Simulated Fruit Juice Research Articles

Development of a predictive model of the microbial inactivation of L. monocytogenes during low thermal treatment of fruit juices in combination with carvacrol as aroma compound

Mild heat treatment of fruit juices in combination with natural aroma compounds has been reported as an alternative to conventional pasteurization to better preserve their nutritional value. However, its antimicrobial efficiency varies from one juice to another. This study aims at developing a secondary predictive model of microbial inactivation scale during such combined process. Carvacrol was used as aroma compound and acid-adapted L. monocytogenes as target microorganism. The inactivation kinetics of this bacteria were followed in simulated fruit juices using a Central Composite Design with pH (2-6), °Brix (0–24), temperature (55–65 °C), and carvacrol concentration (0–60 μL/L) as independent variables. Curves were fitted to the Weibull inactivation model, and data collected used to generate two predictive models of the inactivation scale parameter through multiple regression analysis following an empirical and a mechanistic (based on Gamma concept) approach. The best of the two models was then validated using real fruit (orange, pineapple, and watermelon) juices. The empirical model where only the four variables tested were considered showed a lower statistical performance compared to the mechanistic model where octanol-water partition coefficient (Ko/w) and vapour pressure (Vp) of carvacrol at the treatment temperature were integrated (R2 0.6 and 0.9; Accuracy factor 1.5 and 1.3; Sum of Squared Error 3.6 and 1.1, respectively). No significant difference was observed between inactivation scale values obtained with real juices and the predicted values calculated using this mechanistic model. The Ko/w and Vp of the aroma compound used are key parameters that determine the efficiency of the above-described combined treatment.

Juice composition, physicochemistry, and efficacy of ultraviolet radiation against Cryptococcus albidus

To the knowledge of the investigators, this is the first report of the establishment, validation, and application of a model that quantifies the effects of relevant physicochemical properties namely, pH (2.0–8.0), soluble solids (SS, 0.0–70.0 °Brix from sucrose), insoluble solids (IS, 0.0–3.0% wt/vol cellulose), and ascorbic acid (AA, 0–1000 mg/L) on the UV-C inactivation kinetic parameter, decimal reduction dose (DUV-C), of a UV-C resistant spoilage yeast in simulated fruit juice (SFJ). Cryptococcus albidus (LJY1) was grown to mid-stationary phase and thereafter suspended in SFJs with varying combinations of physicochemical properties as determined by a Rotatable Central Composite Design. Response Surface Modelling showed that the individual linear effects of all variables significantly (P < 0.05) influenced DUV-C. Only the individual quadratic effect AA2 significantly influenced the response. The interaction effects namely, (pH × IS) and (SS × AA) also significantly influenced DUV-C. The established model overestimated the DUV-C value by 54.88 to 139.62%, which could result in overly severe predicted process schedules. However, application in the processing and finished product quality evaluations showed that the model may be used as a food processing technique for a tested real orange juice sample.

Effects of distribution of sugars and organic acids on the taste of strawberries.

The concentrations of sugars and organic acids as well as the total soluble solid (TSS) in different parts of the strawberry fruit were characterized. The data were used to create simulated fruit juice jellies, in order to clarify how the sugar and organic acid levels affect the taste. Such an approach eliminates the influence of external factors such as size, color, and texture when using real fruits in sensory evaluations. Further, the use of a jelly allowed us to simulate the concentration differences between various parts of the fruit. In the strawberry fruit, the sugar content is higher in the apex than in the peduncle; however, the level of organic acids is the same throughout. It was revealed that the sweetness and sourness in the apex and peduncle could be sufficiently recognized by humans as tastes. Also, a layered jelly sample replicating the sugar and acid distribution in real strawberry was perceived as less sweet and more sour, compared to a homogeneous one with the same overall composition. The likely reason is that the sourness in the peduncle is accentuated by the low TSS level, which decreases the TSS/total organic acid ratio that affects the sweetness/sour perceptions. Based on these results, factors for the appropriate sensory evaluation of fresh fruits in general were considered. Specifically, the distribution of sugars and organic acids in the fruit should be analyzed first, and bite‐sized parts with concentrations close to the average provide the most accurate evaluation results.

