Microbial and enzymatic stability of fruit juice-milk beverages treated by high intensity pulsed electric fields or heat during refrigerated storage

The influence of high intensity pulsed electric fields (HIPEF) treatment (35 kV/cm, bipolar 4 μs square wave pulses at 200 Hz) on the inactivation of Listeria innocua in fruit juice–whole (FJ–WM) or skim milk (FJ–SM) beverages was assessed. As well, the effects of HIPEF or conventional thermal (90 °C 60 s) processing in terms of microbial and enzymatic stability and changes on physicochemical parameters of the beverages during refrigerated storage were also studied. HIPEF and thermal processing ensured the microbial stability of the beverages during 56 days at 4 °C without significant changes on pH, acidity and soluble solid content values. Thermal processing was more effective than HIPEF in reducing Pectin Methyl Esterase (PME) activity in FJ–SM and FJ–WM beverages since its activity was reduced by 70.66% and 87.33%, respectively. With regards to Polygalacturonase (PG), HIPEF treatment reduced by 26.92% and 20.93% the enzyme activity in the FJ–WM and FJ–SM beverages, respectively, whereas thermal treatment did not inactivate PG in both beverages. HIPEF or thermally-treated samples showed higher viscosity than the untreated ones, being this increment more pronounced in the beverages with whole milk. Therefore, HIPEF processing may be a feasible technology in order to obtain shelf stable and fresh-like fruit juice-milk beverages.     

Physicochemical Characterization of Lemongrass Essential Oil–Alginate Nanoemulsions: Effect of Ultrasound Processing Parameters

The formation of lemongrass oil (1 %?v/v) nanoemulsions in aqueous sodium alginate solution (1 %?w/v) containing Tween 80 (1 %?v/v) as nonionic surfactant was studied in terms of droplet size, electrical charge, viscosity, and whiteness index considering different ultrasonication times (0, 30, 60, 120, and 180 s) and amplitudes (30, 60, and 100 μm). The droplet size and size distribution of the emulsions decreased at increasing treatment time and amplitude. The minimum average droplet size observed in nanoemulsions was 4.31?±?0.18 nm with a narrow size distribution. The interface electrical charge of the coarse emulsion was ?18.0?±?2.9 mV, whereas in ultrasonicated nanoemulsions, it diminished up to ?55.8?±?6.4 mV when the sonication time was extended for 180 s. The viscosity of nanoemulsions also decreased at increasing treatment time and amplitude. Moreover, nanoemulsions became translucent after sonicating for 180 s at 30, 60, or 100 μm with whiteness indices of 28.61?±?0.17, 27.93?±?0.21, and 27.86?±?0.33, respectively. Therefore, it can be stated that ultrasound processing might be a feasible technology to produce highly translucent lemongrass oil–alginate nanoemulsions, with extremely small droplet sizes and high stability to be used as delivery systems of essential oils in food products. However, it is necessary to investigate the effect of ultrasound processing parameters on the antimicrobial potential of essential oils incorporated to nanoemulsions.     

Physical and structural changes in liquid whole egg treated with high-intensity pulsed electric fields

Liquid whole egg (LWE) is currently pasteurized through the application of heat; however, this treatment entails deleterious effects against some of the functional and technological properties of the product. In this study, the effect of high-intensity pulsed electric fields (HIPEF) processing (field strength: 19, 32, and 37 kV/cm) was compared to the traditional heat pasteurization (66 °C for 4.5 min). Different physical and structural characteristics of LWE, subjected or not to homogenization, were evaluated and compared, having the untreated LWE as a reference. Thermal treatment caused an increase in the viscosity of LWE, especially in nonhomogenized samples. HIPEF treatments did not modify the original color of LWE, whereas thermally treated samples developed an opaque appearance. LWE treated at 19 and 32 kV/cm exhibited a similar foaming capacity as fresh untreated egg, whereas thermal processing and PEF treatments of 37 kV/cm caused a substantial decrease in the foaming capacity of untreated liquid egg. Regarding the microstructure, the lipoprotein matrix appeared to be less affected by the HIPEF than by heat treatment if compared to the control. In addition, heat pasteurization had a significant impact on both the water-soluble protein content of the LWE samples (19.5% to 23.6% decrease) and the mechanical properties of the egg gels (up to 21.3% and 14.5% increase in hardness and cohesiveness, respectively). On the other hand, these parameters were not substantially affected in the HIPEF-treated samples. Heat-induced gels obtained from HIPEF-treated samples did not exhibit remarkable differences in the water-holding capacity (WHC) with respect to heat-pasteurized samples. PRACTICAL APPLICATION: The impact of high-intensity pulsed electric fields (HIPEF) processing on technological properties of liquid-whole egg was investigated and compared to that of thermal processing. Heat treatments cause a severe impact on the foaming capacity, the water-soluble protein content, and the rheological properties of liquid egg samples, whereas HIPEF treatments better preserved the food matrix structure. Microscopic observations support these results, thus suggesting that HIPEF-processing has potential application for the preservation of liquid egg through nonthermal means.     

