Introduction
Solid state fermentation (SSF) is the fermentation
process where microorganisms are grow in an environment without free water, or
with very low content of free water on solid substrate and complex material is converted
into simpler forms, moreover this solid substratum itself act as carbon/energy
source. Egyptians were reported to make bread using a notable technique SSF and
has been used in Asian continent from the ancient time in 2000 BC. In natural
condition with little moist or in near absence of water, the microorganisms
obtain carbon, nitrogen and other nutrients for growth and show degradative
activity. In recent years, SSF has shown much development in bio processing in
food, pharmaceutical, textile, biochemical and bioenergy. Solid state
fermentation is processed through fungi, bacteria or yeast.
With an increasing the expansion of
agro-industrial activity, accumulates a bulk quantity of residues over every
year. This agricultural based biomass is highly lignified as per the
composition and having lignocellulosic in nature, that causing elimination
issue with ultimate environmental pollution. Worldwide bid of animal based
products are augmented in a blooming rate thus emphasizing the inevitability of
applying strategies to improvise animal productivity. The major constraints in
livestock’s sector have lack of availability of feed resources, poor quality of
available feed sources, and high feed cost particularly in tropical countries. The
worsening animal health and their sustainability have necessitates the use of
certain substitute such as agricultural by products, crop residues and grasses
as a feed source (a lignocellulosic biomass). These agro industrial residues
used for animal feeds, having highly lignified fiber, poor in nitrogen and
minerals, reduced digestibility and contains anti nutritional factors, owing to
this these, are not to utilized judiciously and therefore they are receiving
more consideration for quality control.
In view of high nutritional perspective these residues are not described
as a waste but known to be as raw materials for further product formation and
developments. With an advance, in a field of animal nutrition, animal
nutritionist developed various physical, chemical and biological methods to
overcome the problem associated with animal’s feed stuffs. As a biological
treatment has fascinated an interest of researchers and it has become a widely
discussed theme in a current period.
The huge nutritious potential of agricultural based
byproducts has generated an interest of nutritionist for utilizing these
efficient ways and improves the production of animals. In concern to this,
solid state fermentation (SSF) is a promising novel technique. The
lignocellulosic structural characters of plant residues provides a solid
support and act as a substrates for the microbial fermentation to produce a
certain value added products through SSF. SSF has a wide scope in the field of
animal nutrition in terms for the production of enzymes, bioactive components,
organic acids, vitamins, and feed additives, bio transforming products,
biological degradation and detoxification of agricultural residues/wastes. The
research studies shown the inclusion of SSF biomass has a great impact on
nutritive composition of feed, performance, hemo-biochemical status, gut
morphology, gut microbiota, carcass attributes, rumen fermentation along with
the reduction in enteric methane emission of ruminants, non ruminants animals
and poultry birds.
Types
of fermentation
There are two type of
fermentation process namely solid state fermentation (SSF) and Liquid or
submerged state fermentation (SmF). Solid state fermentation (SSF), a
process that takes place in a solid matrix (inert support or
support/substrate) without or with smaller quantity of free water. However, moisture needed to support the growth and
metabolic activity of microorganisms on solid substrate. On the other hand, in liquid-state fermentation (LSF) the
substrate is solubilized or suspended as free particles in a large volume of
water. The differentiating feature between SSF and SmF has been described in
Table 1.
Table:
1 Differentiating points in SSF and SmF.
Features
|
SSF
|
SmF
|
Medium
|
Not
free – flowing
|
Free
flowing
|
Deepness
|
Shallow
|
Greater
|
Nutrients
|
Solid
substrate
|
Employed
|
Water
|
Medium
absorbs
|
Medium
is dissolved
|
Temp.,
pH
|
Not
uniform
|
Uniform
|
Contamination
|
Less
|
Higher
|
System
|
3
phase
|
2
phase
|
Intra
particle resistances
|
Present
|
No
such resistances
|
Culture
distribution
|
Adhere
to solid and grow
|
Uniformly
distributed
|
Bioreactors
|
Small
|
Large
|
Measurements
of biomass
|
Lots
of difficulties
|
Online
sensors are available
|
Product
|
Highly
concentrated
|
Low
concentration
|
Liquid
waste
|
Not
produced
|
High
quantity
|
Solid
state fermentation
Solid state fermentation
(SSF) is recognized a biotechnological processes in which in the absence or
near absence of free water organisms grow on non-soluble material or solid
substrates. It involves microbial fermentation of byproducts with few
processing steps. At the most general level, the major processing steps of SSF
are not different from those of a submerged liquid fermentation (SLF) process.
