Polyphenol oxidase activity,phenolic acid composition and browning in cashew apple (Anacardium occidentale, L.) after processing

This study describes the extraction and characterisation of cashew apple polyphenol oxidase (PPO) and the effect of wounding on cashew apple phenolic acid composition, PPO activity and fruit browning. Purification factor was 59 at 95% (NH₄)₂SO₄ saturation. For PPO activity, the optimal substrate was catechol and the optimum pH was 6.5. PPO K_m and V_max values were 18.8 mM and 13.6 U min⁻¹ ml⁻¹, respectively. Ascorbic acid, citric acid, sodium sulphite and sodium metabisulphite decreased PPO activity, while sodium chloride increased PPO activity. Wounding at 2 °C and 27 °C for 24 h increased PPO activity but storage at 40 °C reduced PPO activity. Gallic acid, protocatechuic acid and cinnamic acid (free and conjugate) were identified in cashew apple juice. Cutting and subsequent storage at 40 °C hydrolysed cinnamic acid. 5-Hydroxymethylfurfural content in cashew apple juice increased after injury and storage at higher temperatures, indicating non-enzymatic browning.     

Kinetic characterisation and thermal inactivation study of polyphenol oxidase and peroxidase from table grape (Crimson Seedless)

Polyphenol oxidase (PPO) and peroxidase (POD) were extracted from a table grape (Crimson Seedless) using Triton X-114 and characterized using spectrophotometric methods. Both PPO and POD were activated by acid shock. However, in the presence of the anionic detergent sodium dodecil sulphate (SDS), PPO was activated whereas POD was inactivated. The enzymes were kinetically characterized and both followed Michaelis–Menten kinetics, although with different values of their kinetic parameters. The V_m/K_m ratio showed that Crimson Seedless grape PPO presents a similar affinity for 4-tert-butyl-catechol (TBC) whether activated by acid shock (0.018 min⁻¹) or SDS (0.023 min⁻¹). With regards to POD, the K_m and V_m values for 2,2′-azinobis(3-ethylbenzothiazolinesulphonic acid) (ABTS) were 0.79 mM and 1.20 μM/min, respectively. In the case of H₂O₂, the K_m and V_m value were 0.4 mM and 0.93 μM/min, respectively. PPO and POD showed similar thermostability, losing >90% of relative activity after only 5 min of incubation at 78 °C and 75 °C, respectively. In addition, PPO´s activation energy was similar to that obtained for POD (295.5 kJ/mol and 271.9 kJ/mol, respectively).     

Changing soybean isoflavone composition and concentrations under two different storage conditions over three years

Soybean in Asia have been consumed in various forms, including soymilk, tofu and fermented products such as miso, temph and sufu. It is popularly regarded as a healthy food, partly owing to the isoflavones contained in their seeds. The objective of this study was to evaluate the variation of isoflavone concentration in soybean (Glycine max (L.) Merrill) seeds under different storage conditions for long storage periods. Isoflavone concentrations varied from 699.7 to 2581.6 μg g⁻¹ with cropping year, and acetylglucoside groups and glycitein were only detected in small amounts or traces in the eight soybean cultivars. The Daweon cultivar showed a variation between storage at room (−2039.0 μg g⁻¹) and low temperature (−1822.0 μg g⁻¹) over three years, while the isoflavone concentration in the Hannam cultivar only varied slightly (room temperature: −91.6 μg g⁻¹, low temperature: −81.2 μg g⁻¹). With storage at room temperature, the acetylglucoside group (+7.2 μg g⁻¹) slightly increased the isoflavone concentration, while the other three groups decreased it. In particular, the malonylglucoside group (−519.0 μg g⁻¹) showed a severe decrease. In the Myeongjunamul cultivar, genistin (+105.0 μg g⁻¹) resulted in the highest increase, while malonylgenistin (−958.7 μg g⁻¹) resulted in the greatest decrease in the Daweon cultivar. With storage at low temperature, other than malonylglucoside (−438.1 g g⁻¹), the other three groups, aglycon (+11.4 μg g⁻¹), glucoside (+45.2 μg g⁻¹) and acetylglucoside (+12.8 μg g⁻¹), increased the isoflavone concentration. Genistin (+136.0 μg g⁻¹) in the Muhan cultivar showed the highest increase, and malonylgenistin (−833.4 μg g⁻¹) in the Daweon cultivar showed the greatest decrease for storage under low temperature for three years. The variation of isoflavone concentration was positively correlated with the two different storage conditions (r² = 0.33), and total isoflavones were correlated with the concentration of the malonylglucoside (r² = 0.88***) and glucoside (r² = 0.80***) groups. Our study suggests that it may be feasible to improve the preservation method of soybean isoflavones as high functional substances for longer storage periods.     

