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360 PROCEEDINGS OF INTERNATIONAL SCIENTIFIC CONFERENCE ON APPLIED BIOTECHNOLOGY2.3.2. Total acid contentThe total acid content is determined according to the TCVN 4598:88 method. The extract solution and distilled water are pipetted into a 50 ml conical flask at a ratio of 1 ml of distilled water to 9 ml of the sample. Next, 2-3 drops of 1% phenolphthalein indicator are added to the mixture. 0.1N NaOH solution is added drop by drop by a pipette to the diluted sample until it turns a light pink colour that remains stable for 30 seconds. The total acid content is then calculated using the appropriate formula.Wher: V = Volume of titre of 0.1N NaOH (ml), v = Volume of solution pipetted for titration (ml), K = conversion factor for calculating the corresponding acid type (specific to the acid being measured)2.3.3. Total phenolic contentTotal phenolic contents%u2019 measurement is adapted from the method developed by Md. Afroz Bakht et.al in 2019 [5] (pp. 1043%u20131052). 10 grams of the tea are added to 200 mL of 80% methanol solution and subjected to ultrasonic treatment at a frequency of 40 kHz at 40%u00b0C for 30 minutes; each sample is extracted three times. Then, 1 gram of the extract is mixed with 10 mL of methanol 80%, 7.5 mL of distilled water, 0.5 mL of Folin-Ciocalteu reagent, and 1.5 mL of 20% Na2CO3 solution. The mixture is incubated in the dark for 30 minutes at room temperature. The absorbance is measured at a wavelength of 755 nm, and the total phenolic content is calculated based on the gallic acid standard equation.2.3.4. Mold and yeast countThe method for culturing and determining the total mold and yeast count follows AOAC 997.02. This method uses Potato