Natural Product Extraction
Principles and Applications
By Mauricio A. Rostagno, Juliana M. Prado
The Royal Society of Chemistry Copyright © 2013 The Royal Society of Chemistry
All rights reserved.
Uses and Applications of Extracts from Natural Sources
R. N. CAVALCANTI, T. FORSTER-CARNEIRO, M. T. M. S. GOMES, M. A. ROSTAGNO, J. M. PRADO AND M. A. A. MEIRELES
LASEFI/DEA/FEA, (School of Food Engineering)/UNICAMP (University of Campinas), R. Monteiro Lobato, 80, Campinas, 13083-862, SP, Brazil
Current scientific evidence about physiological, nutritional, and medicinal benefits to human health provided by the use of natural products, as well as the potential harmful effects from the use of synthetic products and consequent legislative actions restricting their use, has motivated a significant increase in the consumption of natural products. In this context, extracts from natural sources play an important role as natural additives or industrial inputs to food, cosmetic, textile, perfumery, and pharmaceutical industries (Figure 1.1), influencing many characteristics of the final product. Indeed, the majority of natural extracts have more than one or two functions. They have been used as natural colorants, nutraceuticals, functional foods, preserving agents, flavors and fragrances, edible oils and fats, drugs, vitamin supplements, chemical standards, and perfumes, among others. The major natural extracts are obtained from plant sources such as seeds, leaves, flowers, berries, barks, and roots, although some of them may be obtained from animal sources such as carmine dye from female insect cochineal (Dactylopius coccus), honey from bees, squalene from shark liver, etc.
The applications of natural extracts are generally associated with the functionality derived from their active components. Usually, functional foods are obtained by enrichment with functional compounds, which are ingredients able to promote or provide a beneficial effect on human health. These compounds may also be concentrated, serving as nutritional supplements, known as nutraceuticals, which are commercialized as tablets and capsules. They may also be used for technological roles, as coloring agents, conservation agents, etc., and for the production of chemicals.
Many of the bioactive properties assigned to functional foods and nutraceuticals are provided by compounds derived from the secondary metabolism of plants, also called phytochemicals. 'Phytochemicals' literally means chemicals produced by plants; they play an important role in plant metabolism. Phytochemicals are not established as essential nutrients, but may have a great biological significance. In most cases they are ingested by humans as part of the diet, including in fruit, vegetables, beans, and grains, in beverages such as juices, green or black tea, coffee, etc. There are several phytochemical classes, including polyphenols (flavonoids, phenolic acids, tannins, stilbenes, coumarins, and lignans), carotenoids, phytosterols, alkaloids, terpenes, and sulfur-containing compounds (sulfides and glucosinolates). Although there is already sufficient scientific evidence pointing to the association between effects beneficial to human health and phytochemical intake, the mechanisms of action are not yet fully elucidated. Furthermore, it is believed that many of these beneficial effects are the result of additive and/or synergistic phenomena of these compounds, being attributed to the complex mixture of phytochemicals rather than to a single compound. Products with phytochemical compounds have many other applications in food and other industries, including pharmaceutical, cosmetics, perfumes, and textile industries. For example, many products of personal care include a wide variety of natural products in their formulation including soaps, shampoos, sunscreen, hair dye, make-up, toothpaste, deodorants, etc.
1.2 Uses and Applications
There are many uses of extracts from natural sources which can be grouped according to their technological role: coloring agents, functional food, nutraceuticals, preserving agents, flavors, fragrances, and edible oils.
Coloring agents or color additives are any pigment, dye, or substance that produces color when it is added to a product. The coloring agents may be found in liquid, solid, semi-solid, or gel forms. Due to the large availability of food coloring agents there are several other non-food applications that explore their properties, including cosmetics, pharmaceuticals, and medical devices. Natural colorants are extracted by various processes and classified according to their color, chemical composition/structure, biological function in plant/body (chlorophyll, hemoglobin, etc.), and physical properties (solubility). The main dyes from plant sources are red (Brazil wood, sugar, etc.), orange (saffron flower, Crocus sativus), yellow (chamomile, Anthemis tinctoria), green (ragweed, Ambrosia artemisiifolia), and blue (indigo, Indigofera tinctoria). The main food dyes from animal sources are sepia (cuttlefish bag), red (kermes lice), and purple (murex shellfish).
