桑叶发酵液对酸奶品质的影响
将酸奶于4℃贮藏21天，桑叶发酵液浓度为0。25%、0。5%、0。75%和1%的酸奶的pH分别由4。55、4。53、4。51和4。50降到4。16、4。15、4。11和4。10；保水性由68。0%、66。7%、66。0%和63。3%降到59。3%、55。3%、48。7%和42。0%；黏度由983。7 mPa。s、963。3 mPa。s、949。7 mPa。s和929。5 mPa。s降到962。2 mPa。s、928。0 mPa。s、919。0 mPa。s和910。0 mPa。s。对照组酸奶的pH由4。57降到4。25；保水性由69。3%降到62。7%；黏度由1033。5 mPa。s降到978。0 mPa。s。其结果表明桑叶发酵液会使酸奶在贮藏期内的pH降低，酸奶的酸度变化与pH变化一致；随着桑叶发酵液浓度的增加，酸奶保水性和黏度降低，其中桑叶发酵液浓度为0。75%和1%的酸奶在保存到第14天时出现明显分层现象。在贮藏期间，桑叶发酵液浓度为0。25%和0。5%的酸奶嗜热链球菌数分别为7。3×109个、6。7×109个、3。3×109个、2。32×109个和7。9×109个、5。2×109个、4。2×109个、2。61×109个；均高于对照酸奶中嗜热链球菌数5。9×109个、4。8×109个、2。89×109个2。08×109个；而桑叶发酵液浓度为0。75%和1%的酸奶均低于对照酸奶。
酸奶贮藏21天后，桑叶发酵液浓度为0。25%、0。5%、75%和1%的酸奶的多酚含量分别由1。0028 mg/mL、1。0487 mg/mL、1。0612 mg/mL和1。0799 mg/mL降到0。5010 mg/mL、0。5425 mg/mL、0。5525 mg/mL和0。5534 mg/mL；多糖含量分别由1。2968 mg/mL、1。3309 mg/mL、1。3333 mg/mL和1。3361降到0。6609 mg/mL、0。7050 mg/mL、0。7069 mg/mL和0。7073 mg/mL；DPPH清除能力的IC50值分别由0。318、0。294、0。284和0。243升到0。354、0。346、0。320和0。289；羟基自由基清除能力的IC50值分别由0。360、0。332、0。305和0。278升到0。402、0。378、0。347和0。326。对照酸奶的多酚含量由0。9895 mg/mL降到0。4832 mg/mL；多糖含量由1。2603 mg/mL降到0。6239 mg/mL；DPPH清除能力的IC50值由0。339升到0。373；羟基自由基清除能力的IC50值由0。388升到0。426。结果表明桑叶发酵液浓度越高，酸奶中多酚和多糖含量越高；DPPH清除能力和羟基自由基清除能力越强。
毕业论文关键词：酸奶、桑叶、发酵、乳酸菌、抗氧化性
Abstract Mulberry broth was used as the accessories added to milk and produced yogurt to study the effect of different density mulberry broth on fermentation characteristics and yogurt quality。 The results showed that the fermentation time of achieving pH 4。6 was 330min、330min、320min and 310min respectively in the different density mulberry broth(0。25%, 0。5%, 0。75% and 1%)yogurt。The control yogurt achieved pH 4。6 for 340 min。 The results showed that mulberry broth could accelerate the acidification rate of yogurt。
Storaging yogurt at 4 ℃ for 21 days, the pH of different density mulberry broth (0。25%, 0。5%, 0。75% and 1%) yogurt decreased from 4。55, 4。53, 4。51 and 4。50 to 4。16, 4。15, 4。11 and 4。10。The water holding capacity of different density mulberry broth yogurt decreased from 68。0%, 66。7%, 66。0% and 63。3% to 59。3%, 55。3%, 48。7% and 42。0%。 The viscosity of different density mulberry broth yogurt decreased from 983。7mPa。s, 963。3 mPa。s, 949。7mPa。s and 929。5 mPa。s to 962。2mPa。s, 928。0mPa。s, 919。0mPa。s and 910。0 mPa。s。The pH of control yogurt decreased from 4。57 to 4。25。 The water holding capacity of control yogurt decreased from 69。3% to 62。7%。 The viscosity of control yogurt decreased from 1033。5mPa。s to 978。0mPa。s。These results showed that mulberry broth could reduce the pH of yogurt,the changes of acidity were simultaneous with the pH of yogurt。 With the mulberry broth density increasing,water holding capacity and viscosity of yogurt reduced。 During storage,the amounts of Streptococcus thermophilus in different density mulberry broth(0。25% and 0。5%) yogurt were 7。3×109,6。7×109, 3。3×109, 2。32×109 and 7。9×109, 5。2×109, 4。2×109, 2。61×109。 The amounts of that in control yogurt were 5。9×109, 4。8×109, 2。89×109 and 2。08×109。 The amounts of Streptococcus thermophilus in different density mulberry broth were 0。75% and 1% ,which were less than control yogurt。
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