17A-1 |
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T. AMATAYAKUL1, F. Sherkat2, and N. P. Shah1. (1) School of Molecular Sciences, Victoria University, Melbourne City MC, Melbourne, Vic 8001, Australia, (2) Food Science, RMIT University, City Campus, GPO Box 2476V, Melbourne, Vic 3001, Australia Individual usage of EPS starter cultures or whey protein based ingredients have been known to improve physical properties of yoghurts. This study investigated physical properties of low solid yoghurts made by use of EPS starter cultures and varying casein to whey protein (CN:WP) ratios during storage periods. Set and stirred yoghurts (9% TS) were made by non-EPS, and EPS (capsular or ropy) starter cultures and varying CN:WP ratios from 4:1 to 1:1 by blending skim milk powder, whey protein concentrate and lactose. Physical properties of yogurts were investigated over 4 week storage including firmness and syneresis (in set yoghurt) and flow curve and hysteresis loop (in stirred yoghurt). Composition of the product and EPS and lactic acid concentrations were determined. Microstructure was also investigated. The actual CN:WP ratios were 4.3:1.0, 3.0:1.0, 2.1:1.0 and 1.2:1.0. The lactic acid concentration decreased from 1.00% to 0.60% as the CN:WP ratios were reduced and it increased slightly during the storage period. EPS concentration was in the range of 30-70 mg/L, with slightly higher in yoghurt made from ropy starter culture. No degradation of EPS was found during the storage period. Firmness and syneresis reduced when the CN:WP ratios were reduced. Yoghurt containing EPS showed lower values for firmness and syneresis. No changes in firmness and syneresis were found over the storage period. Fine and compact protein matrix was found in set yoghurt made from milk produced at low CN:WP ratios. Stirred yoghurt made using ropy starter culture at CN:WP ratio 3:1 showed the highest shear stress response and hysteresis loop during the storage period. The results suggest that physical properties of set and stirred yoghurts can be improved by optimising the use of whey protein based ingredients alone (set yoghurt) or by increasing levels of whey protein and use of ropy starter culture (stirred yoghurt).
Session 17A, Dairy Foods: Cheese and microbiology
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