Effect of Lactic-Streptococcal Agglutinins in Milk on Curd Formation and Manufacture of Cottage Cheese

Abstract

Shattered, mealy curd, sediment on the bottom of the vat, and slow acid production were associated with agglutinating strains of Cottage cheese cultures. Agglutinated bacteria formed centers of high acid production and resulted in dense flecks of acid-precipitated casein. These flecks either settled as a sediment or were trapped during coagulation and caused a fragile, mealy curd. The sediment was low in pH and high in protein and bacteria.Acid production in the supernatant skimmilk was retarded through displacement of agglutinated bacteria to the bottom of the vat, indicating that agglutinating antibodies in skimmilk are not inhibitory, per se. Prolonged agitation of skimmilk and starter promoted agglutination and, after agitation ceased, resulted in more sediment and reduced rates of acid production. With agglutinating cultures, the pH of the A-C test sample, receiving less agitation, reduced more quickly than skimmilk in the vat, thereby nullifying the test as a direct indicator of the time to cut the curd.Heating skimmilk (71 C/30min) or removing agglutinins by adsorption on heat-killed cells eliminated the defects. Pasteurization (72 C/16sec) reduced the agglutinating activity of skimmilk by 50–75%.Agglutinating strains differed markedly in the severity of defects produced; two strains settled so extensively that the skimmilk did not coagulate; whereas, defects with some strains were evident only as small amounts of sediment. Auto-agglutination of certain strains also appeared to cause small amounts of sediment. Some commercial cultures contained agglutinating strains and produced sediment. Selection of agglutination-resistant strains for Cottage cheese cultures is recommended.