Immobilization of Rhodococcus by encapsulation and entrapment: a green solution to bitter citrus by-products

Debittering of citrus by-products is required to obtain value-added compounds for application in the food industry (e.g., dietary fiber, bioactive compounds). In this work, the immobilization of Rhodococcus fascians cells by encapsulation in Ca-alginate hollow beads and entrapment in poly(vinyl alcohol)/polyethylene glycol (PVA/PEG) cryogels was studied as an alternative to chemical treatments for degrading the bitter compound limonin. Previously, the Rhodococcus strain was adapted using orange peel extract to increase its tolerance to limonoids. The optimal conditions for the encapsulation of microbial cells were 2% Na-alginate, 4% CaCl2, 4% carboxymethylcellulose (CMC), and a microbial load of 0.6 OD600 (optical density at 600 nm). For immobilization by entrapment, the optimal conditions were 8% PVA, 8% PEG, and 0.6 OD600 microbial load. Immobilization by entrapment protected microbial cells better than encapsulation against the citrus medium stress conditions (acid pH and composition). Thus, under optimal immobilization conditions, limonin degradation was 32 and 28% for immobilization in PVA/PEG gels and in hollow beads, respectively, in synthetic juice (pH 3) after 72 h at 25 °C. Finally, the microbial cells entrapped in the cryogels showed a higher operational stability in orange juice than the encapsulated cells, with four consecutive cycles of reuse (runs of 24 h at 25 °C). KEY POINTS: • Increased tolerance to limonoids by adapting R. fascians with citrus by-products. • Entrapment provided cells with favorable microenvironment for debittering at acid pH. • Cryogel-immobilized cells showed the highest limonin degradation in citrus products.

Detection of Hazelnut and Almond Adulteration in Olive Oil: An Approach by qPCR

Virgin olive oil (VOO), characterized by its unique aroma, flavor, and health benefits, is subject to adulteration with the addition of oils obtained from other edible species. The consumption of adulterated olive oil with nut species, such as hazelnut or almond, leads to health and safety issues for consumers, due to their high allergenic potential. To detect almond and hazelnut in olive oil, several amplification systems have been analyzed by qPCR assay with a SYBR Green post-PCR melting curve analysis. The systems selected were Cora1F2/R2 and Madl, targeting the genes coding the allergenic protein Cor a 1 (hazelnut) and Pru av 1 (almond), respectively. These primers revealed adequate specificity for each of the targeted species. In addition, the result obtained demonstrated that this methodology can be used to detect olive oil adulteration with up to 5% of hazelnut or almond oil by a single qPCR assay, and with a level as low as 2.5% by a nested-qPCR assay. Thus, the present research has shown that the SYBR-based qPCR assay can be a rapid, precise, and accurate method to detect adulteration in olive oil.

Kinetic Modeling, Thermodynamic Approach and Molecular Dynamics Simulation of Thermal Inactivation of Lipases from Burkholderia cepacia and Rhizomucor miehei

The behavior against temperature and thermal stability of enzymes is a topic of importance for industrial biocatalysis. This study focuses on the kinetics and thermodynamics of the thermal inactivation of Lipase PS from B. cepacia and Palatase from R. miehei. Thermal inactivation was investigated using eight inactivation models at a temperature range of 40–70 °C. Kinetic modeling showed that the first-order model and Weibull distribution were the best equations to describe the residual activity of Lipase PS and Palatase, respectively. The results obtained from the kinetic parameters, decimal reduction time (D and t_R), and temperature required (z and z’) indicated a higher thermal stability of Lipase PS compared to Palatase. The activation energy values (Ea) also indicated that higher energy was required to denature bacterial (34.8 kJ mol⁻¹) than fungal (23.3 kJ mol⁻¹) lipase. The thermodynamic inactivation parameters, Gibbs free energy (ΔG^#), entropy (ΔS^#), and enthalpy (ΔH^#) were also determined. The results showed a ΔG^# for Palatase (86.0–92.1 kJ mol⁻¹) lower than for Lipase PS (98.6–104.9 kJ mol⁻¹), and a negative entropic and positive enthalpic contribution for both lipases. A comparative molecular dynamics simulation and structural analysis at 40 °C and 70 °C were also performed.

