- Title
- Extraction and encapsulation of bioactive compounds of bitter melon
- Creator
- Tan, Sing Pei
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2016
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- In the realms of therapeutic ethnobotanical practices and Asian traditional remedies, bitter melon (Momordica charantia L.), a common tropical fruit, is claimed to have several therapeutic effects. These health benefits have been associated with its content of saponins (TSC), phenolics (TPC) and flavonoids (TFC) and its antioxidant capacity (TAA). Many different varieties of bitter melon are cultivated worldwide. However, it remains to be demonstrated whether varieties grown under controlled conditions, such as in a greenhouse, differ in yield and bioactive characteristics. In ethnobotanical practices and Asian traditional medicine, plant materials are usually extracted for their active ingredients. Although organic solvents are often used to extract bioactive compounds from plant materials, water is a more desirable extractant because it is non-toxic, environmentally friendly and inexpensive compared to organic solvents. However, if water is to be the solvent of choice, the optimal conditions for the aqueous extraction of flavonoids, phenolics and saponins from bitter melon need to be determined, as there is a lack of knowledge on the extraction of these bioactives from bitter melon with water. Once active components are extracted from their original source, it is often desirable to remove the solvent in order to prepare dry powders, which are easier to handle and often more stable than solvent extracts. This is especially true for aqueous extracts, which are susceptible to oxidative degradation. Spray-drying, with or without encapsulating agents, is often used to dry aqueous extracts because of its wide availability and low cost. However, little has been published on the optimal conditions for spray-drying bitter melon aqueous extracts. Therefore, the experimental aims of this research were to determine 1) the best variety of bitter melon for greenhouse production in terms of yield, bioactive content and antioxidant activity, 2) the optimal conditions for the extraction of the bioactive compounds and antioxidant activity from bitter melon using water, 3) the optimal infeed emulsion formulation and the optimal drying temperatures for the encapsulation by spray-drying of the optimised bitter melon aqueous extract in terms of yield, bioactive content and antioxidant activity and 4) whether a stable high-quality powdered form of the bitter melon aqueous extract can be produced. In the initial studies (Papers I and II), the production and quality characteristics of six different bitter melon varieties (Big Top Medium, Hanuman, Jade, White, Indra and Niddhi), grown under the same greenhouse conditions were investigated in order to determine the best variety of bitter melon for greenhouse production in terms of yield, bioactive content and antioxidant activity. The variety ‘Big Top Medium’ was the best of the six varieties grown under controlled greenhouse conditions; it was high yielding and had a high bioactive content (Paper I). However, the greenhouse grown bitter melon varieties generally had a lower bioactive content than the field-grown variety ‘Moonlight’, which was purchased from a local market (Paper II). As a result, the ‘Moonlight’ variety was chosen for the subsequent extraction and encapsulation studies (Papers III to VI). This finding suggests that the greenhouse conditions may have limited the production of bioactive compounds. Next, the conditions for the extraction of flavonoids (Paper II), phenolics (Paper III) and saponins (Paper IV) from bitter melon using water were optimised. The parameters studied for the aqueous extraction conditions were extraction temperature, time, ratio of water to bitter melon (mL/g) and number of times the same material was extracted. The conditions for the aqueous extraction of flavonoids from bitter melon were optimised to be a double extraction of the same material at 40°C for 15 min at a water-to-powder ratio of 100:1 mL/g (Paper II). However, after optimisation, the content of flavonoids in the aqueous extract was still much less than that obtained with the best organic solvent extract (acetone). Therefore, as for other plant materials, acetone is the best solvent for extracting flavonoids from bitter melon. For phenolic compounds, the optimal conditions for the aqueous extraction of bitter melon were a single extraction at 80°C for 5 min at a water-to-powder ratio of 40:1 mL/g and a powder particle size of 1mm (Paper III). These aqueous extraction conditions resulted in the same or higher TPC and TAA compared to the 80% ethanol extract. Furthermore, less solvent and less time was required with water than with 80% ethanol. For the aqueous extraction of saponins from bitter melon, the optimal conditions were chosen to be 40°C for 15 min at a water-to-powder ratio of 20:1 mL/g (Paper IV). The conditions for the drying of the bitter melon aqueous extract into a powder were then investigated. In Paper IV, the bitter melon aqueous extract, optimised for saponins, was dried by spray-drying without an encapsulating agent. The results showed that, compared to the extract before spray-drying, the retention of saponins in the powder after drying was only 18%. The spray-dried powder also had a significantly lower retention of saponins than a powder prepared from the aqueous extract by freeze-drying. Therefore, encapsulation of the bitter melon aqueous extract was tried in an attempt to increase the retention of the saponins and the other bioactives compounds after spray-drying. In the encapsulation studies, the formulation of the spray-drying infeed emulsion (Papers V) and the spray-drying temperatures (Paper VI) were optimised. The optimal formulation of the infeed emulsion for spray-drying was a ratio of 1.5:1 g/g of the aqueous extract to the encapsulating agent solution (35% (w/v) of 1:1 (w/w) MD and GA) (Paper V). The optimal inlet and outlet temperatures were 140°C and 80°C, respectively (Paper VI). The retention of the saponins was increased from <20% in the absence to >60% in the presence of encapsulating agents. Similarly the retention for the phenolic and flavonoid compounds and the antioxidant activity was ~70%, >60% and >65%, respectively. The quality of the encapsulated bitter melon powder prepared using the optimal formulation and the optimal inlet and outlet spray-drying temperatures was high due to its small spherical particle sizes, low moisture content, low water activity, high bulk density, high water solubility index and low water absorption index (Paper VI). The stability of the optimised encapsulated bitter melon aqueous extract powder, in terms of the morphology of the powder particles and loss of the bioactive compounds and TAA, was significantly affected by the relative humidity levels (8.2-84.3%) due to water absorption by the powder (Paper VI). The safest range for the relative humidity for preserving the powder at 25°C was determined to be from 22.5 to 33.8%, which gave an equilibrium moisture content from 4.41 to 4.75, which was below the Mo = 5.71% predicted by the BET method. However, the optimised encapsulated bitter melon aqueous extract powder was very stable under storage for 5 months with the greatest observed loss being <15% for the saponins. However, the powder was slightly more stable at -20 and 10°C (<6% loss) than at 30°C (<15% loss), over the 5 months. In conclusion, six bitter melon varieties were successfully grown under controlled greenhouse conditions and the ‘Big Top Medium’ variety was the best of the six varieties in terms of fruit yield and bioactive content. However, the field-grown variety ‘Moonlight’, which was purchased from a local market, had a higher bioactive content than the greenhouse-grown varieties. Water was found to be an effective solvent for the extraction of the bitter melon bioactive compounds, phenolics and saponins but not flavonoids, and the yield was improved by optimising the aqueous conditions for their extraction from the fruit, Finally, optimisation of the spray-drying encapsulation process with MD and GA as encapsulating agents, resulted in a very stable encapsulated powder of the bitter melon aqueous extract.
- Subject
- extraction; encapsulation; bitter melon; bioactive compounds; antioxidant activity; spray drying; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1312223
- Identifier
- uon:22361
- Rights
- Copyright 2016 Sing Pei Tan
- Language
- eng
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