All curds cannot be treated equal – improving quality of low-fat cottage cheese

All curds cannot be treated equal – improving quality of low-fat cottage cheese – includes related article

Moshe Rosenberg

At the last American Cultured Dairy Products Institute annual meeting, the Milk Industry Foundation’s Cultured Products Committee unveiled its findings on cottage cheese (see Dairy Foods, May 1993, p. 17). A parade of speakers attempted to explain the reasons behind the drop in full-fat sales and the leveling of gains in lowfat sales.

Quality is suspected to play a significant role in cottage cheese’s decline–especially in the case of lowfat and fat-free varieties. Yet, it is these very reduced-fat varieties that hold special interest to today’s health-conscious consumer.

In order to match consumer expectations, cottage cheese quality should be enhanced. One enhancement method may be through curd composition.

Firmness, porosity and total solids

Full-fat cottage cheese differs significantly from lowfat and fat-free varieties in composition, physical properties and sensory characteristics. The reduced fat content and the presence of various stabilizers in the fat-reduced varieties are responsible for the different curd/dressing interactions that exist in these products in comparison to those in the full-fat variety. In turn, these differences, affect dressing adsorption and hence the textural properties and the appearance of the final product.

Efforts to enhance the quality of the lowfat and fat-free varieties of cottage cheese have focused solely on manipulating the composition and properties of the dressings while using the same curd. In a recent research project at the department of Food Science and Technology at the University of California, Davis, we challenged this practice and asked whether the same curd can be used for all formulations.

We studied the textural, compositional and structural properties of cottage cheese curd as a function of the pH at cutting (ranging from 4.6 to 4.9) and the cooking-related parameters. The project evaluated cooking rates ranging between 0.14 and 0.77[degrees]C; final cooking temperatures of 45, 50 and 55[degrees]C; and holding times of 30 or 90 minutes.

to determine microporosity (curd structure), we used a new technique based on scanning electron micro-scopy and image analysis. Curd texture or firmness was measured using two methods: a Kramer shear press and a modified curd tension meter.

The results indicated that the pH at cutting and the cooking parameters both critically affect the textural, compositional and structural properties of the curd. Curds with similar total solids and different total solids were found to differ in their porosity. This could be linked to the distribution and size of pores and to the thickness of the “casein walls” in the three-dimensional curd matrix. The results suggest that total solids (TS) cannot be used as the sole predictor for curd firmness; firmness is determined by a combined effect of the composition (TS) and the structural features (microporosity).

Five cottage cheese curd types representing different combinations of total solids, firmness and porosity were selected and incubated with five different cottage cheese dressings: one full-fat (FF), two lowfat (LF1, LF2), and two fat-free (NF1, NF2) forming a 5-by-5 matrix. The interactions between the curd and the dressing (as manifested by the amount of dressing that can be drained from the product), and the textural properties of the products and of the drained curd were studied. (See chart.)


The research yielded two results:

1) A given curd interacts differently with different dressings. Smaller amounts of dressing could be drained off the curd in the lowfat and fat-free systems than off the curd incubated with the full-fat dressing. The frmness of the full-fat systems and their drained curds was higher than that of the low-fat and fat-free systems.

2) Different curds interact differently with any given dressing. Regardless of similarity in composition, curds that differed in their porosity adsorbed different volumes of a given dressing.

The results imply that you cannot achieve the quality attributes of a full-fat product in fat-reduced varieties by adjusting the composition of the dressing alone.

The same curd cannot be used for the three cottage cheese varieties. For each variety, specific, individual structural (porosity), textural and compositional characteristics are necessary in the curd. Such property profiles can be introduced by careful adjustment of the curdmaking process parameters. Typical parameters include: percent starter used, pH of vat when the rennet is added, minutes between addition of starter and cutting the curd, and cooking conditions (e.g., rate, time, and final cooking temperature).

Unfortunately, in many cases, technical and logistical difficulties may hinder curd profile changes. Future research could aid such changes.

Currently we are investigating the possibility of constructing a “new” cottage cheese curd with properties that will be tailored to better interact with the three dressing varieties. Such an approach may offer a more workable solution to the quality difficulties associated with reduced-fat cottage cheese.

A Functional Milkfat

Moshe Rosenberg proposes a model of the microstructure of full-fat cottage cheese where fat globules from the cream dressing “cling” to the surface of the curd particle. This physical interaction between the phospholipid/protein membrane surface of the globules and the protein curd results in the globule “plugging” the curd’s surface pores. The transfer of mass (i.e., moisture and solids) between the exterior dressing and interior of the curd is thus inhibited.

Hydrocolloid gums used in reduced-fat dressings serve to increase dressing viscosity. However, the interaction between the stabilizers and the protein curd itself is very different than what occurs between fat globules and the curd, based on Rosenberg’s model.

The struggle by stabilizer companies and dairies to produce a reduced-fat cottage cheese with identical properties to its full-fat counterpart still has a ways to go.

Armed with a better understanding of fat’s function in the eating quality and shelf stability of cottage cheese, the industry will be able to formulate a more acceptable lowfat product.


For more research information on curd-dressing interactions, contact Moshe Rosenberg, 916/752-4682.

Research was funded by the industry through the California Dairy Foods Research Center and the California Milk Advisory Board.

COPYRIGHT 1993 Business News Publishing Co.

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