Blueberries are well known for their high anthocyanin content and the health benefits. Fresh blueberries have limited shelf life and thus are kept frozen or processed. Since freezing is expensive, low cost processing methods, particularly drying are being devised. Various drying treatments were compared with regard to drying time and quality of the dried product in terms of anthocyanin and polyphenolic contents as well as antioxidant activity. The drying treatments involved high temperature in a cabinet dryer and low temperature in a heat pump dryer. Freeze drying was used as a reference treatment. Highbush (Vaccinium corymbosum L., cultivars Crunchie, Star, and Sharpe) and rabbiteye (Vaccinium ashei, cultivars Climax, Powderblue, and Brightwell) blueberries were used in this study. Pre-treatments included osmotic dehydration or skin abrasion. The temperature and concentration of the osmotic solution were the main parameters contributing to the reduction of drying time. Mechanical skin abrasion was more effective than osmotic dehydration in reducing drying time and minimising the loss of anthocyanin and phenolic contents of the blueberries in air drying treatments. The thickness of cuticle and the structure of epicuticular waxes affected the drying rate of different cultivars of blueberries. Liquid chromatography and mass spectrometry (LC/MS) was used to identify different anthocyanins in the blueberry samples. Delphinidin, petunidin, and malvidin were the main contributors to the total anthocyanin content of the fresh and dried samples. Degradation products of anthocyanins were observed in samples where the anthocyanin contents declined as a result of drying treatments. The anthocyanin content and profile, phenolic content, and antioxidant activity of mulberries (Morus nigra), and Makiang (Cleistocalyx nervosum), a Thai native fruit, were also analysed. There was no significant difference between total anthocyanin content of blueberries and mulberries. In contrast, the total phenolic content and antioxidant effect of mulberry were significantly higher than those of blueberries and Makiang. Skin abrasion and high temperature drying resulted in the fastest drying rate and highest anthocyanin retention. Anthocyanin profiles differed in various cultivars of blueberries. Within the same cultivar, amounts of each anthocyanin varied with pre-treatments and drying methods but the distribution of monomeric anthocyanins was similar.
| Identifer | oai:union.ndltd.org:ADTP/215476 |
| Date | January 2007 |
| Creators | Lohachoompol, Virachnee, Chemical Sciences & Engineering, Faculty of Engineering, UNSW |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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