Encapsulation Review

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Trends in Food Science & Technology 21 (2010) 510e523


Encapsulation of polyphenols e a reviewZhongxiang Fanga,b,* and Bhesh BhandariaSchool of Land, Crop and Food Sciences, The University of Queensland, Brisbane, Qld 4072, Australia b School of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310029, China (School of Land, Crop and Food Sciences, The University of Queensland, Brisbane, Qld 4072, Australia. Tel.: D61 7 33469187; e-mail: z.fang2@uq.edu.au)Research on and the application of polyphenols, have recently attracted great interest in the functional foods, nutraceutical and pharmaceutical industries, due to their potential health benets to humans. However, the effectiveness of polyphenols depends on preserving the stability, bioactivity and bioavailability of the active ingredients. The unpleasant taste of most phenolic compounds also limits their application. The utilization of encapsulated polyphenols, instead of free compounds, can effectively alleviate these deciencies. The technologies of encapsulation of polyphenols, including spray drying, coacervation, liposome entrapment, inclusion complexation, cocrystallization, nanoencapsulation, freeze drying, yeast encapsulation and emulsion, are discussed in this review. Current research, developments and trends are also discussed.a

Introduction Microencapsulation, developed approximately 60 years ago, is dened as a technology of packaging solids, liquids, or gaseous materials in miniature, sealed capsules that can release their contents at controlled rates under specic conditions (Desai & Park, 2005; Vilstrup, 2001). The packaged materials can be pure materials or a mixture, which are also called coated material, core material, actives, ll, internal* Corresponding author.0924-2244/$ - see front matter 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.tifs.2010.08.003

phase or payload. On the other hand, the packaging materials are called coating material, wall material, capsule, membrane, carrier or shell, which can be made of sugars, gums, proteins, natural and modied polysaccharides, lipids and synthetic polymers (Gibbs, Kermasha, Alli, & Mulligan, 1999; Mozafari, 2006) Microcapsules are small vesicles or particulates that may range from sub-micron to several millimeters in size (Dziezak, 1998). Many morphologies can be produced for encapsulation, but two major morphologies are more commonly seen (Fig. 1): one is mononuclear capsules, which have a single core enveloped by a shell, while the other is aggregates, which have many cores embedded in a matrix (Schrooyen, van der Meer, & De Kruif, 2001). Their specic shapes in different systems are inuenced by the process technologies, and by the core and wall materials from which the capsules are made. Various techniques are used for encapsulation. In general, three steps are involved in the encapsulation of bioactive agents: (i) the formation of the wall around the material to be encapsulated; (ii) ensuring that undesired leakage does not occur; (iii) ensuring that undesired materials are kept out (Gibbs et al., 1999; Mozafari et al., 2008). The current encapsulation techniques include spray drying, spray cooling/chilling, extrusion, uidized bed coating, coacervation, liposome entrapment, inclusion complexation, centrifugal suspension separation, lyophilization, cocrystallization and emulsion, etc. (Augustin & Hemar, 2009; Desai & Park, 2005; Gibbs et al., 1999). The main objective of encapsulation is to protect the core material from adverse environmental conditions, such as undesirable effects of light, moisture, and oxygen, thereby contributing to an increase in the shelf life of the product, and promoting a controlled liberation of the encapsulate (Shahidi & Han, 1993). In the food industry, the microencapsulation process can be applied for a variety of reasons, which have been summarized by Desai and Park (2005) as follows: (i) protection of the core material from degradation by reducing its reactivity to its outside environment; (ii) reduction of the evaporation or transfer rate of the core material to the outside environment; (iii) modication of the physical characteristics of the original material to allow easier handling; (iv) tailoring the release of the core material slowly over time, or at a particular time; (v) to mask an unwanted avor or taste of the core material; (vi) dilution of the core material when only small amounts are

Z. Fang, B. Bhandari / Trends in Food Science & Technology 21 (2010) 510e523


Wall material Core material

Wall material Core material

Fig. 1. Two major forms of encapsulation: mononuclear capsule (left) and aggregate (right).

