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1. Introduction
Some agricultural
produces are
perishable that characterized by their short shelf life. Physical, chemical or biological
damages on product accelerate the deterioration of products. The improper
management of storage conditions, i.e., too warm or too cold for a certain product, is
another factor that increases physiological deterioration. The shelf life of certain
products could be extended by applying the
proper packaging
system also.
Temperature and humidity were essential factors
for fresh products shelf-life-
extension-efforts. Respiration rate which indicates many metabolic activities of the
tissues as well as the rate of quality degradation of stored products could be
suppressed through lowering the storage temperature to slightly above the critical
temperature of certain product Saltveit, 2004. The second factor that has great
influence on product quality is humidity. Weight loss can be controlled by reducing
the gradient of water vapor pressure WVP between products surface and
surrounding atmosphere Perkins et al, 2008. Losing 1-2 of water of produce
can reduce sales appeal of produce of fresh produce Kader, 2002. Therefore, the
packaging system that can maintain the oxygen and carbon dioxide at certain
concentration as well as humidity is needed. The characteristics of packaging
system have strong relationship with characteristics of packed product. It has
been proved that every product has their own
unique properties;
therefore, designing of packaging system should be
based on those properties. The initial knowledge that is important on designing
packaging system is respiration rate on different temperature storage. Respiration
rate is main factor that changes the composition of atmosphere dynamically
on
jar’s head
space. The
gases concentration inside jar’s head space is
always changing dynamically until the equilibrium condition is obtained. This
equilibrium condition reached when the respiration rate, transfer of gas oxygen and
carbon dioxide were equal. Oxygen that consumed by packed products
was compensated by oxygen permeating from
the surrounding atmosphere. In the same way to oxygen, the carbon dioxide which
diffuses to surrounding atmosphere is replaced by diffusion
from product’s tissues. On one hand, oxygen must be
available for respiration to avoid anaerobic respiration during storage. On the other
hand, over supply of oxygen makes the packaging has no benefit for prolonging
shelf life. The critical threshold of gas concentration is considered to design the
magnitude of gas transfer of packaging film Beaudry et al., 1992.
The water vapor that produced from respiration and transpiration continuously
adds the water vapor contained in jar’s head space. Water vapor diffuses to
ambient environment with
a certain
magnitude. Most of them condense on product’s or packaging’s surface when
saturated water vapor pressure at certain temperature is exceeded. This liquid water
encourages the microbial development and reduces the diffusivity of packaging film.
Mushroom is one of the vegetables that have short shelf life, only 3 days on
ambient temperature
Czapski and
Szudyga, 2000. Their dermal tissues have no cuticle to protect them from physical
damages or microbial attack or water loss Martine et al., 2000. High moisture
content in their
fruit body’s makes
mushrooms respire and transpire with high rate. Mushroom need low temperature
storage 0 - 2 C, low O
2
concentration and relatively high CO
2
concentration as well
as high
humidity 90-98
Thompson et al, 2002. Oyster
Mushroom Pleurotus
ostreatus becomes commercial product that is highly demanded nowadays in
Yogyakarta. Local farmer and seller pack the mushroom with commercial plastic bag
which was available on traditional market. It was needed physiological properties data
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of Oyster mushroom, that were still rare, to choice the right kind of bag plastic or to
design the proper packaging system. Therefore, the aim of this work is to study
the physiological behaviors of Oyster mushroom on several variations of
temperature storage and gas concentration.
2. Theoretical Approach
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