Behaviour of Listeria monocytogenes and Staphylococcus aureus in sliced,vacuum-packaged raw milk cheese stored at two different temperatures and time periods

The behaviour of Listeria monocytogenes and Staphylococcus aureus in raw milk cheese slices packaged under vacuum was evaluated. Artificially contaminated 80-day ripened cheese was portioned, vacuum packaged, and then stored for 28 days at 4 °C and for 56 days at 10 °C. Bacterial counts were obtained before vacuum packaging and then weekly during storage. At the end of ripening, the initial L. monocytogenes count was 4.46 ± 0.89 log cfu g⁻¹; weekly bacterial counts remained substantially unchanged in the samples stored at 4 °C but decreased to 3.54 ± 1.54 log cfu g⁻¹ in those stored at 10 °C. The initial S. aureus count before vacuum packaging was 3.60 ± 0.78 log cfu g⁻¹; it then gradually decreased to 2.60 ± 1.32 log cfu g⁻¹ in the samples stored at 4 °C and to about 1.9 log cfu g⁻¹ in those stored at 10 °C.     

Identification and quantification of phenolic compounds in kernels,oil and bagasse pellets of common walnut (Juglans regia L.)

Individual phenolic compounds, total phenolic content and antioxidant potential were assessed in kernels, oils and bagasse pellets (residues of oil pressing) of different walnut cultivars. Twenty-seven phenolic compounds were detected in kernels and pellets conducting high-performance liquid chromatography–tandem mass spectrometry. The main polyphenolic subclass comprised hydrolysable tannins, which accounted approximately 60.80% (kernels) and 61.66% (pellets) of the total phenolics identified (TPI). Walnut oil was poor in phenolics and contained only six different compounds but due to their low content (from 0.15 to 1.44 μg g^− 1) just two compounds have been identified. Glansreginin A and glansreginin B were detected in all analyzed walnut products. A comparison of average amount of total phenolic content revealed that walnut oil contains as much as 154 fold less phenolics (0.05 mg GAE g^− 1 FW) compared to kernels (7.7 mg GAE g^− 1 FW) or pellets (7.9 mg GAE g^− 1 FW).     

Identifying critical parameters for extraction of carnosine and anserine from chicken meat with high voltage pulsed electric fields and water

Carnosine (β-alanyl-L-histidine) and its methylated counterpart anserine (β-alanyl-1-methylhistidine) are important functional dipeptides found in various vertebrates' tissues. In this study, we identified the critical parameters of pulsed electric fields (PEF), coupled to mechanical pressing, followed by incubation in water up to 240 min for the extraction of these bioactive dipeptides from chicken meat. We show that PEF improves the kinetics of anserine and carnosine release to water by 7 to 53%, compared to the same water extraction process without PEF when the incubation time is below 120 min. A fractional factorial design showed that the incubation time in the water, after PEF pretreatment, had the most significant effect on dipeptides extraction. The maximum achieved total protein yield was 15.5 mg g_{fresh weight(FW)} ^-1 after 120 min incubation in water. The maximum carnosine extraction yield was 7.48 mg g_FW⁻¹ with a maximum anserine extraction yield of 3.05 mg g_FW⁻¹. The specific energy yield of extraction of protein, carnosine, and anserine was 488.16 mg J⁻¹, 39.43 mg J⁻¹, and 131.63 mg J⁻¹ respectively. The developed method is scalable and could be further explored to extract bioactive compounds from animal tissues.     

