues regard the role of oxidative reactions in flavor formation. A growing body of studies might cast light on these problems and, moreover, reshape a working concept on the role and mechanism of the curing process in the formation of vanilla aroma and flavor.

6.9 ADDENDUM: COMMERCIAL CURING METHODS OF GREEN VANILLA BEAN

6.9.1 Traditional methods

6.9.1.1 Mexican curing method