Besides the technological function of several well-known natural coloring agents, the phytochemicals may have other biological functions and play a role on the prevention of diseases. Functional foods, nutraceuticals, food supplements, and antioxidants belong to an economically important sector of the global food market. Examples of potential applications include reducing the risk of cardiovascular disease, cancer, diabetes, inflammation, and osteoporosis. Among the various functional effects, it is important to highlight the effects on gastrointestinal functions and hormonal modulation.
Furthermore, preserving agent activity, antibacterial activity, and antifungal activity also represent an economically important sector of the global natural products market. Certain types of food preservatives are needed to ensure the quality of the final product. Most chemical preservatives widely used are weak organic acids (e.g. ascorbic acid and benzoic acid) used in synergistic combinations. In this case, the antimicrobial and antifungal properties of essential oils are considered to be the most important.
1.2.1 Coloring Agents
Highly conjugated systems which absorb electromagnetic radiation between wavelengths of 400 nm to 800 nm appear to be colored. Color can provide a pleasant aspect to the substrate as well as express emotions and ideas. Color is often the first notable sensorial characteristic that influences the expectations of consumers and also influences quality-related decisions during visual inspections. Color plays an important role in quality perception indicating our expectations, perceptions, susceptibilities to, and preferences for products, as it is used to indicate good quality, to assist marketing, and to satisfy consumers. The color of food, pharmaceutical, and cosmetic products can be the result of natural pigments present in the matrix used; coloration formed upon heating, processing, or storage; or the addition of natural or synthetic colorants. Colorants or color additives are the terms for all soluble or solubilized coloring agents (dyes or pigments), as well as insoluble pigments, employed to impart color to a material. The mechanism of color production is due to a molecule-specific structure (chromophore) of chemical compounds that absorbs light in the wavelength range of the visible region known as pigments. Those chromophores capture energy and the excitation of an electron from an external orbital to a higher orbital is produced; the non-absorbed energy is reflected and/or refracted to be captured by the eye, and neural impulses are generated, which are transmitted to the brain where they can be interpreted as a color.
Coloring agents can be defined by their origin as natural, synthetic, or inorganic colorants. Natural pigments are produced by living organisms. Synthetic colorants or dyes are synthetized by chemical reactions. Inorganic pigments can be found in nature or can be reproduced by synthesis. Synthetic organic dyes have been recognized for many years as the most reliable and economical coloring agents because they are superior to natural pigments in tinctorial power, consistence of strength, range, and brilliance of shade, hue, stability, ease of application, and cost effectiveness, being the most applied source of color additives used in the food, pharmaceutical, and cosmetic industries. However, during the last few decades, the use of synthetic dyes is gradually receding due to an increased environmental awareness and to potential harmful effects of either toxic degraded products or their non-biodegradable nature. Furthermore, the safety of synthetic dyes has been a matter of concern since high levels of toxicity, allergic reactions, and carcinogenic potential have been identified following their consumption as coloring agents. In this context, there is an increased interest in further use of colorants from natural sources instead of synthetic dyes, as a consequence of perceived consumer preferences as well as legislative actions.
Natural pigments (see Figure 1.2) are defined as dyes or colorants obtained from natural sources, such as plants, animals, and microorganisms. Nevertheless, the majority of commercial natural colorants currently used are extracted from plant sources such as roots, fruits, barks, leaves, wood, fungi, and lichens. Flavonoids, carotenoids, and chlorophyll are the major contributors to the natural colors of most plants, with betalines and curcumin playing a minor yet significant role. However, there are some natural pigments derived from invertebrates, such as the cochineal pigments extracted from female coccid insects; the most well-known is the carminic acid obtained from the female Dactylopius coccus Costa. All natural pigments are unstable and participate in different reactions, so the produced color is strongly dependent on storage and processing conditions. Natural colorants are much more unstable than synthetic dyes with respect to physical (temperature, light), chemical (oxidizing or reducing agents, acids, alkalis), and biological (enzymes, microorganisms) factors.
This section discusses the major natural colorants commercially used and their application in food, pharmaceutical, and cosmetic industries. The main natural pigments are categorized according to their chemical structure as: isoprenoid derivatives (carotenoids); tetrapyrrole derivatives (chlorophylls and hemes); and benzopyran derivatives (anthocyanins, betalains, and curcuminoids).
