Fish oil can be added to goat cheese to deliver high levels of heart-healthy omega-3 fatty acids without compromising taste or shelf life, University of Maine food scientists report.
A study in the Journal of Food Science, published by the Institute of Food Technologists, showed that fish oil delivers higher levels and more balanced proportions of omega-3 fatty acids compared to other sources such as flax and algal oil.
Fish oil oxidizes more quickly, making food fortification a challenge. Given the cost of purified fish oil, maximizing its incorporation efficiency is critical to the commercial viability of fortified cheese.
The Maine researchers said dairy has been shown to be a good matrix for fish oil fortification because it is commonly consumed and has unique properties that seem to protect fish oil.
Soft goat cheese has lower fat than other cheeses making it appealing for those looking for healthy flavorful food choices.
In the latest research, goat cheese was successfully fortified to deliver 127 mg omega-3 fatty acids per 28 g serving without affecting shelf life or consumer purchase intent.
There is a growing body of evidence that omega-3 fatty acids from fish, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are not only beneficial for general health and well-being, but also play a vital role in preventing chronic diseases.
EPA and DHA have been shown to improve insulin sensitivity in type II diabetics, lower blood pressure, and improve arterial elasticity in patients at risk for cardiovascular disease. Omega-3 fatty acids have also been shown to minimize the effects of stroke, improve cognition in the elderly, alleviate symptoms associated with rheumatoid arthritis, and reduce risk for osteoporosis.
Omega-3 fatty acid fortification is one of the fastest growing trends in the food industry with 42% of consumers making efforts to eat more omega-3 fatty acid rich foods.
The most common problem related to fish oil fortification is the "fishy" odor that accompanies lipid oxidation of unstable polyunsaturated fatty acids (PUFA) in the presence of light, oxygen, and heat.
Another challenge of fortifying foods with omega-3 PUFA is that the low levels of fish oil shown to maintain product acceptability require consumers to eat greater quantities of fortified foods to meet recommended levels of PUFA consumption.
Due to their natural emulsion state, dairy products, such as yogurt, butter, milk, and sour cream, have been shown to be an excellent matrix for fish oil fortification.
Although several studies have investigated cheese as a vehicle for fish oil fortification, fish oil fortified cheeses are not available in the U.S. market.
Fish oil fortified cheddar cheese was produced by researchers in 2009, but "fishy" odors were detected by a trained descriptive panel at the highest fortification level, limiting fortification to low levels.
Other researchers added fish oil to a variety of dairy products, including soft cheeses, but found the samples were unacceptable to a trained panel after four weeks of refrigerated storage.
These studies each incorporated the fish oil after the cheese curd had formed, which may have contributed to the early onset of "fishy" flavor detected by trained panels.
The Maine researchers incorporated different levels of purified, liquid fish oil to soft goat cheese prior to curd formation to maximize delivery of EPA and DHA per serving without negatively affecting oxidative stability or consumer acceptance.
Researchers Brianna Hughes, Brian Perkins, Beth Calder and Denise Skonberg fortified soft goat cheese with four levels of purified fish oil—0, 60, 80, and 100 g fish oil per 3,600 g goat milk—prior to curd formation to deliver high levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) per serving.
The cheese was partially vacuum-packed and stored at 35.6°F for four weeks, then evaluated for composition, EPA and DHA content, oxidative stability, color, pH, and consumer acceptability.
The fat content was significantly higher in the fortified treatments compared to the control, but was not significantly different among fortified treatments.
EPA and DHA contents were not significantly different among fortified samples, averaging 127 mg EPA and DHA per 28 g serving.
No significant lipid oxidation was detected by thiobarbituric acid reactive substances (TBARS) or hexanal and propanal headspace analyses over the four-week refrigerated shelf-life study for any treatments.
The fortified cheeses were all liked "moderately" by consumers for overall acceptability, although the 60 g fortification level did rate significantly higher.
The control cheese and the 60 g fortification level had no significant differences in consumer purchase intent.
The researchers said the results show that fortification levels of up to 127 mg EPA and DHA per serving may be added to soft cheese without negatively affecting shelf life or consumer purchase intent.
Despite minor visible loss of fish oil to the whey fraction, which was not quantified, there were no significant differences in yield between the control and the fortified samples suggesting the addition of fish oil did not affect curd formation.
Moisture and fat content did not differ significantly among fortified treatments, but the fortified treatments differed significantly from the control.
Moisture content averaged 62.7% for fortified treatments and 66.2% for the control.
"The 3.5% (percentage point) lower moisture content of the fortified treatments was inversely proportional to the increase in fat due to the addition of the fish oil," the researchers reported.
Fat content ranged from 15% to 19.5% and was significantly higher in fortified samples than the control sample (15%) indicating that the fish oil was incorporated into the curd.
However, oil incorporation was limited above the 60 g fortification level. Fortified treatments, while not significantly different in fat content, did increase from 17.9% (lowest fortification level) to 19.5% (highest fortification level). Improving homogenization efficiency and/or reducing curd formation time may increase oil incorporation above 60 g.
In a study in 2009, Cheddar cheese was fortified with encapsulated fish oil after processing and no significant differences in moisture or fat content between control and fortified samples were found.
