Effects of neutralizing agents on lactic acid production by Rhizopus oryzae using sweet potato starch

• Published in: World journal of microbiology & biotechnology Vol. 26; no. 3; pp. 437 - 441
• Main Authors: Yen, Hong-Wei, Chen, Tsia-Ju, Pan, Wei-Chin, Wu, Hsien-Jen
• Format: Journal Article
• Language: English
• Published: Dordrecht Dordrecht : Springer Netherlands 01.03.2010; Springer Netherlands; Springer; Springer Nature B.V
• Subjects: Acid production; Ammonia; Applied Microbiology; Biochemistry; Biodegradable materials; Biological and medical sciences; Biomedical and Life Sciences; Biotechnology; Calcium carbonate; Carbohydrates; Caustic soda; Environmental Engineering/Biotechnology; Fermentation; Fundamental and applied biological sciences. Psychology; Life Sciences; Microbiology; Microorganisms; Morphology; Original Paper; Plastics; Potatoes; Sodium; Sodium hydroxide; Solubility; Starch; Studies; Starch; Neutralizing; Calcium carbonate; Zygomycota; Calcium; Solanum tuberosum; Fungi; Potato; Rhizopus oryzae; Dicotyledones; Angiospermae; Production; Spermatophyta; Solanaceae; Lactic acid
• ISSN: 0959-3993; 1573-0972
• DOI: 10.1007/s11274-009-0186-0

A neutralizing agent is usually employed to counteract the pH reduction during lactic acid fermentation by Rhizopus oryzae. Calcium carbonate (CaCO₃) is used as such a pH controlling agent. The low solubility of CaCO₃ in the fermentation broth could however lead to low efficiency in pH control and cause problems in the subsequent purification process. Therefore, an alternative agent in place of CaCO₃ was examined in this study. The effect of four different neutralizing agents, including CaCO₃, sodium hydroxide (NaOH), ammoniacal solution and sodium bicarbonate (NaHCO₃) on lactic acid production and the morphology of the pellets were investigated. Results indicated that CaCO₃ was still the preferred choice, because of the pellet morphology and the highest lactic acid concentration (43.3 g/L) obtained in the batch using 60 g/L of sweet potato starch as feedstock. It is noteworthy that the lactic acid purification is relatively easier when using NaHCO₃ instead of CaCO₃, due to the higher solubility of sodium lactate than calcium lactate. Therefore, even the batch with CaCO₃ had a slightly higher productivity (1.23 g/L/h) than the batch with NaHCO₃ (1.14 g/L/h), NaHCO₃ might be the first choice for process designers whenever recovery is vital.