This work aimed at developing a thin and water-resistant food-grade poly(vinyl alcohol) (PVOH)-based matrix able to swell when in contact with high moisture content food products without rupturing to release antimicrobial agents onto the food surface. This film was prepared by blending PVOH and 7.20% (wt/wt of PVOH) of poly(ethylene glycol) (PEG) with citric acid as crosslinking agent. The film-forming solution was then casted onto a flat surface and the obtained film was 60 μm in thickness and showed a good transparency (close to T = 100%) in the visible region (400 to 700 nm). After immersion in water for 72 h at room temperature, the crosslinked matrix loses only 19.2% of its original weight (the percentage includes the amount of unreacted crosslinking agent, antimicrobial in itself). Water content, degree of swelling, and crosslinking density of the film prove that the presence of PEG diminishes the hydrophilic behavior of the material. Also the mechanical properties of the wet and dry film were assessed. Alongside this, 2.5% (wt/wt of dry film) of grapefruit seed extract (GSE), an antimicrobial agent, was added to the film-forming solution just before casting and the ability of the plastic matrix to release the additive was then evaluated in vitro against 2 GSE-susceptible microorganisms, Salmonella enteritidis and Listeria innocua. The results indicate that the developed matrix may be a promising food-grade material for the incorporation of active substances.

Hexanal is a natural antimicrobial molecule that characterizes apples aroma. In this paper, the sensory effects of hexanal, as a component of packaging atmosphere, on fresh sliced Golden Delicious apples after storage at 4 °C for 8 d were evaluated. In particular, a colorimetric analysis of slices treated with different concentrations of hexanal vapor (coming from 3.040 to 0.076 mmol of liquid aldehyde per liter of air) fixed at 0.076 mmol/L the amount of hexanal in evaluating sensory effects in the subsequent analysis. Color and texture evaluation of slices by Two-out-of-Five method did not highlight any significant difference between treatment and control. The results from olfactory evaluation showed instead that treated samples had an intense odor compared with those untreated (P < 0.001). A significant difference between treatment and control was also highlighted during the flavor evaluation (P < 0.01); however, from the panelists' observations it emerged that such an effect would work negatively. The positive effect of the tested dose of hexanal on the odor of Golden Delicious slices and its flavor acceptability were verified by using regular apple consumers. A significant preference (P < 0.001) for the odor of treated apple slices came out, so the small dose of hexanal intensifies the odor of apples pleasantly. The different flavor of treated samples was not identified by the consumers, who altogether expressed positive judgments about it. This suggests the nicety of this difference that in the absence of an untreated reference sample is very difficult to detect.

Enzymatic browning is the main cause of quality loss in minimally processed fresh-cut apples and this study was aimed to control it by evaluating the use of a treatment with α-lipoic acid and ascorbic acid on Golden Delicious apples. Also hexanal, an effective natural enhancer of apple odor, was added to the treatment.At the end of the preservation period, colorimetric analysis demonstrated that α-lipoic acid exerts an anti-browning effect comparable with that of ascorbic acid about 60 times more concentrated and, moreover, chemical assays demonstrated its synergistic interaction with this substance. The application of the “anti-browning mix” does not substantially change the volatile profile of the apple slices while the addition of hexanal (0.076 mmol per liter of air) improves it primarily with an increased production of hexyl acetate (about 86% of the average aromatic component), without modifying the fruit respiration.Practical ApplicationsThe combined treatment has proved to be useful to preserve and improve Golden Delicious apples quality over the span of 8 days (1 day more than the average shelf life recommended by many producers for this kind of product).The presence of hexanal makes the treatment very interesting in the context of minimally processed fruit, where apples are used in an early stage of ripening that best tolerates the processing chain but that is characterized by a low volatile biosynthesis.Moreover, the presence of α-lipoic acid gives to the fruit the connotation of “nutraceutical food.