RESUMO
Lactic acid (LA) is used in food, cosmetic, chemical, and pharmaceutical industries and has recently attracted much attention in the production of biodegradable polymers. The expensive substances including carbon and nitrogen sources involved in its fermentative synthesis and the increasing market demand of LA have prompted scientists to look for inexpensive raw materials from which it can be produced. This research was aimed at determining the optimum conditions of lactic acid (LA) production from pineapple by-products and an inexpensive nitrogen source using Lactiplantibacillus plantarum strain 4O8. After collection and preparation of the carbon source (pineapple by-products) and nitrogen sources (by-products from fish, chicken, and beer brewing industries), they were used for the formulation of 4 different media in terms of nitrogen sources. Then, the proximate compositions of promising nitrogen sources were determined. This was followed by the screening of factors (temperature, carbon source, nitrogen source, MgSO4, MnSO4, FeSO4, KH2PO4, and KHPO4) influencing the production of LA using the definitive plan. Lastly, the optimization process was done using the central composite design. The highest LA productions (14.64 ± 0.05 g/l and 13.4 ± 0.02 g/l) were obtained in production medium supplemented with chicken and fish by-products, respectively, making them the most promising sources of nitrogen. The proximate analysis of these nitrogen sources revealed that their protein contents were 83.00 ± 1.41% DM and 74.00 ± 1.41% DM for chicken by-products and fish by-products, respectively. Concerning the screening of factors, temperature, nitrogen source, and carbon source were the factors that showed a major impact on LA production in the production medium containing chicken by-products as nitrogen source. A pineapple by-product concentration of 141.75 g/l, a nitrogen source volume of 108.99 ml/l, and a temperature of 30.89°C were recorded as the optimum conditions for LA production. The optimization led to a 2.73-fold increase in LA production when compared with the production medium without nitrogen source. According to these results, chicken by-products are a promising and an inexpensive nitrogen source that can be an alternative to yeast extract in lactic acid production.
RESUMO
The present work was aimed at studying the technological properties of lactobacilli isolated from four tropical fruits (banana, papaya, pineapple, and orange) sold in Dschang (a city of the Menoua Division, West-Cameroon), as well as their ability to produce lactic acid (LA) from by-products of these fruits. After isolation and preliminary identification, homofermentative isolates were investigated for acidifying, amylolytic, cellulolytic activities as well as exopolysaccharides production. The chemical composition of the by-products was determined prior to fermentation assays and the most promising isolates were identified by 16S rRNA gene sequencing. From the 54 homofermentative lactobacilli obtained, 9 isolates were pre-selected based on their higher acidifying activity in MRS-Glucose medium. They all showed amylolytic activity, with the most important activity (54.26 ± 0.10 µg of reducing sugar/ml/min) recorded by isolate O31. Relatively to their cellulolytic activity, isolate 1B9 showed the best activity, displaying a production rate of 7.98 ± 0.40 µg glucose/ml/min, while none of them produced exopolysaccharides. The proximate analysis showed that the fruit-derived by-products contained proteins (0.40 ± 0.06% DM to 1.54 ± 0.06% DM), carbohydrates (61.75 ± 0.75% DM to 71.94 ± 2.02% DM) that are main nutrient needs for bacterial growth. Banana-derived and pineapple-derived by-products showed the highest LA production rates with values, 26.37 ± 0.05 g/l (isolate 3A5) and 26.29 ± 0.38 g/l (isolate 1B9) respectively after 16 h of fermentation. Based on the principal component analysis, isolates O31, 1B9, 3A5, 3A9 and 4O8 were selected as the most promising isolates and were identified as Lactobacillus plantarum strains. According to the obtained results, lactobacilli from tropical fruits displayed properties of commerical interest and can be promising candidates in the valorisation of by-products from tropical fruits through LA production.
