Effect of meat addition on microbiological, physicochemical and sensory properties of dairy yoghurt
Addition to dairy yoghurt of minced cooked beef was carried out as a way to provide additional health benefits to probiotic yoghurt. The study aimed to fortify yoghurt with high nutritional quality protein from meat. This novel health food will suit the majority of the population, particularly geriatric people, since foods such as yoghurt enriched with proteins would be suitable to deliver their specific nutritional requirements. The objectives of this study were to develop a new protein-rich yoghurt and determine its microbiological, physicochemical and sensory properties. The main phase was the preparation of yoghurts, with added beef meat (5%, 7%, and 9%) such that the total solids content (around 20%) remained constant, and was followed by homogenisation. Yoghurt containing homogenised meat (HMY), yoghurt containing unhomogenised meat (UHMY) and control plain yoghurt were produced. The yoghurt mixtures were heated at 85°C for 30 minutes followed by inoculation and incubation at 42°C for 5 hours after which they were stored for 21 days at 4°C. The results showed that the production of acidity and microbial counts were not affected by the meat addition during a 21 day storage period at 4°C, compared to the control. The microbiological counts of total lactic acid bacteria after 1 day of storage in meat-fortified yoghurts (around 30 ×10E7 cfu/g) were not significantly different from numbers in the control yoghurt. However, the counts showed significant loss of viability during the period of storage, although the final viable numbers in the yoghurts were high enough (>10E7 cfu/g) for the products to be designated probiotic. Fortifying the yoghurt with meat did not stimulate the growth of contaminating coliforms, Salmonella and Listeria. The fat content decreased while the protein content increased significantly (P<0.05) with increased addition of meat. The fat content of yoghurts ranged between 2.2% (Control) and 1.41% (9% meat addition), hence the yoghurts can be considered as low- fat products. Apparent viscosity and water holding capacity (WHC) decreased significantly (P<0.05) with the addition of meat. The control had the highest viscosity and WHC values followed by 5% meat yoghurts. Colour was different for yoghurts containing different added meat and also in terms of homogenisation. The addition of meat changed the colour of yoghurts particularly in those containing higher meat content that had been homogenised. They were darker with a redder colour. Sensory results revealed that samples fortified with 5% meat received the second highest scores for flavour after that of the control. Meat addition resulted in significant decrease (P<0.05) in the overall flavour quality. Meat addition improved the odour of yoghurts but decreased significantly (P<0.05) the overall scores for appearance and texture. Results showed that addition of 5% meat could be used to produce a meat-added yoghurt without significant adverse effects on the microbial, physicochemical or sensory properties. As expected, 9% meat yoghurt had the highest protein content (9.98 %) compared to the control (6.1%). Further studies are needed to improve the quality of meat yoghurts in terms of apparent viscosity, whey separation, and colour and also enhance the overall flavour.