*1.4.5 Chicken*

Various tests were carried out to feed chickens with bacterial SCP. SCP could maintain chicken growth performance and increase the feed to gain (feed conversion) and reduce the fat content in chicken [120]. *"Replacing soybean meal and small amounts of rendered fat with BPM caused less intensity of odor and less rancid flavor of chicken meat"* [120].

Processed animal protein (PAP) from poultry/pig for poultry/pig [121] is currently being investigated, too, but brings back memories about BSE [122]. Also, potential quantities are limited.

#### *1.4.6 Mink*

Another species where SCP was tested successfully is mink (*Mustela vison*). SCP digestibility tests were carried out in 2009 by the Department of Animal and Aquacultural Sciences at The Norwegian University of Life Sciences, Ås [123]. Mink are of importance for the fur industry.

#### **1.5 Status of single-cell protein as food**

Oral delivery of bacteria is not novel [124]; for an overview of beneficial microorganisms in food and nutraceuticals, see Ref. [125]. Microorganisms in food are covered in Refs. [126–128].

In the literature, there is ample coverage of food trials of SCP in the last 50 years. One example is a trial from 1979 to include SCP "Pekilo" in sausages and meat balls [129].

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

SCP has a peculiar taste. Some variants, which have a high content of glutamic acid, have been proposed and used instead of monosodium glutamate (MSG) [118] as the flavor enhancer in food.

Pekilo is a microfungus-derived SCP from *Paecilomyces varioti* based on pulp and paper waste streams. It is now being revived by Enifer [130]. Another work with SCP from waste is discussed in Ref. [131], SCP with the fungus *P. chrysosporium* in [132].

As early as 1971, single-cell protein had been subjected to clinical testing in tolerance trials in adults [133]. For immunogenicity testing of food proteins, see Ref. [134].

For humans, it is recommended that the daily nucleic acid (NA) intake does not exceed 2 g, as higher quantities (particularly RNA and, to a lesser extent, DNA) have been reported to increase the content of uric acid in blood plasma to an unhealthy level [135], leading to gout [136]. As SCP contains a comparatively large amount of nucleic acids, it needs special processing for food applications. For feed, by contrast, the nucleic acid species do not harm. In **Table 19**, approaches for RNA reduction in SCP are summarized.

**Tables 20**–**23** compare different treatments of SCP to reduce nucleic acids [137].

There is currently a strong movement toward alternative protein (alt protein), as concerns over the healthiness and sustainability of meat, first and foremost imported beef, are increasing all over the world. Hence there is good potential for SCP for food applications. By the end of 2021, Solein™ submitted its dossier for SCP food approval in the EU [138].


Occupational health aspects of SCP are discussed in Ref. [139], where it was found that inhalable dust needs to be avoided.

**Table 19.** *RNA reduction in SCP.*
