Drying kinetics and quality of dried kedondong fruits undergoing hybrid drying processes

Ee, Cheak Theng (2021) Drying kinetics and quality of dried kedondong fruits undergoing hybrid drying processes. PhD thesis, University of Nottingham.

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Abstract

Kedondong fruit (Spondias dulcis Forst.) is an underutilized fruit that is gaining interest in many countries (Malaysia, India, Australia, Philippines and etc) as it is nutritious and can be planted easily. Kedondong fruit is rich in total polyphenols, vitamin C, carotenoids and vitamin A which may prevent degenerative diseases such as cancer, arthritis, arteriosclerosis, heart disease, inflammation, brain dysfunction and ageing. The objectives of this study were to investigate the drying kinetics of hot air, infrared and hybrid drying (freeze drying + hot air drying (FDHA) and freeze drying + infrared drying (FDIR)). Besides, the effects of hot air, infrared and hybrid drying on physical characteristics (colour and texture), chemical characteristics (total polyphenols content, vitamin C and antioxidant capacity) and sensory evaluation were also studied. Kedondong slices were first dried using hot air drying at 50˚C, 60˚C, 70˚C and 80˚C and infrared drying at 60˚C, 70˚C and 80˚C to study the drying kinetics, physical and chemical characteristics of dried kedondong samples. Two falling rate periods were detected in hot air drying at higher temperature (60˚C, 70˚C and 80˚C) whereas constant rate and falling rate periods were observed only at 50˚C. However, there was only one falling rate period detected in infrared drying. Effective diffusivities (Deff) were obtained ranging from 8.56 x 10-10 m2/s to 1.88 x 10-9 m2/s and 1.30 x 10-9 m2/s to 1.96 x 10-9 m2/s as temperature increased for hot air and infrared drying, respectively. Activation energies (Ea) were determined for hot air and infrared drying at 25.28 kJ/mol and 20.13 kJ/mol, respectively. Both drying methods showed the lowest total colour change, lower hardness, higher total polyphenols content, vitamin C and antioxidant capacity at drying temperature of 60˚C and this temperature was selected for hybrid drying.

In hybrid drying, first stage freeze drying at 6 hours and 12 hours were applied before second stage hot air or infrared drying. Drying rate curves of hybrid drying can be classified into three periods namely initial freeze drying, warming up when subjected to second stage drying and falling rate periods to remove remaining internal moisture. Deff values for partially dried kedondong samples by freeze drying (first stage) at 6 and 12 hours were determined at 1.84 x 10-10 m2/s and 1.98 x 10-10 m2/s, respectively which is lower than single stage drying of HA60 and IR60. However, second stage hot air and infrared drying of hybrid drying were found to increase Deff to the range between 1.23 x 10-9 m2/s and 2.20 x 10-9 m2/s. Partial dried kedondong samples by freeze drying in hybrid drying was found to lower total colour change of dried kedondong samples as compared to single stage drying (HA60 and IR60). Hardness results showed that hybrid drying with partial freeze dried kedondong samples at 12 hours was harder than that at 6 hours due to surface crust formation. In terms of chemical characteristics, hybrid drying was found to increase total polyphenols content but did not improve vitamin C retention. Pearson correlation showed that ABTS radical scavenging activity was found to have higher correlation to TPC (R2 = 0.895) but moderate correlation to VC (R2 = 0.662) whereas DPPH was observed to have higher correlation to VC (R2 = 0.757) than TPC (R2 = 0.698). Sensory evaluation analyzed by penalty analysis found that hybrid dried kedondong samples of FD6HA60 and FD12IR60 reduced the overall percentage of panel on penalty attributes as compared to HA60 and IR60 dried kedondong samples and some of the not-JAR attributes are preferred by sensory panel.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Hii, Ching Lik
Ong, Sze Pheng
Law, Chung Lim
Keywords: kedondong; spondias dulcis; hybrid drying; degenerative diseases; infrared drying; polyphenols
Subjects: T Technology > TP Chemical technology
Faculties/Schools: University of Nottingham, Malaysia > Faculty of Science and Engineering — Engineering > Department of Chemical and Environmental Engineering
Item ID: 65121
Depositing User: Ee, Cheak Theng
Date Deposited: 04 Aug 2021 04:41
Last Modified: 04 Aug 2021 04:41
URI: http://eprints.nottingham.ac.uk/id/eprint/65121

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