The effectiveness of ozone and acidulant treatments in extending the refrigerated shelf life of fresh-cut potatoes

Abstract: The objective of the study was to determine the effectiveness of acidulant dip treatments (with or without aqueous ozone) to reduce enzymatic browning and to extend the shelf life of fresh‐cut potato slices during refrigerated storage (4 °C) for 28 d. Potato slices subjected to aqueous ozone (2 ppm) had significantly (P≤ 0.05) higher L‐values and lower a‐values, but ozone did not appear to have any effect on aerobic plate counts (APCs) or polyphenol oxidase (PPO) activity. NatureSeal (NS) and sodium acid sulfate (SAS) were the most effective acidulant treatments in reducing browning (significantly [P≤ 0.05] higher L‐values, lower a‐values, and browning index values) regardless of ozone treatment. NS and SAS also had lower PPO activity compared to other treatments on days 0 and 28, and significantly (P≤ 0.05) lower APCs (≤2.00 log CFU/g) over refrigerated storage. Therefore, the SAS treatment was comparable to NS, a commercially available product, and showed promise as an effective antibrowning dip to reduce browning and spoilage in fresh‐cut potato products. Practical Application: A 1% SAS dip treatment which included 1% citric and 1% ascorbic acid was found to be an effective antibrowning dip for fresh‐cut potatoes along with NatureSeal®'s PS‐10, compared to other treatments. They were both effective in maintaining low microbial counts over refrigerated storage. Additionally, aqueous ozone washes (2 ppm) showed significant benefits to reduce browning; however, ozone did not affect microbial counts or PPO enzyme activity. Therefore, the SAS treatment could have potential use in the fruit and vegetable industry to reduce browning and spoilage in fresh‐cut potato products.     

High pressure processing of cocoyam,Peruvian carrot and sweet potato: Effect on oxidative enzymes and impact in the tuber color

High pressure processing (HPP) is a non-thermal technology used to activate or inactivate enzymes. This study investigated the effects of HPP (600 MPa for 5 or 30 min at 25 °C) on cocoyam, Peruvian carrot and sweet potato color, and the polyphenoloxidase (PPO) and peroxidase (POD) activities in tuber cubes, puree, and enzyme extract subjected to HPP. The results showed enzyme inactivation by HPP in cocoyam (up to 55% PPO inactivation in puree and 81% POD inactivation in extract) and Peruvian carrot (up to 100% PPO and 57% POD inactivation the extract). In contrast, enzyme activation was observed in sweet potato (up to 368% PPO and 27% POD activation in puree). The color results were compatible to enzyme activity: the color parameters remained unchanged in cocoyam and Peruvian carrot, which showed high PPO and POD inactivation after HPP. Furthermore, the impact of HPP on the enzymes was influenced by the matrix in which HPP was carried out, evidencing that the enzyme structure can be protected in the presence of other food constituents.Industrial relevanceThe enzymes PPO and POD are an important concern for vegetable processing, due its ability to induce browning after vegetables are cut. The HPP at 600 MPa for 5 or 30 min can be used to inactivate these enzymes in cocoyam and Peruvian carrot, guaranteeing the color and freshness of the tubers similar to the fresh cut vegetable.     

Polyphenoloxidase Activity and Color of Blanched and High Hydrostatic Pressure Treated Banana Puree

The effects of blanching and high hydrostatic pressure (HHP) treatments on natural flora evolution, polyphenoloxidase (PPO) activity and color of banana puree adjusted to pH 3.4 and water activity (a_w) of 0.97 were evaluated during 15 days storage at 25°C. Standard plate as well as yeast and mold counts of HHP treated purees were <10 CFU/g throughout storage. Blanching time was found to affect (P<0.05) puree color. HHP treatments retained the initial color of the banana purees. Longer browning induction times and slower browning rates were observed when a longer blanching time was combined with a 689 MPa pressure treatment. A residual PPO activity < 5% was observed in the puree when a 7 min blanch was followed by HHP treatment at 689 MPa for 10 min.     

