In order to add value to potato peels and also curb their environmental pollution problems , this study investigated the protein enrichment of potato peels with Saccharomyces cerevisiae via Solid-State Fermentation (SSF). SSF is a fermentation process which involves solid matrix and is carried out in absence or near absence of free water. SSF of potato peel mashed was carried out with S. cerevisiae at 30°C, pH of 5.5, moisture adjustment between 40 and 90%, addition of ammonium sulphate and urea salts as nitrogen supplements for the microorganisms for 3 days. The results showed that the percentage crude protein content of all the fermented samples increased significantly when compared with the unfermented sample. 40% moisture content adjustment and ammonium sulphate as nitrogen source gave the best result. The crude protein increased from 12.5% to 21.86% , which is 74.88% increment for ammonium sulphate supplementation, and 12.5% to 18.42% , which is 47% increment for urea supplementation. Therefore , the fermented peels could serve as good source of cheap protein enriched feed for livestock.
Protein-energy malnutrition remains a major public health problem in many developing countries and there is need to increase the daily intake of protein, especially animal protein, using cheap and non-conventional sources such as agricultural wastes and by-products of food processing [
Micro-organisms have the ability to upgrade low protein plant material to high protein feed via fermentation [
Solid-state fermentation (SSF) is defined as the fermentation process in which micro-organisms grow on solid materials without the presence of free water [
The objective of this study was to evaluate the performance of S. Cerevisiae in the protein enrichment of potato peels by solid-state fermentation.
Saccharomyces cerevisiae was obtained from the culture collection of the department of Microbiology Enugu State University of Science and Technology (ESUT) Nigeria and maintained on slants of sterile yeast agar medium after sub-culturing. The inoculated slants were allowed to incubate at 30˚C for two days after which they were stored at 4˚C and sub-cultured once every fortnight. Spore suspensions were prepared in five ml sterile distilled water.
The Potato peels used in this study were obtained through hand peeling of purchased Irish potatoes from Ogbete main market Enugu. Before the peeling process the potatoes were washed with water and rinsed with distilled water. The peels obtained were also washed with sterile distilled water and dried in an oven at 105˚C for 4 hours. The dried peels were milled inside the Laboratory, sieved to obtain 0.5 mm mesh sized flour and kept ready to be used for SSF process while some quantity was chemically analysed.
Twenty grams of the dried sieved sample was weighed out into 250 ml Erlenmeyer flasks in triplicates and moistened by adding 26.83 ml of sterile distilled water, which corresponded to 60% moisture content adjustment [
For the calculation of the volume of sterile distilled water used for moisture content adjustment of the sample, the formula below was used [
A = B × ( C − D ) 100 − C (1)
A = Amount of water to be added in ml; B = measured weight of the sample; C = % of water to be added; D = Moisture content of the sample obtained by proximate or chemical analysis.
Twenty grams of the dried sieved samples were weighed out into 250 ml Erlenmeyer (Conical) flasks in duplicates and moistened with sterile distilled water according to the calculated volume of the moisture content adjustments of 30%, 40%, 50%, 60%, 70%, 80% and 90% respectively. In studying the effects of nitrogen supplements and their input on the protein enrichment, the mixture were supplemented with each of the mineral salts: 10 g of N2 as (NH4)2SO4/kg of the weighed sample used and 10 g of N2 as CO(NH2)2(Urea)/kg of the weighed sample used respectively. Temperature of 30˚C and pH of 5.5 were found to be the optimum for the growth of S. cerevisiae on the mash [
The samples were analysed for proximate composition (moisture content, crude fat, crude fibre, crude protein, ash and carbohydrate) before and after the yeast fermentation process using the standard AOAC 1990 method [
Twenty grams of the dried sieved samples were weighed into 250 ml Erlenmeyer flasks in triplicates and moistened by adding 26.83 ml of sterile distilled water which corresponded to 60% moisture adjustment. 1.32 g of Ammonium sulphate was added to serve as a nitrogen source, the mixture was sterilized using an autoclave. Solid state fermentation was carried out for 5 days in order to establish a time profile for the SSF where effects of other parameters will be evaluated.
It was observed from
utilized by Saccharomyces, since they were nearly exhausted after 3 days. This behaviour shows that S. cerevisiae is able to efficiently metabolise available sugars as its carbon source for protein enrichment of the residue [
Next to carbon, nitrogen has a pronounced influence on microbial growth and activity. In general inorganic nitrogen sources in their most reduced forms are more efficiently utilized than other forms of nitrogen sources by fungi. In micro-organism, nitrogen (both organic and inorganic forms) is metabolized to produce amino acids, nucleic acids, proteins and cell wall components. It is clear that organisms show slight differences in the growth pattern in the presence of different nitrogen sources due to their relative solubility. In the present study, inorganic compounds such as ammonium sulphate and urea at different moistures were used. It was observed that in the presence of these compounds there was significant increase in the microbial growth and activity, which was buttressed by the increase of the crude protein after fermentation.
