Changes Of Flavor Components And Quality Control Of Toona Sinensis Fermented Tea During Processing

Toona sinensis(TS)is a deciduous tree of Toona in Meliaceae,which has been cultivated for more than 2,300 years.As a unique and precious woody plant in China,TS is a combination of timber,vegetable and medicine.It is worth mentioning that TS is rich in amino acids,proteins,vitamins,flavonoids,polyphenols,polysaccharides,alkaloids and other nutritional active ingredients,which have significant antioxidant,antibacterial,hypoglycemic,antihypertensive,anticancer and other edible and medicinal values.At present,as a sunrise industry in the TS industry,the TS tea processing not only improves the added value of TS and prolongs the TS industrial chain,but also promotes the healthy and sustainable development of the TS industry.However,few in-depth studies have been reported on the system of TS tea.In this research,fresh TS leaves were used as raw materials to produce TS fermented tea by withering,rolling,fermentation,drying and other related processes.The study investigated the effects of processing,exogenous enzymes and harvesting time on the quality of TS fermented tea,as well as the effects of different water qualities on the quality of tea broth,which provides a theoretical basis for further development and quality control of TS tea products.The main results are as follows:1.Effects of processing on the quality of TS fermented teaFresh TS leaves were used as raw materials to produce TS fermented tea by withering,rolling,fermentation and drying to study the changes of main biochemical components and volatile components during this processing.The results showed that the content of water extract in TS fermented tea fluctuated during the processing;the contents of tea polyphenols and thearubigins increased first and then decreased;the contents of free amino acids,caffeine and theabrownin represented an upward trend;the contents of total flavonoids and soluble sugar showed a downward trend,and theaflavins content remained basically unchanged.The volatile components changed significantly with the processing.GC-MS and GC-IMS techniques identified 114 and 43 volatile components in the samples at five different processing stages,mainly including sulfur-containing,terpenes and aldehydes.With the progress of the processing technology,the content of sulfur-containing compounds gradually decreased,and the content of terpenes and aldehydes gradually increased.After fermentation,the content of sulfur-containing compounds decreased significantly,and the content of terpenes and aldehydes increased significantly.The results of electronic nose could completely distinguish the samples in different treatment stages.Among them,the response values of sensors such as WIW(sulfide),W2W(aromatic components,organic sulfide),W1S(methyl),W2S(alcohols,aldehydes and ketones)changed dramatically,but the overall flavor was similar.Overall,the fermentation process has a great influence on the flavor substances and quality of TS fermented tea,which is the key processing step for the formation of quality TS fermented tea.2.The effects of exogenous enzymes and different harvest time on the quality of TS fermented teaIn order to improve the quality of TS fermented tea,three kinds of exogenous enzymes such as cellulase,flavourzyme and polyphenoloxidase were explored.Meanwhile,on the basis of adding exogenous enzymes,the effects of fresh TS leaves in April,May and June on the sensory evaluation,biochemical components and volatile components of TS fermented tea were studied.The results showed that different exogenous enzymes and harvest time produced dramatic different effects on the quality of TS fermented tea.The tea samples treated with cellulase had mild taste and the strongest strength,and the contents of free amino acids(13.02%),total flavonoids(4.49%),theaflavins(0.63%)and thearubigins(10.91%)were the highest.Therefore,cellulase,which significantly improved the quality of TS fermented tea,was added to the fermentation process of fresh TS leaves in April,May and June.With the extension of the harvest period,the TS flavor of TS tea was weakened and the bitterness was enhanced.The content of tea polyphenols,theaflavins,thearubigins and theabrownin showed an upward trend,and the caffeine and free amino groups showed a downward trend.After cellulase fermentation of TS leaves at different harvest times,the sweetness,black tea aroma and concentration of TS tea increased,the contents of tea polyphenols,free amino acids,total flavonoids,theaflavins,thearubigins and theabrownins increased gradually,and the content of caffeine decreased gradually.The tea samples treated with cellulase in May had mild taste and the highest strength,and the contents of water extract(43.13%),free amino acid(12.68%),thearubigins(12.3%)and total flavonoids(5.6%)were higher.A total of 100 volatile components in 10 categories were identified by GC-MS.With the prolongation of the harvest period,the contents of terpenes,alcohols and acids in TS fermented tea increased,and the contents of aldehydes and alcohols increased significantly after adding cellulase.Through the relative odor activity value(ROVA),13 volatile components,including dimethyl sulfide,β-caryophyllene,α-humulene,2-methylbutanal,(E)-2-hexenal,phenylacetaldehyde,p-methylbenzaldehyde,nonanal,4-methoxybenzaldehyde,β-ionone,2-methylnaphthalene,1-methylnaphthalene and eugenol,were selected as the characteristic flavor substances of TS fermented tea.According to the fingerprint and PCA of GC-IMS technology,it can be seen that there are significant differences in the volatile components of six kinds of TS fermented tea.In summary,exogenous enzymes and different harvest periods have significant effects on the quality of TS fermented tea.The TS fermented tea,which used the TS leaves picked in May as raw materials and was made by adding cellulase in the fermentation process,was the best.3.The effect of different water quality on the quality of TS fermented tea soupBy using tap water,purified water and natural mineral water to brew TS fermented tea,determining the physical and chemical indexes of water samples and tea infusion and by analyzing the color,main biochemical components,antioxidant activity and volatile components of tea infusion to study the effects of different types of water quality on the quality of TS fermented tea.The results showed that the Wahaha purified water with a weakly acidic pH value,a conductivity closing to 1,and a metasilicic acid content of 36.17mg/L was suitable for brewing TS fermented tea.The tea infusion had better taste coordination,and ?E was the smallest,which was 29.08.The contents of free amino acids(2739 mg/L),soluble sugars,tea polyphenols and total flavonoids in the tea infusion brewed with Wahaha purified water were as high as 2739 mg/L,727.47 mg/L,652.5 mg/L and 669.44 mg/L,respectively,indicating that pH and conductivity can affect the color and main biochemical components of tea infusion to a certain extent.The results of antioxidant activity showed that the tea soup brewed with Wahaha purified water had the strongest DPPH free radical scavenging ability and total reducing power,and the tea sample brewed with tap water had the strongest OH free radical scavenging ability.Through the analysis of flavor substances,it was found that the contents of sulfur-containing,terpenes and aldehydes were the highest in the tea infusion brewed with tap water,which were 0.087 μg/g,0.064μg/g and 0.127 μg/g,respectively.The content of aromatic flavor substances in tea infusion brewed with mineral water was the highest,which was 0.039 μg/g.