Formation of heat-induced casein gel under acidic conditions (pH≤3.60)

Nakano Tomoki, Takeshita Masahiko, Arima Yuo, Endo Motoi, Sato Kaoru, Tanimoto Morimasa, Aoki Takayoshi

doi:10.11465/milk.67.15

<p>　　Casein formed a gel on cooling after being heated to a temperature of 70-85℃ at pH ≤3.60 and protein concentration of ≥6%. The gel hardness was dependent on pH, protein concentration, and temperature, which decreased by heating at ≥90℃. The addition of NaCl to the whole casein suspension suppressed the formation of heat-induced gel. The viscoelastic moduli measurement by low-amplitude dynamic oscillation revealed that irreversible changes of casein constituents may occur by heating under certain acidic conditions. Unheated 8% casein at pH 2.8 was dominated by the elastic component rather than by the viscous component. The storage modulus (G′) and the loss modulus (G″) decreased with increasing temperature at 3-40℃ and shifted from decrease to increase at 40℃. During heat processing, both G′ and G″ had the maximum value at 70℃. However, when the heated casein was cooled from 80℃ to 3℃, the maximum of G′ and G″ at 70℃ was not observed. G′ and G″ markedly increased linearly with decreasing temperature during cool processing. G′ and G″ of the gel formed by heating and cooling were linearly decreased with increasing temperature. The property of the acidic heat-induced gel was different from that of the acid-induced and rennet gels and was thermoplastic.</p>

Formation of heat-induced casein gel under acidic conditions (pH≤3.60)

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