Increasing stringiness of low-fat mozzarella string cheese using polysaccharides.

When fat content of pasta filata cheese is lowered, a loss of fibrous texture occurs and low-fat (LF) mozzarella cheese loses stringiness, making it unsuitable for the manufacture of string cheese. We investigated the use of various polysaccharides that could act as fat mimetics during the stretching and extruding process to aid in protein strand formation and increase stringiness. Low-fat mozzarella cheese curd was made, salted, and then 3.6-kg batches were heated in hot (80°) 5% brine, stretched, and formed into a homogeneous mass. Hot (80°C) slurries of various polysaccharides were then mixed with the hot cheese and formed into LF string cheese using a small piston-driven extruder. Polysaccharides used included waxy corn starch, waxy rice starch, instant tapioca starch, polydextrose, xanthan gum, and guar gum. Adding starch slurries increased cheese moisture content by up to 1.6% but was not effective at increasing stringiness. Xanthan gum functioned best as a fat mimetic and produced LF string cheese that most closely visually resembled commercial string cheese made using low-moisture part skim (LMPS) mozzarella cheese without any increase in moisture content. Extent of stringiness was determined by pulling apart the cheese longitudinally and observing size, length, and appearance of individual cheese strings. Hardness was determined using a modified Warner-Bratzler shear test. When LF string cheese was made using a 10% xanthan gum slurry added at ~1%, increased consumer flavor liking was observed, with scores after 2wk of storage of 6.44 and 6.24 compared with 5.89 for the LF control cheese; although this was lower than an LMPS string cheese that scored 7.27. The 2-wk-old LF string cheeses containing xanthan gum were considered still slightly too firm using a just-about-right (JAR) test, whereas the LMPS string cheese was considered as JAR for texture. With further storage up to 8wk, all of the LF string cheeses softened (JAR score was closer to 3.0); however, much of the stringiness of the LF string cheeses was also lost during storage. We have demonstrated the potential feasibility of increasing stringiness in LF string cheese using polysaccharides with xanthan gum, although further research is needed to develop quantitative methodology for measuring stringiness and to maintain stringiness through the extended refrigerated shelf life needed for string cheese.

Fate of aflatoxin M(1) during manufacture and storage of feta cheese.

The effect of feta cheese manufacture on aflatoxin M(1) (AFM(1)) content was studied using an enzyme immunoassay technique. Feta cheese was made from milk spiked with 1 and 2 microg AFM(1) per kilogram milk. Pasteurization at 63 degrees C for 30 min caused <10% destruction of AFM(1). During cheese making, the remaining AFM(1) in milk was partitioned between curd and whey with two-thirds retained in the curd and one-third going into the whey. Cheeses were then stored for 2 mo in 8%, 10%, and 12% brine solutions at 6 and 18 degrees C. There was a 22% to 27% reduction of AFM(1) during the first 10 d of storage, with slightly more loss as salt concentration increased and when the cheese was stored at 18 degrees C. Further storage caused only slight decrease in AFM(1) and after 30 d of brining there was no difference in AFM(1) content of the cheese based upon salt concentration of the brine. At 18 degrees C, no further losses of AFM(1) occurred after 30 d, and at 6 degrees C, there was continued slight decrease in AFM(1) levels until 50 d. After 60 d of brining, there was a total loss of 25% and 29% of the AFM(1) originally present for cheese brined at 6 and 18 degrees C, respectively. Thus, the combination of pasteurization, conversion of milk into feta cheese, and at least 50 d storage of cheese in brine caused a total loss of about 50% of the AFM(1) originally present in the raw milk.

Influence of brine concentration and temperature on composition, microstructure, and yield of feta cheese.

The protein matrix of cheese undergoes changes immediately following cheesemaking in response to salting and cooling. Normally, such changes are limited by the amount of water entrapped in the cheese at the time of block formation but for brined cheeses such as feta cheese brine acts as a reservoir of additional water. Our objective was to determine the extent to which the protein matrix of cheese expands or contracts as a function of salt concentration and temperature, and whether such changes are reversible. Blocks of feta cheese made with overnight fermentation at 20 and 31 degrees C yielded cheese of pH 4.92 and pH 4.83 with 50.8 and 48.9 g/100 g of moisture, respectively. These cheeses were then cut into 100-g pieces and placed in plastic bags containing 100 g of whey brine solutions of 6.5, 8.0, and 9.5% salt, and stored at 3, 6, 10, and 22 degrees C for 10 d. After brining, cheese and whey were reweighed, whey volume measured, and cheese salt, moisture, and pH determined. A second set of cheeses were similarly placed in brine (n = 9) and stored for 10 d at 3 degrees C, followed by 10 d at 22 degrees C, followed by 10 d at 3 degrees C, or the complementary treatments starting at 22 degrees C. Cheese weight and whey volume (n = 3) were measured at 10, 20, and 30 d of brining. Cheese structure was examined using laser scanning confocal microscopy. Brining temperature had the greatest influence on cheese composition (except for salt content), cheese weight, and cheese volume. Salt-in-moisture content of the cheeses approached expected levels based on brine concentration and ratio of brine to cheese (i.e., 4.6, 5.7 and 6.7%). Brining at 3 degrees C increased cheese moisture, especially for cheese with an initial pH of 4.92, producing cheese with moisture up to 58 g/100 g. Cheese weight increased after brining at 3, 6, or 10 degrees C. Cold storage also prevented further fermentation and the pH remained constant, whereas at 22 degrees C the pH dropped as low as pH 4.1. At 3 degrees C, the cheese matrix expanded (20 to 30%), whereas at 22 degrees C there was a contraction and a 13 to 18 g/100 g loss in weight. Expansion of the protein matrix at 3 degrees C was reversed by changing to 22 degrees C. However, contraction of the protein matrix was not reversed by changing to 3 degrees C, and the cheese volume remained less than what it was initially.