Effects of pH and sugar concentration in Zygosaccharomyces rouxii growth and time for spoilage in concentrated grape juice at isothermal and non-isothermal conditions

Abstract

The effect of pH (1.7-3.2) and sugar concentration (64-68 °Brix) on the growth of Zygosaccharomyces rouxii MC9 using response surface methodology was studied. Experiments were carried out in concentrated grape juice inoculated with Z. rouxii at isothermal conditions (23 °C) for 60 days. pH was the variable with the highest effect on growth parameters (potential maximum growth rate and lag phase duration), although the effect of sugar concentration were also significant. In a second experiment, the time for spoilage by this microorganism in concentrated grape juice was evaluated at isothermal (23 °C) and non-isothermal conditions, in an effort to reproduce standard storage and overseas shipping temperature conditions, respectively. Results show that pH was again the environmental factor with the highest impact on delaying the spoilage of the product. Thereby, a pH value below 2.0 was enough to increase the shelf life of the product for more than 60 days in both isothermal and non-isothermal conditions. The information obtained in the present work could be used by producers and buyers to predict the growth and time for spoilage of Z. rouxii in concentrated grape juice.

The Effects of Stress Factors on the Growth of Spoilage Yeasts Isolated From Apple‐Related Environments in Apple Juice

“…Comparable results have been reported by Marvig et al (2014) and Vermeulen et al (2014) who tested the growth of some spoilage yeast strains isolated from high sugar foods. Rojo et al (2013) also reported that the pH value below 2.1 was the main limiting factor affecting the growth of Z. rouxii in concentrated grape juice. In maximum tolerance test, the resistance to pH ranged from 1.7 to 2.4, depending on the isolate.…”

“…Overall, a pH value below 2.0 is enough to extend the shelf life of apple juice to more than 50 days except the contamination caused by strains of C. zemplinina and C. glabrata. An extension of the shelf life to over 50 days represents a huge marketing advantage, since by that time, the product should have transported to the destination (Rojo et al 2013).…”

“…Temperatures from 40 to 79C (with intervals of 3C) were applied to apple juices for 23 min. After cooling of apple juices, serial decimal dilution was performed using 30% (w/v) glucose to prevent osmotic shock and to allow the recovery of sublethally injured cells (Combina et al 2008;Rojo et al 2013). Aliquot of 0.1 mL of each dilution was spread on the YPD agar containing 30% (w/v) glucose in triplicate.…”

“…In particular, strains of Zygosaccharomyces rouxii are usually associated with the spoilage of high sugar products such as honey, syrup and concentrated fruit juices due to their unique physiological characteristics, including resistance to low-acid preservatives, extreme osmotolerance, ability to adapt to high glucose concentrations, ability to ferment hexose sugars and ability to grow at low pH values (Dakal et al 2014). Spoilage by these yeasts can be categorized into two groups: (1) visible growth on the surface of the product and (2) fermentative spoilage manifested by alcoholic, esteric or other types of odors and/or visible evidence of gas production, leading to bubbling of the product and/or expansion of flexible packaging (Rojo et al 2013;Vermeulen et al 2014).…”

“…The results showed that the majority of osmotolerant species were capable of growing within a range of glucose concentration, similar to sugar concentrations found in concentrated apple juice (65-70% w/v). Although osmotolerant yeasts generally grow slowly in concentrated fruit juices due to the combined effects of high sugar content and low pH (Rojo et al 2013), their cells may quickly germinate and grow when concentrated apple juice is diluted to the desired sugar content (11.5-12°Brix) for commercial use and therefore cause spoilage in apple juice. In order to develop an effective strategy to prevent the spoilage in apple juice caused by these osmotolerant isolates, it is important to acquire the knowledge of their tolerance toward stress factors, including temperature, pH, sugar content and antimicrobial components.…”