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- Author or Editor: Dennis P. Murr x
- Journal of the American Society for Horticultural Science x
Abstract
Controlled atmosphere (CA) storage prolonged the shelf life of mushrooms (Agaricus bisporus, [Lange] Sing.) if the O2 concentration was 9% or the CO2 concentration was 25 or 50%. Concentrations of 2 to 10% O2 stimulated pileus expansion and stipe elongation with maximal stimulation of growth occurring at 5% O2. Levels of CO2 above 5% markedly inhibited growth, even after air was substituted for the CO2 treatment. Five percent CO2 stimulated stipe elongation and suppressed pileus expansion. Protein degradation, as indicated by protease activity and the level of a-amino N in the tissue, increased during postharvest maturation of mushrooms. As in starving bacteria, it is suggested that the main physiological function of proteolysis in the postharvest maturation of mushrooms is as a source of C and N.
Abstract
Postharvest discoloration of cultivated mushrooms (Agaricus.bisporus [Lange] Sing., ‘tan strain’) was significantly retarded by treatment with succinic acid-2,2-dimethylhydrazide (SADH). The optimum SADH concn was 100 ppm. The effect, however, lasted no longer than 3 days after which time all SADH treatments discolored at rates equal to or greater than controls. The decrease in discoloration was correlated with a decrease in o-diphenol oxidase (o-DPO) activity. Protease activity was higher in SADH treated mushrooms suggesting that reduction in browning was due to degradation of o-DPO rather than direct inhibition of o-DPO by SADH. In vitro SADH competes with proline for quinones produced by enzymatic or non-enzymatic oxidation of diphenols. It is proposed that in vivo SADH exerts a dual effect in reducing mushroom discoloration: first SADH induces degradation of o-DPO through an increase in proteolytic activity, and second it binds to quinones thereby removing intermediates which lead to pigment formation.
Abstract
Storage of mushrooms (Agaricus bisporus, [Lange] Sing.) in 0% O2 reduced discoloration and o-diphenol oxidase (o-DPO) activity for up to 7 days. Levels of O2 above 0% had little or no effect in reducing discoloration and o–DPO activity compared to air controls. Concentrations of CO2 above 5% appeared to increase surface discoloration while markedly inhibiting o-DPO activity. After transfer to air, the effectiveness of the increased CO2 treatments in reducing o-DPO activity in mushrooms depended on storage time in CO2.
In vitro CO2 markedly inhibited o-DPO activity, with 50% inhibition at 25% CO2. Complete inhibition was never attained. The inhibition by CO2 was found to be competitive with respect to catechol and could not be overcome by increasing the O2 concentration above 20%. The action of CO2 in vivo in reducing o-DPO activity could be through a direct competitive inhibition or through the inhibitory effect of CO2 on mushroom maturation.
Abstract
Mushrooms [Agaricus bisporus, (Lange) Sing.] stored at 10° and 20°C showed a sigmoid pattern of growth while at 0°C growth was retarded. The postharvest growth exhibited at 10° and 20°C could be related to a decrease in free a-amino N while at 0°C there was a significant increase in the level of free a-amino N during storage. Protease activity in the tissue increased at all 3 temperatures. It is suggested that postharvest maturation of mushrooms is supported by utilization of low molecular weight nitrogenous compounds formed through increased protein degradation. Mushrooms stored at 20°C toughened and matured faster than those stored at 10° or 0°C. Increases in discoloration during storage appeared to be correlated with decreases in total phenols and with increases in o-diphenol oxidase (o-DPO) activity. The relationship of these biochemical changes to postharvest maturation of mushrooms is discussed.
To decipher the relation between α-farnesene metabolism and the development of superficial scald in apples, trans,trans-α-farnesene synthase, the enzyme that catalyzes the conversion of farnesyl pyrophosphate to α-farnesene, was partially purified from skin tissue of `Delicious' apples (Malus ×domestica Borkh.) and characterized. Total and specific activities of the enzyme were higher in the cytosolic fraction than in membrane fractions. α-Farnesene synthase was purified 70-fold from the cytosolic fraction by ion exchange chromatography and gel permeation, and the native molecular weight was estimated to be 108,000. The enzyme had optimal activity at a pH of 5.6 and absolutely required a divalent metal ion such as Mg2+ or Mn2+ for activity. It exhibited allosteric kinetics, S(0.5) for farnesyl pyrophosphate being 84±18 μmol·L-1, and a Hill coefficient (nH) of 2.9, indicating the number of subunits to be two or three. Enzyme activity was highest between 10 and 20 °C, while 50% of the maximal activity was retained at 0 °C. In vivo α-farnesene synthase activity was minimal at harvest, then increased rapidly during 16 weeks storage in air at 0 °C, and decreased during further storage. Activity of α-farnesene synthase, α-farnesene content, and conjugated triene alcohol (the putative scald-causing oxidation product of α-farnesene) content in skin tissue were not correlated to the inherent nature of scald susceptibility or resistance in 11 apple cultivars tested.