Combined effect of sugar content and pH on the growth of a wild strain of Zygosaccharomyces rouxii and time for spoilage in concentrated apple juice

- Growth of Zygosaccharomyces rouxii B-WHX-12-54 as a function of sugar content and pH was modelled.
- The main limiting factor affecting Z. rouxii B-WHX-12-54 growth in concentrated apple juice was pH.
- A pH value of 2.0 can completely inhibit Z. rouxii B-WHX-12-54 growth in concentrated apple juice.
- A pH value of 2.5 is enough to keep concentrated apple juice at 70 °Brix for 60 days.

The objective of this study was to evaluate the combined effect of sugar content (66-70 °Brix) and pH (2.0-3.5) on the growth of a wild strain of Zygosaccharomyces rouxii B-WHX-12-54 by response surface (RS) methodology. Experiments were performed in concentrated apple juice inoculated with this strain at standard storage condition (isothermal, 25 °C) for 60 days. Results show that pH was the most significant limiting factor that affects the growth parameters (potential maximum growth rate and lag phase duration), although the effect of sugar content was also significant. In a second experiment, the time for spoilage (TFS) by this strain in concentrated apple juice was assessed under isothermal (25 °C) and non-isothermal conditions, in an attempt to simulate standard storage and overseas shipping temperature conditions, respectively. Results show that pH was again the environmental factor with the highest effect on delaying the spoilage of the product caused by this strain. Although concentrated apple juice stored under non-isothermal condition showed lower microbial stability (evidenced in lower TFS values) than that stored under standard isothermal condition, a pH value below 2.3 was sufficient to extend the shelf life of the product to more than 60 days under both temperature conditions. The results obtained in this study could be used by producers and buyers to predict and control the growth and TFS of Z. rouxii strain B-WHX-12-54 in concentrated apple juice.