Milk processed by pulsed electric fields: evaluation of microbial quality, physicochemical characteristics, and selected nutrients at different storage conditions.

Abstract

UNLABELLED: Pulsed electric fields (PEF) technology was used to pasteurize raw milk under selected treatments. Processing conditions were: temperature 20, 30, and 40 °C, electric field 30.76 to 53.84 kV/cm, and pulse numbers 12, 24, and 30 for skim milk (SM), and 12, 21, and 30 for whole milk (WM) (2 μs pulse width, monopolar). Physicochemical parameters (pH, electrical conductivity, density, color, solids nonfat [SNF]) and composition (protein and fat content) were measured after processing. Shelf life of SM and WM was assessed after processing at 46.15 kV/cm, combined with temperature (20 to 60 °C) and 30 pulses. Mesophilic and psychrophilic loads and pH were evaluated during storage at 4 and 21 °C. Results showed minor variations in physicochemical properties after processing. There was an interesting trend in SM in SNF, which decreased as treatment became stronger; similar behavior was observed for fat and protein, showing a 0.18% and 0.17% decrease, respectively, under the strongest conditions. Protein and fat content decreased in WM samples treated at 40 °C, showing a decrease in protein (0.11%), and an even higher decrease in fat content. During storage, PEF-treated milk samples showed higher stability at 4 °C with minor variations in pH; after 33 d, pH was higher than 6. However samples at 21 °C showed faster spoilage and pH dropped to 4 after 5 d. Growth of mesophilic bacteria was delayed in both milks after PEF processing, showing a 6- and 7-log cycles for SM and WM, respectively, after day 25 (4 °C); however, psychrophilic bacteria grew faster in both cases. PRACTICAL APPLICATION: Pulsed electric fields (PEF) technology in the pasteurization of liquid food products has shown positive results. Processing times can be reduced considerably, which in turn reduces the loss of nutrients and offers important savings in energy. PEF has been used successfully to pasteurize some liquid foods, but it is still not used commercially in milk pasteurization, although several trials have shown the positive effects of PEF milk pasteurization, which could allow for its future use at the industrial level.

AI evidence extraction

Main findings

PEF processing of raw skim and whole milk produced minor variations in physicochemical properties; under strongest conditions, skim milk showed decreases in SNF and small decreases in fat (0.18%) and protein (0.17%), and whole milk treated at 40 °C showed decreased protein (0.11%) and a larger decrease in fat. During storage, PEF-treated milk was more stable at 4 °C (minor pH variation; pH >6 after 33 d) but spoiled faster at 21 °C (pH dropped to 4 after 5 d). Mesophilic bacterial growth was delayed after PEF processing, while psychrophilic bacteria grew faster.

Outcomes measured

• Microbial quality (mesophilic and psychrophilic loads)
• Physicochemical characteristics (pH, electrical conductivity, density, color, solids nonfat)
• Nutrient/composition measures (protein and fat content)
• Shelf life/stability during storage at 4 °C and 21 °C

Limitations

• No sample size reported in abstract
• No quantitative statistical testing or uncertainty measures reported in abstract
• Exposure characterization limited to field strength, pulse width, and pulse number; no frequency information provided

{
    "study_type": "other",
    "exposure": {
        "band": null,
        "source": "pulsed electric fields (PEF) food processing",
        "frequency_mhz": null,
        "sar_wkg": null,
        "duration": "2 μs pulse width; pulse numbers 12, 21/24, and 30; storage assessed up to 33 d"
    },
    "population": null,
    "sample_size": null,
    "outcomes": [
        "Microbial quality (mesophilic and psychrophilic loads)",
        "Physicochemical characteristics (pH, electrical conductivity, density, color, solids nonfat)",
        "Nutrient/composition measures (protein and fat content)",
        "Shelf life/stability during storage at 4 °C and 21 °C"
    ],
    "main_findings": "PEF processing of raw skim and whole milk produced minor variations in physicochemical properties; under strongest conditions, skim milk showed decreases in SNF and small decreases in fat (0.18%) and protein (0.17%), and whole milk treated at 40 °C showed decreased protein (0.11%) and a larger decrease in fat. During storage, PEF-treated milk was more stable at 4 °C (minor pH variation; pH >6 after 33 d) but spoiled faster at 21 °C (pH dropped to 4 after 5 d). Mesophilic bacterial growth was delayed after PEF processing, while psychrophilic bacteria grew faster.",
    "effect_direction": "mixed",
    "limitations": [
        "No sample size reported in abstract",
        "No quantitative statistical testing or uncertainty measures reported in abstract",
        "Exposure characterization limited to field strength, pulse width, and pulse number; no frequency information provided"
    ],
    "evidence_strength": "insufficient",
    "confidence": 0.7399999999999999911182158029987476766109466552734375,
    "peer_reviewed_likely": "yes",
    "keywords": [
        "pulsed electric fields",
        "PEF",
        "milk",
        "pasteurization",
        "microbial quality",
        "mesophilic bacteria",
        "psychrophilic bacteria",
        "physicochemical properties",
        "protein",
        "fat",
        "shelf life",
        "storage temperature"
    ],
    "suggested_hubs": []
}

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