Effect of gutting on microbiological,chemical, and sensory properties of aquacultured sea bass (Dicentrarchus labrax) stored in ice

The effect of gutting on microbiological, chemical, and sensory properties of aqua-cultured sea bass (Dicentrarchus labrax) stored in ice was studied. Pseudomonads and H₂S-producing bacteria (including Shewanella putrefaciens) were the dominant bacteria at the end of the 16-day storage period in ice for both whole ungutted and gutted sea bass. Brochothrix thermosphacta and Enterobacteriaceae were also found in the spoilage microflora of ungutted and gutted sea bass but their counts were always less than those of Pseudomonads and H₂S-producing bacteria. Bacterial counts of whole ungutted sea bass were always higher than those obtained for gutted sea bass samples. Mesophilic counts for gutted and ungutted fish exceeded 7 log cfu g⁻¹ after 9 and 15 days of ice storage, respectively. Of the chemical indicators of spoilage, TMA values of ungutted sea bass increased very slowly whereas for gutted samples higher values were obtained reaching a final value of 0.73 and 4.39 mg N 100 g⁻¹, respectively (day 16). TVB-N values showed no significant increase for whole ungutted sea bass during storage reaching a value of 27.7 mg N 100 g⁻¹ (day 16) whereas for gutted fish 36.9 mg N 100 g⁻¹ was recorded. TBA values remained low for ungutted sea bass samples until day 16 of storage, whereas for gutted fish were variable. Of the chemical indices used, none proved useful means of monitoring early ungutted and gutted sea bass freshness in ice. Sensory assessment using the EC freshness scale gave a grade E for up to 5 days for the ungutted sea bass, a grade A for a further 2 days and a grade B for an additional 4 days, after which sea bass was graded as C (unfit). Gutted sea bass was given a grade E for up to 3 days, a grade A for the 4–7th days, and a grade B for the 8–10th days of storage, whereas on day 11 it was graded as unfit. Acceptability scores for odor, taste and texture of cooked ungutted and gutted sea bass decreased with time of storage. Results of this study indicate that the shelf-life of whole ungutted and gutted sea bass stored in ice as determined by the overall acceptability sensory scores and microbiological data is 13 and 8 days, respectively.     

Inactivation kinetics of peroxidase and polyphenol oxidase in peach juice treated with gaseous ozone

The effectiveness of gaseous ozone for inactivating peroxidase (POD) and polyphenoloxidase (PPO) in peach juice was investigated. The suitability of first‐order and Weibull models to describe inactivation kinetics was also analysed. Peach juice was exposed to ozone (0.11 and 0.20 mg O₃ min^?1 mL^?1) in a bubble column up to 12 min at 20 ± 1 °C. Enzyme activities were reduced due to treatments. The magnitude of the inactivation increased with ozone level and exposure time. Reductions in activity after 12 min of treatment ranged between 99.5% and 99.8% for POD and between 93.9% and 97.3% for PPO, depending on ozone concentration. Inactivation curves were successfully fitted with the first‐order and Weibull models; although, based on the root‐mean‐square error, the corrected Akaike and the Bayesian Schwarz criterion, the Weibull model showed stronger capability in all cases.     

Pasteurization of tender coconut water by pulsed light treatment: Microbial safety,enzymatic inactivation,and impact on physicochemical properties

The study investigated the potential of pulsed light (PL) in the pasteurization of tender coconut water (TCW). The initial counts of E. coli, B. cereus and L. monocytogenes in the inoculated TCW were 7.00, 9.14 and 7.8 log₁₀ cfu mL⁻¹, respectively. For a PL fluence of 465 J cm⁻², E. coli, B.cereus and L. monocytogenes exhibited a log reduction of 5.12, 2.97 and 3.40, respectively. Bacillus cereus and Listeria monocytogenes exhibited greater resistance than Escherichia coli in the TCW. Peroxidase (POD) was more sensitive to PL treatments than polyphenoloxidase (PPO) in TCW. Weibull model and n^th order model exhibited excellent fit for microbial inactivation (R² > 0.96) and enzyme inactivation (R² > 0.97) kinetics, respectively. While 5-log₁₀ reduction of B. cereus and L. monocytogenes was achieved at 2.5 kV|2.5 min (1073 J cm⁻²), PPO was inactivated by greater than 99% at 2.9 kV| 5 min (2988 J cm⁻²). While the total reducing sugars increased, the changes in color (0.49 < ΔE* < 1.51), pH, total soluble solids, and acidity were insignificant after the PL pasteurization. The PL condition of 2.9 kV|5 min preserved 21 and 24% more phenolics and ascorbic acid in TCW, along with greater sensory scores than the thermal treatment (90 °C|3 min).Industrial significanceThe outcome of this study determined the intensity (fluence of 2988 J/cm²) and penetration depth (4–5 mm) required for the pasteurization of tender coconut water (TCW). On an industrial scale of large processing volumes, continuous pulsed light (PL) pasteurization of TCW can be undertaken in an annular flow reactor or thin film flat bed chamber. The thickness of the film can be mimicked from this study to ensure adequate penetration of PL in the sample to achieve adequate lethality.     

