Influence of Yoghurt and Cheese Reformulation Strategies on Microbial Ecology and Product Characteristics
Salt and sugar are important ingredients for the production, microbial safety, shelf life and flavour of quality fermented dairy products. However, these ingredients are also modifiable risk factors for non-communicable diseases, such as coronary heart disease and diabetes, whose prevalence accounts for almost half of the global disease burden. Together with legislative action and consumer education, reformulation of foods to contain less salt and sugar can positively influence individual and population health. The aim of this study was therefore to analyse the effect of different reformulation strategies on the microbial ecology and product characteristics of two fermented dairy products. In the first subproject, sweetness-enhanced yoghurt was produced using enhanced milk created using a bi-enzymatic modification of the moderately sweet milk sugar lactose to increase its sweetening power by a factor of 2-3. This aimed to ultimately reduce the added sugar needed to achieve the same sweetness in the end product. The growth and acidification of starter lactic acid bacteria (SLAB) was investigated in reformulated yoghurt, demonstrating that SLAB fermented the enhanced milk in an equal manner to regular milk. Testing for potentially pathogenic or spoilage bacteria indicated that the microbial quality of reformulated samples was not affected. Product characteristics such as pH were monitored throughout fermentation and storage, showing no difference between enhanced and regular samples. High-throughput sequencing (HTS) studies demonstrated comparable microbial diversity in sweetness-enhanced and regular yoghurt, and a quick dominance of SLAB during fermentation. In a parallel study, it was demonstrated that a 10 – 20 % reduction in added sugar was possible without affecting the sensory properties of the reformulated yoghurt samples. Further studies to test the scalability of these pilot plant experiments are necessary to establish the industrial potential of this reformulation approach. In the second subproject, Edam cheese was reformulated to contain < 0.4 % Na by applying a simple NaCl reduction strategy as well as a mineral salt substitution approach during brining. SLAB growth and technological parameters were examined throughout fermentation and a ripening period of six weeks. A 30 % Na reduction was possible through simple reduction, whilst mineral salt substitution achieved a 50 % Na reduction. No difference in SLAB growth or analysed product characteristics such as mineral content and pH was observed between sodium-reduced and control cheeses. A challenge test with the Listeria monocytogenes surrogate Listeria innocua, as well as testing for potentially pathogenic or spoilage bacteria, indicated no loss of microbial safety through sodium-reduction. HTS studies showed a significant difference in microbial ecology between production and ripening, yet no difference in microbial diversity between sodium-reduction strategies was found. However, a parallel study of the sensory attributes demonstrated that the reformulated Edam samples displayed a distinctly bitter taste. A production experiment in the research lab of a commercial dairy indicated that these approaches were scalable to larger cheese loaves, yet further studies are needed to confirm industrial applicability and reduce off-flavours. These two reformulation studies provide a scientific basis for successful reformulation of fermented dairy products, thereby providing avenues for viable approaches to lower salt and sugar with the aim of improving population health if commercialised.