Ohmic heating processing of milk for probiotic fermented milk production: Survival kinetics of Listeria monocytogenes as contaminant post-fermentation, bioactive compounds retention and sensory acceptance.

The survival kinetics of Listeria monocytogenes (9 log CFU/mL) as a post-fermentation contaminant in probiotic fermented milk (Lactobacillus acidophilus La-5, 8-9 log CFU/mL) processed with milk subjected to ohmic heating (0, 4, 6, and 8 V/cm; CONV, OH4, OH6, OH8, 90-95 °C/5 min) was investigated using Weibull predictive model. Additionally, the presence of bioactive compounds (antioxidant activity, inhibition of the enzymes α-glucosidase, α-amylase, and angiotensin-converting) and sensory analysis (consumer test) of probiotic fermented milks were evaluated. Overall, OH provided a decrease in the viability of Listeria monocytogenes, suitable Lactobacillus acidophilus counts, and satisfactory results in the gastrointestinal tract survival. The Weibull model presented an excellent fit to the data of all conditions. Furthermore, lower δ values (217-298 against 665 h, CONV), and increased R2 values (0.99 against 0.98, CONV) were obtained for the OH-treated samples, emphasizing the best performance of OH data. In addition, OH improved the generation of bioactive compounds as well as the sensory acceptance. Indeed, considering functional and safety purposes, OH presented as an interesting technology to be used in milk for manufacturing probiotic fermented milk.

Ohmic heating as a method of obtaining paraprobiotics: Impacts on cell structure and viability by flow cytometry.

This study aimed to evaluate the effects of ohmic heating (OH) on probiotic inactivation, cell viability and morphology of the probiotic strains Lactobacillus acidophilus LA 05 (LA), Lacticaseibacillus casei 01 (LC), and Bifidobacterium animalis Bb 12 (BA) to develop paraprobiotics. OH at different electric field magnitudes (4, 8, and 12 V/cm at 60 Hz) and conventional heat treatment (CONV) were performed to determine the most adequate condition for the obtainment of paraprobiotics. Analysis of culturability, flow cytometry (FC), and Scanning electron microscope (SEM) was carried out. The complete inactivation by CONV was achieved only in the following conditions: LA - 95 °C/5 min, LC and BA - 95 °C/7 min. The same temperature profile was used in OH treatments to study the OH electrical effects. The OH treatment (8 V/cm) caused lower damage to the cell membrane integrity compared to the CONV treatment (p < 0.05). The OH showed to be adequate technology for the efficient production of paraprobiotics.

Ohmic heating increases inactivation and morphological changes of Salmonella sp. and the formation of bioactive compounds in infant formula.

The effect of ohmic heating (OH) (50, 55, and 60 °C, 6 V/cm) on the inactivation kinetics (Weibull model) and morphological changes (scanning electron microscopy and flow cytometry) of Salmonella spp. in infant formula (IF) was evaluated. In addition, thermal load indicators (hydroxymethylfurfural and whey protein nitrogen index, HMF, and WPNI) and bioactive compounds (DPPH, total phenolics, ACE, α-amylase, and α-glucosidase inhibitory activities) were also studied. OH presented a more intense inactivation rate than conventional heating, resulting in a reduction of about 5 log CFU per mL at 60 °C in only 2.91 min, being also noted a greater cell membrane deformation, higher formation of bioactive compounds, and lower values for the thermal load parameters. Overall, OH contributed to retaining the nutritional value and improve food safety in IF processing.

Impact assessment of different electric fields on the quality parameters of blueberry flavored dairy desserts processed by Ohmic Heating.

The effect of ohmic heating (OH) (1.82, 3.64, 5.45, 7.30, 9.1 V cm-1, 90 °C/3 min) and conventional pasteurization in the parameters of quality of dairy desserts with blueberry flavor was investigated. Processes performances (heating rate, thermal load and energy consumption), physicochemical characteristics (fatty acids profile, volatile compounds, rheological assay and color parameters) and bioactive compounds (total phenolics, anthocyanins, antioxidant activity, inhibition of α-glycosidase, α-amylase, and angiotensin-converting enzymes) were evaluated. OH technology proportionated decreased heat generation, energy consumption and heat rate compared to conventional process. OH-treated dairy desserts subjected to higher electric field strength greater inhibition of α-glucosidase and ACE enzymes, without difference in fatty acid profile; however negative effects were observed in color parameters, volatiles profiling and rheological behavior. Overall, the results suggest the influence of ohmic heating on blueberry dairy processing is multidimensional, being the conditions of operation should be carefully chosen to keep the functional and structural aspects of the product.

