Chii-Ming Jiang

Characterization of pectinesterase inhibitor in jelly fig (Ficus awkeotsang Makino) achenes.

Pectinesterase inhibitor (PEI) extract prepared from intact jelly fig (Ficus awkeotsang Makino) achenes was separated by membrane (MWCO 3 and 10 kDa) and fractionated by a Sepharose G-50 gel permeation chromatography. Results from Sepharose G-50 gel permeation chromatography and concanavalin A Sepharose chromatography revealed PEI as polypeptides with molecular weights ranging from 3.5 to 4.5 kDa. Incubation of a PE (1 unit/mL)-PEI (2 mg/mL) mixture for 1 min decreased the PE activity by approximately 50%. On the basis of the results of Lineweaver-Burk double-reciprocal plots, Michaelis constant (K(m)) and V(max) values for jelly fig achenes PE (pH 6.0, 30 degrees C) were 0.78 mM -OCH3 and 1.09 microequiv of -COOH/min, respectively. In addition, PEI competitively inhibited both citrus and jelly fig achenes PEs.

Addition of Phenolic Acids on the Reduction of Methanol Content in Wine

Utilization of phenolic acids, including gallic acid, coumaric acid, caffic acid, cinnamic acid, and ferulic acid, for methanol reduction in wine was investigated. Enzyme activities of pectinesterase and pectin lyase decreased significantly when 0.1 mg/L of gallic acid, coumaric acid, caffic acid, cinnamic acid, or ferulic acid was added. However, no inhibition on polygalacturonase activity was observed when 0.5 mg/L of phenolic acid was added. Methanol content in commercial pectic enzyme (CPE) group increased from 11.53 +/- 1.34 to 56.67 +/- 3.75 ppm in the final products. Adding gallic acid or coumaric acid with CPE inhibited the increase of methanol production. In addition, when 0.2 mg/L of phenolic acid (gallic acid or coumaric acid) was added, the amount of total phenolic acid released from CPE + gallic acid or CPE + coumaric acid groups became higher than CPE group by approximately 466 and 539 mg/L, respectively. In conclusion, the values of lightness, red content, yellow content, total pigment, and total phenolic acid increased in the presence of gallic acid or coumaric acid with CPE, suggesting that adding gallic acid or coumaric acid into winemaking process is a potential method for reducing methanol content, improving wine quality, as well as increasing healthy compounds in wine production.

Changes in physico-chemical properties of pectin from jelly fig (Ficus awkeotsang Makino) seeds during extraction and gelling

Degree of esterification of pectin from jelly fig (Ficus awkeotsang Makino) achene seeds and the pH value decreased rapidly during extraction, while apparent reduction of free calcium content in the pectin extract was observed at the gelling stage. Compared to those of the native pectin, total ester linkages and methyl ester linkages of pectin extract decreased, and the bound calcium content increased during pectin gelling. However, non-methyl ester linkages (the difference between the total ester linkage and the methyl ester linkage) increased by approximately 40% during pectin gelling, revealing esterification reaction between C6 carboxyl groups and hydroxyl groups in the presence of pectinesterase. Scanning electron microscopy showed that pectin fragments from jelly curds were large with flake-like structure, while those from hot (85°C) ethanol-treated achenes were small and porous.

Quantification of L-ascorbic acid and total ascorbic acid in fruits and spinach by capillary zone electrophoresis

A standard curve for the quantification of L‐ascorbic acid (L‐AA) by capillary zone electrophoresis (CZE) was established, and the quantification of ascorbic acid and total ascorbic acid in fruits (lemon, Sunkist, and pineapple) and spinach were performed using D‐isoascorbic acid (D‐IAA) as an internal standard. The minimum detection limits (MDLs) for L‐AA and D‐IAA were determined to be 1 and 2 νg/mL, respectively, at 265 nm. Dehydroascorbic acid (DHAA) in fruits and spinach was quantified in the presence of DL‐homocysteine. The recoveries for L‐AA in these juices were between 95 and 105%.

Transacylation properties of pectin methyl esterase from Aspergillus niger

Transacylation reaction of citrus pectin catalyzed by pectin methyl esterase (PME) from Aspergillus niger observed by laser particle size analyzer was investigated. PME was purified by a highly methoxylation of cross-linked alcohol-insoluble solids (HM-CL-AIS) column chromatography and a subsequent Sephadex G-75 column chromatography from commercial pectic enzyme (CPE) of A. niger . The increases of particle size (transacylation reaction) in PME-treated pectin solution are pectin content and PME activity dependent and expressed a maximum at 0.3% pectin and 0.5 U/ml PME, respectively. PME activity (de-esterification reaction) was highly stable below 50°C but lost completely when above 70°C, while the particle size of PME-treated pectin solution decrease at temperature above 40°C. PME activity was optimum at pH 5.0, while the increase of particle size in PME-treated pectin solution reaches a maximum at pH 3.5. The different characteristics between PME from A. niger and the published plant PME reveal that there are at least two kinds of PME-catalyzed transacylation reaction, one for plant PME and the other for microbial PME.