Lactose in Cottage Cheese as Affected by Fortification of Skimmilk and Washing of the Curd
One of the most advertised qualities of Cottage cheese is its value as a high protein, low calorie food. According to Watt and Marril (52), the protein content of uncreamed and creamed Cottage cheese is 17.0 and 13.6% respectively. Thomas (44) reported that the average level of lactose in commercial uncreamed and creamed Cottage cheese was 1.1 and 2.3% respectively.
Uncreamed Cottage cheese prepared by the direct acidification method (20) contains from 3 to 5% lactose. The higher level of lactose in this curs is due to the use of fortified (16% total solids) milk, less washing of the curd, and absence of lactose fermentation (20). The total solids in curd, made by direct acidification, is essentially the same as that of conventional curd. Therefore, the protein content must necessarily be lower.
The question has been raised by certain individuals both in and out of the Federal lFood and Drug Administration, as to whether Cottage cheese, manufactured by direct acidification, would five the consumer a less nutritious product than curd made under the present standards of identity for Cottage cheese. The addition of cream dressing makes the protein lower and the lactose higher than in dry curd made by the conventional process. Therefore, it is unrealistic to ignore the effect of the cream dressing when considering compositional factors of interest to the consumer. This is especially true because creamed Cottage cheese accounts for over 99% of the total Cottage cheese consumption (1).
The law specifies only the maximum moisture content of Cottage cheese, as far as composition is concerned. Considerable leeway is allowed in the solids content of the skimmilk and in the extent of washing applied to the curd. Indeed, it is not required that the curd be washed at all. Variations in these factors would most certainly affect the composition of the solids in Cottage cheese curd.
The Federal Standard of Identity for (uncreamed) Cottage cheese is as follows (49):
"(a) Cottage cheese is the soft uncured cheese prepared by the procedure set forth in paragraph (b) of this section. The finished Cottage cheese contains not more than 80 percent of moisture, as determined by.....
"(b) (1) One or more of the dairy ingredients specified in subparagraph (2) of this paragraph is pasteurized; calcium chloride may be added in a quantity of not more than 0.02% (calculated as anhydrous calcium chloride) of the weight of the mix; harmless lactic acid producing bacteria, with or without rennet, are added and it is held until it becomes coagulated. The coagulated mass may be cut; it may be warmed; it may be stirred; it is then drained. The curd may be washed with water and further drained; it may be pressed, chilled, worked, seasoned with salt.
"(2) The dairy ingredients referred to in subparagraph (1) of this paragraph are sweet skimmilk, concentrated skimmilk, and nonfat dry milk. If concentrated skimmilk or nonfat dry milk is used, water may be added in a quantity not in excess of that removed when the milk was concentrated or dried...."
The main objective of this investigation was to prepare conventional Cottage cheese curd, made within the limits of the specifications of present Cottage cheese standards, and to study the effect of permitted variations in milk composition and washing on the composition of the curd. Since the lactose content of the curd was of particular interest, a rapid and accurate lactose test was needed. An effort was made to adapt and improve the Phenol-sulfuric acid method (29) for determining lactose in Cottage cheese.
Finally, computations were made to show the composition of creamed Cottage cheese as it would be affected by the composition of the solids in the uncreamed curd.