The increasing
expansion of agro-industrial activity over the last 40 years has led to
the accumulation of a large quantity of lignocellulosic residues all
over the world. In particular, large quantities of rice straw (300.000
t) and citric bagasse (50.000 t) are annually produced in Uruguay.
Alternative methods of utilizing these agricultural residues are needed
to mitigate the environmental pollution problems associated with
current disposal methods, such as open-field burning and soil
incorporation. Mushroom cultivation on rice straw and citric bagasse
may offer economic incentives for growbusiness to examine these
residues as valuable resources and develop new enterprises to use them
to produce nutritious mushroom products.
Agro-residues which
contain three major structural polymers, cellulose, hemicellulose and
lignin, are the main sources of feed for ruminants. However, their
quality as feed, especially in terms of digestibility, depends not only
on the amount and structure of these polymers but also on the amount of
readily available substances such as sugars and amino acids. White-rot
fungi which degrade cellulose and hemicellulose as well as lignin are
widely used to increase the digestibility of agro-residues. The
lignocellulose complex in straw and other plant residues is degraded
very slowly by ruminants, because of the physical and chemical barrier
imposed by lignin polymers, preventing free access of hydrolytic
enzymes, such as cellulases and hemicellulases, to their substrates.
Normally, the rate of decay of plant debris is proportional to its
lignin content. Biological delignification of straw seems to be the
most promising way of improving its digestibility. Several authors have
examined this possibility, using mainly wheat straw and Pleurotus spp.
(oyster mushrooms) under different conditions and substrate
pretreatments.
The use of Pleurotus
spp. for upgrading different substrates into valuable animal feed
products has been reviewed. The advantage of using Pleurotus spp for
this particular application is their preferential degradation of
lignin: the lignin is selectively degraded and the cellulose is exposed
and can be utilized by ruminants. Moreover, as it has been consumed by
humans for centuries, Pleurotus spp may be considered safe for animal
consumption without further investigation.
The cultivation of
Pleurotus spp has expanded in the past few years in Uruguay.
In relation to these
topics the microbiology lab is working in the bioconversion of citric
bagasse and rice straw with different strains of the edible mushroom
Pleurotus spp with a view to increase nutritive values and
digestibilities for animal feed.
The main objectives of
this study are:
- Characterization of
the different strains of Pleurotus spp used in our country (nutritive
values, ligninolytic activity, optimal grow temperature and time)
- Optimization of the
SSF process for the selected strains and evaluation of the products
after different times of the mushroom growth (chemical composition,
fermentation characteristics, levels of spawn to substrate ratio, dry
matter, neutral detergent fiber, acid detergent fiber, crude fiber,
protein)
- Design of animal
feeding studies to define the safety of the degraded substrate for
feeding, their nutritional value and the ruminants readiness to consume
them.
Silvana Alborés
