The effects of acid adaptation on Escherichia coli inactivation using power ultrasound

Inactivation of Escherichia coli in liquids was carried out using power ultrasound. Parameters examined included amplitude levels (0.4 µm, 7.5 µm, 37.5 µm), treatment time, cell condition (non-adapted cells, acid adapted cells), liquid media (TSB, model orange juice and model apple juice) and E. coli strain (ATCC 25922, NCTC 12900). The efficacy of ultrasound treatment was found to be a function of amplitude level, treatment time and media (p < 0.05). The kinetics of inactivation followed zero order kinetics (R > 0.95), with the highest inactivation achieved using an amplitude of 37.5 µm. The D-values of E. coli 25922 at all amplitudes in model orange juice were not significantly different than in TSB media. However, at 0.4 µm and 37.5 µm amplitude D-values of E. coli 12900 were significantly different in model orange juice compared to TSB media. When efficacy of ultrasound was assessed in model apple juice and phosphate buffered saline treatment times were significantly reduced by comparison with TSB. Inactivation of E. coli was found to be influenced by strain, prior acid adaptation and suspension liquid, but the effect was negated at the higher amplitude levels.

Industrial relevance

To facilitate the preservation of unstable nutrients many juice processors have investigated alternatives to thermal pasteurisation, including un-pasteurised short shelf life juices with high retail value. This trend has continued within the European Union. However within the US recent regulations by the FDA have required processors to achieve a 5-log reduction in the numbers of the most resistant pathogens in their finished products. This rule comes after a rise in the number of food borne illness outbreaks and consumer illnesses associated with consumption of untreated juice products. Pathogenic E. coli may survive in acid environments such as fruit juices for long periods. Ultrasound has been identified as one possible non-thermal technology to meet the required microbial log reduction. However it is important to determine if conditions such as acid adaptation and pathogen strain influence ultrasound efficacy, if the technology is to be adopted by industry.     

Non-thermal pasteurization of fruit juices by combining high-intensity pulsed electric fields with natural antimicrobials

The effect of high-intensity pulsed electric fields (HIPEF) on the Salmonella Enteritidis and Escherichia coli O157:H7 populations inoculated in apple, pear, orange and strawberry juices as influenced by treatment time and pulse frequency was investigated. Combinations of HIPEF (35 kV/cm, 4 μs pulse length in bipolar mode without exceeding 40 °C) with citric acid or cinnamon bark oil against these pathogenic microorganisms in fruit juices were also evaluated. Treatment time was the more influential factor on the microbial reduction in all the fruit juices analyzed. S. Enteritidis and E. coli O157:H7 were reduced by more than 5.0 log₁₀ units in orange juice treated by only HIPEF; whereas strawberry, apple and pear juices were pasteurized when HIPEF was combined with citric acid at 0.5, 1.5, 1.5%, respectively, or cinnamon bark oil at 0.05, 0.1 and 0.1%, respectively. Synergistic and additive killing effects against S. Enteritidis and E. coli O157:H7 in fruit juices by combining treatments were observed.

Industrial relevance

The use of high-intensity pulsed electric fields treatment as a non-thermal pasteurization method in combination with organic acids or essential oils is an effective process for eliminating S. Enteritidis and E. coli O157:H7 populations in fruit juices upper 5.0 log₁₀ reductions. Therefore, combinations of those treatments may help to ensure the microbiological safety in juice products, and to reduce the risk of food-borne illness caused by the consumption of these kinds of foods.     

