Optimization and comparison of water soluble proteins, carbohydrates and saponins in tongkat ali species / Husam Eldin Elhag Abugabr Elhag

College of Engineering

Thesis (Doctor of Philosophy) -- Universiti Malaysia Pahang – 2021

Includes bibliographical references

Tongkat Ali is a group of plants that are consumed as tonics due to their various health benefits. The wide consuming of these plants led to numerous studies that focused on investigating the major compounds in these plants without enough consideration of other nutritious metabolites in the extracts. Therefore, this study attempted to focus on the optimization of these metabolites that are water soluble proteins (WSPs), carbohydrates (WSCs) and saponins (WSSs) in water extracts from the roots, stems and leaves of four Tongkat Ali species, namely Tongkat Ali Jack (Eurycoma longifolia) and Tongkat Ali bukit (Eurycoma apiculata), Tongkat Ali Merah (Jackiopsis ornata) and Tongkat Ali Hitam (Polyalthia bullata). The study employed three extraction methods, the first was the conventional heat assisted extraction (HAE) and the other two were the non-conventional microwave assisted extraction (MAE) and ultrasonic assisted extraction (UAE). The elongated extraction durations and energy consumption of conventional extraction methods encouraged the application of non conventional extraction methods such as MAE and UAE. Optimization and prediction of the optimized extraction conditions for maximizing the yields% of the three investigated metabolites were generated by employing circumscribed central composite designs (CCCDs) in Minitab 17. The employment of MAE and UAE resulted in increasing the yields% of the targeted metabolites within shorter extraction times. The predicted optimized conditions were employed to maximize each metabolite. The highest yield% of WSPs (26.026±1.099%) was obtained by MAE from the E. longifolia roots. The highest yield% of WSCs (42.661±0.912%) was obtained by UAE from E. longifolia roots. The highest yield% of WSSs (31.491±1.136) was obtained by MAE from the E. longifolia roots. MAE and UAE favoured less solvent volumes to obtain higher yields% (20:1 – 30:1), finer particle sizes (around 0.029 mm) due to the increase in the surface area. Temperature illustrated various effects based on the type of metabolite and plant part besides the employed extraction methods, WSPs were maximized generally between 40 - 60oC, while WSCs and WSSs were generally between 60 - 70oC. Maximum yields% were obtained with optimal conditions of agitation speeds, microwave powers, amplitudes and duty cycles as well as extraction durations, the yields of WSPs, WSCs and WSSs increased with the increase of these factors until the optima values. Based on the indicated optimized parameters of HAE, MAE and UAE in extracting WSPs, WSCs and WSSs from E. longifolia roots, a sequential extraction method was proposed and investigated by the application of the three extraction methods in a serial combination (one after another) to maximize the targeted metabolites in the extracts. The best criterion was the sequential ultrasound-microwave-heat assisted extraction (SUMHAE) with WSPs yield% (23.613±1.653%), WSCs (33.027±1.363%) and WSSs (28.712±1.135%) with UAE as the initial phase for 10 minutes followed by the MAE phase for 10 minutes. The kinetic investigation demonstrated that the most suitable models for representing the data were the second order extraction rate and the Pelegs model according to their high R2 values. The two site kinetic model illustrated less suitability, but with the consideration of the degraded factor kD, the R2 values increased which indicated a vital mathematical role of kD in the two site kinetic model. As a conclusion, the best extraction methods were the MAE and UAE were more efficient that HAE, besides SUMHAE illustrated high efficiency than the conventional HAE, MAE and UAE.