Effects of plasma-activated water on microbial growth and storage quality of fresh-cut apple

Fresh-cut ‘Fuji’ apples were immersed for 5 min in plasma-activated water (PAW) generated, by plasma generated with sinusoidal voltages at 7.0 kHz with amplitudes of 6 kV, 8 kV, and 10 kV, designated PAW-6, PAW-8, and PAW-10, respectively. The control group was soaked in distilled water for 5 min instead of PAW. The results indicated that the growth of bacteria, molds, and yeasts was inhibited by PAW treatments during storage at 4 ± 1 °C, especially the microbial inactivation with PAW-8, which was the most efficient. PAW-8 reduced the microbial counts by 1.05 log₁₀CFU g⁻¹, 0.64 log₁₀CFU g⁻¹, 1.04 log₁₀CFU g⁻¹ and 0.86 log₁₀CFU g⁻¹ for aerobic bacteria (aerobic plate counts), molds, yeasts and coliforms on day 12, respectively. In addition, the bacterial counts of fresh-cut apples treated with PAW were <5 log₁₀CFU g⁻¹, which did not exceed to the existing China Shanghai local standard (DB 31/2012–2013) during 12 days of storage. PAW treatments reduced superficial browning of fresh-cut apples without affecting their firmness and titratable acidity. In addition, no significant change was observed in antioxidant content and radical scavenging activity between the PAW-treated and control groups. It is suggested that PAW is a promising method for preservation of fresh-cut fruits and vegetables, which is usually beneficial to the quality maintenance of fresh-cut fruits and vegetables during storage.     

Production of volatile aroma compounds by kefir starter cultures

Production of carbonyl compounds by single-strain cultures, kefir starter (Lactobacillus delbrueckii subsp. bulgaricus HP1+Lb. helveticus MP12+Lactococcus lactis subsp. lactis C15+Streptococcus thermophilus T15+Saccharomyces cerevisiae A13) and kefir grains during fermentation and storage of kefir was studied. The content of carbonyl compounds produced by kefir starter was greater than that produced by kefir grains. The maximum acetaldehyde concentration (18.3 μg g⁻¹) in kefir with starter culture was mainly due to the metabolic activity of Lb. delbrueckii subsp. bulgaricus HP1 isolated from kefir grains. The highest diacetyl production activity was recorded in the starter culture (1.87 μg g⁻¹) and the single-strain culture St. thermophilus T15 (1.62 μg g⁻¹), followed by Lb. helveticus MP12 (0.85 μg g⁻¹) and Lc. lactis subsp. lactis C15 (0.42 μg g⁻¹). The lactobacilli Lb. delbrueckii subsp. bulgaricus HP1 and Lb. helveticus MP12 produced acetone, which was not found in the cocci cultures. The presence of 2-butanone was related to the production ability of Lb. helveticus MP12. In comparison, Lc. lactis subsp. lactis C15 synthesized ethyl acetate more actively than the other single-strain cultures included in the starter. S. cerevisiae A13 produced ethanol and CO₂ in amounts (3975 μg g⁻¹; 1.80 g L⁻¹) that lent cultured kefir distinctive flavour and aroma characteristic of authentic kefir.     

A comparative study of polyphenoloxidases from taro (Colocasia esculenta) and potato (Solanum tuberosum var. Romano)

