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Lactic acid (LA) is the most widely used multifunctional organic acid and approximately 50% of it is produced by biotechnological process. Immobilizing microbial cells not only improves cell retention but also protects cells from harsh environmental conditions during LA production. The objectives of this research were therefore to develop a simple method to encapsulate (immobilize) Lactobacillus reuteri for the continuous production of LA and to evaluate LA production in three different types of media using free and immobilized L. reuteri.Five strains of L. reuteri grown in lactobacillusMRS broth at 37°C for 24 h were washed in peptone water and suspended in 2% sodium alginate solution. Encapsulation of cells was performed by dripping the mixture of sodium alginate and culture into ice-cold (2°C) 0.4 M calcium chloride solution using a separator funnel. The beads were then subjected to each of 500 ml MRS, modified MRS and whey-based broth and then incubated at 37°C for 12 h. Samples were withdrawn at 2-hour intervals during incubation period and analyzed for LA as represented in pH. Results show that the developed method is a rapid and simple microbial encapsulation procedure for the continuous production of LA. The efficacy of LA production as measured in pH was not significantly different in all tested media. At the end of fermentation process, pH of whey medium containing conventional (free) and encapsulated cells reached to 4.20 and 3.85, respectively. This indicates that higher amount of acid is yielded with encapsulated cells than free cells. In addition, immobilized cell strain MM2-3 produced the highest pH (3.5) while free cell strain SD2112 produced the lowest pH (4.05). Hence, results from this study suggest that we were able to develop a simple and rapid method for the encapsulation of L. reuteri.

Apple skins generally are not used in food products and often are discarded as waste. Apple skin contains several useful nutrients particularly sugars and more complex carbohydrates. This study was undertaken to determine the feasibility of apple skin waste as a media source for the production of lactic acid (LA) using Lactobacillus reuteri. One to nine ratios (10%) of apple skin to water was boiled for 5 min and its filtrate was then added with each of following supplements, respectively; ammonium phosphate, manganese sulfate, peptone, yeast extract, and potassium phosphate monobasic and dibasic. The efficacy of apple skin filtrates with and without supplements was determined by measuring pH, glucose and lactic acid after 2, 4 and 8 h fermentation at 37°C. Moreover, apple skin filtrate was also compared with MRS broth and G-M17 broth for the efficacy of glucose utilization and LA production. At the end of 8 h incubation, pH of apple skin filtrates with peptone and yeast extract reduced from 7 to ∼4. The LA concentrations produced from the filtrates with either peptone or yeast extract supplement were the greatest ranging from 0.9 g/L to 1.9 g/L. The efficacy of LA production using apple skin filtrate was about the same as G-M17 broth. Higher amount of LA was yielded with media inoculated with immobilized (encapsulated) cells than free cell. Results also indicated that immobilized L. reuteri MM2-3 produced 40% higher amount of LA than free cell. The results obtained from this study indicate that apple skins as a carbohydrate source and immobilization of lactic acid bacteria (LAB) could be a promising method for the production of LA. Further study is necessary to identify ways to increase glucose availability and promote LAB growth and LA production.