Xyloglucan endotransglycosylase activity in apples is ripening-related: Implications for fruit juice processing

In order to assess the role of endogenous enzymes during apple juice manufacturing by enzymic liquefaction, apples of different maturity were assayed for various enzyme activities. Xyloglucan endotransglycosylase (XET) activity increased dramatically from early September to mid October, and decreased slowly during cold storage. It was shown that XET is probably the most important, endo-acting activity in apple. The apples of different maturity were also treated by pectin lyase and various concentrations of cellulase. It appeared that less cellulase was needed for disintegration of apples with a high level of XET activity. This suggests that XET facilitates the liquefaction process. Under certain conditions,'high XET' apples could be transformed into a cloudy apple juice. This cloud may be regarded as a dispersion of particles which is predominantly composed of cellulose and xyloglucan. (C) 1998 Society of Chemical Industry.