Effects on product quality for probiotic yoghurts caused by long storage times during production

Sammanfattning: Recent years there has been a large increase in the worldwide sales of cultured products containing probiotics. The obstacle in the production of fermented products incubated with probiotic strains is its effect on sensory, chemical and physical properties. This Master´s Thesis investigates how extended storage times in fermentation tank as well as buffer tank during production of probiotic yoghurts affect final product quality. Through experimental studies, maximum storage times for probiotic yoghurts were to be recommended. The study includes analyses of pH, viscosity, stability, acetic acid concentration, microbial viability and sensory evaluations. Design of experiments (DOE) was used to construct a 32-factorial design for the experiment where different storage times were tested. The analyses showed that: pH decreases with both storage time in fermentation tank and buffer tank. Viscosity increases with long storage times in fermentation tank, while it decreases with long storage times in buffer tanks. Many samples had a sandy/grainy and slimy texture which could be related to high levels of Bifidobacteria or high fermentation temperatures. High levels of acetic acid was found in all samples. All measurements data where within the specification limits, whereas no recommendation for maximum storage times during production could be given.