Changes in chemical composition and biological activity of essential oil from Thomson navel orange (Citrus sinensis L. Osbeck) peel under freezing, convective, vacuum, and microwave drying methods

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.

Evaluation of dynamic changes in the bioactive components in Citri Reticulatae Pericarpium (Citrus reticulata ‘Chachi’) under different harvesting and drying conditions

“…24,25 Previous studies have revealed that antioxidants may undergo thermal degradation at high temperature, reflected by a change in the phenolic acid content of natural products. 26,27 In this study, oven drying and sun drying did not cause any significant change in TPC of CRCP, which suggests that the phenolic acids in CRCP were not easily damaged below 60°C, but may be degraded at higher temperature.…”

Ultrasound freeze-thawing style pretreatment to improve the efficiency of the vacuum freeze-drying of okra (Abelmoschus esculentus (L.) Moench) and the quality characteristics of the dried product

“…Although the okra quality was deteriorated by the vacuum freeze-drying, it was still better than the heat dried sample. A study on orange drying methods showed that oranges have the highest TPC content after freeze drying [37] . A study of concentrated broccoli showed that the freezing process can maximize the retention of total phenol content [38] .…”

The Chemical Compositions, and Antibacterial and Antioxidant Activities of Four Types of Citrus Essential Oils

“…Yi et al [ 19 ] reported the DPPH and ABTS radical-scavenging activity of cold pressed NMEO with IC 50 values of 22.60 and 1.62 mg/mL, respectively, which are higher values than for our hydrodistilled NMEO (15.20 and 0.80 mg/mL, respectively). Farahmandfar et al [ 40 ] evaluated the DPPH radical scavenging activities of Thomson navel orange peel EOs and found that the IC 50 value of fresh peel EO was 7.86 mg/mL. The much higher IC 50 value (29.70 mg/mL) of PDEO might be attributable to a different maturity stage and variety.…”