required, while achieving uniform dispersion in the host material; (vii) to help separate the components of the mixture that would otherwise react with one another. Food ingredients of acidulants, avoring agents, sweeteners, colorants, lipids, vitamins and minerals, enzymes and microorganisms, are encapsulated using different technologies (Desai & Park, 2005). Recently, research and application of polyphenols have been areas of great interest in the functional foods, nutraceutical and pharmaceutical industries (Manach, Scalbert, Morand, Remesy, & Jimenez, 2004; Scalbert, Manach, Morand, Remesy, & Jimenez, 2005). Polyphenols constitute one of the most numerous and ubiquitous groups of plant metabolites, and are an integral part of both human and animal diets which possess a high spectrum of biological activities, including antioxidant, anti-inammatory, antibacterial, and antiviral functions (Bennick, 2002; Haslam, 1996; Quideau & Feldman, 1996). A large body of preclinical research and epidemiological data suggests that plant polyphenols can slow the progression of certain cancers, reduce the risks of cardiovascular disease, neurodegenerative diseases, diabetes, or osteoporosis, suggesting that plant polyphenols might act as potential chemopreventive and anti-cancer agents in humans (Arts & Hollman, 2005; Scalbert, Johnson, & Saltmarsh, 2005; Scalbert, Manach et al., 2005; Surh, 2003). Unfortunately, the concentrations of polyphenols that appear effective in vitro are often of an order of magnitude higher than the levels measured in vivo. The effectiveness of nutraceutical products in preventing diseases depends on preserving the bioavailability of the active ingredients (Bell, 2001). This is a big challenge, as only a small proportion of the molecules remain available following oral administration, due to insufcient gastric residence time, low permeability and/or solubility within the gut, as well as their instability under conditions encountered in food processing and storage (temperature, oxygen, light), or in the gastrointestinal tract (pH, enzymes, presence of other nutrients), all of which limit the activity and potential health benets of the nutraceutical components, including polyphenols (Bell, 2001). The delivery of these compounds therefore requires product formulators and manufacturers to provide protective mechanisms that can maintain the active molecular form until the time of consumption, and deliver this form to the physiological target within the organism (Chen, Remondetto, & Subirade, 2006). Some physicochemical characteristics and food properties of the

major polyphenols from different plant sources are present in Table 1, which shows their limited stability and conditioned solubility. Another unfortunate trait of polypheonls is their potential unpleasant taste, such as astringency (Table 1), which needs to be masked before incorporation into food products (Haslam & Lilley, 1988). The utilization of encapsulated polyphenols instead of free compounds can overcome the drawbacks of their instability, alleviate unpleasant tastes or avors, as well as improve the bioavailability and half-life of the compound in vivo and in vitro. There have been a number of recent reviews or mini-reviews on the encapsulation of foods or food ingredients (Augustin & Hemar, 2009; Desai & Park, 2005; de Vos, Faas, Spasojevic, & Sikkema, 2010; Flanagan & Singh, 2006; Gouin, 2004; Jafari, Assadpoor, He, & Bhandari, 2008; Khaled & Jagdish, 2007; McClements, Decker, Park, & Weiss, 2009; Mozafari, 2005; Mozafari, 2006; Mozafari et al., 2008; Peter & Given, 2009). This review focuses on the encapsulation of the more widely used polyphenols, discussing their effectiveness, variations, developments and trends. Spray drying Spray drying encapsulation has been used in the food industry since the late 1950s. Because spray drying is an economical, exible, continuous operation, and produces particles of good quality, it is the most widely used microencapsulation technique in the food industry and is typically used for the preparation of dry, stable food additives and avors (Desai & Park, 2005). For encapsulation purposes, modied starch, maltodextrin, gum or other substances are hydrated to be used as the wall materials. The core material for encapsulation is homogenized with the wall materials. The mixture is then fed into a spray dryer and atomized with a nozzle or spinning wheel. Water is evaporated by the hot air contacting the atomized material. The capsules are then collected after they fall to the bottom of the drier (Gibbs et al., 1999). The typical shape of spray dried particles is spherical, with a mean size range of 10e100 mm (Fig. 2). One limitation of the spray-drying technology is the limited number of shell materials available, since the shell material must be soluble in water at an acceptable level (Desai & Park, 2005). Maltodextrins are widely used for encapsulation of avours (Bhandari, 2007), which are also used for polyphenol encapsulation. The ethanol extracts of black carrots, which contain a high level of anthocyani