Inhibitory effect of rice bran extract on polyphenol oxidase of potato and banana

Rice bran was extracted with water and its effects on potato and banana polyphenol oxidase (PPO) were investigated. Rice bran extract (RBE), conc. 0.3 g mL^?1, exhibited PPO inhibition in potato and banana PPO with % inhibition of 69.31% and 47.63%, respectively (P ≤ 0.05). RBE showed a concentration‐dependent inhibition on potato and banana PPO. RBE (conc. 0.3 g mL^?1) inhibited potato PPO higher than ascorbic acid, citric acid, NaCl and EDTA (final conc. 20 mg L^?1); and it also inhibited banana PPO higher than citric acid, NaCl and EDTA (final conc. 20 mg L^?1), respectively. The combination of RBE with citric acid or ascorbic acid appeared to be additive inhibitory effect on banana and potato PPO. Kinetic study of the inhibition on potato and banana PPO by RBE showed that RBE was a mixed‐type inhibitor; however, RBE appeared to be able to act directly on enzyme structure rather than substrate structure.     

Effect of ultrasonic treatment on enzyme activity and bioactives of strawberry puree

The aim of this study was to evaluate the impact of ultrasound (US) at different frequencies (20, 370, and 583 kHz) and power levels (35 and 48 W) on the residual activity (RA) of peroxidase (POD) and polyphenol oxidase (PPO) in strawberry puree. Total anthocyanin content (TAC), total phenolic content (TPC), ferric ion reducing antioxidant power (FRAP) and trolox equivalent antioxidant capacity (TEAC) were also assessed. Results were compared with untreated, thermally treated at 40 °C (control) and pasteurized (90 °C) strawberry puree. POD and PPO RA were significantly (P < 0.05) reduced, whilst there was a significant (P < 0.05) increase in TAC (5%–19%) in all US-treated samples in comparison with the untreated samples and the controls. US at 20 kHz (35 W) increased significantly (P < 0.05) TPC (9%) and FRAP (6%) in strawberry puree, whereas the effect of 583 kHz (48 W) on these parameters was insignificant (P > 0.05). Pasteurization inactivated POD and PPO, however, decreased dramatically TAC (14%), TPC (17%) and FRAP (9.5%) in strawberry puree. These findings suggest that US is a promising novel non-thermal food technology that can be tailored to improve the quality of strawberry puree by inactivating enzymes responsible for food deterioration whilst maintaining the content of bioactive compounds.     

Quality and biochemical changes of longan (Dimocarpus longan Lour cv. Daw) fruit under different controlled atmosphere conditions

Sulphur dioxide has been used to control pericarp browning in longan fruit. However, due to health and regulatory concerns, alternative treatments should be tested. The objective of this study was to find the tolerance levels of longan fruit to low O₂ (2%, 5%, 10% and 15%) and elevated CO₂ (5%, 10%, 15% and 20%) at 2 °C. According to the tolerance study, controlled atmospheres (CA) of 5% O₂ + 5% CO₂, 5% O₂ + 10% CO₂ and 5% O₂ + 15% CO₂ were compared with normal air (control) at 2 °C. Pericarp browning and decay incidence of longan were significantly (P ≤ 0.05) higher in control than all the CA treatments. CA storage reduced polyphenol oxidase (PPO) activity, maintained L* value and slowed down a decrease in total phenolic contents (TPC). Pericarp browning was highly correlated with PPO, L* and TPC.     

Improvement of rheological and physicochemical properties of longan honey by non‐thermal magnetic technique

A non‐thermal technology using magnetic field (MF) can improve flowability of honey while maintaining its physicochemical quality. Effects of MF treatment on rheological and physicochemical properties of longan honey exposed to MF for 2 h at 15 °C and 28 °C were investigated and compared with those of non‐MF samples. Increasing MF strength at 28 °C caused a reduction in firmness (P ≤ 0.05), but not in consistency, index of viscosity and cohesiveness. The effects at 15 °C were greater. Newtonian behaviour was observed for all samples. Shear stress and viscosity were significantly reduced with increasing MF strength at 15 °C (P ≤ 0.05), but less at 28 °C. pH was also decreased. Total soluble solids content was increased at both temperatures (P ≤ 0.05). Colour index was not significantly affected by MF, whereas optical density was slightly increased at high MF strengths (P > 0.05). L* values for the MF treated samples were increased (P ≤ 0.05), giving lighter and more pleasant colour to the honey. MF treatment improved overall qualities of honey.     