Carotenoids are the largest, most important, and most widespread group of pigments found in nature. They are responsible for many of the brilliant red, orange, and yellow colors of fruits, vegetables, fungi, and flowers, and also of birds, insects, crustaceans, and trout. They are usually fat soluble and associated with lipid fractions. However, they can be synthesized only by plants and microorganisms. The chemical structure of carotenoids consist in a symmetrical polyisoprenoid structure formed by head-to-tail condensation of two C20 units, which is modified by cyclization, addition, elimination, rear-rangement, and substitution, as well as oxidation. Due to the presence of the conjugated double bonds, carotenoids can exist in cis and trans forms, but cis isomers are less stable than the trans form due to stoichiometric conformation; therefore the majority of natural carotenoids are in the all-trans configuration. Based on their structure, carotenoids (Figure 1.3) are divided in two classes: (i) carotenes, which are pure polyene hydrocarbons; they contain only carbon and hydrogen atoms, including acyclic lycopene and bicyclic β- and α-carotene; (ii) xanthophylls, containing oxygen in the form of hydroxy (lutein), epoxy (violaxanthin), and oxo (canthaxanthin) groups.
Carotenoids perform important functions in plants as attractants for pollinators, as accessory light-harvesting pigments at wavelengths where chlorophyll does not absorb, and as photoprotective agents preventing photooxidative stress. The most common natural carotenoid extracts used as color additives for foodstuffs are obtained from annatto, paprika, and saffron. Many other sources, including alfalfa, carrot, tomato, citrus peel, and palm oil, are also used. Evidence of trends in looking for natural sources of carotenoids can be noticed from the patents that have been recently deposited worldwide on the subject.
Annatto. Annatto (E160b) is an yellow-red natural carotenoid coloring agent obtained from the seed coat of the tropical shrub Bixa orellana L. The annatto tree is native to Central and South America, but it is also grown in Africa and Asia, being especially popular in Brazil, Peru, Bolivia, Ecuador, Jamaica, the Dominican Republic, East and West Africa, India, and the Philippines. The major coloring component in annatto extract is bixin (>80%). This pigment is primarily present as the cis-bixin isomer, but other pigments derived from bixin as trans-bixin, cis-norbixin, and trans-norbixin are also present, although they may have different colors. Bixin is a dicarboxyl monomethyl ester carotenoid with a C25 skeleton called apocarotenoid, whose biosynthesis has been suggested to take place by the oxidation of a normal C40 carotenoid such as lycopene. Annatto pigments can be separated from annatto seeds basically by two ways: (i) the method most used industrially consists of mechanical abrasion using a suitable suspending agent (e.g. vegetable oil, aqueous potassium hydroxide, or aqueous sodium hydroxide), followed by removal of the seeds (sieving); (ii) the second method consists of extraction with one or more organic solvents, which is also used as a means to produce annatto concentrates.
The most conventional extracts of annatto available are the bixin-rich oil extract and the water-soluble powder norbixin-rich extract. While the bixin-rich oil extract is an orange-red pigment, the norbixin-rich extract (a water-soluble powder) is a yellow-orange pigment. Annatto is used as a coloring agent in a wide range of foodstuffs such as butter, margarine, cheese, fats, cereals, baked goods, snacks, beverages, meat, and fish products. Annatto oil extract is one of the most common colorants used for high-fat food products. Even though conventional methods are widely used extraction techniques, they present many drawbacks such as high energy costs, low selectivity, environmental concerns, toxicity, and the generation/retrieval of large quantities of solvent waste. In this context, many researchers have been studying supercritical and ultrasound-assisted technologies as alternative extraction techniques to obtain annatto pigments.
Paprika. Paprika oleoresin (E160c) is the orange-red, oil-soluble extract generally obtained from dehydrated and milled fruit of certain varieties of red peppers (Capsicum annuum L.). Paprika oleoresin recovery uses hexane as extraction solvent, followed by miscella and meal disolventization, and finally oleoresin degumming. The paprika oleoresin is used in formulating nutraceuticals, colorants, and pharmaceuticals. It can become water soluble by microencapsulation in gelatin or Arabic gum. Because of its high coloring capacity, and in some cases its peculiar pungency, paprika is one of the most widely used food colorants for culinary and industrial purposes; it is applied to modify the color and flavor of soups, sausage, cheese, snacks, salad dressing, sauces, pizza, and confectionary products. Paprika oleoresin is recognized for its self-limiting use for technological and sensorial reasons; as with any other spice or flavor, too high levels can adversely impact the product's flavor profile balance. (Continues...)
Excerpted from Natural Product Extraction by Mauricio A. Rostagno, Juliana M. Prado. Copyright © 2013 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.