Reduced Polyphenol Oxidase Activity Research Articles

Efficient pectin recovery from sugar beet pulp as effective bio-based coating for Pacific white shrimp preservation

This study demonstrates the valorization of sugar beet pulp (SBP)-derived pectin to produce bio-based coatings for shrimp preservation. Pectin extraction was assessed at varying temperatures and extraction times to achieve tailored properties (high methoxyl-pectins, degree of esterification-DE >79.0 %) leading to 11.5 % extraction yield, 78.1 % galactouronic acid content and 80 % DE at optimal conditions (pH 1.5, 80 °C, 2 h). Pectin-based coatings supplemented with ascorbic acid (AA) (0.5–2.0 %) led to organoleptically acceptable shrimps with significantly lower total color differences during 28-days of storage, compared to uncoated and pectin-coated counterparts. AA-based coatings delayed shrimp melanosis, expressed as reduced polyphenoloxidase activity (48–86 %). Rich-in-holocellulose solids derived after pectin extraction were used for bacterial cellulose (BC) production, pinpointing the SBP potential as a multi-purpose feedstock. Fed-batch fermentation enhanced BC concentration (by 110 %) and productivity (1.6-fold higher) compared to batch-cultures. Pectin produced within a SBP-based biorefinery could be applied as bio-based coating with food packaging potential.

Physiological, metabolome, and transcriptome analysis revealed the effect of ethyl 3-amino-3-thioxopropanoate on the browning of fresh-cut banana during storage

The quality of fresh-cut bananas is often affected by surface browning, which does not meet consumer expectations. The ethyl 3-amino-3-thioxopropanoate (EAT) is an ethyl ester organic compound screened from Maillard reaction products that may have browning inhibition effects. However, there is still a lack of research on the practical application of EAT. This study investigated the impact of exogenous EAT on the browning process and the underlying mechanisms in fresh-cut banana through a comprehensive analysis involving physiological, metabolomic, and transcriptomic approaches. Treatment with EAT effectively mitigated the discoloration of the cut surface of slices and decreased the browning index by 74 % at the end of storage. Additionally, EAT application significantly reduced polyphenol oxidase activity, increased phenylalanine ammonia-lyase activity and total phenolic content, inhibited lipoxygenase activity, decreased malondialdehyde accumulation, enhanced antioxidant enzyme activity, and improved DPPH free radical scavenging rate to 68.49 %. Moreover, 839 metabolites were identified through non-targeted metabolomics analysis. Metabolomic and transcriptomic analysis further highlighted the importance of lipid metabolism, amino acid metabolism and secondary metabolites in influencing the sensitivity to post-cutting browning. EAT treatment also influenced the expression levels of key genes related to browning. Thus, it could be speculated that the mechanism by which EAT produces its anti-browning effect may be by reducing phenolase activity, improving levels of phenols and amino acids, enhancing the antioxidant capacity of the fruit, and alleviating membrane lipid peroxidation. In summary, this study provides valuable insights into the response mechanism employed by exogenous EAT to inhibit browning in freshly cut bananas. However, the application security and mass production methods of EAT still need further clarification.

Spraying zinc oxide nanoparticles on pistachios (Pistacia vera L.) for preservation in cold storage

ABSTRACT The ability of zinc oxide nanoparticles to extend the shelf life of fresh pistachios in polyethylene packages in cold storage was evaluated. Independent variables were the type and concentration of the disinfectant (0.5%, 1%, 1.5%, and 2% nano-ZnO and 2% peracetic acid) and storage time (at harvest, 25, 50 and 75 days after harvest). Aflatoxin was not detected in the kernels of the disinfectant treatments after storage. A decrease occurred in firmness, chlorophylls and carotenoids in hulls and kernels over time. Phenolics and flavonoids of kernels decreased, parallel to a decrease in weight. Nano-ZnO (2%) prevented this reduction well. In hulls and kernels, nano-ZnO (2%) revealed the highest anthocyanin. Antioxidant activity in kernels remained stable or even increased in response to ZnO (1.5%) on day 75. All ZnO treatments prevented ion leakage while limiting hydrogen peroxide and malondialdehyde production in hulls. Peracetic acid reduced polyphenol oxidase activity on 75th day. ZnO (1% and 1.5%) and peracetic acid increased phenylalanine ammonia lyase activity. On 75th day, ZnO-treated samples had higher peroxidase activity. All ZnO treatments, especially 1.5% and 2%, prevented the loss of quality in hulls, shells, taste, and aroma. Nano-ZnO (2%) can be recommended for fresh pistachio preservation in cold storage.

