The science of (delicious and healthy) marbling

The role of marbling in the eating experience of beef and other red meats is well established. However, claims about the benefits of marbling
are often quoted without sufficient scientific support and this may confuse the consumer, working against the efforts to promote marbling as a quality trait in beef and other red meat species. What follows is a discussion concerning some facts around certain issues about marbling.

Marbling is the fine, evenly distributed flecks of fat found through muscle. While fat in the form of phospholipids is found within muscle tissue (cell membranes), marbling fat occurs in the spaces between muscle bundles. It is one of the three fat depots of the carcass, the other two being subcutaneous fat (on the surface of the carcass) and intermuscular fat (found between major muscle groups). It is also important to note that these fat depots are laid down in a different sequence during the animal’s life.

Taste versus waste

Intermuscular (or seam fat) is normally deposited at a higher rate at first, followed by subcutaneous fat, and then marbling fat. This is, of course, important in the context of striving for optimum levels of marbling, also called the ‘taste’ fat, because in most cases it means that there is also an abundance of ‘waste’ fat in the carcass when this point is reached.

Marbling contributes to the eating experience of red meat through positive effects on the consumer’s perception of tenderness, juiciness, and flavour.

It is difficult to separate tenderness, juiciness, and flavour from each other when discussing marbling as the effect is integrated. It is interesting to note that the positive effect of marbling on flavour and juiciness (in taste panel scores) increases as the level of marbling increases, but there is a turning point or plateau at about 15% marbling fat. This is important when considering that breeds such as pure and cross-bred Wagyu show marbling fat at the upper twenty and thirty percentage levels.

Certain studies indicate that a minimum level of marbling required to improve flavour is 3%, and above 8% is required to show an effect on texture. Researchers from the United States established a window of acceptability and report a dramatic increase in palatability scores by consumers when marbling increases from 0% to 3%. Between 3% and 6%, the increase in response is still positive but not as dramatic. Above 6% to 7%, the response to increasing levels of marbling tapered off further. In addition, above 7,3%, health-conscious consumers started to protest against too much visual fat, which they related to health problems. Therefore, the window of acceptability for marbling was set at 3% to 7,3%. Up to 15% marbling, as indicated earlier, may be recommended for niche markets, for example, Eastern countries, where eating culture in relation to portioning and culinary methods differ from Western countries.

The mechanism involved in improvement of tenderness is three-fold:
1) Marbling fat reduces the bulk density of a steak, meaning there is less muscle structure (resistance) to bite through or to chew the meat.
2) Secondly, marbling fat has a lubricating effect, which stimulates salivation and enhances the perception of juiciness and flavour, which will also contribute to the perception of better texture and overall eating quality.
3) Thirdly, marbling fat is deposited in the connective tissue structure and reduces the connective tissue toughness as marbling increases.

Palatable pattern

The quality of marbling and contribution to eating quality is not only defined by the level but also by the deposition pattern. Equal distribution of marbling as small flecks of fat across the steak surface area is most important. Large islands of fat may contribute to total fat or marbling level but are visually unappealing and cause an inconsistent eating experience, with exposure to either too much or too little fat.

The response of consumers to visual fat in raw steaks should be considered carefully, especially in certain Western markets. Consumers will often respond negatively when confronted with high levels of marbling in uncooked steaks. This response is driven by the negative connotation to visual animal fat.

Consumer studies performed in the 1990s in Australia confirmed that consumers preferred beef with the lowest fat trim (subcutaneous fat) and, interestingly, marbling fat had a larger influence on perception of fatty meat than fat trim/subcutaneous fat thickness. Consumers responded consistently (linear scale) negatively concerning “liking of raw appearance” and “expected eating quality” over ranges of marbling scores 1–3 (marbling fat 4% to 7%). On fat-trim there was no negative response between 2 mm and 5 mm fat cover and a negative response was recorded only when fat thickness increased from 5 mm to 10 mm. Consumers believed that lean trim meat does not only look more appealing but will also taste better. Interestingly, this negative response made a 180° turn when consumers tasted meat without being exposed to the raw cuts.

Consumer panel MQ4 scores (used in Australia as a collective response to tenderness, juiciness, flavour, and overall liking) showed a 4% to 8% increase in overall score, even with a small range of marbling levels from score 0 (no marbling) to 3 (5,4% to 7%).

Fat and nutrition

The composition of fat is important when considering the nutritional value and contribution to the health status of the consumer. Saturated fatty acids (SFAs), commonly associated with animal products, are often blamed for their contribution to health problems such as cancer, diabetes, and heart disease. However, today we know that stearic acid and palmitic acid (comprising about 45% of the total fatty acids of muscle) do not raise plasma cholesterol, while myristic acid does, but only comprises about 3% of the total muscle fatty acid (FA).

Monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) are generally regarded as healthier fatty acids. Any fat, also in meat, consists of different proportions of these three groups of FA (apart from other co-structures of fat) which give the fat its unique physical (e.g., melting point), chemical, and nutritional characteristics. The composition of animal fat in terms of the said fatty acids may also vary across animals within breeds, and between breeds and feeding regimes, but only to a limited extent across fat type/depot namely, marbling, subcutaneous fat, and seam fat (intermuscular).

So, the claim often made that marbling fat is healthier than other fat (in the same animal) is not true. True marbling fat is high in SFA and MUFA (almost in equal proportions), just like subcutaneous and seam fat. When meat is trimmed clean of external fat, higher marbling means that total fat intake increases both SFA and MUFA, and that could (potentially) become a health concern.

When considering the effect of diet on PUFA and the different types of PUFA (omega 3 and 6), grass feeding will cause a favourable healthwise) increase in omega 3 to omega 6 PUFA ratio but, once again, the favourable effect of this change will be diluted at high levels of marbling because an increase in marbling fat coincides with an increase in mainly MUFA, but also SFAs at the cost of PUFAs.

Quite interesting information was found in a local study, where beef steaks with very high (30%), medium (4,5%), and low (2,5%) muscle fat/marbling were analysed for contribution of types of fatty acids on a weight basis. This (weight basis) is in contrast to presenting FA values on a percentage basis, which often look very impressive but do not give an account of the actual intake of FA when consuming a 200 g or 300 g steak.

The study showed that consuming the very highly marbled steak would result in about six times higher total fat intake compared to the medium marbled steak. This ratio also translated into more or less a six times higher intake of MUFA and SFA.

Although many secondary factors play a role when considering health guidelines for fat consumption, the rule of thumb states that not more than 30% of total calories consumed per day should be from fat and not more than 10% from SFAs. Considering these guidelines, consuming a 200 g highly marbled steak will mean that the daily quota for calories from any fat has been reached and the proportion from SFAs has been exceeded. We may, therefore, need to reconsider the way highly marbled beef is consumed and scale down on portion size like as Eastern cultures.

In summary, marbling certainly contributes to good eating quality. However, consumers need to be educated to accept that visual fat in the form of marbling translates to good eating quality, but always within certain limits. Consumption of steaks with extreme levels of marbling should signal health threats. Marbling fat is not healthier than other fat in the same animal, and consumers should be guided by recommended calorie intake in the form of fat when selecting marbled steak portions.

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