Effect of oligofructose and microencapsulation on viability of Lactobacillus rhamnosus and physicochemical and sensory properties of functional jelly

Nowadays, with the development of probiotic products on the world market, the need for developing new products containing probiotic bacteria becomes more apparent. Probiotics are defined as living microorganisms that, if consumed in sufficient quantities, will have beneficial effects on the health of the host. Probiotics are now widely used in the production of food products and account for approximately 65% of functional foods. Probiotics often belong to either the genus Lactobacillus or Bifidobacterium. Lactobacillus rhamnosus is one of the known probiotic bacteria with beneficial properties. Prebiotics are defined as indigestible compounds, mainly carbohydrates that can be used as carbon source for probiotic bacteria and stimulate their growth and viability. Oligofructose is a type of short chain inulin and is one of the most well- known prebiotics. Moreover, microencapsulation of probiotic bacteria can improve the survival of these bacteria. In this approach, living probiotic cells are covered or trapped by various compounds. Hydrocolloids such as alginate and carbohydrates such as starch can be suitable compounds for microencapsulation. The purpose of this study was to investigate the effect of oligofructose and microencapsulation on the viability of Lactobacillus rhamnosus, textural, physicochemical and sensory characteristics of functional jelly. 

In this study, different concentrations (0, 1.5 and 3 percent) of oligofructose as prebiotic were used to produce jelly samples, and 107 CFU/mL of probiotic bacteria (free and microencapsulated Lactobacillus rhamnosus) was inoculated. Microencapsulation of probiotic bacteria was performed by emulsion method using sodium alginate and corn resistant starch. The jelly samples were stored at 4˚C for two weeks. pH, acidity, dry matter, firmness, probiotic bacterial count and sensory properties (taste, odor, texture, color and overall acceptance) of the samples were evaluated on the first, 7th and 14th days of jelly production. Seven samples including 6 treatments and 1 control sample (without probiotic bacteria and prebiotic compound) with three replications were studied. The data were subjected to analysis of variance (ANOVA), followed by the Duncan’s multiple range test to determine the significant difference between samples at 95% confidence level (p<0.05)  using the SAS 9.4 M4  Software. The charts were drawn by Excel 2013. 

The results of sensory evaluation showed that the effect of different percentages of oligofructose on the sensory parameters, except for the taste, was not significant (p>0.05). Using 1.5% oligofructose and probiotic bacteria (free or microencapsulated) did not change the score of taste but the use of 3% oligofructose and free probiotic bacteria decreased the score of this parameter. The effect of storage time on sensory properties (taste, odor, texture, color and overall acceptance) was significant (p<0.05) so that with increasing storage time, the score of sensory parameters decreased. The results of physicochemical tests indicated that with increasing oligofructose, dry matter increased and acidity decreased (p<0.05). The results of texture analysis showed that the microencapsulation of probiotic bacteria and addition of oligofructose significantly (p<0.05) increased the firmness of jelly texture. During storage period, pH and dry matter significantly (p<0.05) decreased but acidity and firmness of jelly texture increased. The results of probiotic bacterial count indicated that the use of microencapsulated probiotic bacteria and oligofructose significantly (p<0.05) increased the survival of Lactobacillus rhamnosus. The viability of probiotic bacterai decreased during storage period, t however, the number of probiotic bacteria in the samples was in the range of 106- 107 CFU/g. On the first and 7th days, no mold and yeast contamination was observed in the samples and on the 14th day, the number of molds and yeasts was less than 10 CFU/g. The sample containing microencapsulated probiotic bacteria and 3% oligofructose (sample 4) was selected as the best sample in terms of probiotic bacterial count and textural, physicochemical and sensory quality. Therefore, it is possible to produce synbiotic jelly with the desired quality