Enzymic Deactivation in Tender Coconut Water by Supercritical Carbon Dioxide

Polyphenol oxidase (PPO) and peroxidase (POD) are target enzymes in the processing of tender coconut water (TCW). This study primarily evaluated the combined effect of supercritical carbon dioxide (SC-CO2) and mild temperatures on the PPO and POD deactivation of TCW. A factorial design was performed to investigate the effect of temperature (in the range of 35 to 85 °C), pressure (75 to 370 bar), and holding time (13 to 47 min) on the enzymic deactivation, physicochemical parameters, and color of the TCW. The percentages of reduction in PPO activity ranged from 3.7 to 100%, and POD ranged from 43.4 to 100%. The pH values of the freshly extracted and processed TCW were 5.09 and 4.90, and the soluble solids content were 5.5 and 5.4 °Brix, respectively. The holding time (t) had a significant effect (p ≤ 0.1) on the total color variation. As for the reduction of PPO activity, the temperature (T) and the interaction between pressure (P) and t had a significant effect. None of variables (P, T, or t) affected (p > 0.1) the POD reduction, pH, and soluble solids variation. The combination of SC-CO2 and mild temperatures is a promising intervention in the enzymic stabilization of TCW.

Promotion of Thermal Inactivation Treatment of Apple Polyphenol Oxidase in the Presence of Trehalose.

Trehalose is known to protect enzymes from denaturation. In the present study, we observed promotion of apple polyphenol oxidase (PPO) inactivation in a trehalose solution with thermal treatment. Crude PPO from Fuji apple was mixed with either sucrose or trehalose solutions, then the samples treated at 25 or 65 °C. In the presence of trehalose, PPO activities were markedly decreased upon treatment at 65 °C with increasing trehalose concentration. Furthermore, the reduction in PPO activity in the presence of trehalose was proportional to storage time after thermal treatment and thermal treatment time. Comparing PPO activities between treatment time 0 and 90 min at 65 °C, activities decreased 89 % for trehalose concentration of 0.2 M. These results indicates that trehalose acts not only as inhibitor but as promoter of inactivation of PPO. The Lineweaver-Burk plot indicated that trehalose acts on PPO as a non-competitive inhibitor during the 65 °C treatment. Two mechanisms of PPO inactivation in the presence of trehalose were suggested; one is the suppression of PPO activation cause by a thermal treatment, and another is the conformational change to inactivation form of PPO in conjunction with trehalose and a thermal treatment. Additionally, apple juice including 0.2 or 0.5 M trehalose with 65 °C treatment indicated slow browning than the juice with 0.2 or 0.5 M sucrose or without sugars. This result demonstrates that the preventing of browning with trehalose is a viable industrial food process.

Enhanced antioxidant activity and quality of olecranon peach fruits (Prunus persica L.) through synergistic application of exogenous nano-selenium and melatonin

