Why there is a need to adjust the pH of the mixture to 4-.5-5.5 first before proceeding to the next step of putting the yeasts? can anyone answer it please

Amino acids may be acidic amino acids, or basic amino acids, due to the R group on the amino acids. If the pH is increased, this affects the shape of proteins, by disrupting the bonds in the protein. In the case of fermentation, you say the rate increases when it get's more acidic - when the pH is lower.

b.