Abstract
The growing demand for minimally processed foods with a long shelf life and environmentally friendly materials has forced industry to develop new technologies for food preservation and handling. The use of edible films has emerged as an alternative solution to this problem, and mixtures of carbohydrates and proteins, may be formulated to improve their properties. The objective of this work was to evaluate the effect of protein cross-linking with transglutaminase (TG) of two varieties of quinoa protein isolate (Chenopodium quinoa) [Willd (QW), and Pasankalla (QP)] on the physicochemical and barrier properties of edible films based on chitosan (CT)-quinoa protein. The evaluated properties were water vapor permeability (WVP), solubility, adsorption, roughness determined by atomic force microscopy, and the interactions among the main film components determined by Raman spectroscopy. The results indicated that TG interacted with lysine of QW and QP. CT:QW (1:5, w/w) showed the lowest solubility (14.02 ± 2.17% w/w). WVP varied with the composition of the mixture. The WVP of CT:quinoa protein ranged from 2.85 to 9.95 × 10−11 g cm Pa−1 cm−2 s−1 without TG, whereas adding TG reduced this range to 2.42–4.69 × 10−11 g cm Pa−1 cm−2 s−1. The addition of TG to CT:QP (1:10, w/w) reduced the film surface roughness from 8.0 ± 0.5 nm to 4.4 ± 0.3 nm. According to the sorption isotherm, the addition of TG to CT-QW films improved their stability [monolayer (Xm) = 0.13 ± 0.02 %]. Films with a higher amount of cross-linking showed the highest improvement in the evaluated physical properties, but interactions among proteins that were catalyzed by TG depended on the protein source and profile.
Highlights
Edible films and coatings have attracted great interest due to their ability to preserve the quality and safety of foods, maintaining their flavor, color, and nutritional value during storage [1]
Duodenal simulated digestion with trypsin and chymotrypsin led to full protein hydrolysis (Figure 7e,f). These results indicate that, depending on the quinoa protein variety used to produce the films, partial or insignificant gastric hydrolysis was completed upon duodenal digestion
Cross-linking with TG allowed for the enhancement of edible film properties; interactions among protein and TG depended on the quinoa protein variety in combination with its protein profile
Summary
Edible films and coatings have attracted great interest due to their ability to preserve the quality and safety of foods, maintaining their flavor, color, and nutritional value during storage [1]. Edible films that are based on proteins are transparent and show good gas barrier properties; the most popular are zein, collagen, whey protein concentrate or isolate, wheat gluten, egg white protein, myofibrillar protein, keratin, and quinoa protein [3]. Quinoa protein concentrate has been used in edible films to extend the shelf life of food products, showing good extensibility due to its plasticizing effect [5]. These films display good mechanical properties, but poor water vapor barrier, lipids have been incorporated into the matrix. Lipids have demonstrated an adverse effect on mechanical properties [6] and, for this reason, some studies have focused on chitosan-quinoa protein mixtures, since chitosan (CT) allows the formation of hydrogen bonds and other intermolecular interactions with quinoa protein producing films with enhanced mechanical properties [5]
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