Effects of pH and Salts on Physical and Mechanical Properties of Pea Starch Films

Abstract

To identify the significant contribution of intermolecular hydrogen bonds of starch molecules to the film structure formation, pH of film-forming solutions was adjusted and also various salts (NaCl, CaCl2 , CaSO4 , and K2 SO4 ) were mixed into the glycerol-plasticized pea starch film. The film made from pH 7 possessed the highest tensile strength-at-break (2 times) and elastic modulus (4 to 15 times) and the lowest elongation-at-break compared with those of the films made from acid and alkali environments. The pH 7 film also has the highest film density and the lowest total soluble matter. At the level of 0.01 to 0.1 M of CaSO4 and 0.1 M of K2 SO4 in a kilogram of starch, the water solubility of the film increased, while chloride salts slightly lowered the solubility. NaCl and CaSO4 reduced water vapor permeability (WVP), while CaCl2 slightly increased WVP at 0.01 and 0.06 M concentrations, and K2 SO4 significantly increased WVP at 0.03 and 0.15 M. Presence of salts increased tensile strength (5 to 14 times than the control films) and elastic modulus (35 to 180 times) of starch film at 0.01 to 0.03 M of CaSO4 and K2 SO4 . Elongation-at-break increased significantly as salt concentration increases to an optimal level. However, when the concentration exceeded above the optimal level, the E of starch films decreased and showed no significant difference from the control film. Overall, the addition of salts modified physical and mechanical properties of pea starch films more than pH adjustment without any salt addition.

Effects of Acid and Salt Solutions on the Pasting, Rheology and Texture of Lotus Root Starch–Konjac Glucomannan Mixture

“…The results show that the LRS/KGM mixture had a lower peak viscosity, final viscosity, setback viscosity, pasting time, peak time, and a higher breakdown viscosity in acidic conditions than in a neutral environment. Given that acid hydrolysis destroys glycosidic bonds in molecules [22], the complete pasting of starch molecules in acidic conditions requires less energy and therefore LRS is gelatinized faster and at lower temperatures. The hydrolysis of the LRS/KGM mixture in acidic environments is irreversible and influences the rearrangement of starch molecules upon temperature reduction, accompanied by a decrease in the retrogradation rate and value.…”

Development of novel pea flour‐based nanofibres by electrospinning method

“…The reason could be low pea flour and HPMC concentration leading no branching of nanofibres. Edible films of pea protein isolate and pea starch gave 8.4 9 10 À14 kg m À1 s À1 Pa À1 (Kowalczyk & Baraniak, 2011) and 7.3 9 10 À13 kg m À1 s À1 Pa À1 (Choi et al, 2016), respectively. The branching was attributed to uneven distribution of the charge carried by the jets, which was caused by jet elongation and solvent evaporation.…”

“…In this current study, WVP values of fibres varied in 12.18-17.54 9 10 À16 kg m À1 s À1 Pa À1 which was lower compared to edible films in literature. Edible films of pea protein isolate and pea starch gave 8.4 9 10 À14 kg m À1 s À1 Pa À1 (Kowalczyk & Baraniak, 2011) and 7.3 9 10 À13 kg m À1 s À1 Pa À1 (Choi et al, 2016), respectively. This showed that combining pea flour with HPMC and PEO is an advantage in food packaging area in terms of reduction in WVP values.…”

A current review of structure, functional properties, and industrial applications of pulse starches for value‐added utilization

“…Other strategies, including chemical modifications (e.g., oxidation or hydroxypropylation) (Lafargue et al., 2007; Wu et al., 2010), incorporation of hydrophobic compounds (e.g., beeswax) (Han et al., 2006), altering pH (Choi et al., 2016), and adding salts (e.g., NaCl) (Choi et al., 2016), have also been developed to produce starch‐based films with enhanced mechanical and barrier properties. In addition, different types of fillers, such as starch nanocrystals and cellulose nano‐whiskers, can reinforce the microstructure of starch films and create a torturous path for water molecules to penetrate, which therefore improves the mechanical and barrier properties of the final film products (Cano, Fortunati, Cháfer, & González‐Martínez et al., 2015; Chen et al., 2009; Farrag et al., 2018; Li, Qiu et al., 2015).…”