María Elvira Zúñiga

Thermal inactivation of immobilized penicillin acylase in the presence of substrate and products

Inactivation of immobilized penicillin acylase has been studied in the presence of substrate (penicillin G) and products (phenylacetic acid and 6‐aminopenicillanic acid), under the hypothesis that substances which interact with the enzyme molecule during catalysis will have an effect on enzyme stability. The kinetics of immobilized penicillin acylase inactivation was a multistage process, decay constants being evaluated for the free‐enzyme and enzyme complexes, from whose values modulation factors were determined for the effectors in each enzyme complex at each stage. 6‐Aminopenicillanic acid and penicillin G stabilized the enzyme in the first stage of decay. Modulation factors in that stage were 0.96 for penicillin G and 0.98 for 6‐aminopenicillanic acid. Phenylacetic acid increased the rate of inactivation in both stages, modulating factors being −2.31 and −2.23, respectively. Modulation factors influence enzyme performance in a reactor and are useful parameters for a proper evaluation.

Enzymic pre-treatment of Guevina avellana mol oil extraction by pressing

Abstract Cosmetic oil of Guevina avellana mol is industrially extracted by cold pressing, producing a residual meal with 10–12% on dry base of oil, which spoils, limiting its application for human consumption. An enzymic pre-treatment was incorporated into the conventional oil extraction process by cold pressing, with the purpose of improving the oil yield and the residual meal quality. The effect of enzyme/substrate ratio, temperature and moisture was analysed during hydrolysis using two commercial enzyme mixtures. Pressing conditions during this stage were also studied. An increase in extracted oil was obtained for both enzymic mixtures. The best result was a yield up to 98% of extracted oil and residual meal with 1.5% of oil. An oil extraction yield up to 98% and a residual meal with 1.5% of oil. This result was further validated in an industrial plant scale.

Characterisation of protein concentrates from pressed cakes of Guevina avellana (Chilean hazelnut)

Protein concentrates, produced by aqueous extraction and membrane filtration from Guevina avellana pressing cakes, were characterized with regard to nutritional and functional properties. The effect of a previous enzymatic treatment, carried out with the aim of enhancing oil extractability during pressing, was also evaluated. Thermal conditioning of the seeds, before pressing, influenced oil and protein extractability, as well as the nutritional quality and functional properties. The protein concentrates contained up to 65% protein with an in vitro apparent digestibility coefficient in the range 75–80%. They presented a reduced ability to bind water, but they retained almost up to ten times their weight of oil.

Packed-bed reactor performance with immobilized lactase under thermal inactivation

Thermal inactivation of immobilized lactase has been studied in the presence of substrate and products. Modulation factors of thermal inactivation have been determined for lactose and galactose based on a two-stage series-type mechanism of inactivation. Galactose was a positive modulator of enzyme stability while the opposite occurred with lactose; the glucose effect was negligible. A model for packed-bed continuous reactor operation with chitin-immobilized lactase from Kluyveromyces marxianus var. marxianus was developed considering modulated thermal inactivation and appropriate kinetic expression for lactose hydrolysis. Experimental results were in good agreement with the model which was a far better representation of reactor performance than the conventional model not considering the effect of substrate and products on enzyme inactivation.

The enhancement of antioxidant compounds extracted from Thymus vulgaris using enzymes and the effect of extracting solvent

We evaluate the total phenolic compounds (TPC) content and the antioxidant activity (AA) of extracts obtained from ground fresh thyme (FT) and depleted thyme (DT), a by-product of the process of essential oil extraction. In addition, enzymatic treatments were evaluated to improve the extraction yields of polyphenolic compounds from thyme. Extractions were performed using several solvents as methanol, ethanol, and water. Enzymes were applied prior to extraction or during the extraction process. The best results were obtained using a mixture of methanol and water, resulting in 2790 and 220 mg Gallic acid equivalent (GAE)/L of TPC for FT and DT, respectively. A similar result was observed for AA. With regard to enzymatic treatment, application of Grindamyl CA 150 enzyme as a pre-treatment resulted in the production of an extract from DT with 614 mg TE (trolox equivalent)/L of AA, 70% more than the control, and an AA of 621 mg TE/L (74% more than the control sample) was obtained using Grindamyl CA 150 during the extraction process. These results suggest that enzymatic treatment is an interesting alternative for producing antioxidant extracts from DT.

Production of pectic extracts from sugar beet pulp with antiproliferative activity on a breast cancer cell line

In the last years, sugar beet pectins have been the subject of several investigations involving extraction methodologies, chemical composition and functional properties. The structure of pectins, which depends on the extraction method, is decisive in their capacity to induce apoptosis on several cancer cell lines like colon, prostate and breast. In this work, sugar beet pectin extraction was performed in the following steps: lipid extraction with hexane, removal of soluble complex carbohydrates and proteins, and enzymatic treatment with amyloglucosidase, protease, and pectinase. The enzymatic treatment was carried out with Rohapect DA6L under the following conditions: 50°C, pH 4.0, 2% enzyme/substrate (E/S) ratio, 15 h, and a solid to liquid ratio of 1 : 10. The pectic extract showed a degree of polymerization (DP) profile of 55.8% with DP ⩾ 7; 4.9% with DP6; 5.8% between DP2 and DP6 ; 4.7% with DP2; and 28.8% with DP1. The pectic extract was examined for its antiproliferative activity on the MCF-7 breast cancer cell line. At a concentration range of 12.5–25 mg/mL the pectic extract killed 80.6% of the cells, exhibiting a higher antiproliferative activity than 4-hydroxytamoxifen (4-OHT), a classical anticancer drug, which killed 56.5% of the cells.