Study On The Phenolics Compositions Of Shiitake Mushrooms And Their Variation During Storage

Shiitake mushrooms are one of the most widely cultivated edible fungi in the world,which not only have a unique flavor and high nutritional value,but also are rich in phenolics.Therefore,shiitake mushrooms show positive effects in antioxidant,antiinflammatory and antiaging.In addition,shiitake mushrooms contain high moisture content and show strong respiration,which make them easy to lose commercial value during postharvest storage.Therefore,in our study,shiitake mushrooms are used as experimental materials to study the free phenolics and bound phenolics in shiitake mushrooms,and different packages are used to extend the storage period of mushrooms and study the changing trends of phenolics.The experimental results are as follows:In this experiment,the extraction methods of free phenolics and bound phenolics of shiitake mushrooms were optimized.For free phenolics,response surface methodology was used,base on the results of the single factor experiment,the Box-Behnken response surface method was conducted,with the liquid-to-material ratio,ultrasonic time and ultrasonic power as the experimental factors,the free phenolics content as the response value.Results showed that water was used as the extraction solvent,the liquid-to-material ratio was 6 m L/g,the ultrasonic time was 80 min and the ultrasonic power was 310 W,the theoretical content was101.047 mg/100 g and the actual content was 100.60 ± 4.80 mg/100 g,indicating the response surface model has good fit and can be used for the extraction of free phenolics.For bound phenolics,chemical methods(acid hydrolysis and alkaline hydrolysis)were used to release them from the residue of shiitake mushrooms.The results showed that the combination of alkaline hydrolysis and further acid sequential hydrolysis were the best extraction methods with a content of 25.67 ± 1.15 mg/100 g.In addition,the results of antioxidant experiments showed that free phenolics had stronger antioxidant capacity than bound phenolics,and the antioxidant capacities of bound phenolics obtained by different hydrolysis methods were different,the bound phenolics under optimal extraction conditions had the highest antioxidant activity,DPPH,ABTS and FRAP values were 9.20 ± 0.56 mg VC/100 g,7.84 ± 0.38 mg VC/100 g and 346.08 ± 8.98 ?mol FE/100 g,respectively.The detection of phenolics in shiitake mushrooms was performed using the high performance liquid chromatography-tandem mass spectrometry.The twelve of phenolic compounds were analyzed.The optimized detection conditions were: Agilent ZORBAX Eclipse XDB-C18(4.6 mm × 150 mm,3.5 ?m)column;0.1% formic acid water(A)and acetonitrile(B)were used as mobile phases;the elution gradient was 0-10 min,20-30% B;10-20 min,30-40% B;20-35 min,40-50% B;flow rate was 0.2 m L/min;injection volume was 10 ?L;column temperature was maintained at 30 ?;ESI ion source;MRM negative ion scan mode;capillary voltage 4.0 k V;drying gas temperature 350 °C;drying gas flow rate10.0 L/min;nebulizer pressure 35 psi.Under this detection conditions,the twelve of compound standard solutions had good linear relationship,and the instrument had high precision and its state was stable.The analysis results showed that there were eight phenolic compounds in free phenolics including gallic acid,chlorogenic acid,protocatechuic acid,hesperidin,luteolin,quercetin,ferulic acid and cinnamic acid,and found that different hydrolysis methods and procedures had important effects on the phenolic compositions,and gallic acid,protocatechuic acid,caffeic acid and ferulic acid were all present in the bound phenolics fractions.The postharvest shiitake mushrooms were packaged in polyethylene packaging and polylactic acid packaging,stored at 4 ± 0.2 ? for 14 days,and investigated the effects of different packaging on the contents of phenolics and their variation.The content of free phenolics was increased with storage time and then decreased,and content of bound phenolics showed a decrease trend.In addition,the results of quality analysis showed that the polylactic acid packaging effectively maintained the sensory quality of shiitake mushrooms,and properly discharged water vapor in the bag,kept the surface of shiitake mushrooms dry,delayed the opening of the cap and the decrease of hardness,reduced respiration and the release of ethylene,maintained the activity of phenylalanine ammonia lyase,and inhibited the activities of polyphenol oxidase and peroxidase.Therefore,this study clarified the variations of phenolics during storage,and proved that polylactic acid packaging was an effective and feasible method for preservation to shiitake mushrooms.