Dibyakanta Seth

Functional and reconstitution properties of spray-dried sweetened yogurt powder as influenced by processing conditions

ABSTRACT The influence of spray-drying conditions on functional and reconstitution properties of sweetened yogurt powder was studied. Twenty experiments with different spray-drying conditions (140–180°C inlet air temperature, 0.3–0.6 L/h feed rate and 500–1000 kPa atomization pressure) were performed according to central composite experimental design. Analysis of experimental data of solubility and dispersibility of yogurt powder revealed negative correlation with inlet air temperature and atomization pressure. Solubility of powder was significantly (p < 0.05) affected by feed rate. Wetting time of powder increased significantly (p < 0.001) with the increase of spray-drying temperature. The bulk, tapped, and particle densities were in the range of 344.8–475.7, 551.7–782.5, and 1187.5–1666.7 kg/m3, respectively. A significant quadratic effect (p < 0.001) of inlet air temperature and atomization pressure was observed on bulk density. Particle density increased with the increase in inlet air temperature and atomization pressure (p < 0.001). The results of the present investigation has the credible evidence to support that the processing conditions viz. inlet air temperature and atomization pressure decreased the water activity and flow property of the sweetened yogurt powder, whereas feed rate showed positive effect.

Effect of microencapsulation using extrusion technique on viability of bacterial cells during spray drying of sweetened yoghurt

An improved extrusion spraying technique was employed for encapsulation of mixed bacteria culture of Streptococcus thermophilus and Lactobacillus bulgaricus using sodium alginate as the coating material for the purpose of better survival during spray drying of sweetened yoghurt. The effects of nozzle air pressure (200, 300, 400 and 500kPa), sodium alginate concentration (1%, 1.5%, 2%, 2.5% and 3% w/v), calcium chloride concentration (0.1, 0.2, 1M) and hardening time (15, 30, 45 and 60min) on the viability of encapsulated bacteria were investigated. Alginate concentration increased the microcapsule size whereas, nozzle air pressure decreased the size. The encapsulation efficiency increased with the size of microcapsules. Hardening time exhibited a positive effect up to 30min then the effect was non-significant. Increased level of sodium alginate significantly increased the survival ratio of encapsulated bacteria cells. The survival ratio of bacteria cells during spray drying of sweetened yoghurt were 2.48×10-1 and 2.36×10-3 for encapsulated and free cells of S. thermophilus, respectively and 7.26×10-1 and 8.27×10-3 for L. bulgaricus. This study demonstrated that microencapsulation of yoghurt culture in sodium alginate is an effective technique of protecting bacterial cells against extreme drying conditions.

Optimization of the extraction of phenolic compounds from Cyclosorus extensa with solvents of varying polarities

ABSTRACT The leaves of Cyclosorus extensa are used in the preparation of rice beer in Assam, India. The optimal conditions of time and temperature of fermentation for extraction of bioactive compounds from the dried leaves were obtained using response surface methodology. The central composite rotatable design was used and 13 experimental runs based on two-factor-five-level design were generated and performed for each of the solvents. The independent variables were extraction time (12 and 48 h) and temperature (25 and 55°C). The responses studied were total polyphenol content, radical scavenging activity, antibacterial activity, and antifungal activity. The analysis of variance of the test data was performed and the sequential sum of squares, F-value, R2, and adjusted R2 were deduced. The predicted models for all the response variables were adequately fitted to the observed experimental data (p ≤ 0.001). The maximum extraction of bioactive compounds under the optimum conditions of extraction temperature and time for hexane, ethyl acetate, methanol, and distilled water were found to be 25°C for 29.43 h, 28.28°C for 41.27 h, 43.95°C for 29.61 h, and 55.00°C for 48.00 h, respectively. It was also observed that the solubility of the polyphenols was higher in methanol, followed by ethyl acetate, and the highest antibacterial activity against Escherichia coli was shown by the ethyl acetate extracts.