Development and optimization of an efficient qPCR system for olive authentication in edible oils

The applicability of qPCR in olive-oil authentication depends on the DNA obtained from the oils and the amplification primers. Therefore, four olive-specific amplification systems based on the trnL gene were designed (A-, B-, C- and D-trnL systems). The qPCR conditions, primer concentration and annealing temperature, were optimized. The systems were tested for efficiency and sensitivity to select the most suitable for olive oil authentication. The selected system (D-trnL) demonstrated specificity toward olive in contrast to other oleaginous species (canola, soybean, sunflower, maize, peanut and coconut) and showed high sensitivity in a broad linear dynamic range (LOD and LOQ: 500ng - 0.0625pg). This qPCR system enabled detection, with high sensitivity and specificity, of olive DNA isolated from oils processed in different ways, establishing it as an efficient method for the authentication of olive oil regardless of its category.

Synthesis and characterization of a stable humic-urease complex: application to barley seed encapsulation for improving N uptake

BACKGROUND

Most N fertilizers added to soil are not efficiently used by plants and are lost to the atmosphere or leached from the soil, causing environmental pollution and increasing cost. Barley seed encapsulation in calcium alginate gels containing free or immobilized urease to enhance plant utilization of soil N was investigated.

RESULTS

Urease was immobilized with soil humic acids (HA). A central composite face-centered design was applied to optimize the immobilization process, reaching an immobilization yield of 127%. Soil stability of urease was enhanced after the immobilization. Seed encapsulation with free urease (FU) and humic-urease complex (HUC) resulted in a urease activity retention in the coating layer of 46% and 24%, and in germination rates of 87% and 92%, respectively. Under pot culture conditions, the pots planted with seeds encapsulated with FU and HUC showed higher ammonium N (NH4 (+) -N) (26% and 64%, respectively) than the control soil at 28 days after planting (DAP). Moreover, the seed encapsulation with FU and HUC increased the N uptake 83% and 97%, respectively, at 35 DAP.

CONCLUSION

Seed encapsulation with urease could substantially contribute to enhancing plant N nutrition in the early stages of seedling establishment. © 2015 Society of Chemical Industry.

Novel qPCR systems for olive (Olea europaea L.) authentication in oils and food

The traceability of olive oil is an unresolved issue that remains a challenge. In this field, DNA-based techniques are very powerful tools for discrimination that are less negatively influenced by environmental conditions than other techniques. More specifically, quantitative real time PCR (qPCR) achieves a high degree of sensitivity, although the DNA that it can directly isolate from these oils presents drawbacks. Our study reports the analysis of eight systems, in order to determine their suitability for olive detection in oil and oil-derived foodstuffs. The eight systems were analyzed on the basis of their sensitivity and specificity in the qPCR assay, their relative sensitivity to olive DNA detection and DNA mixtures, their sensitivity and specificity to olive in vegetable oils and the detection of olive in commercial products. The results show that the PetN-PsbM system, designed in this study, is a suitable and reliable technique in relation to olive oil and olive ingredients in both food authentication and food safety processes.

Alkaline phosphatase-polyresorcinol complex: characterization and application to seed coating

An alkaline phosphatase (EC 3.1.3.1) from Escherichia coli ATCC27257 was immobilized by copolymerization with resorcinol. The phosphatase-polyresorcinol complex synthesized retained about 74% of the original enzymatic activity. The pH and temperature profile of the immobilized and free enzyme revealed a similar behavior. Kinetic parameters were determined: K(m) and K(i) values were 2.44 and 0.423 mM, respectively, for the phosphatase-polyresorcinol complex and 1.07 and 0.069 mM, respectively, for free phosphatase. The thermal and storage stabilities of the immobilized phosphatase were higher than those of the native one. On addition to soil, free enzyme was completely inactivated in 4 days, whereas the phosphatase-polyresorcinol complex was comparatively stable. Barley seed coated with the immobilized enzyme exhibited higher rhizosphere phosphatase activity. Under pot culture conditions, an increase in the soil inorganic phosphorus was detected when the seed was encapsulated with the phosphatase-polyresorcinol complex, and a positive influence on biomass and inorganic phosphorus concentration of shoot was observed.

