Although juice content is important when assessing the quality of juice drink, there are no published methods to determine it, particularly simple ones for routine inspection of juice drinks. Buffering coefficient is one of the characteristic index of fruit juice, which has a linear relationship with juice content. However, if there are differences between different varieties of the same fruit and if there are some ingredient closely related to buffering capacity is not clear. The buffering coefficient, ash and nitrogen in four citrus cultivars, Nanfen, Shatang, Huangdi, and Qicheng were detected. Citric acid was added to pure citrus dilutions in distilled water containing 100%, 80%, 60%, 40%, 20% citrus juice. The pH of the dilutions was measured to obtain a linear model for the molar H+ concentration as a function of the added citric acid (g/L) amount. The slope was conducted and defined as buffering coefficient. Nitrogen content was detected by using kjeldahl method and ash content was detected by using ashing method. Results show that the buffering coefficient has binary linear regression relationship with nitrogen and ash. The relationship can be expressed as, buffering coefficient = 50.83N +2088A+2331, where N is nitrogen content in unit of mg/100 g and A is ash content in unit of mg/g.
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