Evaluation of thermomechanical pretreatment for enzymatic hydrolysis of pure microcrystalline cellulose and cellulose from Brewers’ spent grain

Microcrystalline cellulose (Avicel PH102) and Brewers’ spent grain (BSG) were subjected to Détente Instantanée Contrôlée (DIC) thermomechanical pre-treatment before exposure to cellulases (Celluclast 1.5 L). In a first part, we showed that the addition of β-glucosidase (Novozym-188) increased the hydrolysis yield of Avicel. A maximal theoretical yield (100%), was obtained for 5 and 10 g/L of Avicel using a mixture of Celluclast 1.5 L/Novozym-188. After DIC pre-treatments, the initial rate and final yield of hydrolysis decreased in comparison with those from untreated microcrystalline cellulose. This phenomenon may be due to the modification of the crystallinity of pure cellulose and the formation of inhibitors during the pre-treatment. In a second part, BSG was thermomechanically pre-treated and hydrolyzed. The results showed that the hydrolysis yield of BSG treated at pressure levels between 2 and 7 bar during 15 min was strongly improved compared to hydrolysis yield of untreated BSG. The optimized hydrolysis process, under intensive DIC conditions, achieved a glucose yield corresponding to 100% of the theoretical cellulose value. The morphology of BSG samples was studied with Scanning Electronic Microscopy (SEM) and highlighted that the structure of pre-treated BSG showed an important disruption compared to the rigid structure of untreated BSG.     

Eucalyptus occidentalis plantlets are naturally infected by pathogenic Agrobacterium tumefaciens

In the Sidi M’djahed nursery (Algeria), over 60,000 eucalyptus (Eucalyptus occidentalis) plantlets exhibited tumour-like growths localized at the crown of the plants that resembled crown galls caused by Agrobacterium tumefaciens. Bacteria colonizing the galls were isolated and purified. Most (22 out of 24) of the isolates had cultural and biochemical characteristics similar to those of strains of the biovar 1 of A. tumefaciens. Twenty out of 22 Agrobacterium isolates induced tumour formation on various test plants. In PCR experiments, DNA extracted from these virulent strains yielded an amplification signal corresponding to a 247-bp fragment located within the virulence region of nopaline type Ti plasmid. Consistent with this, the opine nopaline was detected in the tumours induced on test plants – but not on eucalyptus plants. Nopaline was degraded by the 20 pathogenic isolates that were also sensitive to agrocin 84, indicating the presence of a nopaline-type pTi in these strains. The chromosomal region encoding the 16S rRNA was analyzed in a sub-population of the pathogenic agrobacterial isolates. The analyzed strains were found to belong to the ribogroup of the reference strain B6. Interestingly, Eucalyptus camaldulensis and Eucalyptus cladocalyx grown in the same nursery and in the same soil substrate developed no galls.     

Study of the effect of hydrothermal process conditions on pasta quality

The effect of hydrothermal treatment on the pasting, hydration properties and colour quality of commercial fresh pasta were studied following an Instantaneous Controlled Pressure Drop treatment. This hydrothermal procedure involves a physical modification at high temperature (<144 °C) and restricted moisture content (<30%) during a very short time (15–40 s) followed by a rapid pressure drop to a vacuum (50 mbar). Two process variables (steam pressure level and processing time) were investigated using response surface methodology. Steam pressure level had the greatest effect on hydration and pasting parameters. Increased pressure resulted in elevation of mass ratio between cooked and uncooked pasta (W_i/W₀)_{100 °C} and reduction of for all treated pasta. The optimum cooking time of untreated pasta was 7 min (W/W₀=2.4), whereas for the same ratio it was less than 1 min for pasta treated at pressures ranging between 2.5 and 3.5 bar. The viscosity at 10 min (V₁₀) increased linearly when the pressure level increased. V₁₀ was 146 cP for untreated pasta whereas it reached 2659 cP for pasta treated at 3.9 bar (144 °C) for 25 s. The cold paste viscosity and setback viscosity decreased when the pressure varied from 1 to 3.9 bar.     

