Zygosaccharomyces Bailii - Spoilage Activities

Spoilage Activities

According to Thomas and Davenport (1985), early reports of spoilage in mayonnaise and salad dressing due to Z. bailii date back to the beginning of the 20th century. More detailed investigations in the 1940s and 1950s confirmed that Z. bailii was the main spoiler in cucumber pickles, sundry pickled vegetable mixes, acidified sauces, etc. Around the same time, fermentation spoilage incidents occasionally appeared in fruit syrups and beverages preserved with moderate benzoic acid levels (0.04 - 0.05% (w/w)). Again, Z. bailii was identified as the spoilage source. Nowadays, despite great improvements in formulation control, food processing equipment and sanitation technologies (e.g. automated clean-in-place), the yeast remains highly problematic in sauces, acidified foods, pickled or brined vegetables, fruit concentrates and various non-carbonated fruit drinks. Z. bailii is also well recognized as one of the main spoilers in wines due to its high resistance to combinations of ethanol and organic acids at low pH. Furthermore, the spoilage by this yeast has been expanding into new food categories such as prepared mustards, fruit-flavoured carbonated soft drinks containing citrus, apple and grape juice concentrates. The ability of Z. bailii in spoiling a wide range of foods is a reflection of its high resistance to many stress factors. Therefore, it has been included in the list of most dangerous spoilage yeasts by several authors.

Spoilage by Z. bailii often occurs in acidic shelf-stable foods, which rely upon the combined effects of acidity (e.g. vinegar), salt and sugar to suppress microbial growth. The spoiled foods usually display sensorial changes that can be easily recognized by consumers, thus resulting in significant economic losses due to consumers’ complaints or product recalls Observable signs of spoilage include product leakage from containers, colour change, emission of unpleasant yeasty odours, emulsion separation (in mayonnaises, dressings), turbidity, flocculation or sediment formation (in wines, beverages) and visible colonies or brown film development on product surfaces. The specific off-flavour that has been attributed to Z. bailii is related to H₂S. In addition, the taste of spoiled foods can be modified by the production of acetic acid and fruity esters. It has been reported that growth of Z. bailii also results in significant gas and ethanol formation, causing a typical alcoholic taste. The excessive gas production is a direct consequence of high fermentable ability of this yeast and in more solid food, gas bubbles can appear within the product. Under extreme circumstances, the produced gas pressure inside glass jars or bottles can reach such a level that explosions may take place, creating an additional hazard of injuries from broken glass. It should be mentioned that in general, detectable spoilage by yeasts requires the presence of a high number of cells, approximately 5 - 6 log CFU/ml.

Apart from spoiling foods, as a direct consequent of growth, Z. bailii can modify the product texture and composition such that it may be more readily colonized by other spoilage microorganisms. For example, by utilizing acetic acid, the yeast can raise the pH of pickles sufficiently to allow the growth of less acid-tolerant bacteria. Besides, as with other yeasts, the concentration of fermentable sugar in a product affects the rate of spoilage by Z. bailii, e.g. the yeast grows faster in the presence of 10% (w/w) than 1% (w/w) glucose. Particularly, Z. bailii can grow and cause spoilage from extremely low inocula, as few as one viable cell in ≥ 10 liters of beverages. That means detection of low numbers of yeast cells in a product does not guarantee its stability. No sanitation or microbiological quality control program can cope with this degree of risk. Hence, the only alternatives would be reformulation of food to increase the stability and/or application of high-lethality thermal-processing parameters.