Effect of plasticizer on properties of Mung Bean starch film and its application

Abstract

This research determines the effects of starch concentration (3.5-5.0 %w/w) and plasticizer type and concentration [sorbitol (10-60 %w/w) or glycerol (10-30 %w/w)] on thickness, tensile strength (TS), percent elongation (%E), % solubility, water vapor permeability (WVP), oxygen permeability (OP), seal strength and thermal properties of mung bean starch (MBS) films and to determine the onset of the plasticizer concentration at which film can be formed without cracking. Films were prepared by mixing starch, plasticizer and water and heating at 85 ºC for 30 min. The paste was poured over the acrylic plate, and dried in a hot air oven at 35 ºC for 20 hr. MBS films were translucent. In general, increasing starch concentration significantly increased thickness, decreased % solubilityand WVP but did not affect TS, %E and seal strength of the films at controlled plasticizer type and concentration (p≤0.05). At controlled starch concentration, increasing the plasticizer concentration decreased TS and OP but increased thickness, %E, % solubility, WVP and seal strength (p≤0.05) of films. In this research, glycerol showed better plasticizer efficiency than sorbitol as shown by the onset plasticizer concentration that significantly change TS and %E of MBS film. The onset glycerol concentration for TS and %E were > 10 and > 20 %w/w at all controlled MBS concentration, respectively. The onset sorbitol concentration for TS and %E were > 30 and > 40 %w/w, respectively. Films containing sorbitol had higher TS but lower thickness, %E, WVP, OP and seal strength than films containing glycerol. At 30 %w/w plasticizer concentration, film containing sorbitol had lower %E and seal strength than film containing glycerol. According to differential scanning calorimetry study, MBS films exhibited a single endothermic peak with onset temperature (To) ranged between 48.00-63.50 °C and peak temperature (To) between 59.35-70.05 °C. Films having the glycerol or sorbitol concentration ≤ 10 or ≤ 30 %w/w were brittle. The glycerol or sorbitol concentration of ≥ 20 and ≥ 40 %w/w, respectively, was required to form flexible film for wrapping without breaking. To study the effects of storage condition on physical properties [water activity (aw), moisture content (%MC) and total color differrence (ΔE)] and antioxidant capacity[total phenolic content (TPC), 2,2-diphenyl-1-picrylhydrazyl(DPPH) radical scavenging activity and ferric reducing antioxidant power (FRAP)], dried chili powder which packed inside MBS sachet (5 %w/w starch : 40 %w/w sorbitol) and polypropylene (PP) sachet were stored at 50 % RH and 35, 45 and 55 °C for 50 days. The aw, %MC and ΔE of dried chili powder in all sachets tended to increase over storage time at all temperatures. The kinetics of changes in aw and % MC followed the first-order rate law, while the kinetics of changes in other properties were best fitted by the zero-order model. PP sachet showed a higher moisture barrier ability compared to MBS sachet. The rate constants (k) for changes in color, TPC, DPPH and FRAP of dried chili powder packed in MBS sachets were lower than those packed in PP sachets, except for DPPH at 55 °C. For the effect of storage temperature, TPC, DPPH and FRAP of dried chili powder packed in MBS and PP sachets decreased as the temperature increased. Overall, MBS sachet was a better package for dried chili powder than PP sachet.