Inactivation of Escherichia coli by ozone treatment of apple juice at different pH levels

This research investigated the efficacy of gaseous ozone on the inactivation of Escherichia coli ATCC 25922 and NCTC 12900 strains in apple juice of a range of pH levels, using an ozone bubble column. The pH levels investigated were 3.0, 3.5, 4.0, 4.5 and 5.0. Apple juice inoculated with E. coli strains (10⁶ CFU/mL) was treated with ozone gas at a flow rate of 0.12 L/min and ozone concentration of 0.048 mg/min/mL for up to 18 min. Results show that inactivation kinetics of E. coli by ozone were affected by pH of the juice. The ozone treatment duration required for achieving a 5-log reduction was faster (4 min) at the lowest pH than at the highest pH (18 min) studied. The relationship between time required to achieve 5 log reduction (t_5d) and pH for both strains was described mathematically by two exponential equations. Ozone treatment appears to be an effective process for reducing bacteria in apple juice and the required applied treatment for producing a safe apple juice is dependant on its acidity level.     

Radio frequency electric fields processing of orange juice

The non-thermal process of radio frequency electric fields (RFEF) has been shown to inactivate bacteria in apple juice at moderately low temperatures, but has yet to be extended to inactivate bacteria in orange juice. An 80 kW RFEF pasteurizer was used to process pulp-free orange juice at flow rates of 1.0 and 1.4 l/min. Escherichia coli K12 in orange juice was exposed to electric field strengths of 15 and 20 kV/cm at frequencies of 21, 30, and 40 kHz. Ascorbic acid (Vitamin C) content and color of the juice before and after treatment were analyzed. Electrical energy costs were calculated using the measured voltage and current. An energy balance was performed using the inlet and outlet temperatures. Processing at an outlet temperature of 65 °C reduced the population of E. coli by 3.3 log relative to the control. Increasing the treatment time and temperature and decreasing the frequency enhanced the level of inactivation. Varying the electric field strength over the range of conditions used had no effect on the inactivation. No loss in ascorbic acid or enzymatic browning was observed due to RFEF processing. The electrical energy determined using the voltage and current was 180 J/ml. This was in good agreement with the energy calculated using the temperature data. The electrical cost was $0.0026/l of orange juice. The results provided the first evidence that the RFEF process inactivates bacteria in orange juice at moderately low temperatures.

Industrial relevance

The RFEF process has been shown to inactivate E. coli in apple juice at moderately low temperatures, but has yet to be extended to inactivate bacteria in orange juice. An RFEF pilot plant pasteurizer was used to process orange juice at rates of up to 1.4 l/min. RFEF processing reduced the population of E. coli by 99.3% at 60 °C and a hold time of 3 s, whereas conventional heating at the same conditions had no effect on the E. coli. This work demonstrated that the non-thermal RFEF process can be extended to inactivate bacteria in orange juice.     

Response of Escherichia coli O157:H7 in apple and orange juices by hydrostatic pressure treatment with rapid decompression

The bactericidal efficiency of hydrostatic pressure treatment combined with a slow decompression (SD; about 30 s) or a rapid decompression (RD; about 2 ms) against clinically isolated Escherichia coli O157:H7 was investigated in apple juice, orange juice and McIlvaine buffers having the same pH values of the juices used. Effects of the SD and RD treatments on survivability of E. coli O157:H7 cells during storage at 4°C in the juices were also investigated. The RD treatment showed higher inactivation effect than the SD treatment in both the juices and buffers. Untreated E. coli O157:H7 cells were not inactivated during storage for 5 days; however, post-treatment storage after both the SD and RD treatments reduced survivability of E. coli O157:H7 cells in the juices. The degree of the reduction was higher in the cells subjected to the RD treatment than to the SD treatment.     

Study of pulsed light inactivation and growth dynamics during storage of Escherichia coli ATCC 35218, Listeria innocua ATCC 33090, Salmonella Enteritidis MA44 and Saccharomyces cerevisiae KE162 and native flora in apple,orange and strawberry juices

The response of some inoculated strains and native flora to PL treatment (Xenon lamp, 3 pulses s^?1, 10 cm distance from the lamp, 71.6 J cm^?2) in apple, orange and strawberry fresh juices with different absorbance, turbidity and particle size was investigated. Microbial growth dynamics during 12‐day storage (5 °C) of PL‐treated juices was also evaluated. PL treatments provoked 0.3–2.6 log reductions for inoculated microorganisms and 0.1–0.7 for native flora. High turbidity and particles with high UV absorbance seemed to play a major role in the PL efficiency compared to particle size. Cold storage of PL‐processed juices provoked an increase in Salmonella Enteritidis and Listeria innocua inactivation, achieving 5.0–8.0 log reductions, while no recovery of Escherichia coli and retardation for yeast growth was observed, compared to untreated samples. This study gives valuable information regarding the influence of juice variables on PL effectiveness and emphasises the beneficial effect of a postcold storage on microbial safety of PL‐treated juices.     

