Bacteria Associated with a Gelatinous or Slimy Curd Defect of Cottage Cheese

Abstract

Cottage cheese plants in various parts of the United States in recent years have reported difficulty with a gelatinous curd defect in both creamed and uncreamed curd.The defect was first described in ]949 (2), but all available evidence indicates that it has been widespread and frequent, and losses due to this type of spoilage have been extensive for several years.The defect may develop in 24 hr.during refrigerated storage or may be delayed for several (lays.Creamed curd usually has shown more frequent and rapid spoilage than nnereamed.The defect is characterized by formation of a thick, gelatinous, slimy film around each curd particle.In one form of the defect the gelatinous fihn has been whitish or yellowish in color and somewhat translucent.This form may be accompanied by little change in odor, and in other cases a fruity odor may be apparent.In still another form of the defect the fihn surrounding the curd particles may be yellowish or tinged with brown, extensive proteolysis may occur, the odor may be rotten or putrid and slightly rancid and the flavor quite bitter.Terms that have been used in the trade to refer to the curd defect include: gelatinous, slimy, glassy, scummy, tapioca and fruity.Such terms usually indicating changes in physical appearance actually may refer only to the final, late stages of the spoilage.A number of off-flavors such as fruity, rancid or bitter may precede the formation of the gelatinous film around the curd particle.Studies carried out several years ago in the Midwest and more recently on the West Coast suggested certain bacteria as causative agents.This paper presents a number of observations made during a study of the bacteri~flogy of the defect.EXPEIgIM ENTAI~ Microscopic examination of defeetive curd on different occasions always revealed large nmnbers of gram-negative rods in addition to the normal lactic streptococcus flora.Plating on both veal infusion and tryptone-glueose-skimmilk agar resulted in nmnerous colonies of gram-negative rods.Representative types were picked into litmus milk and the cultures segregated into four groups on basis of change in reaction in the milk after 5 days at 15 ° C. First attempts to reproduee the typical gelatinous defect with representative isolated cultures by inoculating normal creamed and unereamed cottage cheese curd were unsuccessful.Later, the inoculation was repeated in uncreamed curd that had been soaked and washed a number of times with sterile alkaline tap water to raise the pH of the curd.Within 48-hr.storage at 15 ° C. following this treatment, a slimy film