Abstract:
Probiotics must be safeguarded from severe environmental stressors such as harsh acidic
conditions, high temperatures, excessive salt, and enzyme degradation, among others, to avoid a
detrimental sensory influence on food incorporation. One of the potential ways for preserving
probiotic bacteria appears to be microencapsulation. In the current study, Streptococcus
thermophilus STI – 15 cells were microencapsulated in Inulin (IN), Soy protein isolate + Inulin (SPI
+ IN), Ultrasound treated soy protein isolate + Inulin (US-SPI + IN) as capsule matrixes and free
cells (Unencapsulated cells) by freeze drying as the microencapsulation method. Activated STI –
15 cells were grown in MRS agar at 37˚C for 24 h, cells were harvested and mixed with either IN,
SPI + IN, US-SPI + IN in 300 mL separately and freeze dried to microencapsulate.
Microencapsulated (ME) ST (10%) were dissolved in sterilized skim milk and stored at 5°C, -18°C
and enumerated at 28 days to assess the storage survivability. Different aliquots of distilled water
adjusted at pH 1.5, 2.5, 3.5, 4.5 and 5.5 using HCl and NaCl were inoculated separately with ME ST
kept for 60 mins and survivability was investigated. A comparison between the effects of different
pH values resulted pH 1.5 is more lethal than the higher pH values. It was found that the
survivability of the probiotic bacteria in their free form was significantly (p<0.05) lower than that
of the encapsulated form, demonstrating the effective role of the wall components in shielding
probiotics from acidic pH (Gastro-intestinal pH). Among three different wall material types of USSPI+
IN showed the highest survivability of S. thermophilus STI – 15 in all pH values. Probiotic
entrapped within US-SPI+IN significantly (p<0.05) showed the highest survivability during both
refrigerated (5°C) and freezing (-18°C) storage for 28 days of period by resulting the lowest
reduction of the viable cell count (0.27 and 0.19 log CFU/mL for refrigerated and freezing storage
respectively). Microencapsulation by freeze drying in soy protein isolate - inulin matrices, as well
as soy protein isolate modification using power ultrasonography, showed to be a promising
microencapsulation strategy for improving probiotic survivability to storage and stress
conditions such as pH.
