【作者】 马栋；

【导师】 李理；

【作者基本信息】 华南理工大学 ， 粮食油脂及植物蛋白工程， 2010， 硕士

【摘要】 Saccharomyces cerevisiae SCY1由本课题组从发酵蔬菜汁中分离,前期研究用于荔枝酒发酵,所酿果酒风味良好,有很好的发酵特性。Kefir是由乳酸菌和酵母菌混合发酵的乳制品,具有降低血清胆固醇、增强人体免疫力、抗衰老和抗癌等作用,因此本课题组拟将SCY1用于发酵kefir,并以Kluyveromyces marxianus LAF-4为对照。研究了SCY1在牛乳、菠萝果汁及果汁复合乳中的发酵特性。SCY1在牛乳中32℃生长36 h达到最大菌数106个/mL,加入蔗糖、葡萄糖或菠萝果汁后,其24 h内可以长到107个/mL。SCY1在牛乳中28℃和35℃经36 h生长仅达到10 5个/mL,由此可见,SCY1不能利用乳糖,但加入合适碳源后,可在牛乳中较好生长,最适生长温度为32℃。而LAF-4可以利用乳糖,最适生长温度在32~35℃之间。研究了SCY1发酵kefir的工艺条件。通过研究SCY1接种量、灭菌条件、发酵温度、加糖量对kefir pH值、滴定酸度、粘附性、CO2含量的影响,结合感官评定,确定最佳工艺条件:SCY1接种量为103个/mL;85~90℃灭菌10 min;发酵温度为32℃;加糖量为4 %。LAF-4的工艺条件和SCY1一样,但产品的风味及品质不同。研究了kefir在4℃贮藏过程中品质的变化情况。SCY1发酵所得kefir在贮藏12 d时pH降到最低,其中原味为4.32,果味为4.31,滴定酸度变化不明显。原味kefir的CO2含量在12 d时达到最大58.93 mg/100g,果味16 d时达到最大93.55 mg/100g,随后略有下降。乳酸活菌数12 d时增加至108 cfu/mL,随后减少到107 cfu/mL,而酵母菌在贮藏过程中由103 cfu/mL增加至106 cfu/mL。在贮藏期间始终未检出大肠菌群。SDS-PAGE表明,酪蛋白在发酵、贮藏过程中微弱降解。感官记录表明,原味kefir 12 d后凝乳变稀薄,口味过酸,果味则有明显酒味,因此推荐贮藏不应超过12 d,在8 d之前食用品质较佳。分析了kefir的营养成分,并与普通酸奶做比较。Kefir的pH、滴定酸度、蛋白质及氨基氮含量均明显高于普通酸奶。乳酸分析表明,kefir中含10 g/L的L-乳酸,且不含D-乳酸,普通酸奶中含1.1 %的D-乳酸,L-乳酸的含量仅有5.64 g/L。kefir中游离氨基酸总量为17~24 mg/100mL,普通酸奶仅有8.65 mg/100mL,kefir在发酵后游离氨基酸总量有所增加,增加较多的有谷氨酸、脯氨酸、苯丙氨酸,但丝氨酸、甘氨酸、组氨酸、精氨酸、丙氨酸、蛋氨酸的含量略有减少。更多还原

【Abstract】 Saccharomyces cerevisiae SCY1 was isolated from fermented vegetable juice by our research group. Because of its favourable fermentability, SCY1 was applied to ferment litchi fruit wine. Kefir is the product of fermentation of milk with LAB and yeast. Compared with yogurt, kefir can lower cholesterol, improve immunity, anti-aging and anticancer. So we wanted apply SCY1 to ferment kefir, contrasting with Kluyveromyces marxianus LAF-4.The fermentability of SCY1 growing in milk, pineapple juice and milk with juice was studied. The maximum value of SCY1 was 106 cfu/mL after growing 36 h in milk without any saccharides at 32℃. After adding sucrose, glucose and pineapple juice, SCY1 could grow to 107 cfu/mL after 24 h. The maximum value of SCY1 was 105 cfu/mL after 36 h in milk without any saccharides at 30℃or 35℃. The results indicated the SCY1 did’nt use lactose, but it could grow well in milk after adding suitable carbon source or juice. The optimum growth temperature of SCY1 was 32℃. But LAF-4 could make use of lactose, and the optimum temperature was between 32~35℃.The process conditions of kefir were also studied. The effects of inoculum concentration, sterilization temperature, fermentation temperature and sugar on pH, titratable acidity, adhesion anlysis and content of CO2 were studied. Combined with sensory evaluation, the optimum technological parameters were: inoculum concentration: SCY1: 103 cfu/mL; sterilizatin temperature: 85~90℃, 10 min; fermentation temperature: 32℃; sugar: 4 %. The technological parameters of kefir fermented by LAF-4 were same to SCY1, but the flavor and quality were different.The changes of kefir during storage at 4℃were studied. The kefir fermented by SCY1 had the lowest pH at 12 d. The plain kefir was 4.32 and the fruit kefir was 4.31. But the titratable acidity had an unconspicuous change. The highest CO2 content of plain kefir was 58.93 mg/100g at 12 d, and fruity was 93.55 mg/100g at 16 d, soon afterwards falling off weakly. The largest viable count of LAB was 108 cfu/mL when 12 d, but slightly declined after 12 d. The viable count of yeast grew from 103 cfu/mL to 106 cfu/mL. Coliform was not detected during storage. Because of adhesion decrease and taste sour, the optimal storage was 12 d.The nutrient contents of kefir were analyzed comparing with yogurt. pH of kefir (4.42~4.43) was higher than yogurt (3.89), and titratable acidity was higher than yogurt too. Protein content of yogurt(2.52 g/100g) was obviously lower than kefir(3.7~4.2 g/100g) and national standards(2.9 g/100g). The type of lactic acid was all L-lactic acid in kefir, and the conten was 10 g/L. But there was 1.1 % D-lactic acid in yogurt, the content of L-lactic acid was only 5.64 g/L. The content of amino acid was 17~24 mg/100mL in kefir and 8.65 mg/100mL in yogurt. After fermented, the increased amino acids were glutamic acid, proline, phenylalanine, and the decreased amino acids were serine, glycocll, histidine, arginine, alanine and methionine.更多还原