Inactivation of food spoilage bacteria and Escherichia coli O157:H7 in phosphate buffer and orange juice using dynamic high pressure

This study aimed to evaluate the potential of dynamic high pressure (DHP) technology to inactivate pathogenic and spoilage microflora in orange juice. Escherichia coli O157:H7 ATCC 35150, Lactobacillus plantarum ATCC 14917, Leuconostoc mesenteroides ATCC 23386 and two orange juice isolates: Saccharomyces cerevisiae and Penicillium ssp. were subjected individually to different DHP treatments. The effectiveness of DHP treatment was first evaluated in phosphate buffered saline (PBS) before application in orange juice samples. The inactivation efficacy of DHP depended on the pressure applied and the number of passes. It was more efficient against Gram-negative strains than Gram-positives. Complete inactivation and 5 log reduction of E. coli O157:H7 were achieved in orange juice at 200 MPa after 5 and 3 passes at 25 °C, respectively. Lower inactivation was obtained with Penicillium ssp. (4 log), S. cerevisiae (2.5 log), L. plantarum (2.3 log) and L. mesenteroides (1.6 log). The gathered results revealed the potential of DHP to inactivate all the tested microorganisms and then, it could constitute a promising alternative technology for cold pasteurization of fruit juices.     

Ultraviolet Treatment of Orange Juice to Inactivate <Emphasis Type="Italic">E. coli</Emphasis> O157:H7 as Affected by Native Microflora

The effect of yeast concentration on ultraviolet (UV) inactivation of five strains of Escherichia coli O157:H7 from different sources, inoculated both individually and simultaneously in orange juice, was analyzed and mathematically modeled. The presence of yeast cells in orange juice decreases the performance of UV radiation on E. coli inactivation. UV absorption coefficients in the juice increased with increasing yeast concentration, and higher UV doses were necessary to inactivate bacterial strains. UV intensities of I = 3.00 ± 0.3 mW/cm² and exposure times (t) between 0 and 10 min were applied; radiation doses (energy, E = I × t) ranging between 0 and 2 J/cm² were measured using a UV digital radiometer. All the tested individual strains showed higher resistance to the treatment when UV radiation was applied at 4 °C in comparison to 20 °C. UV inactivation of E. coli O157:H7 individual strain was satisfactory fitted with a first order kinetic model. A linear relationship was found between UV absorptivities and D values (radiation doses required to decrease microbial population by 90%) for each strain. The dose required to reach 5-log reduction for the most unfavorable conditions that is the most UV resistant strain, and maximum background yeast concentration was 2.19 J/cm² at 4 °C (corresponding to 11 min of UV treatment) and 2.09 J/cm² at 20 °C (corresponding to 10.55 min of UV treatment). When a cocktail of strains was inoculated in orange juice, the logistic equation was the best model that fits the experimental results due to the deviation from the log-linear kinetics. The UV resistance between strain cocktail and single strain were mathematically compared. Slopes of the decline curves for strain cocktail at high UV doses were lower than the slopes of the log-linear equation calculated for the individual strains, even for the most resistant one. Therefore, microbial inactivation tests using a cocktail of strains are particularly important to determine the performance of the UV inactivation treatment.     

