| In recent years,China’s Stropharia rugoso-annulata industry has been developing rapidly,and the production has been increasing year by year,showing good market prospect.As an emerging edible mushroom,S.rugoso-annulata is mainly used for fresh food or made into dried mushroom,and the product form is single,and the public awareness of it is still low.The high moisture content and strong respiration of fresh S.rugoso-annulata are not resistant to storage and inconvenient to transport off-site,which also limits its market promotion and reduces its economic value.The pileus is fat,colorful and tasty,so it is suitable for direct cooking and processing,while the stipe is white and thick,with relatively light taste and insufficient texture,so it is suitable for slicing and processing to enhance the taste and added value.In daily life,fried foods have good market competitiveness and can provide a reliable reference direction for the development of new products.Based on the above points,this project developed a new deep-fried Stropharia rugoso-annulata(DFS)product using fresh S.rugoso-annulata as raw material and its stipe,and deeply investigated the change pattern of quality and volatile flavor substances during its processing,and further explored the change pattern of quality during its storage period and clarified the shelf life.The main research contents and results are as follows:(1)Batter is an important part of many fried foods,which has an important influence on the color,flavor and taste of fried foods.In this project,the batter composition of DFS was optimized by mixing design and response surface model construction,combined with entropy-weighted fuzzy mathematical sensory evaluation method.The results showed that the optimum ratio of the four starches or flours in the batter was corn starch: tapioca starch: sweet potato starch: wheat flour = 30:14:29:27;the optimum addition of the three acidic bulking agents,glucono--lactone,tartaric acid and sodium dihydrogen phosphate,in the fixed batter with 0.4% sodium bicarbonate was 0.21%,0.10% and 0.17%.After validation,it is found that the relative errors of both models are small and the models are reliable,indicating that the processing process of this DFS is feasible.(2)DFS mainly consists of the stipe and batter.Based on the research of processing process,the quality change pattern of this product during the processing(pre-frying and re-frying)was systematically studied in this project with fresh stipe and fresh batter as the control.The results showed that the microstructure of the stipe gradually collapsed and the edges curled after deep-frying,with obvious sense of fragmentation;the textural properties such as hardness,cohesiveness,adhesiveness,chewiness and reversibility were significantly reduced;and the moisture content was significantly reduced,while the ash,protein,fat,carbohydrate content and total energy were significantly increased.After frying,the microstructure of the batter gradually changed from a well-defined grain to a block with a hard texture,and the trend of other components(moisture,ash,protein,fat,carbohydrate,total energy)was basically the same as that of the stipe.A total of 17 free amino acids,including 7 essential amino acids and 10 non-essential amino acids,were detected during the DFS processing.In the samples of all processing stages,the stipe was dominated by sweet amino acids,while the batter was dominated by sweet and bitter amino acids with similar contents;in addition,the TAV values,nucleotide contents and iso-fresh concentration values of free amino acids in both stipe and batter were lower.However,in terms of nutritional evaluation,the E/T values(percentage of essential amino acids and non-essential amino acids)of both stipe and batter were around 30%,which was close to the FAO/WHO standard protein model E/T value of 36.35%,indicating that DFS could be used as a high-quality protein source to some extent protein source.The correlation analysis showed that moisture content had a significant negative correlation with ash content and fat content,and a larger but non-significant negative correlation with protein content(r =-0.78).In addition,moisture content had a large effect on the content of free amino acids(r=0.71)but a small effect on the content of hydrolyzed amino acids(r=0.17),but none of them was significant.(3)The composition and change patterns of volatile flavor substances during DFS processing were analyzed qualitatively and quantitatively from the perspectives of stipe and intact product(stipe + batter)of DFS using headspace solid-phase microextraction gas chromatography-mass spectrometry(HS-SPME-GC-MS)and electronic nose technique.The results showed that a total of 166 volatile flavor substances were identified during the DFS processing.By calculating the relative contents and odor activity values,it was found that the volatile flavor substances of the unfried samples were mainly alcohols and esters,and the substance with the largest flavor contribution was 1-octen-3-one;the aldehyde content of the fried samples accounted for the largest proportion,and(E)-2-nonenal was the compound with the largest flavor contribution,and the richness of the flavor substances increased significantly after frying.The electronic nose could effectively distinguish the volatile flavor substances between the pre-and post-frying samples,and its sensor response values performed more consistent with the detection results of HS-SPME-GC-MS.(4)The quality change pattern of pre-fried and shaped DFS semi-finished products during storage was investigated,and their shelf life at different temperatures(4°C,0°C,-3°C and-18°C)was clarified.The results showed that the initial acid value,peroxide value and malondialdehyde content of DFS were low,with good safety,and the storage conditions at 4℃,0℃ and-3℃ did not exceed the upper limit of the national standard even if they reached the spoilage point.With the extension of storage time,the yellowness value b* and sensory score of DFS gradually decreased,and the closer to the spoilage point,the faster the two decreased.Correlation analysis showed that at each storage temperature,the aerobic plate count,acid value and malondialdehyde content of DFS were negatively correlated with the sensory composite score.The storage periods of DFS in 4℃,0℃,-3℃ and-18℃ were 20 days,36 days,58 days and 345 days,respectively,by actual testing or constructing shelf-life models based on the aerobic plate count. |
PDF Full Text Request