Screening of Lactobacillus producers of lactic acid by fermentation of xylose.
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Lactic acid bacteria comprise several genera of miaoorganisms. among them Lactobacillus, which are capable of fermenting carbohydrates by different metabolic pathways producing only lactic acid (homofermentation) or various metabolites such as lactic acid, ethanol, CO2 and others • (heterofermentation). Studies report that Lactobacilfus is capable of fermenting xylose with significant lactic acid productin. The objective this work was selecting strains of lactic acid bacteria capable of converting lese to lactic acid. One hundred strains of lactic bacteria of the genus Lactobadllus, from the Collection of Microrganisms of lnterest from Agroindustry Tropical from Embrapa Agroindústria Tropical were studied. ·_Microorganisms were cultured in medium (pH 5.0) containing sodium acetate (lgll); MgS0 •. 6Hp (0.2g/L); MnS0 • .4H 1 0 (0.01 g/L); FeS0 • .7H 2 0 (0.01 ~ /L), NaCI (O.O 1 _g /L), yeast extract (5 g/L), peptone (5g/L) and .xylose or glucose (2 g/l) as carbon sour~e. Srxty seven bacte_na abl~ to utilize xylose as single carbon source ,were select_ed. Then, these m1Croorgamsms were cultured in med1um containing xylose as carbon source ,under shakin~ (50 rpm) a_t 35 ºC for 16 h~urs. After growth, the consumption of xylose was determined by the format,on of reducing sugar, DNS, wrth spectrophotometer (Varian; model Cary 50) at 540 nm and actic acid production was quantified by HPLC (Varian Pro Star model 355). lhe consumption of xylose ranged from 785.90 to 2386.1_4 g /L and lactic acid productiion, between 0.13 and 1. 73 g/L The results .were evaluated by Tukey test w,th 5% significance level, which allowed the choice of seven isolares which will be used in later stages of this work, due they have a higher production of latic acid.
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Ácido lácteo, Fermentação, Lactobacillus, xylose