Study On The Effect Of Tea Processing On The Chemical Components And Bioactivities In Coffee Leaves

Coffee leaves are the by-products of coffee plants produced when trimming the twigs.In recent years,coffee leaf tea is considered as a novel healthy beverage that is equivalent to coffee and the traditional tea made of the leaves of Camellia sinensis and getting more and more attention due to its rich in bioactive components that are beneficial for human health.Compared with the tea and coffee beans that have been extensively studied,the researches related to coffee leaf tea are still scarce,which limits the production of high-quality coffee leaf tea.In the present study,firstly,the effects of withering and fermentation conditions on the chemical composition and antioxidant activity of coffee leaves were investigated.Secondly,the change patterns of the proximate compositions,total phenols,phytochemicals,and biological activities in coffee leaves during the processing using two tea processing methods were studied and the main differences between the coffee leaf teas prepared by these two processing methods were compared.Finally,the volatile flavor compounds in coffee leaf tea were identified and the influence of the processing steps on these flavor compounds was explored.The main differentiated volatile components in these two coffee leaf teas were compared,color and sensory analyses were performed to evaluate the differences between them.The major findings are as follows:(1)Appropriately increasing the environmental temperature and relative humidity during withering can increase the amino acids and protein content in coffee leaves,but the increased temperature caused the decreases of total phenol content(TPC)and antioxidant activity.The increase in relative humidity helped retain the TPC and chlorogenic acids.The enhanced fermentation temperature and relative humidity accelerated the degradation of phenolic compounds,thus reduced the antioxidant activity.When the withered coffee leaves underwent fermentation after the kill-green process,the TPC was decreased faster under the higher temperature and relative humidity condition,indicating that the polyphenol oxidase(PPO)activity was not completely inactivated by kill-green process.(2)Two processing methods were used to process coffee leaves and the procedures included(1)fresh leaves(S0)? withering(S1)? kill-green(S2-K)?rolling(S3-K)? fermentation(S4-K)? drying(S5-K);(2)fresh leaves(S0)?withering(S1)? rolling(S3-NK)? fermentation(S4-NK)? drying(S5-NK).The proximate compositions,phytochemicals,the activities of PPO,peroxidase(POD),and ?-glucosidase(?-Glu),and antioxidant and anti-inflammatory activities in each tea processing steps were investigated.The results showed that the processing method significantly affected the phytochemical composition,free phenol content(FPC),and antioxidant and anti-inflammatory activities of coffee leaves.The FPC,mangiferin,rutin,and chlorogenic acids in coffee leaves decreased during the processing,thereby reducing the ability to inhibit DPPH and ABTS free radicals.It was found that the kill-green process was critical to reteain the phenolic compounds and antioxidant activity in coffee leaves.The phenolics and antioxidant activity of the coffee leaves with the kill-green process were significantly higher than that of the coffee leaves without the kill-green,whereas,the impacts on the activities of PPO,POD,and ?-Glu vice versa.Coffee leaf extract significantly inhibited various inflammatory mediators,including nitric oxide(NO),tumor necrosis factor-alpha(TNF-?),prostaglandin E2(PGE-2),inducible nitric oxide synthase(i NOS),and cyclooxygenase-2(COX-2)in lipopolysaccharide(LPS)induced Raw 264.7 cells.The NO inhibitory activity of coffee leaf extract was first increased when the leaves underwent wethering and kill-green processes followed by a decrease in the leaves that were treated by the sequential steps,including rolling,fermentation,and drying.The temporal pattern for the TNF-? inhibitory activity was different from that of NO inhibitory activity.The effects of processing steps on the inhibitory capacities on the PGE-2 production and i NOS and COX-2 gene expressions of coffee leaf extract were not significant.(3)The 53 volatile compounds,mainly alcohols,aldehydes,and hydrocarbons were identified in coffee leaves using HS-SPME-GC-MS.The results showed that the volatile components changed the least during the withering period and D-limonene and myrcene were the only two volatiles that was changed significantly compared with the fresh coffee leaves.The volatile compounds of coffee leaves were mainly produced during the fermentation and drying periods.There were 12 significantly differentiated volatile components,including pentadecaldehyde,linalool,?-farnesene,2-hexenal,salicylic acid,Methyl acid,2,4-heptadienal,phenethyl alcohol,plant alcohol,2-pentylfuran,2,4-hexadienal,n-tetradecane,and geranyl acetone were identified when compared the two dry coffee leaves(S5-K vs S5-NK).The changes in the colors of coffee leaves and their hot water diffusion were mainly affected by the the kill-green,rolling and drying processes and the hot water infusion of coffee leaf tea without the kill-green process was darker in color.The sensory analysis results indicated that the taste of the coffee leaf tea without kill-green was better than that of with kill-green step.Coffee leaf tea without the kill-green process has a milder taste and the smell is closer to the fragrance of tea.On the contrary,the coffee leaf tea with the kill-green processed has a bitter and lighter taste.