attributes when added in low (NWP:C-ratio 23.7:76.3) or medium levels (NWP:C-ratio 34.3:65.7).

[0074] Furthermore, the examples of the present invention show that commercially acceptable high protein yoghurt (i.e. 8\% protein) containing native whey proteins ($\alpha$-lactalbumin, 2.13--2.61 mg mL$^{-1}$; $\beta$-lactoglobulin B, 5.48--6.39 mg mL$^{-1}$; $\beta$-lactoglobulin A, 5.40--6.09 mg mL$^{-1}$) can be produced by addition of low (whey:casein ratio 25:75) or medium (whey:casein ratio 35:65) levels of native whey protein concentrate in combination with a reduction in temperature from 95~$^{\circ}$C for 5 minutes to 75~$^{\circ}$C for 5 minutes.

[0075] The present invention provides yoghurt products with high amounts of native whey protein having positive nutritional and health effects.

[0076] Furthermore, the present invention provides methods of preparing nutritious and healthy yoghurt products without producing acid whey which is an unwanted by-product of low value and difficult to dispose.

\section{Detailed description of the drawings}

[0077]

Fig.~1 shows a flow chart illustrating the production of yoghurt based on microfiltration and ultrafiltration fractions from unpasteurized skim milk according to the present invention.

Fig.~2 shows pictures of stirred yoghurts with no addition of UFR and heat treated at 75~$^{\circ}$C for 5 minutes (C-75), with no addition of UFR and heat treated at 95~$^{\circ}$C for 5 minutes (C-95), added low (L) level of UFR and heat treated at 75~$^{\circ}$C for 5 minutes (L-75), added low (L) level of UFR and heat treated at 95~$^{\circ}$C for 5 minutes (L-95), added medium (M) level of UFR and heat treated at 75~$^{\circ}$C for 5 minutes (M-75), and added medium (M) level of UFR and heat treated at 95~$^{\circ}$C for 5 minutes (M-95).

Fig.~3 shows a flow chart illustrating the production of yoghurt based on microfiltration and ultrafiltration fractions of unpasteurized skim milk wherein UFR is added after heat treatment according to Example 6 (reference example).

Fig.~4 shows pictures of stirred yoghurts with addition of UFR before heat treatment at 75~$^{\circ}$C for 5 minutes and fermentation (Control), addition of UFR before heat treatment at 75~$^{\circ}$C for 5 minutes and fermentation (Extra), added low level of UFR after heat treatment at 95~$^{\circ}$C for 5 minutes but before fermentation (BFL), added high level of UFR after heat treatment at 95~$^{\circ}$C for 5 minutes but before fermentation (BFH), added high level of UFR after heat treatment at 95~$^{\circ}$C for 5 minutes and fermentation (AFH).

[0078] The invention is explained in more detail in the examples below. The examples are only meant to be illustrative and shall not be considered as limiting.

\section{Examples}

\subsection{Example 1}

[0079] Stirred and set yoghurts were produced using three whey protein:casein ratios (10:90, 25:75 or 35:65) and two heat treatment temperatures (75 or 95~$^{\circ}$C for 5 minutes) leading to a total of six factor combinations. Two replication blocks gave a total of 12 yoghurt batches.

[0080] Cow's milk (Norwegian red cattle) was obtained from the university farm. The milk was separated (Westfalia separator AG, SA 1-01-175, Oelde, Germany) at 63~$^{\circ}$C. Unpasteurized skim milk was temporarily collected in a double-O vat (Landteknikk A/L, Trondheim, Norway) and kept at 50 $\pm$ 2~$^{\circ}$C until microfiltration (MF) in an MF pilot plant (APV Anhydro AS, Silkeborg, Denmark). Microfiltration was performed at a uniform transmembrane pressure with a module containing seven ceramic membranes, each with pore size 0.14 $\mu$m and 0.303 m$^{2}$ filter area (INSIDE CERAMTM, TAMI Industries, Nyons, France). Filtration temperature varied between 55 and 58~$^{\circ}$C with an average temperature of 56.5~$^{\circ}$C. The permeate circulation was cooled to an average temperature of 51.7~$^{\circ}$C using a separate cooling system according to the International patent WO 2011/115498 A1 (Hoffmann, 2011). Microfiltration retentates (MFR) with average volume concentration factors of 1.6 and 2.9 were produced. The MFRs were pasteurized (type A3-HRB, Alfa Laval, Nakskov, Denmark) at 72~$^{\circ}$C for 15 seconds. The MF permeate was concentrated on an ultrafiltration (UF) pilot plant Alfa Laval UFS-4 (Alfa Laval, Nakskov, Denmark) containing a single spiral wound membrane (GR60PP-6338/48, Alfa Laval, Nakskov, Denmark) with 25\,000 Da cut-off. Filtration temperature was kept between 45 and 50~$^{\circ}$C with an average temperature of 47.8~$^{\circ}$C. The ultrafiltration retentate (UFR) had an average volume concentration factor of approximately 18.8. The chemical composition of the pasteurized MFRs and UFR is shown in Table 1, while Fig.~1 gives a flow chart of the production of fractions and yoghurts. It should be noted that the terms ``MFR 1.6'' and ``MRF 2.9'' in Table 1 and