Abstract
Thomson navel orange peel is a by‐product of citrus processing, which contains high levels of bioactive compounds advantageous to human health, nevertheless due to its high moisture content it is exceedingly perishable. Drying is among the most common preservation methods, which could prolong the plants shelf‐life via reducing their moisture value. Taking this into account, depending on their type and conditions, drying techniques could degrade plant heat‐sensitive metabolites and lead to quality decline. Therefore, the goal of this paper was to investigate the influence of seven drying methods named sun, shade, oven, vacuum oven, microwave, and freeze‐drying with different drying conditions on the physical properties, for example, bulk density and color (L*, a*, b*, ΔE, and browning index (BI)) and essential oil characteristics such as extraction yield, chemical composition, antioxidant (total phenolic content (TPC), DPPH, and FRAP essays), and antimicrobial (MIC and MBC) activities of Thomson peel and determine the superior drying procedure. Results showed that freeze‐dried sample had the highest retention of L* (48.54) and b* (49.00) values, lowest BI (216.11) as well as highest EO extraction yield (6.90%), TPC (60.10 GAE/100 g), FRAP (0.52% at 80 mg/ml), and lowest IC50 (5.00 mg/ml), MIC and MBC compared with other drying treatments. Therefore, it could be inferred that freeze‐drying is the most efficient drying approach in respect of preserving both physical and EO attributes of Thomson peel.
Highlights
Orange, Citrus sinensis L. of the family Rutaceae, is one of the most abundant fruit crops in the world and is well-received by consumers due to its attractive color, pleasant aroma, and flavor (Juhaimi, Matthäus, Özcan, & Ghafoor, 2016; Matthaus & Özcan, 2012; Smeriglio et al, 2019)
Bulk density is well correlated with particle size of dried powders, where smaller powder particles would reduce the porosity and enhance the coherence of dried sample which would lead to a denser product (Sogi, Garg, & Bawa, 2002)
The results showed that various drying methods notably effects the EO content of Thomson peel (Figure 2) and depending on the type of drying method, duration, and temperature both increment and reduction in the quantities of EO yields were observed (Rahimmalek & Goli, 2013)
Summary
Citrus sinensis L. of the family Rutaceae, is one of the most abundant fruit crops in the world and is well-received by consumers due to its attractive color, pleasant aroma, and flavor (Juhaimi, Matthäus, Özcan, & Ghafoor, 2016; Matthaus & Özcan, 2012; Smeriglio et al, 2019). This work was carried out to determine the possible effect of drying techniques on the physical aspects of dried matter, and on the chemical profile, antioxidant and antibacterial activities of EOs extracted from this valuable by-product. Oranges were brought to a laboratory at Sari Agricultural Sciences and Natural Resources University, Mazandaran province and were rapidly processed on the same day They were washed under running tap water and patted dry in an attentive manner.
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