The extraction, identification, and encapsulation of phenolic compounds from Prunus domestica subsp. institia towards their incorporation into a functional milk product : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Manawatū, New Zealand
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Date
2022
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Massey University
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Abstract
Damson plums are rich in bioactive compounds such as polyphenols, flavonoids, and anthocyanins, which are potent antioxidants with proven health-promoting properties. However, to date, there is no systematic publication/report about the type and concentration of various bioactive compounds in damson plums or using this type of plum as a food ingredient in the food industry. This study aimed to: 1) optimise the extraction of the bioactive compounds from Prunus domestica subsp. Institia (damson plums) grown in New Zealand using efficient extraction methods such as accelerated solvent extraction (ASE), ultrasound-assisted extraction (UAE), enzyme-assisted extraction (EAE), and their combined (E+UAE) extraction, in water or ethanol as the solvents; 2) analyse the total phenolic content (TPC), total flavonoid content (TFC), total anthocyanin content (TAC), and total antioxidant activities of the damson plums extract; 3) encapsulate the above-mentioned extract to protect the bioefficacy of its phenolic compounds; 4) compare the physical and chemical stabilities of the manufactured encapsulated ingredient in freeze-dried or liquid form during storage; and 5) assess the behaviour of the encapsulated plum extract after its incorporation into a functional milk product.
Fresh New Zealand damson plums were freeze-dried and ground into a powder and extracted with different methods explained above. The freeze-dried damson plum powder (FDDPP) was then encapsulated in liposomes made of soy lecithin granules using high-shear homogenisation and/or microfluidisation. The encapsulation efficiency (EE) was assessed by the determination of various phenolic compounds using high-performance liquid chromatography (HPLC) before and after the application of Sephadex filtration to separate free phenolics and encapsulated phenolics. Finally, the encapsulants containing damson plum powder were incorporated into milk (whole/full-fat) as a functional beverage, and the effect on the physiochemical properties of the milk product was assessed.
The results showed that the plum samples extracted using the ASE with water as the solvent for 40 min showed the highest phenolic, anthocyanin, and antioxidant properties. The EAE method appeared to improve the extraction of anthocyanins, possibly due to the retardation of anthocyanin hydrolysis as the consequence of inhibition of polyphenol oxidase (PPO). However, the UAE was likely to suppress the extraction of TAC because of the degradation of anthocyanin glucosides, resulting from the action of PPO induced by ultrasound. The E+UAE method demonstrated the maximum extraction efficacy for the TFC as the extraction time was increased to 60 min. Different extraction methods obtained various extraction efficacies for the seven phenolic compounds (neochlorogenic acid, gallic acid, rosmarinic acid, catechin, epicatechin, rutin, and naringenin) found in the FDDPP. For example, neochlorogenic acid, the predominant phenolic compound of New Zealand damson plums was significantly (p<0.05) higher in the samples extracted using the ASE method (with ethanol as the solvent) for 40 min (1393.2±29.7) than the other samples. On the other hand, rutin, one of the major flavonoids in damson plums, showed a significantly higher content (67.51±1.52) in the samples extracted using EAE for 40 min than the other extraction methods (p<0.05).
Neochlorogenic acid achieved the highest EE (98.86%) with the additional
microfluidisation step in liquid liposomal encapsulants. In comparison, EE was around 81.40% in the liquid liposomes produced by microfluidisation; whereas, high-shear homogenisation alone produced liposomes with a much lower recovery rate (about 75.52%) for this important phenolic component of damson plum extract. Thus, the additional microfluidisation step resulted in the manufacture of liposomes with higher physical stability and with a smaller average particle size (73.2±1.5 nm), and the highest zeta potential (-35.39±0.97 mV) for the empty liposomes in liquid form. This confirms the stability of the liposomal system manufactured for the current experiment.
Milk was chosen as a suitable delivery vehicle (functional food) for the incorporation of the manufactured liposomes containing plum extract, due to its availability, convenience, and potential nutritional benefits. The physical and chemical stabilities of the phenolic compounds in the functional milk containing free and encapsulated plum extract were assessed using a pH meter, heometer, and HPLC analysis. No significant differences were seen in the viscosity of different milk samples containing free extract, encapsulated extract, and freeze-dried encapsulants. The encapsulants achieved by various homogenisation techniques showed different recovery rates for rutin, catechin, epicatechin, neochlorogenic acid, and rosmarinic acid from the milk containing the extract of New Zealand damson plum. However, further investigation is required to determine the effect of the extraction technique (i.e., ASE) and the liposomal encapsulation on the extraction and encapsulation efficiencies of New Zealand damson plums, respectively. Further study is also required to investigate the behaviour of encapsulated damson plum extract in different functional foods, the effect on their sensorial properties, and the bioaccessibility and bioavailability of its phenolic compounds after food consumption.
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Figure 2.5 is re-used with permission.