Enzymes are key proteins that catalyze biochemical reactions in microorganisms, and their activity is significantly affected by environmental pH. Each enzyme has a specific optimal pH range, in which the enzyme maintains the highest catalytic activity. When the environmental pH deviates from the optimal range, enzyme activity decreases gradually and may even be completely inactivated. This blocks the biochemical metabolic processes of microorganisms, inhibits the absorption and utilization of nutrients, and ultimately reduces seed quality.
Changes in pH can also induce shifts in microbial metabolic pathways. For example, under acidic conditions, some microorganisms activate the lactic acid fermentation pathway to maintain intracellular pH homeostasis, which alters the type and proportion of microbial metabolites and indirectly affects seed quality.
pH can change the charge state of microbial cell membranes, thereby regulating membrane permeability. As the core channel for material exchange between microorganisms and the external environment, the cell membrane’s permeability directly affects the efficiency of nutrient uptake and metabolic waste excretion. Extreme pH conditions can destroy the complete structure of cell membranes, leading to the leakage of intracellular substances and the invasion of external harmful substances, disrupting normal cellular physiological functions and inhibiting microbial growth and metabolism.
The dissociation degree of nutrients such as amino acids and minerals in the medium varies with pH changes, which directly affects the absorption and utilization efficiency of nutrients by microorganisms.
In mixed microbial culture systems, different strains have distinct nutrient utilization capabilities. pH fluctuations can alter the nutrient competition relationship among strains, thereby affecting the growth and reproduction of dominant microflora.
Non-optimal pH conditions will slow down or even stagnate microbial growth, hinder microbial biomass accumulation, and restrict the improvement of seed quality. Long-term exposure to inappropriate pH conditions may cause microbial genetic variations such as gene mutation and gene recombination, damaging the genetic stability of seeds and the stability of subsequent fermentation production. A suitable pH environment can enhance the stress resistance of microorganisms (such as antioxidant and anti-osmotic capabilities), help them adapt to complex production environments, and maintain stable growth and metabolism.
1. Anion absorption and nitrogen metabolism: The absorption and utilization of anions such as acetate and phosphate in the medium, or the production of ammonia (NH₃) during nitrogen source metabolism, will increase the system pH.
2. Cation absorption and organic acid accumulation: The absorption of cations such as ammonium (NH₄⁺) and potassium (K⁺) by microorganisms, or the continuous accumulation of organic acids in the system, will decrease the system pH.
3. Effect of C/N ratio: The pH of high-carbon medium decreases during fermentation, while the pH of high-nitrogen medium increases during fermentation.
a. Acid-base solution regulation: Directly adjust pH by adding acid or base solutions;
b. Buffer solution regulation: Use a buffer system to maintain medium pH stability and reduce pH fluctuation;
c. Physiological buffer regulation: Add physiologically acidic or alkaline salts to realize long-term pH steady-state regulation through microbial metabolism.