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lnfluence of membrane flltration on the physico-chemical and sensory properties of sugar-reduced yogurt

Art der Arbeit:

Masterthesis

Veröffentlichung:

30.10.2019

Studiengang:

Masterstudiengang Process Engineering and Energy Technology

Zusammenfassung der Arbeit:

ln the scope of the national sugar reduction strategy, the demand for products with reduced carbohydrate content increases. Sugar reduction in yogurt reduces its calorific value and may mitigate health diseases linked to obesity. A new technological approach for the development of a sugar-reduced yogurt could be the application of ultrafiltration (UF) in order to produce a milk retentate with different protein/lactose ratios which can be directly used for yogurt fermentation. By using a lactose-reduced milk concentrate, it might be possible to reduce the overall carbohydrate content of the yogurt without affecting its sensory properties and the use of skim milk concentrate or powder can be avoided. ln order to assess the effect of filtration on the product properties of yogurt, the total solids required for yogurt preparation are obtained by UF of standardized milk in a pilot filtration unit equipped with spiral wound modules. Retentates with different concentration factors (CF) are investigated. The lactose-reduced milk retentate is fermented and various chemical, physical and sensory properties of the yogurts are evaluated. ln optimisätion trials sucrose is added prior to fermentation to adjust the level of sweetness. Applying UF with the optimized process parameters (i.e. CF) concerning rheological and sensory properties a reduction in carbohydrate content of about 25 % compared to the reference is reached. Yogurts made from retentates with smaller CFs are watery with low ranking in sensory whereas for higher CFs the yogurt has a viscous consistency due to its high protein content, leading to a strong protein network and improved stability. Applying UF with subsequent water-rodilution to a standardized protein content higher sugar reductions up to 40 oÄ are reached. However, a CF of 3.5 is identified as process boundary, as ferm6ntation is inhibited due to lot amounts of lactose present in the substrate. This leads to a watery mouthfeel and low viscosity. With CF 2.5, redilution and addition of a small amount of sucro66 as sweet equivalent, the sensory differences compared to the reference product are less significant. Yet, the€ product{ is still valued as watery with the impression of an altered perception regarding its underlying composition. In general, sugar reduction in yogurt via UF membranes is industrially applicable as a yogurt with acceptable sensory properties could be manufactured by simultaneously reducing its total carbohydrate content significantly. However, for a product{ with optimized sensory and rheological properties, the challenge of mineral losses and shift in composition during filtration remains A possible improvement method to lessen the flat taste could be a nanofiltration (NF) of the permeate in order to re-introduce lost minerals by redilution of UF-retentate with NF-permeate.

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