COLOR, POLYPHENOLOXIDASE, AND SENSORY CHANGES IN BANANA JUICE AS AFFECTED BY HEAT AND ULTRAFILTRATION

A study was conducted to determine the effects of banana maturity (less mature; maturity stage 3, more mature; maturity stage 7), heat treatment of banana puree, heat pasteurization of juice, and ultrafiltration (UF) of juice on color, polyphenoloxidase (PPO) activity, and flavor of puree and juice. Heating puree to 90C inactivated PPO and reduced browning in puree and juice, especially in puree from more mature bananas which had greater PPO activity. PPO activity decreased considerably during cold-setting and filtration of juice, and was not detectable in unheated, pad-filtered juice from less mature bananas. UF of juice through a 10,000 mwco membrance, but not a 30,000, removed all PPO activity and reduced juice browning. Pasteurization of juice (hot fill at 90C) increased browning, but not as much as PPO activity in the puree. Pasteurization had no effect on juice flavor if the puree had been heated to 90C previously as puree, but altered the flavor (i. e., more cooked banana flavor) of juice that had not been previously heated to 90C. Pasteurized juice that had not been heated to 90C as puree had similar flavor (no significant difference) as pasteurized juice that had been heated to 90C as puree.     

Purification and enzymatic characteristics of a novel polyphenol oxidase from lotus seed (Nelumbo nucifera Gaertn.)

A polyphenol oxidase (PPO) from lotus seed was purified by the procedures including ammonium sulphate precipitation and affinity chromatography. The apparent molecular mass was 38.6 kDa by SDS‐PAGE. Kinetic studies showed that the K_m and V_max values for catechol were 6.04 mm and 416.67 U, respectively. The PPO performed optimal activity in 20 °C and pH 7.0. The enzymatic activity could be mainly maintained up to 50 °C and pH 4.0–7.0. The activity could be inhibited by various inhibitors including thiourea, urea, sodium hydrogen sulphite, EDTA·2Na, SDS, citric acid, guanidine hydrochloride, ascorbic acid, sodium sulphite and sodium thiosulphate. The metal ions Ba²⁺, Mg²⁺, Ca²⁺, Mn²⁺, Co²⁺ and Zn²⁺ could inhibit the activity of PPO, while Cu²⁺ performed obvious enhancement. The enzymatic properties of PPO could probably provide practical application in inhibiting the PPO activity and preventing enzymatic browning in the process of picking, transportation, processing and storage of fresh lotus seeds.     

A study of the effect of the drying process on the composition and physicochemical properties of flours obtained from durian fruits of two ripening stages

Durian cv. Monthong with two ripening stages (unripe and fully ripe) was subjected to microwave vacuum drying (MWD) at 5.49 W g^?1 and hot air drying (HAD) at 60 °C. With an increase in ripening degree, the starch content was significantly (P ≤ 0.05) decreased from 40.08–40.42% to 9.44–11.76%. X‐ray diffraction indicated that the crystalline pattern was changed from starch to sucrose. The starch granule morphology of durian flour was conserved for both drying conditions. Peak gelatinisation temperatures of MWD and HAD flours were increased significantly (P ≤ 0.05) from 56.71–57.32 to 60.71–61.23 °C. Using different drying methods, MWD flour had less a*‐value (P ≤ 0.05) than HAD flour. The peak viscosity and trough of the HAD unripe durian flour (5.92 RVU and 3.45 RVU, respectively) were significantly (P ≤ 0.05) lower than those of the MWD unripe durian flour (34.32 RVU and 11.57 RVU, respectively).     

