Thermal Food Processing

302 Thermal Food Processing: New Technologies and Quality Issues
TABLE 10.1
Content of Lactulose (mg/100 ml) in Different Heat-Treated
Milk Samples
Minimum Maximum Mean Type of Treatment References
5 10 UHT direct 3
15 75 UHT indirect 3
4 15 Pasteurized 3
49 114 74 Sterilized 6
28 42 35 UHT indirect 6
13 24 17 UHT direct with injection system 6
9 12 11 UHT direct with infusion system 6
3.2 7.9 5.8 High-temperature pasteurized 6
0.2 0.6 0.4 Pasteurized 6
36 High-temperature pasteurized 10
230 Dried milk 10
2451 Condensed milk 10
19 62 UHT, whole milk 11
64 Sterilized, whole milk 11
115 Sterilized, low-fat milk 11
12 UHT direct 12
25.0 45.6 UHT indirect 12
112 Sterilized 12
further found that lactulose levels in all the UHT milk samples analyzed were below
the proposed limit (600 mg/l) necessary for differentiation of UHT from sterilized
milk. 10 Average contents were found to be very low (35.5 mg/l) in high-temperaturetreated
milk (Table 10.1), low in dried milk (229.7 mg/kg), and very high in
condensed milk (2451.3 mg/l). 10
This research confirms the earlier work of Mosso and coworkers, 11 who
analyzed lactulose in 14 samples of UHT milk and 2 samples of sterilized milk.
For the UHT milk samples (whole, skimmed, and partially skimmed), lactulose
content ranged from 18.6 to 62.0 mg/100 ml. The two sterilized milk samples
had lactulose contents of 115 mg/100 ml (showing a brown color) and 64
mg/100 ml. 11
During storage, lactulose concentration in UHT milk can either decrease (via
beta-elimination to galactose, tagatose, and formic acid) or increase (via lactose
isomerization), the former process being more temperature dependent than the
latter. 13 Andrews 13 found that light did not affect lactulose concentration during
milk storage at 18°C for 115 days. Lactulose formation increased as a direct
function of OH concentration and lactose concentration, but was unaffected by
protein concentration or dissolved oxygen.