Crude drugs contain an array of bioactive compounds which have been considered as valuable and effective pharmacological agents. They are broadly classified as organized (cellular) and unorganized (acellular) drugs. Natural latex, an unorganized crude drug, is a milky fluid produced by flowering plants which contains complex mixture of bioactive compounds responsible for various biological activities. Latex produced by plants is more vulnerable to environmental degradation therefore adequate protection measures should be adopted to prevent the degradation of its bioactive compounds and to preserve its biochemical based functional properties. Various environmental factors including biotic (e.g., microbial degradation) and abiotic (e.g., radiations, heat, and oxygen) often affect physico-chemical and biological properties of latex. Due to these factors such as solubility and bioavailability in different biological fluids are also affected which can ultimately affects biological potential of latex (Tresserra-rimbau et al. 2018; Ray et al. 2016; Ballesteros et al. 2017; Yamashita et al. 2017; Kuck & Noreña 2016). Microbial degradation is one of the major causes of degradation which can affects biological activity of phytochemicals mainly phenolic compounds in latex during the storage (Srivastava et al. 2007).
Drying of the latex from the plants is considered as the most reliable method as it can remove water content to avoid microbial degradation of phytochemicals present in the extract. Additionally, drying process increases the shelf life of latex by slowing or preventing microbial growth and preventing certain biochemical reactions that might alter its organoleptic characteristics (Rahimmalek & Goli 2013). Numerous drying procedures have been recently introduced to ensure microbiological stability, reduce product degradation due to chemical reactions, facilitate storage, and lower transportation costs. Selection of the suitable drying process is critical as it affects retention of bioactive compounds and other organoleptic characters of natural product. Freeze drying or lyophilization is the most recent procedures for the drying of natural products however their application in drying of latex hasn’t been explored yet.
Freeze drying or lyophilization is an effective procedure which has been recently utilized during post collection mainly to enhance the shelf life of natural products. Freeze drying involves sublimation process, in which structural changes are minimized and bioactive compounds present in dried sample are retained (Ceballos et al. 2012). This process involves three major steps: product freezing, primary drying (removing the ice by direct sublimation under reduced pressure), and secondary drying (release of unfrozen water by desorption and diffusion) (Geidobler & Winter 2013). In addition to its merits this process also has major disadvantage as it may cause damage to the intrinsic bioactive compounds which always results in products with different characteristics. Thus, this process requires careful optimization to improve the retention bioactive compounds and prevent its successive damage (Akdaş & Başlar 2015; Salazar et al. 2018). Freezing is the initial step of freeze-drying (during which the ice is formed) which includes three main stages (nucleation, growth of ice crystals, recrystallization) (D'Andrea et al. 2014). Rate of freezing always determines final properties (productivity and quality) of the dried product, as it affects the pore size, or inherent structure, primary drying rate, and rate of nucleation (Grajales et al. 2005; Franceschinis et al. 2015). Freezing variables such as variation in pressure, nucleation temperature, surface freezing, annealing, vacuum-induced freezing, and addition of nucleating agent can be controlled to get more process benefits mainly to accelerate the subsequent ice sublimation process (Kramer et al. 2002; Oddone et al. 2014; Oddone et al. 2016; Liu et al. 2005; Rezende et al. 2018).
Bio-integrity of investigated samples with outstanding characteristics can be preserved by freeze–drying mediated encapsulation which is always performed at low temperatures. Based on nature of products, particularly in case of plant-based products such as extracts, exudates, latex, natural polysaccharides working conditions of freeze-drying varies or optimized. Moreover, mere lyophilization is not effective to extend the shelf life of extract. An effective procedure microencapsulation of dried latex by a polymer or blend of polymers is required to prevent its degradation (Carpentier et al. 2007). Freeze drying is the most suitable technique for dehydration of all heat-sensitive materials and for microencapsulation (Desai & Park 2007). Microencapsulation procedure involves the encapsulation of sample by using bio-compatible, non-toxic, and edible material to form stable capsules with several useful properties. This procedure is used to enhance the stability of encapsulated material by protecting them from adverse environmental conditions. Homogeneous or heterogeneous material can be used to develop an efficient process however selection of the encapsulation agent is usually depending on the final application of the encapsulated material (Mahdavee et al., 2014). Various encapsulating agents and their blends have reported with key characteristics such as their ability to form films, biodegradability, and resistance to gastrointestinal tract, viscosity, solids content, hygroscopicity, and cost. However, some of the basic characteristics are essential such as it should colorless and provides good protection against oxidation. Current study is designed for the long-term preservation of latex at different conditions to encapsulate latex as a core material and to further retain and protect more sensitive bioactive compounds present in it (Zhu et al. 2019; Gomes et al., 2018). Herbal treatment for headache disorders is considered as an ancient treatment which is now increasing worldwide (Levin 2012). Vast majority of episodic headaches is migraine which is now considered as most common disabling brain disorder characterized by a pulsating headache affected an estimated population of 12% worldwide (Yeh et al. 2018; Mirshekari et al. 2020; Song et al. 2021; Tirumanyam et al. 2019; Kinawy 2019). One of the most promising tools to treat migraine patients are herbal products (D'Andrea et al. 2014). Calotropis genus plants (C. procera and C. gigantea) have been traditionally used to cure migraine (Ahmed et al. 2005). Leaves are externally applied to treat headache in Malaysia (Lin 2005). Leaves of C. procera are effective in treating migraines (Prasad 1985). C. gigantea (Ait.) R.Br. (Apocynaceae) commonly known, as 'Akra' is a traditional medicinal plant which is used in many ayurvedic formulations like Arkelavana. This plant is identified as ‘milkweed’ as it’s abundantly available and contains latex in its leaf and stem. It has been observed that parts of this plant are traditionally used to treat headache disorders (Pathak & Argal 2007). This milky fluid is a complex mixture of various bioactive compounds such as cardiac glycosides which show diverse biological activities (Deshmukh et al. 2009; Rajesh et al. 2005).
Nevertheless, the chemical profile and stability of latex remains under mystery. One of best ways to identify the cause behind degradation is to investigate degradation products those are degraded due to the oxidative cleavage of the double bond in the polymer backbone. Certain intrinsic and extrinsic factors such as treatment with solvents, pH and temperature variation, oxygen, light, and enzymes can affect the overall therapeutic potential of latex. Post collection immediate treatment or processing is required to overcome these problems. In this respect freeze drying gained importance as it maintain the inherent structure (i.e., pore morphology etc.) of the sample with minimal shrinkage, retain bioactive compounds and their physico-chemical properties and improve rehydration behavior of the sample. Due to their different operating procedures, they always result in products with different characteristics (Çam et al. 2014). Thus, by selecting a suitable procedure and appropriate conditions, the final product quality can be handled (Hamrouni-Sallami et al. 2011).
An objective of the present work is to improve the shelf life of freeze-dried alkali treated C. gigantea latex and evaluate its anti-migraine potential. For the first-time freeze-drying process with certain modifications was used for latex to limit oxidative changes of chemical metabolites. Stability studies of FDCG were performed till 10 weeks and it was compared with non-lyophilized samples, sun rays dried sample from C. gigantea milk (AECD). Several physico-chemical parameters such as product rehydration capacity, water activity, hygroscopicity, solubility, the total color difference (ΔEab), total polyphenols content (TPC), core phenolic content (CPC), moisture content and microencapsulation efficiency were determined to evaluate the quality of dried samples. Further anti-migraine potential of FDCG and AECG was evaluated by apomorphine induced climbing behavior, l-5-HTP induced syndrome and MK 801 induced hyperactivity assays.