Slow rehydration improves the recovery of dried bacterial populations

Abstract

Slow rehydration of bacteria from dried inoculant formulations provided higher viable counts than did rapid rehydration. Estimates were higher when clay and peat powder formulations of Rhizobium meliloti, Rhizobium leguminosarum biovar trifolii, and Pseudomonas putida, with water activities between 0.280 and 0.650, were slowly rehydrated to water activities of approximately 0.992 before continuing the dilution plating sequence. Rhizobium meliloti populations averaged 6.8 x 10(8) cfu/g and 1328 cfu/alfalfa seed greater when slowly rehydrated from bulk powder and preinoculated seeds, respectively. Bulk powder samples were slowly rehydrated to 0.992 water activity by the gradual addition of diluent, followed by a 10-min period for moisture equilibration. Preinoculated seed samples were placed in an environmental chamber at 24 degrees C with relative humidity greater than 80% for 1 h to allow moisture absorption. "Upshock," osmotic cellular stresses that occur during rehydration, was reduced when dried microbial formulations were slowly rehydrated and equilibrated before becoming fully hydrated in the dilution plating sequence. These procedures may also be applicable when estimating total viable bacterial populations from dried soil or other dry formulations.

Enhanced Survival of GroESL-Overproducing Lactobacillus paracasei NFBC 338 under Stressful Conditions Induced by Drying

“…The water activity (a w ) in the dried powders was measured in duplicate using an Aqualab model series 3 (Decagon Devices Inc., Pullman, WA) according to the manufacturer's instructions. The a w for spraydried powders was 0.373, while freeze-dried powders produced in this study had an a w of 0.320; these values were within the range (0.28 to 0.65) considered suitable for survival of bacterial populations dried in milk-based powders (14).…”

Improved viability ofLactobacillus acidophilusNRRL-B 4495 during freeze-drying in whey protein-pullulan microcapsules

“…Aw (water activity) value of FD microcapsules was also found to be within desirable limits (0.28-0.65) for the survival of probiotic bacteria (Kosanke et al, 1992) and colour values (L*, a*, b*) of the formed microcapsules showed that these microcapsules had white colour. On the other hand, maximum level moisture content of dry products required for prolonged storage was stated to be at or below 4%.…”

A Brief Historical Background

“…The latter is done by delivering the inoculant directly into the sowing furrow with the seeds (Gault, 1982). Seed inoculation is the most popular method worldwide, as long as the farmer is willing to take the extra step of mixing the inoculant with the seeds immediately The quantity of bacteria that can be attached to the seed surface is limited, especially for small seeds Brockwell et al 1977;Smith, 1992 A small quantity of inoculant is used Bacteria may have direct contact with pesticides applied to seeds Kosanke et al 1992 Seed precoated with inoculant provide a convenience to the farmer who purchases seeds that have already been inoculated Possibility of movement of the inoculant upward with the cotyledons instead of downward with the roots The inoculant can be applied by the farmer…”

“…Until now, the most common solutions to this problem of survival time have been air-dried and lyophilized preparations (Bashan 1986a;Fages 1992;Kosanke et al 1992). The lowered water content in the final product is responsible for long-term survival during storage.…”