Development of Gelatin/Polyvinyl Alcohol Films Incorporated with Blueberry Extracts for Freshness Detection of Shrimp

The objective of this study was to evaluate the physical, chemical, mechanical, thermal, and topological properties of polyvinyl alcohol (PVA) and gelatin (GL) films after incorporating three different fractions of blueberry extract: crude extract (EB, without purification), phenolic portion (EF), and concentrated anthocyanins (EA). Additionally, the study aimed to analyze the efficiency of these colorimetric indicator films in monitoring the freshness quality of shrimp. The experiment followed a completely randomized design with one factor-different types of films-studied at six levels: film incorporated with crude blueberry extract (FB), film incorporated with phenolic extract (FF), and film incorporated with anthocyanin extract (FA), in addition to the control films: the plasticized blend containing glycerol, PVA, and GL (FC), the pristine gelatin film (FG), and the pristine PVA film (FPVA). To evaluate the colorimetric sensitivity of the indicators applied to shrimp, storage time was studied at two levels: T0 (before storage-on the day of collection) and T7 (after 7 days of storage at 6.5 ± 1 °C) for the FB and FA films. Regarding thermal properties, the degradation profile occurred in three stages, with the FC film being the most thermally stable. In terms of mechanical behavior, the isolated anthocyanin content increased the elasticity of FA, while the crude extract and other phenolic compounds contributed to the stiffness of FB (Young's modulus, YM = 22.52) and FF (YM = 37.33). Structurally, the FC film exhibited a smooth and well-blended polymeric surface, whereas FF, FB, and FA displayed heterogeneous and discontinuous phases. The incorporation of blueberry extracts reduced water absorption, leading to decreased swelling and solubility. FF showed the lowest solubility (S = 16.14%), likely due to hydrogen bonding between phenolic compounds and the polymer matrix. Notably, FB demonstrated superior physical, chemical, and mechanical performance, as well as the highest thermal stability among the extract-containing films. It also showed a visible color change (from purple to green/brown) after 7 days of shrimp storage, corresponding with spoilage and pH values unsuitable for consumption. Both FA and FB effectively monitored shrimp freshness, offering a sustainable approach to quality assurance and food waste reduction. Among them, FB was the most practical for visual detection. Overall, these films demonstrated strong potential as pH-sensitive indicators for evaluating the freshness of shrimp.