Producer: Popular Science China
Author: Su Chengyu
Producer: Computer Network Information Center, Chinese Academy of Sciences
When surfing the web, you will always see some interesting questions, such as: Is strawberry flavored milk made for cows to eat strawberries every day and then milked out? In that case, will the cows eat matcha squeeze out matcha-flavored milk?
Of course, the following answers are all mockeries of the questioner, such as "The cow eats the gold nugget, you can produce golden milk", and asks the questioner to go back and read the high school biology book.
△ Image source: pinterest
Strawberry-flavored milk sold in stores is, of course, not produced by dairy cows eating strawberries every day, but by adding strawberry concentrate or strawberry flavor to the milk. Strawberry concentrate is still more conscientious, it is a deeply processed product of strawberries, and strawberry flavor is simulated by a variety of spice combinations to simulate strawberry flavor.
Therefore, strawberry milk only adds a strawberry flavor substance in the milk processing process to have a strawberry flavor. The problem seems to be solved at this point, but have you ever wondered if if you actually feed a cow strawberries, the milk it produces will have a strawberry flavor?
The first thing that is certain is that diet will definitely affect the taste of milk in mammals, including humans. In 2008, researchers at the University of Copenhagen conducted an experiment in which lactating women took carvacrol,
Capsules of flavor compounds such as menthol, isoamyl acetate and anise brain are then determined for the corresponding substances in the milk.
Of course, these flavor substances are naturally present in plants, carvacrol, menthol, anise brain these substances can literally know which plants exist, isoamyl acetate looks like a chemical synthetic substance, in fact, also exists in bananas, apples, pears and other fruits. Moreover, the dosage of all substances is 100mg, which belongs to the safe dose range, and the safety of the experiment is guaranteed.
△ The researchers recorded the concentration of various substances in the milk at different times, as can be seen from the figure, the concentration of fennel brain reached a peak after 2 hours, and it is also the most flavored flavor substance among the 3 substances that can be clearly detected. (Source: Literature 1)
The researchers then collected the milk over different time periods and analyzed the samples with a mass spectrometry. It was found that these substances appear in milk as soon as 5 minutes, but their presence does not mean that they can be tasted, because the flavor substance must reach a certain amount to be felt by the taste receptors. Carvacrol and anise concentrations peaked after 2 hours and then gradually decreased, while menthol stabilized. The detected content of isoamyl acetate is relatively low, but it is not nothing.
But this experiment only shows that human milk can be affected by diet, but what about cattle?
△ Image source: wikipedia
The various flavors of milk in the market are certainly more attractive to consumers than pure milk, so in the 50s of the last century, people began to study the flavor of milk.
At that time, people knew that the taste of a milk mainly came from the following three sources:
One is the ester substance of the milk itself; one is the ingredient of the feed; and the other is the source of the environmental taste in the farmhouse and the chemical changes during processing.
In fact, dairy farmers with extensive feeding experience have known for a long time that hay affects the flavor of milk, but there is no scientific research to explain this experience. And for cows, it's not as simple as eating something and producing something flavorful milk.
To give a few examples:
If you add cruciferous plants to the feed you give to cows, the resulting milk will have a strong radish flavor that tastes spicy and makes the milk harder to drink. The reason why there is a radish flavor, because the cruciferous family contains radish genus, which contains black mustard thiotide has a special spicy taste, it will directly enter the secreted milk, milk naturally becomes spicy radish milk.
△ Cabbage, cruciferous Source: wikipedia
If you add beets to the feed that cows eat, the resulting milk will have a fishy smell. Why not the beet flavor, but the fishy smell? Because there is a substance in beet called trimethylamine ethyllide (betaine), this substance does not enter the breast in its original form after being digested, but forms trimethylamine in the digestive tract and finally enters the milk.
△ Beet Source: wikipedia
Once the word "amine" is brought, it is conceivable that the taste will not taste good. Low concentrations of trimethylamine will have a fishy smell, or the kind of rotten. The high concentration of trimethylamine will have an ammonia smell, that is, the smell of urine. However, high concentrations of trimethylamine generally do not appear, so milk is at most putrid fishy smell. If a cow eats rye or barley, it will have the same effect as beets – milk becomes fishy milk.
If you add lemongrass to the cow's feed, the resulting milk will have a faint lemon flavor because a small amount of the flavor substance in lemon tea, citral, will enter the milk. Other plants, such as legumes, can cause milk to have a bitter taste, while grasses can produce a foul odor.
