L (+)-lactic acid production by pellet-form Rhizopus oryzae NRRL 395 on biodiesel crude glycerol

Abstract

Background: Given its availability and low price, glycerol derived from biodiesel industry has become an ideal feedstock for the production of fuels and chemicals. A solution to reduce the negative environmental problems and the cost of biodiesel is to use crude glycerol as carbon source for microbial growth media in order to produce valuable organic chemicals. In the present paper, crude glycerol was used as carbon substrate for production of L (+)-lactic acid using pelletized fungus R. oryzae NRRL 395 on batch fermentation. More, the experiments were conducted on media supplemented with inorganic nutrients and lucerne green juice.

Results: Crude and pure glycerols were first used to produce the highest biomass yield of R. oryzae NRRL 395. An enhanced lactic acid production then followed up using fed-batch fermentation with crude glycerol, inorganic nutrients and lucerne green juice. The optimal crude glycerol concentration for cultivating R. oryzae NRRL 395 was 75 g l(-1), which resulted in a fungal biomass yield of 0.72 g g(-1) in trial without lucerne green juice addition and 0.83 g g(-1) in trial with lucerne green juice. The glycerol consumption rate was 1.04 g l(-1) h(-1) after 48 h in trial with crude glycerol 75 g l(-1) while in trial with crude glycerol 10 g l(-1) the lowest rate of 0.12 g l(-1) h(-1) was registered. The highest L (+)-lactic acid yield (3.72 g g(-1)) was obtained at the crude glycerol concentration of 75 g l(-1) and LGJ 25 g l(-1), and the concentration of lactic acid was approximately 48 g l(-1).

Conclusions: This work introduced sustainable opportunities for L (+)-lactic acid production via R. oryzae NRRL 395 fermentation on biodiesel crude glycerol media. The results showed good fungal growth on crude glycerol at 75 g l(-1) concentration with lucerne green juice supplementation of 25 g l(-1). Lucerne green juice provided a good source of nutrients for crude glycerol fermentation, without needs for supplementation with inorganic nutrients. Crude glycerol and lucerne green juice ratio influence the L (+)-lactic acid production, increasing the lactate productivity with the concentration of crude glycerol.

Figure 1

Specific fungal biomass yield for samples with pure glycerol and crude glycerol (30 g l^-1) supplemented with inorganic nutrients (IN). The bars are means of three determinations ± SD. *** Extremly significant according to T-test.

Figure 2

R. oryzae NRRL 395 biomass yield (g biomass increase/g initial biomass) on media containing different ratio of crude glycerol (CG) (10, 40, 75, 100 g l^-1) supplemented with inorganic nutrients (IN) or with lucerne green juice (LGJ 90, 60, 25 g l^-1). Means (n = 3) ± SD. Means with different letter are significantly different (p < 0.05).

Figure 3

Substrate consumption and product yield curves of R. oryzae NRRL 395 during the fermentation conditions on media with glucose (101 g l^-1). The bars are means of three determinations ± SD.

Figure 4

L (+)-lactic acid production and glycerol consumption obtained in trials with crude glycerol (CG) (10, 40, and 75 g l^-1) supplemented with inorganic nutrients. The bars are means of three determinations ± SD.

Figure 5

L (+)-lactic acid yield (g L (+)-lactic acid/g glycerol) during R. oryzae NRRL 395 fermentation in media containing different ratio of crude glycerol (CG) (10, 40, and 75 g l^-1) supplemented with inorganic nutrients (IN) or with lucerne green juice (LGJ) (90, 60, and 25 g l^-1). The error bars in the figure indicate the standard deviations of three parallel replicates ± SD.

Figure 6

L (+)-lactic acid productivity [concentration of L (+)-lactic acid (in g l^-1) / fermentation time (in h)] duringR. oryzae NRRL 395fermentation in media containing different ration of crude glycerol (CG) (10, 40, and 75 g l^-1) supplemented with inorganic nutrients (IN) or with lucerne green juice (LGJ) (90, 60, and 25 g l^-1). The error bars in the figure indicate the standard deviations of three parallel replicates ± SD.

Figure 7

L (+)-lactic acid production and glycerol consumption obtained in trials with crude glycerol (CG) (10, 40, and75 g l^-1) supplemented with lucerne green juice (LGJ) (90, 60, and 25 g l^-1). The bars are means of three determinations ± SD.

Figure 8

Consumption rate of glycerol [initial concentration of glycerol (g l^-1) - residual concentration of glycerol (g l^-1)]/fermentation time [in h], during R. oryzae NRRL 395 fermentation in media containing crude glycerol (CG) (10, 40, and 75 g l^-1) supplemented with inorganic nutrients (IN) or with lucerne green juice (LGJ) (90, 60, and 25 g l^-1). The error bars in the figure indicate the standard deviations of three parallel replicates ± SD.

Figure 9

Comparative FTIR fingerprint of glycerol, lactic acid and the sample at the end of the fermentation process from trial with crude glycerol (CG) (75 g l ^-1 ) supplemented with inorganic nutrients (IN).