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Yeoh, Wei Keat (2017) Optimisation of ultrasound treatment to enhance the postharvest life of fresh-cut pineapple. PhD thesis, University of Nottingham.

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Abstract

Minimal processing of fresh-cut pineapple (Ananas comosus L.) is time and labour consuming as it has thick inedible skin and large crown. Liberation of cellular contents at the site of wounding can promote the growth of microorganisms and limit the storage life of fresh-cut pineapple. Therefore, ultrasound treatment at different power input and exposure time was used to investigate its effectiveness on the storage life of fresh-cut pineapple. To determine the antimicrobial effect of ultrasound on the proliferation of spoilage microorganisms three different ultrasound power inputs (17, 25 and 29 W) and treatment times (5, 10 and 15 min) during 7 days of storage at 7 oC were applied on co. Josapine. The application of ultrasound at the power input of 25 and 29 W for 10 and 15 min, respectively, inhibited the growth of mesophilic, lactic acid bacteria and yeast and moulds. On day 5, it was found that 29 W for 15 min treatment resulted in the lowest growth of mesophilic, lactic acid bacteria and yeast and mould counts. However, changes in the proliferation of spoilage microorganism were observed among samples treated at 25 W: 10 min, 25 W: 15 min and 29 W: 10 min. The storage life of ultrasound treated fresh-cut pineapple was extended by 2 days in comparison to those washed in distilled water (dH2O).

The ideal ultrasound power input (25 and 29 W) and treatment time (10 and 15 min) were then used to study the effect of treatment on the production of intracellular ROS and extent of oxidative damage in fresh-cut pineapple. Increments in ROS concentration when exposed to ultrasound treatment negatively correlated with populations of mesophiles, lactic acid bacteria and yeast and mould. Higher ROS contents may have induced disease resistance in fresh-cut pineapple. However, increments in power input and treatment time to 29 W and 15 min resulted in the oxidation of polyunsaturated fatty acid (PUFA) as indicated by higher malondialdehyde (MDA) content during cold storage.

Ultrasound treatment also invoked oxidative stress and induced defence mechanisms in fresh-cut pineapple by regulating phenolic metabolism and recycling of ascorbate concentration. Induction of phenylalanine ammonia lyase and inhibition of polyphenol oxidase and polyphenol peroxidase activity in fresh-cut pineapple upon exposure to ultrasound treatment resulted in higher total phenolic concentration. Similarly, the redox state of ascorbate as indicated by lower concentrations of dehydroascorbic acid was better maintained following ultrasound treatment due to the induction of monodehydroascorbate reductase and dehydroascorbate reductase activity. Likewise, the total antioxidant capacity of fresh-cut pineapple treated at 25 W for 10 was found higher in comparison to other treatments during 5 days of storage at 7 oC.

The effect of ultrasound treatment on the physico-chemical and physiological changes in fresh-cut pineapple was also assessed in this study. Ultrasound treatment at 25 W for 10 min retained 98% of initial firmness and did not result in changes in the juice leakage, colour parameters, soluble solid concentration and titratable acidity in regards to control after 5 days of storage. Meanwhile, the increment of ultrasound power input and treatment time to 29 W and 15 min had resulted in the lowest SSC concentration with the highest volume of juice leakage and respiration rate in fresh-cut pineapple during 5 days of cold storage.

In conclusion, an ultrasound treatment at 25 W for 10 min optimally inhibited the growth of spoilage microorganisms and extended the storage life for 2 days. Higher reduction of spoilage microorganisms was achieved when the ultrasound power input and treatment time was increased to 29 W and 15 min but it caused higher accumulation of ROS which reduced the nutraceutical concentration of fresh-cut pineapple following 5 days of cold storage.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Ali, Asgar
Keywords:	Ananas comosus L., ultrasound treatment, storage life, postharvest technology, pineapple
Subjects:	S Agriculture > SB Plant culture
Faculties/Schools:	University of Nottingham, Malaysia > Faculty of Science and Engineering — Science > School of Biosciences
Item ID:	37761
Depositing User:	YEOH, WEI KEAT
Date Deposited:	30 Oct 2017 06:58
Last Modified:	30 Oct 2017 17:05
URI:	https://eprints.nottingham.ac.uk/id/eprint/37761

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