Screening and selection of media components for lactic acid production using Plackett–Burman design

Abstract

Plackett±Burman design was used to ef®ciently select important media components in¯uencing lactic acid production in a two step screening procedure. A total of 36 screening experiments were conducted for studying the effect of various media components such as carbon and nitrogen (simple and complex) sources, minerals/buffering agents and a speci®c inducer for the production of lactic acid by Lactobacillus plantarum NCIM 2084. The eleven ingredients chosen after the ®rst screening experiments were further screened by a Plackett-Burman design consisting of 12 experiments. Lique®ed starch, wheat bran extract, ammonium nitrate, manganese sulphate and sodium acetate were chosen as promising ingredients for further optimisation studies. The highest yield of 41.9 g/l of lactic acid was obtained at the end of 24 hours of fermentation which corresponded to 90% conversion, on the basis of sugar supplied. IntroductionLactic acid ®nds application in food industry, as an additive to soft drinks and essences, in pharmaceuticals, leather and plastic industries. The fermentation route, is gaining importance in recent years in the context of rising cost of petrochemicals, and the availability of improved and better methods of fermentation. Work on the development of an ef®cient and economical process for lactic acid in our laboratory involved the optimisation of the nutritional parameters of the fermentation medium. This required the screening and selection of the media components including carbon, and nitrogen sources, minerals and trace elements etc.Screening of various nutrients by conventional single dimensional search, involves changing one independent variable, at a time while ®xing the others at a constant level which is time consuming and cumbersome. Statistical approach for the optimisation of media effectively tackles the problem which involves speci®c design of experiments which minimises the error in determining the effect of parameters and the results are achieved in an economical manner.Plackett±Burman saturated orthogonal designs [1] work at two levels, and can be constructed on the basis of fractional replication of a full factorial design. This design allows reliable short listing of a small number of ingredients for further optimisation and allows one to obtain, unbiased estimates of linear effects of all the factors with maximum accuracy for a given number of observations, the accuracy being the same for all effects [2].A number of reports are available on the effect of various carbon and nitrogen sources on lactic acid production. Molasses, whey, corn starch are some of the commonly used carbon sources while malt sprouts, malt extract, yeast extract, corn steep liquor are the nitrogenous sources used for lactic acid production. Media optimisation for lactic acid production has generally been carried out by the conventional single factor approach which is time consuming and cumbersome. The use of Plackett±Burman design for screening a large number of carbon and nitrogen sources, minerals, inducers etc, for lact...

Optimization of probiotic and lactic acid production by Lactobacillus plantarum in submerged bioreactor systems

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