Dairy Foods: Yogurt and Ice Cream

Pectin is commonly used as a gelling agent in the manufacture of yogurt. The objective of our study was to evaluate the impact of 4 different types of pectin that had different degrees of esterification (DE) and amidation (DA), on the physical properties of set type yogurt. The pectin samples included 2 types of low methoxyl (LM) pectin with 38% and 45% DE, one type of low methoxyl amidate (LMA) with 39% DE and 14% DA, and one of high methoxyl (HM) with 72% DE. Other pectin types resulted in phase separation in milk. Pectins were added to heated reconstituted skim milk at various concentrations (0.005, 0.05, 0.1 and 0.2%). Gelation properties were monitored using dynamic low amplitude oscillatory rheology and infrared light backscatter. Microstructure was studied using fluorescence microscopy. Wheying off and permeability (porosity) were analyzed at pH 4.6. At pectin concentration of 0.005% no significant differences were observed in yogurts. Yogurt made with 0.05 or 0.1% LMA, LM with 38% DE, and LM with 45% DE, had significantly lower storage modulus (G’), light back scatter ratio at pH 4.6 (RpH4.6), wheying off and permeability compared with control yogurt (no pectin). Permeability and wheying off increased with increasing LMA concentration from 0.1 to 0.2%, while the G’ and RpH4.6 values were reduced. Complete inhibition of wheying off was observed when 0.2% LM (38% DE) pectin was used in yogurt and this sample also had the lowest permeability. In yogurt made with 0.2% of HM pectin, the R value gradually decreased after gelation pH until pH 4.6. Wheying off and permeability increased with an increase in the concentration of HM (from 0.005 to 0.2%). HM pectin produced yogurt with the lowest G’ and RpH4.6 values compared with other treatments. The microstructure results indicated that yogurt made with HM pectin had an open network, especially at 0.2% pectin, while yogurt made with LM (38% DE) had higher degree of interconnectivity of strands. In conclusion, pectin types greatly impact gelation behavior and yogurt texture. LM pectin with low DE value and without amidation gives the best gelation properties.