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 Printable version |
Modelling growth of the spoilage yeast Candida holmii
in pineapple juice |
Cahiers Agricultures. Volume 9, Number 1, 55-8, Janvier - Février 2000, Méthodes et techniques
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 Résumé
Article gratuit
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Author(s) : Jean Tchango Tchango, Thomas Njiné, Jean-Pierre Hornez, Roger Tailliez |
Summary : Yeasts and mould are the most important spoilage microorganisms in beverages with high levels of sugar and low pH. The use of turbidity or other rapid microbilogy methods such as indirect conductmetry seems to be convenient for monitoring yeast activity and generating data to be used in predictive models for the growth of food and beverage spoilage yeasts as a function of different environmental conditions/ Our study established a mathematical model for predicting the growth of Candida holmii in pineapple juice, as a function of pH and storage temperature. The spoilage yeasts used for the study were isolated from pasteurized pineapple juice, guava and passion fruit nectars produced at the industrial level in Cameroon, and identified as Candida holmii (p = 0.991), Candida pelliculosa (p = 0.999) and Kloeckera apis (p 0.999) using Biomérieux ID 32 strips.
A factorial design was used to determine the effects and interactions of pH and storage temperature on Candida holmii growth in pineapple juice. The growth kinetics were established in duplicate, in pineapple juice adjusted to different pH levels (2.00, 2.50, 3.15, 4.00, 5.00 and 6.25) with 20% citric acid or 2 N NaOH, and stored at different temperatures (2, 5, 10, 15, 25, 32, 35 and 37°C). Growth was estimated by measuring the optical density at 630 nm using a spectrophotometer. A quadratic polynomial model was constructed to predict the effects and interactions of pH and temperature on maximal optical density (r2 = 0.96; Figure 1). The relationship between optical density and Candida holmii population density (CFU.ml– 1) was also established using an exponential regression (r2 = 0.998). According to the model maximal growth conditions were 30°C and pH 5 for a maximum optical density of 2.34 (about 49.106 CFU.ml– 1). The model provided a close fit between predicted and observed maximum optical density values (figure 2). The model was validated (Table 1) with experimental maximum optical density values obtained with C. holmii, C. pelliculosa and K. apis in commercial pineapple juice (pH 3.95) and passion fruit nectar (pH 3.03).
This type of model could be useful in industries for predicting storage periods for foods and beverages, along with expiry dates for these products. |
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