Performance of a freeze concentration pilot plant during the start-up phase

In this paper are presented the findings obtained during the start-up of a freeze concentration pilot plant, that operated with suspension crystallisation and with simulated fruit juices. Solutions with different initial concentrations were tested, with and without acidification, to simulate fruit characteristics and behaviour. The experimental runs demonstrated that solution acidity has negligible effects on the process performance, whereas the results showed that the initial solution concentration influences the start-up duration. During this time, the solution concentration grows by about 10 °Brix, and the maximum quantity of ice content inside the crystalliser is always lower than 40% by weight. These findings can help to predict the performance of a freeze concentration plant and may facilitate achieving target concentrations in a more efficient mode. Taken together, the data suggest that the initial concentration of the processed juice influences start-up duration and the achievable final concentration.

Adsorption of 1-naphthyl methyl carbamate in water by utilizing a surface molecularly imprinted polymer

Surface molecularly imprinting polymer (SMIP) was utilized in the removal of a residual pesticide (carbaryl (CBL)) in water and simulated fruit juice. Being the crosslinking agent, ethylene glycol dimethacrylate (EGDMA) was copolymerized with the monomer, methacrylic acid (MAA) and CBL as the template molecules on the surface of the silica gel particles to produce the SMIP adsorbents. The SMIP adsorbents showed good selectivity and good adsorption capacity for CBL in the competitive adsorptions with two structurally related carbamate pesticides. The effect of the pretreatment solvents on the adsorption capacity of the SMIP adsorbent was investigated with the results of the numerical simulations. The adsorption isotherms and the adsorption kinetics were well described by the Freundlich equilibrium model and the pseudo-second-order kinetic model, respectively. Scatchard plot analysis revealed that there were two classes of binding sites populated in the SMIP adsorbents. In addition, the good selective adsorption of CBL by the SMIP adsorbent in a simulated fruit juice containing vitamin C and fructose indicated the great potential of the SMIP adsorbents to remove residual pesticide in food industry and processing industry for agricultural products.

A model for the influences of soluble and insoluble solids, and treated volume on the ultraviolet-C resistance of heat-stressed Salmonella enterica in simulated fruit juices

This study was conducted to determine the effects of intrinsic juice characteristics namely insoluble solids (IS, 0–3 %w/v), and soluble solids (SS, 0–70 °Brix), and extrinsic process parameter treated volume (250–1000 mL) on the UV-C inactivation rates of heat-stressed Salmonella enterica in simulated fruit juices (SFJs). A Rotatable Central Composite Design of Experiment (CCRD) was used to determine combinations of the test variables, while Response Surface Methodology (RSM) was used to characterize and quantify the influences of the test variables on microbial inactivation. The heat-stressed cells exhibited log-linear UV-C inactivation behavior (R2 0.952 to 0.999) in all CCRD combinations with DUV-C values ranging from 10.0 to 80.2 mJ/cm2. The DUV-C values obtained from the CCRD significantly fitted into a quadratic model (P < 0.0001). RSM results showed that individual linear (IS, SS, volume), individual quadratic (IS2 and volume2), and factor interactions (IS × volume and SS × volume) were found to significantly influence UV-C inactivation. Validation of the model in SFJs with combinations not included in the CCRD showed that the predictions were within acceptable error margins.

Effect of Acid Adaptation of Listeria monocytogenes on Its Mild Thermal Inactivation in a Simulated Fruit Juice Supplemented with Carvacrol

Effect of Acid Adaptation of Listeria monocytogenes on Its Mild Thermal Inactivation in a Simulated Fruit Juice Supplemented with Carvacrol

Estimation of ascorbic acid reduction in heated simulated fruit juice systems using predictive model equations

Predictive models for the estimation of residual ascorbic acid (rAA) and ascorbic acid percent change (%AAr) in heat-treated simulated fruit juices were established. The tested ranges of predictor product properties (pH and initial AA level) were based on initial surveys conducted involving processed and freshly squeezed juices, while those of predictor process parameters (heating temperature and treatment time) were based on thermal inactivation of Escherichia coli O157:H7 modeled earlier in our lab. Results showed that both rAA and %AAr data sets had highly significant (P < 0.0001) fit in a linear and quadratic model, respectively. Temperature, time, and initial AA were found significant predictors of rAA. On the other hand, temperature, time, initial AA, temperature2 and initial AA2 were found to be significant predictors of %AAr. Predictive performance indices were within acceptable values, confirming model utility in decision making for a more comprehensive control of juice nutritional functional quality and safety.

