Bong D D, Moraru C I
Department of Food Science, Cornell University, Ithaca, NY 14853.
Department of Food Science, Cornell University, Ithaca, NY 14853.
J Dairy Sci. 2014 Mar;97(3):1259-69. doi: 10.3168/jds.2013-7488. Epub 2014 Jan 17.
The objective of this work was to develop and optimize an alternative make process for Greek-style yogurt (GSY), in which the desired level of protein was reached by fortification with micellar casein concentrate (MCC) obtained from milk by microfiltration. Two MCC preparations with 58 and 88% total protein (MCC-58 and MCC-88) were used to fortify yogurt milk to 9.80% (wt/wt) protein. Strained GSY of similar protein content was used as the control. Yogurt milk bases were inoculated with 0.02% (wt/wt) or 0.04% (wt/wt) direct vat set starter culture and fermented until pH 4.5. The acidification rate was faster for the MCC-fortified GSY than for the control, regardless of the inoculation level, which was attributed to the higher nonprotein nitrogen content in the MCC-fortified milk. Steady shear rate rheological analysis indicated a shear-thinning behavior for all GSY samples, which fitted well with the power law model. Dynamic rheological analysis at 5°C showed a weak frequency dependency of the elastic modulus (G') and viscous modulus (G") for all GSY samples, with G' > G", indicating a weak gel structure. Differences in the magnitude of viscoelastic parameters between the 2 types of GSY were found, with G' of MCC-fortified GSY < G' of control, indicating a different extent of protein interactionsin the 2 types of yogurt. Differences were also noticed in water-holding capacity, which was lower for the MCC-fortified GSY compared with the control, attributed to lower serum protein content in the former. Despite some differences in the physicochemical characteristics of the final product compared with GSY manufactured by straining, the alternative process developed here is a feasible alternative to the traditional GSY make process, with environmental and possibly financial benefits to the dairy industry.
这项工作的目标是开发并优化希腊式酸奶（GSY）的替代制作工艺，通过用微滤法从牛奶中获得的胶束酪蛋白浓缩物（MCC）进行强化，使蛋白质达到所需水平。使用两种总蛋白含量分别为58%和88%的MCC制剂（MCC - 58和MCC - 88）将酸奶奶中的蛋白质强化至9.80%（重量/重量）。将蛋白质含量相似的过滤后的GSY用作对照。向酸奶奶基中接种0.02%（重量/重量）或0.04%（重量/重量）的直投式发酵剂，并发酵至pH值为4.5。无论接种水平如何，MCC强化的GSY的酸化速率都比对照更快，这归因于MCC强化奶中较高的非蛋白氮含量。稳态剪切速率流变学分析表明，所有GSY样品均表现出剪切变稀行为，这与幂律模型拟合良好。在5°C下的动态流变学分析表明，所有GSY样品的弹性模量（G'）和粘性模量（G''）对频率的依赖性较弱，G' > G''，表明凝胶结构较弱。发现两种类型的GSY之间的粘弹性参数大小存在差异，MCC强化的GSY的G' < 对照的G'，表明两种类型的酸奶中蛋白质相互作用的程度不同。在持水能力方面也发现了差异，MCC强化的GSY的持水能力低于对照，这归因于前者较低的血清蛋白含量。尽管与通过过滤制造的GSY相比，最终产品的理化特性存在一些差异，但此处开发的替代工艺是传统GSY制作工艺的可行替代方案，对乳制品行业具有环境和可能的经济效益。
