– INTELLIGENT SELECTION AND MANUFACTURE OF NATURAL EXTRACTS

MANUFACTURE OF NATURAL EXTRACTS

Author

Satish Nayak, PhD

Kemin Industries,

2100 Maury Street, Des Moines, Iowa – 50317, USA.

ABSTRACT

Consumers and ingredient suppliers are both concerned about the quality of personal care products used on the hair, face, and body. In today’s Internet-connected world, consumers want to know the source of the ingredients that are being used in the manufacture of their cosmetic and personal care products. Ingredient suppliers understand that the products containing ingredients derived from plants have more consumer appeal, and are viewed by them as being safer than those obtained synthetically.

In response to this consumer trend, many personal care products are being launched that contain natural extracts. These provide a wide variety of benefits to the user, and have claims such as being anti-inflammatory, antioxidants, skin whiteners, skin firming, etc. For these natural extracts to be successful, it is important to understand the key active molecule, or a group of molecules, responsible for the observed effect in the specified application. It is furthermore important that the right plant source and extraction method is chosen for the extraction of these actives in order to ensure that natural extracts are produced at a reasonable cost.

This chapter provides several examples of selection of the right plant source, for a variety of actives and different manufacturing processes in order to be used to produce a safe, consistent, and efficacious natural extract.

TABLE OF CONTENTS

13.3.1 Introduction

13.3.2 Sources of Natural Ingredients

a. Plants

b. Microorganisms

c. Algae

13.3.3 Extraction Technologies

a. Solvent Extraction

b. Microwave Assisted Extraction (MAE)

c. Factors affecting efficiency of MAE

d. Ultrasonic Assisted Extraction (UAE)

e. Factors Affecting Efficiency of UAE

f. Supercritical Fluid Extraction (SCFE)

g. Factors affecting efficiency of SCFE

Conclusion

References

13.3.1 INTRODUCTION

The trend for using natural products is ever increasing, primarily due to the consumer perception that natural ingredients are safe. To accommodate this consumer perception, the same trend is mirrored in product labels that claim to have natural or nature-derived ingredients. Ingredient suppliers are now focusing more on supplying natural and plant or bio-based products. The functionality of these ingredients spans a wide range from antioxidants to antimicrobials to emulsifiers. The active molecules to which these functionalities have been attributed tend to be produced in small quantities in their parent sources. Also, the complexity that Mother Nature has incorporated in these molecules makes their synthetic production economically unfeasible. Hence choosing the right source and the extraction technique plays a vital role in the optimal functionality of these ingredients in a cosmetics formulation.

Traditionally, the active components from plants or other biological sources have been extracted by using water or hydrocarbon solvents. Along with the objection of having residual solvents in the extracts as well as recent advancements in analytical and physical chemistry, several sophisticated extraction techniques have been developed. These techniques have substantially improved the extraction yields, reduced the usage of organic solvents, and reduced the time and investment that is needed to introduce commercially viable natural extracts in the market. There are several factors that need to be taken into account before choosing the right extraction technique.

• Target Molecule – The chemical properties of the active compound or the class of compound to be extracted. Primarily polarity and molecular weight, if known.
• Source – The source of the active molecule; plant, algae, microbes. Also the ability of the source to accumulate the desired molecule and any potential of impurities or nondesired molecules that might interfere with the extraction.
• Regulatory/Certifications – The natural certification or the regulatory approval that is desired for the obtained extract. Many extraction techniques and solvents are on the not-allowed list of regulatory and certification agencies. The list is not universal but is region-specific to the intended geographical market for the extract.
• Efficacy – The chosen extraction technique should not affect the efficacy of the desired molecule by degrading it or making it inactive during the extraction process.

The primary aim of this chapter is to give readers a general overview of the principles and abilities of different extraction technologies for extracting actives from natural sources. Some of the techniques discussed are Microwave Assisted Extraction (MAE), Ultrasonic Assisted Extraction (UAE), and Supercritical Fluid Extraction (SCFE). In addition to the extraction techniques, consideration should be given to the natural sources for the active molecules, which can have a major impact on the commercial value of an extract. Most often the activity of an extract could be attributed to a combination of molecules rather than a single molecule. The amount of complexity and redundancy that Mother Nature imparts to a particular functionality, such as antioxidants or antimicrobials, is immense. Usually it is more than one molecule that is responsible for these functionalities, and care should be taken that the majority of the molecules from that group are extracted for the resulting extract to provide “complete” functionality.