Olecranon peach, a significant economic crop in southern China, faces quality degradation due to pests, diseases, and pesticide residues. Melatonin (MT) and nano-selenium (Nano-Se) applied individually have been found to improve crop growth and abiotic stress resistance. However, the impact of different Nano-Se and MT ratios on olecranon peach quality remains uncertain. Plants were foliar sprayed with varying Nano-Se and MT ratios during the fruit set phase. A combined 5 mg/L Nano-Se and 10 mg/L MT (Nano-Se5 + MT10) effect outperformed individual treatments and the control in enhancing fruit quality. Nano-Se5 + MT10 notably increased peroxidase (190.3%) and superoxide dismutase (112.2%) activities, and reduced polyphenol oxidase activity (-13.2%), raised total sugars (33.3%), soluble protein (18.5%), and phenolic contents like apigenin (51.9%), vanillic acid (21.4%), ferulic acid (29.4%), and p-hydroxybenzoic acid (317.2%) compared to the control. Correlation analysis linked antioxidant enzymes and phenolics in olecranon peach fruits to nutrient accumulation. Nano-Se5 + MT10 improves sweetness and quality by enhancing antioxidant ability (increased peroxidase and superoxide dismutase, decreased polyphenol oxidase and phenolics), and promoting soluble protein, total sugar, and phenolic accumulation. In conclusion, Nano-Se5 + MT10 application shows promise in enhancing olecranon peach quality and antioxidant attributes.Graphical

Preservation of Fresh-Cut 'Maradol' Papaya with Polymeric Nanocapsules of Lemon Essential Oil or Curcumin.

Papaya is one of the most consumed fruits in the world; however, tissue damage caused by cuts quickly leads to its decay. Therefore, this study aimed to prepare and characterize lemon oil and curcumin nanocapsules to evaluate their capacity for preserving fresh-cut papaya. Lemon essential oil and curcumin nanocapsules were prepared using ethyl cellulose (EC) and poly-(ε-caprolactone) (PCL) by the emulsification-diffusion method coupled with ultrasound. The particles had sizes smaller than 120 nm, with polydispersity indices below 0.25 and zeta potentials exceeding -12 mV, as confirmed by scanning electron microscopy. The nanoparticles remained stable for 27 days, with sedimentation being the instability mechanism observed. These nanoparticles were employed to coat fresh-cut papaya, which was stored for 17 days. The results demonstrated their remarkable efficacy in reducing the respiration rate. Furthermore, nanocapsules maintained the pH and acidity levels of the papayas for an extended period. The lemon oil/EC nanocapsule treatment retained the color better. Additionally, all systems exhibited the ability to minimize texture loss associated with reduced pectin methylesterase activity. Finally, the nanocapsules showed a notable reduction in polyphenol oxidase activity correlating with preserving total phenolic compounds in the fruit. Therefore, the lemon oil and curcumin nanoparticles formed using EC and PCL demonstrated their effectiveness in preserving fresh-cut 'Maradol' papaya.

Effect of sourdough on the quality of whole wheat fresh noodles fermented with exopolysaccharide lactic acid bacteria

In this study, the impact of exopolysaccharides (EPS)-positive strain Weissella cibaria (W. cibaria) fermented sourdough on the quality of whole wheat fresh noodles (WWNs) and its improvement mechanisms were studied. The optimal fermentation conditions were found to be 30% sucrose content, fermented at 25 °C for 12 h, which yielded the highest EPS, 28.06 g/kg, in the W. cibaria fermented sourdough with sucrose (DW+). During storage, the sourdough reduced polyphenol oxidase activities and delayed the browning rate of noodles. The DW+ increased the hardness by 11.98% from 2184.99 to 2446.83 g, and the adhesiveness increased by 19.60%, i.e., from 72.01 to 86.13 g∙s of the noodles. The EPS mitigated acidification of sourdough, prevented the disaggregation of glutenin macropolymers (GMP), and increased sourdough elastic modulus. In addition, scanning electron microscope and confocal laser scanning microscopy of noodles containing EPS sourdough also demonstrated the uniform distribution of gluten proteins. The starch granules were also closely embedded in the gluten network. Thus, the present work indicated that the EPS produced sourdough delayed browning and improved the WWNs texture, indicating its potential to enhance the quality of whole grain noodles.

