**Table 9.**

*Commercial-scale SCP processes with hydrocarbons and alcohols and feedstocks.*

Kuzniar et al. have suggested the use of methanotrophic bacterial biomass as a mineral feed ingredient for animals [87].

Also, applications in paper processing, leather processing, and foam stabilization are mentioned in the literature [33, 48].

In Ref. [88], SCP is discussed as a basis for microbial growth media, and in Ref. [89] for wood adhesives.

For (animal) *feed* applications, the dried bacterial biomass, which typically contains 70% of protein, can be fed directly. In SCP for (human) *food* applications, the content of nucleic acids (NA) has to be reduced from 10–15 to approximately 1–2%, which can be done thermally or enzymatically. Nucleic acid reduction by heat shocks is described in Ref. [90].

#### *1.4.3 Properties of bacterial SCP*

**Table 12** summarizes the properties of different SCPs:

Bacteria are very well suited to make SCP, see **Table 5**. They exhibit the highest growth rates. On the other hand, the nucleic acid content is elevated compared to SCP by other microorganisms. The extraordinary growth performance of bacteria is also visible in **Table 13**.

With doubling times of the mass on the order of 10–100 minutes, bacteria and yeasts grow incomparably faster than plants or animals. This translates into unsurpassed productivity, as **Table 14** illustrates.


*Value-Added Products from Natural Gas Using Fermentation Processes: Products… DOI: http://dx.doi.org/10.5772/intechopen.104643*



**Table 10.**

*Additional SCP projects as of 1977.*


**Table 11.** *Where SCP could be used.*

Within 24 h, a starting mass of bacteria of 1000 kg can yield, theoretically, 10<sup>12</sup> kg of protein, whereas beef would only produce 0.1 kg and soy in the order of 10 kg. An analysis of bacterial meal (BM) derived from methane is given in **Table 15**.

As one can infer from **Table 15**, the protein content approaches and exceeds 70%. **Table 16** shows the protein content of SCP from selected microorganisms.

Another important aspect of SCP is its quality, which can be expressed by the amino acid profile. In **Table 17**, the composition of amino acids of bacterial SCP compared to other proteins is shown.

Bacterial SCP is approved as a feed ingredient in the EU feed catalog (EU 68/ 2013) [63]. SCP for feed has been tested extensively, see **Table 18** for an overview.

SCP feed trials were made with Drosophila [87] several monogastric species [98], including rats [99, 100], pigs [61, 100–102], dogs [45, 103], (lactating) cows [104], veal calves [105], chickens (broilers) [72], mink (*Mustela vison*), fox (*Alopex lagopus*), Atlantic salmon (*Salmo salar*), rainbow trout (*Oncorhynchus mykiss*) [106], Pacific White Shrimp (*Penaeus vannamei*) [107, 108], Atlantic halibut (*Hippoglossus hippoglossus*), tilapia (*Oreochromis niloticus, Oreochromis mossambicus*) [109, 110],


*Value-Added Products from Natural Gas Using Fermentation Processes: Products… DOI: http://dx.doi.org/10.5772/intechopen.104643*

#### **Table 12.**

*Comparison of some cultural and biochemical characteristics of various microbe groups to make SCP.*

Japanese yellowtail (*Seriola quinqueradiata)* [111], zebrafish (*Danio rerio*) [112] and other aquaculture species [113, 114]. In feed, SCP can replace fish meal and soy. It was found in Ref. [65] that *"bacterial meal (BM) derived from natural gas fermentation, utilizing a bacteria culture containing mainly the methanotroph Methylococcus capsulatus (Bath), is a promising source of protein based on criteria*, *such as amino acid composition, digestibility, and animal performance and health."* [65].

The oral immunogenicity of bacterial SCP was tested by [115].

The use of SCP for feed and food was also proposed by John H. Litchfield in 1979 [116].

An example from Germany (1943–1949) is the "wood sausage," a spread made in Wildshausen from paper production waste (sugars) using the fungus *Oidium laktis*. The process was licensed from Biosyn GmbH [117]. Other yeast spreads on


### **Table 13.**

*Mass doubling time of different organisms.*


#### **Table 14.**

*Comparison of protein production efficiency of selected organisms over 24 h.*


#### **Table 15.**

*Properties of BM (bacterial meal) made from methane and methanol, based on g/100g of dry mass.*

the market are Marmite, Cenovis, and Vegemite: *"Spent brewer's yeast (Saccharomyces cerevisiae) have been sold for more than a century in yeast extracts such as Marmite® (Unilever and Sanitarium Health Food), Vegemite® (Bega Cheese Ltd.), Cenovis® (Gustav Gerig AG), and Vitam-R® (VITAM Hefe-Produkt GmbH)."* [117]

"Another commercially available yeast, Torula (*Candida utilis*, renamed as *Pichia jadinii*), a widely used flavoring agent, is also high in protein. Torula was used in Provesteen® T, produced by the Provesta Corporation in the 1980s, along with similar products using *Pichia* and *Kluyveromyces* yeast)" [118].

*Value-Added Products from Natural Gas Using Fermentation Processes: Products… DOI: http://dx.doi.org/10.5772/intechopen.104643*


#### **Table 16.**

*Protein content of bacteria expressed as SCP (single-cell protein) grown on different substrates.*


*For reference, the data for soybean meal and fishmeal are provided. The rightmost SCP was obtained from methanol, Pruteen™, by* Methylophilus methylotrophus *[g/16 g N standard deviation of free, hydrated amino acids]. Source: [65].*

#### **Table 17.**

*Amino acid profile of SCP made from natural gas (BM = bacterial meal).*


### **Table 18.**

*As early as 1981, SCP was tested for feed.*

#### *1.4.4 Aquatic species*

Approximately half of the global fish and aquatic species production comes from aquaculture operations, with an increasing share. Fish meal is volatile in price and, due to overfishing, is not a sustainable feed material. The same holds true for soy; while soy is cheap, its immense monoculture production has resulted in rainforest destruction on a global level. It was shown that soybean meal-induced enteritis in Atlantic salmon (*Salmo salar*) can be prevented by cell wall fractions obtained from *Methylococcus capsulatus* [119].
