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Pomelo (Citrus grandis (L.) Osbeck) is an important cultivar of the Citrus genus, which contains a number of nutrients advantageous to human health. Non-edible parts of pomelo consist of flavedo, albedo, lamella and waste obtained from juice extraction (pulp waste). The peels are also thought to be part of waste products, which generally being discarded. Therefore, the objective of the present study was to evaluate changes in total phenolic contents (TPC) and antioxidant activity of processed pomelo peels after oven drying (50 and 60 °C) and freeze drying treatments in comparison with fresh pomelo peels. A slightly different (4%-6%) in TPC was observed in oven dried pomelo peels in comparison with fresh peels, indicating that there was a slightly effect of post-drying methods on retaining the antioxidant potential of these natural byproducts. In vitro assays revealed that post-drying methods involved oven drying exerted a higher TPC compared to freeze drying in overall parts of pomelo byproducts. Highest retention of bioactive compounds was found in fresh pomelo peels (437-1876 mg GAE/100 g DM), followed by oven dried at 50 and 60 °C (892-1336 mg GAE/100 g DM), and freeze dried (555-1267 mg GAE/100 g DM). In terms of oven dried pomelo byproducts, the highest TPC was retained in albedo (1337 mg GAE/100 g DW), followed by flavedo (1226 mg GAE/100 g DW), lamella (998 mg GAE/100 g DW) and pulp waste (962 mg GAE/100 g DW) respectively. Therefore, oven drying was the most suitable post-drying method to retain the bioactive compounds for pomelo byproducts. This knowledge may inspire consumer or pomelo industry operators to re-evaluate their byproducts, reduce the waste and expand the application of pomelo fruits.

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Background: Coconut sugar has a caramel color with a taste like brown sugar. It is commonly used as natural sweetener. However, coconut sugar has been produced from coconut sap using a traditional method that involves heating the sap at high temperature (>100 °C) in an open pan for a long period (3-5 h). This conventional method results in an over-cooked sugar, which leads to quality deterioration in terms of both its physical and chemical properties. The current study aimed to investigate the processing of coconut sap into sugar syrup using alternative processing techniques such as rotary vacuum evaporation (RE) and microwave evaporation (ME), comparing them with open-heat evaporation (OHE) technique. Results: Coconut sugar syrup produced by rotary evaporation at 60 °C and 250 mbar vacuum (RE-60) required the shortest production time (12.2 min) and the lowest processing temperature (54.8 °C) when compared with ME (13 min and 103.2 °C) and OHE (46.8 min and 101.6 °C). It also had a light brownish color with a higher L* value (35.17) than the ME (29.84) and OHE (23.84) methods.It was found to contain higher amounts of monosaccharides (fructose and glucose) and lower amounts of disaccharides (sucrose). Furthermore, the amount of energy required for RE-60 (0.35 kWh) was much less than for OHE (0.83 kWh). Conclusion: This study provided an alternative processing method for the sugar processing industry to produce coconut sugar using the rotary evaporation method at 60 °C under 250 mbar vacuum with better physicochemical qualities, shorter processing time, and minimum input energy.