Can biological structures be natural and sustainable capsules?

Abstract

Flavor and fragrance molecules are used in many industrial fields such as food, cosmetics, tissues, pharmacy, agriculture (pheromones) etc. As most actives have a specific target and are fragile molecules, encapsulation processes have been developed for their use. These technologies are efficient to avoid loss of actives, dissemination out of the target and subsequent pollution, and to protect molecules up to their target. Several processes have been developed responding to the numerous situations encountered (e.g., protection against air, temperature, light, pH; masking or revealing sensorial properties of the molecule; release during the process, in the plate, in the mouth, etc.). However, the general trend for natural products and for processes friendly for the environment has put forward several constraints. According to the various regulations (CFR 1990, CE 1334/2008 etc.), to be natural, a product has to come from plant or animal raw materials with only a physical, enzymatic or microbial process at the exclusion of any chemical step. This definition results from a consensus between jurists, philosophers, industry, consumers, politics etc. It must be noted that this concept of naturality is neither universal nor consensual. In philosophy, although defined by Aristotle in his Book II as one thing that has “within itself a principle of motion and of stationariness,” natural things are not always easy to recognize from their opposite, artifactual things. With the completed and extended definition of artifactual things to what has been done in a project or purpose [discussed by J. Monod in the introduction of “Chance and necessity” (1971)], agriculture and biotechnology products would become mainly artifactual. This concept of naturality is thus quite controversial and regulation may evolve in the future. However, despite the fact that many definitions are hidden behind the word of naturality, this concept has attracted consumers, first in Germanic countries in the 1980s, spreading over Europe, then to North America, and from there to the whole World. The demand for natural product first appeared in food, reached cosmetics recently and is now expanding to other fields. However, to keep the label, natural flavors and fragrances require natural capsules, i.e., capsules coming from natural materials that have not been modified through chemical steps. As a result, the issue of naturality is closely related to the sustainability of the process, i.e., its impact on the environment (release of solvents, carbon impact etc.), which is also getting more and more important. In the field of encapsulation, among the numerous technologies developed at the lab scale, just few are ready for industrial implementation and it is often difficult to obtain an up-scalable process without any use of toxic solvents or not-natural materials. These technologies are based on various principles often trying to polymerise and coat a suspension of active. One could notice however that the presence of compartments has been a prerequisite to evolution and natural capsules have thus been developed from the apparition of the first cell. Among biological structures, cells are indeed a good protection for actives that have to interact together and with the environment. When the protection needs to be stronger and fewer relations are required between actives and the environment, specific structures are produced like microbial spores. Eventually, specialized structures are able to disseminate actives in the environment like pollen grains. With such nice model systems, humanity has developed biomimetics to synthesize efficient artificial capsules (Cai et al., 2015) but tries also to use already existing natural capsules (Pham-Hoang et al., 2013). Although several works have been carried out on this subject and some products have been developed from years, these natural capsules are difficult to utilize, precisely because of their envelope properties (Table ​(Table1).1). Indeed, the envelope, that makes the active protected inside the cell, is difficult to cross in a controlled way, making loading and controlled release difficult. Industrial encapsulation in these natural structures might also be difficult to carry out in a fully natural and sustainable process. In this opinion article, we propose to discuss the utilization of biological structure as microcapsules for natural and sustainable odorant products. Table 1 Performances of various biological structures as natural capsules.