Thermal degradation kinetics and controlled release study of labisia pumila polyphenols extracted via ultrasonic asissted extraction / Jessinta Sandanasamy

Faculty of Chemical and Natural Resources Engineering

Thesis (Doctor of Philosophy) -- Universiti Malaysia Pahang – 2018

Includes bibliographical references

Labisia pumila (ver. name Kacip fatimah), a traditional herb that exhibits numerous health applications; such as in the treatment of postmenopausal cardiovascular, osteoporosis and obesity owing to its polyphenolic content. Firstly, the polyphenols should be extracted before it can be routinely used. Unfortunately, the extraction process involves elevated temperature, which causes polyphenols degradation. Therefore, extraction of L. pumila var alata (LPva) polyphenols via non-thermal intensive method, ultrasonic-assisted extraction (UAE) were selected as aim of this work. Preparation of the dry powder extract involves drying at high temperature, which causes polyphenols degradation. Thus, ample understanding of the thermal properties of polyphenols is essential for the accurate design of thermal processes. In order to minimize the polyphenols degradation, thermal degradation kinetics and microencapsulation is also targeted in this work. The UAE is employed for the maximum simultaneous recovery of gallic acid, protocatechuic acid, epigallocatechin and rutin. The UAE was performed (solid-to-solvent ratio, 0.2:100 to 8.7:100 (g/mL); solvent, water and 10 to 100 % v/v ethanol; time, 1 to 20 min; and amplitude, 10 to 100 %) to identify the variables for two level factorial analysis (2LF). The most influencing factors from 2LF were further analyzed via central composite design experiments and response surface methodology to obtain the best extraction condition. The heat induced changes in the polyphenols were performed via heat treatment (at 90, 100 and 120 °C) from 0 to 90 min. The degradation kinetic parameters were conveyed in terms of reaction rate constants (k) and half-life (t1/2). The microencapsulation were accomplished via spray drying using four formulations of 2.81 wt.% maltodextrin (MD); and 10 wt.% of MD, whey protein isolate (WPI) and MD:WPI (9:1), respectively. The stability of the microcapsules upon 6 months of encapsulation were studied at different storage conditions of room temperature (ambient and amber) and at -80 °C. The polyphenols controlled release from the microcapsules were studied under simulated gastric (pH 1.2) and intestinal (pH 7.4) condition. The highest extraction yield of gallic acid, protocatechuic acid, epigallocatechin and rutin (0.16, 0.179, 0.024 and 0.012 mg/g DW, respectively) were obtained at solid-to-solvent ratio of 2:100 (g/mL), 46.74 % v/v of ethanol, sonication time of 11 min and 66.10 % of amplitude. The thermal degradation of gallic acid, protocatechuic acid and epigallocatechin followed second-order reaction kinetics which results in single (0.004 min-1), double (0.0036 and 0.0008 min-1) and triple (33.536, 3.2836 and 9.9561 min-1) reaction k, respectively. Only rutin fits the zero-order reaction kinetics with k values of 0.0265 and 0.0071 min-1. The t1/2 were of the following sequence; epigallocatechin (4.78 min), rutin (120.55 min), gallic acid (251 min) and protocatechuic acid (469.59 min) in the order of shortest to the least short. Shortest t1/2 of epigallocatechin indicates its high thermolability. Microencapsulation via 10 wt.% MD yielded better polyphenols retention compared to 2.81 wt.%. The mixture of MD:WPI (9:1) provides the highest retention (gallic acid, 88.73 %; protocatechuic acid, 83.9 %; epigallocatechin, 74.35 % and rutin, 89.89 %) due to the presence of protein-polysaccharide conjugates that protects the polyphenols from heat. Stability analysis indicates minor degradation with retention of at least 99.83 %. Formulation of MD:WPI (9:1) affects the microcapsules stability, showing improved controlled release in the intestinal fluid with 93.71 % of total polyphenols release. The extraction conditions, kinetic parameters and microencapsulation formulation of this work believed to be useful in developing highly preserved L. pumila functional food product.