- Title
- Extraction and utilisation of apple juice pomace phenolics
- Creator
- Candrawinata, Vincent I.
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2015
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Apples are one of the most cultivated and consumed fruits worldwide. In the Western diet, apples are a major contributor of dietary phenolics. Approximately a third of the apples produced are processed into apple juice. Upon being processed into juice, there is a significant loss in the total phenolic content and antioxidant activity, indicating that most of the phenolics are retained in the waste, called pomace. The current industrial practice of discarding the pomace as waste makes this raw material a potential economical source of phenolics. This study focused on investigating the: (1) availability of the apple pomace as a potential source of phenolics throughout the year from apple juice production, (2) efficiency of using water instead of organic solvents, such as methanol, to extract phenolics from apple pomace, (3) optimisation of the water extraction parameters, such as time, temperature and pomace to water ratio as well as the application of pre-treatments (microwave and ultrasound), (4) effect of processing and storage on the bioactivity of the aqueous extracts, (5) effect of encapsulation via spray drying and simple coacervation – co-extrusion on preserving the bioactivity of the extracts and (6) utilisation of the extract powders as a food additive to improve and maintain the phenolic content and antioxidant activity of apple juice. The phenolic content was measured using the Folin-Ciocalteu assay and the antioxidant activity was measured using the DPPH, FRAP and ABTS assays. The seasonality study showed that there was a 10% variation in the phenolic concentration of apple juice produced at different times of the year. This indicated that phenolics were always present in the apple pomace throughout the year. The optimal water extraction technique was extraction at 85°C for 30 min with 0.05 g/mL pomace to water ratio, along with the application of pre-treatments, namely microwave (3 min at 800 W power output) and ultrasound (6 min). This optimal water extraction technique had a 75% extraction efficiency compared to the methanolic extraction. However, the phenolic content and the antioxidant activity of the aqueous extracts were shown to degrade during heat processing using a rotary evaporator. It was also shown that encapsulation with: (1) 18% maltodextrin – 2% rice protein by spray drying, (2) alginate and (3) alginate – chitosan by coacervation significantly improved the retention of the bioactivity of the extracts during storage. The spray dried apple pomace extract powder was better in protecting the phenolics compared to the coacervation-produced beads, during prolonged storage. However, the coacervation-produced beads were shown to be able to release the phenolics under alkaline pH conditions (pH 7.4), which simulated the human small intestines. Finally, the spray dried apple pomace extract powder was successfully incorporated as a food additive in apple juice. Juice enriched with pomace extract powder was shown to have a better storage stability. The results showed that, at the end of a 7 day storage trial at 4°C, the enriched juice retained 87% of the phenolic content as opposed to only 50% observed for the juice without pomace extract powder addition. An aqueous apple pomace extract containing phenolics and antioxidant activity was successfully produced using optimal conditions. Encapsulation using alginate and chitosan by coacervation, and especially maltodextrin and rice protein with spray drying, was shown to protect the phenolics from degradation during storage. The addition of the spray dried apple pomace extract powder to apple juice was also shown to increase the phenolic retention of the juice during storage.
- Subject
- apples; phenolics; waste
- Identifier
- http://hdl.handle.net/1959.13/1060198
- Identifier
- uon:16750
- Rights
- This thesis is currently under embargo and will be available from 01.03.2025, Copyright 2015 Vincent I. Candrawinata
- Language
- eng
- Full Text
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