The final stage of the reaction was evaluated by color measurement.
L⁄, a⁄ and b⁄ values during storage of whey protein-lactose
and whey protein-glucose systems at 37 C were determined
(Table 1). As can be seen, no appreciable changes were observed
in L⁄ and a⁄ values along the experiment, being b⁄ the only sensitive
parameter. The total color difference (DE⁄) was calculated
using these parameters and taking time zero as a point of reference
(Fig. 5). The threshold for visual perception of browning in milk
was reported by Pagliarini, Vernile, and Peri (1990) to correspond
to a DE⁄ of 3.8. According to this statement, in the system containing
lactose, color was noticeable only at prolonged times of storage,
when the loss of lysine exceeded 50%. Instead, in the system
with glucose, DE⁄ significantly increased (P < 0.05) from the beginning
of storage and color was perceptible before the loss of lysine
reached 30%. As was expected, above 50% of lysine loss, color was
considerably darker than in the system with lactose for a similar
loss of lysine. In agreement, also
found faster reaction rates for glucose when analyzed color development
during storage of milk protein concentrate with added glucose
or lactose via the tristimulus colorimeter. These results
corresponded with those obtained for total and free HMF in
the same systems. Thus, the occurrence of the intermediate and
final stages of Maillard reaction at storage temperatures were not
significant in the system with lactose, but were noticeable in the
whey protein-glucose system. compared aminocarbonyl
reaction of ovalbumin with glucose and lactose at
reaction accelerating storage conditions and observed that sugars
glycosylated at the C4 position of the glucopyranose were difficult
to cleave and browned slowly. Hence, the prevailing of the initial
stage along the experiment in the former system could be attributed
to a higher stability at mild temperatures of the Amadori compound
formed with the disaccharide compared to that formed with
glucose
The final stage of the reaction was evaluated by color measurement.L⁄, a⁄ and b⁄ values during storage of whey protein-lactoseand whey protein-glucose systems at 37 C were determined(Table 1). As can be seen, no appreciable changes were observedin L⁄ and a⁄ values along the experiment, being b⁄ the only sensitiveparameter. The total color difference (DE⁄) was calculatedusing these parameters and taking time zero as a point of reference(Fig. 5). The threshold for visual perception of browning in milkwas reported by Pagliarini, Vernile, and Peri (1990) to correspondto a DE⁄ of 3.8. According to this statement, in the system containinglactose, color was noticeable only at prolonged times of storage,when the loss of lysine exceeded 50%. Instead, in the systemwith glucose, DE⁄ significantly increased (P < 0.05) from the beginningof storage and color was perceptible before the loss of lysinereached 30%. As was expected, above 50% of lysine loss, color wasconsiderably darker than in the system with lactose for a similarloss of lysine. In agreement, alsofound faster reaction rates for glucose when analyzed color developmentduring storage of milk protein concentrate with added glucoseor lactose via the tristimulus colorimeter. These resultscorresponded with those obtained for total and free HMF inthe same systems. Thus, the occurrence of the intermediate andfinal stages of Maillard reaction at storage temperatures were notsignificant in the system with lactose, but were noticeable in thewhey protein-glucose system. compared aminocarbonylreaction of ovalbumin with glucose and lactose atreaction accelerating storage conditions and observed that sugarsglycosylated at the C4 position of the glucopyranose were difficultto cleave and browned slowly. Hence, the prevailing of the initialstage along the experiment in the former system could be attributedto a higher stability at mild temperatures of the Amadori compoundformed with the disaccharide compared to that formed withglucose
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