Isolation of volatils from maritime pine sawdust waste by different processes: Ultrasound,microwave, turbohydrodistillation,and hydrodistillation

This study concerns the transformation of maritime pine (Pinus pinaster) sawdust waste into potentially novel products through isolation of volatile compounds in the form of valuable oil. Different techniques, namely, turbohydrodistillation (THD), solvent-free microwave extraction (SFME), microwave hydrodiffusion and gravity (MHG), and ultrasound-assisted extraction (UAE) were tested. These different processes were compared to conventional hydrodistillation (HD) and allowed to extract almost similar yields of isolated oils. THD which consists in a permanent agitation during extraction and UAE improve the kinetics of extraction, but MHG and SFME required the shortest extraction times, 60 min to reach a maximal yield of 0.272 and 0.266% (w/w), respectively. The compositions of isolated oils are almost similar with a high proportion of oxygenated compounds for MHG and SFME, respectively, 56.9% and 54.5% compared with 37.7%, 44.1% and 34.1%, respectively, for THD, UAE, and for the conventional HD method.     

Effect of instantaneous controlled pressure drop (DIC) on physicochemical properties of wheat, waxy and standard maize starches

Standard maize starch (SMS), waxy maize starch (WMS) and wheat starch (WTS) were hydrothermally treated by the Instantaneous Controlled Pressure Drop (DIC) process. This process consists in a short pressurisation obtained by the injection of saturated steam at fixed pressure during a predetermined time followed by a sudden pressure drop towards vacuum. The effects of DIC conditions on thermal characteristics, enzyme susceptibility, pasting (Brabender) and rheological properties of treated starches were investigated. For treated starches, an increase of transition temperatures (T_o and T_p), a narrowing of the width of gelatinization endotherms and a decrease of the gelatinization enthalpies (ΔH) were observed as the severity of processing conditions increased. WMS, SMS and WTS showed a significant increase in enzymatic hydrolysis after treatment. The saccharification yield showed an increase from 19% (native) to 44%, 21% (native) to 59% and 55% (native) to 79% for SMS, WMS and WTS, respectively. The study suggests that the structural modifications due to the previous DIC treatment influence the in-vitro hydrolysis and the access to the ultrastructure of starch granules; the susceptibility to hydrolysis increases from SMS to WMS and WTS. For all treated starches, the decrease in peak viscosity and in apparent viscosity was related to the processing conditions.     

Influence of hydrothermal treatment on rheological and cooking characteristics of fresh egg pasta

The effect of D.I.C. processing conditions on rheological and cooking properties of commercial fresh egg pasta was studied. The mechanical properties of pasta before and after cooking were evaluated by empirical test and characterised by maximal apparent force (F_max) and apparent relaxation coefficient (ARC). Structural (apparent density) and cooking quality were evaluated by determining mass ratio (W/Wo), optimal cooking time (OCT), swelling index (SI), solid, soluble and total cooking losses (TCL) and compared to untreated pasta. The hydrothermal treatment caused a reduction in firmness and relaxation capacity of treated pasta. The increase of processing conditions induced a decrease of F_max and the processing time has an influence when it is associated to the low pressures. The values of ARC vary from 51% (untreated pasta) to 37% (D.I.C. treated pasta). The increase of processing time from 30 to 60 s does not seem to have a significant influence on ARC. The apparent density of treated pasta is a function of processing pressure and time but it is always lower than untreated pasta density. Treated pasta had a higher quality score based on water sorption and SI and matter losses (TCL values and solid and soluble losses) as compared to untreated pasta.     

Impact of single and co-inoculations with Rhizobial and PGPR isolates on chickpea (Cicer arietinum) in cereal-growing zone soil

Strains isolated from chickpea (Cicer arietinum L.) rhizospheric soil from selected sites in Algeria were screened for their plant-growth-promoting potential, for indole acetic acid production and P solubilization ability. Then, we selected native rhizobial strains with high nitrogen-fixing potential. On the basis of their efficiency under controlled conditions, two plant-growth-promoting rhizobacteria (PGPR) isolates and three nodulating bacteria were selected. Then, the effect of single PGPR isolates inoculation was compared to their combination with rhizobial inoculants on plant growth, on native cereal-growing soils under greenhouse conditions. No effects were observed on chickpea yield by using rhizobial inoculation alone, nor by PGPR-rhizobial co-inoculation on two soils presenting weak and no nodulation pattern in natural conditions. Only PGPR inoculation improved growth of plants on soil with no nodulation pattern. These findings emphasized inoculation on native soils at a little scale before large assays on field because no one could predict inocula behavior with native soil microflora.