Comparative Study of Commercial Starter and Gum-producing Lactic Acid Bacteria Isolated from Palm-sap on Yoghurt

Abstract

Yoghurt remains a fermented milk of choice globally but its desirability is limited by quality attributes and syneresis. In this study, the effect of using exopolysaccharide (EPS) producing starter cultures and EPS on the quality attribute of yoghurt produced from cow milk was examined. Two starter cultures of EPS-producing LAB were used singly and in combination in three treatments portions (YEPSLa, Lactobacillus acidophilus yoghurt; YEPSLs, Leuconostoc suionicum; YEPSLa + YEPSLs, Lactobacillus acidophilus and Leuconostoc suionicum); Yxg, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. Bulgaricus to produced yoghurt while reference yoghurt (RY) was obtained from the market and refrigerated stored at 4oC. Sensory, proximate composition, textural, rheological properties and whey separation were carried out after 1 and 28 days only, while physicochemical and microbiological were analyzed after 1, 7, 14 and 28 days. No significant difference (p ˂0.05) between RY (8.60 ± 0.60), (7.21±0.10) and YEPSLa + YEPSLs (8.54 ± 0.71), (7.25 ± 0.21) in overall acceptability for day 1 and 28. Moisture (82.45 ± 0.12 - 81.31 ± 0.06%), fat (3.46 ± 0.01 - 3.42 ± 0.03%) and carbohydrate (13.05 ± 0.11 to 12.51 ± 0.10%) contents decreased while total solids (17.57 ± 0.12 - 17.97 ± 0.12%), ash (0.56 ± 0.02 - 0.57 ± 0.02%) and protein (3.74 ± 0.01 - 4.30%) contents increased respectively across the yoghurts. The result showed that the highest cohesiveness and syneresis was observed in YEPSLa + YEPSLs (27.52 ± 0.63) and commercial yoghurt (29.10 ± 0.31), the lowest in Yxg (16.71 ± 0.21) and YEPSLa + YEPSLs (21.50 ± 0.51). The highest viscosity was observed in YEPSLa + YEPSLs across the rotation speeds.  The pH and titratable acid ranged (4.28 – 4.50; 0.90 – 1.41) while the total bacteria colony count (5.5×108 – 11.0×108cfu/ml) during 28 days storage period. Overall, EPS produced by EPS-producing LAB both In-vitro and In-vivo improve texture, mouthfeel, viscosity and reduce syneresis in yoghurt. Combine cultures of Lactobacillus acidophilus and Leuconostoc suionicum and their EPSs competed favourably with conventional starter, and other stabilizing agents in cow milk yoghurt.