Process optimisation, nutrient stability and digestibility of green powder from spinach juice

Mansor, Syamila (2019) Process optimisation, nutrient stability and digestibility of green powder from spinach juice. PhD thesis, University of Nottingham.

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The lipid group in food sciences at the University of Nottingham has recognised that ‘Chloroplast-Rich Fraction’ (CRF) are nutrients-rich. The removal of cell wall should increase its bioaccessibility.

The quality of chloroplasts recovered using a blending and a screw-slow-juicing were compared. No published reports exist into the liberation of chloroplasts from their cell confines by juicing. Slow-juicing proved to be the simplest method to disrupt spinach leaf and extract intact chloroplasts, compared with the blending method with 0.3M sucrose or water, but producing a lower CRFs’ yield. There was no significant difference in nutrient quality of CRFs recovered by these three methods: α-tocopherol (around 420 µg/g dry mass (DM)); β-carotene (3.61-3.84 mg/g DM); lutein (4.25-5.37 mg/g DM); omega-3 fatty acids (around 34 mg/g DM). To overcome the limitations of the juicing method, the centrifugation stage is skipped and merely dry the filtered-juice.

Drying spinach juice using spray-drying and freeze-drying shows better nutrient retention compared to oven-drying (with and without vacuum). There is no significant difference between the nutrient concentration of the spray-dried and freeze-dried juice. Encapsulation of juice using skimmed-milk powder gave full protection to β-carotene and lutein spray-dried at 195°C.

A spray-dried spinach juice stored at different conditions for 56 days shows β-carotene was more susceptible to degradation compared with lutein and α-tocopherol. Under our experimental conditions, it was observed that excluding low fluorescent light intensity and vacuum packaging at 20°C did not seem to improve nutrient retention loss over time. The rate of β-carotene, lutein and α-tocopherol loss displayed first-order reaction kinetic with low activation energy (0.665, 2.650 and 13.893 kJ/mol for vacuum; 1.089, 4.923 and 14.142 kJ/mol for non-vacuum). The reaction kinetics and half-life for β-carotene, lutein and α-tocopherol at 4°C and non-vacuumed were 2.2x10-2, 1.2x10-2, and 0.8x10-2 day-1, and 32.08, 58.25 and 85.37 day, respectively.

Nutrient retention post-digest is the highest in freeze- and spray-dried spinach juice. Compared with fresh cut-whole leaf, liberating more chloroplasts allows better micellarisation of lipid soluble vitamin, hence, is a much better source of nutrients. Pureeing leaf prior to exposure to the in-vitro digestion model appears to significantly improve the nutrients available for uptake (NA). The digestive stability and bioaccessibility of β-carotene and lutein from dried-juice and fresh-juice has better micellarisation than fresh cut-whole leaf and freeze-dried CRF. Dried-juice is a better source of bioaccessible nutrients compared with pureed leaf simply because you can consume less mass to get the same nutritional benefit, and more stable than fresh leaves.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Gray, David A.
Keywords: nutrient stability, green powder, carotenoids, nutrient digestibility, spinach juice
Subjects: T Technology > TP Chemical technology > TP 368 Food processing and manufacture
Faculties/Schools: UK Campuses > Faculty of Science > School of Biosciences
Item ID: 57074
Depositing User: Mansor, Syamila
Date Deposited: 29 Sep 2023 06:30
Last Modified: 29 Sep 2023 06:30

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