In contrast, this goat cheese study showed significant differences between control and fortified cheese for both moisture and fat content suggesting greater incorporation of fish oil into the cheese curd than was seen in other fortified cheese studies.
The researchers said that it can be concluded from the fat content and EPA and DHA levels that the lowest level of fortification, 60 g of added fish oil, was the only level efficiently incorporated into the cheese.
This is enough to provide a high level (about 127 mg) of omega-3 fatty acids per serving. The researchers say the delivery of higher fortification levels requires further investigation to maximize incorporation of the oil into the curd.
The processing and packaging methods used in this project were sufficient to limit the oxidation of both the goat cheese (seen by the control) and the fish oil (seen by the fortified treatments).
"The lack of oxidation during four-weeks of storage is encouraging, and longer shelf life tests are warranted to determine when and if oxidative changes occur in the highly fortified goat cheese," the researchers report.
They said no differences in cheese color were observed during cheese processing or throughout the shelf life study. Initial cheese color did not change appreciably as the level of fish oil increased.
Cheese for the consumer acceptability study was prepared in the same manner as the cheese prepared for the analytical study and at the same fortification levels.
Consumer testing was conducted at the University of Maine’s Consumer Testing Center with 105 untrained participants from the community.
The four samples were coded and randomized before being presented to participants with 5 g cheese samples on plain wheat crackers and participants were given a cup of water to cleanse their palates between samples.
A questionnaire asked participants to indicate how often they ate goat cheese, as well as to rate the appearance, color, aroma, flavor, creaminess, and overall acceptability of each sample using the Hedonic Scale, the most widely used measure of food acceptability with a nine-point range from dislike extremely to like extremely.
The participants’ purchase intent for each sample was rated with a five-point hedonic scale from definitely won’t buy to definitely will buy.
The scores among treatments for appearance, color, and aroma did not show any significant differences, indicating consumers found the fish oil fortified samples to be as acceptable as the control sample for these three attributes.
Appearance and color scores averaged 7.5, while aroma scores were slightly lower with an average of 6.9, equal to "like moderately."
The control sample rated significantly higher for creaminess, taste, and overall acceptability when compared to the fortified samples, which may be attributed to the higher fat content of the fortified samples.
Scores for taste were similar to those for creaminess, with the control sample having significantly higher acceptability (7.5) than the fortified samples that had scores ranging from 6.7 to 7. Overall acceptability of the control averaged 7.6, followed by the 60 g fish oil treatment with a score of 7.2.
The higher fortification treatments, 80 g and 100 g added fish oil, averaged a score of 7.0 for overall acceptability but were significantly lower than the 60 g fish oil treatment for overall acceptance.
The majority of comments made by consumer panelists were about the tangy, sharp, acid flavor of the goat cheese and the pleasant smoothness of the texture, although a small number of panelists perceived oiliness in the fortified cheese. This may have been due to the greater amount of fat in the cheese, and not specifically the addition of fish oil.
The researchers say textural attributes could be easily modified with gums or by slight adjustments to cheese processing methods.
There were only five comments from the 105 participants that mentioned "fishy" or "seafood" aromas, flavors, or aftertastes even with the fortification levels of about 127 mg EPA and DHA per serving.
Despite the statistically significant differences in overall acceptability of the goat cheese treatments, the hedonic values among treatments were close with an average acceptability in the "like moderately" range (6.5 to 7.5).
This level of acceptance of the fortified cheese is seen as promising considering that 40% of participants "never or rarely" eat goat cheese, which may have slightly depressed some values.
Improved scores could be attained by using only panelists who commonly consume goat cheese or by adding flavor compounds to the cheese such as herbs and spices.
Of the 105 respondents, 74% indicated they "might" or "definitely" would purchase the cheese with the lowest level of fortification (60 g fish oil).
Similar purchase intent was observed for the control, which indicates that despite significant differences between the two for overall acceptability, 60 g of added fish oil may be a marketable level for fortification.
This conclusion is further supported by results that demonstrated no significant differences among fortified treatments for proximate composition, oxidative stability, or EPA and DHA content.
"Excellent Source" labeling has been proposed for foods containing at least 20% of the proposed RDI of 160 mg EPA and DHA, or 32 mg, per serving. If approved, the fortified goat cheese would qualify for the "Excellent Source" claim as it provides 79% of the proposed RDI for EPA and DHA.
The researchers said soft goat cheese was successfully fortified with fish oil yielding a product that contained about 127 mg EPA and DHA per 28 g serving—nearly four times the level required to meet the proposed "Excellent Source" guidelines.
Proximate composition, color, pH, and yield were not negatively affected by fish oil fortification of the cheese. In addition to partial vacuum packaging, the addition of fish oil to goat cheese prior to curd formation may have contributed to the enhanced oxidative stability of the fish oil observed in this study.
No change in oxidative stability was seen during four weeks of refrigerated storage and there was negligible difference in consumer purchase intent between fish oil fortified goat cheese and the control cheese.
"These results have positive implications for high-level fish oil fortification of dairy products," the researchers’ report stated. "Important directions for future research include assessing fish oil fortification pre- and post-processing of dairy products, determining the upper threshold of fish oil incorporation into soft curd cheeses, and conducting longer shelf life studies to demonstrate commercial feasibility of fish oil fortified cheese."