Quality properties of non-fat yogurt with addition of whey protein concentrate

Abstract

The aim of the study was investigation of quality of fat-free, settype yoghurt made at 5% (w/w) protein level with addition of skim milk powder (SMP) and whey protein concentrate (WPC) blends. The ratio SMP/WPC in used blends was: 1/0; 2/1; 1/2; 0/1. On 1st, 7th and 21st day of refrigerated storage yoghurt was analysed for sensory properties, titrable acidity, pH, free fatty acids (FFA), acetaldehyde, and diacethyl. Also enumeration of viable L. delbrueckii ssp. bulgaricus and S. thermophilus was carried out. During the whole storage period products with SMP/WPC ratio at 1/2 and 2/1 obtained the best sensory score. Addition of WPC to yoghurt significantly decreased lactic acid concentration which positively influenced its stability during shelf life. It was shown that during storage acidity of yoghurt was growing up in concern of pH level. The acetaldehyde content tended to increase significantly in the yoghurt fortified with higher proportion of WPC opposite to diacethyl level which was the lowest in yoghurt with an SMP/WPC addition at 0/1. During storage concentration of both volatile compounds were the highest on 7th day and the lowest on 21st day. The maximum concentration of FFA was stated in products with SMP/WPC ratio 1/2. During the storage period FFA content significantly increased after 7th days and had no changed during next 14 days. The total number of yoghurt bacteria during the whole storage time was up to 1010 and did not vary depending on SMP/WPC ratio. Amount of L. delbrueckii ssp. bulgaricus was about one log cycle lower than S. thermophilus in all kinds of yoghurt.