Barrera C., Calabuig-Jiménez L., Balau M., Seguí L., Betoret N.
Instituto Universitario de Ingeniería de Alimentos para el Desarrollo. Universitat Politècnica de València. Valencia, Spain

There is an increasing interest in developing probiotic foods alternative to the dairy ones commonly found on the market. In agreement with this, the research group running this study succeeded in incorporating mandarin juice inoculated with Lactobacillus salivarius spp. salivarius in the structural matrix of apple slices by vacuum impregnation (Betoret et al., 2012). However, the number of viable cells in such samples felt sharply after their convective drying at 40 ºC and became below 103 CFU/g after 7 days of storage. Probably, the water activity of the dried product (aw ≈ 0.45) was not low enough to ensure the probiotic stability (Vesterlund et al., 2012). Apart from reducing the water activity, this study poses the incorporation of trehalose and the homogenization in order to increase the probiotic viability in the snack.

Probiotic apple snacks were obtained by vacuum impregnation and further convective drying. Commercial mandarin juice prepared as reported by Betoret et al. (2012) was employed as impregnating solution. A peculiar thing about this study involved adding different concentrations of food grade trehalose (0 and 0.1 g/g) to the juice before its inoculation with 4 mL/L of MRS Broth containing 109 CFU of Lactobacillus salivarius spp. salivarius per mL. Moreover, fermented juices were subjected to different homogenization pressures (0 and 100 MPa) before being incorporated into the porous structure of apple slices (var. Granny Smith) by the vacuum impregnation technique. Once impregnated, apple samples were dried at 40 ºC until they reached a water activity value around 0.45 or 0.35. Dried samples were placed in hermetic opaque bags and the number of viable cells was analyse at different times over 30 days of storage at room temperature.

Due to the longer exposure to the air stream, samples reaching lower activity value at the end of the drying process had lower counts at the beginning of the storage. However, the microbial population remained more stable and in concentrations of around 106 CFU/g during the storage than the set of samples with a water activity of around 0.35. Thus confirming the decisive role of water activity in the survival of the probiotic microorganism. Even the effect of the trehalose content and the homogenization pressure on the microbial population was dependent on the water activity of the stored samples. Under adverse conditions (aw ≈ 0.45), adding 10% (w/w) of threalose to the impregnating solution or homogenizing the juice at 100 MPa improved the viability of Lactobacillus salivarius spp. salivarius. Under optimal conditions (aw ≈ 0.35), the highest counts were obtained when neither trehalose nor pressure were applied to the impregnating solution.

The study shows the protective effect separately exerted by trehalose and the homogenization pressure on the survival of Lactobacillus salivarius spp. salivarius during the storage of apple snacks with a water activity of around 0.45. However, these treatments do not improve the viability of the microorganism when the water activity snack reaches lower values around 0.35.

Keywords: Probiotic, Apple-snack, Vacuum impregnation, Trehalose, Homogenization, Convective drying

Barrera C., et al. (2016). Improving the viability of Lactobacillus salivarius spp. salivarius in apple snacks by adding trehalose and or applying high pressure homogenization. Conference Proceedings of IPC2016. Paper presented at the International Scientific Conference on Probiotics and Prebiotics, Budapest (p. 85.). IPC2016

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