Prevention of Enzymatic Browning of Chinese Yam (Dioscorea spp.) Using Electrolyzed Oxidizing Water

In this study, the effects of electrolyzed oxidizing water (EOW) on the prevention of enzymatic browning of fresh‐cut “Jiu Jinhuang” Chinese yam were investigated. The yams were immersed in the inhibitors for 25 min at 20 °C. Compared with the tap water (TW) treatment, the chromatic attributes were significantly different after 72 h of storage (P < 0.05). The activities of polyphenol oxidase (PPO, EC 1.10.3.1), peroxidase (POD, EC 1.11.1.7), and _L‐phenylalanine ammonia lyase (PAL, EC 4.3.1.5) were inhibited when measured at 24 h. The contents of phenolic acids, including gallic and chlorogenic acid, in the group treated with the slightly acidic electrolyzed water (SAEW) were higher than those treated with TW and neutral electrolyzed water (NEW). The group treated with NEW had the highest total phenol content (P < 0.05, at 24 h), while the group treated with SAEW had the highest flavonoid content (P < 0.05) during storage. Without being treated with inhibitors, the K_m and V_max values of yam PPO were 0.0044 mol/L and 0.02627 U/min, respectively, and the K_i of samples treated with SAEW and citric acid (CA) were 15.6607 and 2.3969 μmol/L, respectively. These results indicate that EOW is beneficial as a browning inhibitor.     

Elucidation of the mechanism of enzymatic browning inhibition by sodium chlorite

Sodium chlorite (SC) is a well known anti-microbial agent and its strong inhibitory effect on enzymatic browning of fresh-cut produce has recently been identified. We investigated the effect of SC on polyphenol oxidase (PPO) and its substrate, chlorogenic acid (CA), as it relates to the mechanisms of browning inhibition by SC. Results indicate that the browning reaction of CA (1.0 mM) catalyzed by PPO (33 U/mL) was significantly inhibited by 1.0 mM SC at pH 4.6. Two PPO isoforms were identified by native polyacrylamide gel electrophoresis, and both were inactivated by SC (3.0 mM). This suggests that SC serves as a PPO inhibitor to prevent enzymatic browning. Furthermore, the effect of SC on the stability of CA in both acidic (pH 4.5) and basic conditions (pH 8.3) was studied by UV–Vis scan and LC–MS analysis. The results showed that at the presence of SC (3.0 mM), CA (0.1 mM) degraded to quinic acid and caffeic acid as well as other intermediates. Hence, the anti-browning property of SC can be attributed to the two modes of action: the inactivation of polyphenol oxidase directly and the oxidative degradation of phenolic substrates.     

Effect of vacuum cooking treatment on physicochemical and structural characteristics of purple‐flesh potato

Cook‐vide (CV, vacuum boiling) and sous‐vide (SV, cooking in a vacuum‐sealed pouch) have been applied to cook purple‐flesh potatoes. Response surface methodology (RSM) sets up the work conditions of temperatures (78–92 °C) and times (16–44 min). Textural parameters, colour and anthocyanins have been measured in cooked samples, and microstructure of cooked tissues was observed with cryo‐SEM technique. CV and SV provided similar hardness (P > 0.05), while SV treatments provided samples more adhesive and cohesive than CV ones (P ≤ 0.05). Micrographs of cooked samples showed rounder cells in cook‐vide samples and higher swelling than in sous‐vide ones. SV treatment avoided the leaching into the water of anthocyanins (chromophore) retaining more of them in potatoes (P ≤ 0.05), as a consequence of which total colour difference was lower in SV samples compared with CV ones (P ≤ 0.05). Particularly, CV samples were lighter (higher values of L*) and less reddish (lower values of +a*) than SV ones (P ≤ 0.05).     

Effects of hot-water and steam blanching of sliced potato on polyphenol oxidase activity

The worldwide potato production is considered the fourth-most important food sector due to the increasing use of potatoes as raw materials for high-convenience food. Enzymatic browning, due to polyphenol oxidase (PPO), is related to unacceptability by consumer. Among antibrowning agents, thermal treatments are viable alternatives. In this study, the efficacy of hot-water and steam blanching at 80–90 °C of potato slices (1-cm thick) was evaluated in terms of colour changes as well as PPO inactivation kinetics, substrate specificity and transition state parameters. In general, all treatments [1] bleached the slices, [2] inactivated PPO and [3] reduced its kinetic efficiency. Results from thermal inactivation kinetics promoted hot-water blanching at 90 °C for approx. 2 min as the fastest treatment to obtain enzymatic-stable potato slices. Moreover, steam blanching required more energy (53.93 ± 1.24 kJ mol⁻¹) than hot-water treatment (41.41 ± 4.51 kJ mol⁻¹) to reach the transition state and then to unfold the PPO enzyme.     

