Biotechnology to Improve Shelf Life and Quality Traits of Foods - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 342

ranges from 6 to 11%. The values vary not only from study to study, but also between
flushes within a given crop. Environmental conditions are important factors affecting
the solids content of fresh mushroom. 102
Apart from the high water content (89 to 94%), fresh mushrooms also contain
2.5 to 5.8% of carbohydrates, 2.6 to 4.0% of proteins, 0.2 to 0.7% of crude fat,
0.6 to 1.1% of fiber, and more than 1% of ash. The protein content of fresh mushroom
is about twice as high as that of most vegetables. Based on its content and relative
proportion of amino acids, mushrooms protein appears to be intermediate in nutri-
tional quality between meat and vegetable proteins. 102 Mushroom carbohydrates are
present in lower proportions than in other vegetables and provide a very small fraction
of the energy requirement. Due to their low energy value (20 to 30 kcal/100 g),
mushrooms can be used in low calorie diets. Since the mushroom contains more
than 1% of ash, its mineral content is generally higher than in many fruits and
vegetables. However, mushrooms are found to be low in sodium which is recom-
mended in special diets.
It is well established that compost is a prime factor for increasing yield. Mau
et al. 114 proved that nutrient supplementation at spawing increased the yield of
mushrooms and supplementation at casting resulted in better color for the first two
flushes of the crop cycle.
Quality Parameters of Fresh Mushrooms
There are several parameters that should be consider in order to diminish the quality
deterioration of mushrooms after harvesting; among them the following can be
mentioned:
Respiration rate : Fresh mushrooms are living organisms and after harvest
they continue to develop. They take in oxygen, and through the process
of respiration convert previously stored substances (primarily sugars) into
energy, carbon dioxide, and water. Mushrooms have a higher rate of
respiration than fruits and vegetables and much of the energy yielded by
respiration is used in the ongoing processes of maturation. This leads to
senescence giving a general deterioration of cells with a concurrent loss
of moisture and increase in browning, all factors that most consumers find
unacceptable. 102 Refrigeration, overwrapping of mushrooms packages with
a permeable film, controlled or modified atmosphere storage, and irradi-
ation will all slow, but not stop, these processes.
Postharvest development : Harvested mushrooms undergo a course of post-
harvest development similar to those allowed to remain growing on the
bed. The development of harvested mushrooms goes from veil intact (tight)
to veil open, gill surface flat. Ryall and Lipton reported that mushrooms
of high quality should have closed veils, should not have elongated stipes,
and gills should not be visible. 102 Mushrooms harvested at the bottom stage
have a longer shelf life than mushrooms in the cap or open stage of
development.