Abstract
The effects of different treatment methods on the stability and antioxidant capacity of the bioactive phenolic compounds of litchi pericarps were investigated. Fresh litchi pericarps were open air–dried, steam-blanched for 3 min in combination with hot air oven drying at 60 and 80 °C, and unblanched pericarps were dried in a hot air oven at 40, 60, 70 and 80 °C until equilibrium weight was reached. The total phenolic compounds, flavonoids, anthocyanins, proanthocyanidins and individual procyanidins, and antioxidant activity were analyzed. The combination of blanching and drying at 60 °C significantly (p < 0.05) improved the release of phenolic compounds, individual procyanidins, and the extracts′ antioxidant capacity compared with the unblanched hot air oven-dried and open air–dried pericarps. Drying of fresh unblanched litchi pericarps in either open air or a hot air oven caused significant losses (p < 0.05) in phenolic compounds and individual procyanidins, leading to a reduction in the antioxidant activity. A similar increase, retention or reduction was reflected in flavonoids, proanthocyanidins and anthocyanins because they are sub-groups of phenolic compounds. Ferric reducing antioxidant power (FRAP) and 1,1-diphenyl-2-picryldydrazyl (DPPH) radical-scavenging capacity of the treated pericarps were significantly correlated (r ≥ 0.927, p < 0.01) with the total phenolic compounds. Thus, the combination of steam blanching and drying treatments of fresh litchi pericarps could produce a stable and dry litchi pericarp that maintains phenolic compounds and antioxidant capacity as a raw material for further recovery of the phytochemicals.
Highlights
Litchi processing such as wine and juice production generates large amounts of peels/pericarps, seeds and pulp as by-products, where the bioactive phenolic compounds are mostly concentrated [1,2,3].The litchi pericarp is credited as a potential source of health-promoting bioactive phenolic compounds and as an ingredient in the formulation of oligonol, a low molecular weight proanthocyanidin supplement [3]
Despite litchi pericarps being composed of a high content of bioactive phenolic compounds, they are highly perishable due to the high activity of endogenous enzymes such as polyphenol oxidases (PPO) and peroxidase (POD) which catalyze the oxidation of the phenolic compounds [4,5]
This study evaluated the effects of steam blanching and oven drying under different conditions on the phenols, flavonoids, proanthocyanins, anthocyanins and procyanidin monomers in litchi pericarps
Summary
Litchi processing such as wine and juice production generates large amounts of peels/pericarps, seeds and pulp as by-products, where the bioactive phenolic compounds are mostly concentrated [1,2,3].The litchi pericarp is credited as a potential source of health-promoting bioactive phenolic compounds and as an ingredient in the formulation of oligonol, a low molecular weight proanthocyanidin supplement [3]. Despite litchi pericarps being composed of a high content of bioactive phenolic compounds, they are highly perishable due to the high activity of endogenous enzymes such as polyphenol oxidases (PPO) and peroxidase (POD) which catalyze the oxidation of the phenolic compounds [4,5]. This factor can hinder utilization of litchi pericarps in the recovery of phenolic compounds, especially during peak harvest and processing season if no initiatives are taken for the treatment of the pericarps for further utilization.
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