Effects of milling condition on nutritional, physicochemical, and textural properties of highland barley grains

AbstractBackground and ObjectivesA lower degree milling to obtain cereal grains with acceptable cooking qualities was recommended for the higher retainment of bioactive compounds. The aim of this work was to investigate effects of milling condition on nutritional, physicochemical and cooking qualities of highland barley (HB) grains.FindingsEffects of tempering results showed that increased water addition amount caused decrease in degree of milling (DOM) and increase in head rice yield (HRY). Effects of milling condition results showed that activities of polyphenol oxidase (PPO) and peroxidase (POD) showed significantly decreasing tendency as DOM increased. When DOM increased from 0% to 8%, the POD activity decreased from 140 to 3.75 Ug−1 min−1, with inactivation rate of 97.3%. Milling also witnessed a 70.1% reduction of PPO activity, from 27.74 to 8.30 Ug−1 min−1. Pasting results showed that viscosity parameters gradually increased and pasting temperature decreased as DOM increased. Texture results showed that the hardness, gumminess and chewiness of HB grains gradually decreased with the increase of DOM, while there was no significant difference in resilience, adhesiveness and springiness.ConclusionsBased on the nutritional, physicochemical and cooking qualities of HB grains, the optimal milling condition of HB grains was fixed at 6% of tempering water, 10 min of tempering time and 10% of DOM.

Influence of Convective and Vacuum-Type Drying on Quality, Microstructural, Antioxidant and Thermal Properties of Pretreated Boletus edulis Mushrooms.

Freshly harvested Boletus edulis mushrooms are subjected to rapid loss of quality due to the high moisture content and enzymatic activity. Drying time, quality characteristics, microstructural and thermal properties were studied in mushrooms ground to puree subjected to hot air drying (HAD), freeze drying (FD) and centrifugal vacuum drying (CVD). The influence of hot water blanching and UV-C pretreatments was additionally investigated. The rehydration ability of mushroom powders was improved by FD, especially without pretreatment or combined to UV-C exposure. The HAD and CVD, with no pretreatment or combined to UV-C, ensured good preservation of phenolics and antioxidant activity of dried mushrooms. The total difference in color of mushroom pigments extracted in acetone was lower in samples dried by CVD and higher in ones by FD. Blanching before HAD produced whiter product probably due to the reduced polyphenoloxidase activity. Scanning Electron Microscopy (SEM) analysis showed fewer physical changes in FD-samples. Heat-induced structural changes were noticed by Differential Scanning Calorimetry (DSC), Thermogravimetry (TG) and Derivative Thermogravimetry (DTG) analysis, in particular of biopolymers, confirmed by ATR-FTIR analysis. Based on our complex approach, the UV pretreatment of mushrooms could be a better alternative to water blanching. Centrifugal vacuum emerged as a new efficient drying method in terms of bioactive compounds, color and thermal stability, while FD led to better rehydration ability and microstructure.

Effects of short-wave ultraviolet light, ultrasonic and microwave treatments on banana puree during refrigerated storage.

Enzymatic browning is a major problem in minimally processed banana puree; it reduces consumer's acceptability and affects nutritional quality. The objective of this work was to evaluate the effects ultrasound (40 kHz/10 min), microwave (800 W/ 25 s) and UV-C radiation (1.97 kJ/m2) applied to banana puree. Colour parameters (L*, a*, b*, chroma and hue), browning index (BI), polyphenol oxidase (PPO) and peroxidase (POD) activities, total phenolic compounds (TPC), antioxidant capacity (AOC) and microbiological counts were monitored throughout storage at 4 °C. Ultrasound (US) and microwave (MW) treatments achieved a significant (p < 0.05) reduction in PPO activity and BI; moreover, ultrasound effectively retained phenolic compounds content (75% of initial value). The AOC was in coincidence with TPC values. POD activity was partially inhibited by UV-C while MW and US increase its activity. Although UV-C treatment was not effective to control browning development, it was effective to maintain microbiological stability after 20 days of storage (1.48 ± 0.01 log CFU/g). The evaluated treatments have the advantage of being less aggressive than conventional thermal treatments while maintaining fresh characteristics of the product.

