Figure 1.
Modular experimental setup for heat-treatments of orange juice and milk.
Panel A: flow-through heating; Panel B: heating with recirculation; MH – treated with microwave; TH – traditional heat treatment; WH – untreated control.
Figure 2.
Both the microwave-based and the traditional heat treatment effectively delays surface deterioration of freshly squeezed orange juice samples at room temperature.
MH – treated with microwave; TH – traditional heat treatment; WH – untreated control.
Figure 3.
Storage of orange juice produced from concentrate in open containers, in sealed containers and in sealed containers shaken daily.
Treatment groups of three: First 3 samples: open; second 3 samples: sealed and undisturbed; third 3 samples: sealed, shaken daily. Markings on the bottles: 1- microwave treated, 2- untreated control, 3- treated with water bath thermostat. The storage test was performed in two parallel experiments and each gave the results presented in the figure.
Figure 4.
The CO2 content of gas in the bottles decreased similarly in microwave-treated and traditional heat-treated orange juice samples both in ‘closed’ and ‘closed and shaken’ situations.
MH – treated with microwave; TH – traditional heat treatment; WH – untreated control. Each bar shows the average of six technical replicates.
Figure 5.
Colour parameters change of orange juice from concentrate in the period of 10 days following the treatment.
The measured parameters: a* - red-green colour coordinate, b* - blue-yellow colour coordinate. MH – treated with microwave; TH – traditional heat treatment; WH – untreated control. (The L*-index of samples are shown in Figure 6.).
Figure 6.
Lightness index (L*) change of orange juice from concentrate in the 10 days following the treatment.
MH – treated with microwave; TH – traditional heat treatment; WH – untreated control. (The a* and b* of samples are shown in Figure 5.).
Figure 7.
The vitamin C content of orange juice has not changed in microwave-treated or heat-treated samples at 85°C.
WH: untreated control; MH-A: flow-through microwave treatment with no temperature holding; TH-A: flow-through traditional heat treatment with no temperature holding; MH-B: microwave heating of recirculated liquid; TH-B: traditional heating of recirculated liquid.
Table 1.
Statistics for evaluating the decrease in vitamin C contents [mg/100 ml] in orange juice due to heat treatment.
Table 2.
Test results for comparison of taste of heat treated and untreated orange juice.
Figure 8.
The total viable cell count in freshly milked milk significantly decreased after either of the two heat treatment methods.
The average, maximum, minimum and median values of 24 statistical samples are shown per sample group.
Figure 9.
The colour parameters of milk were different after microwave treated vs. traditionally heat-treated samples.
The error bar shows the 95% confidence interval (CI) of L*a*b* values at the three groups. The measured parameters: a* - red-green colour coordinate, b* - blue-yellow colour coordinate, L*- lightness index. The results of 12 statistical samples are shown by sample group.