【作者】 张平；

【导师】 李汴生； 林光明；

【作者基本信息】 华南理工大学 ， 食品工程（专业学位）， 2021， 硕士

【摘要】 蛹虫草是公认的具有诸多药理活性的食用真菌,然而其产品形式单一,相关基础研究少。发酵是提高食品附加值最流行的方法之一,本文筛选出适合发酵蛹虫草浆液的乳酸菌后,探究了乳酸发酵过程中蛹虫草浆液主要活性物质及抗氧化能力的动态变化,并进一步评估了前处理杀菌工艺对乳酸菌发酵蛹虫草浆液风味的影响。本文研究结果如下:(1)蛹虫草浆液含抗菌物质,且可溶性固形物含量低(约1.0%),这可能不利于乳酸菌的生长。植物乳杆菌(LP)和戊糖片球菌(PP)对蛹虫草浆液基质的适应性显著优于嗜酸乳杆菌(LA)和嗜热链球菌(ST),具有良好的耐酸性、耗糖产酸及增殖代谢能力。相比于PP,LP对低糖和低蛋白基质的适应性更高,生长活性更强,且发酵蛹虫草浆液无不良风味产生,综合考虑选择LP进行后续实验。(2)LP有效降解了蛹虫草浆液中的7种核苷类化合物,并生成尿嘧啶;本实验用的LP菌株可产胞外多糖,发酵过程中,胞外(粗)多糖含量持续升高,而蛹虫草浆液中的粗多糖含量先降低后升高;LP发酵对蛹虫草浆液中D-甘露醇的含量无显著影响;发酵过程中,类胡萝卜素含量显著降低,对应b~*显著减小,而总酚、总黄酮含量显著升高;发酵后,蛹虫草浆液的DPPH自由基清除率、FRAP还原能力和SOD活力均显著升高;发酵过程中,蛹虫草浆液中主要活性物质组与抗氧化能力组呈极显著正相关(p<0.01)。(3)LP主要利用蛹虫草浆液中的葡萄糖产乳酸,并代谢柠檬酸和苹果酸,超高压前处理更利于LP耗糖产酸。巴氏杀菌前处理更能促进LP代谢氨基酸,而超高压前处理促进发酵后芳香族氨基酸的生成。巴氏杀菌和超高压前处理蛹虫草浆液经LP发酵后,5种5’-核苷酸的含量均显著增加,5’-尿苷酸含量变化最明显。(4)两种前处理均提高了蛹虫草浆液的风味物质总量,但降低了其种类数。巴氏杀菌前处理使浆液的醛含量显著增加,对应蛹虫草浆液的蒸煮味和刺激性气味的增强。超高压前处理则使醇的含量显著升高,利用蛹虫草特殊香气的形成。通过风味感官评价可知,相比于巴氏杀菌蛹虫草浆液,超高压前处理蛹虫草浆液在发酵前的风味与鲜浆液更接近,在发酵后的香气和鲜味更浓。更多还原

【Abstract】 Cordyceps militaris is recognized as an edible fungus with many pharmacological activities.However,it’s product form is single,and the related basic research is few.Fermentation is one of the most popular method in enhancing the added value of the food.In this paper,the main active substances and antioxidant capacity of C.militaris pulp were studied after selecting the suitable lactic acid bacteria for the fermentation of C.militaris pulp,and the effect of pre-treatment sterilization on the flavor quality of the lactic acid bacteria fermented C.militaris pulp was further evaluated.The research results are as follows:(1)C.militaris pulp contains antimicrobial substances and low content of soluble solids(about 1.0%),which may be detrimental to the growth of lactic acid bacteria.The adaptability of Lactobacillus plantarum(LP)and Pediococcus pentosaceus(PP)to C.militaris pulp was significantly better than that of Lactobacillus acidophilus(LA)and Streptococcus thermophilus(ST),with good acid tolerance,sugar consumption and acid production,proliferation and metabolism ability.Compared with PP,LP had higher adaptability to low-sugar and low-protein substrates,stronger growth activity,and no adverse flavor was produced in fermented C.militaris pulp.Therefore,LP was selected for subsequent experiments.(2)LP effectively degraded 7 nucleoside compounds in C.militaris pulp and produced uracil.The LP strain used in this experiment could produce extracellular polysaccharide.During the fermentation process,the extracellular polysaccharide(crude)content continued to increase,while the crude polysaccharide content in C.militaris pulp first decreased and then increased.LP fermentation had no significant effect on the content of D-mannitol in C.militaris pulp.During fermentation,the content of carotenoids decreased significantly,corresponding to b~*value decreased significantly,while the contents of total phenols and total flavonoids increased significantly.After fermentation,the DPPH free radical scavenging rate,total antioxidant capacity of FRAP and SOD activity of C.militaris pulp were significantly increased.In the fermentation process,the main active substance group in C.militaris pulp was significantly positively correlated with the antioxidant capacity group(p<0.01).(3)LP mainly uses glucose in C.militaris pulp to produce lactic acid,and metabolizes citric acid and malic acid.Ultra-high pressure(UHP)pretreatment is more beneficial to LP’s consumption of sugar to produce acid.Pasteurization pretreatment can promote the metabolism of amino acids in LP,and UHP pretreatment can promote the generation of aromatic amino acids after fermentation.After pasteurization and UHP pretreatment of C.militaris pulp by LP fermentation,the contents of five 5’-nucleotides were significantly increased,and the content of 5’-uridine was the most obvious change.(4)Both pretreatments increased the total amount of flavor substances in C.militaris pulp,but decreased the number of species.The pasteurization pretreatment significantly increased the content of aldehyde in the pulp,corresponding to the enhancement of cooking taste and pungent smell.UHP pretreatment significantly increased the content of alcohol and promoted the formation of special aroma of C.militaris.According to the sensory evaluation of flavor,compared with the pasteurized C.militaris pulp,the flavor of the UHP pretreated C.militaris pulp before fermentation was closer to that of the fresh pulp,and the aroma and umami after fermentation were more concentrated.更多还原