Application of high pressure-thermal treatment (600 MPa and 70 °C, 20 min) for obtaining edible films functionalized with thyme extracts have been studied in order to evaluate the antimicrobial capacity of films structure to retain and release the bioactive compounds. The high pressure-thermally treated films (HPT) were compared with the thermally treated (TT) ones (80 ± 0.5 °C, 35 min). The film structures were analyzed and the sorption isotherms, water vapor permeability, antimicrobial activity and the volatile fingerprints by GC/MS were performed. The HPT film presented more binding sites for water chemi-sorption than TT films and displayed significantly lower WVP than TT films (p < 0.05). TT films displayed slightly, but significant higher, antimicrobial activity (p < 0.05) against Geotrichum candidum in the first day and against Bacillus subtilis in the 10th day of storage. The HPT film structure had ~1.5-fold higher capacity to retain volatiles after drying compared to TT films. From the HPT films higher amount of p-cymene and α-terpinene was volatilized during 10 days of storage at 25 °C, 50% RH while from the TT films higher amount of caryophyllene and carvacrol were released. During storage HPT films had a 2-fold lower capacity to retain monoterpenes compared to TT films.
This study has investigated the inactivation of polyphenoloxidase (PPO) in peach puree during thermal (50–60 °C, 2–30 min) and combined high pressure‐mild thermal treatment (HPMT) (200–600 MPa, 25–45 °C, and 2–23 min). HPMT resulted immediately after treatment in an increase in PPO activity up to 66.50% at 200 MPa and 45 °C compared with the untreated samples. The reaction order (nth) of PPO thermal inactivation was 1.951 (0.1 MPa, 50–60 °C) and 0.953 for the HPMT treatment (200–600 MPa, 25–45 °C). Fractional kinetic models were applied in PPO thermal (~89% labile fraction, 11% stabile fraction) and HPMT inactivation (up to ~67% stabile fraction at 200 MPa, 25 °C). The activation energy estimated for the thermal inactivation in 50–60 °C range at 0.1 MPa was 148.26 kJ/mol, while for the HPMT inactivation varied from 82.31 kJ/mol at 300 MPa to 226.16 kJ/mol at 500 MPa. A third order polynomial model described the PPO inactivation by HPMT.
Practical application
Inactivation of polyphenoloxidase (PPO), enzyme responsible for browning is a mandatory condition for maintaining quality of the processed fruits. As this enzyme is generally known to display variable thermal and/or barostability, depending on the type of food matrix, kinetic data are required to optimize the processing parameters. The data on peach puree PPO and the models provided in the current study could help producers to identify the optimum peach processing condition necessary for the inactivation of PPO by high pressure‐mild thermal treatment, leading to the extension of puree shelf life. However, methods for limitation of the oxygen presence in the peach puree mixtures should also be employed during processing and storage.
Whey edible films (EFs) functionalized with essential oils have a high potential to be used on various foods due to their antimicrobial and antioxidant activities. Encapsulation is applied for a better retention of volatiles in EFs; however, the functional properties of EFs are modified. The properties of EFs containing thyme essential oil (TEO) encapsulated by co-precipitation in β-CD, developed in three formulae, with inclusion complexes (EF/IC1, EF/IC2, and EF/IC3, respectively) in 15:85, 26:74, and 35:65 mass ratios were studied. Thymol is the main volatile in the ICs with TEO/β-CD (50%–60% of the total volatiles). In comparison with EF/TEO, all three formulae with EF/ICs had better, but similar, WVPs (p > 0.05). The EF/IC2 displayed a different FTIR profile than EF/IC1 and EF/IC3, suggesting a smaller number of free functional groups. The EF/IC2 showed better transparency in comparison with EF/IC1 and EF/IC3. All EF/ICs moderately inhibited R. glutinis, with the strongest activity registered by EF/IC3 (p < 0.05), but did not inhibit G. candidum, while showing a strong antibacterial activity against B. cereus. All EF/ICs inhibited 65%–70% of the total free radicals. The EF/ICs ensured a gradual release of VOCs in food simulants, with a higher rate in 95% ethanol than in water. These results have demonstrated the properties of EF/ICs with TEO/β-CD as bioactive packaging systems for foods.
Edible coatings are important for horticulture crops preservation and reducing food waste. Application of edible coatings followed by low-temperature storage prolongs the storability, preserves quality, and decreases the overall postharvest losses. This study evaluated the efficacy of two nanoemulsions formulae containing thyme essential oil and whey proteins as coatings for zucchini, with the purpose of extending their shelf-life. The nanoemulsions were rheologically evaluated and the formula with guar and arabic gum mix stabilizer (S) showed a better capacity to restructure after strain compared to the formulae with Tween 20 (T). The S coating material had a better capacity to integrate nanoparticles compared to T. However, when applied on zucchini, T coating was more effective in reducing weight loss showing 16% weight loss compared to 21% in S, after 42 days. At the end of storage at 10 °C, the T-coated zucchini had better firmness (p < 0.05) compared with S and both coatings were superior to control (p < 0.05). POD (peroxidase) activity was high in peel at the end of storage when also CAT (catalase) showed a sudden increase. On the 42nd day of storage, the highest enzymes activity (CAT, POD, and APX (ascorbate peroxidase)) was present in the S-coated zucchini peel. The most abundant volatile in T coating was α-pinene and 4-carene in S. Sensory analysis showed that T coating delayed the appearance of senescence while S exhibited surface cracks.
A bottom-up approach identifying equivalent effects of high-pressure processing (HPP—600 MPa, 20 °C, 10 min), thermal treatment (TT—70 °C, 15 min) and high pressure-mild thermal processing (HPMT—600 MPa, 50 °C, 10 min) on quality and stability of peach–strawberry puree was applied during refrigerated storage. TT and HPP ensured 3-log aerobic bacteria inactivation at first, while HPMT reduction was below the detection limit. After 21 days all samples had equivalent microbiological stability. A 2.6-fold increase in the residual activity of PPO and POD was found in the HPP sample compared to TT and HPMT samples (1st day); after 21 days PPO, POD and TPC were equivalent for TT and HPP peach–strawberry purees. Equivalent volatile profile and rheology behavior was observed after 21 days of all samples’ storage. Meanwhile, the color of the HPP, TT and HMPT samples remained significantly different (p < 0.05) throughout the whole storage period, with the lowest browning index registered for HPP samples.
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