IMPACT OF FORTIFYING COW'S MILK WITH WHEY PROTEIN HYDROLYSATE ON YOGHURT QUALITY

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.