Smoking hot – Heat-induced uncoupling of growth & acidification in yoghurt production helps save costs and results in reduced post-acidification and improved shelf life

Abstract

Yoghurt is a popular fermented milk that is consumed worldwide. Industrial production is typically carried out using thermophilic starters comprised of two Lactic Acid Bacteria (LAB), namely Streptococcus thermophilus and Lactobacillus bulgaricus. We propose a novel approach for manufacturing yoghurt, which alleviates problems associated with the traditional approach, i.e., post-acidification and growth of spoilage yeast during storage. The novel approach is based on the observation that non-growing LAB, at elevated temperatures, retain a capacity for producing lactic acid. First, the capacity of a commercial yoghurt culture to acidify milk was evaluated at different temperatures, and it was found that growth was hampered at temperatures above 50 °C, while lactic acid could still be produced. By increasing the inoculum, it was possible to reach the desired pH of 4.6, even at 51 °C. This prompted us to test a novel way of producing yoghurt. Freshly prepared yoghurt was added to milk, pre-warmed to 51 °C, in different amounts. Using as little as 20 % yoghurt, the milk acidified to the desired pH of 4.6 within 2 h. Thus, by using this approach, it was possible to reduce the extent of microbial growth and to reduce culture expenses by a factor of 5. It was observed that post-acidification could be virtually eliminated, which helps prolong shelf-life. The 51 °C treatment also helped reduce yeast and mold content in the yoghurt, which is important for prolonging shelf life. To summarize, we have developed a simple method for producing long shelf-life yoghurt at a lower cost to the benefit of dairies and consumers.