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dc.contributor.authorKasim, Khairul
dc.date.accessioned2016-05-09T03:06:08Z
dc.date.available2016-05-09T03:06:08Z
dc.date.issued2015
dc.identifier.urihttp://hdl.handle.net/10179/7755
dc.description.abstractBlueberry is regarded as a ‘super fruit’ by many consumers and believed to offer health benefits for humans. It is well known for its high antioxidant levels and for the diversity of its anthocyanins. Blueberries can be eaten fresh but are very perishable, so are commonly kept frozen and available all year round. Frozen blueberries are suitable for a range of products including juice. During juicing, there are likely to be changes in phytochemical constituents arising from the various processing steps. These changes lead to variable composition of the finished juice and uncertain impacts on the ‘health value’ of the product. Therefore, this study focused on evaluating three major phytochemicals (anthocyanins, chlorogenic acid (CGA), and procyanidin B2) throughout juice processing in order to model compositional change. Blueberry juice processing involves a series of unit operations: thawing, blanching, mincing, enzyme treatment, separation of juice from pomace, pasteurisation, and bottling. Enzymatic degradation occurs during thawing of blueberries as they still contain ‘live’ oxidases. Prolonged thawing at warm temperatures would therefore be particularly bad for phytochemical degradation. If these oxidases are destroyed by blanching, thermal degradation also occurs but was found to be less aggressive than polyphenoloxidase (PPO) activity. Blanching at high temperature (= 70 °C) for 3 min eliminated PPO and significantly increased the phytochemical concentration in the juice but it induced pectin gel formation which reduced juice recovery. Depectinisation is essential after berry blanching to dissolve pectin gel and to avoid juice volume penalty. Significant losses of phytochemicals were also observed during pressing of the berries into juice, due to physical associations between the phytochemicals and the berry matrix, and entrapment. Blanching at 90 °C for 3 min followed by pectinase enzyme treatment at 50 °C for 2 h was the best way to deliver high phytochemical concentration in the juice with high juice volume recovery and acceptable viscosity. There is a risk that juices with high phytochemical concentration will seem bitter or astringent. This was found not to be the case in sensory trials, with consumers consistently preferring the high-phytochemical juices; it seems sugars in the juice masked any adverse perceptions. Because of the complexity of blueberry juice processing, the processing model developed in this study was simplified into three components: a defrost model, a recovery model and a thermal model. In short, the defrost model was used for the whole berry phase during thawing when PPO was still active; the recovery model accounted for losses into the pomace; and the thermal model covered the subsequent liquid phase. These processing models were able to predict anthocyanin and CGA changes throughout processing (particularly in blanched products) but procyanidin B2 behaviour was not predictable. This modelling approach provides the ability to predict variations in composition arising from changes in the juicing process and offers manufacturers the opportunity to produce consistent blueberry juice with a high phytochemical concentration.en_US
dc.language.isoenen_US
dc.publisherMassey Universityen_US
dc.rightsThe Authoren_US
dc.subjectBlueberriesen_US
dc.subjectFruit juicesen_US
dc.subjectAnalysisen_US
dc.titlePhytochemical variation during blueberry juice processing : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Biotechnology at Massey University, New Zealanden_US
dc.typeThesisen_US
thesis.degree.disciplineBiotechnologyen_US
thesis.degree.grantorMassey Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophy (Ph.D.)en_US


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