**4. Application of acetic acid in food industry**

Direct applications of acetic acid are reported from ancient times. It was used as a medicine and food preservative. Over the period, applications of acetic have diversified as per the demands of modern life. Using different concentrations, it is utilized in food additives, food preservation, antimicrobial agent, acidulant, flavour and taste enhancer, edible packaging material, artificial food ripening agent, etc. Some of the applications such as acidulant and as acetification agents are described in detail here.

#### **4.1 Acetification**

*Biotechnological Applications of Biomass*

acid. The pathways are discussed briefly.

**3.1 CO and CO2 as valuable feedstock**

**3.2 Membrane-based technologies**

for this process to increase the rate of the acetification. The yield of acetic acid is 98%. The pure substrates are required to achieve the high quality of acetic acid. This fermentation process is much economical, of simple design with easy process control. The Fermentation process for acetic acid is economically feasible with comparatively simple operations. The application of this process is very limited to the present global demand. Whereas, the conventional process involves several steps such as fractional distillation, condensation and crystallization, which add to the high machinery cost. The operating conditions are harsh considering the process temperature and pressure along with the corrosive nature of acetic acid [12]. The purification of acetic acid from water is a multi-step process consuming a high amount of energy, which makes overall process complex and critical. In addition to this, the process requires huge manpower with stringent safety protocols and norms.

**3. Need for development of novel sustainable technologies**

Looking at the ever-increasing threats of global warming and ever-increasing global demand of acetic leads to an urgent need to develop a novel technological approach and sustainable feedstock for the generation of acetic acid. Even though many processes and technological developments are reported recently, they fail to sustain the production cost to profit margins. The separation of acetic acid remains the key issue to overcome the economical and energy consumption barriers. The different operations such as distillation, evaporation, absorption, filtration crystallization and alkali neutralization are time and energy consuming. Even though these processes involve multiple steps, the ever-growing demand forces to follow this path. On the other hand, fermentation process is reliable but cannot match the scale of current demand. Thus, the development of a novel route for generation or process intensification in separation can drastically reduce the overall production cost of acetic acid. Utilization of CO and CO2 as feedstock generated from natural gas can offer long-term sustainability of acetic acid production. This technology offers high purity of acetic acid with eco-friendly production. Furthermore, membrane-based separation processes can provide efficient way to produce acetic

Utilization of CO2 and syngas can offer sustainable alternatives to produce acetic

acid. BP has announced the breakthrough process, wherein, acetic acid will be manufactured from syngas as a feedstock derived from natural gas. This will give an alternative to SaaBre process that produces acetic acid in three integrated steps. The production of acetic acid from syngas will avoid the purification of CO and purchase of methanol. Though the technology is not fully developed, it provides better alternatives in terms of sustainability. Similarly, acetic acid can be synthesized via reacting CO2 and H2 to give methanol followed by subsequent carbonylation step.

The membrane technology can offer the separation of liquid, vapour and gas selectively with controlled mass transfer rates. These processes are easy to operate and simple to design. The technology can offer development on energy intensification. Several types of processes are reported based on the pore size of the membrane for separation of different components. These are namely microfiltration, ultrafiltration

This route gives liberty to utilize CO2 as value-added feedstock.

**286**

Acetification is simply the bacterial oxidation of ethanol to produce acetic acid and water (**Figure 5**). The process is also termed as oxidative fermentation. The rate of the reaction in acetification mainly depends on the type of microorganism used to catalyse and the concentration of available oxygen in the media [13].

There are different types of microorganisms that occur naturally in food and are responsible for the different natural processes such as acetification, alcoholism, proteolysis and enzymatic reactions, which alter the natural condition of the food. This bioprocess technology is studied and systematically utilized to improve the quality of food s in terms of texture, taste, mouthfeel, colour and prolonged shelf life. The overall concept has grown into generating different types of food and beverages produced in a cheap and sustainable way.

Acetification of different food categories using acetic acid bacteria (AAB) has led to the production of several food products [14]. AAB are naturally found on fruits, flowers, and plants, which naturally react and convert carbohydrate sugars into organic acids in the presence of oxygen. The same concept is biotechnologically utilized to prepare a diverse variety of food and beverages.

#### **4.2 Flavouring agent**

Different parts of the world have utilized the acetification process to generate a variety of foods and beverages. The famous Lambic beer is produced from malted barley, aged dry hops and unmalted wheat. The different AAB and yeast are responsible for the generation of this beer, which is matured for over a period of 3 years. The typical acidic flavour of the beer is achieved with the help AAB

**Figure 5.** *Production of acetic acid by fermentative oxidation of alcohol.*

together with lactic acid. The sparkling water is another famous example, which gives typical acidic and fruity flavour via fermentation of water and natural sucrose. Water kefir is one of the examples of such type. Kombucha is another type of beverage produced by oxidative fermentation. It is prepared from Kombucha (tea fungus), water and sugar. Similarly, Cocoa is fermented from cocoa beans with the help of AAB and yeast, which is used as raw material for chocolate production.
