Sensory Acceptability and Viability of Lactobacillus casei and L. plantarum in Sweet Potato Mixed Chocolate under Gastrointestinal Stresses

Abstract


Sweet potato mixed chocolate have high potential as carrier for probiotics that could improve gut health. The introduction of sweet potato-chocolate mixes with probiotics will provide consumers with an alternative product in addition to the traditional yogurt and milk based drink. It could be a perfect solution to an upset stomach and helps supply the required probiotics making it a delicious option for maintaining optimum digestive health. Major benefits probiotic could offer includes possible enhance response to the immune system, increased ability to digest food, reduced lactose intolerance, increased ability to assimilate the nutrients from food, among others. This study was conducted to determine the sensory acceptability, the survival ability of Lactobacillus plantarum and L. casei in sweet potato-filled chocolate mixes, and to determine the resistance of L. casei and L. plantarum to gastro-intestinal (GI) stresses. The sensory acceptability of sweet potato-chocolate mixes were determined following a 9-point Hedonic scale.

The sweet potato used in this study contains 57.34% moisture, 2.68% protein, 4.47% dietary fiber, 0.61% lipid and 1.32% ash. Results showed that sweet potato-chocolate mixes are high in fat (38.12%), moisture (19.21%) and carbohydrate (33.54%) contents. It has protein content of 5.72% and ash content of 3.41%. The probiotic L plantarum increases from 11 log CFU/gram to 18 log CFU/gram on the 2nd week of chilled storage, which value is significantly higher than its initial population. L. casei increases from 11 log CFU/gram to 17 log CFU/gram. Sensory acceptability is not significantly different for sweet potato-chocolate mixes that contain probiotic and those that do not have.

Prior to inoculation in sweet poatato mixes, Lactobacillus strains were examined for their survival in acidic conditions (pH 1.0 and 3.0), presence of bile and digestive enzymes pepsin (at pH 2.0) and pancreatin (at pH 8.0). L. plantarum was found to be more tolerant at pH 1.0 and 3.0 at 0, 1, and 3 h as well as in the presence of digestive enzymes pepsin and pancreatin at 0 and 4h, compared to L. casei (p<0.001); both strains were found to be tolerant against bile salts and showed growth in a modified media (1.0% w/v bile salts) after 48 h at 37°C. Sweet potatochocolate mixes were then inoculated with the two strains of lactic acid bacteria and stored at 25 ± 2°C and 4°C up to 4 weeks. Cell viability, change in total acidity computed as % lactic acid production and change in pH were monitored at weekly intervals. It was concluded that L. casei and L. plantarum remained viable (≥106cfu ml-1) up to 3 weeks and 4 weeks of storage. Therefore, starch containing substrate from sweet potato is highly recommended to enhance its viability when inoculated into chocolate based foods.

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