# Trends and Opportunities in the Dairy Industry: A2 Milk and Processing Methods
## 5 Milk Processing
### Non-Thermal Methods
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Method** & **Parameters** & **Study Subject** & **Impact** & **Ref.** \\ \hline \multirow{8}{*}{Nonthermal plasma (NTP)} & Resonant frequency & & \(\bullet\) & Lower treatment time resulted in lower degree of hydrolysis during shelf-life \\  & of & Reducing activity of Pseudomonas-secreted & \(\bullet\) & Reduced the activity of Pseudomonas-secreted proteases by more than 60\% with a 10 min \\  & 32 kV discharge and frequency 1 kHz & & \(\bullet\) & pH was not affected \\ \cline{2-5}  & 9 kV AC power & & \(\bullet\) & No changes to the lipid composition \\  & supply & Changes in protein, free fatty acids, and volatile & \(\bullet\) & Increased the total aldehyde content during 20 min treatment \\  & \textless{}35 °C & & fatty acids, and volatile & \(\bullet\) & No changes to the total ketone and alcohol levels \\  & 0–20 min & & \(\bullet\) & Significant changes occurred in volatile compounds profile \\ \cline{2-5}  & \multirow{4}{*}{N\({}_{2}\)-O\({}_{2}\) plasma} & & \(\bullet\) & Sulfhydryl content decreased with treatment time—fast for N\({}_{2}\)-O\({}_{2}\) and gradual for O\({}_{2}\) treatment \\  & & Acid gelation properties of skim milk & \(\bullet\) & Increased skim milk viscosity over time \\  & \multirow{2}{*}{O\({}_{2}\) plasma} & & \(\bullet\) & Longer exposure times led to lower gel firmness \\  & & & \(\bullet\) & Spheres in acid gels decreased below 60\% after 2 min but increase to 70\% after 4 min for N\({}_{2}\)-O\({}_{2}\) treatment \\ \hline \multirow{8}{*}{High-pressure processing (HPP)} & \multirow{4}{*}{200–600 MPa} & & \(\bullet\) & 150 MPa was efficient in reducing the proteolytic rate \\  & & Coagulation of protein and fat globules in whole and skim milk & \(\bullet\) & Clotting formation was faster by 29\% after 100 MPa treatment and 51\% after 150 MPa \\ \cline{2-5}  & 20 °C & & \(\bullet\) & No reduction in proteolysis was observed \\ \cline{2-5}  & \multirow{4}{*}{250–550 MPa} & & \(\bullet\) & Inactivation of the Pseudomonas fluorescers protease was not effective \\ \cline{2-5}  & & & \(\bullet\) & Pressures over 400 MPa caused looser and more fragmented gastric clot structures \\ \cline{2-5}  & \multirow{2}{*}{200–550} & Coagulation of protein and fat globules in whole and skim milk & \(\bullet\) & Weight of the dried clots milk treated at 600 MPa were significantly lower than in untreated milk samples \\ \cline{2-5}  & & & \(\bullet\) & Moisture content in the clots milk treated at 600 MPa were significantly higher than in untreated milk samples \\ \cline{2-5}  & \multirow{4}{*}{3–15 min} & & \(\bullet\) & HPP treatment at 400 MPa ensures the same bacterial load reduction as pasteurization \\  & & Microbiological quality of skim milk & \(\bullet\) & For shelf-life elongation, pressure \textgreater{} 400 MPa and a holding time of at least 15 min are necessary \\  & & & \(\bullet\) & 250 MPa/3 min/room temperature—1.51 log CFU/mL reduction \\ \hline \multirow{8}{*}{Ultrasounds (US)} & Frequency 24 kHz & & \(\bullet\) & Samples treated with ultrasound power 200 °C for max. 7.5 min had best sensory characteristic \\  & 200–400 W & Chemical composition and sensory properties of the milk & \(\bullet\) & Milk pH slightly dropped at 400 W and 20 °C \\  & 2.5–10 min & milk & \(\bullet\) & No changes in total solids, solids-non-fat, fat, and protein mass fractions \\  & 20–55 °C & & \(\bullet\) & Samples treated with 200 and 400 W US had a small increase in fat content \\ \cline{2-5}  & \multirow{4}{*}{4 °C} & & \(\bullet\) & Farmness gel of non-sonicated samples was higher, but when highest energy density was used, gel firmness started to increase \\ \cline{2-5}  & & & \(\bullet\) & Remnet coagulation time doubled when 674.3 J/was applied \\ \cline{2-5}  & \multirow{4}{*}{28 W} & & \(\bullet\) & Coagulant strength and curd fixation rate decreased when the energy density was increased to 2016.9 J/g \\ \cline{2-5}  & & & \(\bullet\) & US and energy density manipulations can be used to prolong the rementing time of milk \\ \cline{2-5}  & \multirow{4}{*}{22.5 kHz} & & \(\bullet\) & Integrity of casein micelles was not damaged by 30 min US, but turbidity started to decrease after 5 min \\  & & & \(\bullet\) & Secondary structure of protein in skim milk changed after 1 min \\ \cline{2-5}  & \multirow{4}{*}{28 W} & Protein changes in fresh skim milk & \(\bullet\) & Secondary structure of protein in skim milk changed after 1 min \\ \cline{2-5}  & & & \(\bullet\) & pH of fresh skim milk was unaltered by sonication up to 30 min \\ \cline{2-5}  & & & \(\bullet\) & Excessive sonication (\textgreater{}20 min) could disrupt the aggregates of whey–whey and whey–casein \\ \hline \hline \end{tabular}
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