Impact of high intensity pulsed electric fields or heat treatments on the fatty acid and mineral profiles of a fruit juice–soymilk beverage during storage

Effects of high intensity pulsed electric field (HIPEF) (35 kV/cm with 4 μs bipolar pulses at 200 Hz for 800 and 1400 μs) or thermal (90 °C for 60 s) treatments on fatty acid and mineral profiles of a fruit juice-soymilk (FJ–SM) beverage during storage (56 days) at 4 °C were evaluated, having the just prepared beverage as a reference. Linoleic, oleic, linolenic, palmitic and stearic acids were found at highest concentration in the FJ–SM beverages; whereas, Ca and Mg were identified as the most abundant minerals, irrespectively of the treatment applied. Initial concentration of most fatty acids and minerals was not affected by HIPEF or thermal processes; only elaidic and linoleic acid concentration decreased after HIPEF or heat treatments, and Fe and Zn content was significantly enhanced in HIPEF beverages. Along the storage, total fatty acid content showed a significant increase in untreated and treated beverages; whereas minerals remained highly stable. Nevertheless, HIPEF beverages always showed higher concentration of fatty acids and minerals than those heat processed. Hence, HIPEF could be a potential alternative to obtain FJ–SM beverages with a long shelf-life and elevated amounts of health related compounds.     

Aroma profile and volatiles odor activity along gold cultivar pineapple flesh

Physicochemical attributes, aroma profile, and odor contribution of pineapple flesh were studied for the top, middle, and bottom cross-sections cut along the central axis of Gold cultivar pineapple. Relationships between volatile and nonvolatile compounds were also studied. Aroma profile constituents were determined by headspace solid-phase microextraction at 30 °C, followed by gas chromatography/mass spectrometry analysis. A total of 20 volatile compounds were identified and quantified. Among them, esters were the major components which accounted for 90% of total extracted aroma. Methyl butanoate, methyl 2-methyl butanoate, and methyl hexanoate were the 3 most abundant components representing 74% of total volatiles in pineapple samples. Most odor active contributors were methyl and ethyl 2-methyl butanoate and 2,5-dimethyl 4-methoxy 3(2H)-furanone (mesifuran). Aroma profile components did not vary along the fruit, but volatile compounds content significantly varied (P < 0.05) along the fruit, from 7560 to 10910 μg/kg, from the top to the bottom cross-sections of the fruit, respectively. In addition, most odor-active volatiles concentration increased from the top to the bottom 3rd of the fruit, concurrently with soluble solids content (SSC) and titratable acidity (TA) differences attributed to fruitlets distinct degree of ripening. Large changes in SSC/TA ratio and volatiles content throughout the fruit found through this study are likely to provoke important differences among individual fresh-cut pineapple trays, compromising consumer perception and acceptance of the product. Such finding highlighted the need to include volatiles content and SSC/TA ratio and their variability along the fruit as selection criteria for pineapples to be processed and quality assessment of the fresh-cut fruit.     

Alginate- and gellan-based edible films for probiotic coatings on fresh-cut fruits

ABSTRACT:  Alginate- (2% w/v) or gellan-based (0.5%) edible films, containing glycerol (0.6% to 2.0%), N-acetylcysteine (1%), and/or ascorbic acid (1%) and citric acid (1%), were formulated and used to coat fresh-cut apple and papaya cylinders. Water vapor permeability (WVP) was significantly higher ( P < 0.05) in alginate films (0.30 to 0.31 × 10⁻⁹g m/Pa s m²) than in the gellan ones (0.26 to 0.27 × 10⁻⁹g m/Pa s m²). Addition of 0.025% (w/v) sunflower oil decreased WVP of gellan films (0.20 to 0.22 × 10⁻⁹ g m/Pa s m²). Water solubility of gellan and alginate films at 25 °C (0.47 to 0.59 and 0.74 to 0.79, respectively) and their swelling ratios (2.3 to 2.6 and 1.6 to 2.0, respectively) indicate their potential for coating high moisture fresh-cut fruits. Fresh-cut apple and papaya cylinders were successfully coated with 2% (w/v) alginate or gellan film-forming solutions containing viable bifidobacteria. WVP in alginate (6.31 and 5.52 × 10⁻⁹g m/Pa s m²) or gellan (3.65 and 4.89 × 10⁻⁹ g m/Pa s m²) probiotic coatings of papaya and apple, respectively, were higher than in the corresponding cast films. The gellan coatings and films exhibited better water vapor properties in comparison with the alginate coatings. Values > 10⁶ CFU/g B. lactis Bb -12 were maintained for 10 d during refrigerated storage of fresh-cut fruits, demonstrating the feasibility of alginate- and gellan-based edible coatings to carry and support viable probiotics on fresh-cut fruit.     

