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Processing food waste for the production of platform chemicals 435

19.2.2.5 Fermentation

Food waste has a high amount of protein, lipid, starch, etc., which can be changed
to the value-added product through fermentation process profoundly. It involves
reaction with microorganisms. Fermentation can be divided into three categories as
described next.

19.2.2.5.1 Solid state fermentation
The solid-state fermentation (SSF) process is done in the absence of water on non-
soluble material which acts both as physical support and nutrient source. This pro-
cess is useful for production of platform chemicals [citric acid, levulinic acid (LA),
adipic acid (AA), etc.] and enzymes (lipase, fructosyl transferase, α-amylase,
pectinase, etc.) (Hang and Woodams, 1986; Couto and Sanroma ´n, 2006). A natural
biological process, such as composting and ensiling, is produced by SSF.
19.2.2.5.2 Submerged fermentation
The submerged fermentation (SmF) process is useful for the production of enzymes
derived from microbes. This process typically involves submersion of microorgan-
ism in aqueous solution to get all the nutrients. Different types of reactor are used
in this process. The most common is aerated stirred tank batch fermentor.

19.2.2.5.3 Surface fermentation
Surface fermentation process involves cultivation of microorganism on the surface
of the solid or liquid substrate. This process does not require either aeration or agi-
tation; only the temperature or humidity is to be controlled.
SSF has more advantage over SmF. The advantages are easy downstream proces-
sing, easy aeration requirements, high productivity, and resemblance as natural hab-
itat, low-cost media, temperature control, and controlled nutrient availability.
SSF find more application such as bioremediation and detoxification of toxic
compounds, organic residue, and agro-based residue.

19.3 Platform chemicals: classes and applications

Biomass can be transformed into chemical building blocks containing an electro-
philic or nucleophilic character that can be exploited in further reactions. Platform
chemicals can be generated through both chemical routes and biological processes.
Table 19.3 shows key market players globally for the production of platform chemi-
cals. A brief description of platform chemicals and their market potential is
provided in the following subsections.

19.3.1 3-Hydroxy propionic acid
3-Hydroxy propionic (3-HP) acid is a 3-carbon, nonchiral organic molecule and a
structural isomer of lactic acid. The two functional groups, carboxyl and
β-hydroxyl, render high reactivity and make suitable precursor for synthesizing