Effects of drying on physical properties, phenolic compounds and antioxidant capacity of Robusta wet coffee pulp (Coffea canephora)

Thy Minh Kieu Tran; Timothy Kirkman; Minh Nguyen; Quan Van Vuong

doi:10.1016/j.heliyon.2020.e04498

Effects of drying on physical properties, phenolic compounds and antioxidant capacity of Robusta wet coffee pulp (Coffea canephora)

Heliyon. 2020 Jul 21;6(7):e04498. doi: 10.1016/j.heliyon.2020.e04498. eCollection 2020 Jul.

Authors

Thy Minh Kieu Tran^{1

2}, Timothy Kirkman¹, Minh Nguyen^{1

3}, Quan Van Vuong¹

Affiliations

¹ School of Environmental and Life Sciences, Faculty of Science and Information Technology, University of Newcastle, Ourimbah, New South Wales, Australia.
² School of Post-harvest Technology, Faculty of Agriculture and Forest, Tay Nguyen University, Buon Ma Thuot, Dak Lak, Viet Nam.
³ School of Science and Health, Western Sydney University, Penrith, NSW, 2751, Australia.

Abstract

Wet coffee pulp (WCP), produced as waste from coffee production, is a rich source of bioactive compounds, especially caffeine and chlorogenic acid. However, it contains high moisture content, thus it is challenging for further utilization due to degradation and microbial deterioration. Dehydration is, therefore, necessary to minimize degradation and ease storage and transportation. As a waste, the common drying methods should be prioritized to be feasible for industrial application. This study aimed to determine the impact of different drying conditions of the three common drying methods including low temperature and pressure, vacuum and hot air drying on physical, phytochemical and antioxidant properties of WCP to identify the most suitable drying conditions. Browning index, moisture content, total phenolic content (TPC), flavonoids (TFC), proanthocyanidins, and chlorogenic acid as well as the antioxidant properties of the dried coffee pulp were significantly influenced by different tested conditions. Vacuum drying was found to be more suitable for drying the wet coffee pulp as compared to low temperature and pressure and hot air drying methods. Vacuum drying at 110 °C retained the highest TPC (14.4 mg gallic acid equivalents (GAE)/g dry weight (DW)), proanthocyanidins (6.8 mg catechin equivalents (CE)/g DW), TFC (13.2 CE/g DW), caffeine (2.9 mg/g DW) and antioxidant capacity. Chlorogenic acid (3.4 mg/g DW) was 13% lower, but energy consumption was 37% less than vacuum drying at 90 °C. Therefore, vacuum drying (3.75 mmHg) at 110 °C for 4h 05 min was suggested for dehydration of the wet coffee pulp for subsequent recovery and processing.

Keywords: Antioxidant capacity; Bioactive compounds; Coffea canephora; Coffee by-products; Coffee pulp; Food analysis; Food science; Robusta.