Pectin methylesterase activity and other factors affecting pH and titratable acidity in processing tomatoes

Pectin methylesterase (PME) rapidly hydrolyzes pectin methylesters in cold break tomato juice to form methanol and to increase titratable acidity (TA). Within 30 min, the juice methanol concentration increased from 35 to over 400 μg g⁻¹ while the pH dropped from 4.45 to 4.20. On average, cold break juice pH values were 0.21 U lower and TAs 12.4 μeq g⁻¹ higher than those for hot break juices prepared from the same tomatoes. The greater TA in the cold break juices equalled the amount of methanol formed, consistent with both resulting from PME activity in the cold break juice. For 16 cultivars evaluated, there was a correlation between the methanol content of the cold break juices and the consistency of hot break juices, which could be the result of different pectin contents in the different cultivars. Differences in the citric, glutamic, and malic acid contents between these cultivars were small.