Development and validation of a predictive model for the influences of selected product and process variables on ascorbic acid degradation in simulated fruit juice

A predictive response surface model for the influences of product (soluble solids and titratable acidity) and process (temperature and heating time) parameters on the degradation of ascorbic acid (AA) in heated simulated fruit juices (SFJs) was established. Physicochemical property ranges of freshly squeezed and processed juices, and a previously established decimal reduction times of Escherichiacoli O157:H7 at different heating temperatures were used in establishing a Central Composite Design of Experiment that determined the combinations of product and process variable used in the model building. Only the individual linear effects of temperature and heating time significantly (P<0.05) affected AA reduction (%AAr). Validating systems either over- or underestimated actual %AAr with bias factors 0.80–1.20. However, all validating systems still resulted in acceptable predictive efficacy, with accuracy factor 1.00–1.26. The model may be useful in establishing unique process schedules for specific products, for the simultaneous control and improvement of food safety and quality.

Optical evaluation of deposition thickness and measurement of permeate flux enhancement of simulated fruit juice in presence of turbulence promoters

Ultrafiltration of simulated fruit juice (pectin and sucrose) is performed in continuous cross-flow mode with an organic ultrafiltration membrane (poly phenylene ethersulfone, PPE 30) of 30 K molecular weight cut off. The permeate fluxes are measured under different operating conditions of pressure, cross-flow velocity and pectin concentration. Significant enhancement of permeate flux is achieved by incorporation of straight cylindrical promoters placed across the flow. The optimum number of such promoters and their sizes are evaluated. Image analyzing video microscopy is successfully used to accurately quantify the deposition of pectin molecules on the membrane surface. The deposition thickness decreases with increase in cross-flow velocity, increases with pectin concentration but is less susceptible to increases in pressure. The effects of the shape of the promoters on flux enhancement and deposition thickness are also investigated in detail and approximately parabolic shaped promoters are chosen with further increases in flux enhancement (keeping the number of promoters same as in the case of straight promoters). The deposition thickness profiles around a promoter and the average deposition thickness on the whole membrane are optically measured and the consistency of the results in relation to enhancement of permeate flux are examined.

Fiber entrapment of naringinase from Penicillium sp. and application to fruit juice debittering

Naringinase from Penicillium sp. was immobilized on cellulose triacetate by the fiber entrapment method. Although the optimum pH (3.7) and optimum temperature (55°C) of the fiber-entrapped enzyme were similar to those of the native form, the immobilized enzyme had better heat stability. Kinetic studies showed that the immobilized enzyme had higher K m values than its native form. When this immobilized naringinase was successively used in a column reactor for the hydrolysis of ρ-nitrophenyl-α- l-rhamnoside or naringin in a simulated fruit juice system or grapefruit juice, the enzyme column could be operated with satisfactory stability. In addition, when the natural grapefruit juice was recycled through the column reactor, no column blocking or filtering action of the catalyst bed was observed.

Comparison of the kinetics and factors affecting the stabilities of chitin-immobilized naringinases from two fungal sources

Naringinases from both Penicillium sp. and Aspergillus niger were compared for their enzyme kinetics and the effects of sugars on the enzyme activities. Lineweaver-Burk plots showed that glucose, fructose and rhamnose were all competitive inhibitors for α-rhamnosidase of naringinase from Penicillium sp. and non-competitive inhibitors for the same enzyme from A. niger, When naringinase from Penicillium sp. was immobilized on chitin and used successively for the hydrolysis of p-nitrophenyl- α-rhamnoside or naringin in a simulated fruit juice system or grapefruit juice, it was observed that the enzyme column was very stable. Such results are in contrast to what has bee observed for naringinase fron A. niger. Therefore, it is quite possible that the sugars in the fruit juice which play a role as competitive or non-competitive inhibitors on naringinase may account for the stability of the enzyme column during successive debittering of grapefruits juice.