Stability of ultra-high temperature (UHT) processed beverages infused with white tea (Camellia sinensis) and grape seed (Vitis vinifera) extracts : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Food Technology, Massey University, Albany, New Zealand.
Camellia sinensis and grape seed extracts have been associated with health benefits due to their high phenolic content. White tea, derived from young buds and leaves of Camellia sinensis, is high in catechins. Grape seeds are also high in catechins, as well as gallic acid and proanthocyanidins. In addition, it has been suggested that grape phenolics may interact synergistically with Camellia sinensis extracts, increasing their biological activities.
Although white tea and grape seed extracts can be easily incorporated into beverages, the impact of processing conditions on the stability of bioactive compounds ought to be considered when developing functional beverages. The stability of white tea and grape seed phenolics can be affected by processing and storage conditions, such as temperature, pH and beverage ingredients. Catechins may undergo changes through epimerisation, oxidation and polymerisation, altering the chemical profile of the finished product. The impact of heat treatment on the stability of catechins may be reduced by applying heat for a shorter period of time. Hence, ultra-high temperature (UHT) processing might be a suitable technique to commercially sterilise functional beverages without significantly affecting grape seed and white tea phenolic compounds. There is, however, a lack of information available on the impact of UHT treatment on white tea and grape seed polyphenols. The aim of this project was to evaluate the stability of phenolics, methylxanthines and antioxidant activity in UHT-treated beverages infused with white tea and grape seed (Vitis vinifera var. Sauvignon Blanc) extracts during storage.
This study comprised two integrated phases. The first phase aimed at determining the optimum UHT processing temperature based on chemical, microbiological and sensory characteristics of the beverages infused with white tea and grape seed extracts. In this experiment, one commercial formulation (mango-flavoured beverage) was UHT-treated at four temperature levels (110, 120, 130 and 140 °C) for 5 s. The UHT-treated beverages in this study contained catechins, gallic acid, caffeine, and theobromine. The beverages were also expected to contain other phenolics and methylxanthines, which were not investigated. The levels of theobromine and caffeine in the beverages were stable following UHT processing. Even though the impact of UHT-treatment (at 110, 120, 130 and 140 °C for 5 s) on the stability of phenolics in the RTD mango-flavoured beverages was not significant (P > 0.05), the levels of GCG increased slightly following UHT processing, and EGCG decreased following treatment at 140 °C, suggesting that epimerisation of catechins may have occurred. Therefore, the optimum UHT treatment conditions chosen for further work were 130 °C for 5 s.