Effects of maturity level, steam treatment, or active packaging to maintain the quality of minimally processed mango ( Mangifera indica cv. José)

The shelf-life of minimally processed José mango is primarily limited by browning during refrigerated storage. Three approaches were assayed to increase product shelf-life. Processing fruit sampled at an earlier ripening stage reduced browning during storage but fruit remained acidic. Steam treatment at 60°C for 3 min reduced polyphenol oxidase activity by 72%, and microbial population remained below 2.5 log CFU/g after 10 days of storage. However, the visual aspect of steam-treated mango pieces turned to dully green. Lastly, different multilayer film configurations containing an oxygen scavenger were tested. Two films, having a thickness of the active layer of 40 µm, limited color change by 32%–36% and hardness decrease of mango cuts after 7 days of storage at 4°C. Both active and passive layers of films contribute to maintain fruit quality. The use of active packaging was promising but requires further examination and possibly combination with other physical or chemical treatments. Novelty impact statement A short steam treatment partly inactivates PPO and increases microbiological quality but failed to maintain fruit color during storage. On the opposite, active packaging with oxygen scavenger limits browning and hardness loss during storage. Active and passive layers of films both play a role in maintaining fruit quality.

Enhancement in physicochemical parameters and microbial populations of mushrooms as influenced by nano-coating treatments

White button mushrooms are greatly high perishable and can deteriorate within a few days after harvesting due to physicomechanical damage, respiration, microbial growth of the delicate epidermal structure. For that reason, the present research work was applied to evaluate the effect of chitosan combination with nano-coating treatments on physicochemical parameters and microbial populations on button mushrooms at chilling storage. Nano coating with the addition of nisin 1% (CHSSN/M) established the minimum value for weight loss 12.18%, maintained firmness 11.55 N, and color index profile. Moreover, O2% rate of (CHSSN/M) mushrooms was the lowest at 1.78%; while the highest rate was reported for CO2 24.88% compared to the untreated samples (Control/M) on day 12. Both pH and total soluble solid concentrations increased during storage. Results reported that the (CHSS/M) mushroom significantly (P < 0.05) reduced polyphenol oxidase activity (24.31 U mg−1 Protein) compared with (Control/M) mushrooms that increased faster than the treated samples. (CHSSN/M) treatment was the most efficient in the reduction of yeast and mold, aerobic plate microorganisms (5.27–5.10 log CFU/g), respectively. The results established that nano-coating film might delay the aging degree and accompany by marked prolongation of postharvest mushroom freshness.

Characterization of polyphenol oxidase from purple sweet potato (Ipomoea batatas L. Lam) and its affinity towards acylated anthocyanins and caffeoylquinic acid derivatives

Biochemical characterization of polyphenol oxidase (PPO) present in purple sweet potato (PSP) is a key step in developing efficient methodologies to control oxidative damage caused by this enzyme to the valuable components of PSP, such as caffeoylquinic acid derivatives and acylated anthocyanins. Thus, this work focused on the assessment of the effects of pH, temperature, and chemical agents on the PPO activity as well as characterization of the PPO substrate specificity towards major phenolic compounds found in PSP. The optimum conditions of enzyme activity were pH 7 and a temperature range of 20–30 °C at which phenolic substrates were oxidized with 72.5–99.8% yield. Zn2+ ions remarkably reduced PPO activity while Cu2+ ions improved enzyme performance. The highest substrate preference was shown for 3,4,5-tri-caffeoylquinic and 3,5-di-caffeoylquinic acid, followed by 5-caffeoylquinic and caffeic acid, 3,4- and 4,5-di-caffeoylquinic acids, peonidin-3-caffeoyl-p-hydroxybenzoyl-sophoroside-5-glucoside. The highest Km values were found for 4,5-feruloyl-caffeoylquinic acid and catechol.

