30G-13 |
Demethylation of apple parenchyma alcohol insoluble solids by fungal pectinesterase |
F. K. DELGADO-VIDAL1, R. Talamas-Abbud1, G. V. NEVÁREZ-MOORILLÓN1, C. N. Aguilar-González2, and J. C. Contreras-Esquivel2. (1) Food Science and Technology Graduate Program, Universidad Autonoma de Chihuahua, P.O.Box 1542-C, Chihuahua, 31170, Mexico, (2) Departamento de Investigación en Alimentos, Universidad Autonoma de Coahuila A commercial pectinesterase (PE) has recently been used in apple juice production for mash treatment. After PE mash treatment, apple pomace can be recover and used to obtain a high-methoxyl pectin, a valuable by-product. Another choice is to take advantage of PE mash treatment to obtain a low-methoxyl pectin. The aim of this work was to study the effect of enzyme concentration, apple alcohol insoluble solids (AIS) ratio, and reaction time on in situ pectin demethoxylation. AIS were obtained from Golden Delicious apple parenchyma. AIS (200, 300 or 500 mg) were suspended in a 50 mM sodium citrate buffer, pH 4.5. Enzyme preparation with 48 U was added and the suspensions were stirred at 40°C during 0, 2, 4, 6 and 12 h reaction times. The effect of PE concentration was determined using 500 mg AIS added with 48, 96, and 144 U under the same conditions as before. The galacturonic acid (GA) content and degree of methoxylation (DM) were assayed on dry AIS apple parenchyma after PE treatments. Fungal and lemon PE extract was assayed for adsorption on AIS at 40ºC. AIS ratio had not effect on the enzymatic demethoxylation rate. DM decreased by 20% over 12 h. Under the conditions studied, the best enzyme concentration was 144 U. GA content ratio remained constant regardless kinetic conditions. At pH 5.0 most of the PE fungal enzyme was not adsorbed, while at pH 3.0 only 50% was adsorbed. In comparison, a lime PE extract was 95% adsorbed on AIS at pH 3.0, while at pH 5.0 80% adsorption was observed. Furthermore, non oxidized apple parenchyma was more susceptible to enzymatic demethylation (DM 17%) than oxidized material (DM 56%). Loss of the enzyme efficiency was mainly due to fungal enzyme adsorption phenomena and inhibition by polyphenols.
Session 30G, Fruit & Vegetable Product: Processed Fruits and Vegetables
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