The question of what to do with acid whey and whey permeates is raised more and more urgently by producers of yogurt and related products, such as quark. As Greek yogurt is becoming more popular, the acid whey streams are growing significantly as well. To answer this question, a detailed understanding of product-process interactions in high-lactose products will assist in gaining knowledge that is so far lacking in the industry.
Acid whey and whey permeates are ingredient sources that are generally characterised by a high lactose and low protein content. Acid whey differs from whey permeates with its high lactic acid content and richness in calcium. The most optimal use of acid whey is direct application in food and/or drying of the whey to a powder for a value-added application. In the latter case, drying of acid whey and acid whey permeates is known to result in considerable challenges, such as stickiness of powders. One common step to improve powder handling properties is pre-crystallisation of lactose. However, the whey and permeate streams that are available from the producers are usually inhomogeneous. This affects lactose crystallisation and related processing times. Controlling this step reduces process time and improves powder properties.
Our studies so far have showed that pre-treatment of acid whey and whey permeates prior to drying could be optimised by using total solids content and temperature as primary determinants of the degree of saturation of lactose and viscosity of the concentrate. For this study we used nine high-lactose, low-protein dairy streams from one batch of skimmed milk on pilot plant scale, including:
Viscosity and lactose crystallisation were monitored during controlled cooling cycles and subsequent incubation. The crystallisation process used in the study was without the addition of lactose crystals.
We found that the degree of saturation, viscosity and the presence of protein and salts strongly affects lactose crystallisation, whereas the presence of both lactic acid and proteins hinders crystallisation. This can at least partially be related to increased viscosity and the presence of other constituents hindering lactose mobility in the concentrates. Extensive viscosity build-up in yogurt permeate compared to milk permeate was primarily related to lactic acid. Whey permeates from caseinate production do not show an extensive build-up of viscosity. Microscopic evaluation of concentrated permeates showed different crystal shapes and sizes.
For acid whey, various processing routes were used in Nizo’s processing centre. Acid whey was evaporated to different dry matter contents and flash-cooled followed by crystallisation at different temperatures. We used our expertise on process-product interactions and analysing techniques to characterise powders on for example stickiness and powder flow properties.
Based on the knowledge and understanding gained from these studies, pre-treatment of acid whey and acid whey permeates prior to drying could be optimised by using total solids content and temperature as primary determinants of the degree of saturation of lactose and viscosity of the concentrate. This can be applied to improve whey (permeate) powders of inhomogeneous whey streams that are supplied by the producers.
We are using this knowledge to identify application areas for acid whey in food in sufficient amounts resulting in added functionality and/or ingredient cost reduction.
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