## 6 Opportunities and Challenges for the Single-Cell Protein (SCP) Market
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Type of** & **Name of** & **Producer** & **Microorganisms** & **Ingredients** & **Nutritional** & **References** \\ \hline \multirow{4}{*}{Paste} & \multirow{4}{*}{Crunchy peanut butter} & \multirow{4}{*}{Marmite} & \multirow{4}{*}{_S. cerevisiae_} & peanuts (87\%), yeast extract powder & & \\  & & & & (9.5\%), peanut oil, locoprohed extract & & \\ \cline{1-1}  & & & & (antioxidant), vitamins (thiamin, riboflavin, niacin, vitamin b12 and folic acid), may contain other nuts & 574 kcal/100 g & [127] \\ \hline \multirow{4}{*}{\
\begin{tabular}{c} Protein supplement \\ \end{tabular} } & \multirow{4}{*}{Yeast protein} & \multirow{4}{*}{Allnutrition} & \multirow{4}{*}{_S. cerevisiae_} & Saccharomyces cerevisiae & \multirow{4}{*}{360 kcal/100 g} & \multirow{4}{*}{[128]} \\  & & & & reduced fat cocoa, flavouring, salt, thickeners: cellulose gum, guar gum, xanthan gum, sweeteners: steviol & \\ \cline{1-1}  & & & & glycolysis from stevia, acesulfame k, sucxclose & & \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Food supplement \\ \end{tabular} } & \multirow{2}{*}{Yeast protein, vegan} & \multirow{2}{*}{Enkioo} & \multirow{2}{*}{_S. cerevisiae_} & Yeast protein (derived from the yeast Saccharomyces cerevisiae) 100\% & 411 kcal/100 g & [129] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._waste, extracting the protein, and then producing packaging with microbial proteins, sustainable valorization and promotion of a closed-loop economy is possible [132]. Furthermore, the microbial protein can be used as an alternative source of organic fertilizer. By growing microorganisms in substrates containing agricultural waste, essential nutrients such as nitrogen, phosphorus and potassium are recovered, which are later applied to agricultural soils for bio-enrichment and consequently improved plant growth. However, further research is needed on the potential use of microbial protein as a nutrition for plants [133]. In addition to the use of agricultural waste, municipal wastewater can be a favorable substrate for microbial protein production. By using the organic fraction of municipal solid waste, it is possible to valorize it carried out in biorefineries [134]. There are many animal protein alternatives available on the market. When analyzing the composition of such products, it is important to pay attention not only to the protein content, but also to its quality. Mycoprotein preparations produced by _F. venenatum_ have an actual protein digestibility of 86%. The natural structure of mycoprotein is porous, so proteases can diffuse through cell walls during the digestion phase in the small intestine. The extracted from _Agaricus bisporus_ has a digestibility of 64%. In contrast, the application of alkaline extraction to _Pleurotus ostreatus_ biomass contributes to preparation with a digestibility of 100%. In contrast, the total amino acid digestibility of _Saccharomyces cerevisiae_ yeast is 97%. The digestibility values of such proteins of fungal origin contribute to the significant advantage of these products over plant proteins. The protein digestibility of the dry extruded mixture of chickpea and barley flour was 59%, while the digestibility of barley flour is only 33% [135]. Plant-based protein alternatives, in addition to their low digestibility, are low in micro and macronutrients. Vegan products should be supplemented with various nutrients, including iron, zinc, iodine, selenium, calcium, vitamin B\({}_{12}\), vitamin D, and vitamin B\({}_{2}\)[136]. Microbial proteins, on the other hand, are characterized by their high vitamin content. The most common vitamins present in microbial proteins are riboflavin, thiamin, pyridoxine, niacin, choline, folic acid, pantothenic acid, biotin, and para-aminobenz acid [137]. Single-cell proteins for which algae, fungi, and bacteria are used also carry several risks. The issue of food safety risks from proteins of microbial origin is not yet fully understood.