The combined use of progressive and block freeze concentration in lactose-free milk: Effect of process parameters and influence on the content of carbohydrates and proteins

This work focuses on the study of the concentration of lactose-free milk using a combination of progressive freezing concentration (PFC) with block freezing concentration (BFC). First, we investigated the PFC of skim lactose-free milk applying response surface methodology. To analyze the influence of three factors (stirring rate, coolant temperature, and assay time) on the response variables (concentrate yield, efficiency of the process, concentration index, and average ice growth rate), a central composite design was used previously. It was found that all factors had a significate influence on the responses. Then, once the optimized condition for this step was chosen (time of 58 min, coolant temperature of 5 C, and mechanical stirring of 1,035 rpm), the ice obtained from it was subjected to a new freeze concentration cycle using the BFC assisted by vacuum. In the concentrated fraction of this cycle, protein and carbohydrate contents were equals to 6.7 g 100 g 1 and 10.24 g 100 g 1, respectively. The results suggest that in PFC carbohydrates accumulate more in the concentrated phase, while in BFC it is the protein that has the greatest tendency to pass into the concentrated liquid. In this approach, we believe that it is possible to combine the two techniques (PFC + vacuum-assisted BFC) to obtain concentrates, and that they can be used for the development of innovative lactose-free dairy products. The authors are grateful to the Coordination of Improvement of Higher Education Personnel (CAPES, Brazil) (CAPES-PRINT, Project number 88887.310560/2018-00); to National Council for Scientific and Technological Development (CNPq, Brazil) by the financial sup- port (CNPq, 405965/2016-8); and to Coordination of Improvement of Higher Education Personnel (CAPES, Brazil) by the scholarship (001) Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura Objectius de Desenvolupament Sostenible::12 - Producció i Consum Responsables