The production of lactic acid on liquid distillery stillage by Lactobacillus rhamnosus ATCC 7469

Abstract

The production of lactic acid on a liquid distillery stillage remaining after the bioethanol production on a mixture of waste bread and waste water from the production of wheat gluten was studied in this work. The lactic acid fermentation was performed with a probiotic lactic acid bacteria Lactobacillus rhamnosus ATCC 7469. During the fermentation, parameters such as the concentration of lactic acid (according to Taylor method), the concentration of reducing sugars (spectrophotometric method according to Miller), pH, and the bacterial growth (counting method on agar plates) were followed. The optimal conditions for the production of lactic acid such as: temperature, inoculum concentration, concentration of added CaCO3 for neutralization and shaking intensity were determined. Under these conditions, a yield of over 80% of the theoretical yield was achieved. The highest intensity of the lactic acid production was noticed during the first 24 hours of fermentation, while the fermentation completely ended after 72 hours. An intensive growth of the L. rhamnosus ATCC 7469 was detected under the optimal conditions, indicating a possibility of the parallel production of lactic acid and probiotic biomass. This approach could be economically more favorable. The liquid stillage used in this study was shown as a good substrate for lactic acid fermentation.

U radu je ispitivana proizvodnja mlečne kiseline na tečnoj destilerijskoj džibri nastaloj nakon proizvodnje bioetanola iz smeše otpadnog hleba i otpadne vode iz proizvodnje glutena. Mlečno-kiselinska fermentacija je vršena pomoću probiotički aktivne bakterije Lactobacillus rhamnosus ATCC 7469. U toku fermentacije praćen je sadržaj mlečne kiseline (po metodi Taylor-a), sadržaj redukujućih šećera (spektrofotometrijski metodom po Miller-u), pH, kao i rast bakterije (brojanjem ćelija Koh-ovom metodom na agarnim pločama). Utvrđeni su optimalni uslovi za proizvodnju mlečne kiseline: temperatura, koncentracija inokuluma, koncentracija dodatog CaCO3 kao sredstva za neutralizaciju i intenzitet mešanja. Pri utvrđenim optimalnim uslovima ostvareni su prinosi od preko 80% od teorijskog prinosa mlečne kiseline u mikroaerofilnoj fermentaciji sa mešanjem. Najveći intezitet fermentacije ostvaren je u toku prvih 24 časa, a fermentacija je završena nakon 72 časa. Pri optimalnim uslovima mlečnokiselinske fermentacije uočen je intenzivan rast bakterije Lactobacillus rhamnosus ATCC 7469 što ukazuje na mogućnost paralelne proizvodnje mlečne kiseline i probiotičke biomase, čime bi se mogli postići bolji ekonomski efekti. Ispitivana džibra se pokazala kao pogodan medijum za mlečno kiselinsku fermentaciju.