The survival of lactococcus lactis in a convective-air-drying environment: The role of protectant solids, oxygen injury, and mechanism of protection
- Authors: Ghandi, Amir , Powell, Ian , Chen, Xiao Dong , Adhikari, Benu
- Date: 2013
- Type: Text , Journal article
- Relation: Drying Technology Vol. 31, no. 13-14 (2013), p. 1661-1674
- Full Text:
- Reviewed:
- Description: The effect of protectant solids (lactose, sodium caseinate, and their mixture) on the survival of Lactococcus lactis subsp. cremoris was studied in a convective-air-drying environment using single droplet drying. The effect of drying the bacteria in the presence or absence of sodium ascorbate was evaluated, and the evolution of glass transition temperature in the drying process was examined. It was found that the protective efficiency of lactose and sodium caseinate was comparable at the concentrations tested. A mixed protectant matrix (lactose:sodium caseinate, 3:1) gave higher survival than with lactose or sodium caseinate alone at the same total solids level. Protectants enhanced bacterial survival by moderating the drying rate and achieving dryness at lower temperatures, and by facilitating the formation of a glassy matrix earlier in the drying process. The addition of sodium ascorbate was also examined. © 2013 Copyright Taylor and Francis Group, LLC.
- Description: C1
Drying kinetics and survival studies of dairy fermentation bacteria in convective air drying environment using single droplet drying
- Authors: Ghandi, Amir , Powell, Ian , Chen, Xiao Dong , Adhikari, Benu
- Date: 2012
- Type: Text , Journal article
- Relation: Journal of Food Engineering Vol. 110, no. 3 (2012), p. 405-417
- Full Text:
- Reviewed:
- Description: The drying and survival kinetics of Lactococcus lactis ssp. cremoris in a convective air drying environment were measured using single droplet drying experiments. Tests were carried out at five different drying temperatures (45-95°C) at a constant air velocity (0.5 m/s) and within 2.4-11% relative humidity. The effect of protective agents (10% w/w) of lactose, sodium caseinate and lactose:sodium caseinate (3:1) was also evaluated. The thermal inactivation kinetics parameters in convective air drying and isothermal water bath heating were determined and compared. The results showed that the final temperature attained by the droplet affected the survival of the bacteria significantly, however, most of the bacterial death occurred in early stage of drying while evaporative cooling kept the drop temperature relatively low. At higher droplet temperatures (≥65°C) the bacterial cultures were inactivated by both dehydration and thermal stresses. At lower droplet temperatures (≤55°C) the rate of change in droplet moisture content had much stronger effect on the bacterial survival. Lactose and sodium caseinate, as protective agents, enhanced the survival of bacterial cells significantly at all the test conditions. The lactose:sodium caseinate (3:1) mixture synergistically enhanced the survival of the bacterial cultures. The death of these bacteria followed first-order kinetics during convective single droplet drying as well as during isothermal water-bath heating. However, the inactivation energy in convective single droplet drying (181.3 kJ/mol) was much higher than the inactivation energy in isothermal water bath heating (16.8 kJ/mol) within the medium temperature of 45-95°C. © 2012 Elsevier Ltd. All rights reserved.
Effect of shear rate and oxygen stresses on the survival of Lactococcus lactis during the atomization and drying stages of spray drying : A laboratory and pilot scale study
- Authors: Ghandi, Amir , Powell, Ian , Howes, Tony , Chen, Xiao Dong , Adhikari, Benu
- Date: 2012
- Type: Text , Journal article
- Relation: Journal of Food Engineering Vol. 113, no. 2 (2012), p. 194-200
- Full Text:
- Reviewed:
- Description: The effect of shear rate and oxygen injury during atomization and the combination of these factors on the survival of Lactococcus lactis subsp. cremoris in spray drying was studied using laboratory and pilot scale spray dryers. The atomization was carried out using a two-fluid nozzle in the laboratory study and a two-fluid nozzle or rotary atomizer in the pilot scale study. The extent of oxygen-induced death was determined using ascorbic acid in the feed and atomizing the feed with gaseous nitrogen. The lowest levels of bacterial death were observed at lowest characteristic shear rate and in the presence of nitrogen and ascorbic acid. Quantitative analysis showed that lower shear rate, creating an oxygen-limiting environment during atomization and drying, and using oxygen scavengers in the feed were successful in enhancing bacterial survival in spray drying. We also report for the first time that, at least for L. lactis, the extent of death during the atomization stage far outweighs death during the drying stage, and that the majority of bacterial death (up to 93%) occurs during the atomization stage. The death of bacteria was found to be less when using a rotary atomizer or when using a two-fluid nozzle atomizer at lower flow rate. This work shows that bacterial death during spray drying can be minimized by using oxygen scavengers such as ascorbic acid and/or an anaerobic atomizing medium (such as nitrogen), and by altering the spraying conditions. © 2012 Elsevier Ltd. All rights reserved.
The effect of dryer inlet and outlet air temperatures and protectant solids on the survival of Lactococcus lactis during spray drying
- Authors: Ghandi, Amir , Powell, Ian , Chen, Xiao Dong , Adhikari, Benu
- Date: 2012
- Type: Text , Journal article
- Relation: Drying Technology Vol. 30, no. 14 (2012), p. 1649-1657
- Full Text: false
- Reviewed:
- Description: The influence of spray-drying conditions, inlet air temperature (130 degrees C to 200 degrees C), outlet air temperature (38 degrees C to 65 degrees C), drying medium (air and nitrogen) and milk-derived protectants (10%, 15%, and 25% lactose; 5% and 10% sodium caseinate; 10%, 25%, and 35% lactose: sodium caseinate (Lac: NaCas, 3:1)) on the survival of Lactococcus lactis ssp. cremoris was studied using a laboratory-scale spray dryer. An inlet air temperature of 130 degrees C and 65 degrees C as the outlet air temperature maintained high survival of the bacteria without sacrificing low moisture content. Inlet air temperature, previously considered to have no significant effect, was shown to play an important role in the survival of bacteria during spray drying. A mixture of Lac:NaCas (3: 1) showed a better protective effect on the survival of bacteria than lactose and sodium caseinate individually, and this effect increased with increasing amount of protectant. The results were generalized by substituting whey protein isolate for sodium caseinate. Finally, the positive effect of elimination of oxygen was demonstrated both by replacing air with nitrogen and adding ascorbic acid as an oxygen scavenger to improve survival of the bacteria. Adding an oxygen scavenger would be a better candidate for industrial application considering the potential high cost of manufacturing if nitrogen was used as the atomization and/or drying medium.
- Description: C1