Low thermal inactivation of Escherichia coli ATCC 25922 in pineapple,orange and watermelon juices: Effect of a prior acid‐adaptation and of carvacrol supplementation

Past research on the association of natural antimicrobials and low temperatures for fruit juices pasteurization has not targeted acid‐adapted strains which are yet the most relevant strains in these products. We found that previously acid‐adapted Escherichia coli ATCC 25922 cells exhibited an increase of their resistance to thermal inactivation at 55 °C for 5 min both in the presence and absence of carvacrol (30 µL/L). The inactivation of E. coli was more intense in pineapple (pH 3.25) and orange (pH 3.61) juice, than in watermelon juice (pH 5.4). Supplementation of juices with carvacrol decreased the survival of both acid‐adapted and non‐adapted bacterial cells. Our results suggest that the supplementation of fruit juices with natural antimicrobials, such as carvacrol, may contribute to counteract the mild thermal tolerance developed by acid‐adapted bacteria. Given the different properties of fruit juices, such combined treatments need to be developed specifically for each fruit product.

Practical applications

Supplementation of fruit juices with natural antimicrobials has been described to increase the efficiency of microbial mild thermal inactivation treatments. However, its effect on the thermal resistance of acid‐adapted cells has not previously been addressed. We observed that acid adaptation enhances mild thermal tolerance. Our results suggest that natural antimicrobials can effectively counteract the mild thermal tolerance of acid‐adapted cells. The combination of mild temperature treatments and natural antimicrobials is a firm alternative to conventional pasteurization to ensure the safety of fruit juices without affecting their nutritional properties. Moreover, this combined strategy does not require expensive novel technologies or high energy consumption.     

Bacterial inactivation in fruit juices using a continuous flow Pulsed Light (PL) system

In this work, the susceptibility to pulsed light (PL) treatments of both a Gram-positive (L. innocua 11288) and a Gram-negative (E. coli DH5-??) bacteria inoculated in apple (pH = 3.49, absorption coefficient 13.9 cm^− 1) and orange juices (pH = 3.78, absorption coefficient 52.4 cm^− 1) was investigated in a range of energy dosages from 1.8 to 5.5 J/cm². A laboratory scale continuous flow PL system was set up for the experiments, using a xenon flash-lamp emitting high intensity light in the range of 100-1100 nm. The flashes lasted 360 ??s at a constant frequency of 3 Hz.The results highlighted how the lethal effect of pulsed light depended on the energy dose supplied, the absorption properties of liquid food as well as the bacterial strain examined. The higher the quantity of the energy delivered to the juice stream, the greater the inactivation level. However, the absorbance of the inoculated juice strongly influenced the dose deliver and, therefore, the efficiency of the PL treatment. Among the bacteria tested, E. coli cells showed a greater susceptibility to the PL treatment than L. innocua cells in both apple and orange juices. Following treatment at 4 J/cm², microbial reductions in apple and orange juices were, respectively, 4.00 and 2.90 Log-cycles for E. coli and 2.98 and 0.93 Log-cycles for L. innocua.Sublethally injured cells were also detected for both bacterial strains, thus confirming that membrane damage is an important event in bacterial inactivation by PL.     

High-pressure homogenization of orange juice to inactivate pectinmethylesterase

A homogenizer was used to treat orange juice at five pressures (0–250 MPa) and three initial temperatures (22, 35 and 45 °C). A maximum of five passes for the selected conditions were used to process orange juice. Pectinmethylesterase (PME) activity, microbial load, cloudy appearance, and vitamin C were evaluated in just squeezed and homogenized orange juices. A reduction of 50.4, 49.4 and 37.8% of PME activity was observed in juice homogenized by one pass at 250 MPa at the initial temperatures of 22, 35, and 45 °C, respectively. Pectinmethylesterase activity in orange juice was reduced as passes number was increased. The final temperature of the five times homogenized orange juice was not beyond 28 and 37 °C after being treated at 100 and 250 MPa, respectively. More than 30 and 80% of enzyme activity was reduced after five passes at 100 and 250 MPa, respectively. Less that 8.7 × 10² and 1.85 × 10³ CFU/mL of mesophiles and yeasts plus molds, respectively, were counted in orange juice treated five times at 100 MPa. The cloudy appearance of the homogenized orange juice was maintained for 12 days under low temperature conditions.

