Development and quality evaluation of spray dried probiotic flavoured yoghurt containing Lactobacillus bulgaricus

Abstract

Yoghurt is one of the most popular fermented milk products, it is a product of the lactic acid fermentation of milk by addition of a starter culture containing Lactobacillus bulgaricus and Streptococcus thermophilus . Commercial production of yoghurt has not been able to prove its supremacy in market due to its shorter shelf life. The shelf life of yoghurt can be improved by reducing its water content by drying. The dried products obtained are in shelf stable powder form which can be stored at ambient temperature. Spray drying technique has showed to be highly successful in prolonging the shelf life of food products. Considering these facts, a study was undertaken to develop a process protocol for flavored yoghurt powder. The objectives of the study are 1) Development of spray dried yoghurt powder using different carrier blend ratio and process conditions, 2) Standardisation of the process parameters and 3) Storage studies of the developed product. The physico-chemical characteristics of freshly prepared yoghurt were carried out. The spray drying of yoghurt was carried out in lab scale spray dryer with twin fluid atomizer. The spray drying experiments were conducted with different process parameters viz., carrier blend ratio (B 1 , B 2 , B 3 , B 4 and B 5 ), inlet air temperatures (T 1 , T 2 and T 3 ) and feed rates (F 1 , F 2 and F 3 ). Maltodextrin, corn starch and their combinations were used as wall material to produce yoghurt powder. Physicochemical properties of spray dried yoghurt powder were evaluated by standard procedures. The reconstituted yoghurt samples prepared from spray dried yoghurt powder were evaluated in terms of solubility and wettability. The process parameters were optimized based on the physico-chemical and microbiological properties of the developed yoghurt powder. By considering all the physico chemical and microbiological analyses done on the spray dried yoghurt powder at different processing conditions, powder sample processed at 170 ̊ C inlet temperature with carrier blend B 2 (3:1) at feed rate of 10 rpm was selected as optimized sample.The quality of plain yoghurt powder was improved by incorporating dried white pepper extract (C 1 - 2%, C 2 -2.5 % and C 3 - 3%) and ginger extract (G1-2%, G2- 3% and G3-4%) at different combinations. The spices incorporated yoghurt product was spray dried at optimized operating parameters. The parameters of the flavored yoghurt powder were optimized based on physic-chemical and microbiological properties. By considering the physico-chemical qualities of the flavoured yoghurt under different processing conditions, the sample incorporated with 2.5 percent white pepper extract and 3 percent ginger extract (C 2 G 2 ) was selected as the optimized sample. Flavoured yoghurt powder was packed in laminated aluminium pouches and sealed using a hand sealing machine and subjected to storage studies . Sealed pouches were stored at ambient and refrigerated storage(4°C) for a period of three months and the effect of physical, chemical and microbiological characteristics during storage was studied. The product stored at ambient condition is acceptable only up to 50 -75 days. But the product stored at refrigerated condition found safe up to 3 months.Cost analysis of the products wasdone and cost of production of one kilo gram was estimated as Rs.722/-.