Nonthermal inactivation of polyphenol oxidase in apple juice influenced by moderate electric fields: Effects of periodic on-off and constant exposure electrical treatments

Inactivation of polyphenol oxidase (PPO) in fresh apple juice was studied in moderate electric field (MEF) treatments at field strengths in the range of 85–110 V/cm. The apple juice was subjected to periodic on-off treatments at 50 °C and constant exposure MEF treatments at 50 and 65 °C using two different electro-processing devices, specially constructed for the purpose. PPO inactivation by the electric fields was determined with respect to the corresponding control (nofield) treatments. The application of periodic on-off treatments resulted in about 100% increase (P ≤ 0.05) of the thermal inactivation rate constant of PPO at 50 °C. A similar relative increase of the thermal inactivation rate constant was observed with the constant exposure MEF treatment at 50 °C. The electric field influence was improved significantly (P ≤ 0.05) in the constant exposure MEF treatment at 65 °C. Differences in electrical energy input among the MEF treatments were observed. Results indicate both the electric field strength and the treatment temperature play critical roles in enzyme inactivation by moderate electric fields.Industrial relevanceThis study shows polyphenol oxidase enzyme in fresh apple juice can be significantly inactivated by moderate electric fields applied at below thermal pasteurization temperatures. Therefore, moderate electric field treatment applications are beneficial for the minimally processed fruit and vegetable industry.     

Enhancing the antioxidant activity of immature calamondin by heat treatment

The purpose of this study was to investigate the enhancing effect of heat treatment (110 and 130 °C for 0.5, 1.0, 1.5 and 2.0 h, and 150 °C for 1.5 h) on antioxidant activity and phenolic compounds of immature calamondin (Citrus mitis Blanco). The results indicated that heat treatment could enhance the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) scavenging potency, oxygen radical absorbance capacity (ORAC) and total phenolic content. However, the major flavonoid, 3′,5′‐di‐C‐β‐glucopyranosylphloretin (DGPP), decreased drastically after being heated at ≥130 °C over 1.5 h. The increasing ratio of absorbance at UV₄₂₀ nm coincided with the change of the antioxidant activity. Therefore, it was concluded that the browning products resulted in the increase of the antioxidant activity of immature calamondin heated at ≥130 °C over 1.5 h, while the increase of antioxidant activity at 110 and 130 °C ≤ 1.0 h heating was due to increased phenolic content.     

Effect of processing and storage on the fatty acid composition of n‐3 or n‐6 fatty acid‐enriched eggs

Fresh eggs from hens fed diets supplemented with 4% linseed oil (LO) or sunflower oil (SO) were either directly submitted to pasteurisation, hard‐boiling or scrambling processing, or first submitted to refrigerated storage at 4 °C for 60 day and then to processing. Fresh LO eggs showed higher (P ≤ 0.05) proportions of monounsaturated fatty acids (MUFAs) and n‐3 polyunsaturated fatty acids (PUFAs), but lower (P ≤ 0.05) proportions of saturated fatty acids (SFAs), PUFAs and n‐6 PUFAs than the SO eggs. Storage decreased (P ≤ 0.05) the proportion of PUFAs and increased (P ≤ 0.05) that of MUFAs in egg yolks from both treatments. The pasteurisation process had no effect on the fatty acid composition of fresh eggs from both treatments, but increased (P ≤ 0.05) n‐6 PUFAs and decreased (P ≤ 0.05) n‐3 PUFAs in stored LO eggs. Hard‐boiling and scrambling modified the fatty acid composition of fresh and stored eggs from both treatments by decreasing (P ≤ 0.05) the proportion of PUFAs, particularly of the very long‐chain n‐3 eicosapentaenoic, docosapentaenoic and docosahexaenoic PUFAs. LO eggs showed a higher susceptibility to fatty acid modification upon processing as compared to the SO eggs.     

