Use of milk permeate as an inducer of lactose crystallisation in sweetened condensed milk

Sweetened condensed milk (SCM) is a widely consumed dairy product used in desserts. However, lactose crystallisation during storage creates a sandy texture, a quality defect. The traditional approach to controlling crystal size involves adding pure lactose to induce microcrystallisation. A cost-effective alternative is milk permeate, a by-product of milk ultrafiltration with up to 90% lactose. This study evaluates milk permeate as a nucleating agent compared with pure lactose, aiming to improve SCM texture and reduce costs. This study assessed the ability of milk ultrafiltration (UF) permeate to induce lactose crystallisation in SCM compared with pure lactose powder. The influence of micronised and non-micronised forms on crystal size, number and viscosity over 30 days was also examined. The samples were produced using whole milk and sucrose in a laboratory-scale rotary evaporator. Four treatments were applied: (T1) non-micronised lactose, (T2) micronised lactose, (T3) non-micronised UF permeate and (T4) micronised UF permeate. Crystallisation was monitored using optical microscopy and analysed with ImageJ software at 1, 7, 15 and 30 days. Viscosity was measured with a rotational viscometer and a Ford cup viscometer. Statistical analysis was performed using Tukey's test (P < 0.05). Micronised ingredients (T2 and T4) formed smaller (~11 μm) and more numerous (~700 crystals/microscopic field) crystals than non-micronised treatments (~15 μm, ~200 crystals/microscopic field). UF permeate showed similar nucleation capacity to pure lactose without altering viscosity. Viscosity increased over time, with T4 showing the highest values at day 30. Smaller, more numerous crystals in micronised treatments reduced the risk of a sandy texture. Milk UF permeate can replace pure lactose as a nucleating agent in SCM, offering a cost-effective alternative without compromising quality. Micronised permeate is especially effective, producing a smooth-textured product like traditional formulations. This innovation could enhance industry competitiveness by reducing costs and waste while maintaining quality.