△ Lemongrass Image source: wikipedia
These are the cheaper forages mentioned earlier, and some dairy farmers also feed their cows fruit. What, someone will feed the cows fruit to eat? How expensive is this cow? In fact, it is imperative to feed cows fruits such as strawberries, and many of them occur when the fruits are unsalable or the hay is too expensive.
For example, this year, many fruit farmers are unable to deliver their agricultural products to consumers because of the impact of the epidemic lockdown, most of the vegetables and fruits may be discarded due to rot, in order to reduce waste, farmers can only choose to feed vegetables and fruits to animals to eat. No, Indian farmers feed their own strawberries to cows.
△ Because of the epidemic lockdown, a farmer in India feeds strawberries to a cow Source: cnbc tv18
As a result of drought in eastern Australia, the price of hay has tripled, and one farmer has started using watermelon as supplementary feed for his livestock. Image source: abc
Although it is common to feed cows to eat fruit, few people have specifically studied the effect of fruit on cow milk production. There is a study in China that uses fruit flavoring agents to feed cows to study its effects on cow milk production. Fruit flavor agent is based on a variety of natural flavor substances, the main components are esters, aldehydes, ketones, acids, alcohols and volatile acids, etc., which constitute fruit flavor in a certain concentration and proportion. Therefore, there is not much difference between feeding fruit flavor and feeding real fruits in the experiment, because real fruits also rely on these compounds to have a unique fruit aroma.
There are 44 kinds of fruit fragrance substances in the fruit flavor agent used in the experiment, and there are 14 kinds of fruit fragrance substances that finally enter the milk and are detected, including isobutyl acetate, isoamyl acetate, isoamyl propionate, amyl propionate, isobutyl butyrate, amyl butyrate, ethyl butyrate, diisobutyl phthalate and other substances. Through the test, it was found that the proportion of some fruity substances in milk increased, the number of some fruity substances decreased, and some fruity substances completely disappeared.
△ Source: Literature 6
As can be seen from the table, the most detected components in milk are isoamyl acetate, isobutyl butyrate, isoamyl propionate, amyl propionate, pentyl butyrate and dibutyl hydroxytoluene, that is to say, a variety of substances combined to synthesize the fruit flavor of milk in the experiment, that is, the so-called flavor substance combination effect.
It can be seen that it is not what cows eat that will produce what flavor milk, because flavor substances will also be digested, absorbed, metabolized, and synthesized. The stomach of the cow is composed of rumen, mesh stomach, flap stomach, wrinkle stomach four stomach, after the stomach digestion and absorption of food also into the liver metabolism, so some flavor substances into the body after synthesis or decomposition, the last part of the substance may disappear, part of the substance may be recombined to generate a new substance. After these processes, even if the fragrance substance may exist in the body, it will eventually be metabolized out of the body, and milk must be produced within a limited time before it can produce fruity milk.
So if you feed cows to eat strawberries, will the milk produced have a strawberry flavor?
The fruity flavor substances in strawberries mainly include isoamyl acetate, according to the results of the experiment, after feeding the milk with fruity substances, the milk will still retain this substance, and it is also one of the main flavor sources. In other words, if you give the cow enough strawberries, the concentration of isoamyl acetate in the milk is high enough, and the milk is fresh enough, maybe there will really be a hint of strawberry flavor!
bibliography:
hausner, h., bredie, w. l. p., mølgaard, c., petersen, m. a., & møller, p. (2008). differential transfer of dietary flavour compounds into human breast milk. physiology & behavior, 95(1-2), 118–124. doi:10.1016/j.physbeh.2008.05.007
davies w l. the metabolism of betaine and allied tertiary nitrogenous bases in the ruminant [j]. j dairy res, 1936a,7:14
davies w l. the fishy flavor of milk caused by feeding beet by-products [j]. agric prog, 1936b, 13:112
johnson p e, bush l j, well g v, smith e l. the undesirable flavor of milk resulting from grazing cows on wheat pasture [j]. agric, 1973, 274
Ding Yi. Study on the growth characteristics of lemongrass and its use as a feed additive for dairy cows[d]. Nanjing Agricultural University, 2008.
MA Yanfen. Preliminary study on fruity milk production technology and metabolic mechanism of fruity substances in cattle[d]. Doctoral dissertation. Hohhot: Inner Mongolia Agricultural University, 2009.