|
In an effort to improve yield and quality of pear juice, the pulp tissue of pear fruit (Pyrus pyrifolia) was extracted in the presence of various cell wall hydrolytic enzymes, and their conditions for fruit liquefaction were determined. Among 11 different commercial enzymes tested, Pectinex Ultra SP-L, Cytolase M102, Viscozyme L, and Rapidase liq^(+) showed a higher juice yield, ranging 88.0-91.0% of fresh weight of tissue. Less than 0.025% (v/w) of enzymes was enough to yield a consistent juice recovery, enhancing the yield 7-9% by volume. Turbidity of the aqueous solution after extraction was decreased when treated with Pectinex Ultra SP-L and Viscozyme L, however, it increased in Cytolase M102 treatment. In addition, total soluble solids content of the extracts also increased by 0.1-0.5 Brix with those enzyme treatment. In vitro assay confirmed that enzymes selected for pear pulp liquefaction have both endo- and exo- degrading activities toward various cell wall substrates, showing that polygalacturonase is the most active enzyme. The composition of pear cell walls were changed rapidly during hydrolysis by the enzymes used in pericarp liquefaction. The amount of polyuronides in the cell walls were decreased from 24-28% to 11-16% by the enzyme treatment for 2hrs. Cellulose, comprising 37% of the cell walls, decreased to 28% in 8hrs. Among the neutral sugars, arabinose decreased the most, followed by galactose and glucose. However, the composition of xylosyl residues, which is the most abundant neutral sugar in pear cell wall, rather increased at the expense of the decrease in the other sugars.
|