Probably it is because concentrated enzymes facilitate the decomposition of celulose and starch, therefore the protein concentration get higher compared to the initial concentration in the fermentable solid mass, reported to other organic macromolecules.

Thank you.

Dear Singha

Solid state fermentation increases crude protein content due to the secretion of microbial proteins like enzymes, hydrolyzed peptides and other nitrogenous microbial components like chitin (Oseni & Akindahunsi 2011). In general, microorganisms utilize carbohydrates as a source of energy and bio-converted them into microbial proteins through intermediary metabolism (Rajesh et al. 2010). The reduction of carbohydrates (crude fiber and/or NFE) and lipids after fermentation confirmed that the carbon required for the de novo synthesis of amino acids are provided by degraded carbohydrates and lipids, but the source of nitrogen for amino acids synthesis might be from external origin. Lipman (1911) reported that A. niger had assimilated 0.63-2.23 mg 100cc-1 nitrogen and then it was further confirmed by Schober (1930) who reported the fixation of nitrogen was much higher (4 mg 100cc-1) than the previous reports. Recently, Sharma & Kumawat (2011) also confirmed the possible role of A. niger on plant growth in terms of nitrogen fixation. These reports clearly indicate the ability of certain microorganisms in the fixation of atmospheric nitrogen. Though the quantity of nitrogen fixed may be small, but it is of considerable importance for the microbial growth as well as for the production of metabolites like amino acids etc. However, this phenomenon needs to be evidenced by further investigations.

Thank you Dr Jannathulla R. for your kind information.

Hi Krishna,

Aforementioned answers have addressed your question. However, it is worth to underline the possible basic mechanisms:

1. Adding microbes to cereal by itself would increase the protein content due to microbial proteins (intracellular and extracellular)

2. Microbial addition to cereal would only increase protein content of the cereal if protein rich substrates are also added simultaneously, or the microbial consortium contains nitrogen fixating microbes. This is when the microbial protein content is omitted.

3. The microbial process (hydrolysis and/or fermentation) has released simple nitrogen compounds from complex compounds/polymers within the cereal, thus making it more biodegradable. In this case, the overall N content was not increased, instead only its biodegradable fraction was increased.

Dear researchers, your answers are very interesting but I think we should consider the biological system (vegetal mass and its microbial load) as a relatively "closed" system, in sense of mass balance. In other words, nothing will be added from outside, not vegetal, neither microbial cells but new cells will arise by division using the available compounds. During my PhD theoretical study I learned that Nitrogen source to support the bacterial multiplication and growth comes just from the N-based end products resulted from protein decomposition(specifically NH3 as metabolism gas from proteins). It is like a closed loop, proteins are transformed to NH3 that will be needed to make new proteins in bacterial structures. I wouldn't think that N comes from atmosphere in such processes, solid state and submerged fermentation are more likely anaerobic processes but N resources are provided just from the system itself. Indeed this is a topic to be investigated more thoroughly. In some papers I noticed a kind of confusion between proteins and aminoacids, many papers report more aminoacids compared to initial state and this is very normal, due to fermentation.

Regards.

Dear Researchers

I believe that Krishna should better explain the term "protein" in the context of the question so it would be better understood by us all. The term "protein" in this question attracts me to assume "crude protein" obtained from calculation of the N content (e.g. Kjehldahl methods).

I totally agree with Dr. Carmen that in a "closed" system, there would be no change in elemental composition within the system. Therefore, there would be no N (and protein) increase in this closed system. If there is such an increase, it means that something has been added and the system is not a "closed" system.

Thank you Mr. Alam Surya Wijaya. You have rightly mentioned above about the CP. Actually in simple words we can say CP= True Protein (i.e., having more than 50 amino acids in polypeptide chain) + NPN(Non-protein nitrogen).

I have gone through some papers which are mentioned by Dr Jannathulla R. and I got the following information-

Probable reasons behind the increase in Protein Content by Solid State Fermentation:

The increase in protein content of the substrate may be-

1. Due to the ability of the microorganisms to secret some cellular enzyme which are nothing but protein (Oseni and Akindahunsi, 2011; Nambi et al.).

2. Due to increase in microbial cell mass which constitutes higher level of protein in contrast to the raw material (Antai and Obong, 1992).

3. Due to the bioconversion of soluble carbohydrates in the substrate (wheat £our) to bacterial protein as reported by Vijayan et al., 2009. It was reported that Lactobacillus plantarum and Bacillus licheniformis produce different enzymes and biomolecules, which are proteinaceous in nature during fermentation (Nwanna, 2003; Hassan, 2003).

4. Due to production of non-protein nitrogen compounds-like ammonia, amines, amino acids and peptides due to autolysis during fermentation as these all are included in the crude protein content (Haard et al., 1985).

5. Due to repletion of a variety of enzymes and free hydrolysed peptides which are proteinaceous (Bhatnagar et al., 2010).

Due to increasing biomass content and subsequently improvement of intera and extra cellular proteins.

This question relates to the most fundamentals of any fermentation. In case of a complete medium, the microorganisms would utilize the carbon source both anabolically and catabolically (producing required energy). On the other hand nitrogen content (like proteins) would be utilized mainly anabolically and less catabolically). This would reduce the carbon source content drastically keeping the protein content (or nitrogen content) more or less the same. It would therefore, appear that the protein content has increased in the medium as compared to the carbon source content.