The processing steps of solid state fermentation involves are as follows.
General processing steps in SSF
process
- Inoculum
preparation
- Substrate
selection and preparation
- Bioreactor
preparation
- Inoculation
and Loading
- Bioreactor
operation
- Unloading
- Downstream
processing
- Waste
disposal
Characteristics
of the fibrous components of crop residues
The major portion of
the agricultural residues are carbohydrates mainly lignocellulose. These
Cellulose, hemicellulose and lignin bonding in the cell wall matrix need to be
broken. The dietary fibers components of plant
walls are influenced by both the content and physical characteristics of wall
polysaccharides such as degree of crystallinity and polymerization thus not
completely digested by enzymes of the animal’s digestive system. With increasing
the plant maturity lignin content is also elevated and has directly impacted on
digestibility of neutral detergent fiber (NDF) and it has a correlation with
other nutrient utilization.
Use of certain alternative options such as the
agricultural crop residues and grasses (lignocellulosic biomass) as animal feed
stuffs. If these are utilized judiciously this may provide enough energy and
nutrients to the animals. However, high lignin content and lower digestibility,
protein content and poor palatability of crop residues and grasses discourage
their use as the sole animal feed. Lignin, being a cementing material in plant
cell wall restricts the fullest accessibility of carbohydrates, the energy
reserve, to the microorganisms inside the gut of ruminating animals. Among
various microorganisms known for lignin degradation, white- rot fungi (majorly
basidiomycetes) have been adjudged most promising lignin degraders and have
been largely studied for bioconversion of plant residues into nutritionally
digestible animal feed under solid-state fermentation (SSF) conditions.
Application of SSF in Animal Nutrition
Solid state
fermentation has an extensive scope and a novel technology in the field animal
nutrition for utilizing these highly lignified by products. SSF having wide no
of applications (Table 3) includes enzyme production, bioactive metabolites,
organic acids production, vitamins, biological degradation of anti-nutritional
factors from the various byproducts and animal feed stuffs. Enzymes are
important products obtained from microorganisms and useful for human as well as
animals and birds. Enzyme production is higher in solid state fermentation
(Pandey et al. 1999) [44]. Plant cell wall has two phases
including micro-fibrilar phase, it contains micro fibrils of cellulose and second
is matrix phase (non-crystalline phase) which contains polysaccharides (Pectin
and hemicelluloses), proteins and phenolic compounds. Recently renewed
interests have been seen in enzyme production, mainly celluloses, xylanases, Xylanases,
Laccases etc. Besides bacteria, fungi are considered the best source of enzyme
production through the SSF. The various substrates and microbes used for the
production of various products used for feed stuffs are shown in Table 4 and 5.
Table:
3 Applications of SSF in animal nutrition
Economic Sector
|
Application
|
Examples
|
Industrial Fermentation
|
Enzymes
production
|
Amylases,
amyloglucosidase, cellulases,
proteases,
pectinases, xylanases, glucoamylases
|
Bioactive
products
|
Mycotoxins,
gibberellins, alkaloids, antibiotics, hormones
|
|
Organic
acid production
|
Citric
acid, fumaric acid, itaconic acid, lacticacid
|
|
Biofuel
|
Ethanol
production
|
|
Miscellaneous
compounds
|
Pigments,
biosurfactants, vitamins, xantham
|
|
Agro-Food
Industry
|
Biotransformation
of crop residues
|
Traditional
food fermented (Koji, sake, ragi, tempeh), protein enrichment and single cell
protein production, mushrooms production.
|
Food
additives
|
Aroma
compounds, dye stuffs, essential fat and organic acids
|
|
Environmental control
|
Bioremediation
& biodegradation of hazardous compounds
|
Caffeinated
residues, pesticides, polychlorinated biphenyls (PCBs)
|
Biological
detoxification of agroindustrial wastes
|
Coffee
pulp, cassava peels, canola meal, coffee
husk
|
(Source: Guerra et
al. 2003[21]; Mienda et al. 2011[36]).
