**3.8 Other acids**

*Lactose and Lactose Derivatives*

process) [109].

China, and India.

Lactic acid (C3H6O3, MW 90.078 g mol<sup>−</sup><sup>1</sup>

Succinic acid (C4H6O4, MW 118.088 g mol<sup>−</sup><sup>1</sup>

with corn steep liquor powder [129].

acetic acid in addition to LA [115].

**3.6 Lactic acid**

**3.7 Succinic acid**

(PA) is a valuable mono-carboxylic acid used in chemical, pharmaceutical, and food industries, as a mold inhibitor, as a preservative of foods, as a significant element in the vitamin E production, and as a chemical intermediate in the chemical synthesis of cellulose fiber, perfumes, herbicides, etc. [16, 106, 107]. Today, propionate is mainly obtained for two processes. From ethylene, a nonrenewable source synthesized from oil, through the Reppe process [108], or from ethanol and carbon monoxide catalyzed by boron trifluoride (by the Larson

Although chemical synthesis is the primary way of its production, the microbial

, IUPAC Name: 2-Hydroxypropanoic

, IUPAC Name: Butanedioic acid)

production of PA is gaining attention and importance due to the depletion of petroleum sources and due to pieces of evidence of the more environmentally friendly microbial process [107, 110]. Propionibacterium is the most employed microorganism used for PA large-scale production [107, 111]. In 2020, the worldwide production of PA would reach 470 ktpa. The leading producers remain to be in Germany (BASF SE), USA (Dow Chemical Co. and Eastman Chemical), and Sweden (Perstorp). At the same time, the primary consumers are in the EU, USA,

acid) was the first organic acid commercially produced by microbial fermentation [112]. Bacterial fermentation of carbohydrates had been the main way for the industrial production of lactic acid (LA) with production level between 70 and 90% for 2009 [113]. The rest of production was achieved by chemical synthesis mainly from acetaldehyde coming from crude oil [114]. A racemic mixture of LA commonly is obtained by chemical synthesis, while L-lactic acid can be obtained by homofermentative anaerobic bacteria like *Lactobacillus casei* and *Lactococcus lactis*. Otherwise, heterofermentative bacteria produced carbon dioxide, ethanol, and/or

LA is currently used and has been approved as a food additive, preservative, decontaminant, and flavoring agent (with a code E270) [116, 117]. Also, it is used for chemical synthesis [118], mainly to produce poly-lactic acid (PLA), a thermaland bioplastic polyester with widespread use in many applications [119, 120]. PLA is used, for example, in medical implants [121], as plastic fiber material in 3D-printing [122, 123], and as a decomposable packing material [124, 125].

In 2020, LA and PLA worldwide production will be around 1571 and 800 ktpa, respectively, with China, USA, EU, and Japan being the primary producers [126].

has been widely used in many industries, as a food, detergent, and toner additive, for solders and fluxes, and as an intermediary commodity in the chemical and pharma industry [127]. After the increment of oil prices and diminishing availability of nonrenewable sources, researchers turned their attention over to the renewable feedstocks to produce succinic acid. SA as an intermediate in many biochemical

pathways could be produced by many microorganisms and use many carbon sources [127]. For instance, the anaerobic-facultative bacteria *Actinobacillus succinogenes* can produce succinic acid from sugar cane molasses alone [128] or supplement

Glucose as a carbon source has also been used to produce succinic acid by engineering strains of *Corynebacterium glutamicum* [130], *Escherichia coli* [131], and

**58**

No reports of microbial obtention of tartaric (C4H6O6, dicarboxylic acid), itaconic (C5H6O4, dicarboxylic acid), and fumaric acid (C4H4O4, dicarboxylic acid) from lactose have been found. Some of those, however, can be obtained indirectly, since there are published studies of the biosynthesis of itaconic acid [135–137], fumaric acid [138, 139] from glucose, and the latter can be obtained from the chemical or enzymatic hydrolysis of lactose.
