Unveiling the Impact of Infrared Drying on the Quality of Coffee Leaves: A Comprehensive Analysis of Physicochemical Indices, Antioxidant Potential, Maillard Reaction Products, and Aroma Profile

Coffee leaves, known for their health-promoting phytochemicals, have emerged as a potential functional tea ingredient. However, the effect of infrared drying (IFD) on its properties and sensory quality remains unexplored, limiting its industrial utilization. This study systematically elucidated the impact of IFD on drying kinetics, chemical compositions, Maillard reaction products (MRPs), flavor formation, and sensory characteristics of coffee leaves. IFD significantly reduced drying time by more than 50% and decreased protein loss by more than 5.79% compared to hot-air drying, while increasing total phenolic content (27.86% increase at 1300 W) and antioxidant activity (more than 50% increase). However, IFD resulted in higher levels of 5-hydroxymethylfurfural and α-dicarbonyl intermediates (glyoxal and methylglyoxal) compared to freeze-drying. Volatile analysis using HS-SPME-GC-MS revealed distinct aroma profiles: freeze-dried leaves showed a grassy aroma primarily characterized by hexanal, whereas IFD generated a more fruity-floral aroma with elevated levels of (E)-2-hexen-1-ol, octanal, and thermally derived pyrazine/pyridine. Key flavor markers such as 2,3-pentanedione and 6-methyl-5-hepten-2-one were uniquely elevated in IFD blades. The sensory evaluation confirmed that IFD-processed tea leaves received a score of 71.18 ± 3.04 and were characterized by a black tea-like flavor with caramel and fermented undertones. These findings suggest IFD as a time- and energy-efficient method to produce coffee leaf tea with dual advantages: (1) enhanced retention of bioactive compounds and (2) targeted generation of consumer-desired sensory attributes through controlled MRPs. These findings establish a scientific basis for scaling up IFD processing, offering the tea industry a sustainable approach to valorizing coffee leaves into value-added functional products. Practical Application Infrared drying offers coffee leaf tea producers a faster, energy-saving method to create flavorful functional teas. It enhances antioxidant activity while developing appealing caramel and fruity notes similar to black tea, providing consumers with a nutritious beverage option. This technique enables sustainable upcycling of coffee leaves into premium tea products with consistent quality for commercial markets.