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Processing of high-protein yogurt from milk concentrates: Power ultrasound as an innovative tool to generate specific texture properties.

A. Körzendörfer

Abstract:

99
Processing of high-protein yogurt from milk concentrates: Power ultrasound as an innovative tool to generate specific texture properties.
A. Körzendörfer*, J. Hinrichs. University of Hohenheim Stuttgart, Germany.

The fermentation of preconcentrated milk is a challenging method to avoid acid whey during the manufacture of high-protein fermented milks like Greek yogurt and skyr. Since acid whey is undesired as a by-product due to environmental concerns, alternative processes that involve a concentration step before the fermentation, e.g., by microfiltration, are of economic and ecological interest. However, acid milk gels from concentrated milk (>8% protein) exhibit a high interconnectivity and an excessive firmness, resulting in technical and sensory problems. As the reduction of the microgel particle size is impaired, products are often not smooth and perceived as too viscous. The aim of our research was to improve the processing of high-protein yogurt from concentrates. For this purpose, power ultrasound (US) was applied as an innovative post-processing technology. Skim milk was fortified with milk protein powder to 10% protein, heated, and fermented at 43°C. Fermentations were stopped at pH 5.0, 4.8, and 4.6, respectively, by breaking up the gel with a perforated disc and immersing the containers in iced water. Yogurts were processed into stirred yogurt by shearing. Half of the samples were additionally treated with an US sonotrode for 5 s at a frequency of 20 kHz. Several physical properties were then analyzed. The short-term sonication considerably decreased the apparent viscosity of the yogurts by 30—40%, whereas the particle size and water-holding capacity were only slightly affected. Further experiments were performed by studying the effects of sonication time. Strong negative exponential correlations (R2 > 0.99) were found between the sonication time and various rheological properties (storage modulus, apparent viscosity, yield stress). Moreover, the visual smoothness of the yogurts increased with the sonication time. The application of power US is a highly effective tool to control the rheological properties of high-protein fermented milks from concentrates. This offers the potential to develop innovative products and will help to establish sustainable processes.

Keywords: Greek yogurt, ultrasound, fermented milk product.