| Summary: | 碩士 === 國立高雄海洋科技大學 === 水產食品科學研究所 === 98 === It was well known that the de-esterification yield free carboxyl group and methanol to reduce the degree of esterification (DE) by pectinesterase(PE), however, it majorly occurred at neutral to slightly alkaline environment rather than at pH 3.5 to 4.0 which are the normal ranges in fruit or vegetable juices and in wines. In other words, the normal PE activities, under these non optimal pH ranges in general fruit juices, should be too low to yield massive methanol content in theoretic views. With the fact of highly accumulated methanol content in fruit or vegetable juices and
in wines, we proposed that exist of acidic stable PE play the crucial role in yield of methanol. To elucidate whether the yield of methanol caused by the acidic PE, the isolated acidic PE and normal PE incubated in juices to proceed manufacturing process, respectively. In our data have shown that
the normal PE exhibit the great activities in optimal pH ranges at neutral to slightly alkaline but the relative tiny activities at lower pH ranges. The accumulated methanol contents were relative to activities in acidic PE. The other interesting phenomenon observed in our experiment was that the PE activities determined by traditional titration method exhibit relative lower at pH 3.5 than at 4.0 and at 3.0. We assumed it caused by the under esteem
of acid-dissociation in carboxyl group, which the acid-dissociation constant is at 3.55-4.10. To determine the PE activities at pH 3 to 5 accurately, the utilization of Gas Chromatography (GC) was suggested in our study.
Key words：pectinesterase, methanol, pectin, acidic PE
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