13.3.2 SOURCES OF NATURAL INGREDIENTS

Natural actives can be obtained from variety of sources. Since there is no firm legal definition for natural ingredients, many animal-based ingredients could also be considered as natural. This chapter focuses only on non-animal-based sources.

a. Plants

Medicinal disciplines such as Ayurveda, Yunani, and Traditional Chinese Medicines have developed practices that rely heavily on plant-based ingredients for curing various ailments. It is a common belief among all the traditional medicinal practices that Mother Nature provides solutions to all the health problems. Most of these practices are based on empirical evidence and trial and error. It is only recently, due to advances in various scientific disciplines, we have started to understand the active compounds that are the cause for such benefits. For example, it was always known that eating green leafy vegetables such as broccoli, kale, and spinach was beneficial to the eyes. It was only recently, when these vegetables were analyzed, it was found that they were high in carotenoids such as lutein and zeaxanthin that contribute to eye health. [1] In Ayurveda, turmeric is used extensively as an anti-inflammatory and antiseptic. By analyzing the turmeric root extracts this efficacy has been attributed to a class of compound called curcuminoids. [2] [3]

Plants produce a variety of phytochemicals such as terpenes, polyphenols, lipids, organic acids, protein inhibitors, etc. These phytochemicals have variety of functionalities such as being antimicrobials, antioxidants, anti-inflammatory, and thermogenic. [4] These phytochemicals are secondary metabolites that are produced by plants for a variety of internal functions. Their production is highly dependent on the season, environmental conditions, and age of the plant. [5] [6] The choice of the right plant for extracting a certain active is crucial to the commercial viability of that extract. Several factors such as the application of the extract, market value, yield of the active on per acre basis, and extraction technology need to be taken into account.

b. Microorganisms

Microorganisms have been a source of a variety of ingredients used in foods and personal care. Both bacteria and fungi have been used to produce these ingredients. One of the most common ingredients used in cosmetics produced by fermentation is citric acid. Citric acid is also produced by extracting from citrus fruits, but this process is substantially more expensive than fermentation. In the fermentation process, Aspergillus niger cultures are fed on glucose or sucrose obtained from natural sources that then metabolize the sugars to produce citric acid. The obtained citric acid is then extracted from the media by using an acid and a base. [7] Similarly, Lactobacillus strains are used in production of lactic acid, [8] which is widely known to have several skin benefits. [9] Ingredients produced by microbes have a wide range of functionalities such as antimicrobial, flavors, emulsifiers, thickeners, or surfactants. Biosurfactants such as rhamnolipids and sphorolipids have been produced by fermentation of Pseudomonas aeruginosa and Candida bomicola, respectively. [10]

Choosing an appropriate microbial strain that can produce high yields of the desired molecule is crucial for production using fermentation. Subsequent downstream processing, to separate the actives from the broth, may involve cell separation and concentration of the extract followed by precipitation or drying of the broth on a carrier or extraction by using an organic solvent.

c. Algae

In the past decade, interest in algae as a source of novel natural compounds has been growing rapidly. Algae of many types floating on the oceans are common in various regions of the world. Some of the most common ingredients extracted from algae are alginates, carrageenan, and agar, which are used for thickening and emulsifying formulations. [11] Algae have also been found to have molecules with diverse biological activities such as being antioxidant, antimicrobial, and antiviral. [12] It is understood that many of these algae live in extreme conditions and must adapt to their environment. The result of such adaptation is production of secondary metabolites that can participate in the natural defense of these organisms, which can lead to formation of complex and diverse molecules. [11] Figure 1 illustrates some of the novel molecules that are found in algae. Mycosporine glycine belongs to a class of compounds called Mycosporine-like amino acids, which have antioxidant ability. [11] Eckol belongs to class of compounds called phlorotannins, which are also antioxidants and have photoprotective effect. [11] Fucoxanthin is a xanthophyll and has been found to promote fat burning in adipose tissues. [13]

Figure 1. Structures of unique molecules found in algae.