Neutrase immobilization on alginate-glutaraldehyde beads by covalent attachment

Neutrase, a commercial preparation of Bacillus subtilis , was covalently immobilized on alginate-glutaraldehyde beads. Immobilization conditions and characterization of the immobilized enzyme were investigated. Central composite design and response surface methods were employed to evaluate the effects of immobilization parameters, such as glutaraldehyde concentration, enzyme loading, immobilization pH, and immobilization time. Under optimized working conditions (2% alginate, 6.2% glutaraldehyde, 61.84 U mL(-1) Neutrase, pH 6.2, and 60 min) the immobilization yield was about 50%. The immobilized enzyme exhibited higher K(m) compared to the soluble enzyme. The pH-activity profile was widened upon immobilization. The optimum temperature was shifted from 50 to 60 degrees C, and the apparent activation energy was decreased from 47.7 to 22.0 kJ mol(-1) by immobilization. The immobilized enzyme also showed significantly enhanced thermal stability.

Prediction of the ripening times of ewe's milk cheese by multivariate regression analysis of capillary electrophoresis casein fractions

The effect of the ripening time on the proteolytic process in cheeses made from ewe's milk during a 139-day ripening period was monitored by the use of capillary electrophoresis of pH 4.6 insoluble fraction. Totals of 18 and 21 peaks were recognized and matched in the electropherograms obtained with a fused-silica capillary and a neutral capillary (hydrophilically coated), respectively. These peaks correspond to intact ovine caseins and their hydrolysis products (alpha(s1)-casein I, alpha(s1)-casein II, alpha(s1)-casein III, alpha(s2)-casein, beta(1)-casein, beta(2)-casein, p-kappa-casein, alpha(s1)-I-casein, gamma(1)-casein, gamma(2)-casein, and gamma(3)-casein). The alpha(s)-caseins (alpha(s1)- and alpha(s2)-casein) displayed similar degradation pattern to one another, but different from those of beta-caseins (beta(1)- and beta(2)-casein). beta-Caseins were very much undergoing lesser degradation during the ripening time than alpha(s)-casein. Finally, partial least-squares regression and principal components regression were used to predict the ripening time in cheeses. The models obtained yielded good results since the root-mean-square error in prediction by cross validation was <8.6 days in all cases.

Preparation and properties of an immobilized pectinlyase for the treatment of fruit juices

Pectinlyase, present in different commercial pectinases used in juice technology, was immobilized on alginate beads. The optimal conditions were: 0.17 g alginate ml(-1), 1.2% (w/v or v/v) enzyme concentration and acetic-HCl/glycine-HCl buffer at pH 3.6 or tris-HCl/imidazole buffer at pH 6.4. Maximum percentage of immobilization (10.6%) was obtained with Rapidase C80. Kinetic parameters of free and immobilized pectinlyase were also determined. The pH and temperature at which activity of soluble and immobilized enzyme was maximum were 7.2 and 55 degrees C. Thermal stability was not significantly altered by immobilization, especially at 40 degrees C, showing two periods of different stability. Free and immobilized preparation reduced the viscosity of highly esterified pectin from 1.09 to 0.70 and 0.72 mm(2) s(-1), respectively, after 30 min at 40 degrees C. Furthermore, the immobilized enzyme could be re-used through 4 cycles and the efficiency loss in viscosity reduction was found to be only 9.2%.

Chemometrical analysis of capillary electrophoresis casein fractions for predicting ripening times of milk mixture cheese

The effect of the ripening time on the proteolytic process in cheeses manufactured from mixtures of cow's and ewe's milk during a 167-day ripening period was monitored by capillary electrophoresis of the pH 4.6-insoluble fraction. Totals of 21 and 16 peaks were recognized and matched in the electropherograms obtained with a fused-silica capillary and a neutral capillary (hydrophilically coated), respectively. These peaks corresponded to intact bovine and ovine caseins and their hydrolysis products (e.g., alpha(s1)-casein, gamma-caseins). In 167-day-old cheeses, bovine alpha(s0)-casein (alpha(s1)-casein 9P) had been completely degraded and 6% of the residual bovine alpha(s1)-casein remained intact. Breakdown of the beta-casein fraction was lower than that of the alpha(s)-casein fraction. Finally, partial least-squares regression and principal component regression were used to predict the ripening time in cheeses. The root-mean-square errors in prediction by cross-validation were <7.8 days in all cases.