Fermentation of cassava (Manihot esculenta Crantz) pulp with yeast, urea and di-ammonium phosphate (DAP)

Phoutnapha Sengxayalth and T R Preston¹

Champasak University, Lao PDR
Alounptc@gmail.com
¹ Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia

Abstract

A solid-state fermentation with yeast was used to increase the protein content of cassava pulp. The organism was grown in a cassava pulp medium with (% in DM) 4% urea, 1% DAP and 2% yeast, with and without steaming before fermentation. The fermentation time was 0, 3, 6 and 9 days.

Fermentation increased the true protein of the cassava pulp from 2 to 12% in DM over the 9 day period; corresponding values for increases in crude protein were 9.5 to 18.4%. It appeared that only some 60% of the NPN (urea and DAP) had been converted to yeast protein. The composition of the residual NPN is not known but presumably was in the form of ammonium salts or related compounds. The apparent increases in crude protein content during fermentation appeared to be due to the loss of 40% of the DM of the substrate during fermentation which resulted in “enrichment” of the crude protein fraction during the course of the fermentation. There were no advantages in prior steaming of the pulp before fermentation.

Key words: anaerobic, crude protein, steaming, true protein

Introduction

Cassava (Manihot esculenta Crantz) is grown in tropical countries in Africa, Asia, and Latin America, with 70% of the world’s cassava production coming from Nigeria, Brazil, Thailand, Indonesia, and the Democratic Republic of the Congo. Cassava root can be used to produce cassava chips, cassava pellets, and cassava starch, which are in high demand throughout the world. Thailand, Indonesia, and Brazil are the most prominent exporters of cassava starch, with their production accounting for 95% of the world’s supply. Cassava pulp is the solid, moist by-product of cassava starch manufacture, and it represents approximately 10 to 15% of the original root weight. As cassava starch production increases, so does the large volume of waste by-product generated. In Thailand, at least 1 million tonnes of pulp are generated annually. Some of the by-product is used to produce fertilizer or is included in diets for ruminants and swine. Recently feeding systems have been developed in which ensiled cassava pulp is the basis of intensive fattening of local “Yellow”cattle (Phanthavong et al 2015, 2016). The low content of protein in cassava pulp (less than 3% in DM) is not a constraint for cattle as use can be made of non-protein-nitrogen in the form of urea. However, for monogastric animals like pigs a supplementary source of true protein is needed.

One way to improve the protein content of carbohydrate-rich feeds is by solid-state fermentation with fungi and yeasts (Hong and Ca 2013). According to Oboh and Akindahunsi (2005), the fermentation of cassava root meal with S. cerevisiae enhanced the protein level from 4.4% to 10.9% in DM and decreased the cyanide content. Other reports indicate that by solid state fermentation, the protein content in cassava pulp can be increased thus improving its feeding value (Oboh and Akindahunsi 200 3; Srinorakutara et al 2006; Ubalua 2007).

Hypothesis

Fermentation of cassava root pulp with yeast, after supplementation with urea and diammonium phosphate (DAP) will increase the content of true protein.

Materials and methods

Location and duration

The experiment was carried out at the Integrated Farming Demonstration Center of Champasack University, Champasak province, Lao PDR, from January to March 2016.

Experimental design

The experiment was arranged as a 2*4 factorial with 4 replications: steaming (ST) or no steaming (NS); and 4 periods of fermentation (0, 3, 6 and 9 days).

Procedure

The fresh cassava pulp was collected from the starch factory (Photo1). It was fermented like the farmers do in making rice wine, but with added urea and DAP. For the ST treatment, the pulp was steamed for 30 minutes; it was then allowed to cool before adding the urea, DAP and the yeast ( Saccharomyces cerevisiae) (Table 1). The pulp with additives was then placed in polyethylene bags (Photo 2) and allowed to ferment for 9 days in semi-anaerobic conditions

Measurements

The pH and the composition of the substrates were determined at the beginning, and after 3, 6 and 9 days of fermentation. The pH, DM, crude protein (CP) and true protein (TP) were determined by AOAC (1990) procedures.

Photo 1. Cassava pulp in the starch factory	Photo 2. Fermenting the cassava pulp

Statistical analysis

The data were analysed using the general linear model option of the ANOVA program in the Minitab software (Minitab 2000). Sources of variation were: steaming, days of fermentation, interaction steaming*fermentation time and error.

Results and discussion

Chemical composition of feed sources

The DM content and the pH decreased with fermentation time (Table 2; Figure 1). There were no advantages in steaming the cassava pulp prior to the fermentation (Figure 2).