Industrial relevance

“Cold pasteurization” of orange juice, using a homogenizer as a high-pressure procedure, could be an alternative to thermal processing to avoid sensory, nutritional and physiochemical changes in juice. This process may deliver a pasteurized orange juice with characteristics similar to just squeezed orange juice. In addition to reduce the microbial load, homogenization may reduce pectinmethylesterase enzyme, which may cause phase-separation in juice and consequently give an unwanted appearance that consumers dislike. Additionally, homogenized orange juice appearance could be stable during several days before being brought to the consumers' daily eating table.     

Inactivation kinetics of pectin methylesterase and cloud retention in sonicated orange juice

The effect of sonication on pectin methylesterase (PME) activity and cloud stability of orange juice was studied. Ultrasonic acoustic energy density (AED) levels of 0.42, 0.47, 0.61, 0.79 and 1.05 W/mL and treatment times of 0 (Control), 2, 4, 6, 8 and 10 min were investigated. The highest PME inactivation level observed was 62% for sonication at the highest AED level and treatment time. A fraction conversion model adequately described the PME inactivation compared to first order or polynomial models. A significant change in particle size distribution was observed in sonicated samples due to cavitational effects. These results indicate that the cloud stability of sonicated orange juice depends not only on PME inactivation but also on particle size reduction.Industrial relevancePower ultrasound is a non thermal pasteurisation method that has been identified to meet the US FDA requirement for a 5 log reduction in E. coli pertinent to fruit juices. Apart from microbial inactivation, cloud stability is a critical orange juice quality parameter influencing product shelf life and consumer acceptance. This work demonstrates that sonication at low AED levels and temperatures can be employed to achieve the desired cloud stability.     

Use of High-Intensity Ultrasound and UV-C Light to Inactivate Some Microorganisms in Fruit Juices

Novel technologies that involve non-thermal processes have been investigated in the last two decades as full or partial alternatives to conventional heat treatment. The main objective of this study was to evaluate the survival of single or strain cocktail of Escherichia coli, Saccharomyces cerevisiae, and a yeast cocktail in orange (pH 3.5; 9° Brix) and/or apple (pH 3.1; 12° Brix) juices and in 0.1% w/w peptone water processed by two non-thermal techniques: high-intensity ultrasound (USc) and/or short-wave ultraviolet radiation (UV-C). USc treatments (20 kHz, 95 μm-wave amplitude) were performed using a stainless steel continuous flow cell with a 13-mm probe (0.2 L/min; 40°C). The UV-C device consisted of a 90-cm long UV-C-lamp (100 W) placed inside a glass tube leaving an annular flow space (0.2 L/min; 40°C). Inoculated systems were recirculated through simultaneous or consecutive USc and UV-C devices and samples were taken at preset time intervals. Microbial populations were monitored by plate count technique. In peptone water and apple juice, UV-C radiation provoked higher E. coli ATCC 35218 inactivation than USc treatment. E. coli ATCC 35218 and its cocktail were more sensitive than S. cerevisiae KE162 and the cocktail of yeasts. UV-C efficiency was highly dependent on media nature. The poor single effect of UV-C light in orange juice was enhanced by the combination with USc. Combined treatment was more effective in simultaneous rather than in a series of USc − UV-C arrangement.     

Effect of storage in juice with or without pulp and/or calcium lactate on the subsequent survival of Escherichia coli O157:H7 in simulated gastric fluid

