**2. The development of fermentation technology in the production of acetic acid**

In principle, the production of acetic acid from raw material is performed in two phases: the acetic acid fermentation process occurs under aerobic conditions, while alcoholic fermentation occurs under anaerobic conditions. Traditionally, the two processes are performed separately, under static and uncontrolled conditions [5, 6]. However, in its development, the production of acetic acid tends to occur in two or more stages, using either batch, fed-batch, or continuous types of operations. Many modifications have been made to the process, some of which are listed in **Table 1**. These modifications include the identification of alternative raw materials, the use

### **Table 1.**

*The various fermentation processes used during acetic acid production from raw materials.*

**193**

*Streamlining the Fermentation Process Using Mixed Cultures*

of different types of microorganisms, the implementation of different fermentation process operations and stages, and the manipulation of environmental conditions. The identification of alternative raw materials is performed not only to identify new sources of material but also to address economic problems, such as the existence of surplus agricultural products, including onions [7], palm [8], or apples [9], and the utilization of sugar-containing waste materials, including pineapple peels [10]. The fermentation processes use different types of microorganisms. The identification and use of new types of microorganisms is performed with the aim of obtaining new strains with superior properties and abilities to produce high-quality and highyield products [11–15]. Furthermore, various types of fermentation operations and modifications to the stages within these operations have been tested to determine the most simple and efficient methods capable of producing high yields because the operational procedures of acetic acid fermentation can be complicated and require a long time when multiple processes are required. Finally, the manipulation of environmental conditions, such as altering temperatures and aeration/agitation rates, is

performed to obtain the optimal fermentation conditions [7, 9, 10, 16].

**cultures during batch-type fermentation**

anaerobic and unsuitable for AAB growth [5].

agitation speed is also important to consider.

**3. Enhanced acetic acid production from raw materials using mixed** 

Acetic acid fermentation has been studied using apples as a substrate. The fermentation was performed using submerged batch cultivation with mixed cultures of *S. cerevisiae* and *A. aceti*, which were inoculated simultaneously at the beginning of the process. These two microorganisms have different physiological properties: *S. cerevisiae* is a facultative anaerobe and requires anaerobic conditions to produce alcohol, and *A. aceti* is strictly aerobic. Because these microorganisms have opposing characteristics, using both cultures simultaneously is challenging, especially because acetic acid is a strong inhibitor of yeast, whereas yeast makes the medium

During this fermentation process, the first thing to be considered is the availability of sugar in the substrate, which represents a carbon source for the growth of the two microorganisms and the production of acetic acid. We must determine whether the sugar requirements are met by the substrate or whether sugar must be added, as described in previous studies [7, 8, 16]. Another factor that must be considered during this process is the inoculum ratio between the two microbes, as the strong competition between the two microbial groups must be anticipated and balanced to allow the production of acetic acid. Furthermore, because the different stages of acetic acid fermentation demand different oxygen requirements, the appropriate

**3.1 Availability of sugar for microbial growth and acetic acid production**

The microbial requirements for sugar during acetic acid fermentation and the availability of sugar in the substrate can be observed using different experiments, such as those shown in **Figure 1**. The system uses one-third of the working volume. Because this type of fermentation uses a batch culture with only one stage, all materials are added simultaneously at the beginning of the process, including sugar, at concentration of 0, 10, and 20% (w/v). Changes in the sugar, alcohol, and acetic acid contents and changes in the pH values during this process were evaluated, as previously described [9]. The results demonstrated that the conversions of sugar into alcohol and of alcohol into acetic acid were accompanied by decreases in the pH of the medium. This result indicates that the fermentation process has been successfully performed.

*DOI: http://dx.doi.org/10.5772/intechopen.87205*

#### *Streamlining the Fermentation Process Using Mixed Cultures DOI: http://dx.doi.org/10.5772/intechopen.87205*

*New Advances on Fermentation Processes*

**No. Type of operation Number** 

4 Fed-batch

(successive stage)

**of stages**

**setup**

1 Batch 2 [17]

2 Batch 2 [10]

3 Batch 2 [8]

5 Continuous 1 [18]

6 Semicontinuous 2 [7]

7 Batch 1 [9]

*The various fermentation processes used during acetic acid production from raw materials.*

**acetic acid**

**2. The development of fermentation technology in the production of** 

In principle, the production of acetic acid from raw material is performed in two phases: the acetic acid fermentation process occurs under aerobic conditions, while alcoholic fermentation occurs under anaerobic conditions. Traditionally, the two processes are performed separately, under static and uncontrolled conditions [5, 6]. However, in its development, the production of acetic acid tends to occur in two or more stages, using either batch, fed-batch, or continuous types of operations. Many modifications have been made to the process, some of which are listed in **Table 1**. These modifications include the identification of alternative raw materials, the use

**Simplified schematic diagram of the fermentation** 

3 [16]

**Ref.**

**192**

**Table 1.**

of different types of microorganisms, the implementation of different fermentation process operations and stages, and the manipulation of environmental conditions.

The identification of alternative raw materials is performed not only to identify new sources of material but also to address economic problems, such as the existence of surplus agricultural products, including onions [7], palm [8], or apples [9], and the utilization of sugar-containing waste materials, including pineapple peels [10]. The fermentation processes use different types of microorganisms. The identification and use of new types of microorganisms is performed with the aim of obtaining new strains with superior properties and abilities to produce high-quality and highyield products [11–15]. Furthermore, various types of fermentation operations and modifications to the stages within these operations have been tested to determine the most simple and efficient methods capable of producing high yields because the operational procedures of acetic acid fermentation can be complicated and require a long time when multiple processes are required. Finally, the manipulation of environmental conditions, such as altering temperatures and aeration/agitation rates, is performed to obtain the optimal fermentation conditions [7, 9, 10, 16].
