Enzyme infusion prior to thermal/high pressure processing of strawberries: Mechanistic insight into firmness evolution

Strawberries were infused with fungal pectinmethylesterase (PME) and calcium chloride, followed by a thermal (70 °C–0.1 MPa), a high pressure (25 °C–550 MPa) or a combined thermal-high pressure (70 °C–550 MPa) process. Macroscopic (firmness) and microscopic characteristics were assessed to evaluate the texture of the fruits. In order to interpret the texture changes, the chemical structure of pectin was investigated. Processing of strawberries caused a decrease in firmness, which was limited by infusion of PME and calcium chloride, although the extent of beneficial effects depended on the type of processing. PME was able to decrease the degree of methoxylation of pectin, which was accompanied by an increased crosslinking of the chains. During high pressure or combined thermal-high pressure processing, the degree of methoxylation of pectin in infused strawberries was even further decreased, probably due to a higher activity of the fungal PME under high pressure. In case of the high pressure process, this was reflected in a very firm texture. However, the combined thermal-high pressure process caused more severe tissue damage, in spite of the advantageous pectin properties.Industrial relevanceDuring high pressure processing of strawberries many nutritional and sensorial characteristics are quite well preserved. Unfortunately, texture of strawberries deteriorates during such processes. This paper provides mechanistic insight into how infusion of fungal pectinmethylesterase and calcium ions in strawberries can preserve the firmness of these fruits during high pressure processing.