Sucharit, Poramat
(2022)
Establishing the functional properties of chloroplast membrane material for food applications.
PhD thesis, University of Nottingham.
Abstract
Chloroplasts are abundant photosynthetic organelles tightly packed with a complex membrane system containing lipophilic nutrients such as carotenoids and tocopherol. Through physical extraction methods, the chloroplastidial membrane material (CMM) can be prepared with different degrees of membrane integrity. While some centrifuged pellet samples show a more condensed membrane material, additional osmotic pressure and high-pressure treatment could lead to a more dispersed and a completely disintegrated membrane system, respectively. All the CMMs prepared are rich in bioactive molecules with the pellet CMMs enriched in lipophilic nutrients (i.e., Chl a, Chl b, lutein, β-carotene, α-tocopherol and various fatty acids) and micronutrients such as iron; supernatant samples are enriched in minerals (e.g., P and Mg). The use of a juicer to isolate chloroplasts from the confinement of undigestible cell walls proved to be a simple and efficient method to prepare a chloroplast-rich extract.
Enriched in nutrients and other amphiphilic molecules (e.g., omega-3 fatty acids enriched galactolipids), chloroplasts are promising interfacial-active material for application in food. In this work, freeze-dried CMMs were tested for their flow enhancing ability in an oil-based suspension food, namely a chocolate model system (65% w/w sugar-in-oil (s/o) suspension, 53.4% v/v). The ability of these CMMs to act as a flow enhancer was compared with a chemically synthesised emulsifier, polyglycerol polyricinoleate (PGPR). Throughout the confectionery industry, rheological parameters (i.e., σ_c, τ_5, η_40, TFP and COP) are commonly used in specifications to guide manufacturing processes and to control the quality of chocolate products. Using these rheological parameters, the results demonstrated that CMMs are interfacial-active and can aid the flow of an oil-based suspension in a concentration-dependent fashion. Although the ability observed for CMMs is not as significant as PGPR, it is still comparable to PGPR at 0.2%. With the drive towards clean label products, CMM, being clean and natural, could become a replacement for synthetic PGPR in the chocolate industry.
As a potential functional ingredient in food, the digestion of CMM was also investigated using in-vitro methods. CMM (i.e., P-CRF) oil-in-water (o/w) emulsions are stable for up to 3 days at pH 7. Interestingly, a CMM stabilised o/w emulsion is also stable throughout all the simulated digestive conditions tested (i.e., oral, gastric and intestinal). Upon addition of enzymes in the in-vitro digestion experiment, the majority of CMM was hydrolysed during the intestinal phase. On its own, the majority of CMM’s galactolipids (i.e., MGDG and DGDG) were hydrolysed by the end of the incubation. However, when CMM and oil were combined in an in-vitro digestion trial, the hydrolysis of both CMM and oil were reduced. This phenomenon is further enhanced when CMM and oil were ‘pre-emulsified’ to maximise the CMM-and-oil interactions.
This natural ingredient not only offers nutritional benefits but it also possesses interfacial-active properties suitable for a wide range of applications such as a flow enhancer in oil-based system, o/w emulsion stabiliser and fat digestion retarding agent. This work has established that CMM is an attractive candidate for a clean, green functional ingredient for a range of food, feed, and pharmaceutical applications.
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