Optimization of Solid State Fermentation Conditions for Cyanide Content Reduction in Cassava Leaves using Response Surface Methodology
Corresponding email: gunawan@chem-eng.its.ac.id
Published at : 24 May 2019
Volume : IJtech
Vol 10, No 3 (2019)
DOI : https://doi.org/10.14716/ijtech.v10i3.2923
Hawashi, M., Aparamarta, H., Widjaja, T., Gunawan, S., 2019. Optimization of Solid State Fermentation Conditions for Cyanide Content Reduction in Cassava Leaves using Response Surface Methodology. International Journal of Technology. Volume 10(3), pp. 624-633
| Mohamed Hawashi | -Department of Chemical Engineering, Institut Teknologi Sepuluh Nopember (ITS) -Central Scientific Research Laboratory, Sebha University, Sebha |
| Hakun Aparamarta | Department of Chemical Engineering, Institut Teknologi Sepuluh Nopember (ITS), Surabaya, 60111, Indonesia |
| Tri Widjaja | Department of Chemical Engineering, Institut Teknologi Sepuluh Nopember (ITS), Surabaya 60111, Indonesia |
| Setiyo Gunawan | Department of Chemical Engineering, Institut Teknologi Sepuluh Nopember (ITS), Surabaya 60111, Indonesia |
Cassava
leaves are a good source of protein. However, their use is limited because of
the presence of cyanogenic glucosides. These require a further detoxification
process in order to reduce the cyanide to a safe level prior to human
consumption. The
main objectives of this work are: (i) to demonstrate the effectiveness of
solid-state fermentation using Saccharomyces
cerevisiae on the cyanide content degradation of cassava leaves; and (ii) to
optimize the independent variables for the minimum cyanide content level of
cassava leaves by the application of response surface methodology (RSM). The various
process parameters investigated for these purposes were sucrose concentration,
urea concentration, moisture content, and fermentation time. The degradation of
cyanide content was described by the quadratic model, which resulted in an
excellent fit of the experimental data (p < 0.01). The statistical tests
show that linear terms for sucrose concentration, urea concentration, moisture
content and fermentation time had a significant effect on cyanide content (p <
0.01). Moreover, the interaction coefficients between sucrose concentration and
fermentation time; urea concentration and moisture content; and nitrogen
concentration and fermentation time were significant model terms (p < 0.05).
A minimum cyanide content of 0.81 ppm was obtained at 1% (w/w) sucrose
concentration, 0.5% (w/w) urea concentration, 60% (v/w) moisture content and
with a fermentation time of 78 hours. The optimal level made a significant reduction in cyanide
content of 97.96%, which is lower than the toxicity level suggested by
the World Health Organization of 10 ppm.
Cassava leaves; Cyanide content; Response surface methodology; Solid state fermentation
With the growth in food
consumption, the majority of people rely heavily on food crops as their primary
food sources. Root crops, such as cassava, are grown in developing countries as
a primary source of carbohydrates (Hawashi et al., 2018). This crop represents one of the primary sources
of food for Indonesian people, along with other staples such as rice, sago and
corn. Reports indicate a production rate of nearly 20 million tons per year, harvested from 1.93 million hectares (Agustian, 2016). Cultivation of cassava plants can take place even in marginal environmental conditions,
due to their high drought tolerance, with an optimal yield of
Reduction of cyanide levels
can also be made in cyanide-rich raw food sources such as cassava.
Worldwide, the most common
methods of cassava leaf processing include boiling and soaking in water,
steaming, sun drying, and oven drying. These approaches aim to
reduce the toxic compounds in the leaves for human consumption (Fasuyi, 2005). Cassava leaf processing is
mainly based on the endogenous cassava enzyme (linamarase), which catalyzes the
conversion of cyanide-containing compounds (linamarin)
into acetone cyanohydrin, which either
enzymatically or spontaneously decomposes into HCN and acetone (Montagnac et
al., 2009). However, some methods (such as steaming and oven drying) have been proven to be
ineffective for lowering the cyanide content in cassava leaves to the safe
limit. Studies have shown that the fermentation of cassava leaves is a
promising method for reducing cyanide content (Kobawila et al., 2005; Morales
et al., 2018). These reports show respective reductions of at least 70% and
94.18% in cyanide content during fermentation. They further validate the
preference for the fermentation technique over conventional methods. The SSF
technique has several advantages, including high
productivity and reduced processing time (Febrianti et al., 2017). However, reports indicating the efficiency of
cassava leaf fermentation are quite scarce compared to those which investigate
tubers.
Various
process conditions such as moisture
content, pH, inoculum size, fermentation time, concentration of nutrient supplementation and temperature can affect
the microbial growth, enzyme production, and formation of the product during
the fermentation process (Ezekiel & Aworh, 2013). The optimization
processes using the “One Variable at One Time (OVAT)” technique (changing one
single variable, while keeping others at constant levels) is an inefficient way
of determining the interaction between the process variables as it involves
high cost and requires various experiments to obtain the optimum levels (Braga
et al., 2011;
Hadiyat & Wahyudi, 2013). Recently, the application of RSM has attracted the attention of
researchers working with fermentation to optimize process conditions and evaluate the correlation
between independent variables and their responses (Istianah et al., 2018).
Yeast
and lactic acid bacteria (LAB) are the most investigated microorganisms for the
production of linamarase during cassava fermentation and the development of flavor. Yeast, such as Saccharomyces cerevisiae, has
several advantages, including its availability, low cost, ability to secrete
extracellular enzymes, non-pathogenic character, and widespread use in
traditional fermentation, particularly in fermented foods (Oboh &
Akindahunsi, 2003). Furthermore, Saccharomyces
cerevisiae is able to use cyanogenic glucosides and their metabolites
during food processing, making it one of the micro-organisms which is most
involved in the cassava fermentation process (Lambri et al., 2013). Therefore, the
objective of this work is to demonstrate the effectiveness of solid-state fermentation using Saccharomyces
cerevisiae in the reduction of cyanide in cassava leaves. Furthermore, the
optimization of the independent variables (moisture content, incubation time
and nutrient supplementation) to achieve a minimum cyanide content level in cassava
leaves by employing response surface methodology (RSM), is also studied in detail.
The research has investigated the effect of
solid state fermentation using Saccharomyces
cerevisiae on the removal of cyanide content from cassava leaves. The study has shown that response surface
methodology (RSM) was a high-performance technique for optimization of the
process conditions for minimizing cyanide content in fermented cassava leaves
through solid-state fermentation. The optimal process condition was obtained
at 1% (w/w) sucrose concentration, 0.5% (w/w) urea concentration and 60% (v/w)
moisture content, with a fermentation time of 78 hours. It was observed that an
exponential decrease in cyanide content over time can lead to satisfactory
detoxification in cassava leaves, with cyanide concentration falling to levels
lower than 10 ppm after 60 hours of fermentation, and thus providing a safe and
healthy food source.
This work was supported by grant no. 849/PKS/ITS/2018
provided by the Ministry of Research,
Technology and Higher Education of the Republic of Indonesia.
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