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Age-Thickening and Gelation of Sterilized Evaporated Milk¹

Food Research Institute, Research Branch, Agriculture Canada, Ottawa, Ontario, Canada K1A 0C6

G. E. Doyle

Perfection Foods Ltd., Charlottetown, Prince Edward Island, Canada C1A 7M8

ABSTRACT

Evaporated milk containing 26% total solids (15 batches) and evaporated skim milk containing 18% total solids (1 batch) were held at 4°C before canning and sterilization. Sterilized samples were stored at 28°C and examined periodically for 1 yr for changes in relative viscosity, gelation, granulation, and fat separation.

Samples sterilized without cold storage remained liquid for 12 mo. As time of cold storage of concentrates before sterilization increased, this tendency to thicken or gel during storage increased. Ten of 15 batches of evaporated milk cold stored for 3 days before sterilization had gelled after 12 mo along with 6 that had been held for 2 days. Samples stored cold for 3 days that did not gel after 12 mo had thickened more than controls.

Samples that gelled contained no microorganisms capable of growth at 30°C and showed no appreciable change in proteolysis or pH.

Heating samples at 55 to 60°C for 30 min after 3 days cold storage and then cooling to 20°C (so-called "anti-cool-aging treatment") before canning and sterilization did not prevent gelation or increase in viscosity during storage.

Oxidizing conditions such as aeration and peroxide treatments accelerated whereas reducing conditions such as antioxidant treatments tended to delay but not prevent age-thickening and gelation.

¹ Contribution No. 494 from the Food Research Institute.