BSG were sterilized at 120 °C for 15min prior treatment.
They were then used in their original form and after deligniWcation.
DeligniWcation was performed according to
Bardi and Koutinas (1994). SpeciWcally, 600 g BSG were
mixed with 1600ml of 1% NaOH solution and were boiled
with continuous stirring for about 3 h. After that the deligniWed
BSG (DBSG) were washed well with water and then
drained. Cell immobilization on BSG and DBSG was carried
out by suspending 16 g of S. cerevisiae AXAZ-1 cells in
800ml of glucose synthetic medium, containing 4 g/l yeast
extract, 1 g/l (NH4)2SO4, 1 g/l KH2PO4, 7 g/l MgSO4 ·7H2O
and 120 g/l glucose monohydrate, and mixing with 200 g of sterilized deligniWed BSG (DBSG) or non-deligniWed BSG
(BSG2). In addition, fresh, non-deligniWed BSG (BSG1)
and BSG defrosted after storage at ¡20 °C (BSGd) were
also used as immobilization supports, following the same
immobilization procedure, using glucose medium without
addition of nutrient salts or yeast extract. All the above systems
were allowed to ferment for 10–1 h until the density of
the fermented liquids was reduced to a Wnal value of 0–
0.5 °Be. The liquids were then decanted and the immobilized
biocatalysts were washed twice with 400ml of sterilized
molasses medium and were used for repeated
fermentation batches. Therefore, four immobilized biocatalysts
were prepared by the above procedures: (i) BSG2:
immobilization of yeast cells on fresh brewer’s spent grains
with nutrients, (ii) DBSG: immobilization of yeast cells on
deligniWed brewer’s spent grains with nutrients, (iii) BSG1:
immobilization of yeast cells on fresh brewer’s spent grains
without nutrients, and (iv) BSGd: immobilization of yeast
cells on defrosted spent grains without nutrients.
BSG were sterilized at 120 °C for 15min prior treatment.They were then used in their original form and after deligniWcation.DeligniWcation was performed according toBardi and Koutinas (1994). SpeciWcally, 600 g BSG weremixed with 1600ml of 1% NaOH solution and were boiledwith continuous stirring for about 3 h. After that the deligniWedBSG (DBSG) were washed well with water and thendrained. Cell immobilization on BSG and DBSG was carriedout by suspending 16 g of S. cerevisiae AXAZ-1 cells in800ml of glucose synthetic medium, containing 4 g/l yeastextract, 1 g/l (NH4)2SO4, 1 g/l KH2PO4, 7 g/l MgSO4 ·7H2Oand 120 g/l glucose monohydrate, and mixing with 200 g of sterilized deligniWed BSG (DBSG) or non-deligniWed BSG(BSG2). In addition, fresh, non-deligniWed BSG (BSG1)and BSG defrosted after storage at ¡20 °C (BSGd) werealso used as immobilization supports, following the sameimmobilization procedure, using glucose medium withoutaddition of nutrient salts or yeast extract. All the above systemswere allowed to ferment for 10–1 h until the density ofthe fermented liquids was reduced to a Wnal value of 0–0.5 °Be. The liquids were then decanted and the immobilizedbiocatalysts were washed twice with 400ml of sterilizedmolasses medium and were used for repeatedfermentation batches. Therefore, four immobilized biocatalystswere prepared by the above procedures: (i) BSG2:immobilization of yeast cells on fresh brewer’s spent grainswith nutrients, (ii) DBSG: immobilization of yeast cells ondeligniWed brewer’s spent grains with nutrients, (iii) BSG1:immobilization of yeast cells on fresh brewer’s spent grainswithout nutrients, and (iv) BSGd: immobilization of yeastcells on defrosted spent grains without nutrients.
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