Abstract
A simple and sensitive method was developed for the determination of protease A activity (PAA) using the resonance light scattering (RLS) technique. The PAA was measured by a spectrofluorimeter (468 nm, 40 °C, pH 3.0). This method was rapid and convenient with low detection limit of detection (0.662 µg/ml), wide linear range (1–500 µg/ml), and long-term stability (at least 150 min). Using the established RLS method, impact factors of proteinase A secretion were investigated from the angle of yeast strains, physiological state, the generation time (GT), yeast vitality (VT) and yeast mortality. The results showed that there were great differences among the PAA from different yeast strains. For the yeast in the stationary stage, the PAA ascended significantly. The PAA in the yeast with long GT was larger than that with short GT. Early in the fermentation process, the yeast did not secrete proteinase A, but during the final fermentation process, the PAA increased gradually. Meanwhile, The PAA was proportional to yeast mortality, and inversely proportional to yeast VT. Therefore, it is important to select a favorable yeast strains with a shorter GT, higher VT, and lower mortality to produce beers with good foam performance.
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