3.2.3. Effect of lactose–zinc complex fortification on physicochemical properties of milk
pH of both control and the fortified milk samples decreased during storage. From 3rd day onwards the pH of milk fortified with zinc salt showed significant difference (P < 0.05) from both control and lactose – zinc complex fortified milk. Whereas, changes in pH of milk fortified with lactose–zinc complex was comparable with control were observed throughout the storage period (Fig 5a). Milk fortified with zinc salt showed significantly increased titratable acidity (P < 0.05) than control from 5th day of storage. Whereas, similar kind of changes in case of milk fortified with lactose–zinc complex and control throughout the storage period (Fig 5b). Based on these findings, it could be concluded that the fortification of lactose–zinc complex in milk did not affect the pH and acidity of milk adversely till 7th day of storage. This might be due to the protective effect of lactose–zinc complex towards zinc interaction with other milk components especially proteins. Viscosity of control and milk fortified with lactose–zinc complex did not differ significantly (P < 0.05) from each other throughout the storage. Whereas, milk fortified with zinc salt showed significant difference (P < 0.05) in viscosity from 3rd day of storage (Fig 5c). Milk fortified with zinc salt and lactose–zinc complex showed significant difference (P < 0.05) in HMF content than control from 3rd day of storage. HMF content increased in milk after addition of zinc both in free and complex form. Kato, Watanahe, and Sato (1981) reported that the maillard reaction was activated by the high lactose content and metal ions particularly the formation of carboxy methyl lysine (Ahmed, Thorpe, & Baynes, 1986). Moreover, HMF content of milk fortified with zinc salt was higher than that of milk fortified with lactose–zinc complex (Fig 5d). This could be due to inaccessibility of free lactose and zinc for the maillard browning reaction in pasteurized milk. The addition of zinc both in the form of zinc salt and lactose–zinc complex to milk resulted in slight increase in TBA value which was almost similar to control milk (Fig 5e). EI-Din,Gamal, Hussan, Behairy, and Mohammed (2012) also reported that addition of zinc salt in Domiati cheese resulted in slight increase in TBA value, which was very close to the control cheese.
3.2.3 3.2.3. Effect of lactose–zinc complex fortification on physicochemical properties of milk
pH of both control and the fortified milk samples decreased during storage. From 3rd day onwards the pH of milk fortified with zinc salt showed significant difference (P < 0.05) from both control and lactose – zinc complex fortified milk. Whereas, changes in pH of milk fortified with lactose–zinc complex was comparable with control were observed throughout the storage period (Fig 5a). Milk fortified with zinc salt showed significantly increased titratable acidity (P < 0.05) than control from 5th day of storage. Whereas, similar kind of changes in case of milk fortified with lactose–zinc complex and control throughout the storage period (Fig 5b). Based on these findings, it could be concluded that the fortification of lactose–zinc complex in milk did not affect the pH and acidity of milk adversely till 7th day of storage. This might be due to the protective effect of lactose–zinc complex towards zinc interaction with other milk components especially proteins. Viscosity of control and milk fortified with lactose–zinc complex did not differ significantly (P < 0.05) from each other throughout the storage. Whereas, milk fortified with zinc salt showed significant difference (P < 0.05) in viscosity from 3rd day of storage (Fig 5c). Milk fortified with zinc salt and lactose–zinc complex showed significant difference (P < 0.05) in HMF content than control from 3rd day of storage. HMF content increased in milk after addition of zinc both in free and complex form. Kato, Watanahe, and Sato (1981) reported that the maillard reaction was activated by the high lactose content and metal ions particularly the formation of carboxy methyl lysine (Ahmed, Thorpe, & Baynes, 1986). Moreover, HMF content of milk fortified with zinc salt was higher than that of milk fortified with lactose–zinc complex (Fig 5d). This could be due to inaccessibility of free lactose and zinc for the maillard browning reaction in pasteurized milk. The addition of zinc both in the form of zinc salt and lactose–zinc complex to milk resulted in slight increase in TBA value which was almost similar to control milk (Fig 5e). EI-Din,Gamal, Hussan, Behairy, and Mohammed (2012) also reported that addition of zinc salt in Domiati cheese resulted in slight increase in TBA value, which was very close to the control cheese.
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