From
Among the two nitrogen sources investigated, the supplementation of potato peel mash with ammonium sulphate resulted in the highest crude protein yield of 21.86% compared to the best value of 18.42% obtained using urea as a nitrogen supplement. This could be attributed to high solubility of ammonium sulphate in water, and also to the fact that apart from providing nitrogen, it also provides sulphur, an element required by S. cerevisiae for growth in the medium.
The moisture content is one of the critical factors in SSF media that attributes to biosynthesis and secretion of the enzymes [
Crude Protein (%) | Crude Fat (%) | Crude Fibre (%) | Moisture Content (%) | Carbohydrate (%) | Ash (%) |
---|---|---|---|---|---|
12.5 ± 0.15 | 2.2 ± 0.10 | 8.71 ± 0.10 | 6.35 ± 0.05 | 66.74 ± 0.00 | 3.5 ± 0.26 |
Values are mean ± standard deviation, based on triplicate values.
in solid state fermentation processes vary between 30% - 85% and have marked effect on growth kinetics of fermenting organism [
Moisture optimization can be used to regulate and to modify the metabolic activity of the microorganisms [
This agrees with the report of [
According to literatures high moisture results in low substrate porosity which in turn prevents oxygen penetration, whereas low moisture content may lead to poor accessibility of nutrients resulting in hampered microbial growth. Also a previous work done in this area that investigated moisture contents from 10% to
Moisture Content in % | Ammonium sulphate supplementation (%) | Urea supplementation (%) |
---|---|---|
30 | 12.80 ± 0.14 | 12.60 ± 0.14 |
40 | 21.86 ± 0.03 | 18.42 ± 0.08 |
50 | 21.51 ± 0.01 | 17.48 ± 0.03 |
60 | 20.66 ± 0.11 | 15.01 ± 0.27 |
70 | 17.21 ± 0.07 | 14.79 ± 0.01 |
80 | 16.61 ± 0.04 | 13.66 ± 0.04 |
90 | 14.73 ± 0.01 | 13.01 ± 0.04 |
Moisture content in % | Corresponding volume of sterile water added in ml |
---|---|
30 | 6.76 |
40 | 11.22 |
50 | 17.46 |
60 | 26.83 |
70 | 42.43 |
80 | 73.65 |
90 | 167.30 |
60% [
Based on the observation that 40% moisture content produced the best results for crude protein enrichment, below are the tabulated results for the proximate analysis of the fermented potato peel sample.
Micro-fungi solid state fermentation of potato peel mash caused a significant decrease in the carbohydrate content [
Nutrients (%) | Fermented sample with Ammonium sulphate | Fermented sample with Urea | Unfermented potato sample |
---|---|---|---|
Crude Protein | 21.86 ± 0.03 | 18.42 ± 0.08 | 12.50 ± 0.15 |
Crude Fat | 2.00 ± 0.01 | 2.10 ± 0.14 | 2.20 ± 0.10 |
Ash | 5.00 ± 0.03 | 5.21 ± 0.01 | 3.50 ± 0.26 |
Crude Fibre | 12.81 ± 0.06 | 13.50 ± 0.44 | 8.71 ± 0.10 |
Carbohydrate | 58.33 ± 0.07 | 60.77 ± 0.37 | 66.74 ± 0.00 |
Values are mean values ± standard deviation, based on duplicate values.
Moisture Content in (%) | Ammonium sulphate supplementation (%) | Urea supplementation (%) |
---|---|---|
50 | 1.92 ± 0.04 | 1.93 ± 0.04 |
60 | 1.80 ± 0.00 | 1.86 ± 0.03 |
70 | 1.50 ± 0.11 | 1.68 ± 0.01 |
80 | 1.43 ± 0.01 | 1.46 ± 0.01 |
90 | 1.20 ± 0.01 | 1.30 ± 0.14 |
Values are mean values ± standard deviation, based on duplicates.
The ash and fibre concentrations of the fermented potato samples increased relatively to the increase in moisture content. The increment in the ash and fibre concentration could be attributed to the inorganic content of the nutrient medium [
It was demonstrated in this research that the percentage crude protein content of potato peels can be improved (protein-enrichment) via solid state fermentation (SSF). This research is an immense addition in areas of biotransformation of tuber peels (abundant agrowastes) that are rich in carbohydrate to equally serve as protein source for livestock feed, as well as curbing their pollution menace. Solid-state fermentation of potato peel mash was carried out with S. cerevisiae at temperature of 30˚C, pH of 5.5 for 3 days with moisture adjustment ranging from 40% to 90%, and nitrogen supplementation using ammonium sulphate and urea salts respectively. The results obtained showed significant protein enrichment with both nitrogen salts and at different ranges of the moisture adjustments. The best results for both nitrogen salts supplementation were obtained at 40% moisture adjustment, which was in agreement with the finding that excessive moisture content could cause the pores to be over saturated with water, thereby reduce oxygen mass transfer [
The authors declare no conflicts of interest regarding the publication of this paper.
Maxwell, O.I., Chinwuba, U.B. and Onyebuchukwu, M.G. (2019) Protein Enrichment of Potato Peels Using Saccharomyces cerevisiae via Solid-State Fermentation Process. Advances in Chemical Engineering and Science, 9, 99-108. https://doi.org/10.4236/aces.2019.91008