RESULTS
Effect of drying method on cell survival and shelf life Rice
cooked at 121 °C for 15 min (containing 21.17–22.39% moisture
content) gave the best result when used for producing starter culture
by either air-drying or vacuum drying. The moisture contents of
starter cultures after air-drying, vacuum drying and freeze-drying are
shown in Table S1. The moisture contents of air-dried and vacuum-dried starter cultures were 10.55 – 13.42%, and the moisture content of
fre eze -d rie d st a rte r c ult ur e wa s 11. 25 – 12. 27% (bo th si ngle an d
mixed-strain cultures). The results showed that the viable cell count
of LAB strains before drying was N 1×10
9
cfu/g in all methods and
after drying was N 1× 10
7
cfu/g. In comparing the drying times of each
method, air-drying was faster than vacuum drying and freeze-drying;
starter cultures were air-dried within 4 –5 h, as opposed to 12–24 h for
vacuum drying or freeze-drying. Freeze-drying gave a high viable cell
count (N 1×10
8
cfu/g) that was similar to air-drying and better than
vacuum drying and at a lower cost. Therefore, we selected an air-dried
starter culture to produceplaa-somfor subsequent experiments. As
shown in S1, the initial cell count of the starter culture at 0 h was
higher than 1 × 10
10
cfu/g for all-drying methods. After 20 weeks of
shelf life, the amount of freeze-dried LAB cells remained N 1×10
9
cfu/
g, as opposed to N 1×10
8
and N 1× 10
6
cfu/g for air-drying and
vacuum drying, r espect ive l y. When compar ing t he numbe r of
surviving cells of the starter culture, freeze-drying was better than
air-drying, and vacuum drying produced a starter culture that could
be maintained for more than 20 weeks at 4 °C.