Utilization of orange peel, a food industrial waste, in the production of exo-polygalacturonase by pellet forming Aspergillus sojae.

The production of exo-polygalacturonase (exo-PG) from orange peel (OP), a food industrial waste, using Aspergillus sojae was studied in submerged culture. A simple, low-cost, industrially significant medium formulation, composed of only OP and (NH4)2SO4 (AS) was developed. At an inoculum size of 2.8 × 10(3) spores/mL, growth was in the form of pellets, which provided better mixing of the culture broth and higher exo-PG activity. These pellets were successfully used as an inoculum for bioreactors and 173.0 U/mL exo-PG was produced. Fed-batch cultivation further enhanced the exo-PG activity to 244.0 U/mL in 127.5 h. The final morphology in the form of pellets is significant to industrial fermentation easing the subsequent downstream processing. Furthermore, the low pH trend obtained during this fermentation serves an advantage to fungal fermentations prone to contamination problems. As a result, an economical exo-PG production process was defined utilizing a food industrial by-product and producing high amount of enzyme.

Utilization of xylan-type polysaccharides in co-culture fermentations of Bifidobacterium and Bacteroides species.

Although most members of the genus Bifidobacterium are unable to utilize xylan as a carbon source, the growth of these species can be induced by this polysaccharide in the gut environment. This indicates a requirement for an association between Bifidobacterium species and some other members of gut microbiota. In this study, the role of cross-feeding between Bifidobacterium and Bacteroides species in the bifidogenic effect of xylan was investigated using in-vitro pure and co-culture fermentations. The pure culture studies showed that among the Bifidobacterium species tested, only Bifidobacterium animalis subsp. lactis was able to utilize xylooligosaccharides. The co-culture of this strain with Bacteroides species enabled it to grow in the presence of xylan. These results suggest that the ability of Bacteroides species to hydrolyze xylan could allow the proliferation of specific Bifidobacterium species in the gut through substrate cross-feeding.

Comparison of liquid hot water, very dilute acid and alkali treatments for enhancing enzymatic digestibility of hazelnut tree pruning residues.

The effect of pretreatments on the composition of the hazelnut tree pruning residue (HTPR) and on the digestibility of the cellulose was investigated. The liquid hot water (LHW) and the very dilute acid (VDA) treatments were effective in solubilizing hemicellulose. The cellulose conversion increased up to around 60% (corresponding to 32-36 g/L glucose) with decreasing hemicellulose concentration in the pretreated HTPR. The alkali treatment provided partial delignification, however, the glucose production was comparably lower. Combining the hemicellulose removal and the delignification effect of different pretreatments in two-stage processes (LHW-alkali and VDA-alkali treatments) enhanced the cellulose concentration in the solids, but not the amount of glucose released in the enzymatic digestion. These results suggested that the hemicellulose was the main barrier against the conversion of cellulose in the LHW and VDA treated HTPR and the glucose in the hydrolysis medium inhibited the cellulase activity, which prevented the complete conversion of cellulose.

Production of xylooligosaccharides by autohydrolysis of hazelnut (Corylus avellana L.) shell.

Hazelnut shell (HS), husk and pruning residues were characterized and evaluated for xylooligosaccharides (XOS) production by autohydrolysis. HS contained the highest amount of xylan and yielded more XOS compared to other hazelnut residues. The temperature and holding time of HS autohydrolysis greatly influenced the composition of the liquor and the remaining solid. The highest XOS yield (62% of the feedstock xylan) was obtained at 190°C and 5min of holding time. At this temperature, 30min of holding time was required to maximize the percentage of XOS with low degree of polymerization. Xylose, acetic acid and furfural concentrations increased with treatment severity. The concentrations of the products in the autohydrolysis liquors followed specific trends with changing severity factor (log Ro) values. Solubilization of xylan in the treatments enhanced the cellulose and lignin contents in the remaining solids.

Lactate and ethanol productions by Rhizopus oryzae ATCC 9363 and activities of related pyruvate branch point enzymes.

In Rhizopus oryzae cultivations, lactate production decreased and ethanol and biomass productions increased as inoculated spore concentration increased. Spore concentrations of 1 x 10(3) and 1 x 10(4) spores ml(-1) induced tightly packed clumps, whereas 1 x 10(5) and 1 x 10(6) spores ml(-1) induced filamentous growth.