Enzyme infusion and thermal processing of strawberries: Pectin conversions related to firmness evolution

Strawberries were infused with fungal pectinmethylesterase (PME) and/or calcium chloride with the aim of minimising tissue damage during subsequent thermal processing (95 degrees C). Firmness measurements and micrographs provided information on the extent of tissue damage. These observations were linked to the chemical structure of pectin. When PME was infused in absence of Ca2+, the degree of methoxylation of pectin was lowered, but chains remained water soluble, indicating that they were not crosslinked. Thermal processing of PME-infused strawberries resulted in pectin solubilisation and depolymerisation which was reflected in pronounced firmness decrease and tissue damage, comparable to non-infused processed strawberries. On the other hand, when a combination of both PME and Ca2+ was infused, an important decrease in processing-related tissue damage was perceived. This can be explained by increased cross-linking of pectin chains with low degree of methoxylation, rendering them insoluble and less susceptible to thermal depolymerisation. (c) 2008 Elsevier Ltd. All rights reserved.