酒精糟液厌氧生物处理技术研究进展

根据酒精糟液的组成、性质,从厌氧生物处理方面介绍了厌氧反应器的特点及它们在酒精糟液处理中的研究现状、运用效果,提出厌氧生物处理技术存在的问题和发展方向。     

Effect of frying parameters on crispiness and sound emission of cassava crackers

Cassava crackers, based in cassava starch and water, were produced by deep-fat frying in oil at 140, 150 and 160 °C. Physical properties of cassava crackers were monitored at 5, 10 and 15 s of the frying process, moisture contents, bulk density, linear expansion and penetration forces and sound emission were evaluated. The results showed that with increasing frying (time and temperature), the moisture content, the linear expansion, the number of force and sound peaks significantly increased while the density and maximum and mean of force peaks decreased. Further it could be seen that with higher temperature the number of small size air cells increased. Correlations were found between physical and textural properties and sound emission. Moisture content, bulk density, maximum of sound peak, maximum force and mean force were negatively correlated with linear expansion, number of sound peaks and number of force peaks.     

Biohydrogen production from cassava starch processing wastewater by thermophilic mixed cultures

Natural microbial consortia from hot spring samples were used to developed thermophilic mixed cultures for biohydrogen production from cassava starch processing wastewater (CSPW). Significant hydrogen production potentials were obtained from three thermophilic mixed cultures namely PK, SW and PR with maximum hydrogen production yields of 249.3, 180 and 124.9 mL H₂/g starch, respectively from raw cassava starch and 252.4, 224.4 and 165.4 mL H₂/g starch, respectively from gelatinized cassava starch. Acetic acid-ethanol and acetic-lactic acid type fermentation were observed in cassava starch fermentation, based on three thermophilic mixed cultures performance. The thermophilic mixed cultures PK, SW and PR exhibited the maximum hydrogen yield of 287, 264 and 232 mL H₂/g starch in CSPW, respectively corresponding to 53%, 48.7% and 42.8% of the theoretical values. Phylogenetic analysis of thermophilic mixed cultures revealed that members involved cassava starch degrading bacteria and hydrogen producers in both raw cassava starch and CSPW were phylogenetically related to the Thermoanaerobacterium saccharolyticum, Thermoanaerobacterium thermosaccharolyticum, Anoxybacillus sp., Geobacillus sp. and Clostridium sp.     

Mild methods of processing cassava leaves to remove cyanogens and conserve key nutrients

Current methods for processing cassava leaves to remove cyanogens involve pounding followed by boiling in water or boiling intact leaves for 30 min or longer. Boiling in water rapidly removes cyanogens but also breaks down vitamins, proteins and S-containing amino acids, which are necessary to detoxify ingested cyanide. Two methods have been developed to remove cyanogens whilst conserving these key nutrients present in cassava leaves. The first method involves pounding leaves in a pestle and mortar for a minimum of 10 min until the leaves are well macerated, followed by washing the pounded leaves twice in twice their weight of water at ambient temperature, which reduces the total cyanide remaining to 8%. Two further washes reduce the total cyanide to 3%. The second method is to immerse cassava leaves in ten times their weight of water at 50 ± 3 °C for 2 h followed by one change of water and further immersion for 2 h at 50 °C which reduces the total cyanide remaining to 7%.     

Exploring optimal conditions for thermophilic fermentative hydrogen production from cassava stillage

This study investigated the effects of seed sludges, alkalinity and HRT on the thermophilic fermentative hydrogen production from cassava stillage. Five different kinds of sludges were used as inocula without any pretreatment. Though batch experiments showed that mesophilic anaerobic sludge was the best inoculum, the hydrogen yields with different seed sludges were quite similar in continuous experiments in the range of 82.9–92.3 ml H₂/gVS without significant differences which could be attributed to the establishment of Uncultured Thermoanaerobacteriaceae bacterium-dominant microbial communities in all reactors. It is indicated that results obtained from batch experiments are not consistent with those from continuous experiments and all the tested seed sludges are good sources for continuous thermophilic hydrogen production from cassava stillage. The influent alkalinity of 6 g NaHCO₃/L and HRT 24 h were optimal for hydrogen production with hydrogen yield of 76 ml H₂/gVS and hydrogen production rate of 3215 ml H₂/L/d. Butyrate was the predominant metabolite in all experiments. With the increase in alkalinity of more than 6 g/L, the concentration of VFA/ethanol increased while hydrogen yield decreased due to the higher concentration of acetate and propionate. The decrease in HRT resulted in the higher hydrogen production rate but lower hydrogen yield. Variation of hydrogen yields were quite correlated with butyrate/acetate (B/A) ratio with different influent alkalinities, however, butyrate was important parameter to justify the hydrogen yields with various HRTs.     

Screening and HPLC methods for carotenoids in sweetpotato, cassava and maize for plant breeding trials

Analytical methods for sweetpotato, cassava and maize were developed. In orange and salmon-fleshed sweetpotatoes, (all-E)-β-carotene predominated and results of spectrophotometric screening and HPLC quantification did not differ significantly. In yellow-fleshed sweetpotato and cassava, however, spectrophotometric screening overestimated the HPLC values because of the presence of several minor carotenoids. Aside from (all-E)-β-carotene, Z-isomers were present in cassava in appreciable amounts. For both crops, extraction with acetone or tetrahydrofuran:methanol (1:1), using a mortar and pestle or a Polytron homogenizer, gave equivalent results. Rehydration of dry maize at room temperature for 30 min or at 85 °C for 5, 10 or 15 min gave equivalent results. Concentrations obtained with the C18 and C30 columns did not differ significantly for zeaxanthin, lutein, β-cryptoxanthin and β-carotene in the all-E-configuration, but their Z-isomers were difficult to locate in the chromatogram obtained with the C30 column. Extraction with tetrahydrofuran:methanol (1:1) gave significantly lower results for zeaxanthin and lutein.     

Starch and pectin solubilization and texture modification during pre-cooking and cooking of cassava root (Manihot esculenta Crantz)

Physico-chemical alterations of cell-wall constituents and of substances stored in the cell characterize the behavior of fresh vegetables during cooking. Pre-cooking for 1 h at three different temperatures was used to identify alterations in hydration, pectin and starch solubilization and the relation to texture determination by a compression and a shear test. Samples of cassava (Catarina amarela) harvested 8 months after planting date were used. Soluble galacturonic acid in the treatment water varied from 0.07 to 0.2.1 mg/100 ml while soluble solids varied from 271.3 to 599.6 mg/100 ml. Soluble starch varied from 114.3 to 437.7 mg/100 ml and total solids varied from 292.4 to 611.4 mg/100 ml during pre-cooking from 55 to 75 °C. There was weight reduction of 4 and 2 g/100 g of material and reduction of compression force in the treatments at 55 and 65 °C in relation to the raw sample and weight gain of 6.7 g/100 g and increase in compression force at 75 °C. Shear force decreased from the raw sample to the 65 °C treated sample while pectin solubility increased up to 75 °C. Samples cooked in boiling water had weight gain of 6.8 g/100 g of material, 493.3 mg/100 ml of soluble solids and 588 mg/ 100 ml of total solids of which 507.6 mg was starch.     

The quality assessment of gari produced by using microwave energy

Summary A novel technique using microwave energy for roasting and drying or garification of fermented cassava mash is investigated. The quality of gari produced using this method compared favourably with the standards quoted in the literature and with those of commercial gari purchased from a London market, in terms of colour, swelling capacity, moisture, pH and total acidity.