Dairy Science and Technology Research Centre (STELA), Quebec City, QC G1V 0A6, Canada; Institute of Nutrition and Functional Foods (INAF), Université Laval, Quebec City, QC G1V 0A6, Canada; St-Hyacinthe Research and Development Centre, Agriculture and Agri-Food Canada, 3600 Casavant Boulevard West, St-Hyacinthe, Qc, J2S 8E3, Canada.
Institute of Nutrition and Functional Foods (INAF), Université Laval, Quebec City, QC G1V 0A6, Canada; St-Hyacinthe Research and Development Centre, Agriculture and Agri-Food Canada, 3600 Casavant Boulevard West, St-Hyacinthe, Qc, J2S 8E3, Canada.
J Dairy Sci. 2019 Jan;102(1):190-201. doi: 10.3168/jds.2018-14565. Epub 2018 Oct 19.
Few studies have considered the impact of unit operations during stirred yogurt manufacture because their operational sequence is difficult to replicate at the laboratory scale. The aim of this study was to investigate the individual and sequential effects of stirring in the yogurt vat, smoothing, and cooling on the rheological properties of yogurts, using a technical scale unit simulating some industrial conditions. The yogurts were prepared from a milk mixture that was standardized to contain 14% total solids, 0% fat, and 4% protein, and then homogenized, heated (94.5°C, 5 min), and inoculated at 41°C with the same thermophilic lactic starter. The operating parameters under investigation were 2 stirring durations in the yogurt vat (5 or 10 min), 2 cooling systems (plate or tubular heat exchanger), and 2 smoothing temperatures (38°C for smoothing before cooling; 20°C for smoothing after cooling). Sampling valves were installed at critical points on the technical scale unit so that the effect of each operation on the properties of stirred yogurt could be quantified individually. Syneresis, apparent viscosity, firmness, and consistency were analyzed after 1 d of storage at 4°C. In general, as the yogurts moved through the technical scale unit, the properties of the yogurts (evaluated after 1 d) changed: viscosity increased but syneresis, firmness, and consistency decreased. The individual effects of the operations showed that smoothing and cooling, compared with stirring duration, made the greatest contribution in terms of modifying yogurt properties. The stirring parameters (5 or 10 min) had similar effects on the yogurts. The use of a plate heat exchanger promoted a decrease in syneresis, whereas a tubular heat exchanger had a greater effect in terms of increasing firmness and consistency. The type of cooling system had no effect on stirred yogurt viscosity. Smoothing at 38°C had a greater effect on the increase in firmness, whereas smoothing at 20°C contributed more to a decrease in syneresis and increases in viscosity and consistency. This study confirms that each unit operation has a defined effect on the rheological properties of a nonfat stirred yogurt, which also depends on the operation sequence.
很少有研究考虑搅拌酸奶制作过程中的单元操作的影响，因为它们的操作顺序很难在实验室规模上复制。本研究的目的是使用模拟某些工业条件的技术规模装置，研究酸奶罐搅拌、平滑和冷却对酸奶流变特性的单独和连续影响。酸奶是由标准化至含有 14%总固体、0%脂肪和 4%蛋白质的牛奶混合物制成，然后进行均质、加热（94.5°C，5 分钟），并在 41°C 下用相同的嗜热乳酸菌接种。研究的操作参数为酸奶罐搅拌时间（5 分钟或 10 分钟）、冷却系统（板式或管式换热器）和平滑温度（冷却前平滑 38°C；冷却后平滑 20°C）各两个。在技术规模装置的关键点安装了取样阀，以便可以单独量化每个操作对搅拌酸奶特性的影响。在 4°C 下储存 1 天后分析了离析、表观粘度、硬度和稠度。一般来说，随着酸奶通过技术规模装置，酸奶的特性（在 1 天后评估）发生变化：粘度增加，但离析、硬度和稠度降低。操作的单独影响表明，与搅拌时间相比，平滑和冷却在改变酸奶特性方面做出了最大贡献。搅拌参数（5 分钟或 10 分钟）对酸奶的影响相似。板式换热器的使用促进了离析的减少，而管式换热器在提高硬度和稠度方面的效果更大。冷却系统的类型对搅拌酸奶的粘度没有影响。38°C 平滑对硬度的增加影响更大，而 20°C 平滑对离析减少、粘度和稠度增加的贡献更大。本研究证实，每个单元操作对非脂搅拌酸奶的流变特性都有明确的影响，并且还取决于操作顺序。
