Effects of High Pressure Homogenization on Beer Quality Attributes

The aim of the present study was to evaluate the use of high pressure homogenization (HPH) as an alternative to thermal pasteurization for beer stabilization and to evaluate the effect of processing on colour, haze and redox potential immediately after the process and during the product shelf‐life (100 days). The results obtained showed good colour retention, changes in the redox potential and greater values for turbidity, presenting a higher value for the product treated by HPH than for the thermally treated samples reported in literature. The evaluation of the results indicated that the HPH process is a promising process for beer treatment in terms of guaranteeing better colour retention. However to make this product stable, it would be necessary to perform stabilization treatments to minimize the negative effects of processing on the haze of the final product.     

Inactivation of Aspergillus niger in Mango Nectar by High-Pressure Homogenization Combined with Heat Shock

ABSTRACT:  This research evaluated the inactivation of a heat-resistant  Aspergillus niger  conidia in mango nectar by high-pressure homogenization (HPH) combined with heat shock.  A.niger  were inoculated in mango nectar (10⁶ conidia mL⁻¹) and subjected to HPH (300 to 100 MPa) and heat shock (80 °C for 5 to 20 min) before or after HPH. Processes were evaluated according to number of decimal reductions reached by each isolated or combined process. Scanning electron microscopy was performed to observe conidia wall after pressure treatment. Pressures below 150 MPa did not inactivate  A. niger  while pressures of 200 and 300 MPa resulted in 2 and more than 6 log reductions, respectively. D_{80 °C} of  A. niger  was determined as 5.03 min. A heat shock of 80 °C/15 min, reaching 3 decimal conidia reductions, was applied before or after a 200 MPa pressure treatment to improve the decimal reduction to 5 log cycles. Results indicated that HPH inactivated  A. niger  in mango nectar at 300 MPa (>6.24 log cycles) and that, with pressure (200 MPa) combined with post heat shock, it was possible to obtain the same decimal reduction, showing a synergistic effect. On the other hand, pre heat shock associated with HPH resulted in an additive effect. The observation of  A. niger  conidia treated by HPH at 100 and 200 MPa by scanning electron microscopy indicated that HPH promoted intense cell wall damage, which can sensitize the conidia to post heat shock and possibly explain the synergistic effect observed.
Practical Application : The results obtained in this paper are relevant to elucidate the mechanism of conidia inactivation in order to develop the application of HPH as an alternative pasteurization process for the fruit nectar industry.     

The effect of the high pressure homogenisation on the activity and stability of a commercial neutral protease from Bacillus subtilis

The activity of a commercial neutral protease from Bacillus subtilis after high pressure homogenisation (HPH) was investigated. The enzyme was processed up to 2000 bar, and the residual activity was measured from 20 to 70 °C during refrigerated storage. Moreover, the effect of HPH at high temperatures was evaluated. No improvement in the activities at 55–70 °C were observed after HPH, while an increase of approximately 30% in the 20 °C‐activity was reached after 2000 bar processing. Thus, HPH shifted the optimum temperature from 55 to 20 °C. The high temperature homogenisation caused no changes in 55 °C‐activity, but reduced 20 °C‐activity three times. It suggests that HPH modifies the protease configuration, changing enzyme performance (maximum activity condition), as the efficacy of lock‐and‐key mechanism is strictly dependent on enzyme spatial structure. The changes can be permanent or not, depending on homogenisation pressure, inlet temperature and enzyme storage conditions. Therefore, the HPH is a promising method to change protease characteristics.     

