C. Brothersen

Manufacture and sensory analysis of reduced- and low-sodium Cheddar and Mozzarella cheeses.

High sodium intake negatively affects consumer health, thus there is active interest in lowering sodium levels in dairy foods. Cheddar and low-moisture, part-skim Mozzarella cheeses were made with total salt levels of 0.7, 1.0, 1.25, 1.35, and 1.8% (wt/wt) in triplicate, thus reducing sodium by 25 to 60%. Multiple manufacturing protocols for salt reduction were used to produce cheeses with similar postpress moisture and pH, independent of the final salt levels in cheese, in order to study the role of salt in cheese acceptability. Cheese flavor was evaluated by a descriptive taste panel on a 15-point intensity scale. Consumer acceptance was evaluated by a consumer panel on a 9-point hedonic scale. Taste panels conducted with cubed Cheddar cheese (at 3 and 6mo) and cold shredded Mozzarella cheese (at 3wk) showed that consumer liking for cheese was low at 0.7 and 0.9% salt, but all cheeses containing higher salt levels (1.25, 1.35, and 1.8% salt) were comparably preferred. The cheeses had acceptable liking scores (≥6) when served as quesadilla or pizza toppings, and consumers were able to differentiate cheeses at alternate salt levels; for example, 1.8 and 1.5% salt cheeses scored similarly, as did cheeses with 1.5% and 1.35% salt, but 1.35% salt cheese scored lower than and was discernible from 1.8% salt cheese. Descriptive panelists perceived salty, sour, umami, bitter, brothy, lactone/fatty acid, and sulfur attributes as different across Mozzarella cheeses, with the perception of each significantly increasing along with salt level. Salty and buttery attributes were perceived more with increasing salt levels of Cheddar cheese by the descriptive panel at 3mo, whereas bitter, brothy, and umami attributes were perceived less at the higher salt levels. However, this trend reversed at 6mo, when perception of salty, sour, bitter, buttery, lactone/fatty acid, and umami attributes increased with salt level. We conclude that consumers can distinguish even a 30% salt reduction and a gradually phased sodium reduction is needed to improve acceptability of lower sodium cheeses.

Fortification of reduced-fat Cheddar cheese with n-3 fatty acids: effect on off-flavor generation.

The objective of this study was to fortify 50% reduced fat Cheddar cheese with n-3 fatty acids and evaluate whether this fortification generated specific off-flavors in the cheese. Docosahexaenoic (DHA) and eicosapentaenoic (EPA) fatty acids were added to the cheese to obtain 3 final fortification levels [18, 35, and 71 mg of DHA/EPA per serving size (28 g) of cheese] representing 10, 20, and 40% of the suggested daily intake level for DHA/EPA. The presence of oxidized, rancid, and fishy flavors as a function of fortification level and cheese aging (6 mo) was evaluated using a sensory descriptive panel. No differences were found in the oxidized and rancid flavors as a consequence of DHA/EPA fortification, with only slight intensities of these flavors. The presence of fishy off-flavor was dependent on the fortification level. Cheeses with low fortification levels (18 and 35 mg of DHA/EPA per serving size) did not develop significant fishy off-flavor compared with the control, whereas at the highest fortification level (71 mg of DHA/EPA per serving size) the fishy off-flavor was significantly stronger in young cheeses. The fishy flavor decreased as a function of age and became nonsignificant compared with the control at 3 mo of storage. Even though fishy flavors were detected in the fortified cheeses, the DHA/EPA content during storage remained constant and complied with the suggested values for food fortification. Results obtained from this research indicate that 50% reduced-fat Cheddar cheese aged for 3 mo can be used as a vehicle for delivery of n-3 fatty acids without generation of off-flavors.

Survival of probiotic adjunct cultures in cheese and challenges in their enumeration using selective media