Taro (C. esculenta) is a staple food in many tropical regions. A comparative study of crude polyphenoloxidases from taro (tPPO) and potatoes (pPPO) was carried out to provide information useful for guiding food processing operations. Crude PPO was prepared by cold acetone precipitation using ascorbic acid as antioxidant. The PPO content of taro acetone powder was 770±17 units (mg protein)⁻¹ as compared with 3848±180 units (mg protein)⁻¹ in potato acetone powder. The pH-activity optimum was pH 4.6 for tPPO and pH 6.8 for pPPO. Both enzymes retained >80% activity after incubation at pH 4.5–8 but there was rapid activity loss at pH < 4. The temperature-activity optimum (T_opt) was 30°C for tPPO and 25°C for pPPO with 75 and 27% of their respective maximum activity retained at 60°C. Both tPPO and pPPO were irreversibly inactivated by 10 min heating at 70°C. The activation enthalpy (ΔH^#) and activation entropy (ΔS^#) for tPPO heat-inactivation were 87.4 (±0.1) kJ mol⁻¹ and −56.2 (±4) J mol⁻¹ K⁻¹, respectively. For pPPO, ΔH^# was 59.1 (±0.1) kJ mol⁻¹ whilst ΔS^# was −141 (±4) J mol⁻¹ K⁻¹. The apparent substrate specificity was established from values V_max/K_m as: 4-methylcatechol>chlorogenic acid>dl-dopa>catechol>pyrogallol> dopamine>>caffeic acid for tPPO. There was no detectable activity towards caffeic acid. The substrate specificity for pPPO was: 4-methylcatechol>caffeic acid>pyrogallol>catechol>chlorogenic acid >dl-dopa>dopamine. According to the order of inhibitor effectiveness (sodium metabisulphite>ascorbic acid>NaCl≈ (EDTA), there was a significant lag-phase before increases occurred in the absorbance at 420 nm. Preincubation of PPO with inhibitors increased the extent of inhibition, indicating a direct effect on the structure of the enzyme.     

Biochemical changes throughout the ripening of a traditional Spanish goat cheese variety (Babia-Laciana)

The physico-chemical characteristics, proteolysis (classical nitrogen fractions, caseins and their degradation products and free amino acids), and lipolysis (fat acidity and free fatty acids) were studied throughout the ripening of three batches of Babia-Laciana cheese, a Spanish traditional variety made from raw goats’ milk. The main compositional characteristics of this cheese at the end of the ripening are its high content of total solids (TS) (78.0±2.4 g 100 g⁻¹ of cheese) and fat (61.1±1.2 g 100 g⁻¹ of TS), the presence of residual lactose (1.6±0.8 g 100 g⁻¹ of TS) and its low content of sodium chloride (1.1±0.7 g 100 g⁻¹ of TS) and ash (2.8±0.5 g 100 g⁻¹ of TS). Its pH values (4.44±0.72) are extraordinarily low. The evolution and final values of the different nitrogen fractions show that this cheese undergoes a very slight proteolysis, a fact which was corroborated when the caseins and their degradation products were quantified: β-casein did not undergo any modification throughout ripening, while only 21% of the α_s-caseins were degraded. Free amino acids content increased by a factor of about 7 throughout ripening, resulting in a high content of γ-amino butyric acid and a low content of glutamic acid at the end of the process. Fat acidity increased very slightly, approximately 4.5 times, during ripening, reaching final values of 3.5±2.2 mg KOH g⁻¹ of fat. The total free fatty acids content showed a similar evolution to fat acidity. At the end of the ripening process, the main free fatty acid was C_18:1, followed by C₁₆ and C₁₀.     

Residual polyphenol oxidase and peroxidase activities in high pressure processed bok choy (Brassica rapa subsp. chinensis) juice did not accelerate nutrient degradation during storage

Polyphenol oxidase (PPO) and peroxidase (POD) cannot be fully inactivated by commercial high pressure processing (HPP) operations, and their residual activities may accelerate nutrient degradation during storage. This study hence aimed to establish the effect of residual enzyme activity on nutrient preservation in bok choy (Brassica rapa subsp. chinensis) juice. Bok choy juice was treated at 600 MPa for up to 20 min and enzyme inactivation, nutrient retention immediately after treatment and nutrient preservation during storage were determined. High residual PPO (85.1 ± 2.6%) and POD (68.5 ± 1.0%) activities remained after 20 min of treatment. Increasing the pressure holding time to enhance enzyme inactivation did not compromise total antioxidant capacity, vitamin C, carotenoids, isothiocyanates and vitamin K levels. Neither did it significantly reduce the vitamin C degradation rate during refrigerated storage. Maximising enzyme inactivation may thus not be necessary for nutrient preservation during the storage of HPP-treated bok choy juice.Industrial relevance textWith HPP, an increase in pressure or holding time is required to achieve higher levels of enzyme inactivation. Without the need to maximize PPO and POD inactivation, juice processors may employ the minimum pressure and holding time required for microbial inactivation. As vegetative bacteria are typically less resistant to HPP inactivation than these enzymes, this could translate to reduced energy costs and increased throughput.     

