Abstract
This study aimed to produce and characterize edible biofilms based on whey protein isolate (WPI). Two formulations were prepared: (1) without and (2) with probiotic Lactobacillus casei. Subsequently, the effect of the biofilms as a fruit cover on the characteristics of Cherry tomatoes and Thompson grapes was evaluated. The films (with or without probiotic culture) were transparent, malleable, homogeneous, continuous and without cracking. In the infrared spectroscopy, characteristic bands of the N-H bonds (protein structure), the amide bonds (1640 to 1560 cm -1) and the C = O and C-N bands were observed. The addition of the probiotic culture had no effect on the density (1.272-1.303 g/cm3) and water vapor permeation (0.28-0.35 g.mm/m2.day.kPa) of the films. However, the film containing probiotic culture was yellowish, thicker (16.18 vs 13.15 µm), more soluble (42.8 vs 34.8%), had higher resistance (higher tensile strength, 23.3 vs 12.6 N) and was less flexible (lower elongation at break, 5.27 vs 45.4%). Scanning Electron Microscopy images evidenced that the probiotic biofilm presented agglomerates in all superficial extension and a higher number of orifices. The L. casei remained viable (5.70 to 7.77 log cfu/g) throughout the storage period of the films (25 oC/28 days), however, recommended counts (> 6 log cfu/g) were observed up to the 14th day. The application of the films did not result in positive impact on the shelf life of the tomatoes but reduced the mass loss and TSS of grapes. The application of the film with probiotic culture resulted in lower TSS values in tomatoes and grapes and higher mass loss in grapes. It can be concluded that the use of WPI originated films with suitable characteristics and could increase the shelf life of grapes. The addition of L. casei resulted in alterations on the mechanical properties of the films and suitable probiotic counts for 14 days, with positive effect on the ripening process of the tomatoes and grapes (lower TSS values).
