Historical PerspectiveCarotenoid-loaded nanocarriers: A comprehensive review
Graphical abstract
Schematic illustration of niosomes loaded with carotenoids.
Introduction
Carotenoids are lipophilic natural pigments synthesized by plants and microorganisms, which are widely distributed in the nature [1]. They are mainly categorized into two leading classes (carotenes and xanthophylls; [2]). Carotenoids have been successfully gained more popularity because of their diverse functions particularly in food and pharmaceutical industries; including their role as pro-vitamin A ingredients, effective antioxidants [3], anti-tumour [[4], [5], [6]], anti-cardiac [6], anti-ageing [7] and anti-inflammatory [8] properties. The foremost constraints which limit their applications are their degradation due to environmental stresses like high heat, exposure to oxygen, less solubility in water, and unfavourable pH in digestive environment [9,10]. To overcome these limitations, and in order to serve them to humans as a functional food and to increase their applications in food and pharmaceutical industries, encapsulation is a successful and most realistic strategy which not only enhances their solubility but also provides resistance against stresses during processing and digestion [11].
Encapsulation is an auspicious approach which is used for entrapment of bioactive compounds such as carotenoids inside a carrier through micro/nano-encapsulation techniques [12]. There is an increasing interest in nanoencapsulation of bioactive compounds because of its distinct benefits i.e. high efficiency of encapsulation and loading capacity, increased solubility, bioavailability, improved stability and hiding unwanted flavours [13]. Nanocarriers (<100 nm), provide a larger surface area to water molecules which enhances dissolution rate [14,15]. For successful incorporation of carotenoids, fabrication of nanocarriers is a crucial parameter. Nanocarriers such as nanoemulsions, nano-liposomes, nano-hydrogels, nano-structured lipid carriers (NLCs) and solid lipid nano-particles (SLNs) are some examples for protection and conveyance of carotenoids [16]. Recently, many studies have revealed that lipid based nanocarriers are successful candidates for carotenoids encapsulation [[17], [18], [19], [20], [21], [22]].
Encapsulating materials used for fabrication of nanocarriers must fall under GRAS (generally recognised as safe) categories [23]. Biopolymers (GRAS) are recognised as environment friendly and also they do basic nutritional and structural functions in the humans; so they are highly desirable in food product manufacturing [24]. Mostly, food grade biopolymers are being used as a wall material or coating agent in food industries or pharmaceutical industries such as, carbohydrates, lipids, proteins, and other biodegradable polymers. Polysaccharides are very common natural biomaterials which are used vastly since they are abundantly present in nature and cheap in price, are non-toxic and non-reactogeic, and have a high biodegradability and biocompatibility [[25], [26], [27]]. Their physiochemical properties provide easy assembly of particles and hydrogels for delivery purposes and enable easy handling for chemical modification when needed [25,28]. Moreover, some specific polysaccharides have the ability to be recognised and bind with their specific targets and can have targeting release [29], site specific enzymatic degradation [30], environmental triggering [31,32] and mucosal adhesion and transport [33].
Recently, many investigations have reported that biopolymeric and lipid-based nanocarriers have the potential for incorporation of different carotenoids [17,18,20,22,[34], [35], [36]]. These nanocarriers have shown many benefits including improved solubility of bioactives, easy fabrication via nature-inspired constituents and targetability within the food products as well as in the human body [[37], [38], [39]]. Moreover, the release profile of these carriers can be easily observed through in vivo evaluations either by passive (targeting based on the particle dimeter) or active (owing to surface receptors) measures [40,41]. In addition to offering an effective encapsulation and preservation, these systems also enhance the bioavailability and biostability of carotenoids in foodstuff/medication preparations [42,43].
In this review article we have discussed subsequent features: (i) a fleeting summary of carotenoids regarding their classification, sources, characterization and health promotional features, (ii) a brief discussion on the importance of encapsulation, (iii) an overview of biopolymeric nanocarriers (polysaccharides and proteins) for carotenoids, (iv) a review of available investigations on nanoencapsulation of carotenoids inside lipid based nanocarriers, and (v) absorption of carotenoids in the intestine and their bioavailability loaded in different nanocarriers. To the best of our knowledge, there is no comprehensive review article focusing on all kinds of nanocarriers for encapsulation of carotenoids.
Section snippets
Background, classification, and health aspects of carotenoids
The word carotenoid expresses a miscellaneous family of natural pigments such as red, yellow and orange that can absorb the light between 400 and 500 nm; they are produced by photosynthetic organisms and microorganisms e.g. some groups of bacteria [1,44]. Inspite of their diversity in nature, only <30 carotenoids play a vital role in photosynthesis [45]. Usually in photosynthetic plants, carotenoids are present inside the chloroplasts not in free form but as fusing or binding and play a
Different nanocarriers for encapsulation of carotenoids
In recent era, nanoencapsulation has attained an increasing interest of the researchers due to efficient controlled release of encapsulated ingredients, greater stability and effective delivery [60,61]. Production of nanocarriers is more difficult than microencapsulation techniques [15,62]. Basically, there are two leading tactics (top-down and bottom-up), which are being applied in fabrication of nanoparticles for decades. Bottom up techniques include self-organisation and self-assembly of
Release of carotenoids from nanocarriers during in vitro and in vivo GIT studies
An active nanocarrier should be capable of protecting the carotenoids during handling or storing from stressors without any chemical interaction with carotenoids [13]. It should also have the potential of accurate and defined targeting with confronting acidic or enzymatic environments of the stomach. However, biopolymeric and lipid-based nanocarriers are highly recommended to enhance the bioavailability by improving surface to volume ratio and therefore, raise muco-adhesive prospect in the
Conclusion and future remarks
It is obviously proved that carotenoids have many health beneficial and nutritional effects and can reduce the risks of many disorders. But, they are very sensitive to the processing and storage conditions and can lose their nutritional value before going into human body. Nanoencapsulation is an approach which can be used to reserve carotenoids with their original value and to improve their functionalities including bioaccessibility, digestibility and controlled release. An efficacious
Declaration of Competing Interest
The authors declare that they have no conflicts of interest.
Acknowledgement
The authors are grateful to the International Education School at Jiangnan University and Chinese Scholarship Council (CSC) for financial support throughout the study. The author Abdur Rehman would like to thanks Jiangnan University and Chinese Government Scholarship for giving opportunity, support and stay in China for carrying study.
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