Osmotic pretreatment to assure retention of phenolics and anthocyanins in berry jams
Introduction
Blueberry (Vaccinium corymbosum) and strawberry (Fragaria x ananassa) are important sources of bioactive chemicals such as flavonoids, stilbenes, tanins, and phenolic compounds (Tulipani et al., 2008). These compounds may protect against degenerative diseases, and their effects on health have been commonly attributed to their antioxidant properties (Seeram, 2008).
Although these fruits may be consumed raw, their preservation in processed food, such as jams, jellies, and cakes is attractive as it improves shelf life and allows for year-long enjoyment (Côté et al., 2010, Garzón et al., 2009, Olsson et al., 2004, Scibisz and Mitek, 2009). However, preparation of jams (Figuerola, 2007) brings a number of challenges, one of which is to preserve the beneficial compounds in the raw fruit, while simultaneously inhibiting spoilage (Kowalska, 2005). Duration of heat treatment, identity and amount of ingredients, and pretreatment of the fruit are all reasonable preparation steps to optimize. Indeed, heat treatment and addition of sugar and citric acid can affect jam quality and final concentrations of flavones and anthocyanin (Wu et al., 2010, Scibisz and Mitek, 2009).
A common pretreatment method is osmotic dehydration, which involves immersion of the fruit in a hypertonic solution (Castañeda, Arteaga, Siche, & Rodriguez, 2010). This process may preserve desirable characteristics of the fruit later used in jam making by decreasing water activity in the fruit (Rahman, 2008; Phisut, 2012). The driving force of the process is the difference in solute concentration between the solution and interstitial fluid which causes the exit of water from and the entrance of solutes to the cells until osmotic equilibrium is reached (Phisut, 2012; Rahman, 2008).
Research suggests that osmotic dehydration of strawberries with sucrose before jam preparation stabilizes anthocyanin more than the mere addition of sucrose during jam preparation (Watanabe, Yoshimoto, Okada, & Nomura, 2011). However, the identity and concentration of solute (typically sucrose); temperature; immersion time; pressure; ratio of food to solution; and the structure, permeability, shape, and size of raw food all have an influence on the process (Osorio et al., 2007). In the present work, the concentration of phenolic compounds, anthocyanin content and color were optimized in the prepared jam by varying the sucrose concentration and time of osmotic pretreatment.
To design the optimization efficiently, response surface methodology (RSM) was used. This technique allows for varying of multiple parameters simultaneously with a defined set of experiments. The results are used to prepare a surface predicting the response of the dependent variables in the experiment. The main advantage of RSM is use of minimum experimental runs necessary for statistical validity. RSM is faster and gives more information than the classical one-variable-at-a-time approach or the use of full factorial designs (Ozdemir, Ozen, Dock, & Floros, 2008).
Section snippets
Raw material
Blueberries (Vaccinium corymbosum, Biloxi variety) and strawberries (Fragaria × ananassa, Tioga variety) were obtained from Virú and Trujillo Provinces, respectively, Department of La Libertad, Peru. Fruits were harvested at commercial ripeness and shipped under refrigeration to the Department of Agroindustrial Engineering at the National University of Trujillo. Fruit was packed in 300 g clamshell containers and stored in the dark at 2.0±0.5 °C and 95±2% RH. The following day, samples of the
Results and discussion
Variance analysis indicates that time and sucrose concentration during pretreatment have a statistically significant (p<0.05) effect on anthocyanins and phenolic compounds in both blueberry and strawberry jams. On the other hand, regression analysis of the experimental results allowed for the preparation of response surfaces to locate the optimal treatment time and sucrose concentration for anthocyanins and phenolic compounds (Fig. 1A–D). The obtained models had a good predictive capacity (R2
Conclusion
Response surface analysis has allowed for determination of the optimum conditions for osmotic pretreatment (sucrose concentration of 1.65 M for blueberry and 1.46 M for strawberry, and immersion time of 242 min for blueberry and 219 for strawberry jam) to obtain the highest retention of anthocyanin (41.9 mg/100 g for blueberry jam and 15.3 mg/100 g for strawberry jam) and the highest total phenolic compound retention (231.9 mg GAE/g for blueberry jam and 22.8 mg GAE/g for strawberry jam). Although we
Acknowledgements
The authors thank Kevin Andrew Wilkinson of Antenor Orrego Private University for his help in preparing and organizing this manuscript in English. The authors also thank the Multidisciplinary Research Laboratory of Antenor Orrego Private University for the use of their UV–vis spectrophotometer.
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