- Title
- Effects of different drying processes on the physicochemical and antioxidant properties of gac fruit powder
- Creator
- Kha, Tuyen
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2010
- Description
- Masters Research - Master of Philosophy (MPhil)
- Description
- Gac fruit, Momordica cochinchinensis Spreng contains extraordinarily high levels of carotenoids, especially β-carotene and lycopene, and a comparatively high content of alpha-tocopherol (vitamin E) and of polyunsaturated fatty acids. The aim of this study was therefore to develop an understanding of suitable conditions for the processing of Gac fruit and the preparation of Gac fruit powder. The objectives of this study were to investigate the effect of 1) pre-treatments; blanching, ascorbic acid and bisulfite, and 2) drying techniques; air, vacuum, freeze and spray drying, on the physicochemical and antioxidant properties of powders produced from Gac arils. In addition, Gac arils (mixed with added maltodextrin) and untreated Gac skin and yellow pulp were air-dried and their properties were evaluated. The shelf life of a number of the Gac powder products was periodically evaluated during an extended storage period. The moisture sorption isotherms of various Gac powders were also constructed. Furthermore, the stability of three different types of Gac fruit powders was also tested when used in food and beverage products. Results showed that freeze drying of fresh Gac aril without any pre-treatment produced powders of high quality as determined by colour (hue angle of 33.93, total carotenoid content (TCC) of 7.24 mg/g and total antioxidant activity (TAA) of 0.39 mmole TE/g). However, pre-treatment of fresh Gac fruit aril with 1% (w/v) ascorbic acid or bisulfite solution before vacuum drying at 40 oC for 45 hours was just as effective as freeze drying in preserving colour (hue angle of 34.18 and 36.25, respectively), TCC (7.28 and 6.99 mg/g, respectively) and TAA of 0.36-0.40 mmole TE/g. Pre-treatment with 1% (w/v) ascorbic acid or bisulfite solution before air drying at 40 oC for 48 hours was also effective (TCC of 6.36 and 6.11 mg/g, respectively and TAA of 0.33 mmole TE/g) but not to the extent of vacuum or freeze drying. In respect of the spray drying process, taking into account the dilution effect of the added maltodextrin, the addition of 10% maltodextrin to the feed mixture and drying at 120 oC effectively preserved the physicochemical and antioxidant properties of the powder (hue angle of 66.85, TCC of 2.77 mg/g and TAA of 0.14 mmole TE/g). In addition, in a comparison of fresh and frozen arils, both were found to be equally useful for production of Gac powder in terms of preservation of colour (hue angle of 33.93 and 31.28, respectively), TCC (7.24 and 6.27 mg/g, respectively) and TAA (0.39 and 0.33 mmole TE/g, respectively). However, the dried aril was found to be very difficult to grind due to its stickiness. The addition of maltodextrin (0.5 or 1 g maltodextrin/g of total fruit solids) prior to drying solved this problem and also maintained the quality of the powder (hue angle of 28.04-30.55; TCC of 5.65-6.29 mg/g and TAA of 0.29-0.31 mmole TE/g, respectively). The storage study indicated that the degradation of TCC and TAA of freeze-dried and spray-dried powders for up to 8 and 3 months, respectively, was lowest when samples were packed into laminated bags and stored at temperature of 10 oC (TCC loss of 11% and 5% and TAA loss of 44% and 15%, respectively). The highest losses for freeze-dried and spray-dried powders (TCC of 70% and 42%; and TAA of 88% and 42%, respectively) occurred when stored at conditions of 37 oC. Isotherm curves of all the Gac powders have sigmoid shapes. By comparing different drying methods for aril, the lowest hygroscopicity was observed in SD powder, followed by VD, AD and FD powders. Results also showed that the air-dried skin and yellow pulp powders contained low levels of TCC and TAA compared to the aril powders, but these are still high levels of TCC (0.90 and 0.42 mg/g, respectively) as compared to cherry tomatoes (0.36) and pumpkin (0.14). The skin (18%) and yellow pulp (49%) account for 67% of the total weight of the Gac fruit and as such comprise significantly high components. Therefore, utilisation of these components can prevent environmental pollution due to waste issues, and also enhances the overall value of Gac fruit. Freeze-dried, vacuum-dried and spray-dried Gac fruit aril powders were found to be easily incorporated into cooked glutinous rice, pasteurised Gac juice and pasteurised Gac milk mixtures. The colour, TCC and TAA of the juice and the milk mixtures were maintained after storage for 30 days under refrigeration temperature of 40 oC. Overall the study established that, the quality of Gac aril powders, in terms of colour, TCC and TAA, is most effectively preserved by applying pre-treatments prior to vacuum drying at 40 oC. These powders should be packed in laminated bags and stored at 10 oC for any lengthy storage period. It was also found that the Gac powders can be satisfactorily incorporated into “Xoi Gac”, juice and milk products. Finally, the overall value of Gac fruit could be enhanced through utilisation of all the anatomical components.
- Subject
- Gac fruit powder; antioxidants; carotenoid; drying techniques
- Identifier
- http://hdl.handle.net/1959.13/802339
- Identifier
- uon:6074
- Rights
- Copyright 2010 Tuyen Kha
- Language
- eng
- Full Text
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