Optimization of fermentation process of date syrup by Lactobacillus delbrueckii and Lactobacillus acidophilus : Microbial growth, carbohydrate metabolism, and peptide content

Abstract

Response surface methodology was employed to investigate the combined effects of syrup concentration (10%, 20%, 30%), incubation temperature (35, 37, 39°C), fermentation time (16, 20, 24 h), and strain type (Lactobacillus delbrueckii and Lactobacillus acidophilus) on glucose and fructose content, biomass concentration and peptide content of fermented date syrup as responses. The fitted second‐order polynomial models were highly adequate to predict the responses. Fermentation temperature had a significant effect on all responses, while none of them were significantly affected by the strain type. The estimated optimal conditions of fermented date syrup for the highest biomass and peptide content were 16 h of fermentation time, 38.43°C of incubation temperature, 19.92% of syrup concentration and L. acidophilus as a starter culture. Consequently, the quadratic model was validated by applying the estimated optimum conditions, which confirmed the model validity where 4.55 g/L glucose, 2.59 g/L fructose, 4.83 biomass, and 10.30 g/L of peptide were produced. Novelty impact statement The high content of sugar, high amounts of fiber, the presence of natural antioxidants, and having functional properties, justify the industrial use of date syrup as a suitable fermentation substrate for the production of fermented food products. No study has yet been conducted to optimize the fermentation conditions (temperature and time of fermentation and sugar concentration) of date syrup. In this research, we optimized the mentioned conditions using response surface methodology to maximize lactic acid bacteria growth and increase final product functionality.