Production of organic acids from local raw materials.

Abstract

The liquid pineapple wastes from pineapple cannery industries contain mainly sucrose, glucose, fructose and other nutrients. Lactic acid, a normal organic acid, has long been of use in the pharmaceutical, chemical, cosmetic and food industry. Recently, lactic acid has been considered as an important raw material for production of biodegradable lactide polymer. The objective of this project is to study the feasibility of lactic acid production from liquid pineapple waste as a substrate using Lactobacillus delbrueckii. Batch fermentation of pineapple waste was studied in a 3-litre stirred fermenter (Biostat B Model). In order to know the physical and chemical properties of liquid pineapple waste, characterisation study was carried out. During the fermentation process, 0.5 ml sample was withdrawn from the fermentation broth at regular time intervals in order to measure the variation of sugar concentration, lactic acid concentration, pH and biomass with fermentation time. The microbial cells were separated by centrifugation for dry biomass determination. The supernatant was immediately frozen for further determination of the concentrations of lactic acid, glucose, fructose and sucrose. Effects of some parameters such as temperature, pH, inoculum size, substrate concentrations and nitrogen source were studied. Mathematical modelling and kinetic parameters estimation as a function of pH and inoculum size were also studied. By using the concept of material balance, an unstructured model based on a Monod type kinetic equation for cell growth, substrate utilisation and product formation were developed. During fermentation, the concentrations of the substrate, product and cell were measured. The data were used for the estimation of kinetic parameters in the differential equation for the balance of the substrate, cell and product by computer program. To obtain the best fitting, a nonlinear regression analysis combined with a Runge-Kutta method was used. The standard deviation and standard error between the measured and calculated concentrations of lactic acid are used as statistical criterion for testing the adequacy of the model. Optimisation studies were also carried out for selected parameters in the Erlenmeyer flask containing 100 ml of production medium. CaCO3 (3% w/v) was added to control the pH in the shake flask fermentation. A fractional factorial central composite design (FFCCD) was used to determine the optimum values of the process variables such as temperature, speed, concentration of yeast extract, concentration of substrate and the time by the response surface methodology (RSM) for obtaining the maximum yield of lactic acid. The result of the second order response surface model fitting was tested for adequacy by the analysis of variance. The optimal values of tested variables for maximal lactic acid production were found to be: temperature 40°C, speed 50 rpm, yeast extract 10 g/l, sugar concentration 52.5 g/l and time 7 iv days. A techno-economic evaluation of the process understudy showed that the utilisation of pineapple waste as substrate for lactic acid production using lactobacillus delbruekii is feasible process even though its profitability is lower than molasses and wheat flour. This is due to the fact that the yield obtained from this study was only 79 % compared to industrial yield is about 97 %. Therefore, increasing the yield through continuous or fed-batch fermentation couple with immobilised cells could enhance the profitability of the process.