Peracetic acid pretreatment of sugarcane bagasse for enzymatic hydrolysis: a continued work

Previous work has shown that the enzymatic hydrolysis of sugarcane bagasse could be greatly enhanced by peracetic acid (PAA) pretreatment. There are several factors affecting the enzymatic digestibility of the biomass, including lignin and hemicelluloses content, cellulose crystallinity, acetyl group content, accessible surface area and so on. The objective of this work is to analyze the mechanism of the enhancement of enzymatic digestibility caused by PAA pretreatment. Delignification resulted in an increase of the surface area and reduction of the irreversible absorption of cellulase, which helped to increase the enzymatic digestibility. The Fourier transform infrared (FTIR) spectrum showed that the absorption peaks of aromatic skeletal vibrations were weakened or disappeared after PAA pretreatment. However, the infrared crystallization index (N.O'KI) was increased. X‐ray diffraction (XRD) analysis indicated that the crystallinity of PAA‐treated samples was increased owing to the partial removal of amorphous lignin and hemicelluloses and probable physical change of cellulose. The effect of acetyl group content on enzymatic digestibility is negligible compared with the degree of delignification and crystallinity. The results indicate that enhancement of enzymatic digestibility of sugarcane bagasse by PAA pretreatment is achieved mainly by delignification and an increase in the surface area and exposure of cellulose fibers. Copyright © 2008 Society of Chemical Industry     

酶法提取树莓汁的研究

本试验以澳洲红、早红、美国22三个品种树莓为原料，通过不同的酶处理方法来制原果汁，优选适于制汁的品种和酶处理方法。     

General rate equations and their applications for cyclic reaction networks: multi-cycle systems

The network reduction technique and the Bodenstein approximation of quasi-stationary behavior of reaction intermediates were systematically applied to derive general yield ratio and rate equations for multi-cycle reaction networks in homogeneous catalysis. Dual-cycle reaction networks connected by a linear pathway, multi-cycle networks stemming from the same intermediate, and single-cycle with arbitrary number of pathways between two intermediates were considered. The general yield ratio and rate equations derived in this study are applicable for most enzymatic reactions and for homogeneous catalytic reactions. Examples of homogeneous catalysis were used to illustrate the application of the general yield ratio and rate equations for network elucidation.     

The effect of cooking on proteins from acha (Digitaria exilis) and durum wheat

The effect of cooking on proteins from acha and durum wheat was assessed from an analysis of protein extractability, gel electrophoretic profiles, in-vitro protein digestibility (IVPD) and the amino acid compositions of wholemeal flour and residue proteins. Heating wholemeal flour samples at 100–140°C (t = 10–40 min) resulted in 0–30% and 45–55% decreases in acha and durum protein solubility, respectively. In general, high molecular weight (30–70 k Da) protein subunits were more susceptible to heat damage. For both cereals, sodium dodecyl sulphate (SDS; 10 g litre^?1) and/or dithiothrcitol (DTT; 10 mM ) increased protein solubility in unheated and heated samples. The IVPD index was 90–91% and was not significantly altered by cooking (100–120°C, t = 40 min). Cooking at extreme temperatures (140°C, t = 40 min) reduced the IVPD by 8% (P = 0.05). Osborne fractionation resulted in a durum or acha residue level of 7.8% or 55.2%. Treatment with solvent containing propanol, SDS and/or DTT at room temperature followed by SDS-polyacrylamide gel electrophoresis of non-solubilised proteins showed that the glutelin fraction of acha, with the exception of a 65 kDa subunit, was insoluble owing to strong inter-subunit hydrophobic and disulphide interactions. Wholemeal acha flour and residue protein showed a significantly greater level of hydrophobic and sulphur amino acids as well as glutamine which is associated with H-bonding. The possibility that cereal protein solubility is also dependent on protein-carbohydrate links is discussed.     

Effect of precooking time and drying temperature on the physico-chemical characteristics and in-vitro carbohydrate digestibility of taro flour

Achu is a thick porridge obtained by cooking and pounding taro (Colocasia esculenta) corms and cormels in a mortar. This study was undertaken with the objective of producing precooked taro flour that can be used in the preparation of achu. Taro slices were precooked to times of 0, 20, 45 and 90 min and dried in an air convection oven at varying temperatures of 50, 60, 70 or 80 °C before milling into flour which was then analysed for its water absorption capacity (WAC), water solubility index, emulsion activity and stability, bulk density, foam capacity and least gelation concentration (LGC). Achu made from the flours were equally analysed for their relative penetrometric index, bulk density and colour. The results showed that precooking induced significant (P<0.05) decrease in foam capacity, penetrometric index, and increase in LGC, emulsion stability and WAC. The drying temperature also induces significant reduction in emulsion capacity and stability, penetrometric index, and increase in LGC, WAC. Long precooking time (>45 min) and drying temperature (>60 °C) induced significant reduction of the in-vitro carbohydrate digestibility of taro achu.     