Mechanical and chemical properties of Gold cultivar pineapple flesh (Ananas comosus)

Pineapple flesh cut from three cross sections along the central axis were used to determine mechanical response to compression, penetration, shear and extrusion forces, color and related enzymes activity, antioxidant properties and other quality attributes and how they vary along the central axis of the fruit to determine the key factors to define Gold cultivar pineapple quality requirements for fresh-cut processing. Hardness, fracturability and associated work did not significantly vary among fruit pieces from different sections of the fruit, except for shear hardness (from 6.5 ± 1.2 to 10.0 ± 3.5 N) and related work (from 19 ± 6 to 41 ± 24 N mm). Color parameters, L*and b*, increased from the bottom to the upper third, while a* and POD activity (6.70 ± 0.15 to 6.02 ± 0.11/min/mL) significantly decreased while PPO activity was not detected. Vitamin C and total phenol content to acidity ratio were lower in the upper third of the fruit (305 ± 40 mg/100 g_fw and 40.3 ± 1.0 mg _{gallic acid}/100 g_fw, respectively), contrary to titratable acidity (0.45 ± 0.05 to 0.70 ± 0.05 g/100 g_fw) and water content (81.2 ± 0.8 to 85.7 ± 1.4%). POD activity, water content, total phenolic compounds and the ratio soluble solids to acidity were the four parameters which allowed better discrimination between Gold cultivar pineapple flesh cut from the three cross sections along the central axis of the fruit and showed the highest correlation coefficients between each pair of parameters.     

Comparative study on essential oils incorporated into an alginate-based edible coating to assure the safety and quality of fresh-cut Fuji apples

Cinnamon, clove, and lemongrass essential oils (EOs) and their active compounds cinnamaldehyde, eugenol, and citral, respectively, were investigated for their effectiveness as antimicrobial agents in an alginate-based edible coating (EC) on fresh-cut Fuji apples. This EC also contained malic acid, N-acetyl-L-cysteine, glutathione, and calcium lactate as quality stabilizing compounds. The EC applied on apple pieces effectively maintained the physicochemical characteristics of the apple pieces for more than 30 days, decreased the respiration rate, reduced the Escherichia coli O157:H7 population by about 1.23 log CFU/g at day 0, and extended the microbiological shelf life by at least 19 days. The addition of EOs at 0.7% (vol/vol) or their active compounds at 0.5% (vol/vol) into the EC increased its antimicrobial effect, reduced the E. coli O157:H7 population by more than 4 log CFU/g, and extended the microbiological shelf life by more than 30 days. However, those concentrations of EOs affected the physicochemical characteristics of fresh-cut apples and thus limited their shelf life from 7 to 21 days. Lemongrass and cinnamon EOs (0.7%), citral (0.5%), and cinnamaldehyde (0.5%) were the most effective compounds for extending microbiological shelf life, whereas lemongrass, cinnamon, and clove EOs at 0.3% (vol/vol) best maintained the physicochemical characteristics of the product. Apple pieces with EC at day 0 and with EC with or without lemongrass EO at 0.7% at day 15 were preferred by the panelists. ECs containing natural antimicrobials and quality stabilizing compounds may be useful for extending the shelf life of fresh-cut fruits.     

Quality changes in fresh-cut Fuji apple as affected by ripeness stage, antibrowning agents, and storage atmosphere

ABSTRACT:  The effect of ripening state, modified atmosphere, and the use of antibrowning agents was investigated in an attempt to determine optimum ripeness and processing conditions for extending the shelf-life of fresh-cut Fuji apple. Apples were classified in 3 groups: mature-green, partially ripe, and ripe; after peeling and slicing, fruits were treated with 1% (w/v) N -acetylcysteine, or 1% (w/v) ascorbic acid (control), and then packed into polypropylene trays with air or a gas mixture (2.5% O₂+ 7% CO₂+ 90.5% N₂) and sealed. Trays containing the apple slices were stored in darkness at 4 °C ± 1 °C and analyzed periodically during 43 d. Changes in atmosphere composition, color, and firmness were examined. Partially ripe apples, based on their lower ethanol production and maintenance of their original color and firmness, were the most suitable to prepare the fresh-cut commodities. A postcutting dip in 1% (w/v) N -acetylcysteine was the most effective treatment to prevent cut surface browning and preserve the initial appearance of Fuji apple slices during more than 1 mo at 4 °C. Low O₂ and elevated CO₂ (2.5% O₂+ 7% CO₂) atmosphere extended the shelf life of apple slices because of a significant inhibition of ethylene production.