Effect of drying methods and parameters on the antioxidant properties of tea (Camellia sinensis) leaves

Abstract

Background: Conventional drying using heated air oven is commonly used as a method for preserving the product but often affects the nutritional value, taste, and texture. However, the heat from the drying method can oxidize and destroy heat-sensitive compounds. Superheated steam (SHS) drying uses superheated steam instead of hot air or combustion gases in a direct dryer and was reported better at preserving the nutritional values of food products. Aim: To evaluate the effect of SHS drying on antioxidant properties of tea leaves. The study also compared SHS drying with conventional and freeze-drying methods. Results: Tea leaves dried using freeze drying retained the highest level of antioxidant properties compared to other drying methods. The leaves dried using SHS exhibited significantly higher radical scavenging activity, ORAC and FRAP values compared to oven drying method. At different drying temperatures (150°C and 175°C), oven dried leaves showed significantly higher (p < 0.05) antioxidant properties than that of SHS dried ones. Tea leaves dried for 60, 75, and 90 min using SHS showed significantly higher (p < 0.05) FRAP and ORAC values, and also total phenolic content compared to oven dried tea leaves. Conclusion: Tea leaves dried using SHS drying method retained higher level of antioxidant properties compared to oven drying. The drying method also retained lower antioxidant properties as drying time increased. Further study involving SHS drying in food-related fields should be conducted to support its usefulness.

Unfermented Freeze-Dried Leaf Extract of Tongkat Ali (Eurycoma longifolia Jack.) Induced Cytotoxicity and Apoptosis in MDA-MB-231 and MCF-7 Breast Cancer Cell Lines

“…The primary structure of dried leaves was preserved during drying due to the developed frozen water molecules or ice crystal within the leaf tissue matrix has lower movement compared to its liquid form [ 31 ]. This present finding was in agreement with a recent study by Roslan et al [ 32 ], as the freeze-dried leaves of Camellia sinensis or authentic tea showed the highest phenolics, flavonoids, and antioxidant activity compared to superheated steam and oven drying techniques.…”

Hop Leaves as an Alternative Source of Health-Active Compounds: Effect of Genotype and Drying Conditions

“…Regarding treatments, on average, OD samples showed significantly lower TPC than FD ones (−82%), as also observed in the literature data on different plant matrices [ 47 , 48 ]. Among FD samples, Chinook showed the highest TPC (V1; 39 ± 1 mg GAE g −1 ), followed by Columbus (V4; 35.9 ± 0.8 mg GAE g −1 ) and Cascade (V5; 28.9 ± 0.2 mg GAE g −1 ).…”

Determination of Moisture, Ash, Protein, Polyphenolic, Flavonoids, and Amino Acid Contents and Antioxidant Capacity of Dried Mekai (Pycnarrhena tumefacta Miers) Leaf as Potential Herbal Flavor Enhancers

“…However, oven drying showed a detrimental effect on retaining phenolic and flavonoids content when drying at higher temperature (> 100 °C). Therefore, it is better to limit the oven drying temperature to not more than 100 °C as observed in a tea product [11].…”

“…Regarding the preparation of dried Mekai, gas and electric drying can be utilized as the technologies are readily available in the market. Furthermore, the drying method may play a role in the active substance and amino acid contents of Mekai leaf, as indicated from research with other leaves [10,11]. Therefore, this research aims to characterize moisture, ash, protein, polyphenolic, flavonoids, amino acid contents, and the antioxidant capacity of Mekai leaves dried with sun exposure, gas, and electric oven at various temperatures and times.…”