γ-癸内酯的酶法拆分研究

研究了脂肪酶对γ-癸内酯(GDL)对映催化选择性水解反应,考察了各种因素对酶促水解拆分过程的影响。试验结果表明,水解产物-大量的酸会抑制脂肪酶的活性,采用高浓度的磷酸盐缓冲液可有效地稳定系统的酸碱度,使酶促反应顺利进行。在磷酸缓冲溶液体系中缓冲液pH=7.8,底物浓度为0.6mol/L,反应时间2.5小时,反应温度43℃为γ-癸内酯酶促水解拆分的最佳工艺条件。     

淀粉基干燥剂的化学性质与性能

讨论了淀粉、粗玉米粉及可以被淀粉所依附的纤维素框架的化学结构及性质,它们可能成为一系列用途广泛的干燥剂。     

Enzymatic Firming of Processed Red Pepper by Means of Exogenous Pectinesterase

The objective of this investigation was to demonstrate that the firmness of a commercial vegetable product, diced and frozen red pepper (Capsicum annum var. Sendt), could be improved by the use of exogenous pectinesterase in an industrially relevant process. The diced pepper pieces 10 × 10 × 7 mm³ were infused under vacuum with a commercially available pectinesterase. The range of optimal process conditions was: 15-20°C, 45 min infusion time, a 10-25 mM CaCl₂ infusion brine, a w/w ratio of pepper fruit to infusion brine of 1.5:1, and an enzyme dosage of 30-60 pectinesterase units (PEU) per kg pepper fruit. The firmness as measured by back extrusion was improved by a factor of two to three. The effect of firming was robust and conserved after freezing and heating in a simulated household cooking process. The firming process seems easily adaptable to industrial conditions and may be applicable to other vegetable and fruit products.     

Continuous production of structured phospholipids in a packed bed reactor with lipase from <Emphasis Type="Italic">Thermomyces lanuginosa</Emphasis>

The possibilities of producing structured phospholipids between soybean phospholipids and caprylic acid by lipase-catalyzed acidolysis were examined in continuous packedbed enzyme reactors. Acidolysis reactions were performed in both a solvent system and a solvent-free system with the commercially immobilized lipase from Thermomyces lanuginosa (Lipozyme TL IM) as catalyst. In the packed bed reactors, different parameters for the lipase-catalyzed acidolysis were elucidated, such as solvent ratio (solvent system), temperature, substrate ratio, residence time, water content, and operation stability. The water content was observed to be very crucial for the acidolysis reaction in packed bed reactors. If no water was added to the substrate during reactions under the solvent-free system, very low incorporation corporation of caprylic acid was observed. In both solvent and solvent-free systems, acyl incorporation was favored by a high substrate ratio between acyl donor and phospholipids, a longer residence time, and a higher reaction temperature. Under certain conditions, the incorporation of around 30% caprylic acid can be obtained in continuous operation with hexane as the solvent. Presented at the 95th American Oil Chemists' Society Annual Meeting and Expo in Cincinnati, Ohio, May 10, 2004.     

Activation of plant foliar oxidases by insect feeding reduces nutritive quality of foliage for noctuid herbivores

The foliage and fruit of the tomato plantLycopersicon esculentum contains polyphenol oxidases (PPO) and peroxidases (POD) that are compartmentally separated from orthodihydroxyphenolic substrates in situ. However, when leaf tissue is damaged by insect feeding, the enzyme and phenolic substrates come in contact, resulting in the rapid oxidation of phenolics to orthoquinones. When the tomato fruitwormHeliothis zea or the beet army-wormSpodoptera exigua feed on tomato foliage, a substantial amount of the ingested chlorogenic acid is oxidized to chlorogenoquinone by PPO in the insect gut. Additionally, the digestive enzymes of the fruitworm have the potential to further activate foliar oxidase activity in the gut. Chlorogenoquinone is a highly reactive electrophilic molecule that readily binds cova-lently to nucleophilic groups of amino acids and proteins. In particular, the —SH and —NH₂ groups of amino acids are susceptible to binding or alkylation. In experiments with tomato foliage, the relative growth rate of the fruitworm was negatively correlated with PPO activity. As the tomato plant matures, foliar PPO activity may increase nearly 10-fold while the growth rate of the fruitworm is severely depressed. In tomato fruit, the levels of PPO are highest in small immature fruit but are essentially negligible in mature fruit. The growth rate of larvae on fruit was also negatively correlated with PPO activity, with the fastest larval growth rate occurring when larvae fed on mature fruit. The reduction in larval growth is proposed to result from the alkylation of amino acids/protein byo-quinones, and the subsequent reduction in the nutritive quality of foliage. This alkylation reduces the digestibility of dietary protein and the bioavailability of amino acids. We believe that this mechanism of digestibility reduction may be extrapolatable to other plant-insect systems because of the ubiquitous cooccurrence of PPO and phenolic substrates among vascular plant species.