Effect of natural antioxidants on heat‐induced,copper(II)‐catalysed,oxidative degradation of quercetin and rutin (quercetin 3‐O‐rutinoside) in aqueous model systems

The citrate/Cu²⁺‐catalysed degradation of quercetin and rutin (1.0 mM ) was studied in an aqueous model system, pH 8.0, at 97 °C, with respect to the addition of natural, water‐soluble antioxidants, including ascorbic acid (ASA), catechin (CT) and cysteine (CY). Quercetin decomposition was found to be inhibited to a significant extent by the addition of ASA and CY at millimolar ratios of 1:1 and 1:2, but CT gave significantly lower inhibition (P < 0.05) compared with both ASA and CY. In rutin solutions, significant inhibition (P < 0.05) was achieved only with the addition of CT and CY at a millimolar ratio of 1:2. The addition of both ASA and CY to solutions of either flavonol also inhibited browning (A₄₂₀) development, but CT provoked significant increases. © 2002 Society of Chemical Industry     

Inhibition kinetics of catechin and ferulic acid on polyphenoloxidase from cephalothorax of Pacific white shrimp (Litopenaeus vannamei)

Inhibition kinetics and mode of catechin and ferulic acid towards polyphenoloxidase (PPO) from cephalothorax of Pacific white shrimp were investigated. Catechin or ferulic acid inhibited quinone formation catalysed by PPO in a dose dependent manner. Catechin showed mixed type reversible inhibition with K_i value of 1.4 mM, whereas ferulic acid exhibited non-competitive reversible inhibition with K_i value of 37 mM. With increasing concentrations, both catechin and ferulic acid had higher copper (Cu²⁺) reduction and copper chelating capacity (P < 0.05). Catechin or ferulic acid could react with intermediated browning reaction products, thereby preventing dopachrome formation. Thus, catechin or ferulic acid could inhibit melanosis in Pacific white shrimp with different modes of inhibition towards PPO.     

Effect of processing parameters on the properties of transglutaminase-treated soy protein isolate films

The effects of processing parameters, including the applied amount of microbial transglutaminase (MTGase), the pH of film-forming solution, air-drying temperature, as well as the additional pre-incubation, on the properties of MTGase-treated soy protein isolate (SPI) films were investigated. The treatment with low concentration of MTGase (4–10 units per gram of SPI, U g^− 1) significantly increased the tensile strength (TS) values of SPI films, while high concentration of MTGase (over 20 U g^− 1) resulted in significant decrease in the TS values (P ≤ 0.05). The elongation at break (EB) values of corresponding films gradually decreased, and the contact angle values persistently increased with the enzyme concentration. At alkaline pH range, the TS and EB values of MTGase-treated SPI films were significantly higher than that at pH 7.0 (P ≤ 0.05). Meanwhile, the contact angle values significantly decreased with increasing pH from 7.0 to 10.0 (P ≤ 0.05). The TS, EB and contact angle values of MTGase-treated films gradually but insignificantly decreased with increasing the air-drying temperature from 18 to 50 °C (P > 0.05). The properties of MTGase-treated films were also affected by the additional pre-incubation of film-forming solutions with MTGase before casting. Furthermore, the aggregation of SPI or its components induced by MTGase has been proved to mainly account for the influence of processing parameters on the properties of SPI films (MTGase-treated). Thus, low concentration of enzyme, alkaline pH range and low air-drying temperature, at which conditions the MTGase-induced aggregation of SPI in film-forming solutions could be in some extent inhibited or delayed, might facilitate the improvement of the properties of SPI films by MTGase, especially the mechanical and surface hydrophobic properties.Industrial relevanceThe development of biodegradable protein film has attracted a lot of attention worldwide. The enzymatic cross-linking induced by transglutaminase has been confirmed to improve mechanical and surface hydrophobic properties of cast films from most of food proteins, including soy proteins. Results of this study show that, the improvement of properties of cast films of soy proteins by transglutaminase treatment is largely dependent upon many processing parameters, e.g., enzyme concentration, the pH of film-forming solution and temperature.