Lactic Acid Production from Apple Skin Waste by Immobilized Cells of Lactobacillus reuteri

Abstract

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.