Survival of Listeria monocytogenes in Galotyri,a traditional Greek soft acid-curd cheese,stored aerobically at 4°C and 12°C

Galotyri is a traditional Greek soft acid-curd cheese, which is made from ewes’ or goats’ milk and is consumed fresh. Because cheese processing may allow Listeria monocytogenes post-process contamination, this study evaluated survival of the pathogen in fresh cheese during storage. Portions (0.5 kg) of two commercial types (<2% salt) of Galotyri, one artisan (pH 4.0±0.1) and the other industrial (pH 3.8±0.1), were inoculated with ca. 3 or 7 log cfu g⁻¹ of a five-strain cocktail of L. monocytogenes and stored aerobically at 4°C and 12°C. After 3 days, average declines of pathogen's populations (PALCAM agar) were 1.3–1.6 and 3.7–4.6 log cfu g⁻¹ in cheese samples for the low and high inocula, respectively. These declines were independent (P>0.05) of the cheese type or the storage temperature. From day 3, however, declines shifted to small or minimal to result in 1.4–1.8 log cfu g⁻¹ of survivors at 28 days of storage of all cheeses at 4°C, indicating a strong “tailing” independent of initial level of contamination. Low (1.2–1.7 log cfu g⁻¹) survival of L. monocytogenes also occurred in cheeses at 12°C for 14 days, which were prone to surface yeast spoilage. When ca. 3 log cfu g⁻¹ of L. monocytogenes were inoculated in laboratory scale prepared Galotyri of pH ≅4.4 and ≅3% salt, the pathogen died off at 14 and 21 days at 12°C and 4°C, respectively, in artisan type cheeses fermented with the natural starter. In contrast, the pathogen survived for 28 days in cheeses fermented with the industrial starter. These results indicate that L. monocytogenes cannot grow but may survive during retail storage of Galotyri despite its low pH of or slightly below 4.0. Although contamination of Galotyri with L. monocytogenes may be expected low (<100 cfu g⁻¹) in practice, that long-term survival of the pathogen in commercial cheeses was shown to be unaffected by the artificial contamination level (3 or 7 logs) and the storage temperature (4°C or 12°C), which should be a concern.     

Routine and sensitive SPE-HPLC method for quantitative determination of pheophytin a and pyropheophytin a in olive oils

A sensitive and specific HPLC method with tandem diode array-fluorescence detection (DAD-FL) has been developed and validated for the simultaneous determination of pheophytin a (phy a) and pyropheophytin a (pyrophy a) in olive oils. Pigments were extracted with reverse phase solid phase extraction (RP-SPE) and subsequently analysed by HPLC-DAD-FL. The chromatographic analysis was carried out isocratically on ODS2 RP column using methanol–acetone (1:1 v/v) at flow-rate of 2.0 ml min⁻¹. Specificity of the method was assured by the simultaneous detection by UV–visible (410 nm) and FL (λ_Ex: 410 nm; λ_Em: 672 nm). Both compounds could be baseline separated within 7 min. The method was validated and applied in olive oil samples recently extracted as well as stored during 12 months. The limit of detection (LOD) defined at a signal-to-noise ratio of about 3 was ∼21.6 ng g⁻¹ for pyrophy a and ∼24.6 ng g⁻¹ for phy a under FL detection, and ∼148.0 ng g⁻¹ for both analytes under UV–visible detection. The calibration graphs were linear (r² > 0.9999; p < 0.01) between 0.25–14.00 ng μl⁻¹ for pyrophy a and 0.25–19.00 ng μl⁻¹ for phy a, under both fluorescence and UV–visible detection conditions. Recoveries of phy a and pyrophy a were over 94% as estimated by the standard addition method. Relative standard deviation for the intra-day and inter-day determination of phy a and pyrophy a were lower than 3.7% and 8.0%, respectively.     

Macro- and microelement contents in fruiting bodies of wild mushrooms from the Notecka forest in west-central Poland