Impact of high pressure and thermal processing on probiotic mixed mango and carrot juices

This study aimed to elaborate a mixed mango and carrot juice processed thermally and by high isostatic pressure (HIP) added L. plantarum. L. plantarum caused a decrease in pH and increase in acidity of the juices, but did not change the antioxidant capacity (AC), and α- and β-carotene contents. HIP maintained the microbiological quality, whereas the pasteurized juices showed high psychrotrophic counts after 35 storage days. HIP did not influence the AC, whereas the pasteurized juices showed a decrease in AC and a 30% reduction in carotenoid contents. Pasteurization reduced the polyphenoloxidase and peroxidase activities and HIP promoted a reduction in polyphenoloxidase activity but increased the peroxidase activity (~30%). Mixed juices presented good sensory acceptance (HIP juice showed the highest score). Thus, HIP showed to be more effective than thermal process, the matrix proved to be capable of maintaining the L. plantarum viability, and could be an alternative for dairy products. Practical applications The results showed that the production of the probiotics mixed juices processed by high pressure is industrially interesting, since this process was able to better preserve sensory and nutritional characteristics of the juices compared to the thermal process. In addition, this probiotic product emerges as an alternative for vegetarian’s individuals who have diets with cholesterol restriction or allergy and/or intolerance to dairy products. Furthermore, due the effectiveness of applied conservation processes and biopreservation, these products were safe for consumption during the assessed refrigerated storage period.

Spray Golden Pothos and Croton Plants with Glutathione and Bilirubin to Purify the Indoor Air from Pollutants

Indoor air pollution is considered as one of the greatest risks to human health by many international health organizations. Therefore, there is a global trend to increase awareness among people of the importance of indoor plants as well as its important role in the purification of indoor air pollutants. So, this investigation was performed in Plexiglas chamber for evaluating the effects of foliar spraying of golden pothos and croton plants with non-enzymatic antioxidants: glutathione(GSH)and bilirubin(BI)at 300 mg L-1 and 600mg L-1 to increase their resistance and abilities to absorb formaldehyde and ammonia gases. Results showed that pothos and croton plants exposed to ammonia gas were extremely injured with a high number of dead leaves and decreased in fresh and dry weights as well as the total chlorophyll and carotenoids compared with the plants exposed to formaldehyde gas. GSH increased the total chlorophyll and carotenoids of pothos and croton under the formaldehyde gas. Treated pothos and croton plants with glutathione or bilirubin before exposure to the gases decreased the generation of reactive oxygen species(ROS),increase the guaiacol peroxidase and reduced polyphenol oxidase activities. Chloroplasts composition and stomatal index were injured with exposing croton and pothos plants to formaldehyde and ammonia gases with partially opening of stomata and moderately decrease the number of stomata. Pothos plants were greatly resistant and more growth efficiency when treated with BI at 600mgL-1 before exposed to formaldehyde gas.In conclusion, spraying pothos and croton plants with GSH at 600mgL-1 increased their resistance to formaldehyde and ammonia gases.

Effect of vacuum-thermosonication on the inactivation of Escherichia coli, Staphylococcus aureus, polyphenol oxidase and the quality parameters of soursop puree

Abstract The combined effect of vacuum, heat and ultrasound (vacuum-thermosonication, VTS) on soursop puree was investigated with regard to the viability of Escherichia coli and Staphylococcus aureus, inactivation of polyphenol oxidase and sensory quality. The VTS conditions were: vacuum (8.46, 11 and 16.93 kPa), heat (40, 45 and 50 °C), 1–3 intermittent vacuum pulses and ultrasound (24 kHz and 0.34 W/g of acoustic energy density) during 10 min. According to response surface methodology, the best conditions to obtain the highest microbial inactivation of ≥7 log CFU of inoculated E. coli and S. aureus, and reduction in polyphenol oxidase activity (94%) were 16.5 kPa vacuum, 50 °C, and three intermittent vacuum pulses for 10 min with ultrasound. The best VTS conditions did not negatively affect the quality parameters, and there were no significant changes in sensory attributes of the puree (a panel of 50 untrained judges). Therefore, we conclude that VTS appears a viable option in the processing of soursop.