A study was conducted to evaluate the effect of storing Escherichia coli O157:H7 in fruit or vegetable juices with or without pulp and/or calcium lactate, on the bacterial resistance to a simulated gastric fluid (SGF, pH 1.5). Apple, carrot, orange, and tomato juices containing pulp or freed from pulp by filtration were used in this study. Calcium lactate at about 1.4 g/l was added to juices to obtain calcium supplemented juices. Juices with or without pulp and/or calcium lactate were inoculated with E. coli O157:H7 and then were stored at 7 degrees C for 0, 1, 2, or 4 days. The acid resistance of cells stored in juices with or without pulp and/or calcium lactate was determined by incubating in SGF for 90 or 240 min at 37 degrees C. Cells stored in apple juice for 4 days, carrot juice for 2 days, and orange juice for 4 days with pulp only had greater acid resistance, while all cells stored in tomato juice with pulp had greater acid resistance than cells stored in juice without pulp. The D-values of cells stored in supplemented apple and orange juices with calcium lactate declined 1.7-3.5 fold, whereas D-values of cells stored in supplemented tomato juice decreased by about 1.4-fold when compared to cells stored in juice without calcium lactate after exposure in SGF. These results indicate that storing E. coli O157:H7 in juices with pulp had little or no effect on the acid resistance of cells during subsequent exposure in SGF. Calcium lactate supplemented into juices could dramatically decrease the ability of E. coli O157:H7 to survive in SGF, possibly reducing the risk of foodborne illness by juice products.     

Application of a multi-pass high-pressure homogenization treatment for the pasteurization of fruit juices

This work evaluates both the effects of a multiple-pass high-pressure homogenization treatment on the microbial inactivation of selected microbial strains (Saccharomyces cerevisiae, Lactobacillus delbrueckii, Escherichia coli) inoculated into commercial fruit juices (orange, red orange, pineapple) as well as the application of this non-thermal technology to the pasteurization of fresh juices (Annurca apple juice). The pressure level ranged from 50 to 250 MPa, the number of passes from 1 to 5 and the inlet temperature from 2 to 20 °C.Preliminary tests in distilled water showed that the efficiency of the multiple-pass treatment significantly depends on both the homogenizing pressure as well as the microbial species. The subsequent extension of the multiple-pass treatment to the inactivation of S. cerevisiae inoculated into three different fruit juices (orange, red-orange and pineapple juice) highlighted that the inactivation induced by the high pressure treatment did not depend on the properties of the tested juices and was not statistically different from inactivation in water (p value < 0.05). These findings were supported by the comparison of two different mathematical models used to fit the inactivation kinetics, whose fitting parameters were not significantly different for water and the fruit juices for any pressure level applied.Three homogenization passes at 150 MPa and 25 °C, which resulted to be optimal for yeast inactivation in fruit juices, were effective for the stabilization of the endogenous microbial load of fresh Annurca apple juice. The treated apple juice showed a minimum shelf-life of 28 days under refrigerated conditions, during which the natural qualities of the fresh juice were completely preserved.     

Inactivation of pectinmethylesterase in fresh orange juice by cold atmospheric plasma technology: A kinetic study

Preservation of fruit juices requires the inactivation of natural endogenous enzymes, such as pectinmethylesterase (PME). Within this work, cold atmospheric plasma (CAP), and in particular a dielectric barrier plasma jet fed with helium gas, was demonstrated to effectively inactivate PME of freshly squeezed orange juice in short treatment times (2–30 min). By a combination of temperature measurements and a multidimensional heat transfer model, the temperature profile of the whole sample during plasma treatment was extracted. It was found that the thermal phenomena were not a driving factor for PME inactivation. Plasma treatment of orange juices resulted in inactivation of 55–80% of PME with <5.0% of PME inactivation caused by the temperature increase from 20 to 90 °C. The Weibull distribution model compared to the first-order fractional, the sigmoidal logistic and the Hulsheger's kinetic models was found to better describe mathematically (R² > 0.99; A_f = 1.002–1.052) the effect of CAP processing on residual PME activity. Multi-parameter equation fits allowed the prediction of residual PME activity as a function of the applied voltage, helium flow, and treatment time. Generally, higher voltages and lower helium flows applied led to higher PME inactivation rates in fresh orange juice.     