Various selective media for enumerating probiotic and cheese cultures were screened, with 6 media then used to study survival of probiotic bacteria in full-fat and low-fat Cheddar cheese. Commercial strains of Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus paracasei, or Bifidobacterium lactis were added as probiotic adjuncts. The selective media, designed to promote growth of certain lactic acid bacteria (LAB) over others or to differentiate between LAB, were used to detect individual LAB types during cheese storage. Commercial strains of Lactococcus, Lactobacillus, and Bifidobacterium spp. were initially screened on the 6 selective media along with nonstarter LAB (NSLAB) isolates. The microbial flora of the cheeses was analyzed during 9 mo of storage at 6°C. Many NSLAB were able to grow on media presumed selective for Lactococcus, Bifidobacterium spp., or Lb. acidophilus, which became apparent after 90 d of cheese storage, Between 90 and 120 d of storage, bacterial counts changed on media selective for Bifidobacterium spp., suggesting growth of NSLAB. Appearance of NSLAB on Lb. casei selective media [de man, Rogosa, and Sharpe (MRS)+vancomycin] occurred sooner (30 d) in low-fat cheese than in full-fat control cheeses. Differentiation between NSLAB and Lactococcus was achieved by counting after 18 to 24h when the NSLAB colonies were only pinpoint in size. Growth of NSLAB on the various selective media during aging means that probiotic adjunct cultures added during cheesemaking can only be enumerated with confidence on selective media for up to 3 or 4 mo. After this time, growth of NSLAB obfuscates enumeration of probiotic adjuncts. When adjunct Lb. casei or Lb. paracasei cultures are added during cheesemaking, they appear to remain at high numbers for a long time (9 mo) when counted on MRS+vancomycin medium, but a reasonable probability exists that they have been overtaken by NSLAB, which also grow readily on this medium. Enumeration using multiple selective media can provide insight into whether it is the actual adjunct culture or a NSLAB strain that is being enumerated.

Fortification of Cheese with Vitamin D3 using Dairy Protein Emulsions as Delivery Systems

Vitamin D is an essential vitamin that is synthesized when the body is exposed to sunlight or after the consumption of fortified foods and supplements. The purpose of this research was to increase the retention of vitamin D(3) in Cheddar cheese by incorporating it as part of an oil-in-water emulsion using a milk protein emulsifier to obtain a fortification level of 280 IU/serving. Four oil-in-water vitamin D emulsions were made using sodium caseinate, calcium caseinate, nonfat dry milk (NDM), or whey protein. These emulsions were used to fortify milk, and the retention of vitamin D(3) in cheese curd in a model cheesemaking system was calculated. A nonemulsified vitamin D(3) oil was used as a control to fortify milk. Significantly more vitamin D(3) was retained in the curd when using the emulsified vitamin D(3) than the nonemulsified vitamin D(3) oil (control). No significant differences were observed in the retention of vitamin D(3) when emulsions were formulated with different emulsifiers. Mean vitamin D(3) retention in the model system cheese curd was 96% when the emulsions were added to either whole or skim milk compared with using the nonemulsified oil, which gave mean retentions of only 71% and 64% when added to whole and skim milk, respectively. A similar improvement in retention was achieved when cheese was made from whole and reduced-fat milk using standard manufacturing procedures on a small scale. When sufficient vitamin D(3) was added to produce cheese containing a target level of approximately 280 IU per 28-g serving, retention was greater when the vitamin D(3) was emulsified with NDM than when using nonemulsified vitamin D(3) oil. Only 58±3% of the nonemulsified vitamin D(3) oil was retained in full-fat Cheddar cheese, whereas 78±8% and 74±1% were retained when using the vitamin D(3) emulsion in full-fat and reduced-fat Cheddar cheese, respectively.

Fortification of Cheddar cheese with vitamin D does not alter cheese flavor perception

Currently, dietary guidelines for vitamin D consumption are under review, considering new information that >50% of the US population is vitamin D deficient, and may lead to a recommendation of a higher dietary intake of this vitamin. Vitamin D fortification of cheese aims to improve the current availability of fortified dairy foods beyond liquid milk. However, cheese is susceptible to undesirable flavor changes during long-term cheese ripening, and cheese bacteria and enzymes may degrade added vitamins. To test the retention of vitamin D(3) in Cheddar cheese curd, cheese milk was fortified initially during manufacture at a level of 150 IU/serving, using commercial sources that contained vitamin D(3) in powder, oil, or emulsion form, with and without homogenization of the fortified milk. When fortification was done directly to the cheese milk, we found that more than 80% vitamin D(3) was retained in cheese curd, irrespective of homogenization or form of fortification. Further, Cheddar cheese was fortified with the emulsion form of vitamin D(3) directly in cheese milk at 200 and 400 IU/serving to test stability and flavor changes. Vitamin D(3) fortified in this manner was stable for up to 9 mo in Cheddar cheese. Consumer acceptance and descriptive analysis of flavor profiles of cheese were also conducted and showed that vitamin D(3) fortified cheeses were equally liked by consumers, and cheese taste and flavor remained unaltered with vitamin D(3) addition even after aging for 9 mo.

