| During MA storage, high relative humidity (RH) conditions prevail in the packages due to the higher transpiration rates and lower water vapour transmission rates of fresh Agaricus bisporous. High humidity conditions lead to moisture condensation and favour microbial growth, which induce decay and deteriorate of the product. Moisture absorption characteristics of twelve moisture absorbers at different temperatures and humidities were investigated in this paper. The optimum compound absorbers and their ratios for MA storage of Agaricus bisporous were screened and verified. The results will provide theoretical basis and technique reference for the RH control during MA storage of Agaricus bisporous. The main research contents and conclusions are as follows:1. Static adsorption method was employed to investigate the moisture absorption characteristics of12different moisture absorbers or desiccants viz. calcium chloride (CaCl2),3A molecular sieve, activated aluminium oxide ball, diatomite, bentonite, sodium hexametaphoshpate, microcrystalline cellulose (MC), activated aluminium oxide powder, xylitol, sorbital, konjac glucomannan (KGM) and chitosan at different temperatures (2,10and18℃) and RHs (76%-,86%and96%).The results showed that moisture uptake increased with increasing RH for the same absorber at fixed temperature, while moisture uptake varied little with elevated temperature at fixed RH. The ranking sequence of moisture uptake capacity at different temperatures and RHs are CaCl2(1.013-1.445g H2O g-1), xylitol (0.006～0.833g H2O g-1, with the maximum moisture uptake of0.833g H2O g-1at10℃and96%RH, and0.006～0.507g H2O g-1at other temperature range), sodium hexametaphoshpate (0.251～0.791g H2O g-1), sorbital (0.073-0.547g H2O g-1), KGM (0.143-0.531g H2O g-1), activated aluminium oxide ball (0.178～0.409g H2O g-1), chitosan (0.149-0.314g H2O g-1), activated aluminium oxide powder (0.133～0.240g H2O g-1),3A molecular sieve (0.046～0.158g H2O g-1), MC (0.052-0.145g H2O g-1), bentonite (0.002～0.114g H2O g-1) and diatomite (0.004～0.021g H2O g-1). 2. The Weibull equation was used to fit the moisture content data of different desiccants and the model parameters of M∞and β were acquired. Non-linear regression analysis was adopted to develop the moisture absorption kinetics.The results showed that Weibull equation fitted well to the experimental data for all the desiccants except xylitol and sorbital. The moisture holding capacity (M∞) was higher for CaCl2(1.117～2.137g H2O g-1), sodium hexametaphoshpate (0.297～0.856g H2O g-1) and sorbital (0.083～38.567g H2O g-1) with β ranges of25.5～119.8h,91.2～290.0h and1.1～185.6h, respectively. The moisture holding capacity has higher correlation (R2>81.2%) with temperature and RH for3A molecular sieve, chitosan, bentonite, sodium hexametaphoshpate, MC, xylitol and sorbital. The moisture holding capacity was found to be dependent on the temperature and RH for chitosan, bentonite and MC. However, moisture holding capacity was only affected by RH for3A molecular sieve, sodium hexametaphoshpate, xylitol and sorbital.3. Consistency between moisture absorption kinetics data and Weibull model fitting can be observed. Because single desiccant can’t satisfy the need for RH control of MA storage of Agaricus bisporous, the CaCl2, sodium hexametaphoshpate and sorbital were therefore selected and the mixture design was used to ascertain the optimum mixture ratio of compound desiccants.The results showed that at temperature of2and10℃, RH of96%, the optimum code values of CaCl2, sodium hexametaphoshpate and sorbital were0.3,0.2and0.5, respectively. The actual ratio of CaCl2, sodium hexametaphoshpate and sorbital were0.16,0.24and0.60, respectively.4. The Agaricus bisporous of200g per package were stored at2℃with and without compound desiccants added to verify the RH control effectiveness and determine the optimum dosage of compound desiccants. The physicochemical and microbial indexes were detected during12-day storage.The results showed that compared with CK, the time of respiratory climacteric and polyphenol oxidase (PPO) activity peak dramatically delayed, while L*value and hardness of Agaricus bisporous increased. The microbial growth of Agaricus bisporous during MA storage was significantly inhibited by adding compound desiccants. The weight loss and member permeability of Agaricus bisporous significantly increased for treatments of8and12g compound desiccants, while they varied little for the treatment of4g and CK. Generally, the optimum dosage of compound desiccants for MA storage (200g/bag) of Agaricus bisporous was4g. |
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