The amorphous state of spray-dried maltodextrin: sub-sub-Tg enthalpy relaxation and impact of temperature and water annealing

The annealing behaviour of a spray-dried maltodextrin was investigated by differential scanning calorimetry. Special attention was paid to the effect of temperature and humidity on the annealing process. Comparison was also made with the glassy state of the same compound prepared by various cooling processes. The presence of a very pronounced sub-T_g peak upon ageing reveals the specificities of the glass and the complexity of the relaxation spectrum of the spray-dried material. This peak seems actually to correspond to a partial ergodicity recovery that may be attributed to onset of molecular mobility occurring below T_g. The position of the sub-T_g peak with regard to the conventional T_g was systematically studied. It clearly showed the difference between the effect of temperature and water plasticization on the relaxations occurring in the glassy state of materials prepared by spray-drying.     

Culture and spray-drying of Tsukamurella paurometabola C-924: stability of formulated powders

The nematocidal agent, Tsukamurella paurometabola C-924, was cultured in a 300 l bioreactor. Spray-dried formulations of this microorganism were prepared using sucrose. At an outlet temperature 62°C, survival rates between 12 and 85% were reached with sucrose up to 10% (w/w). The stability study of the powders showed that the best storage condition was at 4°C under vacuum. A new method for the calculation of cell death order for bacteria stored at low temperatures was developed. Powders stored under vacuum showed an Arrhenius behavior in relation to cell death kinetics.     

Development of a Spray-drying Technique for Submerged Spores of Entomopathogenic Fungi

The stability of blastospores or submerged conidia of entomopathogenic fungi is one of the key problems associated with the practical use of fungal biopreparations. A spray-drying technique was developed which allows the drying of blastospores and/or submerged conidia, here called submerged spores, without a significant loss of viability and with only a slight delay in eY cacy. The method was tested successfully using the fungal species Metarhizium anisopliae , M. flavoviride, Beauveria bassiana and Paecilomyces fumosoroseus . For all experiments, a laboratory spray dryer was used. The optimum inlet and outlet temperatures were found to be 64 2oC and 48 2oC respectively. The best protective agent for submerged spores was skimmed milk powder at concentrations of 10 or 20%. The addition of sugars, especially 2.5% sugar-beet syrup, slightly improved the viability after spray-drying. Submerged spores of eight isolates of M. anisopliae, M. flavoviride, B. bassiana and P. fumosoroseus were suspended in 20% skimmed milk powder and 2.5% sugar-beet syrup, and spray-dried. Germination rates of about 90% were achieved, which were comparable to those of freshly produced submerged spores. Finally, the virulences of spray-dried submerged spores of M. anisopliae (Ma 97) and M. flavoviride (Mfl 5) were tested in bioassays using third- and fourth-instar nymphs of the African locust, Locusta migratoria . In contrast to M. flavoviride , there was no significant diVerence in the median lethal time between spray-dried and fresh submerged spores of M. anisopliae . The investigations demonstrated that spray-drying is possible to preserve sensitive submerged spores of entomopathogenic fungi.     

Optimisation of the spray drying process of formulating the post-harvest biocontrol agent Meyerozyma caribbica

In this study, conditions of the spray-drying process of Meyerozyma caribbica were optimised using response surface methodology (RSM). The effect of three parameters (protective agent, inlet air temperature and protective agent concentration) on the cell viability of Meyerozyma caribbica was evaluated. Each parameter was evaluated at three levels. All of the evaluated factors presented an effect on the viability of the control agent. According to RSM, optimal conditions include the use of trehalose with a concentration of 7.75% (w/v) and inlet air temperature of 112.5°C. The validation of the optimal spray-drying conditions allows obtaining a formulation of M. caribbica with 95.41?±?0.93% viability, 5?±?0.37% humidity and a_w of 0.33?±?0.11. Storage for six months at 4°C presented a 5% loss in cell viability.