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De Chirico, Simone (2019) Optimising the recovery and stabilisation of intact oil bodies from oilseed rape. PhD thesis, University of Nottingham.

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Abstract

Oil bodies (oleosomes) are sub-cellular droplets representing the main form of energy storage in oleaginous plant seeds. The release of intact oil bodies by wet milling oilseeds results in a natural emulsion (no need for additional emulsifiers) and is likely to have a lower environmental impact than conventional oilseed processing. During the aqueous recovery of oil bodies, other water-soluble seed material is solubilised and carried-over in the final product. The aims presented in this thesis were:

1. Recover intact oil bodies free from exogenous seed materials

2. Understand which the mechanisms of oil body instability during storage are

3. Stabilise the oil body material

4. Assess emulsion physicochemical stability during storage

The degree to which recovered oil bodies remained intact was established by exposing the recovered crude cream to urea (9M) and measuring any changes to droplet size; no change indicates a high degree of intact oil bodies. A lipase assay was used to monitor enzyme carry-over in oil body preparations and to measure thermal process effectiveness. Chemical (hydrolysis of lipids and integral proteins) and physical (particle size and zeta potential) stability were measured during oil body storage. The correlation between thermal treatment, lipase activity, and oil body stability was tested.

The use of alkaline pH solutions (>8.5) to soak and grind oilseed rapeseed were more effective against the contamination of oil body material with seed proteins/enzymes, compared with neutral pHs. Soaking and grinding seeds with a NaHCO3 solution (0.1 M, pH 9.5) yielded oil bodies with a similar composition to those prepared in urea (9 M); despite this ‘clean up’ by bicarbonate solutions, the physical stability over storage was compromised, due to the presence of hydrolytic enzymes. Heating a dispersion of oil bodies (milk or resuspended cream) for 6 minutes at 95°C significantly reduced lipolytic activity (>90% enzyme inactivation) and resulted in oil bodies that were stable physically and chemically.

Using the optimized recovery protocol and thermal treatment, oil bodies retained during storage (1 month, 20 °C) a particle size (D4,3) of about 1.4 μm; as the pH was increased from 3 to 10 the zeta potential changed from around +55 mV to -65 mV (pI of 6). In terms of chemical stability, thermally treated emulsions did not show signs of either proteolytic or lipolytic activity. The oxidative stability of oil bodies was significantly improved after thermal treatment.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Gray, David Wolf, Bettina
Keywords:	Oil bodies; Oleaginous plant seeds; Oil body instability; Emulsion physicochemical stability
Subjects:	T Technology > TP Chemical technology
Faculties/Schools:	UK Campuses > Faculty of Science > School of Biosciences
Item ID:	56058
Depositing User:	De Chirico, Simone
Date Deposited:	20 Aug 2019 14:18
Last Modified:	17 Jul 2021 04:30
URI:	https://eprints.nottingham.ac.uk/id/eprint/56058

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