مجله پژوهشهای علوم و صنایع غذایی ایران (Jul 2022)
Improving the survival of lactic acid bacteria in Tarhana soup as a non-dairy matrix: Improving the survival of probiotics
Abstract
The objective of this study was to improve the survival of lactic acid bacteria (LAB) in Tarhana soup as a non-dairy matrix. Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophiles were encapsulated in electrospun nanofiber mats fabricated from corn starch (CS) and sodium alginate (SA) and the protective effect of the nanofibers were investigated on the cells during the preparation of Tarhana and in the gastrointestinal tract. The moisture content of the control and nanofiber- loaded dried Tarhana samples was 8.75 and 8.71%, respectively; therefore, using nanofiber mats in the formulation had no significant effect on the moisture content of the samples. A negative zeta potential value of -15.1 mV was found for LAB- loaded nanofibers. The nanofibers mats prepared from SA and CS mix showed a bead- free and clean structure with uniformity in size. The diameter size of most of the fibers ranged from 175- 338 with an average of 265 nm. Loading nanofiber mats with L. delbrueckii subsp. bulgaricus and S. thermophilus cells led to a uniform distributed beaded structure and the average diameter enhanced to approximately 763 nm. The viability of L. delbrueckii and S. thermophilus at the end of the electrospinning process was 92.82% and 95.83%, respectively, which indicating a slight loss in their population. Survival of nanoencapsulated S. thermophilus and L. delbrueckii was 93.50% and 89.16% respectively, while for free cells it was 85.3 and 76.4% that showed considerable protective effect of CS/SA fibers on the cells against dehydration of Tarhana medium. Nanofiber mats improved the stability of the cells against ordinary heat treatment used in preparing Tarhana soup. The survival rate of S. thermophilus was higher than L. delbrueckii subsp. bulgaricus and a significant difference was observed between the viability of free and nanoencapsulated bacteria. The survival of CS/SA nanoencapsulated S. thermophilus and L. delbrueckii subsp. bulgaricus was 83.25% and 80.21%, respectively, which is indicative of the significant protective effect of fibers on the cells against the heating process. The nanofibers also provided good stability for the cells in the gastrointestinal tract as 106 to 107 CFUg-1 of the cells were survived which is within the recommended level of potential probiotic dose to be effective. There was no significant difference in the color of all samples. Nanoencapsulation in CS/ SA nanofiber mats improved the protection of both LAB strains in simulated fluids of the stomach and intestine (Table 4). After continuous exposure to simulated gastrointestinal fluid, a significant loss of viable free LAB cells (higher than 4 log CFU/ml) was found while the population of S. thermophilus and L. delbrueckii subsp. bulgaricus encapsulated in CS/ SA nanofibers decreased only 0.45 and 0.37 log CFU after 120 min (p> 0.01), 0.93 and 0.80 log CFU after 180 min (p< 0.01), respectively. Tarhana soup prepared with probiotic– loaded nanofibers gained higher scores in terms of consistency, mouth feel, odor, taste, flavor, and overall acceptability attributes. Tarhana soup with nanofibers possessed much sour taste and flavor than samples prepared with free cells of probiotics. The results of the present study indicated that the protection obtained from CS/ SA capsules secured around106 to 107 CFU/g of the probiotic cells which are within the recommended level of probiotic dose to be functional in consumers’ body. Therefore, this product can be used by the consumers like vegetarians and lactose or milk peptide intolerants who do not consume dairy products but need potential fermented probiotic food.
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