Whey acerola-flavoured drink submitted Ohmic Heating: Bioactive compounds, antioxidant capacity, thermal behavior, water mobility, fatty acid profile and volatile compounds.

Whey acerola-flavoured drink was subjected to Ohmic Heating (OH) under different operational conditions (45, 60, 80 V at 60 Hz and 10, 100, 1000 Hz with 25 V, 65 °C/30 min) and conventional pasteurization (65 °C/30 min). Bioactive compounds (total phenolics, DPPH, FRAP, ACE levels), fatty acid profile, volatile compounds (CG-MS), thermal behaviors (DSC) and water mobility (TD-NMR) were performed. Reduction of frequency (1000-10 Hz) resulted in a lower bioactive compounds and antioxidant capacity of the samples, except for the DPPH values. Concerning the thermal behaviors, fatty acids profile and volatile compounds, different findings were observed as a function of the parameters used (voltage and frequency). In respect of TD-NMR parameters, OH led to a slightly reduction of the relaxation time when compared to the conventional treatment, suggesting more viscous beverages. Overall, OH may be interesting option to whey acerola-flavoured drink processing.

Ohmic Heating: A potential technology for sweet whey processing.

The use of Ohmic Heating (OH) for sweet whey processing was investigated in this study. Whey samples were subjected to both different OH parameters (2, 4, 5, 7 and 9 V·cm-1 at 60 Hz, up to 72-75 °C/15 s) and conventional processing (72-75 °C/15 s). Physicochemical analyses (pH), color measurements (L*, a*, b*), rheological properties (flow curves and particle size distribution), microstructure (optical microscopy), bioactive compounds (ACE and antioxidant capacity), microbiological characterization (mesophilic bacteria, total coliforms, and thermotolerant coliforms), water mobility (TD-magnetic resonance domain), and sensory evaluation (descriptive analysis) were carried out. The OH effects on sweet whey characteristics depended on the applied electric field intensity. Higher saturation, higher color variation (ΔE*), and higher luminosity (L*) were observed in low electric fields. For bioactive compounds, the increase of the electric field negatively affected the preservation of the antioxidant capacity and the ACE Inhibitory Activity of bioactive peptides. OH and conventional samples exhibited a pseudo-plastic behavior (n < 1). OH performed at 4 and 5 V·cm-1 was able to provide similar levels of sensory profile and higher volatile compounds levels. The results suggested the OH technology as an interesting alternative to whey processing.

Whey acerola-flavoured drink submitted ohmic heating processing: Is there an optimal combination of the operational parameters?

Whey acerola-flavoured drink was treated using ohmic heating (OH) at 65°C for 30min to evaluate different frequencies (10, 100 and 1000Hz with 25V) and voltages (45, 60 and 80V at 60Hz) and by conventional heating (CH) with the same temperature profile (65°C/30min). Rheology parameters, color changes (h°, C∗, ΔE) microstructure (optical microscopy), and ascorbic acid (AA) degradation kinetics were performed. AA degradation rates ranged from 1.7 to 29.3% and from 2.8 to 24.8% for OH and CH, respectively. The beverages treated with both processes exhibited a pseudo-plastic behavior (n<1), higher saturation (C∗), lesser reddish color (h°), and higher color variations (ΔE∗). In microstructure analysis, OH (1000Hz-25V and 80V-60Hz) was able to rupture the cell structure. The best results were observed at low frequencies and voltage OH processes on whey acerola-flavoured drinks should be performed at low frequencies and voltages (≤100Hz and 45V), an alternating current (A/C). However, despite the use of inert electrodes, the existence of corrosion was not evaluated, being an important information to be investigated.