Diacetyl and acetoin production by Lactobacillus casei

Area of Science:

• Microbiology
• Food Science
• Biochemistry

Background:

• Lactobacillus casei is crucial in fermented foods.
• Diacetyl and acetoin are key flavor compounds.
• Factors influencing their production require further investigation.

Purpose of the Study:

• To investigate the effects of agitation, pyruvate, and citrate on Lactobacillus casei growth and diacetyl/acetoin production.
• To determine the optimal conditions for flavor compound biosynthesis.

Main Methods:

• Culturing Lactobacillus casei under agitated and non-agitated conditions.
• Supplementing cultures with pyruvate, citrate, and sulfhydryl-protecting reagents.
• Measuring cellular dry weight, diacetyl, and acetoin concentrations.
• Assessing pyruvate conversion by isolated cells at different growth phases and pH levels.

Main Results:

• Agitation decreased dry weight but increased diacetyl and acetoin. Pyruvate addition reversed growth inhibition and enhanced production.
• Pyruvate and citrate increased dry weight without agitation; only pyruvate boosted diacetyl.
• Cells efficiently converted pyruvate to diacetyl/acetoin, especially during late logarithmic/early stationary phases and at pH 4.5-5.5.
• Citrate and acetate enhanced production in cell suspensions.

Conclusions:

• Pyruvate is essential for overcoming agitation-induced growth inhibition and maximizing diacetyl/acetoin production in Lactobacillus casei.
• Optimizing pH, growth phase, and nutrient availability (pyruvate, citrate) is key for enhanced flavor compound biosynthesis.