The Influence Of UHP On Instant Pleurotus Eryngii Slices’s Quality

In this thesis, Pleurotus eryngii were choosed as raw materials, and instant Pleurotus eryngii slice processed by Ultra-high pressure technology was investigated in order to confirm effect of the technology on Pleurotus eryngii’s quality. The main results as follows:1. Ultra-high pressure technology was used to process instant Pleurotus eryngi slice. The effects of UHP on Pleurotus eryngii’s quality, the sterilization rate of colony counts and nutrients in exudates were studied. Optimal processing conditions were found by comparing the percentage of proteins, free amino acids, total sugar, polysaccharide in processed Pleurotus eryngii slice and exudate. The results showed that: appearance of Pleurotus eryngii slices was8.35, nutrients can be reserved most and loss least when the conditions were450MPa and10min. In this processing condition, the content of proteins, free amino acids, total sugar and polysaccharides in the Pleurotus eryngii were1.55%,1.07%,2.28%,1.95%, and0.471%,0.580%,0.491%,0.405%in the exudate. It also showed that treatment of450Mpa for10min was best to keep nutrients of raw materials, and almost99%microorganisms were killed.2. Sensory evaluation, the sterilization rate of colony counts and DSC(Differential Scanning Calorimeter), LF-NMR(Low filed nuclear magnetic resonance), electronic nose,chromatic meter and Texture analyser were used to test Pleurotus eryngii slices processed by UHP, Stir-fry and control groups for sensory properties, colony counts, protein thermal denature curve, moisture state, odor, color and texture.Sensory evaluation results showed that appearance of Pleurotus eryngii slices treated by UHP was better than those by Stir-fry, however, those treated by Stir-fry were accepted more easily in odor, texture, and taste. The score of Pleurotus eryngii slices treated by Stir-fry was8.86, and those processed by UHP was8.1.Measurements of the total number of bacteria of Pleurotus eryngii showed that both UHP and Stir-fry processing method had good sterilization effect.DSC described the protein thermal denature curve and found the thermal denature temperatures of fresh cut, slices cooked by Stir-fry and UHP were120.6℃,12℃,23℃. And peak area of them were451J/g,759.6J/g,1621J/g. It showed that the amount of protein denature caused by UHP were less than by Stir-fry.Moisture migration in processed Pleurotus eryngii was determined by LF-NMR. The results showed that bonding strength of bound water dropped after treatment by UHP and Stir-fry, bonding strength of moderate bound water, immobile water and free water increased. However, both free water and bound water increased after processing from the relaxation peak area.Ele-nose was used to determine the odor of three groups of Pleurotus eryngii. The results showed that through PCA (principal component analysis) and LDA (linear discriminant method), the contribution rate of two principal components reached99%. The differentiation degree of odor about fresh sample, samples cooked with UHP and Stir-fry were obtained by PCA. The degrees of differentiation between fresh sample and Stir-fry treated sample, fresh sample and UHP treated sample, UHP treated sample and Stir-fried sample were0.751,0.849and0.819respectively.The color of the three groups of samples was measured by chromatic meter, and fresh sample used to calibrate the instrument, the results showed, value of L, a*and b*of samples dealing with the UHP and Stir-fry increased, and no significant difference between UHP treatment and Stir-fry in L value was found(P>0.05), but there was a significant difference in a*and b*values(P<0.05).Texture analyser was used to test Pleurotus eryngiis structure, results showed that the springiness, cohesiveness and chewiness of processed Pleurotus eryngii were higher than fresh cut samples, but hardness and resilience was lower than fresh ones.3. Quality changes of Pleurotus eryngii cooked by UHP at different storage temperatures were studied. With the extension of storage time, sensory scores, moisture content, pH value, acid value, L value, hardness, springiness, chewiness, resilience of Pleurotus eryngii at different storage temperature(0,5,10℃) have showed a downward trend, but peroxide value presented fluctuate Trend.