**3.1. Pulsed electric field (PEF)**

**Technology and process** 

**Food matrix Results Source**

scavenging activity

overall color

improvement in TSS, polyphenol, anthocyanin; increase in antioxidant

resulted in lower phenolic content, ascorbic acid; minimal impact on

retention in firmness during storage

increase in total carotenoid and

Retention in firmness, pH, TSS, TA, color; no significant effect on phenols; ascorbic acid content decreased significantly on stored samples subjected to higher-fluence

Significant increase in total carotenoid, lycopene, phenolics and antioxidant activity noted in both

firmness; significant reduction in

Insignificant changes on pH, color, firmness, weight loss in both

Significant loss in *"crunchiness"* in apple texture, melons exhibited no significant texture impact; linear reduction in PPO and POD activity

Slight initial reduction in chlorophyll and carotenoid but improved color retention during storage; slight reduction in phenols but no significant impact on antioxidant activity

fruits

microbial flora

varieties

of irradiated samples

antioxidant activity.

and antioxidant activity with increasing sonication power and prolonged treatment time

Zou, Hou [47]

Dias et al. [48]

Yao et al. [49]

Manzocco et al. [54]

Lopes et al. [55]

Koh et al. [56]

Pataro et al. [57]

Misra et al. [63]

Misra et al. [61] Vukic et al. [64]

Tappi et al. [65, 66]

Ramazinna et al. [67]

40 kHz, 0.5Wcm−1, 20/40/60 min Blueberry juice Enhancement of viscosity, color;

194 Phytochemicals - Source of Antioxidants and Role in Disease Prevention

19 kHz, 20–100%, 2–10 min Soursop juice Increasing sonication intensity

200–500 W, 15–90 min Blueberry extract Degradation of cyanidin-3-glucoside

17.5 J/cm, 0.5 μs, 0.5 Hz Fresh-cut apple Reduction in browning and slight

0.7 J/cm, 250 μs, 4 pulses per day Fresh-cut mango Reduced color and fresh mass loss;

Fresh-cut cantaloupe

and Annurca apple

60 kV, 50 Hz, RH 42% Strawberry Minimal impact on color and

Uncut cherry; uncut tomato

Fresh-cut apple; and fresh-cut melon

Fresh-cut kiwifruit

**Table 1.** Impact of nonthermal processes on food quality and phytochemical compounds.

**conditions**

**Pulsed light (PL)**

**Cold plasma (CP)**

30 kV, 50 Hz, RH 45% 7.5–15 kV, 30 s, RH 42%

15 kV, RH 60%, 10/20/30 min for apple; 30/60 min for melon

15 kV, RH 60%, 1/5/10 min

treatment

2.7, 7.8, 11.7, 15.6 J/cm at 9, 26, 39 and 52 pulses respectively

2-4 J/cm, 360 μs, 3 pulses Uncut tomato

Pulsed electric field (PEF) involves the direct application of short, high current voltage pulses that create an intense electric field, applied to a food matrix placed between two electrodes [31]. PEF has been used as an alternative nonthermal treatment in the pasteurization of liquid or pumpable foods. Fruit juices, milk, smoothies, yogurt, sauces, wine, and soup-based products contain large amounts of water and dipolar molecules making them more conductive for passage of electrical currents compared to solid type foods. The PEF system discharges a high voltage pulse uniformly throughout the food in a treatment chamber (see **Figure 1a**) [29, 32]. Typical field strengths varies from 0.1 to 80 kV/cm with the time duration of the pulse cycles ranging from *μs* to *ms* depending on the application of PEF. The mechanism of PEF is best explained using the *"electroporation"* model in which the strong electric fields generated induce either reversible or irreversible (depending on electric field intensity) perforation of the cytoplasmic membrane promoting cell leakage (see **Figure 1b**) [31]. This effect has shown inactivation of microorganisms and food spoilage enzymes, thereby enhancing food safety, quality and phytochemical yield and extraction.

**Figure 1.** (a) Configuration of treatment chambers for continuous PEF processing: (i) parallel plate, (ii) coaxial, and (iii) co-linear; and (b) effects of exposure of biological cells at different electric field strengths and applications in food. Adapted from Toepfl et al. [32].

Kumar et al. on investigating the effect of PEF on carotenoids, microbial stability and different physicochemical changes on ready-to-drink (RTD) mango nectar, noted a high retention of carotene content (94.2%) and minimal changes in total soluble solids (TSS), pH acidity and color [33]. In a separate study [34], a higher retention of volatile monoterpene compounds, in particular (Z)-Ocimene, in mango nectar pasteurized at 96°C for 300 and 600 s was observed. Sensory scores conducted also found PEF samples to be insignificantly different from control samples owing to retention in volatile components and reduction in nonenzymatic 5-hydroxy methyl furfural (HMF) brown compounds. As cited in Buckow et al. several studies surveyed the effects of PEF on orange juice treated at ≤68°C, resulted in maintenance of vitamin C, carotenoid, polyphenol, and volatile aroma compounds compared to thermal pasteurization (95°C for 30 s) both after processing and refrigerated storage [35].

PEF is capable of extracting compounds such as pigments, antioxidants and flavors through the ability of the electric fields to induce cell membrane breakdown in plant tissue, increasing the bioaccessibility of phytochemicals [29, 31]. As cited in Ricci et al. investigations using PEF assisted maceration on Tempranillo grape skin with treatments of 5 and 10 kV/cm increased the polyphenol and anthocyanin extraction in wine processing [31]. Results showed total polyphenols index in PEF treated wines was 13.7% higher (5 kV/cm treatment) and 29.0% higher (10 kV/cm treatment) with respect to the control after 96 h maceration; and at the end of fermentation color intensity also improved of 23.93 (control), 27.04 (5 kV/cm treatment), and 29.33 (10 kV/cm treatment). Increased juice recovery (9–25%) and higher amounts of total phenolics (up to 22%) and total anthocyanins (up to 26%) in PEF treated raspberries and press cakes extracts were reported [36]. With sweet cherries, PEF applied at low field strengths, increased production of volatiles, (aldehydes and alcohols) known to have desirable odors was reported by Sotelo et al. [37].