The crude and true protein content of the fermented cassava pulp increased with time of fermentation (Table 2, Figure 3). The DM content of the fermented pulp decreased with fermentation time as the yeast metabolized carbohydrate for growth of the organism. Assuming that no moisture was lost in the fermentation it can be calculated that 35% of the original substrate DM had been lost during the fermentation.

The loss of substrate with time led to the apparent content of crude protein increasing (from 9.5% to 18.4% in DM) during the 9 days of fermentation. However, based on the calculated enrichment rate due to loss of substrate the content of crude protein prior to fermentation should have been 12%. The fact that the analyzed level of crude protein in the zero hour sample was only 9.5% implies that some N (probably as ammonia) was lost during the initial process of mixing the urea, DAP and yeast with the cassava pulp.

Figure 1. Effect of fermentation time on pH of cassava pulp, steamed (ST) and not steamed (NS)

Figure 2. No effect of steaming (ST versus NS) on percent of true protein with fermentation time

Figure 3. Effect of fermentation time on true protein and crude protein content of cassava pulp

Fermentation increased the true protein of the cassava pulp from 2 to 12% in DM over the 9 day period; corresponding values for increases in crude protein were 9.5 to 18.4%. Thus it appeared that only some 60% of the NPN (urea and DAP) had been converted to yeast protein. The composition of the residual NPN is not known but presumably was in the form of ammonium salts or related compounds. The apparent increases in crude protein content during fermentation appeared to be due to the loss of some 35% of the DM of the substrate during fermentation which resulted in “enrichment” of the crude protein fraction during the course of the fermentation. There were no advantages in prior steaming of the pulp before fermentation.

Conclusions

• A nine-day anaerobic fermentation of cassava pulp by yeast, in presence of urea and DAP, increased the true protein from 2 to 12% in DM and reduced the content of DM in the substrate from 29.4 to 19.2%, implying that some 35% of the cassava pulp carbohydrate had been metabolized in the growth of the yeast (ie: 35 g carbohydrate werre needed to produce 10 g of yeast protein.
  
  
• There were no advantages in prior steaming of the pulp before fermentation.

Acknowledgements

This research was done by the senior author as part of the requirements for the MSc degree in Animal Production "Improving Livelihood and Food Security of the people in Lower Mekong Basin through Climate Change Mitigation" in Cantho University, Vietnam. The authors would like to express sincere gratitude to the MEKARN II program, financed by Sida (Swedish International Development Agency) for supporting this research. We appreciate the advice received from the PhD students of MEKARN II project in the Faculty of Agriculture and Forest Resource, Department of Animal Science, Souphanouvong University, Lao PDR.

References

AOAC 1990 Association of official analytical Chemists. 1990.Official methods of analysis. 15th ed. AOAC, Washington, D.C

Hong T T T and Ca L T 2013 The protein content of cassava residue, soybean waste and rice bran is increased through fermentation with Aspergillus oryzae. Livestock Research for Rural Development. Volume 25, Article #132. http://www.lrrd.org/lrrd25/7/hong25132.htm

Minitab 2000 User's guide to statistics; Minitab Statistical Software Version 13.31, Minitab Inc, USA.

Oboh G and Akindahunsi AA. 2003 Biochemical changes in cassava products (flour & gari) subjected to Saccharomyces cerevisiae solid media fermentation. Food Chemistry, v.82, p.599-602.

Oboh G and Akindahunsi AA 2005 Nutritional and toxicological evaluation of Saccharomyces cerevisiae fermented cassava flour. Journal of Food Composition and Analysis, v.18, p.731-738.

Phanthavong V, Viengsakoun N, Sangkhom I and Preston T R 2015 Effect of biochar and leaves from sweet or bitter cassava on gas and methane production in an in vitro rumen incubation using cassava root pulp as source of energy. Livestock Research for Rural Development. Volume 27, Article #72. http://www.lrrd.org/lrrd27/4/phan27072.html

Phanthavong V, Khamla S and Preston T R 2016 : Fattening cattle in Lao PDR with cassava pulp. Livestock Research for Rural Development. Volume 28, Article #10. Retrieved February 1, 2017, from http://www.lrrd.org/lrrd28/1/phan28010.html

Srinorakutara T, Kaewvimol L, and Saengow L 2006 Approach of cassava waste pretreatments for fuel ethanol production in Thailand. J. Sci. Res. Chula. Univ., 31:77-84.

Ubalua A O 2007 Cassava wastes: treatment options and value addition alternatives. Afr. J. Biotech., 6 (18): 2065-2073

Received 28 July 2017; Accepted 9 August 2017; Published 1 September 2017

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