Fruiting bodies of wild mushrooms and forest soil samples were collected and analyzed for macro- (N, P, K, S, Ca, Mg) and microelement (Al, Zn, Fe, Mn, Cd, Pb) contents in pine stands of the Notecka Forest in west-central Poland. Elements were determined by atomic absorption spectrometry in 160 samples of 8 fungal species and 15 underlying soil samples. Macro- and microelement contents in soil were low and characteristic of the poor and acidic sandy soils of the Polish lowlands not influenced by industrial pollution. In fruiting bodies, the highest mean concentration of macroelements (dry mass basis) was found for N (40.0 g kg⁻¹), followed by K (33.0 g kg⁻¹), P (5.4 g kg⁻¹), S (2.2 g kg⁻¹), Ca (1.0 g kg⁻¹) and Mg (0.7 g kg⁻¹). All macroelements (except for Ca) were concentrated in considerably higher levels in the fruiting bodies than in the forest soil. Nitrogen, P, K, S and Mg were preferably translocated into the cap rather than the stipes. Calcium, however, was often found in higher concentration in stipes than in caps. The mean microelement concentrations, across all tested fungi, were in the following order: Al > Zn > Fe > Mn > Pb > Cd. Microelements showed different distributions, depending on the part of the fruiting body. Some were more concentrated in the caps and some in stipes and distributions varied among species. Xerocomus badius is the most often harvested edible mushroom in the Notecka Forest. Pb and Cd distributions in fruiting bodies of this mushroom were evaluated in order to assess health risks to consumers. The estimated dietary exposures to Pb and Cd for consumers of this mushroom were in excess of guidelines on safe exposures.     

Extraction of antioxidant and antimicrobial compounds from Inga marginata Willd bark and pulp using different extraction techniques and phytochemical characterization

This study aimed to identify the least aggressive and highest yield extraction method to obtain bioactive compounds from Inga marginata Willd fruits, determine the chemical components, and evaluate the extracts’' antimicrobial and cytotoxic activity. The extraction efficiency was expressed by the total phenolic and total flavonoid content and antioxidant activity (DPPH, IC₅₀, and ORAC) using conventional, ultrasound, and microwave-assisted extraction. The highest bioactive compound content was achieved using 5 min at 60 °C for total phenolic content (214.98 mg GAE g⁻¹), total flavonoid content (22.90 mg EQ g⁻¹), DPPH (45.98 μmol TEAC g⁻¹), inhibitory capacity (0.80 mg mL⁻¹), and ORAC (167.25 μmol Trolox g⁻¹) using ultrasonic extraction, and the extract inhibited the growth of all microorganisms tested. Thirteen chemical compounds were determined by ESI-ToF-MS, confirming the high phytochemical capacity of the extract. Lastly, the Inga extract showed no cytotoxicity at the concentrations used.     

Effects of aqueous chlorine dioxide treatment on browning of fresh-cut lotus root

Effect of aqueous chlorine dioxide (ClO₂) treatment on browning of fresh-cut lotus root (FLR) was investigated to explore the feasibility to apply ClO₂ for browning inhibition of fresh-cut products. Cut lotus roots were treated in ClO₂ solutions at different concentrations (10, 50 and 100 mg/l) for different time (5, 10 and 15 min), followed by chilled storage for 8-10 days at 4 °C. Color parameters (L^∗, a^∗ and b^∗), polyphenol oxidase (PPO) activity and overall visual quality (OVQ) were measured at one-day interval during storage. Results showed that higher ClO₂ concentration and longer treatment time can provide better inhibitory effects on the browning of FLR. ClO₂ concentration, treatment time and storage time were three significant factors (P < 0.05) and some significant interactions were observed. PPO activities were largely inhibited by 100 mg/l ClO₂ treatment for 10 min. The 100 mg/l ClO₂ treatment maintained high OVQ scores during 10-day storage; while 50 mg/l ClO₂ treatment was acceptable for maintaining OVQ during 4-day storage. ClO₂ treatment was demonstrated to be a promising alternative approach to control browning and improve OVQ of FLR.     

Effect of alternating magnetic field on the quality of fresh-cut apples in cold storage

This study evaluated the inhibitory effect of alternating magnetic field (MF) on enzymatic browning, physicochemical properties and microbial proliferation of fresh-cut apples during cold storage. The results showed that after 9-day storage, the browning index of apple slices increased by 174.07% in the conventional refrigerated group but by only 132.32% in the alternating MF group, the total number of colonies in the alternating MF group was 1.32 log CFU g⁻¹, less than that in the conventional refrigerated samples. The soluble solids and firmness of the MF group were 16.47% and 28.79% higher than those of the control group. The alternating MF significantly inhibited the activities of polyphenol oxidase (PPO) and peroxidase (POD) and exerted a significant effect on the tertiary structure of enzymes. Except for maintaining the good sensory quality, the MF also suppressed the growth of microorganisms in fresh-cut apples and extended their shelf life by at least 2 days.