Abstract
The objective of this study was to investigate the effects of low-temperature blanching in calcium chloride (CaCl2) solution before high-temperature processing (90oC for 1 min) on physicochemical properties related to the texture (total calcium content, pectin methylesterase (PME) activity, and firmness) of black cherry tomatoes (Solanum lycopersicum cv. OG) and to determine the optimum conditions to provide the fruits with the highest firmness. Response Surface Methodology (RSM) was applied to design the experiment with three factors of blanching temperature (52 to 68oC), blanching time (12 to 28 mins) and CaCl2 solution concentration (1.2 to 2.8% w/v). A sample without lowtemperature treatment was taken as a control. It was found that the blanching of tomatoes at low-temperatures resulted in higher total calcium content and PME activity in tissue after the treatment, and therefore improved the firmness of fruits after high-temperature processing. The highest firmness of treated tomatoes (566.21 g force) was estimated at blanching temperature of 62.05oC for 23.09 mins in 2.08% CaCl2 solution compared to the control which was blanched at high temperature (218 g force). Under these optimized conditions, the experimental responses (total calcium content, PME activity, and firmness) showed a close agreement with the predicted values.
Highlights
“Black” or “purple” cherry tomatoes are subspecies of Solanum lycopersicum (Zhang et al, 2018) and exhibit a purplish-brown color on their skin (Mes et al, 2008)
Calcium salts bind to free carboxylic acid groups along the polygalacturonic acid backbone of the pectin to form cross-links between pectin chains in the middle lamella leads to greater adhesion between cells and a firmer texture (Anthon et al, 2005)
Ha and Thuy / Food Research 5 (1) (2021) 149 - 157 temperature blanching) results in a firmer product through subsequent high-temperature processing (StolleSmits et al, 2000; Ni et al, 2005; Abu-Ghannam and Crowley, 2006). This is due to the activation of enzyme pectin methylesterase (PME) which is present in the cell wall when the fruits and vegetables are soaked in water at a temperature of 50-70oC for periods of 15-90 mins (Quintero‐Ramos et al, 2002)
Summary
“Black” or “purple” cherry tomatoes are subspecies of Solanum lycopersicum (Zhang et al, 2018) and exhibit a purplish-brown color on their skin (Mes et al, 2008). Calcium salts bind to free carboxylic acid groups along the polygalacturonic acid backbone of the pectin to form cross-links between pectin chains in the middle lamella leads to greater adhesion between cells and a firmer texture (Anthon et al, 2005). Ha and Thuy / Food Research 5 (1) (2021) 149 - 157 temperature blanching) results in a firmer product through subsequent high-temperature processing (StolleSmits et al, 2000; Ni et al, 2005; Abu-Ghannam and Crowley, 2006). This is due to the activation of enzyme pectin methylesterase (PME) which is present in the cell wall when the fruits and vegetables are soaked in water at a temperature of 50-70oC for periods of 15-90 mins (Quintero‐Ramos et al, 2002). Anthon et al (2005) observed that heating diced tomatoes to 70oC either before or after the CaCl2 treatment improved firmness through a subsequent high-temperature treatment, but to a lesser extent than heating during the CaCl2 treatment
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