Mouna Kriaa

Extraction and characterization of three polysaccharides extracted from Opuntia ficus indica cladodes

The chemical extraction and the characterization of polysaccharides from mucilage (MC), pectin (PC) and total pectic mucilage fraction (TFC) of Opuntia ficus indica cladodes as well as the evaluation of their antioxidant activities was investigated. The FTIR spectroscopic analysis revealed the presence of carboxyl and hydroxyl groups corresponding to polysaccharides. Uronic acid and the total sugar contents of PC were higher than those of TFC and MC whereas ash content of MC was considerably more important. In addition, the findings showed that all the samples had little protein content and low average molecular weight compared to the results mentioned in literature. Furthermore, MC reached not only the highest water (WHC) and oil holding (OHC) capacities (7.81g/g and 1.34g/g, respectively) but also the highest antioxidant properties (DPPH and ABTS scavenging activities, β-carotene bleaching inhibition activity and reducing power). However, PC had the strongest emulsifying and foaming properties. As for TFC, it had low WHC, OHC and emulsifying properties whereas it had higher foaming properties than MC and greater antioxidant properties compared to PC. These outcomes can encourage the use of PC as a surfactant and MC and TFC as natural antioxidants in food and pharmaceutical industries.

Aspergillus oryzae S2 alpha-amylase production under solid state fermentation: Optimization of culture conditions

Aspergillus oryzae S2 was assayed for alpha-amylase production under solid state fermentation (SSF). In addition to AmyA and AmyB already produced in monitored submerged culture, the strain was noted to produce new AmyB oligomeric forms, in particular a dominant tetrameric form named AmyC. The latter was purified to homogeneity through fractional acetone precipitation and size exclusion chromatography. SDS-PAGE and native PAGE analyses revealed that, purified AmyC was an approximately 172 kDa tetramer of four 42 kDa subunits. AmyC was also noted to display the same NH2-terminal amino acid sequence residues and approximately the same physico-chemical properties of AmyA and AmyB, to exhibit maximum activity at pH 5.6 and 60 °C, and to produce maltose and maltotriose as major starch hydrolysis end-products. Soyabean meal was the best substitute to yeast extract compared to fish powder waste and wheat gluten waste. AmyC production was optimized under SSF using statistical design methodology. Moisture content of 76.25%, C/N substrate ratio of 0.62, and inoculum size of 10(6.87) spores allowed maximum activity of 22118.34 U/g of dried substrate, which was 33 times higher than the one obtained before the application of the central composite design (CCD).

Ultrasonic extraction of pectin from Opuntia ficus indica cladodes after mucilage removal: Optimization of experimental conditions and evaluation of chemical and functional properties.

Ultrasonic assisted extraction (UAE) of pectin from Opuntia ficus indica (OFI) cladodes after mucilage removal was attempted using the response surface methodology. The process variables were optimized by the isovariant central composite design in order to improve the pectin extraction yield. The optimum condition obtained was: sonication time 70min, temperature 70°C, pH 1.5 and the water-material ratio 30ml/g. This condition was validated and the performance of experimental extraction was 18.14%±1.41%, which was closely linked to the predicted value (19.06%). Thus, UAE present a promising alternative to conventional extraction process thanks to its high efficiency which was achieved in less time and at lower temperatures. The pectin extracted by UAE from OFI cladodes (UAEPC) has a low degree of esterification, high uronic acid content, important functional properties and good anti-radical activity. These results are in favor of the use of UAEPC as potential additive in food industry.

Improvement of cyclodextrin glycosyltransferase (CGTase) production by recombinant Escherichia coli pAD26 immobilized on the cotton

The cyclodextrin glycosyltransferase (CGTase) of the recombinants Escherichia coli pAD26 cells immobilized on cotton was optimally produced by statistical methodology. Primarily, carbon and nitrogen sources were selected by one-factor-at-a-time method. Wheat starch, Casamino acid, Edamin and Hy-soy were identified as the best nutrients. These sources were secondly confirmed by Plackett-Burman design (fifteen variables were studied with sixteen experiments), as the most significant components with respect to CGTase production. In the third step, concentration of most significant factors and their interaction were optimized with a Box-Behnken experimental design. Under the optimized conditions (agitation 200 rpm, yeast extract concentration 20 g/L, wheat starch concentration 10 g/L and Hy-soy concentration 2.5 g/L), CGTase yield 145.11 U/mL was 3.6 and 23 folds higher than those obtained by the use of the initial conditions (39.77 U/mL) and free cells (6.37 U/mL), respectively.

Optimized production and characterization of a detergent-stable protease from Lysinibacillus fusiformis C250R

In this study, we aimed to optimize the cultural and nutritional conditions for protease production by Lysinibacillus fusiformis strain C250R in submerged fermentation process using statistical methodology. The most significant factors (gruel, wheat bran, yeast extract, and FeSO4) were identified by Plackett-Burman design. Response surface methodology (RSM) was used to determine the optimum levels of the screened factors and their interaction. Under the optimized conditions, protease yield 3100U/mL was 4.5 folds higher than those obtained by the use of the initial conditions (680U/mL). Additionally, a new extracellular 51kDa-protease, designated SAPLF, was purified and biochemically characterized from strain C250R. It shows optimum activity at 70°C and pH 10. Its half-life times at 70 and 80°C were 10 and 6-h, respectively. Irreversible inhibition of enzyme activity of SAPLF with serine protease inhibitors demonstrated that it belongs to the serine protease family. Interestingly, its catalytic efficiency was higher than that of SPVP from Aeribacillus pallidus strain VP3 and Alcalase Ultra 2.5L from Bacillus licheniformis. This study demonstrated that SAPLF has a high detergent compatibility and an excellent stain removal compared to Alcalase Ultra 2.5L; which offers an interesting potential for its application in the laundry detergent industry.

Optimization of Aspergillus oryzae S2 α-amylase, ascorbic acid, and glucose oxidase combination for improved French and composite Ukrainian wheat dough properties and bread quality using a mixture design approach

A simplex-centroid experimental design was used for the optimization of both reducing and oxidizing improvers, namely Aspergillus oryzae S2 α-amylase (Amy), ascorbic acid (Asc), and glucose oxidase (GOD). This optimization was performed to enhance the dough and breadmaking qualities of soft French wheat flour and a composite counterpart that contained 30% Ukrainian wheat flour. Statistically significant correlations were calculated between the W index and textural parameters (e.g., dough chewiness and bread cohesiveness). The findings revealed that while the best mixture for French flour comprised 21.8% of Amy, 41.2% of Asc, and 37% of GOD, for the composite counterpart, it comprised 2.3% of Amy, 66% of Asc, and 31.7% of GOD. These optimized mixtures rearranged soft French wheat flour and its composite counterpart to a good quality and an improved flour texture, respectively. Additionally, they increased the loaf specific volumes of the breads made from soft French wheat flour and its counterpart by 25.8 and 45.43%, respectively, significantly decreased the breads’ susceptibility to microbial contamination, and reclassified the breads as “good” in terms of sensory attributes.