Green extraction and protection of bioactives from green tea waste and their incorporation into a functional kiwifruit juice : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Manawatū, New Zealand
Several tea products are manufactured from Camellia sinensis, yet about one-third of tea is wasted globally during harvest and processing. Bioactive compounds (mostly catechins), which possess numerous health-promoting properties in humans, are greatly found in such a huge waste. Thus, the objectives of this study were: 1) to utilise green tea waste by finding an appropriate, efficient, green, and industry-relevant extraction method for its catechins; 2) to protect and deliver the extracted catechins using a suitable encapsulation technology; and, 3) to test the behaviour of the encapsulated extract/catechins in a functional kiwifruit juice. The optimisation and standardisation of catechin extraction from green tea waste were investigated by considering various extraction techniques (hot water, ultrasound-assisted, and ethanol extractions) and ratios of solvents (1:100, 1:50, and 1:20, green tea waste:solvent w/v) with an extraction temperature of 80 °C for 20 min. Distilled water was used in both hot water and ultrasound-assisted extraction methods, while ethanol was applied for the last extraction technique where ethanol was removed using a vacuum evaporation process. The results showed that hot water extraction achieved the highest extraction efficiency in the case of all ratios, and the highest extraction yield was obtained at the ratio of 1:50 over both ultrasonic-assisted and ethanol extractions, indicating that the hot water extraction was more effective than the other two methods. Green tea waste extract (GTWE) was encapsulated into Single- and Double-layer liposomes by using soy lecithin and soy lecithin + chitosan, respectively. Single-layer liposomes possessed high encapsulation efficiency (~70 %), encapsulation yield (~75 %), and loading capacity (~37 %) together with a small particle size (~180 nm) and high values of zeta potential (>-35 mV). However, the Double-layer liposomes showed a large particle size (~430 nm) and the opposite zeta potential values (>25 mV) during the 28 days of storage. These results indicated that both types of liposomes (i.e., Single-layer and Double-layer) had high stability up to the end of the storage period. Kiwifruit juice was chosen as the suitable delivery vehicle for both Single- and Double-layer liposomes, due to the potential synergistic effect between catechins and vitamin C. The enrichment of kiwifruit juice with of the Single-layer liposomes increased the total phenolic content (TPC), total antioxidant activity (TAA), and total catechin concentration in the kiwifruit juice analysed by Folin-Ciocâlteu assay, 2,2-diphenyl-1-picryl-hydrazyl (DPPH) radical assay, and high-performance liquid chromatography (HPLC), respectively, without the alteration of its pH during the entire 28 days of storage. Although the addition of the liposomes caused an increase in the particle size and zeta-potential of the kiwifruit juice, the TEM micrographs illustrated the separation of the Single-layer liposomes and kiwifruit fibre molecules, which confirms their stability in the juice matrix. In terms of the application of Double-layer liposomes in kiwifruit juice, this type of liposomes could not protect the catechins in GTWE as efficiently as the Single-layer liposomes; i.e., both TPC and TAA values were lower, when compared with the Single-layer liposomes. This was possibly due to the leakage of the encapsulated catechins from the sedimented liposomes (caused by the interactions between chitosan and fibre) and their consequent degradation. In addition, TEM images of the kiwifruit juice containing these liposomes showed that the attraction of the chitosan layer and kiwifruit fibre molecules increased the size of the particles in this beverage. Taken together, the findings of this research confirmed that green tea waste can be utilised for the extraction of its high-value bioactive compounds (i.e., catechins) that could be efficiently extracted using a green method (hot water) and be incorporated into a kiwifruit juice for the enhancement of its functionality. This research will be of high interest for the valorisation of a low-value by-product that is currently wasted and its utilisation of its extract as an added-value ingredient that can be used in the food industry for the creation of functional food products. However, further research is required to investigate the behaviour of such a developed ingredient in various functional food products and the bioaccessibility/bioavailability of its catechins after food consumption.