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Production of lactic acid from stillage in production of bioethanol

Olga Pantić

Regional center for talented youth Belgrade II, opantic@rocketmail.com
higher than the yield obtained with the triticale stillage.(2,3)
Figure 1. (A) (B)
Introduction

Lactic acid is a very significant compound used as an acidifier, a
conservanse, an antimicrobial substance, or a monomer during
production of polilactates for the food, pharmaceutical and
cosmetic industry. Because of its traits for the last two decades
there is a growing need for lactic acid and its derivates.
Nowadays, natural renewable and waste compounds from
agricultural industry are investigated as sources for production of
lactic acid in labortaory conditions, which contributes to the
solution of factory waste problem, as well as reduction of CO 2 in
the atmosphere. Stillage as a waste product of bioethanol
production is a cheap raw material, rich in protein and organic
matter that is suitable for growth and development of lactic acid
bacteria and fermentation. The aim of this study was to investigate
the usage of waste stillage as a substrate for bacterial growth and
the production of lactic acid, and its productivity without the pH
value control.
Figure 1. The number of formed colonies (A) and the change of
sugar concentration (B) during 48h.
Study methods (I – initial value, O - outermost value)

Conclusion
Lactic acid fermentation was executed using Lactobacillus
rhamnosus ATCC 7469 stock in a batch process with 100ml of A large number of formed bacterial colonies in fermentation
axenic stillage for the production of bioethanol on waste bread medium and a high yield coefficient of 0,93g/g indicate that this
(Reahem d.o.o., Srvovran Serbia) with an addition of axenic waste stillage is suitable for production of lactic acid. The leftover
50%(w/v) solution of glucose. The stock was cultivated on stillage can be returned in the process or used as livestock food,
nutritious MRS Agar at 37°C, microaerophilically, without the pH because L. rhamnosus ATCC 7469 is a probiotic stock. Liquid
value control. Bacterial growth was followed using a series of stillage, as one of the newest raw material for producing lactic
delutions in 0.9% NaCl. The concentration of reducing sugars in acid, is giving promising results and additional tests will be
the waste stillage and fermentation medium was determined required for characterizing fermentation and targeted yield.
spectrofotometrically at 505nm, after centrifugation (12000
rot/min, 15 min), with 3.5.-dinitrosalicylic acid as a substrate (1).
The measurement included initial sugars in the waste stillage and Literature
sugars that the bacteria were using as food in the fermentation
medium. The amount of produced lactic acid was measured with (1) - Miller G.L., 1959. Use of dinitrosalycilic acid for
acid-base titration with 0.1M NaOH, and 1% phenolphthalein was determining reducing sugars. Anal. Chem. 31, 426–428.
used as an indicator. (2) - L. Mojović, M. Vukašinović Sekulić, A. Đukić, Production
of lactic acid on liquid distillery stillage, Journal on processing
and energy in agriculture (former PTEP), (2011) 15(1)1-5.
Results and discussion (3) - M. Marković, S. Markov, O. Grujić, L. Mojović, (2014) The
applicability of triticale for bioethanol and lactic acid fermentation
as the part of a sustainable development, Biochemical
In this study 18,9 g/L of lactic acid was generated. Without an Engineering Journal, 85, 132-8
addition of a source of nitrogen or mineral, a productivity of
0,388g/Lh was accomplished. At the end of fermentation there
were 4,12×109 CFU/mL. The stillage as a fermentation medium
doesn't contain enough sugar, therefore an addition of glucose was
needed, but it is rich in protein which makes more than 50% of
dry matter and is suitable for microorganism growth. The waste
stillage doesn't have any metals which would interfere with the
process of fermentation. The yield obtained in this study was very
similar to the yield obtained with the use of corn stillage, and