Impact of Fortifying Cow's Milk With Whey Protein Hydrolysate on Yoghurt Quality

Abstract

Quality attributes of yoghurt made from cow's milk fortified with whey protein hydrolysate were studied. Six yoghurt treatments were made, control yoghurt was made by adding 3% non-fat dry milk to cow's milk while the other five treatments were made by fortifying cow's milk by 0.5, 1.0, 1.5, 2.0 and 2.5% whey protein hydrolysate respectively and 3.0% nonfat dry milk to each treatment. All yoghurt treatment was stored in refrigerator for 12 days and was sampled when fresh and at 3, 6, 9 and 12 days for chemical, rheological, microbiological analysis and sensory evaluation. The obtained results indicated that adding whey protein hydrolysate to cow's milk caused a significant increase of total solids, total protein and ash contents, titratable acidity, while decreased pH values and whey syneresis of yoghurt treatments and these effects were proportional to the rate of adding whey protein hydrolysate. Also, adding whey protein hydrolysate up to 2.0% increased the scores of organoleptic properties and treatment T4 that made with adding 2.0% whey protein hydrolysate was the most acceptable yoghurt treatments. Total solids, total protein, ash and fat contents of all yoghurt treatments did not change significantly, (P > 0.05) during storage period, while titratable acidity increased. Whey separation decreased during storage period up to the sixth day of storage period then increased up to the end of storage period, while the scores of organoleptic properties were almost stable up to the ninth day of storage period.

Influence of Adding Inulin as a Fat Replacer on the Characteristics of Yoghurt

“…On the other hand, the soluble nitrogen contents increased in all treatments as the storage period progressed. These results agree with those of Abd EL- Salam et al (1996), Kebary and Hussein (1999) and Kebary et al (2004).…”

“…Results show that developed titratable acidity of yoghurt samples increased gradually (p≤0.05) as the storage period increased. These results are in agreement with those of Abd EL- Salam et al (1996), Harby and EL-Sabie ( 2001), Kebary et al (2004), Badawi et al (2004) and Kebary et al (2009). Replacement of milk fat with inulin significantly increased the titratable acidity (Table 1).…”

“…Scores of all yoghurt treatments decreased gradually up to the end of storage period. These results are in agreement with those reported by Kebary and Hussein (1999), and Kebary et al (2004).…”

“…These results could be explained by the development of acidity. These results agree with those reported by Kebary et al (1996), Kebary and Hussein (1999), Kebary et al (2004), Kebary et al (2007), Badawi et al (2008) and EL-Sonbaty et al (2008). The obtained results also showed that yoghurt with added inulin was of higher counts of LAB than the control, which came in harmony with Menne et al (1997).…”

“…Replacement of milk fat with inulin significantly increased the titratable acidity (Table 1). These results might be due to the prepiotic effect of inulin, which enhances the growth and ability of lactic acid bacteria to grow, to hydrolysis lactose (Gibson and Roberfroid, 1995;Hussein and Kebary, 1999;Kebary et al, 2004 andBadawi et al, 2008). Yoghurt containing 1.2% inulin was of the highest titratable acidity at the coagulation time, compared with other treatments, which came in agreement with that of Guven et al (2005).…”