Study On Physio-Biochemical Changes Associated With Browning And Preservation Technology On Agaricus Bisporus During Storage

Consumption of Agaricus bisporus has been increasing substantially due to their delicacy, flavor and nutritional value. Agaricus bisporus have a short shelf life of 1-2 days during the ambient storage because that they are rich in wate and have no cuticle to protect them from physical or microbial attack or water loss. Especially, browning is a most important role in the decrease in appearance quality. However, there are so many researches on the browning of vegetable and fruit, based on the browning information is lack for the mushroom, Agaricus bisporus is selected as experiment material in this study to investigate the changes of physiological and biochemical characteristics associated with enzymatic browning and non-enzymatic browning during storage; and analyse some polyphenolic compounds before or after browning of Agaricus bisporus by HPLC technology to infer the main browning substrates; and study some properties of peroxidase of Agaricus bisporus to offer some theoretical bases for the browning mechanism; and study the effects of chlorine dioxide (ClO2) treatment or N,O-carboxymethyl chitosan coating on the storage quality of Agaricus bisporus. The conclusions of this thesis as follows:1. The major biochemical indices associated with enzymatic browning of phenol content, PPO, POD activity were all related to the change of L-value. In the course of enzumatic browning, the key enzyme was PPO and POD.The major biochemical indices associated with non-enzymatic browning of reduced sugar and Vc content were also related to the change of L-value, and Vc content was significantly related. The major physiological indices associated with enzymatic browning of membrane permeability was significantly related to the change of L-value, it might promote the browning.2. The main browning substrates of Agaricus bisporus might be guaiacol and L-tyrosine, and the maximum absorption peak of the enzymatic browning products of exogenous guaiaco was similar with natural browning.3 The most suitable reaction pH of POD from Agaricus bisporus was 5.5, and the suitable temperature was 40℃.Under these conditions, Km=0.091mol/L Vmax=454.55mol.L-1.min-1 and the fitting straight line was y=0.0002x+0.0022, R2=0.9829.Therefore, POD from Agaricus bisporus had a high affinity with guaiaco.4. The most suitable concentration of ClO2 solution is 150mg/L with the most suitable time is 10min. Agaricus bisporus were treated with CIO2 solution could maintain the whiteness, reduce browning degree, reduce the respiration rate and PPO activity, delay the activity peak of POD, reduce the loss degree of soluble protein and keep SOD activity at a high level at refrigerated storage.But it had little effect on cap opening and wilting. The one was treated at ambient(7℃-15℃) storage, had a shelf life about 5 days. The one was treated at refrigerated storage could maintain a good whiteness in first 5 days, and have a shelf life about 9 days.5. Chemical modified chitosan coating was seen to delay browning changes and dehydration, decrease PPO activities and reduce membrane lipid peroxidation, especially during ambient storage, with extending the shelf life to 5-6 days. Incorporation of low temperature storage (refrigerated storage), the shelf life could reach 10 days.