Inactivation of Escherichia coli O157:H7, Salmonella typhimurium and Listeria monocytogenes in apple juice with gaseous ozone

This research was initiated to assess the efficacy of gaseous ozone for inactivation Escherichia coli O157:H7, Salmonella typhimurium and Listeria monocytogenes in apple juice. Juice samples with solids content of 18, 36, and 72 °Brix inoculated with a culture cocktail of three foodborne pathogens were treated with gaseous ozone at a flow rate of 3.0 L/min and an ozone generation rate of 0.10, 0.90, 3.51, and 5.57 g/h for 0.5, 1, 5, and 10 min, respectively. The inactivation kinetics of gaseous ozone on foodborne pathogens conformed to the Weibull model. The time required to achieve a 5 log reduction (t_5d) was estimated using the parameters of the Weibull model. The t_5d increased with increasing solids content of apple juice. The ozone generation rate did not impart a significant effect (p > 0.05) on t_5d. Gaseous ozone is effective at inactivating foodborne pathogens in apple juice but the efficacy is dependent on the solids content of the juice sample.     

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.     

Orange juices enriched with chitosan: Optimisation for extending the shelf-life

Optimisation of the incorporation of chitosan in orange juice was accomplished by the evaluation of quality and nutritional markers. Response surface methodology was applied to obtain quadratic and second degree response surface model equations. The analyses showed that increases in chitosan concentration extended the quality of the orange juice significantly (p < 0.05), reducing enzymatic and non-enzymatic browning and controlling the spoilage during the storage time; however, concentrations > 1 g L^− 1 produced a significant (p > 0.05) reduction in the concentrations of ascorbic acid and carotenoids associated with the positive charge of chitosan and its ability to flocculate and coagulate negatively charged substances. Also, concentrations > 1 g L^− 1 were scored as unacceptable for the sensory panel due to an increase in bitterness. The study recommends the use of chitosan at concentrations up to 1 g L^− 1 to extend quality and preserve ascorbic acid and carotenoids during storage time of fresh orange juice, thus avoiding the use of standard thermal treatments which produces a negative impact on the nutritional value.

Industrial relevance

One of the major problems of fresh orange juice is its limited shelf-life. Spoilage and quick degradation of vitamins are two of the most important causes of quality loss during the shelf-life of this product. Moreover, the U. S. Food and Drug Administration issued a warning to consumers against drinking unpasteurised orange juice products because of the potential contamination with Salmonella typhimurium and its association with an outbreak of human disease caused by this organism [FDA issues nationwide health alert on Orchid Island unpasteurised orange juice. Products Recalls, Market Withdrawals and Safety Alerts.]. The main objective of this study was the study of chitosan as a natural preservative for extending the shelf-life of orange juice and as an alternative to pasteurisation.     

The Effect of Ultraviolet Light on Microbial Inactivation and Quality Attributes of Apple Juice

Non-thermal technologies such as UV irradiation can offer advantages for minimal processing of transparent beverages. In this study, reconstituted apple juice was exposed to UV light in a continuous laboratory scale system at energy dosages ranging from 2.66 to 53.10 J/cm² by changing the exposure time. Treated juices were then evaluated for microbial inactivation and selected physical and chemical attributes. Product quality was further assessed by sensory evaluation using a 30-member consumer panel. Microbiological analysis was performed by inoculating apple juice with Escherichia coli K12 and Listeria innocua and microbial numbers were counted pre- and post-processing. UV energy levels did not affect pH, °Brix, or total phenols content, but decreased non-enzymatic browning (p < 0.01) and antioxidant capacity (p < 0.05) compared to unprocessed juice. A colour-lightening effect was noted with increasing energy dose. All UV treatments applied (2.66 J/cm² and above) resulted in a reduction below the detection level (<1 log cfu/ml) for both E. coli and L. innocua in apple juice. Sensory evaluation showed that samples treated with energy dosages up to 10.62 J/cm² were comparable to the control in terms of acceptability, though higher dosages produced adverse effects in terms of flavour and colour. Based on these results, UV treatment with low energy dosages could represent a valid alternative to thermal processing to eliminate pathogenic microorganisms while maintaining quality in reconstituted apple juice.