2.4. Pretreatment and SSF
Dried and ground banana peel powder was suspended in distilled
water at a solid-to-liquid loading of 10% (w/v) in baffled polycarbonate
capped flasks (Fisher Scientific), along with (%; w/v)
yeast extract 0.2, peptone 0.2 and MgSO4 0.1. We had observed
that increasing the substrate concentration to 15% (w/v) resulted
in formation of a solid mass, probably because of higher concentrations
of pectin and hemicellulose in BP. Such a biomass is not easily
accessible to pretreatment and hydrolysis processes. Therefore, the
flasks containing 75 ml fermentation medium composed of 10% (w/
v) BP and nutrients were subjected to autoclave-sterilization process
at 121 C, 15 psi for 15 min. The flasks were removed from
the autoclave and cooled with cold water. The pH of the fermentaH.S.
Oberoi et al. / Waste Management 31 (2011) 1576–1584 1577
tion medium was adjusted to 5.5 with sterilized 5 N sodium
hydroxide solution. The enzyme concentration used during SSF
was obtained using Design Expert software (Table 1). The flasks
were inoculated with 7.5 ml S. cerevisiae cells having a cell concentration
of 3 109 cells/ml. The ratio of filter paper cellulase (FPU)
to b-glucosidase was maintained at 1:2, since we had observed this
ratio as optimum for hydrolysis of banana peels (unpublished
data). Enzyme addition for cellulase (FPU) and pectinase was done
on the basis of cellulose and pectin concentrations, respectively in
the pretreated BP and not on the substrate basis. This was done to
economize the enzyme concentrations as enzyme cost is crucial in
determining the commercial feasibility of ethanol production from
cellulosic biomass. Enzymes were filter-sterilized using 0.45 lm
PVDF membranes (Millipore Inc., USA) and added to the medium
for SSF. Enzyme and inoculum additions were done under positive
air pressure in a P-II biosafety cabinet.
2.4. Pretreatment and SSFDried and ground banana peel powder was suspended in distilledwater at a solid-to-liquid loading of 10% (w/v) in baffled polycarbonatecapped flasks (Fisher Scientific), along with (%; w/v)yeast extract 0.2, peptone 0.2 and MgSO4 0.1. We had observedthat increasing the substrate concentration to 15% (w/v) resultedin formation of a solid mass, probably because of higher concentrationsof pectin and hemicellulose in BP. Such a biomass is not easilyaccessible to pretreatment and hydrolysis processes. Therefore, theflasks containing 75 ml fermentation medium composed of 10% (w/v) BP and nutrients were subjected to autoclave-sterilization processat 121 C, 15 psi for 15 min. The flasks were removed fromthe autoclave and cooled with cold water. The pH of the fermentaH.S.Oberoi et al. / Waste Management 31 (2011) 1576–1584 1577tion medium was adjusted to 5.5 with sterilized 5 N sodiumhydroxide solution. The enzyme concentration used during SSFwas obtained using Design Expert software (Table 1). The flaskswere inoculated with 7.5 ml S. cerevisiae cells having a cell concentrationof 3 109 cells/ml. The ratio of filter paper cellulase (FPU)to b-glucosidase was maintained at 1:2, since we had observed thisratio as optimum for hydrolysis of banana peels (unpublisheddata). Enzyme addition for cellulase (FPU) and pectinase was doneon the basis of cellulose and pectin concentrations, respectively inpretreated BP บนพื้นผิวพื้นฐานไม่ นี้ที่ทำให้ประหยัดความเข้มข้นเอนไซม์เอนไซม์ต้นทุนเป็นสิ่งสำคัญในการกำหนดความเป็นไปได้ในเชิงพาณิชย์ของเอทานอลผลิตจากชีวมวล cellulosic เอนไซม์ถูกกรอง-sterilized ใช้ 0.45 lmสาร PVDF (มาก อิงค์ สหรัฐอเมริกา) และเพิ่มการสื่อสำหรับ SSF ทำภายใต้บวกเพิ่มเอนไซม์และ inoculumอากาศความดันใน biosafety P II ตู้
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