The process of extracting molecules of interest from algae involves the following steps; algal strain development and cultivation followed by harvesting the biomass through separation and downstream processing, which may involve dewatering, extraction, fractionation, and drying. [14]

It is important that the natural source used for extraction is consistent on a batch-to-batch basis. Drastic changes in the level of actives in the source can have unfavorable impact on the subsequent extraction method and hence can affect the quality and cost of the extract. Large genetic variation in the source can lead to accumulation of varying amounts of actives that may produce extracts with different efficacies. Hence it is important to have a good control on both the species of the source and the conditions in which they are allowed to hyper-accumulate the desired actives. Such control could be obtained, for example, by cultivating a single genetic strain of the source (plant, microbial, or algal). Several natural breeding and selection techniques can be used to obtain hyper-accumulating strains that can then be propagated and grown at industrial scale. Going into details of such technologies is beyond the scope of this chapter, and readers are encouraged to read the following references. [15] [16]

13.3.3 EXTRACTION TECHNOLOGIES

Choosing the right extraction technology is as important as choosing the right natural source for a bioactive. The extraction method can have a profound effect on the endproduct that is used in the cosmetic and personal care formulations. If a sub-optimal extraction technology is used, it can result into products that are difficult to formulate. This may be due to color, odor, or impurities that are co-extracted in the process. The following section will discuss the basics of several conventional and modern extraction technologies.

a. Conventional Solvent Extraction

Solvent extraction is the most traditional and most commonly used extraction technique for separating actives from a biomass. [17] In this method, biomass is exposed to different solvents individually or to a mix of solvents depending on the desired polarity. This technology is based on the fundamental principle of “Like dissolves like,” where the polarity of the extracting solvent is closely matched to that of the target molecule or a class of molecules. Most often temperature, pressure, and pH can be tuned to optimize the yields of the extract. Once the target species is extracted into the solvent phase, the spent biomass is then separated by separating technologies like centrifugation or filtration. The obtained enriched solvent can then be used directly as is, as long as the solvent employed has no toxicity associated with it. If there is toxicity associated with the used solvent then it is removed by distillation or precipitation of the target molecule.

Traditional solvent extractions have been carried out using organic solvents such as hexane, ether, dichloromethane, chloroform, and ethanol. [18] They have been used for extracting actives with different polarities; nonpolar, mid-polar, and polar. Most of these solvents have toxicity associated with them, hence they need to be removed to an acceptable level before the extract is used in the endproduct. [19] The choice of solvent will also depend on the regulatory restrictions imposed on the application of the extract. Solvent extraction may be advantageous due to the low processing cost, but the use of toxic solvents that requires their removal, most often by heat, can result in degradation of the active molecule.

Solvent-extraction techniques have been improved immensely in recent years, and have been made more efficient by use of less solvent, recycling of solvents, and concomitant use of heat and pressure during the extraction phase. All of these improvements contribute to higher yield of extraction, which in turn decreases the cost of the extract. [20] However, none of these improvements change the consumer perception about solvent-processed ingredients. The more well-informed consumers of today, relying on the Internet and social media, are more aware of the source and processing of the ingredients used in their product, and they demand that eco-friendly processes be used in the production of ingredients. This trend has led to an increase in the use of more efficient and improved modern extraction technologies for natural ingredients.

b. Microwave Assisted Extraction (MAE)

Microwaves have been applied in many fields such as: communication, navigation, astronomy, spectroscopy, and heating. [21] For extraction purposes, it is the heating aspect of microwaves that is used. In the electromagnetic spectrum, microwaves are between infrared and x-ray regions. Their frequencies are between 300 MHz to 300 GHz. [22] However, for most general applications frequencies, between 915 MHz to 2.45 GHz are used. [23]

Microwaves induce two kinds of molecular motions: ionic conduction and dipole rotation. Ionic conduction is the electrophoretic movement of a molecule under an applied electromagnetic field. If the solution offers resistance to this flow of ions, the solution is heated due to the friction generated between the molecular movement and the surrounding solvent. Dipole rotation is the realignment of the dipoles in the applied field. At 2450 MHz the dipoles align and randomize at 4.9 × 109 times per second, which causes friction between the molecules and generates heat in the system. [24] [25] [23] When a sample is irradiated with microwaves, the rate of absorption of energy is dependent on its dissipation factor (tan d):

tanδ = ε΄

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