Comparison of milk oxidation by exposure to LED and fluorescent light

Light-induced oxidation of milk has been well studied. Exposure of milk to UV light facilitates the oxidation of fats to aldehydes, and the degradation of sulfur-containing amino acids, both of which contribute to off-flavors. In addition, vitamin A and riboflavin are easily degraded by UV light. These reactions occur rapidly and are exacerbated by bright fluorescent lights in retail dairy cases. The invention of white light-emitting diodes (LED) may provide a solution to this oxidation problem. In this study, fresh milk containing 1% fat and fortified with vitamin A and riboflavin was exposed to LED at 4,000 lx, or fluorescent light at 2,200 lx for 24 h. Milk samples exposed to LED or fluorescent light, as well as milk protected from light, were analyzed by a consumer acceptance panel, and a trained flavor panel. In addition, vitamin A, riboflavin, and the production of volatile compounds were quantified. Exposure to light resulted in a reduction of cooked/sweet, milkfat, and sweet flavors and increased the intensity of butterscotch, cardboard, and astringency. In general, exposure to fluorescent light resulted in greater changes in the milk than exposure to LED even though the LED was at higher intensity. Consumers were able detect off-flavors in milk exposed to fluorescent light after 12 h and LED after 24 h of exposure. The riboflavin and vitamin A content was reduced by exposure to fluorescent light, whereas there was no significant reduction caused by LED compared with the non-light-exposed control. Production of hexanal, heptanal, 2-heptanal, octanal, 2-octanal nonanal, dimethyl sulfide, and caproic acid vinyl ester from the light-induced degradation of fats was significantly higher with fluorescent than LED. Production of these compounds was significantly higher with both light treatments than in the control milk. This study indicates that LED is less destructive to milk than fluorescent light.

Evaluation of microbial survival post-incidence on fresh Mozzarella cheese1

Commercial fresh Mozzarella cheese is made by direct acidification and is stored dry or in water without salt addition. The cheese has a shelf life of 6 wk, but usually develops an off-flavor and loses textural integrity by 4 wk, potentially due to the lack of salt and high moisture that allow the outgrowth of undesirable bacteria. To understand how microbial incidence affects cheese quality and how incident pathogen-related bacteria are limited by salt level during refrigerated storage, we made fresh Mozzarella cheese with high (2%) and low (0.5%) salt. The high-salt cheese was packaged and stored dry. The low-salt cheese was packaged and stored either dry or in 0.5% salt brine. One portion of cheeses was evaluated for surviving incident microbes by aerobic plate counts, coliform counts, and psychrophilic bacterial counts, of which coliforms and psychrophiles were not detected over 9 wk. Aerobic plate counts remained at 100 to 300 cfu/g up to 2 wk but increased by 1,000- to 10,000-fold between 4 and 6 wk at all salt levels and storage conditions. Other portions of cheeses were inoculated with either Escherichia coli or Enterococcus faecalis, both of which increased by 100-fold over 90 d of storage. Interestingly, E. coli added to the cheese brine first grew in the brine by 100-fold before attaching to the cheese, whereas Ent. faecalis attached to the cheese within 24h and grew only on the cheese. We conclude that incident bacteria, even from similar environments, may attach to cheese curd and survive differently in fresh Mozzarella cheese than in brine. Overall, 2% salt was insufficient to control bacterial growth, and slow-growing, cold- and salt-tolerant bacteria may survive and spoil fresh Mozzarella cheese.

Rapid and Effective Processing of Macroinvertebrate Samples

ABSTRACT A major Impediment to stream macroinvertebrate production estimation is the extensive time necessary to sort and measure individual organisms. The method presented here significantly decreases time expenditure by separating invertebrates into size classes through the use of sieves, and further reduces effort by subsampling those size classes with excessive numbers. Both invertebrate lengths and ash-free dry weights correlate well with sieve aperture size, but weight is suggested as a better measure of abundance and production. The very high correlation. (.9988) for the combined taxa strongly supports the use of the sieve size versus ash-free dry weight regression, rather than total lengths, for standing crop and size-frequency method production estimates. Index of dispersion and goodness-of-fit tests were calculated for samples divided with a subsampler. Both tests indicated that the subsampler gave random subsamples from the original sample.