Textural, mechanical, and microstructural properties of restructured pimiento alginate‐guar gels

Abstract

Textural, mechanical, microstructural, and thermal properties of reconstituted pimiento alginate‐guar gels subjected to thermal and mechanical stresses during pasteurization process were investigated. Alginate‐guar gelling system at ratio 2:1 at different calcium chloride concentrations (2–8%) and varying acid conditions including citric and lactic acid 1% were evaluated. Textural profile analysis parameters viz. hardness, springiness, gumminess, cohesiveness, adhesiveness as well as mechanical properties, structural, thermal, and morphological characteristics of pimiento strips were examined. Gel strength and elasticity of pimiento strips were increased at higher calcium levels. Fracturability was decreased clearly revealed the gel system, regain its strength in spite of high pulp content (25%) and can maintain its own structure. Increase in hardness and reduction in springiness showed loss of elasticity, which may be attributed to the gel shrinkage during thermal processing, making it more compact and dense. Therefore, the restructured pimiento strips were completely thermo stable at pasteurization temperature. By increasing alginate and calcium level in the pimiento strip, glass transition temperature was reduced from 112 to 98°C. Fourier transform infrared spectroscopy studies confirmed that the gel network structure at acidic conditions was stable and acid type did not has significant effect on the chemical interactions. The microstructural results showed ellipsoidal and compact structure in which can be an evidence of high elasticity and rigidity of pimiento gels. These results completely approved the high elasticity and rigidity of the pimiento strips and their ability to sustain successfully thermal and mechanical stresses with appreciable textural integrity during processing such as pasteurization. Practical applications Restructured pimiento strip for stuffing into cocktail olives is a challenging problem in binary composite hydrogels of alginate and guar gum. The strips should be designed to be strong enough to handle mechanically and cut easily without tearing. Furthermore, it had to withstand to pasteurization process and be flexible to bend like a hairpin into the pit hole of olive. In addition, it also had low syneresis and shrinkage that the strips not fall out of the olive hole during storage. In the view point of marketing and nutritional aspects, it is more advantageous to develop a restructured fruit gel systems several times higher than the limiting 10% pulp because of its weak structure. Therefore, alginate‐gel systems containing 25% pimiento pulp were evaluated at different levels of calcium chloride and thermal processing.

Optimization of textural characteristics of restructured pimiento strips by response surface methodology

“…Increasing in hardness can be related to the more cross‐linking of the alginate by calcium, which improves the gel strength. Similar results were also reported in our previous work (Mousavi et al, ).…”

“…The pimiento strips were prepared according to our previous work (Mousavi, Rafe, & Yeganehzad, ). In brief, pimiento puree was thoroughly mixed with deionized water, potassium sorbate (0.1 g), sodium alginate, and guar for 5 min at 21–48 g over a juicer blender (SHARP ‐ COUNTERTOP BLENDER SBTI172G) in order to achieve no lumps and the mixture became homogenous.…”

“…Then, the mixture was rest for 30 min to remove the entrapped air bubbles. The product, viscous pimiento paste, was extruded by a head cut laboratory syringe (Mousavi et al, ) under gravity into the setting bath containing calcium chloride at concentrations 2.0%, 5.0%, and 8.0% w / w to develop a wide continuous sheet with 2 mm thickness. The setting sheet moved along the bath propelled by more paste was extruded.…”

Effects of Thermal Treatment on the Physical Properties of Edible Calcium Alginate Gel Beads: Response Surface Methodological Approach

“…This study shows that the comparison of the mechanical resistance at different temperatures (80, 110, and 130 °C), for the same period (0, 5, 10, 15, and 20 min) of incubation, shows that a higher resistance is always obtained at the higher temperature. A previous study also reported that the hardness of the alginate-guar gels mixed with pimiento pulp significantly increased when applying thermal treatment (80 °C for 15 min) [24]. The authors reported that the increase in hardness of the alginate-guar gels originated from the occurrence of gel shrinkage, making them more compact during heat treatment [24].…”

“…A previous study also reported that the hardness of the alginate-guar gels mixed with pimiento pulp significantly increased when applying thermal treatment (80 °C for 15 min) [24]. The authors reported that the increase in hardness of the alginate-guar gels originated from the occurrence of gel shrinkage, making them more compact during heat treatment [24].…”