Comparative evaluation of growth kinetics, acidification and technological characteristics of Lactiplantibacillus plantarum NCDC25, Lacticaseibacillus rhamnosus NCDC24 and Streptococcus thermophilus NCDC293 during soymilk fermentation

Abstract:

The present study was undertaken to evaluate the growth kinetics, acidification behaviour and technological characteristics of selected cultures in soymilk fermentation with a view to identifying suitable cultures for fermented soy yoghurt manufacture. Three cultures, namely Streptococcus thermophilus NCDC293, Lactiplantibacillus plantarum NCDC25 and Lacticaseibacillus rhamnosus NCDC24, were evaluated under standardized fermentation conditions (37 ± 1°C for 12 h). Growth performance was assessed through viable cell counts, specific growth rate and generation time, while acidification behaviour was monitored by changes in pH and titratable acidity. Technological suitability was further evaluated based on acetaldehyde and exopolysaccharide (EPS) production.

All cultures exhibited active growth in soymilk, achieving final populations above 8.8 log CFU/mL. S. thermophilus NCDC293 showed the highest viable count (9.28 log CFU/mL), specific growth rate (0.312 h⁻¹) and the shortest generation time (2.22 h). The culture also demonstrated superior acidification, reducing the pH from 6.80 to 4.45 and increasing titratable acidity to 0.82% lactic acid after 12 h of fermentation. Furthermore, S. thermophilus NCDC293 produced significantly higher levels of acetaldehyde (42.50 ppm) and EPS (98.60 mg/L) compared with the probiotic cultures. L. plantarum NCDC25 exhibited intermediate performance, whereas L. rhamnosus NCDC24 showed comparatively lower but acceptable technological characteristics. Comparative evaluation using normalized technological performance scores confirmed the superior overall performance of S. thermophilus NCDC293.

The results indicate that S. thermophilus NCDC293 is the most suitable starter culture for fermented soy yoghurt manufacture, while L. plantarum NCDC25 and L. rhamnosus NCDC24 may be employed as probiotic adjunct cultures to enhance the functional value of fermented soy products.