This research aimed to evaluate the effects of formulation and process conditions on the physical and structural properties of starch–brewers’ spent grain films. Three factors were considered: BSG amounts (0, 1, 3, 5%), a possible ultrasonication pre-treatment, and different microwave gelatinization treatments (450 W for 80 and 90 s; 900 W for 45 and 50 s). An increase in BSG is responsible for increases in moisture (10. 72 → 23. 40%), water absorption (67. 65 → 95. 73%), density (0. 90 → 1. 27 g/cm3), browning index (5. 86 → 85. 88), UV blocking capacity (82. 42% → 99. 96% for UVA; 61. 28% → 99. 86% for UVB), and degradability in the first 7 days (58. 72 → 66. 57%), but dramatically decreases the Young’s modulus and tensile strength (fallen to 2. 90 N/mm2 and 0. 21 N/mm2, at 5% BSG). Sonication contributes to increased browning index (36. 17 → 37. 24), UV blocking capacity, solubility (49. 35 → 51. 49%) and Young’s modulus (4. 40 → 4. 77 N/mm2). The most severe microwave treatment (900 W, 50 s) minimizes moisture (15. 83%) and water absorption (80. 89%) and maximizes density (1. 21 g/cm3), browning index (37. 52), and Young’s modulus (5. 37 N/mm2). SEM micrographs allow us to observe that the film surface appears rough, and the structure becomes increasingly porous as BSG % increases. The regression analysis indicates that the quadratic model effectively describes the relationships between the three factors and each of the most important properties of the films; it is suitable for predicting film behavior and optimizing their characteristics depending on the desired use.
Baiano et al. (Thu,) studied this question.