Table: 4 Microorganisms used for SSF
Microorganisms
|
Substrates/ Solid supports
|
Source
|
Bacteria
|
||
Amycolatopsis
mediterranean
MTCC 14
|
GOC and COC
|
Vastrad and
Neelagund (2011a,b)[71; 72]
|
Pseudomonas spp. BUP6
|
GOC, COC, SOC, and CSC
|
Faisal et
al. (2014)[17]
|
Bacillus
licheniformis
MTCC 1483
|
Wheat straw, sugarcane bagasse, maize
straw, and paddy straw
|
Kaur et al. (2015)[24]
|
(Continued table 5)
|
||
Fungi
|
||
Aspergillus
niger
|
Rice bran, wheat bran, black gram
bran, GOC, and COC
|
Suganthi et al. (2011)[63]
|
Aspergillus
oryzae
|
Soybean meal (waste)
|
Thakur et al. (2015)[68]
|
Rhizopus arrhizus
and Mucors
ubtillissimus
|
Caorn cob cassava peel, soybeans,
wheat bran, and citrus pulp
|
Nascimento et al. (2015)[40]
|
Aspergillus
niger
|
Rice bran, wheat bran, black gram
bran, GOC, and COC
|
Mahalakshmi and Jayalakshmi, (2016)[28]
|
Aspergillus
terreus
|
Palm oil cake
|
Rahman et al. (2016)[49]
|
Table: 5
Substrates used for SSF
Enzymes
|
Microorganisms
|
Substrates/ Solid support
|
Source
|
Lipase
|
Candida rugosa
|
Groundnut oil cake (GOC)
|
Rekha et
al. (2012)[52]
|
Pectin methyl
Esterase
|
Pseudomonas notatum
|
Wheat bran and orange peel
|
Gayen and
Ghosh (2011)[19]
|
Lipase
|
Pseudomonas
aeruginosa
|
Linseed oil cake (LOC)
|
Dharmendra,
(2012)[14]
|
α-Amylase
|
Aspergillus niger
|
Orange peel
|
Sindiri et
al. (2013)[58]
|
α-Amylase
|
Aspergillus oryzae
|
Coconut oil cake (COC)
|
Ramachandran et
al. (2004)[50]
|
α-Amylase
|
Bacillus sp.
|
Rice bran
|
Sodhi et
al.(2005)[61]
|
α-Amylase
|
Bacillus sp.
|
Corn bran
|
Sodhi et
al. (2005)[61]
|
α-Amylase
|
Aspergillus niger
|
Rice bran, wheat bran, black gram
bran, and soybean
|
Akpan et
al. (1999)[1]
|
Invertase
|
Aspergillus niger
|
Fruits peel
waste
|
Mehta and
Duhan (2014)[35]
|
(Source: Sadh et al. 2018)
SSF is most
imperative method used to improve the availability digestibility of fibrous
crop residues by relaxing the lignocellulose network along with increasing
other nutrients digestibility. Further, it resultant in to improved rumen
fermentation (TVFA) range of 10 to 15 % and feed efficiency of animals.
Reported studies prove incorporation of SSF ingredients at the rate of 5-20% in
the ration of both ruminants and non ruminants could be improves growth,
production, health status with reduced methane production and economics of
feeding. However, research is needed to developed methodology for making it
more economical, huge biomass production at farmer's door steps. In addition,
need to produce genetically modified strains of microbes, develop proper
controlling parameters and experimentation for optimize the level of SSF to increase the productive performance in various
species of ruminants and non ruminants animals and poultry birds.
Dr. A.B.
Parmar and Dr. V. R. Patel,
College of Veterinary Science and A.H.
Navsari Agricultural University,
Navsari, Gujarat, India
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