352 DAIRY CHEMISTRY AND BIOCHEMISTRY Table 9.2 Concentration of conjugated linoleic acid ( CLA) isomers in selected foods(modified from Ha, Grimm and Pariza, ng CLA/kg Fat content CLA in fat Sample food 623±150 Cheddar cheese 325±1.7 Romano cheese 3569±63 32.1+0.8 11119 1693+8 49 574.1±24.8 318±1. 18053 3345±13.3 355±1.0 l8150±90.3 206±1,1 10.7 283±19 4.0±0.3 707.5 eurized whole Ground beef grilled 9940±309 7±0.3 92897 uncooked 561.7±220 74±02 isomers of conjugated linoleic acid(CLA)are shown in Figure 9.3. It claimed that CLa has anticarcinogenic properties. The mechanism of CLA formation in foods in general is not clear but heat treatment, free radical type oxidation and microbial enzymatic reactions involving linoleic and linolenic acids in the rumen are thought to be major contributors. Rather high concentrations of Cla have been found in heated dairy products specially processed cheese(Table 9.2). It has been suggested that whey proteins catalyse isomerization 9.3 Lactose The chemistry and physicochemical properties of lactose, a reducing disac- haide containing galactose and glucose linked by a B(1-4)-bond, were escribed in Chapter 2 When severely heated in the solid or molten state, lactose, like other sugars,undergoes numerous changes, including mutarotation, various isomerizations and the formation of numerous volatile compounds, includ- ing acids, furfural, hydroxymethylfurfural, CO2 and CO. In solution under strongly acidic conditions, lactose is degraded on heating to monosacchar- ides and other products, including acids. These changes do not normally occur during the thermal processing of milk. However, lactose is relatively unsta ble under mild alkaline conditions at moderate ter undergoes the Lobry de Bruyn-Alberda van Ekenstein rearrangement of Doses to ketoses(Figure 9.4)352 DAIRY CHEMISTRY AND BIOCHEMISTRY Table 9.2 Concentration of conjugated linoleic acid (CLA) isomers in selected foods (modified from Ha, Grimm and Parka, 1989) Sample mg CLA/kg Fat content CLA in fat food (YO.) (mg kg-') Parmesan cheese Cheddar cheese Romano cheese Blue cheese Processed cheese Cream cheese Blue spread Cheese whiz Milk pasteurized whole non-pasteurized whole Ground beef grilled uncooked 622.3 f 15.0 440.6 f 14.5 356.9 f 6.3 169.3 f 8.9 574.1 f 24.8 334.5 f 13.3 202.6 & 6.1 1815.0 90.3 28.3 f 1.9 34.0 f 1.0 994.0 f 30.9 561.7 f 22.0 32.3 f 0.9 32.5 f 1.7 32.1 f 0.8 30.8 f 1.5 31.8 f 1.1 35.5 f 1.0 20.2 0.8 20.6 & 1.1 4.0 f 0.3 4.1 i 0.1 10.7 f 0.3 27.4 f 0.2 1926.7 1355.7 1111.9 549.8 1805.3 942.3 1003.0 8810.7 707.5 829.3 9289.7 2050.0 isomers of conjugated linoleic acid (CLA) are shown in Figure 9.3. It is claimed that CLA has anticarcinogenic properties. The mechanism of CLA formation in foods in general is not clear but heat treatment, free radical￾type oxidation and microbial enzymatic reactions involving linoleic and linolenic acids in the rumen are thought to be major contributors. Rather high concentrations of CLA have been found in heated dairy products, especially processed cheese (Table 9.2). It has been suggested that whey proteins catalyse isomerization. 9.3 Lactose The chemistry and physicochemical properties of lactose, a reducing disac￾charide containing galactose and glucose linked by a p( l-4)-bond, were described in Chapter 2. When severely heated in the solid or molten state, lactose, like other sugars, undergoes numerous changes, including mutarotation, various isomerizations and the formation of numerous volatile compounds, includ￾ing acids, furfural, hydroxymethylfurfural, CO, and CO. In solution under strongly acidic conditions, lactose is degraded on heating to monosacchar￾ides and other products, including acids. These changes do not normally occur during the thermal processing of milk. However, lactose is relatively unstable under mild alkaline conditions at moderate temperatures where it undergoes the Lobry de Bruyn- Alberda van Ekenstein rearrangement of aldoses to ketoses (Figure 9.4)