Approach to preserve phenolics inThunbergia laurifolialeaves by different drying treatments

Abstract

Different drying methods and blanching were investigated as to their effects on antioxidant and oxidase activities of Thunbergia laurifolia leaves. Results showed that oven‐drying had the highest degradation of total phenolic content (TPC) and antioxidant activity at >85%, while freeze‐drying had the lowest at <20%. However, inactivation of oxidase enzymes by blanching at 100°C resulted in a lesser decrease in TPC for oven‐drying at 50 and 100°C (51% and 65%, respectively), indicating the importance of inactivating the oxidase enzymes for lower degradation of phenolics on drying. The high‐performance liquid chromatography analysis showed that its major antioxidant, rosmarinic acid, degraded tremendously in the presence of oxidase enzymes, but only degraded slightly upon inactivation of oxidase enzymes. Hence, this work showed that by controlling the enzymatic activity, the preservation of phenolics with specific bioactivity in herbal tea leaves can be achieved. Practical applications Thunbergia laurifolia leaves have been frequently consumed in the form of a tea or pill due to its medicinal properties. Processing of fresh herbal plant leaves by drying is required to preserve antioxidant phenolic compounds and quality of the plant leaves. Although the drying effects on the antioxidant properties have been studied, the factors that cause the change in properties have not been investigated in‐depth. Controlling the factors that affect the phenolic content can help to preserve the beneficial antioxidants when processing the leaves by drying. The result of this study will be of relevance and beneficial to the herbal tea industry.

Effects of processing methods on quality, antioxidant capacity, and cytotoxicity of Ginkgo biloba leaf tea product

“…However, heating will reduce the enzyme activity. 29 Amongst heatdried GBLT products, the PPO value of white tea (1.88 U g −1 d. t.) was significantly higher than that of the others, whereas an insignificant difference was found between black tea and dark and green tea. The reason may be that PPOs are easily inactivated by thermal treatment, 9 but the PPO activity of white tea can significantly increase as withering time increases, 30 causing incomplete inactivation in the subsequent drying process.…”

“…The vacuum freeze‐dried leaf product can retain enzyme activity, as the enzyme structure has been shown to preserve its integrity during freezing. However, heating will reduce the enzyme activity 29 . Amongst heat‐dried GBLT products, the PPO value of white tea (1.88 U g −1 d.t.)…”

Metabolic Engineering of Saccharomyces cerevisiae for Rosmarinic Acid Production

“…A major issue with microbial production of bioactive phenolic compounds such as RA is the degradation of these compounds in the presence of oxygen, heat, and light. , Previous electrochemical studies have shown that RA is oxidized in a pH-dependent two-step reaction, withdrawing two electrons from each aromatic ring, four electrons in total . Additionally, when produced in a cell, RA can be hydrolyzed into caffeic acid and 3,4-DHPL by the action of reversible rosmarinic acid synthase .…”