Kinetics and modeling of growth and lactic acid production in Gundruk, a Himalayan fermented vegetable dish

Gundruk is a fermented green leafy vegetable product prepared from fresh leaves of local vegetables called Rayo-sag (Brassica campestris), mustard (Brassica juncea), and cauliflower (Brassica oleracea) indigenous to the Nepali people. Fresh gundruk was prepared in a glass jar by fermenting the Brassica juncea leaves anaerobically for 16 days and the changes in biomass, lactic acid, and pH were evaluated after every 24 hr. The viable cell count increased from 6.03 × 10⁴ cfu/g to 9.55 × 10⁸ cfu/g after 3 days and then decreased gradually to remain constant after 8 days with 6.31 × 10⁷ cfu/g until the end of fermentation. The lactic acid increased by about 12.58 times in 12 days and remained constant for the rest of the fermentation period. Unlike this, pH decreased from 6.59 to 3.71 on the 9th day of fermentation and then increased slightly till the last day of fermentation. The data obtained were fitted to two most widely accepted microbial growth models: Modified Gompertz, and Logistic model and three well-known lactic acid production models: Luedeking- Piret, Monteagudo et al., and Balannec et al. model for lactic acid fermentation. Based on nonlinear regression analysis, Modified Gompertz, and Monteagudo et al. model gave a better fit to describe microbial growth and lactic acid production, respectively. The growth-associated and non-growth-associated coefficients were determined to be 0.1104 and 0.0042, respectively, using Monteagudo et al. model. The findings revealed that lactic acid production in gundruk is a mixed type.