Polyphenol oxidase inactivation in viscous fluids by ohmic heating and conventional thermal processing

AbstractThis study investigated polyphenol oxidase (PPO) inactivation in a viscous solution of carboxymethyl cellulose (CMC) by ohmic processing (OH) and conventional thermal processing (CTP) at several temperatures and to assess the impact of CMC consistency on PPO inactivation. OH affects the PPO activity in temperatures higher than 50°C (reduction to 20% at 50°C, 12 min and complete inactivation after 2 min at 80°C), whereas CTP caused a significant reduction in PPO activity only above 60°C (reduction to 90% at 60°C, 8 min and complete inactivation after 2 min at 80°C). The rate of PPO inactivation by ohmic heating was higher than by CTP under all conditions tested, represented by a reduction of D70°C (OH: 3.61 min, CTP 7.32 min), except D80°C was ∼0.5 for both techniques. The Z‐value was higher for OH (14.68°C) than for CTP (8.60°C). Consistency did not have a major impact on inactivation rate.Practical ApplicationsInactivating enzymes that alter quality aspects of food products, such as polyphenol oxidase (PPO), is an important objective of a food processing technology. PPO is an enzyme commonly found in fruits and vegetables that catalyzes browning reactions. Ohmic heating (OH) is a technology known for its potential for processing highly viscous products. This study corroborates the potential of OH for processing highly viscous fluids over conventional thermal processing (CTP), having a great potential to be an alternative technique to food processing. In addition, it gave more evidence of the nonthermal effects due to the electrical current during the ohmic processing.

Effect of non-thermal hurdles in shelf life enhancement of sugarcane juice

In this work, sugarcane juice was preserved using non-thermal hurdles consisting of microfluidisation and natural polypeptides (nisin and polylysine). The effects were compared with thermal hurdles which comprised of pasteurization and Potassium Metabisulfite (KMS) and the untreated control sample. All the samples were stored in glass bottles at 5±2 °C and evaluated for physico-chemical, microbial and sensory parameters till 63 days. In the untreated sample, pH and total soluble solids (TSS) decreased, whereas, titrable acidity and color (L* and a*) values increased significantly (P ≤ 0.01). Both thermal and non-thermal hurdles were able to cause a complete reduction in polyphenoloxidase activity which was 23 units in the control sample. In the sample treated with thermal hurdles small changes in pH, TSS, titrable acidity, color (L* and a*) occurred during storage. On the contrary, the physico-chemical properties of juice samples treated with non-thermal hurdles were stable throughout the storage period and were more acceptable to the sensory panel than the pasteurized sample. Using non-thermal hurdles, 100% reduction in initial microbial load of 3.19 × 106 CFU/ml was achieved and remained within 50 CFU/ml ensuring the shelf life of 56 days.

Dough browning inhibition of multigrain Indian flatbread (chapatti) using a combination of chemical and microwave treatment

Chapatti is whole wheat based unleavened flatbread which is consumed as a staple in most parts of India. Multigrain variants of chapatti are becoming popular with increased health awareness. The process of making chapatti is tedious; hence the practice of storing chapatti dough under refrigeration is common in many households. However, during storage the dough surface undergoes significant browning which is undesirable. The present study reports browning inhibition of multigrain dough by incorporating chemical inhibitors along with microwave treatment of flour. Browning was estimated in terms of brightness (HunterLab L* values) of the surface of dough stored at different temperatures (28 ± 2, 4 and − 18 °C). Additives such as ascorbic acid (AA), citric acid (CA) and L-cysteine (L-cys) were used singly and in combinations. Combinations of 0.3% AA + 90 ppm L-cys and 0.3% CA + AA (1:2 w/w) were effective in browning inhibition. Microwave (80 s) treatment to multigrain flour reduced polyphenol oxidase activity by 39% and peroxidase activity by 66% which helped to retard dough browning. Combination of microwave (80 s) and additives (0.3% CA + AA on 1:2 w/w basis) was found to be the most effective approach due to a synergistic effect. L* values were 61.08 and 60.72 for combination treated dough, while 47.92 and 50.71 for control dough at 96 h, 4 °C and at 30 days, − 18 °C respectively. The treatments did not adversely affect dough properties and the final product (chapatti) had no significant variation in texture and sensory acceptability.