Viscoelastic Properties of Tomato Juice: Applicability of the Cox–Merz Rule

Tomato is one of the most important vegetables for the food industry. Rheological characterization of food is important for products, equipments, and unit operations design and evaluation. It is necessary for process optimization and high-quality products assurance. However, the works in literature present variable data, and some rheological characterization, as viscoelastic properties, are still scarce. The present work has evaluated the viscoelastic properties of tomato juice, as well as the applicability of the Cox–Merz rule. Tomato juice has shown dominant elastic properties rather than the viscous ones and could be classified as a weak gel (storage modulus higher then loss modulus). Moreover, due to the low pulp content, it has shown low viscoelastic behavior, with small dependency of oscillatory of the storage modulus. The rheological oscillatory and steady-state shear rheological properties of tomato juice were then correlated by two linear modifications on the Cox–Merz rule. The obtained values are in agreement with those described in the literature for other food products. The obtained data are potentially useful for future studies on food properties and process design.     

Influence of fibre addition on the rheological properties of peach juice

The addition of dietary fibres is a tendency in several foods. Understanding the changes in food sensory and physical properties due to fibre addition is thus, essential for food process design. The present work has evaluated the influence of peach fibre addition on the rheological properties of peach juice. Flow behaviour and influence of fibre concentration on Herschel‐Bulkley model’s parameters were evaluated. The flow behaviour of the products was changed due to fibre addition, from Newtonian to pseudoplastic and then, Herschel‐Bulkley behaviour. The parameters could be well modelled by exponential (σ₀), power law (k) and sigmoidal (n) functions (R² > 0.98). The viscoelastic properties were evaluated for the most concentrated products. Variation of storage and loss modulus with the oscillatory frequency were well described by a power function (R² > 0.96), and dependency of its parameters with temperature was well modelled by Arrhenius’ model (k′, k″, R² > 0.94) and quadratic function (n′, n″, R² > 0.90).     

Frozen Concentrated Orange Juice (FCOJ) Processed by the High Pressure Homogenization (HPH) Technology: Effect on the Ready-to-Drink Juice

The high pressure homogenization (HPH) process can be used to reduce the consistency of frozen concentrated orange juice (FCOJ), which is highly desirable in industrial processing due to the reduction in energy costs. The production of FCOJ is almost entirely destined to obtaining the reconstituted (ready-to-drink (RTD)) juice. Consequently, this study aimed to evaluate the effect of the HPH processing on the ready-to-drink juice. FCOJ (66°Brix) was processed by HPH up to 150 MPa and then diluted to 11°Brix for evaluation. The RTD juice was evaluated by pulp sedimentation, instrumental colour, turbidity (serum cloudiness), rheological properties and sensorial perception. The HPH process decreased the absorbance of the serum phase, which was related to the disruption of the suspended particles. Further, the process slightly reduced the RTD juice viscosity. However, the HPH showed no effect on the product colour, pulp sedimentation behaviour and sensorial perception (visual aspect, odour, flavour, viscosity, overall liking). Therefore, it was concluded that the HPH process can be used to promote desirable effects on FCOJ, without affecting the RTD juice properties.     

Effect of high pressure homogenization (HPH) on the rheological properties of tomato juice: Viscoelastic properties and the Cox–Merz rule

High pressure homogenization (HPH) is a non-thermal technology which has been widely studied as a partial or total substitute for the thermal processing of food. Although microbial inactivation has been widely studied, there are only a few papers in the literature reporting on physicochemical changes in fruit products due to HPH, especially regarding their rheological properties. The present work evaluated the effect of HPH (up to 150 MPa) on the viscoelastic properties of tomato juice. HPH increased the tomato juice storage (G′) and loss (G″) moduli. The parameters G′ and G″ were modelled as a power function of the oscillatory frequency (ω), and then evaluated as a function of homogenization pressure. It was observed that HPH processing improved tomato juice consistency more than it modified its nature/behaviour. The changes observed in the viscoelastic properties were attributed to disruption of the suspended particles during processing. Moreover, two modified Cox–Merz rules were used to correlate the products steady-state shear properties with viscoelasticity. The results obtained indicated that this process could be used to improve both product elastic and viscous behaviour, highlighting possible applications of the HPH process as a valuable tool to promote physical property changes in food products.